Physico-chemical processes in seawater-saturated ...elib.suub.uni-bremen.de/diss/docs/00011513.pdfreduced and compensated by irreversible strain. This phenomenon reveals that the consolidation

Physico-chemical processes

in seawater-saturated

subduction zone sediments -

an experimental approach

Dissertation zur Erlangung des

Doktorgrades der Naturwissenschaften

am Fachbereich Geowissenschaften

der Universität Bremen

vorgelegt von

Andre Hüpers

Bremen, Mai 2009

TABLE OF CONTENTS I

Table of contents

ABSTRACT 1

ZUSAMMENFASSUNG 3

CHAPTER 1: INTRODUCTION 6

1.1 Motivation 6

1.2 Outline of the PhD project 7

CHAPTER 2: SEDIMENTS AT CONVERGENT MARGINS 9

2.1 Sediment subduction 9

2.2 Dewatering of subducted sediments 10

2.3 Water-rock interaction 15

2.4 Synthesis and implications for seismogenesis 17

CHAPTER 3: THE GEOLOGY OF THE NANKAI MARGIN 19

CHAPTER 4: MANUSCRIPT 1 23

The thermal influence on the consolidation state of underthrust sediments from the Nankai margin and its implications for excess pore pressure


Ramifications of high in-situ temperatures for laboratory testing and inferred stress states of unlithified sediments – a case study from the Nankai margin


The interaction of underthrust sediments with seawater – an approach by hydrothermal consolidation testing

CHAPTER 7: CONCLUSIONS AND OUTLOOK 97

ACKNOWLEDGEMENTS 99

REFERENCES NOT CITED IN THE MANUSCRIPTS 101

APPENDIX 110

ERKLÄRUNG 166

ABSTRACT 1

AbstractAt convergent margins the plate boundary thrust frequently produces high

magnitude earthquakes. Thermal modelling and direct measurements of heat flow

suggest that the onset of seismogenesis along the plate boundary thrust is associated

with a temperature of approximately 150 °C. The reason for the onset of

seismogenesis is controversially discussed. The sediment on the incoming plate is

initially weak, porous and unable to produce catastrophic slip behaviour. Therefore,

the sediment undergoes substantial changes during the passage from the deep sea

trench down to the updip limit of the seismogenic zone. Several hypotheses have been

proposed based on the importance of increasing effective stress and temperature on

mechanical behaviour and diagenetic processes. Previous laboratory studies focused

mainly on one of these parameters (effective stress or temperature) to shed light on

the fate of subducted sediments. In this thesis, results from a novel experimental

approach are presented, which considers increasing temperature and effective stress,

to study the changes of underthrust sediment.

Lithological end members of the incoming sedimentary sequence at the

Nankai margin were subjected to increasing effective stress and temperature in a

specifically adjusted heated oedometer device. Remoulded aliquots of the same

sediment were loaded to effective stresses of ~70 MPa at temperatures of 20 °C, 100

°C and 150 °C, the latter being equivalent to the updip limit of the seismogenic zone.

Post-hydrothermal research on compacts included SEM investigation, XRD analysis,

direct and ring shear test and geochemical pore water analysis.

The major finding of the heated consolidation tests is the positive correlation

of increasing temperature and pore space reduction under normal consolidation state

and drained conditions. The contraction suggests that the intergranular friction is

reduced and compensated by irreversible strain. This phenomenon reveals that the

consolidation state of subducted sediment is not only dependent of effective stress and

time as previously believed, but also on temperature. With the new findings it is

possible to explain the complex consolidation pattern along the “hot” central portion

of the Nankai prism toe where in-situ temperatures reach up to 110 °C. Inferred

excess pore pressure estimates based on the new data suggest smaller overpressures

than previously believed and are consistent with physical properties of compared

boreholes. A comparison of smectite and illite end member’s consolidation behaviour

ABSTRACT 2

further suggests that during the transition of smectite-to-illite, sediment

compressibility decreases during subduction.

Based on the outcome of the hydrothermal tests available laboratory

consolidation data were compiled and reviewed for the Nankai margin. Large

differences between in-situ and room temperature in the laboratory suggested a severe

implication for the observed overconsolidation. A state-of-the-art up-to-date thermo-

mechanical model was applied to estimate the temperature influence. The results

demonstrate that overconsolidation can be partially explained by the hardening effect

of lower temperatures. In essence, the results remove the discrepancy between

consolidation data and the general perception of a normally consolidated incoming

stratum. The data further imply that decollement formation along the central portion

of the Nankai Trough is governed by excess pore pressure generation and low

intrinsically shear strength of the sediment.

The geochemical analysis of expelled pore water during the heated

consolidation tests suggests that water-rock interaction is largely governed by

desorption-adsorption processes. The increasing temperature is associated with

enrichment of K, Ba and Si and the depletion of Mg. Temperature related release of

solutes may facilitate cementation of underthrust sediments and thus elastic strain

accumulation during seismic slip. Evidence of precipitates is only present in the

compact at the end of the 150 °C test of the smectite-rich sample as sulphates.

Consolidation further affects pore water constituents of the smectite end member. The

smectite-rich sample reveals a depletion of predominantly alkaline and earth alkaline

elements at a threshold of ~10 MPa, which is interpreted by the consecutive release of

free pore water and the residual water from the overlapping double layer of smectite.

XRD data after the experiments attest no significant degree of illitisation despite the

high temperatures and the long duration of the 3-5 month for each run.

In addition to the three first author manuscripts (see the three corresponding

paragraphs above), shear strength and frictional properties were measured of

remoulded end member sediments as well as intact compacts at room temperature.

Both the hydrothermal consolidation experiments and the shear tests were also run

with mineral-end members for calibration purposes. Geochemical analyses on these

materials are underway and will be condensed in additional publications.

ABSTRACT 3

ZusammenfassungAn konvergierenden Plattenrändern entstehen entlang der Plattengrenze

wiederholt große Erdbeben mit hohen Magnituden. Direkte Wäremestrommessungen

und thermische Modellierungen dieser Subduktionszonen deuten darauf hin, dass die

Seismogenese ungefähr bei einer Temperatur von 150 °C einsetzt. Die genauen

Gründe hierfür sind bislang wenig bekannt und werden kontrovers diskutiert. Die

subduzierten Sedimente sind anfangs weich, porös und nicht in der Lage zu instabilem

Reibungsverhalten. Daher müssen die Sedimente grundlegende Veränderungen

erfahren, um seismisches Reibungsgleiten (sog. Stick-slip) zu zeigen. Verschiedene

Hypothesen wurden in der Vergangenheit aufgestellt, die die effektive Spannung und

die Temperatur herausstellen und als Hauptursache des veränderten mechanischen

Verhaltens und diagenetischer Prozesse annehmen. Bisherige Laborversuche

fokussierten entweder auf die effektive Spannung oder die Temperatur. In dieser

Arbeit wird demgegenbüber ein innovativer experimenteller Ansatz durchgeführt, der

beide Parameter separat berücksichtigt, um die Veränderung der Sedimente während

der Subduktion zu charakterisieren.

Für die Laborversuche wurden natürliche Proben der abtauchenden

Sedimentabfolge des Subduktionseintrages aus dem Bereich der Nankai

Subduktionszone (SW Japan) ausgewählt, die die lithologischen Endglieder der

subduzierten Sedimente darstellen. Für die Versuche wurde eine speziell angefertigte,

beheizbare uniaxiale Ödometerapparatur entwickelt und benutzt. Die aufgearbeiteten

Proben wurden bis zu einer effektiven Spannung von ~70 MPa belastet und bei

Temperaturen von 20 °C, 100 °C und 150 °C durchgeführt. Die kompaktierten

Sedimente wurden dann weiterführend durch Elektronenrastermikroskopie,

Röntgendiffraktometrie, Direkt- und Ringscherversuche sowie geochemische

Analysen an den ausgepressten Porenwässern untersucht.

Das wichtigste Ergebnis der beheizten Konsolidierungstests ist die positive

Korrelation von Porenraumreduzierung mit ansteigender Temperatur unter normal

konsolidierten und drainierten Bedingungen. Die Kontraktion weißt darauf hin, dass

die intergranulare Reibung geschwächt ist und durch eine irreversible Verformung

kompensiert wird. Der Konsolidierungszustand der subduzierten Sedimente ist neben

den bekannten Größen Zeit und effektive Spannung deshalb auch abhängig von der

Temperatur. Anhand der Ergebnisse war es möglich den komplexen

ABSTRACT 4

Konsolidierungszustand entlang des zentralen Bereiches des Zehs des Nankai

Akkretionskeils zu erklären, wo die in-situ Temperaturen bis zu 110 °C betragen. Die

aus den Erkenntnissen abgeleiten Porenwasserüberdrücke sind kleiner als bisherige

Abschätzungen und wesentlicher konsistenter mit den beobachteten

petrophysikalischen Eigenschaften. Weiterhin lassen vergleichende Untersuchungen

zwischen den Endgliedern vermuten, dass die subduzierten Sedimente sich mit

fortschreitender diagenetischer Smektit-Illit-Umwandlung in der Subduktionszone

weniger kompressibel verhalten werden.

Basierend auf den Ergebnissen der hydrothermalen Konsolidierungstests

wurden verfügbare Daten zum Konsolidierungsverhalten des Subduktionseintrages

am Nankai Trog zusammengestellt und neu bewertet. Die Anwendung eines

thermoelastischen Models zeigt, dass die bisher bestimmten Überkonsolidierungen

partiell auf eine thermische Verfestigung zurückzuführen sind, die mit

Temperaturunterschieden zwischen in-situ und Laborbedingungen erklärbar sind.

Damit konnte die bisherige Annahme einer moderaten Zementierung der Sedimente

teilweise widerlegt werden, so dass die Entstehung des Decollements am Zeh des

Akkretionskeils in der Nankai Subduktionszone wahrscheinlich auf

Porenwasserüberdrücke und geringer intrinsischer Scherfestigkeit des Sediments

zurückgeht.

Die geochemischen Analysen der auspressten Porenwässer belegen, dass die

Wasser-Sediment Interaktion wesentlich durch Desorption and Adsorption

gekennzeichnet ist. Mit zunehmender Temperatur findet eine Anreichung der

Elemente K, Ba und Si sowie eine Abnahme von Mg statt. Die freigesetzten Elemente

können Zementierung und diagenetische Reaktionen unterstützen. Eine Ausfällung

konnte jedoch nur für den Test des smektitreichen Sediments in Form von Sulfat

nachgewiesen werden. Des Weiteren ließ sich zeigen, dass die Konsolidierung die

Zusammensetzung des Porenwassers bestimmen kann, dergestalt dass das Smektit-

Endglied über einem Grenzwert von ~10 MPa eine Abnahme von Alkali- und

Erdalkalielementen verzeichnet. Diese Beobachtung lässt sich durch das

aufeinanderfolgende Auspressen von freiem und adsorbiertem Porenwasser erklären.

XRD-Analysen der smektitreichen Proben zeigen, dass keine nennenswerte

Illitisierung in den Tests erreicht wurde trotz der über 3-5 Monate andauernden

Versuche.

ABSTRACT 5

Zusätzlich zu den drei Erstautoren-Manuskripten (vgl. die drei vorherigen

Absätze) wurden die Scherfestigkeit und das Reibungsverhalten der Sedimente an

aufgearbeiteten Probenmaterial sowie an den intakten Presslingen aus den

hydrothermalen Konsolidierungstests durchgeführt. Des Weiteren wurden auch Scher-

und Ödometertests mit Mineralstandards durchgeführt. Deren Auswertung und die

geochemischen Analysen sind derzeit in Arbeit und werden in weiteren Publikationen

münden.


Chapter 1: Introduction 1.1 Motivation

More than 90 % of world’s seismic moment is released along convergent

margins (Pacheco and Sykes, 1992). The majority of megathrust earthquakes with

magnitudes >8 occur in the realm where the subducting plate is temporarily coupled

to the overriding plate. To this day subduction zone earthquakes are a live and

economic threat to the large human population and their economy in the vicinity of

these tectonic plate boundaries. Such disastrous earthquake events are numerously

documented throughout human history including the recent Sumatra earthquake in

Dec. 2004 with a magnitude of 9.3 (Stein and Okal, 2005). It is supposed to be the

second most powerful earthquake ever recorded in modern history and 230000 lives

have been wiped out by the aftermath of the shaking followed by a devastating

tsunami.

Little is known about controlling factors for the unstable mechanical

behaviour because the depths of seismogenic processes has prevented closer

investigations by sampling and in-situ monitoring in the past. The increasing

temperature (T) and pressure (P) conditions in subduction zones yield interrelated

mechanical, mineralogical and geochemical processes. These processes alter the

incoming sediments, which show initially elastic deformation and stable sliding (e.g.

Kastner et al., 1991; Moore and Saffer, 2001). Enormous cost-intensive efforts to shed

light on these processes are currently established with the new drilling vessel Chikyu,

which is capable of reaching the region of seismogenesis at the Nankai convergent

margin in the near future (Tobin and Kinoshita, 2006). A cost-saving approach is the

application of specifically adjusted laboratory studies to simulate underthrusting and

to identify mechanical, mineralogical and geochemical repercussions on subducted

sediments. However, the study of increasing pressure with uniaxial and triaxial

deformation devices is often restricted to room temperature. Thus, mechanical tests

show a good agreement with physical properties at initial burial at the toe of the prism

(e.g. Saffer, 2003), but the mechanical response to increasing temperature is less

known. On the other hand, elevated temperatures are common to study water-rock

interaction, but the applied methods often neglect the change in burial conditions by

using autoclave devices at constant P values (e.g. You et al., 1996).


This study represents an attempt to identify the mechanical, mineralogical and

geochemical repercussions of high PT conditions on subducted sediments and its pore

water by laboratory testing during which P and T vary. An uniaxial deformation

device (oedometer) has been modified to allow testing at elevated temperatures. Thus,

it was possible to separate the effect of increasing P and T on the mechanical response

and water-rock interaction. The unique approach assumes that water-rock interaction

and mechanical processes are closely interrelated at active convergent margins.

Specimens for the Nankai Trough (Japan) representing the three end member

compositions in mineralogy were chosen to gather important rock mechanical data in

the area of the planned penetration of the seismogenic subduction thrust within

NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment).

1.2 Outline of the PhD project The PhD project was integrated in the DFG-funded project “Research on

Ocean Margin Earthquakes”. The PhD work comprised the development and

implementation of a heated uniaxial consolidation apparatus (oedometer) at the

MARUM, University of Bremen, which is capable of PT conditions equivalent to the

updip limit of the seismogenic zone (i.e. ~150 °C; Hyndman et al., 1995).

Simultaneously, a large number of samples from the pilot study conducted at the

SCRIPPS Institution of Oceanography was mechanically, geochemically and

mineralogically analysed and interpreted together with the mechanical consolidation

data.

Hydrothermal testing during the pilot study focused among others on

subduction zone sediments from the Nankai margin (SE Japan). The Nankai margin is

an excellent research area because of the high in-situ temperatures of 110 °C along its

central portion. Thus, it was possible to compare laboratory and in-situ influence of

temperature. Three sediment samples got selected from DSDP Site 297, representing

the mineralogical end member of the incoming sequence: A smectite-rich clay (N13),

an illite-rich silty clay (N14) and a dominantly silty to fine sand-grained

quartz/feldspar-rich sample. The samples have consecutively undergone heated

uniaxial consolidation tests at 20 °C, 100 °C and 150 °C. The results showed that

temperature has a significant effect for consolidation behaviour. Two manuscripts

resulted from this finding. The first manuscript (chapter 3) describes the test results


and focuses in the discussion on the explanation of thermo-mechanical behaviour and

its implication for the consolidation state, inferred excess pore pressures and the

change of mechanical response in the subduction zone. In the second manuscript

consolidation data from the Nankai margin was reviewed. A temperature correction

was applied to minimise the effects of temperature differences of high in-situ

temperatures and ambient laboratory testing including a new interpretation of the data

(see Chapter 5).

Geochemical analysis of fluids expelled from heated consolidation tests

allowed the detailed study of water-rock interaction. Major elements and trace

elements were analysed on the fluids, and part of the data set were summarised in a

research article (Chapter 6). Additional analyses on both fluids and the solid phase

before and after the deformation tests were analysed for minor constituents B and

�11B. These data appear in the Appendix and will be published later.

Post-analysis of the hydrothermal experiments also included scanning electron

microscope (SEM) investigation, x-ray diffraction analysis (XRD), direct shear

experiments on intact compacts and large strain ring-shear tests on remoulded sub-

samples (Fig. 1). The data were partially presented on a meeting (see appendix) and

the complete data set (see appendix) is considered for publication in future.

Fig. 1: Flowchart of the applied laboratory methods to identify implications of high PT conditions on mechanical behaviour and water-rock interaction.


The development and implementation of a heated uniaxial consolidation

apparatus is in the mean time completed. Two system were assembled which are

capable of normal stresses of 100 MPa and 300 MPa, respectively, and temperatures

up to 200 °C. A detailed description of the apparatuses is attached in the appendix.

The focus of these new experiments is on mono-mineral samples of the end member

lithologies at the Nankai margin (smectite, illite, quartz). So far, quartz-seawater and

smectite-seawater slurries have been consolidated at various temperatures. The results

are also included in the appendix. After completion, these samples will undergo the

same experimental post analyses as the natural samples.

Chapter 2: Sediments at convergent margins

The following subchapters outline the concept of sediment subduction and

how the sediment changes during subduction. The literature review encompasses the

increasing stress, its implications for excess pore pressure generation and water-rock

interaction as a matter of increasing temperature.

2.1 Sediment subductionThe concept of sediment subduction was developed shortly after the

establishment of plate tectonics in the late 1960ies. Simple balance calculations

revealed that the incoming sediment volume is greater than the observed volume

scraped off in form of an accretionary prism from the oceanic crust (e.g. Scholl and

Marlow, 1974; Scholl et al., 1977). Since then the analogy to the blade of a bulldozer

is used where variable amounts of a sediment pile are scraped off from the incoming

sediments (Chapple, 1978; Davis and Suppe, 1980, Davis et al., 1983).

The material that is scraped off forms a wedge (or prism) shaped accretionary

complex, which grows by ongoing frontal accretion and underplating of subducted

sediment to the base of the prism (Moore et al., 1982; Cloos and Shreve, 1988).

Accretionary prisms favourable form where the plate convergence rate is <6.7 cm/a

and the sediment supply is sufficient to accumulate a trench thickness >1 km (von

Huene and Scholl, 1991; Clift and Vannucchi, 2004). Although some modern

accretionary prisms exhibit large dimensions with up to 200 km width such as

Makran, SE Japan or the Lesser Antilles (Cloos and Shreve, 1988), only the upper 7-


37 % of the sediment pile is scraped off in a sequence of imbricate thrust slices in

front of the upper plate’s abutment of resistive rock structure (Clift and Vannucchi,

2004). The larger volume is subducted which has been estimated to be approximately

1.5 km3/a for contemporary convergent margins (von Huene and Scholl, 1991).

Accreted and subducted sediments are separated by a detachment fault, which

is commonly called the decollement and marks the plate boundary between the

subducted and the overriding plate. While the maximum principle stress in the

incoming sedimentary sequence is vertically orientated, it becomes inclined due to the

horizontal compression in the accretionary thrust belt above the decollement (Davis et

al., 1983, Moore, 1989). Below the decollement the underthrust sediment remains

horizontally largely undeformed, while the maximum principal stress is nearly vertical

(Fisher and Byrne, 1987). Beneath the accretionary prism, the decollement may step

down into the underthrust sediment and attach sediment to overriding plate and thus

contributes to the growth of the wedge (e.g. Moore et al., 1982). The remaining

sediment beneath the decollement may be subducted to greater depth and eventually

participate in magma generation and crustal growth, or mantle recycling (Clift and

Vannucchi, 2004).

2.2 Dewatering of subducted sediments 2.2.1 Fluid sources

The incoming sediment pile on the oceanic plate is initially weak, porous and

contains a substantial fraction of interstitial water (Bray and Karig, 1988). The

increasing load of the overlying prism sediments and the fast thickening of the trench

wedge deposits leads to rapid consolidation from 70-85 % to ~15 % porosity of the

sediments (Bray and Karig, 1985, 1988; Moore and Vrolijk, 1992). The term

consolidation refers to the mechanical pore space reduction as a response of the

sediment to an applied load. The process is a function of the compressibility of a

sediment and the time-dependent fluid expulsion, which is limited by the permeability

and thickness of the sediment (Terzaghi and Peck, 1948). Accordingly, consolidation

is faster for permeable coarse-grained sandy material than for less permeable, fine-

grained clayey material. If the water expulsion cannot keep pace with the loading, the

total stress is partially taken up by the pore water until the excess pore pressure has

dissipated and the total stress is completely taken up by the mineral framework. This


relation is expressed in the law of effective stress where �t is the total stress, �e is the

effective stress which is actually taken up by the mineral framework and P is the pore

water pressure in excess of the hydrostatic pressure:

�t = �e +P [1]

The compaction of a sediment in response to an applied load is material

dependent and may vary from margin to margin (Bekins and Dreiss, 1992). However,

the pore space decreases usually exponentially for all sediments with increasing load

(Athy, 1930). Thus, dewatering by consolidation is thought to be important for fluid

production within the first 5 km. (Moore and Vrolijk, 1992; Fig. 2). This is especially

applicable for a clay-rich sediment which can store much more interstitial water under

low stresses than coarse grained material (Karig and Hou, 1992).

Fig. 2: (A) Sketch of an accretionary prism showing that the underthrust section is rapidly consolidated by the overlying accretionary sediment, the area of mineral dehydration (grey shaded) and high permeable faults. (B) Schematic diagram of fluid generation of the subducted sediment. Fluids are initially expelled by sediment consolidation and later by mineral dehydration. Modified after Moore and Vrolijk (1992).


Subducted sediments may host additional water in the mineral structure, which

is released during diagenetic reactions or lithostatic load (e.g. Fitts and Brown, 1999).

While consolidation is largely completed within the first 5 km, mineral dehydration is

supposed to be the most important remaining fluid source in the subducted sediments

(Vrolijk, 1990; Moore and Vrolijk, 1992). Clay minerals from the smectite group are

believed to be the most important water bearing minerals in the shallow subduction

zone. Smectites are 2:1 phyllosilicate with sheets composed of an octahedral layer

between two tetrahedral layers. Cation substitution in the crystal lattice yields a

negative charge of the clay mineral surface, which is compensated by hydrated cations

in the interlayer of the phyllosilicate sheets. Thus, a fully hydrated smectite can

contain up to ~25 wt-% of water, which can be freed by lithostatic load, high

temperatures or progressively diagenetical smectite-to-illite transformation (e.g.

Colten-Bradley, 1987; Fitts and Brown, 1999). The illitisation starts at a temperature

of ~60 °C (Freed and Peacor, 1989) and is supposed to be completed by ~150°C in

subduction zone systems (Vrolijk, 1990; Moore et al., 2007).

Because of its abundance in many subduction systems (Vrolijk, 1990),

smectite dehydration is thought to be an important key parameter for mechanical and

hydrological processes (Moore and Vrolijk, 1992). Smectite is brought in as a part of

the terrigenous deposits at convergent margins but can also evolve from volcanic ash

alteration (Vrolijk, 1990). Well known examples for smectite-rich subduction inputs

are the Japan Trench (Aoki and Kohyama, 1992), the Barbados Ridge (Deng and

Underwood, 2001), the Nankai margin (e.g. Underwood and Steurer, 2003), or the

Costa Rica segment of Middle America Trench (Underwood, 2007).

Another water bearing phase is the amorphous opal-A. 23 vol-% water is

released during the conversion to quartz, which is completed at 100 °C (Moore and

Vrolijk, 1992; Behl and Garrison, 1994). Opal-A is formed by siliceous microfossil

skeletons of radiolarions and diatoms, which are less common in many subduction

zones and thus considered to be only regionally important (Moore and Vrolijk, 1992).

2.2.2 Physical hydrology

At subduction zones, it is widely acknowledged that the rapid thickening of

the overlying prism is faster than the pore water expulsion of subducted sediments

(von Huene and Lee, 1982; Le Pichon et al., 1993; Saffer and Bekins, 1998; 2006).

This compaction disequilibrium is expressed as excess pore water pressure that was


widely documented (e.g. Costa Rican, Nankai and Cascadian subduction zone) in the

shallow parts (<1500 meters below seafloor [mbsf]) by direct measurements (Becker

et al., 1997; Foucher et al., 1997) or indirectly estimated from the maximum past

effective stress, which can be inferred from consolidation tests (Saffer, 2003) and

calculated porosity from inverted p-wave velocity in combination with porosity-depth

profiles (Cochrane et al., 1996). Numerical modelling shows that excess pore pressure

built-up can start seaward of the trench by rapid sedimentation of the trench wedge

deposits onto the approaching sediment pile (e.g. Shi and Wang, 1985; Moore, 1989).

The increase in effective stress is hindered and reflected in a low shear strength which

is supposed to be an important reason for decollement initiation besides low intrinsic

strength of clay-rich sediment (Moore, 1989).

At deeper portions of the subduction zone the release of bound water into the

consolidated and low permeable sediment contributes to excess pore pressures

formation (Moore and Vrolijk, 1992). Numerical modelling, considering fluid sources

from consolidation and mineral dehydration, shows that fluid overpressure reaches

near lithostatic magnitudes (e.g. Saffer and Bekins, 1998; 2006; Fig. 3). Furthermore,

fluid transport-related parameters such as sediment permeability and drainage path

length are governing excess pore pressure (Saffer and Bekins, 2006).

Fig. 3: Modelled excess pore pressure distribution in percent of the total stress for the Nankai margin modified from Saffer and Bekins (1998). Note that the overpressure peaks between ~15-20 km arcward of the deformation front and diminishes afterwards.

Widespread appearance of veins and fractures in exhumed accretionary prisms

also attests that excess pore pressure ranges near lithostatic (e.g. Fisher and Byrne,

1987, Moore et al., 2007). These high pore pressures were postulated to facilitate fault

formation, decrease fault strength (Hubbert and Rubey, 1959, Brown et al., 2003),


reduce taper angle of accretionary wedges (Davis et al., 1983) and favour down-

cutting of the decollement (e.g. Moore, 1989; Saffer, 2003; 2007; Morgan et al.,

2007). Instead, diminishing excess pore pressure or increasing effective stress are

associated with strain localization and the updip limit for of the seismogenic zone

(Moore and Saffer, 2001).

2.2.3 Fluid flow and fluid pathways

High fluid pressure gradients are the driving force for fluid flow in subduction

zones. Dewatering of subducted sediment occurs as dispersed flow if the rate of pore

fluid flow is sufficiently low and advection can be accommodated by intergranular

permeability (Carson and Screaton, 1998). Although the bulk fluid volume is expelled

as dispersed flow out of the accretionary prism, its significance is supposed to be

diminishing with increasing depth because of the decreasing permeability (Moore and

Vrolijk, 1992; Saffer and Bekins, 1998). Where the dispersive fluid flow is

insufficient, fluid expulsion occurs along permeable fault zones and stratigraphical

layers or is expelled from mud volcanoes (Fig. 2; Moore, 1989; Henry et al., 1992;

Carson et al., 1994).

Field evidence for focused fluid flow along permeable layers comes from

geochemical and thermal anomalies. Low-chlorinity anomalies in fault zones are

widely documented and interpreted by deep-seated sourced fluids which originate

from the seawater freshening by smectite dehydration: e.g. You et al. (1993) for

Nankai margin, Kimura et al. (1997) for Costa Rican margin and Kopf et al. (2003)

for Japan trench. Numerical modelling of low-chloride anomalies along the

decollement suggests that subducted sediments are drained preferably to a permeable

decollement (Saffer and Screaton, 2003) and that fluid flow may occur episodically,

which probably associated to episodic fault displacement of seismic cycling (Moore

and Vrolijk, 1992; Saffer and Bekins, 1998). Localized fluid flow from deep sources

may also be characterized by warmer temperatures compared to the wall-rock, as

attested by subseafloor temperature measurements (Westbrook et al., 1994) and long-

term measurements in a sealed borehole (Davis et al., 1995) at ODP Site 892 at the

Cascadia accretionary margin.


2.3 Water-rock interaction 2.3.1 Conceptual model of fluid geochemistry evolution during deformation

The lithostratigraphic composition exerts a fundamental role for water-rock

interaction and thus fluid geochemistry. However, sediments at convergent margins

are highly variable due to the diversity of depositional settings. They are ranging from

distal abyssal plains on the incoming oceanic plate to the trench wedge and therefore

subduction inputs can range from pelagic ooze to hemipelagic mud and sandy

turbidites (Underwood, 2007). The result is a complex system, which changes from

margin to margin of which a comprehensive overview surely exceeds the scope of this

thesis. However, Kastner et al. (1991) proposed a conceptual model, which is

applicable to all margins: The interstitial fluid of the entering sediment possesses

initially seawater composition. The rapid burial prevents diffusive communication

with ocean seawater at depths greater than a few tens to hundred meters (Kastner et

al., 1991). Thus, the fluid geochemistry is locally dependent on diagenetical fluid

mineral exchange reactions and mineral-dehydration as well as diffusion-advection.

This local fluid is influenced by fluids from within the subduction system or from an

external source. Internal sources are deeper or overpressured regions in the subduction

system. They are characterized by advanced diagenetic reactions, which are

transported by vertical or lateral advection preferably along high permeable faults and

stratigraphic horizons (Moore and Saffer, 2001). External sources comprise meteoric

water, which may be incorporated by short and long-distance seaward transport or

induced by density inversion (Kastner et al., 1991).

2.3.2 Diagenesis in the shallow subduction zone

In the following enumeration, diagenetic reactions and their implication for

fluid geochemistry are presented with a schematic overview in figure 4. The

compilation is based on significant diagenetic reactions in accretionary complexes

according to Kastner et al. (1991) and Moore et al. (2007).

Volcanic ash alteration: The volcanism along convergent margins may accumulate

volcanic ash and tephra in the sediment. Among others volcanic ash was documented

in subduction inputs of the Peru margin (Clayton and Kemp, 1990), Coast Rican

margin (Kimura et al., 1997) and the Nankai margin (Taira et al., 1991; Moore et al.,

2001a). Low temperature alteration transforms the ash into zeolites and hydrous clay


minerals (smectite). The reaction is accompanied by water, alkalis and Mg uptake

(Kastner et al., 1991). The residual pore fluid becomes enhanced in chlorinity as

reported for the forearc at the Peru margin (Martin et al., 1995).

Hydrocarbon formation and gas hydrate dissociation: Hydrocarbon formation,

especially CH4, is accommodated by degradation of organic matter through bacterial

activity at shallow depth and thermal decomposition at greater depth with its

maximum at ~100 °C (Hunt, 1990). Fluid inclusion studies in fossil accretionary

prisms prove that hydrocarbon fluids can be present in depths of up to 10 km (Vrolijk

et al., 1988). There, hydrocarbon production may account for some H2O and low

density fluids, which may enhance excess pore pressure. In the shallow region

hydrocarbons are important for gas hydrate formation, which forms under certain PT

condition within the uppermost 1 km of the sediment (Kastner et al., 1991 and

references therein). A prominent example for gas hydrates at convergent margins is

the Cascadia subduction zone. The destabilization of the gas hydrates leads to fluid

freshening and free gas at depth, which migrates along faults to the sediment surface

(Kastner et al., 1990). The vent sites are characterized by fluids with e.g. low-

chlorinity, sulphide and ammonia. The expulsion is also associated with methane and

isotopically light CO2 discharge (Suess et al., 1999).

Mineral dehydration: The release of water during mineral dehydration leads to

dilution of the pore fluid. The fluid freshening is commonly characterized by the inert

chloride species (see above) and is ubiquitous at the whole variety of convergent

margins: At the Peru continental margin dilution is up to 20 %. Strontium isotopic

composition points to mineral dehydration, most probably clay dehydration and gas

hydrate dissociation (Elderfield et al., 1990; Kastner et al., 1990). At the accretionary

Nankai margin high basement temperatures along its central portion lead to advanced

smectite dehydration at the toe of the prism. The in-situ dehydration has been

proposed to be responsible for the observed chloride anomaly in the underthrust

sequence (Henry and Bourlange, 2004). For the non-accreting Costa Rican margin

low-salinity fluids have been detected along numerous seeps along the whole margin.

The source of these fluids is the dehydration of smectite and biogenic opal in the

subducting sediment with subsequent vertical fluid transport through the overriding

plate (Kimura et al., 1997; Spinelli and Underwood, 2004; Ranero et al., 2004). The

argumentation is confirmed by isotopic data, which is typical for clay dehydration at

temperatures up to ~150°C (Hensen et al., 2004). The smectite-to-illite reaction may


also be accompanied by the release of silicon, sodium, calcium, iron and magnesium

and the consumption of K and Al (Boles and Franks, 1979, Kastner, et al., 1991).

Albitisation: Albitisation is an important diagenetic reaction during the burial of

arkoses and graywackes at a temperature range of 110-120 °C (Fig. 4; Boles, 1982).

The reaction is characterized by the transition of detrital plagioclase to albite. To

accommodate the transition sodium is necessary, which may be either provided by be

surrounding seawater or from smectite-to-illite transformation (Boles and Franks,

1979). The Al and Ca by-products of the albitization foster clay mineral, calcite and

zeolite formation (Boles, 1982).

Carbonate and quartz cementation: Authigenic cements and veins form when the

solubility is sufficient to accommodate precipitation. Carbonate precipitates are

reported for shallow regions of accretionary prism (e.g. Barbados accretionary prism:

Vrolijk and Sheppard, 1991; Cascadia accretionary prism: Kopf et al., 1995).

However, studies of fossil accretionary prisms suggest that they are not common

below ~100°C but appear to be abundant principally above 150 °C (Fig. 4; Ernst,

1990; Moore et al., 2007). Ca but also Mg and Fe are provided by the influx of fluids

from the above mentioned diagenetic reactions (Boles and Franks, 1979; Sample,

1990; Kastner et al., 1991) while carbon can derive from seawater, dissolved

calcareous shells, decomposition of organic matter and methane oxidization (Vrolijk

and Sheppard, 1991; Kopf et al., 1995). Quartz precipitation occurs dominantly

> 200 °C (Fig. 4). Si can be provided by diagenetic reaction (e.g. dissociation of

biogenic opal) but also by pressure solution which begins to work > 150 °C and is

fostered by the presence of illite (Moore et al., 2007 and references therein).

2.4 Synthesis and implications for seismogenesis Earthquake distribution can be differentiated along plate boundaries in an

aseismic updip zone, a seismic zone where 90% of the earthquakes occur, and an

aseismic downdip zone (Fig. 4; Marone and Scholz, 1988; Marone and Saffer, 2007).

The seismic zone is characterized by brittle failure and unstable sliding (stick-slip),

which refers to the accelerating runaway behaviour during slip. This material related

rate dependent frictional behaviour is also called velocity weakening (Scholz, 2002).

Modelling of temperature distribution by Hyndman et al. (1995) and Oleskevich et al.

(1999) suggests that the updip limit is associated with temperature of 100-150 °C and


the downdip limit with temperatures of 350-450 °C (Fig. 4). While the aseismic

behaviour downdip is generally assumed to be related to the onset of crystal plasticity

(Scholz, 2002), the updip limit of seismogenesis is still actively discussed (e.g. Dixon

and Moore, 2007 and contributions therein).

Fig. 4: (A) Comparison of porosity versus depth for accretionary prism sediments in combination with the inferred onset of seismogenesis for the Nankai margin (modified after Moore and Saffer, 2001). (B) Compilation of important diagenetic reactions in the shallow subduction zone and their approximate temperature range (modified after Ernst, [1990] and Moore et al., [2007]). The grey shaded area indicates the temperature interval of the seismogenic zone along the subduction thrust.

There is common sense that the initial incoming sediment on the oceanic plate

is deforming elasto-plastically and is hence unable of seismic slip. The weakness of

these sediments lacks the capability to store energy which eventually allows a stress

drop sufficient to produce seismic slip (e.g. Byrne, 1988; Moore and Saffer, 2001).

Several theories try to explain the change in mechanical behaviour with in creasing

PT conditions. Early workers emphasised the enhanced compaction due to the high

loads (cf. Fig. 4A). They suggested that a consolidated backstop marks the onset,

which is in accordance with assumption of Marone and Scholz (1988) who proposed

that seismic behaviour in strike-slip faults occurs in highly consolidated and lithified

gouges. A variation of this hypothesis is the assumption that a highly compacted

sediment is sufficient to accommodate unstable sliding (Scholz, 1988). More recent

studies emphasized that the updip limit reflects diagenetic changes and thus


temperature. Vrolijk (1990) argued that the transition of smectite-to-illite

coincidences with the onset of seismogenesis which agreed well with later thermal

modelling (e.g. Hyndman et al., 1995). Laboratory tests showed that illitisation causes

a change in frictional strength, but smectite as well as illite favour stable sliding under

stresses equivalent to the updip limit (Saffer and Marone, 2003; Brown et al., 2003).

The latest hypothesis is given by Moore and Saffer (2001) and Moore et al. (2007)

who emphasise the linkage between mechanical and geochemical processes. They

believe that the updip limit relates to the onset of several diagenetic processes (as

described in Chapter 2.3.2), progressed consolidation and a diminishing excess pore

pressure (cf. chapter 2.2.2). The aim of this PhD thesis is to study how high PT

conditions may change consolidation behaviour, excess pore pressure formation and

water-rock interaction towards seismic behaviour.

Chapter 3: The geology of the Nankai margin The samples for this study derive from DSDP Site 297 (Fig. 5), which is

located seaward of the accretionary prism. A detailed description of this and other

related sites at the prism are provided in the manuscript chapters. Thus, this chapter

gives just a brief geological overview of the Nankai margin.

Fig. 5: Geological map of SW Japan region showing major provenances and transportation ways (modified after Moore et al., 2001b; Pickering et al., 1993). Material derived until 2 Ma ago predominantly from the north-eastern Outer belt (SW Japan; large arrows), when it switched to along axis transportation (short arrows) of material from the Izu collision zone (large arrows). The material is partly transported into the Basin or deflected by the basin slope (light arrows). Black dots show locations of DSDP and ODP sites shown in Fig. 6 and the dotted line indicates the location of the cross section of Fig. 7.


The Nankai Margin is located in the southwest of the Japan’s Shikoku Island

and the southwest part of Honshu Island (Fig. 5). Along the 700 km Nankai Trough

the Philippine sea plate is subducted at a rate of 2-4 cm/yr to the northeast under the

Eurasien plate (Karig and Angevine, 1986). The formation of the subducting oceanic

lithosphere began in the Oligocene by rifting of the proto-Izu-Bonin backarc and

consecutive seafloor spreading created the Shikoku Basin. The Shichito-Iwojima

Ridge and the Kyushu-Palau Ridge are relics of the former arc, which were separated

by the spreading until it ceased 15 Ma ago (Okino et al., 1994). The onset of

subduction is believed to be reflected in the 17-12 Ma igneous emplacements located

along the forearc (Fig. 5). The typical volcanic front developed later with deeper

penetration of the subducting slab and is associated with the beginning of volcanic

activity in SW Japan 6 Ma ago (Kamata and Kodama, 1994).

The Shikoku Basin is the north-eastern part of the Philippine sea plate which is

eventually subducted at the Nankai Trough. The Shikoku Basin contains a thick

sedimentary cover, which tapers of to the southeast and fades into a thin pelagic cover

(Karig, 1975). The general stratigraphic architecture of the ~1 km-thick incoming

sediment sequence in the Nankai Trough was penetrated during several DSDP (Deep

Sea Drilling Project), ODP (Ocean Drilling Program) expeditions and can be divided

into four major units (Fig. 6; Karig et al., 1975; Kagami et al., 1986; Taira et al.,

1991; Moore et al., 2001a; Mikada et al., 2002). The oldest is a thin layer of early

Miocene Volcaniclastic facies which is overlain by two dominantly hemipelagic

mudstones, the predominantly Miocene Lower Shikoku Basin facies and the Pliocene

to Quaternary Upper Shikoku Basin facies (Fig. 6). The youngest is the Nankai

Trench-wedge facies, which thickens rapidly to the trench (Moore et al., 2001a).

Evidence from seismic imaging and coring suggests that the decollement lies in a

consistent stratigraphic layer at the top of the Lower Shikoku Basin facies off Shikoku

Island (Moore et al., 2001b). Approximately two thirds of the incoming sediment pile

is currently scraped off including the Trench-wedge facies and the Upper Shikoku

Basin facies while the Lower Shikoku Basin facies comprises the bulk of the

underthrust sequence.


Fig. 6: Lithostratigraphic architecture along the south-western corner of the Nankai margin after Moore et al. (2001b).

Major provenance regions for abundant influx of terrigenous and

volcaniclastic material for Shikoku Basin sediments are Kyushu, western Honshu and

the Izu collision zone (Pickering et al., 1993). Further inputs are volcaniclastics from

the active Izu-Bonin island arc and the Kyushu-Palau ridge. At least since middle

Miocene turbidites arrived from the Outer belt (Southwest Japan) and accretion built-

up a prism by 4 Ma in front of the Cretaceous to Tertiary Shimanto belt (cf. Fig. 5).

With the Izu-collision 2 Ma ago at the eastern corner of the Nankai Trough, the

provenance shifted and the trench was filled by turbidites travelling along the axis of

the trench (Moore et al., 2001a). This sedimentation pattern is complicated by the

topographically high remnants of the fossil spreading ridge and the adjacent volcanic

Kinan seamount chain along the central portion of the margin (cf. Fig. 5). Terrigenous

sands are deflected by the basement highs and lead to a monotonous sedimentary

sequence above (Pickering et al., 1993; Underwood, 2007). This central portion of the

Nankai margin is still characterized by elevated heat flow and high in-situ

temperatures of ~110 °C, which lead to advanced thermal alteration of the overlying

sediments (Underwood and Pickering, 1996; Underwood and Steurer, 2003).


Based on seismic reflection data Moore et al. (2001a) separated the present

accretionary prism into several structural divisions (Fig. 7). The protothrust zone

(PTZ) marks the region where tectonic deformation begins and includes the formation

of the decollement in the Lower Shikoku Basin facies. Tectonic thickening of accreted

sediments is characterized in this region by small faults and ductile strain (Morgan

and Karig, 1995) while it is followed landward by an area of landward dipping

imbricate thrust packages, the imbricate thrust zone (ITZ). The imbricate thrust zone

is cut by a younger out-of-sequence thrust (OOST). This area, where the OOST cuts

from decollement upward is characterized by increased thickening of the accreted as

well as the underthrust sediments. According to the model of Saffer and Bekins

(1998) this area features the highest excess pore pressure ratios (Fig. 3). This

thickening, which is probably accommodated by duplexing, is followed by the deep

down-cut of the decollement into the subducted sediment (Fig. 7). Several packages

above the decollement can be inferred from seismic reflection data according to

Moore et al. (2001a), which may be related to underplating. Seismic imaging suggests

that the down-cutting is associated with a massive drop in excess pore pressures

(Bangs et al., 2004). Above the packages several OOSTs mark the area as a large

thrust-sliced zone (LTSZ), which cut through the prism and lead to substantial

thickening with landward dipping slope sediments. Landward of the LTSZ follow

presumably more rigid and consolidated sediments which are probably capable of

seismogenesis. They are characterized by landward dipping reflectors (LDR zone) and

represent the oldest material of Miocene to Pleistocene age, which is composed of

turbidites from the Outer belt.

Fig. 7: Cross section of the Nankai accretionary prism showing major structural and stratigraphic sequences modified after Moore et al. (2001b). See text for detailed explanation.


Chapter 4: Manuscript 1 The thermal influence on the consolidation state of underthrust

sediments from the Nankai margin and its implications for excess pore pressure

A.Hüpers1 and A.Kopf1

1MARUM - Center for Marine Environmental Sciences, University Bremen, P.O. Box 330440, 28334 Bremen, Germany.

Earth Planetary Science Letters (in press)

Abstract

The Nankai Trough convergent margin has been the focus of many multi-methodological surveys including half a dozen scientific deep-sea drilling expeditions. The boreholes focused on the smectite-dominated area off Cape Ashizuri and the thermally altered, illite-dominated region off Cape Muroto. On the basis of these surveys a number of studies addressed to the stress state of the underthrust sediments and its implications for the plate boundary thrust. Although the basement temperature has been found to be up to ~110 °C, none of these studies drew close attention to temperature effects on the consolidation state of the sediments. To overcome this shortcoming, we selected end member sediment lithologies from the incoming oceanic plate in the Shikoku Basin and subjected them to elevated stresses and temperatures.

We here present results from a series of heated (20 °C, 100 °C, 150 °C) uniaxial consolidation experiments up to effective normal stresses of ca. 70 MPa. The main finding is a positive correlation between temperature and pore space reduction. Based on in-situ temperature information from earlier scientific drilling, our study suggests that temperature has an influence on the consolidation state of underthrust sediments along the Nankai Margin. Together with secondary consolidation, thermal consolidation serves to explain steep log-linear consolidation curves of the incoming Lower Shikoku Basin sediments. The onset of diagenesis in this realm led to the transition of smectite-to-illite and to a different consolidation behaviour. Estimated in-situ pore pressures based on in-situ temperature data results in up to ~1 MPa smaller overpressures than those previously estimated from drilling data alone. Those values, which imply underconsolidation at drill sites near the frontal Nankai accretionary complex, are further believed to facilitate frictional sliding along the subduction thrust.


4.1 Introduction The Nankai Trough accretionary margin (Fig. 1A), off Southwest Japan, has a

1300 yr long record of large earthquakes, including the M>8 events of 1944 and 1946

(Ando, 1975). The margin has been a high priority location for DSDP (Deep-Sea

Drilling Project), ODP (Ocean Drilling Program) and IODP (Integrated Ocean

Drilling Program) drilling including subduction factory research and several studies

addressing to the stress state of underthrust sediments. The area is currently the focus

of the IODP project NanTroSEIZE (Nankai Trough Seismogenic Zone Experiment;

Tobin and Kinoshita, 2007).

Fig. 1: (A) Map of the Nankai subduction zone showing DSDP and ODP drillsites. Sediments of Site 297 were used for hydrothermal deformation experiments. (B) Interpolated temperature profiles of Site 1177, 1173, 1174 and 808 with reliable measurements marked as dots (modified after Moore et al., 2001; Taira et al., 1991; Kagami et al., 1986). The shaded area marks the temperature across the Lower Shikoku Basin with a dotted line to accentuate the decollement zone (DZ). (C) Cross section along the Muroto transect showing major stratigraphic sequences and structure of the toe of the prism (modified after Morgan and Ask, 2004).


The development of earthquakes at accretionary margins is directly linked to

changes in mechanical properties of the incoming sediments with depth. Since

seismogenesis cannot occur in the initially weak sediments, significant consolidation

and lithification have to take place along the plate boundary (e.g. Byrne et al., 1988;

Moore and Saffer, 2001; Saffer and Marone, 2003). While sediments above the plate

boundary undergo vertical and lateral (i.e. tectonic) consolidation with accretion,

underthrust sediments have been proposed to remain largely undeformed laterally

during initial subduction (e.g. Karig and Morgan, 1994). As a result of the applied

load due to the overlying prism, underthrust sediments are subjected to rapid

consolidation. Depending on the pore fluid dissipation as a function of permeability of

the overlying sediments, the progressive consolidation is characterised by pore space

reduction with increasing depth. However, modifications of physical properties and

mechanical strength document that underthrust sediments are not only subjected to the

applied load of the overlying prism, but also to increasing temperature, secondary

consolidation (creep), and counteracting processes such as elevated pore pressures due

to mineral dehydration, hydrocarbon formation, and diagenetic effects such as

cementation and chemical compaction (e.g. Moore and Vrolijk, 1992; Moore and

Saffer, 2001; Karig and Ask, 2003; Morgan and Ask, 2004). Such mechanisms

change the mechanical properties of underthrust sediments that are particularly

important for (1) the location of the main plate boundary fault (i.e. the decollement),

which is situated directly above these sediments and often propagates into them

(Brown et al., 2003), and (2) the onset of unstable sliding behaviour at the updip limit

of the seismogenic zone (Moore and Saffer, 2001; Saffer, 2003). So far, the detailed

influence of the different factors on the consolidation state and strength of underthrust

sediments and its consequences for seismogenesis and decollement localisation is

incompletely understood.

Although uniaxial consolidation testing has been successfully applied to study

effective stress and pore pressure distribution of marine sediments along the Barbados

and Costa Rican convergent margins (e.g. Moore and Tobin, 1997; Saffer et al., 2000;

Saffer, 2003), there are noticeable discrepancies between field consolidation and

laboratory consolidation at the Nankai Trough (Morgan and Ask, 2004). Only few

laboratory consolidation tests investigated the mechanisms influencing the

consolidation state of deep-sea sediments. For instance, Morgan and Ask (2004)

assume from triaxial reconsolidation tests that samples of the Nankai margin are


moderately cemented. Results from experiments by Karig and Ask (2003) suggest that

secondary consolidation occurs with burial of marine sediments, presumably also

closely linked to diagenesis.

Although temperature is supposed to be a key parameter for the onset of

seismogenesis (Oleskevich et al., 1999) its implication for consolidation behaviour of

underthrust sediments has so far been largely neglected. The objective of this study is

to contribute to narrow this gap. Isothermal uniaxial consolidation tests up to

pressure-temperature (PT) conditions similar to those at the onset of the seismogenic

zone (so called updip limit) have been conducted to shed light on thermal behaviour.

Tested specimen comprise different lithologies of the Lower Shikoku Basin facies

representing along strike variation as well as thermal alteration downslab of

subduction inputs at the Nankai margin. The results are discussed in comparison with

standard laboratory tests and shipboard measurements from drill sites at the toe of the

prism, and with respect to their implications for pore pressure distribution and

mechanical strength of underthrust sediments at the Nankai margin.

4.2 Geological Context and Sampling Strategy 4.2.1 Geological Context

Along the Nankai Trough, the Phillipine Sea plate is being subducted to the northeast

at a slightly oblique angle to the margin of southwest Japan (Eurasian plate) at a rate

of 2-4 cm/a (Karig and Angevine, 1986). Ongoing convergence led to the build-up of

a wide accretionary prism by offscraping of Shikoku Basin and Nankai trench wedge

facies from the downgoing plate (Fig. 1A). The Shikoku Basin was targeted in the

Nankai Trough area during DSDP and ODP drilling Legs 31, 87, 131, 190 and 196

(Karig et al., 1975; Kagami et al., 1986; Taira et al., 1991; Moore et al., 2001; Mikada

et al., 2002). Our study focuses on the Pliocene to Miocene Lower Shikoku Basin

(LSB) facies, which comprises the bulk of the underthrust sediments and has been

penetrated along two transects perpendicular to the margin: the Ashizuri and the

Muroto transects (Fig. 1A,C).

Off Cape Ashizuri, the LSB facies consists of hemipelagic mudstone with

abundant terrigeneous sandy turbidites and volcanic ash. Smectite content is ~20 wt-

% at the top of the LSB at Site 1177 (~23 km seaward from the deformation front)

and increases dramatically within the strata at 600 mbsf to ~50 wt-% (Underwood,


2007). It is assumed that no smectite diagenesis has occurred at this depth which is in

accordance with thermal gradients of ~50-56 °C/km along the Ashizuri transect (Fig.

1B). The projected decollement at Site 1177 is at a depth of ~420 mbsf in a

stratigraphic level equivalent to the Muroto transect. With less confidence, it may be

traced to a level of ca. 550 ± 30 mbsf at Site 297 several tens of km outboard of the

trench. The pore space decreases with increasing depth at Site 1177 but is generally

higher compared to equivalent depths of drill Sites at the Muroto transect (Fig. 2).

Fig. 2: Pore space-depth relationships along the Muroto transect (Sites 1173, 1174 and 808) and the Ashizuri transect (Site 1177) based on Shipboard measurements. (modified after Moore et al., 2001; Taira et al., 1991; Kagami et al., 1986). The pore space is presented as void ratio (volume ratio of pore water and solids). The light shaded area shows the Lower Shikoku Basin facies (LSB) and the dark shadings marks the decollement zone (DZ).

The subducting seafloor off Cape Muroto is situated above a basement high,

formed by a fossil spreading ridge and an adjacent chain of volcanic seamounts. The

LSB was penetrated ~11 km (Site 1173), ~0.25 km (Site 1174) seaward of

deformation front, and 1.5 km landward of the deformation front (Site 808; Fig. 1C).

Although sandy turbidites are common within the LSB they have not been sedimented

on this ridge, leading to a monotonous lithological sequence of hemipelagic

mudstone. Due to its location near the fossil spreading ridge, it is characterised by a

high heat flow of ~129-180 mW/m2 and a projected basement temperature of ~110 °C

for Sites 1173 and 808 (Taira et al., 1991; Moore et al., 2001). At Site 1174 the

projected temperatures are up to ~140 °C but may have been overestimated due to the


input of warm fluids and thrust faulting (Moore et al., 2001). Thus, a consistent

basement temperature of 110°C has been assumed for this study (Fig. 1B). Kinetic

reaction models for smectite-to-illite transition found to be highly consistent with

measured illite in I-S clays for these high temperature conditions (Saffer et al., 2008).

At Site 1173, smectite content decreases continuously from ~35 wt-% at the top of the

succession to ~25 wt-% at the bottom (Underwood, 2007). Further landward at Site

808, smectite content is just about <6-7 wt-% and illite is the dominant clay mineral

(Underwood and Pickering, 1996). Hence, it can be assumed that the smectite-rich

layers at the Ashizuri transect will undergo a similar mineralogical change, although

less pronounced owing to lower heat flow values (e.g. Moore et al., 2001).

The pore space decreases continuously with depth within LSB strata at Site

1173 (Fig. 2), but this trend is interrupted in the upper part of the LSB by an abrupt

increase in void ratio (Fig. 2) across the decollement zone at the other holes (808-

840 mbsf at Site 1174; 945-964 mbsf at Site 808). This rapid change has been

interpreted as a change in stress state due to overpressuring of the underthrust

sediments (e.g. Screaton et al., 2002; Saffer, 2003) but also due to excess compressive

strength of these sediments as a matter of cementation (Morgan and Ask, 2004). A

more detailed discussion of this topic can be found in Morgan et al. (2007).

4.2.2 Sampling Strategy

To cover the wealth of lithological differences along the Nankai Trough, end

member lithologies were selected based on semi-quantitative XRD results from

Underwood et al. (1997) and Brown et al. (2003). Samples for this study derive from

the LSB facies of Site 297, which is located SW of Site 1177 (Fig. 1A) along the

Ashizuri transect. The selected samples comprise a smectite-rich clay (N13), an illite-

rich silty clay (N14) and a dominantly silty to fine sand-grained quartz/feldspar-rich

sample with some clay fraction (N18). Sampled depths within the lower part of the

LSB (~330-570 mbsf) are 506.83-506.90 mbsf (N13), 507.12-507.20 mbsf (N14) and

554.47-554.63 mbsf (N18), respectively. The accumulated sample material was

disintegrated and homogenised for the experiments. To provide evidence for

mineralogical composition and integrity, sub-samples underwent semi-quantitative

XRD examination at the University of Bremen (Germany) following the methodology

described in Vogt et al. (2002) after completion of the compaction tests. The results

verify a uniform composition for sub-samples of each end member, which attests that


no significant smectite-to-illite transition has occurred in our tests. This is in

accordance with slow kinetic reaction of smectite-to-illite at these temperatures

proposed by Huang et al. (1993). However, the end members are significantly

different in the main components (cf. Tab. 1), representing a variation of a mainly

three component system (smectite [Sm], illite [Il], and quartz [Qtz]). Sample N13 is

rich in clay minerals and smectite-dominated with contents representative for

smectite-rich interlayers between the turbidites in the lower part of the LSB along the

Ashizuri transect. Sample N18 possesses a high granular fraction (containing quartz,

feldspar, and tephra) and reflects the turbiditic, coarse-grained end member lithology.

The fine-grained sample N14 has a high illite content and may be therefore (1)

comparable to the fine-grained hemipelagics along the thermally overprinted Muroto

transect and (2) simulate consolidation behaviour during deeper underthrusting

beneath Cape Ashizuri. Thus, we simulate both, thermal alteration along-strike as well

as down-slab.

Tab. 1: Results from quantitative XRD showing major mineral content (wt-%). Sample N13 is smectite-rich clay, while samples (N14) and (N18) contain both large fractions of illite, quartz and feldspar. Although mineralogically similar, sample (N14) is a silty clay while sample N18 is dominantly silty to fine sand-grained with some clay fraction.

Quartz + Feldspar

Smectite + Montmorillonite

Illite + Muscovite Chlorite Mixed layer

clays other

N13-20 5.7 43.5 0.0 2.0 35.6 13.2 N13-100 9.2 56.3 19.9 0.0 12.9 1.7 N13-150 15.1 43.3 8.4 1.9 18.2 13.1

N14-20 49.1 4.0 29.9 1.6 1.7 13.7 N14-100 44.2 6.6 27.0 2.6 6.6 13.0 N14-150 52.0 2.8 29.3 2.4 5.6 7.9

N18-20 51.1 1.8 24.2 3.1 6.7 13.1 N18-100 48.8 0.6 8.9 2.9 22.7 16.1 N18-150 60.0 2.3 19.8 3.0 6.2 8.7

4.3 Methods 4.3.1 Consolidation Theory

The compaction of sediments is described by the effective stress law and the

one-dimensional consolidation theory (e.g. Terzaghi and Peck, 1948), which will be

recapitulated briefly in the following. When a vertical load is applied suddenly onto


an unlithified sediment mass, the total pressure is taken up by the mineral framework

and by the water in the pores. The total stress (�t) is, therefore, defined as the sum of

the effective stress on the mineral framework (�e) and the excess pore water (P) in the

effective stress law

�t = �e + P [1].

Over time the water drains from the sediment pores, which causes a transfer of

the stress on the mineral framework and to a plastic deformation of the sediment until

the pore water overpressure dissipates. This process is known as consolidation.

However, if drainage of the pore fluid is hindered, pore space remains high and the

created excess pore pressure reduces the effective stress (�e). The relationship

between pore space and the effective stress can be described after Terzaghi and Peck

(1948) by

e = e0 - Cc * log(�e) [2]

with e being the void ratio (= volume of voids / volume of solids), e0 the void

ratio at an effective stress unity of 1, and Cc the compression index. Although void

ratio is more common in this context some authors also use the porosity as pore space

characterisation for equation [2]. To compare data with such studies, we calculated

void ratio from porosity � for those studies by using the equation

e = � / (1 - �), [3]

and recalculated equation [2] to maintain comparability to our study.

Since the consolidation is material-related, equation [2] has to be determined

by laboratory consolidation tests. Throughout a consolidation test, remoulded

sediments are characterised by plastic deformation. Test results are plotted in a void

ratio vs. log effective stress (�e) diagram where the relationship presented in [2] gives

ideally a straight line, the primary or virgin consolidation line (Fig. 3). It marks the

consolidation state where pore space and effective stress are in equilibrium when the

excess pore pressures has dissipated (�t = �e). The continuing consolidation at a

constant effective stress after pore pressure dissipation is termed secondary

compression (creep). In-situ consolidation is often the result of primary and secondary

consolidation (Karig and Ask, 2003). A sample, which has undergone primary and

secondary consolidation, responds to increasing stress by tertiary consolidation until

primary consolidation is resumed (Fig. 3). Upon unload or reload of a sample

consolidation occurs in an elastic fashion. To avoid relaxation effects due to core

recovery from depth a rebound value of 0.045 % e/log(�e) [= 0.0199 % �/log(�e)] for


all shipboard void ratio data from the Muroto transect has been applied after Morgan

and Ask (2004).

Fig. 3: Schematic view showing the known types of consolidation in the void ratio vs. the logarithm of effective stress (modified after Karig and Ask, 2003). Primary consolidation proceeds along line 1 and marks the equilibrium between pore space and the applied load after the excess pore pressure has dissipated. Further settlement of the sediment at constant stress is termed secondary consolidation (2). Unloading or reloading of a pre-stressed sample results in an elastic behaviour (3). Tertiary consolidation (4) occurs between the maximum consolidation state after secondary consolidation and resuming primary consolidation.

4.3.2 Sample preparation and testing procedure

In preparation of each experiment, the core samples were ground until the

samples were fully disaggregated and re-hydrated in seawater for a period of 1 to 5

days. Thereafter, the samples were placed in a self adjusted high-capacity oedometer

with a diameter of 55 mm. Initial void ratios were 4-5 and sample heights were up to

62 mm. Tests with aliquots of each specimen were carried out at 20 °C, 100 °C and

150 °C, and specimen labelling always provides sample ID – T [in degrees C] (e.g.

N13-20 for a room temperature test at 20°C, N13-100 for a test heated at 100°C, etc.).

For the heated consolidation runs, a band heater was placed on the outside of the

confining chamber. The temperature was monitored in the centre of the sample with a

probe that relayed its reading to the heating and was controlled by a high-precision

heating unit (Omega CN7600). Temperature fluctuations during the tests were smaller

than 2 °C. Heating was conducted at the beginning of the tests in several steps over

two days before loading up to approximately 70 MPa.

Consolidation took place under one-sided drained conditions with rates of

strain of <0.0125 %/min for sample N18 and <0.0042 %/min for sample N14 and


N13, which are in the range of successfully tested strain rates for different clays by

Smith and Wahls (1969). A backpressure of ~500 kPa was applied to get entrapped air

into solution and to prevent the pore fluid from evaporating. Pore pressures were

measured using Validyne™ differential pressure transducers (accuracy ± 25 kPa)

attached to the fluid drainage at the top and to the bottom of the cell. Shortening of the

sample was measured with a Burster™ displacement transducer (accuracy ±

0.075 mm).

In order to determine the void ratio for any given stress state, the final void

ratio and the final sample height must be known. For this, final compacts were

recovered from the cell after unloading and cooling over a period of ~6-12 h. This

span of time eliminates dehydration effects of smectite during the tests (Fitts and

Brown, 1999). Sample height was determined by taking the average of the

measurement at three different positions of the compact with a sliding calliper

(accuracy ± 0.1 mm). For void ratio determination, consolidated samples were placed

in an oven at 80 °C and were allowed to dry for several days until no further loss of

fluid was noted. This procedure was necessary because the insulation made the

apparatus inaccessible to determine the absolute location of the piston in the cell.

Thus, void ratio data possibly include rebound and cooling effects. Nonetheless,

rebound effects may be negligible when results of the same mineralogical sample are

compared and maximum stresses have been the same.

4.4 Results

An overview of the results of the consolidation study is shown in Figure 3.

Apart from runs N14-20 and N18-20, all samples show a more or less arcuate

consolidation curve, which is especially pronounced for the smectite-rich clay. Data

are sparse in the beginning of some tests, because of greater logging intervals for

some experiments and logarithmic presentation of the measured values. For the best

fit calculation of e vs. log �e, we hence regarded only data greater than 4 MPa. For

this range the majority of the samples display the typical log-linear e vs. �e

relationships for remoulded sediment. We calculated the best fit of equation [2] for

the individual sample data (Tab. 2) to describe the pore space reduction with

increasing effective stress following Terzaghi and Peck (1948). Coefficients of

determination for best fits are better than R2=0.97 except for run N13-150 (R2=0.93).


Tab. 2: Best fit of least squares of logarithmic equation [2] describing the virgin consolidation behaviour of each specimen. Only data points >4 MPa have been included in the best fit of e vs. log(�e) because of the bent curve progression. The overall high coefficients of determination (R2) of the best fits indicate a good linear relationship between void ratio and the logarithm of effective stress.

20 °C 100 °C 150 °C

N13 e = 1.51 – 0.52 * log(�e)

R2=0.99 e = 1.17 – 0.43 * log(�e)

R2=1.00 e = 1.64 – 0.70 * log(�e)

R2=0.93

N14 e = 1.71 – 0.41 * log(�e) R2=1.00

e = 0.77 – 0.21 * log(�e)*

R2=0.98 e = 0.86 – 0.32 * log(�e)

R2=0.99

N18 e = 1.11 – 0.33 * log(�e) R2=0.99

e = 0.90 – 0.31 * log(�e) R2=0.99

e = 0.84 – 0.28 * log(�e) R2=0.97

Data for the smectite-rich sample N13 show near-parallel curve progression

for the tests at 20 °C and 100 °C at stresses greater than 10 MPa, where compression

indices reached 0.52 and 0.43, respectively (Fig. 4A). The downshift of the 100 °C

run may be given by the difference in e0 and accounts for a shift of 0.34 between the

curves. Both experiments, at 20 °C and 100 °C, were aborted at effective stresses of

45.3 MPa and 53.8 MPa, respectively, because the fluid pressure approached the

maximum range of the pressure transducers. Sample N13-150 shows a good

agreement with the sample N13-100 at effective stresses greater than 30 MPa. At

lower stresses this sample shows steeper void ratio reduction with depth. Hence, the

best fit reveals a higher Cc and e0 compared to the two other runs. Noticeable is the

halt in void ratio reduction with increasing stress, which is followed by an abrupt

decrease in void ratio over small effective stress ranges (e.g. between 6-7 MPa and

20-30 MPa).

The observed shift in void ratio with increasing temperature can also be seen

for the illite-rich sample N14 (Fig. 4B). The shift in e0 of about 0.93 between sample

N14-20 and N14-100 is significantly bigger than for sample N13. In contrast, the shift

between the heated tests is negligible for effective stresses lower than ~15 MPa. With

increasing stress the N14-150 curve retains the higher rate of void ratio reduction so

that at maximum stresses of ca. 70 MPa the difference in e is only 0.11. The slope of

the three consolidation lines deviates between 0.41 and 0.25 with lower values for the

heated runs. Compared to the smectite-rich sample the compression indices are

noticeable smaller.

The turbiditic specimen N18 shows the lowest variation in compression index

(Fig. 4C). Values range between 0.33 and 0.28 with smaller values for the heated

runs. These compression indices are significantly smaller those of the smectite-rich


sample and on the lower end of the measured range for the illitic sample. Based on the

good agreement of the compression indices the shift in the consolidation curves of the

room temperature test and the heated test at 100 °C is 0.21 given by e0. The difference

between the heated runs increases due to the smaller compression index of sample

N18-150 and is negligible at the maximum effective stress of 70 MPa. The mentioned

halt in void ratio reduction for sample N13-150, although less pronounced, can also be

observed for sample N18-150 at 3-4 MPa (Fig. 4C). The delay in consolidation may

be created by transient elevated pore pressures owing to low permeability of the

samples or blocked filters. The latter seems more reasonable because no excess pore

pressures have been measured.

Fig. 4: Results from the isothermal consolidation tests for (A) the smectite-rich (N13), (B) the illite-rich (N14), and (C) the quartz-rich (N18) lithologies. Note the offset with increasing temperature towards lower void ratios.

4.5 Discussion and Implications 4.5.1 Interpretation of laboratory consolidation data

From isothermal oedometer tests carried out on end member lithologies from

the LSB succession along the Nankai margin at three different temperatures, we

present nine different consolidation curves (Fig. 4) from which three major

observations can be deduced:

(1) The consolidation lines do not show the ideal log-linear behaviour but

have an arcuate shape.

(2) The slopes of the consolidation lines are different for each sample.


(3) The consolidation curve shifts for each sample with increasing

temperature.

Consolidation below 4 MPa reveals a steeper rate of void ratio reduction with

increasing stress than at higher stresses. However, standard soil mechanical testing is

often restricted to lower effective stresses and variation at higher pressures has not

received comparable attention so far. Karig and Hou (1992) commented that the slope

at low stresses smaller than 5 MPa are steeper and cannot be projected to higher

stresses. This is fairly consistent with our results where we set the threshold at 4 MPa.

Accordingly, the change in the slope of the consolidation line indicates that the rate of

compression decreases with increasing effective stress (Karig and Hou, 1992). In fact,

our room temperature tests give compression indices Cc N13 > Cc N14 > Cc N18,

which is in accordance with the proposed order of Lambe and Whitman (1969) for the

compression index of Cc_clay > Cc_silty_clay > Cc_silt. This order represents particle size

and shape as most influencing parameter for the relationship of void ratio and

effective stress.

The most striking finding of this study is the decrease in void ratio at a

constant effective stress with increasing temperature from 20 °C to 100 °C. At higher

temperatures (i.e. between the 100 °C and 150 °C runs), this effect remains observable

but is less pronounced. If the absolute values in the observed offset of the void ratio is

assumed to be linear between 20 °C and 100 °C, the void ratio reduction is 0.012 e/°C

for the illite-rich sample, 0.004 e/°C for the smectite-rich sample and 0.002 e/°C for

the turbiditic sample. Although these data are higher than those of Campanella and

Mitchell (1968), the observed temperature-dependent consolidation trend is in unison

with several studies of thermal clay compaction tests that under fully drained

conditions heat enables greater deformation until a load is compensated by the

mineral framework (e.g. Campanella and Mitchell, 1968; Cekerevac and Laloui,

2004). According to Paaswell (1967) the heating induces a greater motion of water

molecules, which are bond to the clay particles. Coupled with lower water viscosity,

this motion alleviates a pressure-independent resistance between the clay boundary

layers to shear and causes a parallel shift of the consolidation lines for different

temperatures. The latter observation cannot be fully supported by our study up to

70 MPa, most likely because the earlier work focused mainly on low stresses

(<1 MPa; cf. Campanella and Mitchell, 1968; Cekerevac and Laloui, 2004). Although

only slightly, the offset is more pronounced for low stresses in our testing, leading to


lower compression indices for the heated tests, so that we assume that the impact of

temperature on the physico-mechanical factors on intergranular friction decreases

with increasing effective stress.

4.5.2 Application to the consolidation state of underthrust sediments

Along the Ashizuri transect where our samples originate from, in-situ

measurements and also physical properties data such as void ratio and temperature

with depth for LSB sediments are very limited from DSDP drillings, and only one

ODP borehole (Site 1177) provided a comprehensive data set later. For this, we use

data from Sites 1173, 1174 and 808 along the Muroto transect for comparison with

our results. These sites have the added advantages that downhole differences in

lithology are smaller than along the Ashizuri transect (e.g. lack of turbidites) and

temperatures are high (Fig. 1B). Further, these sediments have progressively

undergone illitisation from Site 1173 to 808, which makes them suitable to study

temperature and diagenetic effects otherwise encountered only at depths of several

kilometres. The total stress �t for these Sites can be calculated by integrating the bulk

density downward in the holes and subtracting the hydrostatic pressure owing to the

water column of the respective height. When fluid overpressuring is excluded, as it is

assumed for Site 1173 (e.g. Karig, 1993, Spinelli et al., 2007), the calculated stress

equals the effective stress �e.

4.5.2.1 Influence of temperature

To examine the influence of temperature on in-situ consolidation, Site 1173 is

used as a reference (Fig. 5). Although temperatures are high across the LSB (65 °C to

105 °C, Fig. 1B), the degree of illitisation is small and the strata is believed to be

normally consolidated �t=�e (Screaton et al., 2002; Spinelli et al., 2007). Thus, the

void ratio vs. effective stress relationship should be comparable to laboratory

consolidation.

The best fit of the in-situ data for Site 1173 is e = 1.50-1.38*log(�e) (Fig. 5).

Morgan and Ask (2004) derived from laboratory consolidation a value of Cc�=0.236

from the porosity vs. log (�e) relationship which corresponds to Cc ~0.99. This value

reflects the upper threshold of a variety of consolidation results (cf. Spinelli et al.,

2007). Thus, we examine temperature effects conservatively. Applying the laboratory


Cc from the top of the LSB to model the response according to the overlying load, the

void ratio decreases by 0.40 across the effective stress range studied. This leaves 0.17

unaccounted for (Fig. 5), so that in-situ consolidation must be subjected to another

effect that introduces additional strain. Given the thermal void ratio reduction under

normally consolidated conditions, the increasing temperature across the LSB strata

may explain the residual amount of void ratio reduction (Fig. 5). To estimate the

expected maximum void ratio reduction of thermal consolidation across the LSB

strata, the approximated thermal consolidation rate of 0.004 e/°C (N13) results in an

additional void ratio reduction of 0.16 for a temperature interval of 40 °C. Secondary

consolidation (creep) may additionally affect consolidation behaviour, reducing pore

space with time. Karig and Ask (2003) suggest that at geological time scales

sediments consolidate slowly enough that primary and secondary consolidation

proceed simultaneously. This may be facilitated by the slow sedimentation rate of 27-

37 m/Ma for the LSB facies (Moore et al., 2001). This suggests that the observed

discrepancy is the combined result of thermal and secondary consolidation, with

secondary consolidation known to be more advanced at higher temperatures (Mitchell

and Soga, 2005).

Fig. 5: Void ratio vs effective stress data (circles) for Lower Shikoku Basin facies at Site 1173 (Moore et al., 2001) with best fit given as dashed line [e = 1.50-1.38*log(�e)]. The solid line marks the estimated void ratio reduction due to mechanical loading (weight symbol) from the top of the LSB strata. The residual of 0.17 (thermometer) is explained by thermal consolidation and creep.


Finally, it can be speculated that the observed temperature-dependent

consolidation behaviour may have implications for frictional strength and stability of

underthrust sediments in the seismogenic zone. Our study reveals that thermal

consolidation is a result of decreasing interparticle friction, which suggests a

weakening in sediment strength. Contrariwise, the lower void ratio may compensate

the interparticle weakening by increased compressive strengthening under fully

drained conditions. Under natural conditions pore pressure estimates for accretionary

prisms are generally predicted to be near lithostatic at seismogenic depth, suggesting

that the drainage is hindered (e.g. Saffer and Bekins, 1998). This implies that no

compressive strengthening takes place and that the decrease in interparticle friction

cannot be compensated by thermal consolidation. The greater volume increase of pore

water with increasing temperature may also lead to substantial pore water

overpressure that further weakens the sediment. However, friction experiments under

elevated temperatures have to be conducted to scrutinise these phenomena and their

effect on sliding behaviour.

4.5.2.2 Influence of diagenesis

Once underthrust, sediments are subjected to thermal alteration downslab.

Ongoing illitisation leads to a change in mineralogical composition, fluid release and

thus to different consolidation behaviour. Maximum compression indices reported for

Sites 1173, 1174 and 808 indicate a decrease in the compression index Cc from 0.99 >

0.7 > 0.43, which correspond to the compression indices of 0.236 > 0.186 > 0.160

determined by Morgan and Ask (2004) and Karig and Ask (2003) from the porosity

vs. log (�e) relationship. Similar results on various clays at up to 50 MPa were derived

by Djeran-Maigre et al. (1998) where a decreasing smectite content is also linked with

a decrease compression indices.

The change in consolidation behaviour of the subduction inputs may be

additionally affected by other diagenetic processes and finally by lithification.

Depending on the primary mineralogy, clastic sediments are supposed to be modified

during burial diagenesis by the gradual replacement of smectite, detrital biotite, K-

feldspar and calcic plagioclase by chlorite, illite and albite (Kisch, 1983). Frey (1987)

assumes that more than 95 % of very low-grade metaclastites are a mixture of

muscovite (or illite), chlorite and quartz. Especially quartz formation would foster

earthquake generation because it exhibits unstable frictional sliding behaviour in the


range of 150-300 °C. Quartz cementation occurs due to silica dissolution (e.g.

pressure solution), which precipitates at temperature >150 °C (Moore et al., 2007).

Although the contention that smectite-to-illite transition plays a major role in

seismogenic faulting (Vroljik, 1990; Hyndman et al., 1995) has been questioned based

on shear experiments of seawater-saturated sediment at room temperature (Brown et

al., 2003; Ikari et al., 2007) illitisation may facilitate quartz cementation because the

reaction produces silicon as by-product (Curtis, 1985). These finding may be in

favour of the hypothesis that a threshold in consolidation state (Marone and Scholz,

1988; Marone and Saffer, 2007) or the combination of lithification/consolidation and

diagenesis (Moore and Saffer, 2001) are held responsible for the onset of unstable

sliding behaviour.

4.5.3 Implications for pore pressure estimates

The knowledge of the magnitude of pore fluid pressure fluctuations is

important because excess pressures lower the sediment strength and make it prone for

failure (Hubbert and Rubey, 1959; Moore, 1989; LePichon et al., 1993). Regions with

elevated pore pressures are important for the formation of the decollement near the toe

of the forearc, and also for the onset of seismogenesis (e.g. LePichon et al., 1993;

Moore and Saffer, 2001). High pore pressure transients were measured or inferred in

underthrust sediments for several convergent margins (e.g. Foucher et al., 1997;

Becker et al., 1997; Screaton et al., 2002; Saffer, 2003, 2007).

Previous studies used the void ratio vs. log (�e) relationship inferred from

shipboard data from Site 1173 as a reference to estimate excess pore pressure for the

Nankai margin along the Muroto transect (Fig. 6A, Saffer, 2003, 2007). Estimated

pore pressure suggest a landward increase of 2.5-4.6 MPa for Site 1174 and 4-

5.5 MPa for Site 808 (Saffer, 2007). The determined overpressures have been

assumed from rapid sedimentation and thickening of the prism toe and poor drainage

of the sediments. From numerical simulations that take into account the thermal state,

Gamage and Screaton (2006) conclude that rapid trench sedimentation and prism

thickening may be insufficient to explain the high pore pressures reported from

previous studies. Sedimentation of trench wedge facies and thickening of the prism

toe lead to an increase in sediment thickness above the basin hemipelagites to 483 m

at Site 1174 and 620 m at Site 808 (Taira et al., 1991; Moore et al., 2001), which

correspond to a load of ~4 MPa and ~5.5 MPa respectively. This suggests that in the


deeper parts of the LSB the additional load is either to small to create the excess pore

pressure or totally taken up by the pore water. In the latter case no reduction in void

ratio can occur under these circumstances and void ratios of all Sites should be the

same. However, comparing the top and the bottom of the underthrust section of LSB

shows that void ratio is smaller for Sites 1174 and 808. Thus, the LSB has undergone

consolidation and partial drainage must have reduced the excess pore pressure. We

revisit the problem using the considerations from our thermal experiments.

Consolidation for Site 1173 is governed by low sedimentation rates and high

temperatures for the projected underthrust sequence (~75–105 °C, Fig 1B). Its

downhole void ratio reduction is the result of mechanical, thermal and secondary

consolidation. With beginning underthrusting at Site 1174 and 808 loading rates

increase dramatically, which makes the sediment less prone for time dependent

secondary consolidation (creep). Further, temperature does not increase with depth

when compared to Sites 1174 and 808 (~87-107 °C) and accordingly, no thermal

consolidation takes place here. Without the additional strain of thermal and secondary

consolidation, we assume that consolidation does not follow the steep trend from Site

1173, but a less steep primary consolidation. Following these assumptions, the

consolidation state between Site 1173 and 1174 and 808 are compared at the top and

the base of the LSB (Fig. 6 B,C) where temperatures are similar, using our primary

consolidation data (Cc=0.99).

The primary consolidation results in lower excess pore pressures of 2.2 -

3.9 MPa for Sites 1174 and 3.0 - 4.9 MPa for Site 808 (Fig. 6 B,C). Although the

differences to the previous study are smaller than 1 MPa the new estimates are in

accordance with the general void ratio reduction. Lower pore pressures remain at the

top of the underthrust section, which points to an upward drainage (Fig. 6), probably

to a free drainage boundary along the decollement (Saffer, 2007). The pore water

expulsion at the top is also reflected in the greater void ratio. Between Sites 1174 and

808 excess pore pressure increases uniformly by ~1 MPa, suggesting that the

additional load of 1.5 MPa is largely taken up by the pore water. This is supported by

the fact that void ratio reduction is almost negligible at these Sites. Although these

excess pore pressure estimates are consistent with the observed void ratio reduction,

in-situ pore pressure data from A-CORK observations may be needed to bring

certainty into these estimates (e.g. Davis et al., 2006). The determined increase in

excess pore pressure is nonetheless in agreement with the assumption that pore


pressures increase along the subduction thrust and, together with low basal friction,

are responsible for the small taper angle at the Muroto transect (Saffer and Bekins,

1998; Brown et al., 2003).

Fig. 6: (A) Schematic diagram illustrating our pore pressure estimates. When a load is applied (weight symbol) and no drainage occurs, the additional stress is taken up by the pore water without any reduction in void ratio (1�2). The total stress of (2) is �t=�e+P, and can be inferred from integrating the bulk density down hole. Thus, the excess pore pressure can be directly predicted from the shift relative to the reference line, where �t=�e. Depending on the drainage, the excess pore pressure may partially dissipate and hence cause a reduction in void ratio (3). (B) Previous studies reported the excess pore pressures P (shaded area) directly to the shift of Site 1173 data which is supposed to be normally consolidated (�t=�e). Our approach considers that no thermal or secondary consolidation takes place between the sites. Instead it resumes primary consolidation, which is modelled here exemplarily for the top and the base with a Cc of 0.99. Temperature corrected estimates are presented in (C,D) for Sites 1174 and 808, respectively, showing that excess pore pressures (shaded areas) are smaller. These pore pressures are consistent with the observed void ratio reduction between the sites.


4.6 Conclusions Taken together our results, temperature has a veritable impact on the consolidation

behaviour of underthrust sediments from the Nankai margin, with increasing

temperature leading to an enhanced pore space reduction. This change seems to be

more pronounced for temperatures lower than 100 °C. By combining the observed

trends from consolidation tests with field-based data, we explain the consolidation of

the incoming Lower Shikoku Basin sediments as a complex combination of primary,

secondary and thermal consolidation. Besides the direct influence on consolidation,

temperature is the driving factor for the smectite-to-illite reaction, connected with a

change in consolidation behaviour and possibly facilitated by lithification downslab.

Based on our findings, estimated excess pore pressure for the Nankai Trough are

found significant lower than previously believed, so that overall our results have

profound mechanical implications for IODP NanTroSEIZE (Nankai Trough

Seismogenic Zone Experiment) drilling project to the seismogenic zone.

Acknowledgments

We thank Jill Weinberger for her assistance with some of the experiments and

Kevin Brown for providing laboratory space. Christoph Vogt is thanked for XRD

analyses. Samples and data used in this study have been provided by the Ocean

Drilling Program (ODP). ODP was sponsored by the U.S. National Science

Foundation (NSF) and participating countries under management of Joint

Oceanographic Institutions (JOI). This paper benefited from the discussion with

Demian Saffer and numerous other colleagues working off Japan. Funding was

provided to AK by the German science foundation (project KO2108/4-1).

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Chapter 5: Manuscript 2

Ramifications of high in-situ temperatures for laboratory testing and inferred stress states of unlithified sediments – a case study

from the Nankai margin

A.Hüpers1, S.Kreiter1 and A.Kopf1

1MARUM - Center for Marine Environmental Sciences, University Bremen, P.O. Box 330440, 28334 Bremen, Germany.

Marine and Petroleum Geology (submitted)

Abstract

The recovery of drilling cores involves changes in pressure and temperature conditions, which alter the mechanical properties of unlithified sediments. In particular, high in-situ temperatures have to be regarded for the interpretation of geotechnical tests conducted at standard ambient temperature conditions and especially for the inferred consolidation state. So far, the interpretation of the consolidation state of the Lower Shikoku Basin facies (LSB) entering the accretionary Nankai margin is ambiguous. Laboratory consolidation test results show a high stiffness, which was interpreted as hardening caused by cementation, while the field-based depth trend of porosity points towards normal consolidation. As an explanation for this discrepancy, the change of the mechanical properties by cooling from in-situ to laboratory conditions is proposed. The results of a thermo-mechanical model are compared to published field data. This comparison suggests that the observed hardening is at least partially an artefact from temperature change during core recovery, and that the strata can be considered normally to only slightly cemented. This normal consolidation state, together with other recent geotechnical studies on the incoming sediments, reveals that the LSB is the primary candidate for decollement development at the Nankai margin.


5.1 Introduction Physical properties can serve as proxies for composition, formation and stress

state of the sediment (Casagrande, 1936; Blum, 1997). While some physical

properties can be determined by logging-while-drilling others have to be determined

from core samples. Unfortunately, the sampling leads to changes in pressure and

temperature conditions and thus to sampling artefacts in unlithified sediments. The

pressure release during sampling causes an expansion due to elastic recovery, gas

expansion and mechanical stretching. These effects are widely documented and can

be estimated from laboratory consolidation tests (e.g. Karig and Hou, 1992; Blum,

1997). However, temperature induced artefacts are often ignored although

temperature induced changes may have a severe impact on geotechnical testing

(Campanella and Mitchell, 1968, Sultan et al., 2002).

At the Nankai margin southeast of Japan (Fig. 1), the incoming sediments are

subjected to high in situ temperatures with basement temperatures up to ~110 °C

along its central portion off Cape Muroto (Taira et al., 1991; Moore et al., 2001a). The

consolidation state of these sediments is important for the development of the

decollement zone, which separates frontally accreted from underthrust sediments. The

decollement zone forms along intrinsically weak layers in the incoming sequence such

as clay-rich sediments or underconsolidated layers with excess pore pressure (Moore,

1989). Rapid sedimentation of well-drained turbidites in the trench may cause such

excess pore pressure within the less drained underlying hemipelagic sequence and

make especially its uppermost part prone to decollement formation (Le Pichon et al.,

1993). In contrast, the decollement formation within the incoming Lower Shikoku

Basin facies (LSB), is neither associated with the intrinsically weakest layer

(Underwood, 2007) nor do samples from the LSB exhibit underconsolidation during

laboratory reconsolidation (Morgan and Ask, 2004; Bellew, 2004). Instead, tested

samples show a high stiffness, which was interpreted to be caused by matrix

cementation (Morgan and Ask, 2004; Morgan et al., 2007).

Instead of cementation, thermal hardening is another explanation to cause high

stiffness’s at standard conditions. This possibility has not been tested for subduction

zone settings, so far. Thermal hardening occurs during cooling (Sultan et al., 2002)

and may influence samples from “hot” in-situ conditions such as the Nankai Trough.

Here, we test if the observed stiffness of samples from the LSB succession off the


Nankai margin can be explained by thermal hardening. We apply an up-to-date

thermo-plastic model to estimate the shift in pre-consolidation stress due to

temperature differences between in-situ and laboratory conditions. The results are

compared with published consolidation data, and their implications for stress state of

underthrust sediments as well as decollement location are being discussed.

Fig. 1: (A) Map of the Nankai Trough subduction zone and ODP (Ocean Drilling Program) drill site locations off SW Japan. Grey corridor indicates location of interpreted seismic reflection profile shown in Fig. 2.

5.2 Geology of Nankai margin The Nankai margin is located off SE Japan where the oceanic Philippine Sea

plate is subducted to the northeast beneath the Eurasian plate at a rate of ~4 cm/a

(Karig and Angevine, 1986; Fig. 1). Most of the incoming sedimentary sequence is

scraped off, which has led to a wide accretionary prism (Fig. 2). This study focuses on

Site 1173 located 11 km seaward of the deformation front, which was drilled during

Ocean Drilling Program (ODP) Leg 190 as a tectonically undisturbed reference site of

the incoming sequence (Moore et al., 2001b; Fig. 2). The temperature at Site 1173

increases rapidly with depth towards a basement temperature of ~110 °C (Fig. 2),

because of an ancient spreading ridge and the recently active volcanic Kinan

seamount chain nearby (Taira et al., 1991; Moore et al., 2001b).

At ODP Site 1173, the uppermost sandy trench-wedge facies follows a normal

consolidation curve of decreasing pore space (Fig. 2B). Across the underlying Upper

Shikoku Basin facies (USB), the porosity remains nearly constant. p-wave velocity for

the USB suggests a normally consolidated trend down to 230 mbsf, while from 203 to

343 mbsf p-wave velocity is abnormally high (Spinelli et al., 2007). A laboratory


reconsolidation test showed a typical consolidation curve for cementation which has

been confirmed by the detection of opal-CT cements identified by SEM (Spinelli et

al., 2007).

Underneath, the Lower Shikoku Basin facies (LSB) resumes a normal, uncemented

trend of porosity (Fig. 2). The reconsolidation of undisturbed specimens from this

section exhibits high pre-consolidation stress, which has been interpreted as matrix

strengthening by authigenic clay cementation (Morgan and Ask, 2004). In contrast,

the decrease in porosity with depth as well as with p-wave velocity has been assumed

to be a normal consolidation pattern without cementation (Moore et al., 2001b;

Screaton et al., 2002; Saffer, 2003; Spinelli et al., 2007).

Fig. 2: (A) Cross section after Morgan and Ask (2004) through the Shikoku Basin and Nankai forearc off the Shikoku Island, Japan and (B) porosity depth (diamonds) and temperature profile (dashed line) for ODP Site 1173 after Moore et al. (2001a).

5.3 Methods 5.3.1 Consolidation and pre-consolidation stress determination

During burial the overburden stress (�t) from an overlying sediment pile is

taken up by the vertical effective stress (�e) acting on the mineral framework and the

pore water pressure in excess of the hydrostatic pressure (P).

�t = �e+P [1]


The maximum effective stress �e a sediment has experienced in the past is

termed pre-consolidation stress p’c. It can be determined in laboratory reconsolidation

tests by determining the transition of elastic to plastic deformation (Casagrande, 1936;

Fig. 3A). If the maximum effective stress is p’c = �t, the in-situ stress state is termed

normal consolidated. High loading rates and low permeability often lead to

considerable pore water pressure over geologic timescales and reduce the effective

stress. In this case the determined pre-consolidation stress is smaller than the total

stress. This consolidation state is referred to underconsolidated, which implies that

P>0. For the case that the maximum effective stress p’c is greater than the total stress,

erosion of the overlying sediment can be responsible for the enhanced stiffness. Other

possibilities for a high stiffness of sediments can also be cementation and thermal

hardening (Fig. 3; Burland, 1990; Sultan et al., 2002).

Fig. 3: Schematic consolidation test results of strain measurements vs effective stress. (A) Pre-consolidation stress (white arrow) determination after Casagrande (1936) with minimum and maximum range (dark arrows). Also indicated are the elastic portion and the plastic portion of mechanical behaviour, which are described by the slope Ce and Cc, respectively. (B) Results from Sultan et al. (2002) showing the increasing pre-consolidation stress with decreasing testing temperatures of Boom clay, which was loaded to 4 MPA (dashed line) and 100 °C before reloading. (C) Consolidation is described in the Cam Clay model as specific volume vs mean effective stress with primary consolidation given by � and the elastic value by �.

5.3.2 Temperature sensitivity of pre-consolidation stress and model

To describe soil (or unlithified sediment) consolidation and deformation in

civil engineering an elastoplastic constitutive model, the modified Cam-Clay model,

has been developed (e.g. Schofield and Wroth, 1968). However, this model does not

take the soil’s response to temperature into account which is exemplarily shown in


figure 3B. For a normally consolidated soil the grain skeleton is in equilibrium with

the applied load. During heating the interparticle shear resistance decreases and the

sediment is compressed until enough interparticle bonds are formed to carry the stress

at the increased temperature (Mitchell and Soga, 2005). During cooling the

interparticle shear resistance recovers and the additional bonds formed during heating

increase the stiffness of the sediment (cf. Fig. 3). This hardening factor model was

first incorporated into the modified Cam-Clay model by Hueckel and Baldi (1990).

Based on their work, Picard (1994) introduced a simpler modification for the

hardening which provides very satisfactory predictions concerning the hardening

behaviour of boom clay (Sultan et al., 2002):

�T��

e+p'=p' p

0labcsituinc �

��

��

13exp__ [2]

Where p’c_in-situ is the pre-consolidation stress at in-situ temperatures and p’c_lab

is the pre-consolidation stress at standard conditions; e0 is the initial void ratio (void

ratio = volume ratio of pore space and solids), � is the slope of the plastic

consolidation curve and � is the slope of the elastic rebound curve (cf. Fig. 3C) in the

in the cam clay model (Schofield and Wroth, 1968). �T refers to the temperature

difference between in-situ and standard conditions and ap is a positive scalar

coefficient.

5.3.3 Model inputs

We took in-situ data to determine the expected thermal hardening caused by

temperature differences between in-situ and ambient laboratory conditions. Thus, we

calculated the expected pre-consolidation stress at room temperature p’c_lab. For the

model we assume that the in-situ LSB is normal consolidated as proposed by various

authors (Moore at al., 2001b; Screaton et al., 2002; Saffer, 2003; Spinelli et al., 2007).

Thus, the pre-consolidation stress at in-situ temperatures p’c_in-situ is equal to the total

stress �t and can be calculated from the density-depth trend of Site 1173 shipboard

measurements. To get the best in-situ estimates for e0, standard shipboard data (Moore

et al., 2001a) has been corrected for rebound (4.5% e/MPa from Morgan and Ask) and


temperature dependent volume change of pore water and soil grains (Campanella and

Mitchell, 1968; Sun et al., 2008).

The reconsolidation data of LSB sediments show a great variability for elastic

(Ce) and plastic (Cc) compression indices (Tab. 1; Bellew, 2004; Morgan and Ask,

2004). Cc and Ce are defined for the change of void ratio e in the vertical stress

regimes (�v), while � and � in the model are defined as the change of the specific

volume (�=1+e) with the mean effective stress �’m=1/3(�’1+2*�’3) (�’1 = maximum

effective stress; �’3 = minimum effective stress; (cf. Fig. 3C; e.g. Azizi, 2000).

Vertical and mean effective stresses in a compression test are directly related by earth

pressure at rest K0 = �’3/�’1, which has been determined for Site 1173 LSB by

Morgan and Ask (2004). The ratio is constant with a value of Kop=0.79 for the plastic

deformation and Koe=0.49 for the elastic deformation. The resulting � and � data are

given in Tab.1. We consider the variability of the consolidation data by taking the

data from the tests with the lowest and the highest values of compression indices (cf.

Tab. 1). The value for p=1.10-4K-1 has been taken from Boom clay (Sultan et al.,

2000), because of the similar mineralogy. Both sediments are composed of smectite,

illite and quartz in similar proportions (cf. Underwood, 2007; Baldi et al., 1988).

Therefore the Boom clay value may be considered as a suitable approximation. To

determine �T a linear temperature increase with depth between 65 °C for the top of

the LSB and 105 °C for the bottom is assumed (cp. Fig.2B).

Tab.1: Consolidation data of LSB sediments at site 1173 and calculated slopes of primary consolidation � and elastic values �. All pre-consolidation stresses are determined after Casagrande (1936). Asteriks marks the considered threshold model inputs for the study. See text for explanations.

Data source Depth (mbsf) p’c (MPa) Cc Ce � � Bellew (2004) 391.3 3.17 0.27 0.014 0.117 0.006 Bellew (2004) 443.7 5.69 0.27 0.032 0.117 0.014 Morgan and Ask (2004)* 476 6.10 0.99 0.045 0.423 0.020

Bellew (2004)* 529.6 6.21 0.18 0.023 0.078 0.010


5.4 Results In the following the results of the modelling of the thermal hardening for the

LSB at Site 1173 is presented as pre-consolidation stress p’c_lab and compared to (1)

laboratory derived pre-consolidation stresses p’c by Bellew (2004) and Morgan and

Ask (2004) and (2) the effective stress at normal consolidation state and at in-situ

temperatures.

When fluid overpressuring can be neglected, as we assume it for Site 1173, the

calculated stress equals the effective stress (�t=�e). The total stress �t can be

calculated by integrating the bulk density downward in the hole and subtracting the

hydrostatic pressure produced by the water column of the respective height. The

effective stress determined in this way for the LSB at Site 1173 is shown in figure 4A

plotted against increasing depth and ranges from 2.01 to 5.3 MPa. All laboratory pre-

consolidation stresses p’c determined by Bellew (2004) and Morgan and Ask (2004) at

room temperature plot right of the line showing the above stated high stiffness of the

samples.

Fig. 4: (A) Depth vs. effective stress at in-situ temperature (diamonds) for the LSB at Site 1173 and laboratory pre-consolidation stress (triangles) determined by Bellew (2004) and Morgan and Ask (2004) with range of error; (B) modelled pre-consolidation stresses at room temperature due to thermal hardening for Site 1173 based on model inputs from the sample with the highest � (squares) and (C) the sample with the lowest � (circles). See text for further explanations. The shaded area marks the projected decollement.


The results of the modelled thermal hardening are shown in figures 4B and 4C

as pre-consolidation stress p’c_lab. The model with the high � and � are derived from

Morgan and Ask (2004) (cf. Tab. 1) show lower pre-consolidation stresses than the

laboratory determined pre-consolidation stresses (Fig. 4B). After this model the

deeper samples show a higher stiffness with an excess compressive strength of 2.2 to

2.6 MPa and the sample from 391 mbsf is slightly stiffer.

The modelled thermal hardening using lowest � and � (cf. Tab. 1), are shifted

further to higher stresses (2.9 to 7.58 MPa; Fig. 4C). After this model the laboratory

derived pre-consolidation stresses of Bellew (2004) and Morgan and Ask (2004) show

rather good accordance with the predicted thermal hardening. The deviations are

rather small and in a range of -0.2 MPa and +1.4 MPa. The uppermost sample appears

even slightly underconsolidated in this model, while the other samples can be

considered slightly stiffer than expected for normal consolidation.

5.5 DiscussionThe two considered models yield very different thermal hardening because of

the underlying consolidation data. The model with the higher plastic compression

index expects only slight thermal hardening compared to the normal consolidation

state inferred from the shipboard data (Fig. 4B). Although a high compression index

can also be inferred from shipboard measurements (Saffer, 2003), the majority of the

consolidation data show low compression indices (cp. Tab.1). Because of the varying

compression indices with depth the average values of both models may be the best

possible representative. Regarding an average deviation of 0.2 MPa to +2 MPa and

the uncertainty of laboratory pre-consolidation stress determination (Fig. 4; Saffer,

2003), these average values imply that the LSB sequence is normally consolidated in

the upper part and while the observed stiffness for the deeper part is smaller than

previously believed. The slightly higher stiffness may be explained by a minor

cementation in contrast to the previously proposed moderate cementation of Morgan

and Ask (2004). Thus, thermal hardening due to cooling during recovery explains the

observed stiffness response of the specimen at room temperature.

The stratum being normally consolidated to slightly cemented indicates that,

despite the high sedimentation rate of the overlying trench turbidites (450-650 m/Ma.

[Moore et al., 2001a]), there is no excess pore pressure to hinder or delay


consolidation. On the other hand, strengthening due to cementation seems to be

negligible or very weak. Although, the large secondary porosity and enhanced

stacking of clay minerals points to cementation (Morgan and Ask, 2004; Ujiie et al.,

2003), only a minor amount of cement may be present, because of the lack of direct

evidence from SEM analysis (Spinelli et al., 2007). An additional argument against a

moderate cementation is the lack of a typical cementation trend in the reconsolidation

curve of LSB samples; for typical cementation curves see Burland (1990). Thus, the

consolidation state of underthrust sediments at ODP Site 1173 can be explained by

loading and the ambient temperature. Elevated temperature may also facilitate

secondary consolidation (creep), which may explain differences between laboratory

and field consolidation curves and may be in this case responsible for the slightly

overconsolidation (Karig and Ask, 2003; Mitchell and Sago, 2005). Previously

contradictory results based on seismic velocity data (Spinelli et al., 2007) and

laboratory tests (Morgan and Ask, 2004) have here been mated for the first time by

incorporating temperature effects on consolidation.

5.6 Implications In the past, the different perceptions of the cementation and consolidation state

led to different interpretations of the stress state of the underthrust sequence and thus

decollement location. Screaton et al. (2002) and Saffer (2003) observed a lack in

consolidation of the underthrust sequence (LSB) for drill sites at the toe of the prism

(ODP Sites 1174 and 808; Fig. 2) compared to Site 1173. They concluded that this is

the result of excess pore pressure created by rapid loading of overlying prism and

poor drainage because of low sediment permeability. High pore pressures hinder

compressive strengthening of the sediment and may control the development and

downstepping of subduction thrust faults (Moore, 1989; Saffer, 2007).

Based on previous interpretation of laboratory consolidation data, the

proposed excess strength due to cementation of the underthrust section by Morgan

and Ask (2004) may also explain the position of the fault. In this case, the

decollement forms preferably in the overlying sediments, which are not hardened by

cementation. Downstepping of the decollement may occur in this scenario when the

enhanced strength due to the cementation is overcome by mechanical load (Morgan


and Ask, 2004). However, our data do not support the hypothesis for the decollement

location above a moderately cemented section.

In the following arguments will be discussed for evolution of the decollement

zone in the uppermost part of the LSB at the Nankai margin. It is generally agreed that

the decollement zone forms preferably in a layer with low intrinsically shear strength

or high excess pore pressure (Moore, 1989; Brown et al., 2003). According to the high

average sedimentation rate of the trench turbidites, up to ~1100 m/Ma between Sites

1173 and 1174 (Screaton et al., 2002), the excess pore pressure in the underlying low

permeable hemipelagites should be increased (Moore, 1989). Modelling of this

scenario by Le Pichon et al. (1993) showed that the lowest effective stress is in the

uppermost part of the less drained hemipelagites. For that reason the subduction thrust

fault along the Nankai Trough should be located rather in the Upper Shikoku Basin

facies (USB) than in the LSB (Fig. 2). Instead, opal cementation processes strengthen

the USB sediments and preserve high porosity of >55 % (Spinelli et al., 2007).

Because of this, the formation of excess pore pressure occurs more likely in the

underlying LSB. In addition with the predominant clayey lithology and a rather weak

cementation, LSB sediments may be considered as the weakest portion of the

incoming sequence (Brown et al., 2003). The low effective stresses and low friction

coefficient of clays (Brown et al., 2003) makes them the primary candidate for the

generation of the decollement zone at the Nankai Trough. This is indicated by the

dashed line for the outward-migrating proto-thrust in figure 2A. Progressive

underthrusting may cause the pore pressure to increase, and may hinder further

compressive strengthening of the sediment. This interpretation is in accordance with

previous studies of Saffer (2003) and Screaton (2002) that pore pressures increase in

the underthrust sediments from Site 1174 to Site 808. This would eventually allow

downstepping of the subduction fault deeper into the underthrust sequence, a

phenomenon observed in other subduction systems (Saffer, 2003) and inferred for the

deeper portion of the Nankai plate boundary megathrust off the Kii Peninsula (Moore

et al., 2007).

Acknowledgements

Data used in this study have been provided by the Ocean Drilling Program

(ODP). ODP was sponsored by the U.S. National Science Foundation (NSF) and


participating countries under management of Joint Oceanographic Institutions (JOI).

Funding was provided by the German Science Foundation (project KO2108/4-1).

References

Azizi, F., 2000. Applied Analyses in Geotechnics, E & FN Spon, London.

Baldi, G., Hueckel, T., Pellegrini, R., 1988. Thermal volume changes of the mineral-

water system in low porosity clay soils. Can. Geotech. J. 25 807-825.

Bellew, G., 2004. Consolidation properties, stress history, and modeling of pore

pressures for deep sea sediments at the Nankai Trough, M.S. Thesis,

University of Missouri-Columbia.



thrust: A weak plate boundary. Earth and Planetary Science Letters 214 (3-4),

589-603.

Burland, J.B., 1990. On the compressibility and shear strength of natural clays.

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Campanella, R.G., Mitchell, J.K., 1968. Influence of temperature variations on soil

behaviour. Journal of the Soil Mechanics and Foundations Division 94 (SM3),

709-734.

Casagrande, A., 1936. The determination of the preconsolidation load and its practical

significance, in: Casagrande, A., Rutledge, P.C., Watson, J.D. (Eds.), Proc. 1st

International Conf. Soil Mech. Foun. Eng.. Am. Soc. Civ. Eng., pp. 60-64.

Hueckel, T., Baldi, G., 1990. Thermoplasticity of saturated solis and shales:

experimental constitutive study. J. Geotech. Eng. 116 (12), 1778-1777. Karig,

D.E., Angevine, C.L., 1986. Geologic constraints on subduction rates in the




implications. Journal of Geophysical Research 97 (B1), 289-300.

Karig, D.E., Ask, M.V.S., 2003. Geological perspectives on consolidation of clay-rich

marine sediments. J. Geophys. Res. 108 (B4), 2197,

doi:10.1029/2001JB000652.




Mitchell, J.K., Soga, K., 2005. Fundamentals of soil behavior, 3rd ed. John Wiley &

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Moore, G.F., Taira, A., Klaus, A., al., e., 2001a. Proc. ODP, Init. Repts., College


Moore, G.F., al., e., 2001b. New insights into deformation and fluid flow processes in

the Nankai Trough accretionary prism: Results of Ocean Drilling Program Leg

190. Geochem. Geophys. Geosyst. 2 (10), doi:10.1029/2001GC000166.

Moore, G.F., Bangs, N.L., Taira, A., Kuramoto, S., Pangborn, E., Tobin4, H.J., 2007.

Three-Dimensional Splay Fault Geometry and Implications for Tsunami

Generation. Science 318 (1128), doi: 10.1126/science.1147195.

Morgan, J.K., Ask, M.V.S., 2004. Consolidation state and strength of underthrust

sediments and evolution of the décollement at the Nankai accretionary margin:

Results of uniaxial reconsolidation experiments. J. Geophys. Res. 109 (B3),

B03102, doi:10.1029/2002JB002335.

Picard, J., 1994. Ecrouissage thermique des argiles saturées: application au stockage

des déchets radioactifs, Thèse de Doctorat de l’Ecole Nationale de Ponts et

Chaussées.




doi:10.1029/2002JB001787.




Schofield, A.N., Worth, C.P., 1968. Critical State Soil Mechanics, MacGraw-Hill,

London.

Screaton, E., Saffer, D., Henry, P., Hunze, S., 2002. Porosity loss within the

underthrust sediments of the Nankai accretionary complex: Implications for

overpressures. Geology 30 (1), 19–22.

Spinelli, G.A., Mozley, P.S., Tobin, H.J., Underwood, M.B., Hoffman, N.W., Bellew,

G.M., 2007. Diagenesis, sediment strength, and pore collapse in sediment


approaching the Nankai Trough subduction zone. GSA Bulletin 119 (3/4),

377–390.

Sultan, N., Delage, P., Cui, Y.J., 2002. Temperature effects on the volume change

behaviour of Boom clay. Eng. Geol. 64 (2-3), 135-145.

Sun, H., Feistel, R., Koch, M., Markoe, A., 2008. New equations for density, entropy,

heat capacity, and potential temperature of a saline thermal fluid. Deep-Sea

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Taira, A., Hill, I., Firth, J.V., al., e., 1991. Proc. ODP, Init. Repts., College Station,

TX (Ocean Drilling Program).

Ujiie, K., Hisamitsu, T., Taira, A., 2003. Deformation and fluid pressure variation

during initiation and evolution of the plate boundary décollement zone in the

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doi:10.1029/2002JB002314.





Chapter 6: Manuscript 3

The interaction of underthrust sediments with seawater – an approach by hydrothermal consolidation testing

A.Hüpers1, A.Kopf1, W.Bach2 and M. Zabel1

1MARUM - Center for Marine Environmental Sciences, University Bremen, P.O. Box 330440, 28334 Bremen, Germany. 2Department of Geosciences, University of Bremen, P.O. Box 330440, 28334 Bremen, Germany.

Geochimica et Cosmochimica Acta (submitted)

Abstract

Geochemical, thermal and mechanical processes are closely interrelated at active convergent margins. To shed light on this linkage hydrothermal water-rock interaction has been studied by means of heated consolidation tests. Sediment samples representing end member mineralogical compositions at the Western Nankai subduction zone have been loaded to effective stresses of up to 70 MPa at temperatures of 20 °C, 100 °C and 150 °C and expelled fluids were analyzed for pore water geochemistry. We show that consolidation directly influences pore water constituents in our experiments. The onset of expulsion generally leads to a transient increase of solutes and with ongoing consolidation the smectite-rich sample shows a depletion of predominantly alkaline and earth alkaline elements. This process is governed by the consecutive release of free pore water and the residual water from the overlapping double layer of smectite. Increasing temperature generally leads to the enrichment of K, Ba and Si and to the depletion of Mg. The review of the literature indicates that the majority of investigators agree that this can be inferred from a changing ion exchange capacity of the sediment. Only the test at 150 °C shows hints for precipitation of sulphates. We suggest that stress depended observations have little geological relevance due to the necessary smectite abundance at depth but temperature related release of solutes may facilitate cementation of underthrust sediments and thus elastic strain accumulation for seismic slip.


6.1 Introduction At convergent margins water enters as pore fluid trapped between the particles

or bound in hydrous minerals as an integral part of the subduction inputs. To a greater

extent, the interstitial water will be expelled from the compacting sedimentary

sequence within 3-4 km of burial depth and may impact ocean geochemistry (Bray

and Karig, 1988, Moore and Vrolijk, 1992). Fluid expulsion occurs in this realm as

dispersed flow if the rate of pore fluid flow is sufficiently low and advection can be

accommodated by intergranular permeability (Carson and Screaton, 1998) or as

focused fluid flow along permeable layers such as fault zones (Moore and Vrolijk,

1992; Carson et al., 1994). However, a small fraction of the fluid will be buried with

the sediment to greater depth and thus subjected to the crust and mantle.

The geochemistry of interstitial water at convergent margins is initially close

to seawater and is subsequently affected by mineral dehydration, fluid-mineral

exchange reactions, diffusion-advection and the style of feeding from internal and

external fluid reservoirs (Kastner et al., 1991; Moore and Saffer, 2001). Mineral

transformation causes dehydration processes and has been used to explain the

omnipresent fluid freshening reflected by low-Cl anomalies at convergent margins

(Kastner et al., 1991; Silver et al., 2000; Kopf et al., 2003). This may derive especially

by smectite-to-illite and opal-A-to-quartz transition (e.g. Kastner et al., 1991, Moore

et al., 2001). Dehydration leads to eminent pore pressure generation which has been

postulated to influence fault strength and strain localization of the decollement (e.g.

Moore, 1989), as well as taper angle of accretionary wedges (e.g., Hubbert and

Rubey, 1959; Davis et al., 1983; Saffer and Bekins, 2002). At temperatures of 75–

175 °C carbonate, clay and zeolite cementation may occur (Moore and Saffer, 2001

and references therein) fostering the lithification of the sediments and eventually

allowing accumulation of elastic strain for seismic slip (Moore and Saffer, 2001).

Thus, a detailed insight on water-rock interaction may shed light on the linkage

between mechanical, thermal and geochemical processes within the shallow

subduction zone.

Studying alteration of marine sediment and its interstitial water towards

diagenesis may be complicated when past temperatures and pressures conditions are

unknown or complicated (Rosenbaum, 1976). To overcome this problem controlled

laboratory methods have been applied to study the alteration of marine sediments and


its pore waters in the last decades. Fluid-rock interaction has been most notably

studied in rocking autoclaves at constant isotropic pressures of several hundreds bars

and constant water-rock ratios (r>1) at temperatures of T>>200 °C (e.g. Thornton and

Seyfried, 1985; You et al., 1996; You and Gieskes, 2001). Sampled fluids from these

experiments reveal uniform depletion of Mg and sulphate whereas K, SiO2, B and Li

are increased. Further, the mobilization of volatiles (B and NH4) and incompatible

elements (As, Be, Cs, Li, Pb, Rb) is determined in hydrothermal experiments at

temperatures of ~ 300 °C. You et al. (1996) suggest a linkage between observed

mobility and deep arc magma generation in subduction zones. The observed

hydrothermal fractionation of Pb/Ce, La/Ba, Rb/Cs, B/Nb, and B/Be during these

experiments might explain the ratios in arc and maybe in hotspot lavas (You et al.,

1996). However, the set-up of rocking autoclaves includes several shortcomings

compared to burial conditions of natural sediments. It neglects that the applied load of

the overlying sediment pile is compensated according to the effective stress law. The

effective stress is the part of the total stress that is directly acting on the mineral

framework. Under undrained conditions such as in a rocking autoclave the applied

pressure is taken up mainly by the pore water suggesting low effective stresses. In

contrast to the autoclave experiments, the water-rock ratio is in nature constantly

changing with burial depth and can be considered smaller than 1.

To overcome the above mentioned shortcoming we chose the set-up of a

backpressured uniaxial consolidation apparatus (hydrothermal oedometer), which may

better simulate burial conditions. We modified a high capacity consolidometer to

facilitate hydrothermal conditions and to provide a larger spectrum of pressure (P) and

temperature (T) conditions than previous studies with similar apparatuses (e.g.

Chiligarian et al., 1973, Rosenbaum, 1976). The hydrothermal consolidation tests

were conducted up to pressure and temperature conditions equivalent to the upper

limit of the seismogenic zone. Specimens used were marine sediments of different

mineralogical end member composition from the Nankai Trough subduction zone,

(Japan). We analyzed fluids expelled from the compaction tests at 20 °C, 100 °C and

150 °C to evaluate potential fluid-rock interaction at low PT conditions in the shallow

subduction zone.


6.2 Sampling site and sample description 6.2.1 Sampling site

For the proposed study we focus on natural samples from the Shikoku Basin.

Although more complex to study than defined mixtures of a few standard materials,

results may be more comparable to studies from field measurements. The Shikoku

Basin is part of the Phillipine Sea plate, which is being subducted to the northwest

under the Eurasian plate at a rate of 2-4 cm/yr almost perpendicular to the Nankai

Trough along Southwest Japan (Fig. 1; Karig and Angevine, 1986). The abundant

influx of terrigeneous sediments from the north led to a huge thickness (up to 1.5 km)

of basin sediments which taper of to the SE. A large part of the sediment pile is

scraped off which led to the built-up of a broad accretionary prism.

Fig. 1: (A) Map showing DSDP and ODP drillsites off Shikoku Island, which lie on two transects perpendicular to the trench. (B) Samples for hydrothermal deformation experiments were selected from Lower Shikoku Basin Facies of DSDP Site 297 (modified after Brown et al., 2003). Smectite-rich clay (N13) is has been sampled from 506.83 mbsf and illite-rich silty clay (N14) from 507.12 mbsf

Samples derive from DSDP (Deep Sea Drilling Program) Site 297 (Fig. 1A,B)

where 679.5 m of the 780 m thick sedimentary cover was penetrated during Leg 31

(Karig et al., 1975). It is located ~100 km SE of the Nankai margin and can be

considered as a tectonically undisturbed reference site. Selected samples are taken

from the Lower Shikoku Basin facies (LSB), which comprises the bulk of underthrust

sediments with the projected decollement slightly beneath the lithological boundary of

the Upper Shikoku Basin facies (USB) and the LSB (Fig. 1B). Across the LSB facies


the smectite content increases dramatically to the base of the LSB (~50 to 20 wt-%)

whereas the general clay content increases only slightly (~60 to 50 wt-%; Fig. 1B).

This trend is similar to what has been observed at ODP Site 1177, which is 87 km

northwest (i.e. trenchward) of Site 297 (Brown et al., 2003). The mineralogical

variation might be due to variable fluxes of illite and chlorite from SW Japan relative

to volcaniclastics and smectite derived from the Izu-Bonin arc (Underwood and

Pickering, 1996; Underwood and Steurer, 2003). Although heat flow near the seafloor

is elevated (130-200 mW/m2 [Karig et al., 1975; Yamano et al., 1992]) relative to Site

1177, smectite contents in the deeply buried LSB at Site 297 are not significantly

lower than at Site 1177 and thermal alteration seems to be negligible (Brown et al.,

2003).

6.2.2 Selected samples

On the basis of published XRD-results (Underwood et al., 1997; Brown et al.,

2003; Fig. 1) we selected clay-rich end member lithologies of the incoming LSB. The

samples comprise a smectite-rich clay (N13, 506.83 mbsf) and an illite-rich silty clay

(N14, 507.12 mbsf). The smectite-rich clay is abundant in the lower part of the

Shikoku Basin Facies and may present unaltered sediment input. Sample N14 is more

illite rich and thus may shed light on water-rock interaction of a sediment at the updip

limit of the seismogenic, which has already undergone illitisation. This sample

selection enables us to compare water rock interaction of sediment of different

diagenetically stages, since reaction kinetics are to slow to generate abundant

illitisation at the temperatures during our experiments (Huang et al., 1993). Sub-

samples have also undergone quantitative XRD examination after Vogt et al. (2002) at

the University of Bremen to confirm the proposed end member clay mineralogy (Tab.

1). The results indicate variations of mainly smectite [Sm], illite [Il], and a granular

fraction of quartz [Qtz] and feldspar [Fsp]. As expected, sample N13 is a clay with a

high smectite fraction while sample N14 is silty clay with dominantly illite, quartz

and feldspar. However, grain size distribution is significantly different and may

influence water-sediment interaction due to differences in the specific surface area.


Tab. 1: Results from quantitative XRD showing major mineral content (Qtz=quartz, Fsp=feldspar, Sm=smectite, Mont=montmorillonite, Il=illite, Musc=muscovite, Chl=Chlorite).

Qz + Fsp Sm + Mont Il + Musc Chl Mixed layer clays otherNan14-20 49.1 4.0 29.9 1.6 1.7 13.7 Nan14-100 44.2 6.6 27.0 2.6 6.6 13.0

Nan13-20 5.7 43.5 0.0 2.0 35.6 13.2 Nan13-100 9.2 56.3 19.9 0.0 12.9 1.7 Nan13-150 15.1 43.3 8.4 1.9 18.2 13.1

6.3 Methods 6.3.1 Mechanical compaction and set-up

The compaction of the sediments was conducted in a custom-built high

capacity oedometer. Compared to the rocking autoclave system (e.g. Seyfried et al.,

1979) the sediment is allowed to consolidate in this device. In this study consolidation

refers to the settlement a sediment experiences as a result of an applied normal load.

Settlement can only occur when pore water is expelled. Thus, consolidation is time

dependent, a function of the permeability, dependent on the length of the drainage

path and the compressibility of the sediment (Terzaghi and Peck, 1948). The total

stress �t applied can be differentiated between the stress that is taken up by the water

(excess pore pressure P) and the mineral framework (effective stress �e).

�t = �e + P [1]

During consolidation the pore volume decreases. Following Terzaghi and Peck

(1948) the pore space reduction (presented as void ratio = volume voids/volume

solids) can be described as a linear function of the logarithm of the effective stress.

Thus, the data of increasing effective stress presented in this study is related to a

reduction in pore space. The specific consolidation is material dependent and

described for the very same samples by Hüpers and Kopf (EPSL, in press).

The setup of the oedometer (Fig. 2) consists of a piston situated within a

cylinder, which prevents the sample from lateral extension. A hydraulic press system

pushes the piston into the cylinder and compresses the sample. The sediment is

allowed to drain via a borehole in the piston. To the borehole at the base of the

cylinder a Validyne differential pressure transducer (accuracy ±25 kPa) is attached to

measure the pore pressure. Stainless steel filter slabs prevent solids to get into the

bores. A backpressure regulator at the drainage outlet ensures a pore fluid pressure of

~500 kPa and suppresses pore water evaporation and degassing of trapped air in case


of heated tests. To minimize interaction of the saturated sample with the equipment,

the consolidation cell was made of titanium (grade 2). Other components such as

tubing and fittings also consist of non-corrosive materials like high-grade stainless

steel, PTFE, or PP.

Fig. 2: Schematic setup of the hydrothermal consolidation apparatus. The sample (grey shaded area) is compressed in the cylindrical cell (1) due to the applied load on the upper piston (2) and a spacer (3). A backpressure regulator (4) maintains a fluid pressure of ~ 500 kPa in the system which is measured by a pressure transducer (5). The fluid pressure across the sample is measured by a differential pressure transducer (6). A temperature probe at the bottom of the cell has been used to determine the temperature and to control the bandheater (dark grey shaded).

For each run, a remoulded sample was disintegrated and re-hydrated with

seawater. After 24h the slurry was centrifuged and again re-hydrated. This procedure

was repeated 1-3 times. Thereafter, the sample was placed in the oedometer and

consolidation was started at a constant rate of strain (<0.0042 %/min) over a period of

3-5 months until approximately �e = 70 MPa were reached. Initial water-rock mass

ratios of ~2 were continuously reduced in the course of an experiment until they

approached ~0.1. The applied backpressure, shortening of the sample, applied load

and differential fluid pressure across the sample height was logged continuously

during each experiment. The pore fluid expelled during consolidation was collected in

flasks attached to the upper drainage. Sample height reduction has been measured

with a Burster displacement transducer (accuracy ±0.075 mm). The tests were


repeated with aliquots of fresh specimen at constant temperatures if 20 °C, 100 °C and

150 °C. For the heated experiments, a band heater was placed around the

consolidation cell. Through a temperature probe in the base of the cell the heating was

controlled by a heating unit within a fluctuation range of 2 °C.

6.3.2 Chemical analysis

After detaching the flasks (each containing up to 4 ml fluid), the sampled

fluids were sealed, stored at ~4°C without further treatment and measured after

consolidation tests were completed. The collected fluids and the initial seawater were

analyzed for selected major and minor solutes. Cl and SO4 were measured with a

HPLC system with an anion separation column and indirect UV-detection at 288 nm.

Al, Ba, Ca, Fe, K, Mg, Mn, Na, S, Si, Sr and Ti had been measured by ICP-OES.

Samples had been diluted with acidified, deionised water for this analytical method at

a ratio of 1:10. Rb, Y, La, Ce, Yb, Lu, Pb, Th and U were analyzed by ICP-MS.

Samples had been diluted with acidified pure water at a ratio of up to 1:20 prior to

analyzing. The precision of is for all instruments <2 %. All data are reported in mg/l

except for ICP-OES and ICP-MS measurements which are given as ppb. The data

were normalized to the reactively conservative chloride, to minimize possible leakage

of the consolidation cell. All data are, nonetheless, included in table 2 for complete

documentation.

Concentrations are presented versus effective stress. The related stress value

corresponds to the average pore space that the sediment sample experienced between

mounting and removing a fluid sampling flask. According to the logarithmic

relationship of void ratio and effective stress, individual flasks recovered from the

early part of the consolidation tests span over a narrower effective stress range than

those later in the experiment. In consideration of the wealth of data and to avoid a

detailed description of the data on an element-to-element basis, we will focus our

discussion on first-order patterns in normalized element concentrations.

CH

APT

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: MA

NU

SCR

IPT

3

70

Tab.

2: M

easu

red

data

nor

mal

ized

to a

con

stan

t Cl o

f 186

00 m

g/L.

The

orig

inal

chl

orid

e va

lues

and

the

infe

rred

nor

mal

izat

ion

fact

ors

are

liste

d in

the

first

col

umns

. NN

stan

ds fo

r val

ues b

elow

det

ectio

n lim

it an

d N

D fo

r not

det

erm

ined

in th

e sp

ecifi

c an

alys

is.

P

oros

ity

(%/1

00)

Stre

ss

(MP

a)C

l (m

g/L)

no

rm.

Fact

or

Al (

mg/

L)

Ba

(mg/

L)

Ca

(mg/

L)

Fe (m

g/L)

K

(mg/

L)

seaw

ater

18

600

N

D

0.00

3 39

8 0.

08

393

N13

-20-

1 0.

79

5.88

E-0

5 35

986

0.51

69

3.95

0.

110

434

4.48

41

9 N

13-2

0-3

0.78

1.

88E

-04

4846

1 0.

3838

13

.48

0.12

4 56

5 2.

47

422

N13

-20-

5 0.

76

5.42

E-0

4 33

128

0.56

15

0.75

0.

053

544

0.05

35

4 N

13-2

0-7

0.75

1.

35E

-03

6579

8 0.

2827

0.

00

0.06

4 58

9 0.

13

368

N13

-20-

9 0.

74

3.25

E-0

3 37

331

0.49

82

0.20

0.

030

492

0.02

34

1 N

13-2

0-12

0.

71

1.40

E-0

2 45

097

0.41

24

0.13

0.

023

446

0.01

33

8 N

13-2

0-15

0.

68

6.22

E-0

2 40

097

0.46

39

0.09

0.

019

441

0.01

33

6 N

13-2

0-18

0.

65

2.55

E-0

1 40

399

0.46

04

0.06

0.

022

446

0.02

33

7 N

13-2

0-21

0.

60

1.02

E+0

0 62

671

0.29

68

0.09

0.

016

416

0.01

35

7 N

13-2

0-24

0.

56

2.72

E+0

0 45

652

0.40

74

0.09

0.

015

454

0.02

32

9 N

13-2

0-27

0.

52

7.00

E+0

0 43

808

0.42

46

0.11

0.

015

463

0.02

32

8 N

13-2

0-31

0.

43

2.94

E+0

1 33

242

0.55

95

0.16

0.

020

400

0.03

24

1 N

13-2

0-32

0.

40

4.37

E+0

1 74

349

0.25

02

0.09

0.

012

242

0.01

20

2 N

13-1

00-1

0.

77

6.07

E-0

6 40

453

0.45

98

8.66

0.

205

481

9.63

49

6 N

13-1

00-3

0.

77

1.11

E-0

5 53

082

0.35

04

2.45

0.

184

498

5.86

53

8 N

13-1

00-5

0.

76

2.53

E-0

5 65

562

0.28

37

0.03

0.

139

488

0.13

52

9 N

13-1

00-7

0.

78

4.94

E-0

6 68

233

0.27

26

0.13

0.

128

501

0.13

55

8 N

13-1

00-9

0.

74

1.10

E-0

4 37

874

0.49

11

0.22

0.

098

461

0.01

49

8 N

13-1

00-

13

0.72

5.

48E

-04

5624

4 0.

3307

0.

18

0.07

9 40

5 0.

03

492

CH

APT

ER 6

: MA

NU

SCR

IPT

3

71

Tab.

2: c

ontin

ued.

M

g (m

g/L)

Mn

(mg/

L)N

a (m

g/L)

S (m

g/L)

Si (

mg/

L)S

r (m

g/L)

Ti (m

g/L)

SO

4 (m

g/L)

seaw

ater

12

82

0.00

04

1027

3 88

8 2.

9 7.

83

ND

25

00

N13

-20-

1 13

10

NN

11

796

903

6.71

8.

61

0.29

6 54

75

N13

-20-

3 12

48

0.46

3 12

044

815

24.8

2 10

.92

0.01

7 42

55

N13

-20-

5 11

09

0.91

3 10

866

755

17.8

9 10

.80

NN

22

85

N13

-20-

7 12

07

NN

11

665

803

6.05

12

.33

NN

36

89

N13

-20-

9 11

58

NN

10

764

766

5.44

11

.16

NN

23

33

N13

-20-

12

1181

0.

025

1081

5 76

4 6.

18

10.2

3 N

N

2404

N

13-2

0-15

12

20

0.30

9 10

900

809

7.92

9.

18

NN

25

29

N13

-20-

18

1248

0.

325

1093

1 82

4 7.

66

9.41

N

N

2615

N

13-2

0-21

13

30

0.28

4 11

589

879

7.22

9.

65

NN

26

47

N13

-20-

24

1275

0.

482

1091

6 88

0 8.

22

9.80

N

N

2748

N

13-2

0-27

13

37

0.61

8 11

073

892

8.66

9.

80

NN

26

70

N13

-20-

31

1316

0.

745

1081

3 78

1 13

.05

8.36

N

N

2521

N

13-2

0-32

14

10

0.39

4 10

327

583

9.16

5.

57

NN

24

35

N13

-100

-1

1343

N

N

1256

5 89

8 29

.03

9.48

0.

184

5145

N

13-1

00-3

11

68

0.35

4 12

143

840

36.4

7 10

.58

0.06

6 41

36

N13

-100

-5

1098

N

N

1165

6 81

7 10

.22

10.8

3 N

N

3679

N

13-1

00-7

11

57

NN

12

015

852

7.42

11

.38

0.00

8 37

87

N13

-100

-9

1046

0.

134

1119

8 79

4 6.

15

10.4

8 N

N

2414

N

13-1

00-1

3 10

43

0.52

8 11

096

766

7.79

9.

59

NN

24

78

CH

APT

ER 6

: MA

NU

SCR

IPT

3

72

Tab.

2: c

ontin

ued.

Por

osity

(%

/100

)S

tress

(M

Pa)

Cl (

mg/

L)

norm

.Fa

ctor

A

l (m

g/L)

B

a (m

g/L)

C

a (m

g/L)

Fe

(mg/

L)

K (m

g/L)

se

awat

er

1860

0

ND

0.

003

398

0.08

39

3 N

13-1

00-1

7 0.

70

2.49

E-0

3 59

232

0.31

40

0.17

0.

070

409

0.00

50

4 N

13-1

00-2

1 0.

67

1.21

E-0

2 61

000

0.30

49

0.09

0.

070

424

0.53

48

9 N

13-1

00-2

8 0.

58

2.98

E-0

1 39

882

0.46

64

0.13

0.

074

454

0.02

48

9 N

13-1

00-3

0 0.

55

6.94

E-0

1 38

002

0.48

95

0.39

0.

078

463

1.20

49

3 N

13-1

00-3

4 0.

48

3.94

E+0

0 67

877

0.27

40

0.10

0.

084

440

0.04

47

4 N

13-1

00-3

5 0.

46

5.07

E+0

0 38

414

0.48

42

0.19

0.

096

479

0.01

47

7 N

13-1

00-3

6 0.

45

6.83

E+0

0 36

620

0.50

79

0.12

0.

093

507

0.02

48

1 N

13-1

00-3

8 0.

41

1.21

E+0

1 36

196

0.51

39

0.06

0.

109

499

0.02

46

7 N

13-1

00-3

9 0.

39

1.66

E+0

1 64

680

0.28

76

0.11

0.

111

497

0.01

47

1 N

13-1

00-4

1 0.

34

3.26

E+0

1 52

728

0.35

28

0.00

0.

071

476

0.02

38

5 N

13-1

50-5

0.

76

8.14

E-0

3 53

283

0.34

91

0.66

1.

047

613

0.19

62

4 N

13-1

50-7

0.

64

6.71

E-0

1 61

015

0.30

48

0.14

0.

274

610

0.10

59

7 N

13-1

50-9

0.

62

1.08

E+0

0 72

982

0.25

49

NN

0.

319

552

0.16

55

7 N

13-1

50-1

0 0.

60

1.53

E+0

0 66

867

0.27

82

NN

0.

360

515

0.14

55

3 N

13-1

50-1

1 0.

58

2.20

E+0

0 14

879

1.25

01

NN

1.

152

544

0.79

62

5 N

13-1

50-1

3 0.

54

4.43

E+0

0 68

356

0.27

21

NN

0.

438

475

0.11

54

1 N

13-1

50-1

4 0.

50

8.31

E+0

0 75

682

0.24

58

NN

0.

557

478

0.13

52

9 N

13-1

50-1

6 0.

45

1.56

E+0

1 60

609

0.30

69

0.07

0.

869

468

0.19

53

2 N

13-1

50-1

7 0.

42

2.05

E+0

1 12

416

1.49

81

NN

2.

329

374

2.97

63

3 N

13-1

50-1

8 0.

40

2.39

E+0

1 11

05

16.8

309

12.3

6 10

.372

17

9 77

.23

921

N13

-150

-19

0.36

3.

59E

+01

1014

18

.338

9 50

.88

6.03

2 35

2 95

.76

1161

N

13-1

50-2

0 0.

30

5.42

E+0

1 71

9 25

.867

3 20

1.25

7.

962

133

239.

32

1121

CH

APT

ER 6

: MA

NU

SCR

IPT

3

73

Tab.

2: c

ontin

ued.

M

g (m

g/L)

M

n (m

g/L)

N

a (m

g/L)

S

(mg/

L)

Si (

mg/

L)

Sr (

mg/

L)

Ti (m

g/L)

S

O4

(mg/

L)

seaw

ater

12

82

0.00

04

1027

3 88

8 2.

9 7.

83

ND

25

00

N13

-100

-17

1054

0.

492

1117

3 79

7 10

.76

9.01

N

N

2299

N

13-1

00-2

1 10

32

0.70

2 11

163

807

11.4

1 9.

01

NN

25

98

N13

-100

-28

1054

0.

750

1126

3 81

3 14

.12

9.30

N

N

2581

N

13-1

00-3

0 10

67

0.79

6 11

345

827

15.5

8 9.

42

NN

25

76

N13

-100

-34

1031

0.

564

1105

6 77

5 9.

23

9.14

N

N

2475

N

13-1

00-3

5 10

54

0.24

2 11

254

808

10.9

9 9.

75

NN

25

91

N13

-100

-36

1083

0.

586

1143

1 83

4 11

.23

10.2

9 N

N

2345

N

13-1

00-3

8 10

80

0.41

0 11

477

817

15.0

1 9.

89

NN

23

15

N13

-100

-39

1096

0.

074

1207

2 84

5 13

.05

9.79

N

N

2434

N

13-1

00-4

1 10

18

3.08

4 11

272

803

32.9

6 8.

84

NN

22

87

N13

-150

-5

712

1.80

1 11

517

72

39.7

5 11

.92

NN

0

N13

-150

-7

718

1.88

3 11

388

78

28.6

6 11

.91

0.00

6 0

N13

-150

-9

721

2.06

9 11

392

103

26.0

4 11

.07

NN

0

N13

-150

-10

714

2.07

9 11

481

119

27.1

6 10

.46

NN

0

N13

-150

-11

745

0.83

6 12

989

137

41.3

5 11

.22

0.04

5 0

N13

-150

-13

720

2.19

7 11

331

112

27.1

3 9.

83

NN

0

N13

-150

-14

742

2.36

4 11

109

109

26.2

6 9.

95

0.00

8 0

N13

-150

-16

748

2.32

6 11

655

106

35.0

5 9.

87

0.00

4 0

N13

-150

-17

586

NN

13

980

67

82.5

8 8.

06

0.00

7 0

N13

-150

-18

NN

N

N

1929

0 30

39

1.86

6.

48

0.86

1 0

N13

-150

-19

113

NN

19

617

1108

47

0.84

10

.64

NN

0

N13

-150

-20

NN

N

N

1925

9 14

24

126.

28

7.58

1.

416

0

CH

APT

ER 6

: MA

NU

SCR

IPT

3

74

Tab.

2: c

ontin

ued.

R

b (n

g/m

L)

Y (n

g/m

L)

La (n

g/m

L)

Ce

(ng/

mL)

Y

b (n

g/m

L)

Lu (n

g/m

L)

Pb

(ng/

mL)

Th

(ng/

mL)

U

(ng/

mL)

se

awat

er

120.

40

0.41

0.

51

0.61

0.

46

0.34

1 15

.09

0.59

0.

85

N13

-20-

1 87

.12

43.9

4 33

.11

97.6

6 3.

90

0.57

8 66

9.83

5.

66

18.2

0 N

13-2

0-3

95.2

6 10

6.10

51

.28

119.

96

9.03

1.

369

547.

30

11.3

7 7.

67

N13

-20-

5 12

8.40

73

.97

35.1

5 63

.29

4.58

0.

797

100.

84

7.84

0.

67

N13

-20-

7 86

.96

4.60

2.

77

3.06

0.

17

0.02

9 3.

50

0.90

1.

97

N13

-20-

9 74

763.

32

47.3

3 65

.11

74.0

6 0.

51

0.13

1 51

4.76

3.

41

8355

.97

N13

-20-

12

115.

08

1.21

0.

65

0.76

0.

27

0.11

8 2.

54

0.77

60

.27

N13

-20-

15

123.

95

1.20

0.

63

0.73

0.

28

0.12

9 1.

81

0.75

77

.08

N13

-20-

18

129.

97

1.16

0.

62

0.69

0.

27

0.12

5 1.

32

0.72

80

.68

N13

-20-

21

82.4

6 0.

32

0.29

0.

37

0.16

0.

080

0.66

0.

43

25.7

0 N

13-2

0-24

10

8.82

0.

44

0.46

0.

53

0.23

0.

113

1.48

0.

61

46.5

7 N

13-2

0-27

10

3.77

0.

42

0.40

0.

52

0.23

0.

116

0.98

0.

63

37.2

9 N

13-2

0-31

67

.63

0.70

0.

71

0.92

0.

32

0.15

7 2.

88

0.89

41

.94

N13

-20-

32

16.5

8 0.

39

0.26

0.

34

0.15

0.

069

0.89

0.

43

19.3

3 N

13-1

00-1

12

8.69

47

.98

22.4

1 58

.50

4.19

0.

618

464.

37

11.4

1 7.

34

N13

-100

-3

187.

82

20.9

9 9.

84

23.8

3 1.

55

0.24

9 98

0.99

1.

53

2.03

N

13-1

00-5

16

1.67

0.

31

0.30

0.

40

0.16

0.

078

2.30

0.

43

0.45

N

13-1

00-7

20

8.22

0.

19

0.05

0.

13

0.01

0.

002

3.06

0.

02

0.33

N

13-1

00-9

30

9.98

0.

50

0.54

0.

66

0.28

0.

138

4.23

0.

75

1.54

N

13-1

00-1

3 20

6.83

0.

38

0.32

0.

43

0.18

0.

088

2.18

0.

48

2.25

CH

APT

ER 6

: MA

NU

SCR

IPT

3

75

Tab.

2 co

ntin

ued.

R

b (n

g/m

L)

Y (n

g/m

L)La

(ng/

mL)

Ce

(ng/

mL)

Yb

(ng/

mL)

Lu

(ng/

mL)

Pb

(ng/

mL)

Th (n

g/m

L)U

(ng/

mL)

seaw

ater

12

0.40

0.

41

0.51

0.

61

0.46

0.

341

15.0

9 0.

59

0.85

N

13-1

00-1

7 21

0.16

0.

33

0.29

0.

39

0.17

0.

086

0.86

0.

48

3.49

N

13-1

00-2

1 20

2.57

0.

30

0.30

0.

38

0.16

0.

083

1.21

0.

45

3.14

N

13-1

00-2

8 32

7.11

0.

61

0.46

0.

49

0.45

0.

303

1.07

0.

55

4.85

N

13-1

00-3

0 33

8.52

0.

64

1.14

1.

20

0.41

0.

297

4.75

0.

52

5.11

N

13-1

00-3

4 17

7.25

0.

34

0.25

0.

29

0.23

0.

165

5.88

0.

28

2.26

N

13-1

00-3

5 31

7.18

0.

62

0.51

0.

52

0.40

0.

288

20.5

9 0.

49

3.98

N

13-1

00-3

6 32

6.49

0.

62

0.48

0.

53

0.42

0.

301

3.28

0.

50

3.30

N

13-1

00-3

8 29

9.67

0.

66

0.53

0.

57

0.42

0.

302

97.5

3 0.

51

3.01

N

13-1

00-3

9 15

1.27

0.

37

0.41

0.

45

0.24

0.

172

8.71

0.

29

3.07

N

13-1

00-4

1 13

2.46

0.

43

0.39

0.

42

0.30

0.

218

4.12

0.

37

0.52

N

13-1

50-5

27

9.49

2.

92

3.80

8.

49

0.19

0.

025

127.

41

2.25

0.

77

N13

-150

-7

269.

41

0.35

0.

64

1.35

0.

02

0.00

4 43

.66

0.03

0.

05

N13

-150

-9

255.

17

0.22

0.

31

0.71

0.

01

0.00

1 77

.94

0.01

0.

02

N13

-150

-10

248.

25

0.65

0.

74

1.82

0.

04

0.00

5 22

1.36

0.

33

0.12

N

13-1

50-1

1 27

3.00

0.

67

0.64

1.

59

0.04

0.

010

240.

38

0.19

0.

14

N13

-150

-13

239.

57

0.24

0.

25

0.65

0.

02

0.00

2 16

6.44

0.

02

0.03

N

13-1

50-1

4 24

0.20

0.

23

0.25

0.

63

0.01

0.

002

228.

60

0.02

0.

02

N13

-150

-16

224.

19

0.30

0.

25

0.64

0.

03

0.00

3 19

3.59

0.

03

0.04

N

13-1

50-1

7 N

D

ND

N

D

ND

N

D

ND

N

D

ND

N

D

N13

-150

-18

354.

48

1.31

1.

41

2.24

0.

07

0.00

0 10

97.2

6 0.

24

1.76

N

13-1

50-1

9 47

0.52

2.

48

3.15

4.

58

0.15

0.

075

1223

.65

0.11

1.

50

N13

-150

-20

9718

.36

112.

69

137.

87

217.

12

8.92

0.

831

3850

7.86

4.

95

58.1

0

CH

APT

ER 6

: MA

NU

SCR

IPT

3

76

Ta

b.2:

con

tinue

d.

P

oros

ity (%

/100

)st

ress

(MP

a)C

l (m

g/L)

norm

. fac

tor

Al (

mg/

L)B

a (m

g/L)

Ca

(mg/

L)Fe

(mg/

L)K

(mg/

L)se

awat

er

1860

0

ND

0.

003

398

0.08

39

3 N

14-2

0-1

0.73

4.

24E

-03

3358

0.8

0.55

39

NN

0.

085

429

0.17

43

4 N

14-2

0-4

0.61

2.

26E

+00

3838

4.8

0.48

46

0.04

0.

055

396

0.11

40

1 N

14-2

0-6

0.60

3.

37E

+00

1891

4.9

0.98

34

NN

0.

066

414

0.05

41

1 N

14-2

0-8

0.59

4.

84E

+00

1860

0.8

1.00

00

NN

0.

063

408

0.05

40

3 N

14-2

0-10

0.

57

8.42

E+0

0 19

040.

3 0.

9769

N

N

0.06

5 40

6 0.

11

397

N14

-20-

12

0.57

9.

26E

+00

2337

0.1

0.79

59

0.06

0.

061

397

0.06

39

2 N

14-2

0-13

0.

56

1.11

E+0

1 19

204.

2 0.

9685

N

N

0.06

1 41

0 0.

04

395

N14

-20-

14

0.56

1.

30E

+01

1901

7.3

0.97

81

0.02

0.

060

405

0.03

38

3 N

14-2

0-15

0.

55

1.42

E+0

1 18

960.

2 0.

9810

N

N

0.05

8 40

1 0.

04

371

N14

-100

-1

0.74

1.

00E

-06

1052

9.0

1.76

65

0.08

0.

257

521

0.09

59

9 N

14-1

00-2

0.

66

3.91

E-0

6 12

650.

7 1.

4703

0.

16

0.27

9 56

0 0.

68

759

N14

-100

-4

0.59

5.

29E

-04

1855

6.8

1.00

23

NN

0.

181

535

0.04

57

7 N

14-1

00-6

0.

55

7.32

E-0

3 47

955.

5 0.

3879

0.

00

0.19

1 55

4 0.

12

622

N14

-100

-7

0.53

2.

45E

-02

2914

9.2

0.63

81

0.01

0.

145

522

0.02

54

8 N

14-1

00-9

0.

47

2.68

E-0

1 29

170.

0 0.

6376

0.

03

0.14

9 54

1 0.

10

539

N14

-100

-10

0.43

1.

04E

+00

2912

4.6

0.63

86

0.02

0.

149

545

0.04

54

2 N

14-1

00-1

2 0.

36

8.96

E+0

0 39

082.

1 0.

4759

0.

00

0.14

5 50

3 0.

02

518

N14

-100

-13

0.32

2.

93E

+01

3202

0.6

0.58

09

0.04

0.

168

515

0.02

48

4

CH

APT

ER 6

: MA

NU

SCR

IPT

3

77

Tab.

2: c

ontin

ued.

M

g (m

g/L)

Mn

(mg/

L)N

a (m

g/L)

S (m

g/L)

Si (

mg/

L)S

r (m

g/L)

Ti (m

g/L)

SO

4 (m

g/L)

seaw

ater

12

82

0.00

04

1080

0 88

8 2.

9 7.

83

ND

25

00

N14

-20-

1 13

94

0.00

00

1220

8 93

7 1.

10

8.40

0.

02

5698

N

14-2

0-4

1259

0.

4473

11

175

859

6.07

7.

68

NN

22

42

N14

-20-

6 13

05

0.39

20

1116

1 89

6 3.

12

8.09

0.

00

2530

N

14-2

0-8

1278

0.

4094

11

364

876

2.92

7.

93

NN

25

86

N14

-20-

10

1261

0.

4769

11

022

863

3.07

7.

79

0.00

25

20

N14

-20-

12

1250

0.

5665

11

276

856

3.48

7.

63

0.01

24

79

N14

-20-

13

1276

0.

5258

11

291

874

3.51

7.

88

0.00

26

14

N14

-20-

14

1258

0.

6153

11

079

872

3.65

7.

75

0.00

25

53

N14

-20-

15

1258

0.

6915

11

040

856

3.92

7.

69

NN

26

37

N14

-100

-1

1207

1.

0726

11

422

925

47.0

3 8.

91

0.00

30

97

N14

-100

-2

1276

0.

0863

13

972

993

105.

18

9.28

0.

01

0 N

14-1

00-4

10

71

1.43

79

1080

2 80

4 35

.38

9.10

N

N

2498

N

14-1

00-6

12

30

0.15

99

1189

6 85

4 35

.90

8.81

0.

02

4275

N

14-1

00-7

11

70

0.86

77

1093

9 85

0 27

.51

8.24

N

N

2482

N

14-1

00-9

12

01

4.97

03

1074

1 88

0 34

.66

8.40

N

N

2541

N

14-1

00-1

0 12

16

5.53

67

1042

3 88

0 35

.93

8.45

N

N

2616

N

14-1

00-1

2 11

89

4.30

23

1065

9 84

7 29

.79

7.80

N

N

2374

N

14-1

00-1

3 12

09

4.77

03

1073

0 87

4 37

.68

7.73

N

N

2430

CH

APT

ER 6

: MA

NU

SCR

IPT

3

78

Tab.

2: c

ontin

ued.

R

b (n

g/m

L)

Y (n

g/m

L)La

(ng/

mL)

Ce

(ng/

mL)

Yb

(ng/

mL)

Lu

(ng/

mL)

Pb

(ng/

mL)

Th (n

g/m

L)U

(ng/

mL)

seaw

ater

12

0.40

0.

41

0.51

0.

61

0.46

0.

34

15.0

9 0.

59

0.85

N

14-2

0-1

88.3

8 1.

94

3.47

8.

74

0.11

0.

01

6.05

0.

01

4.44

N

14-2

0-4

73.1

4 0.

42

0.51

0.

73

0.26

0.

13

6.01

0.

72

5.57

N

14-2

0-6

151.

29

1.06

1.

01

1.37

0.

55

0.27

4.

48

1.78

12

.68

N14

-20-

8 14

9.18

0.

84

0.91

1.

21

0.54

0.

27

2.27

1.

54

14.5

3 N

14-2

0-10

26

4.64

3.

07

1.31

1.

51

0.61

0.

29

5.34

1.

63

90.5

5 N

14-2

0-12

12

3.54

0.

65

0.95

1.

29

0.42

0.

21

37.4

1 1.

15

14.1

2 N

14-2

0-13

14

8.50

0.

79

0.92

1.

22

0.52

0.

26

6.30

1.

43

18.8

3 N

14-2

0-14

14

3.97

0.

90

1.02

1.

29

0.59

0.

28

6.40

1.

46

20.6

8 N

14-2

0-15

13

5.70

0.

79

1.07

1.

36

0.53

0.

27

8.22

1.

46

23.7

6 N

14-1

00-1

44

1.62

1.

71

2.46

2.

27

1.46

1.

04

15.0

8 1.

81

2.53

N

14-1

00-2

N

M

NM

N

M

NM

N

M

NM

N

M

NM

N

M

N14

-100

-4

451.

98

1.12

1.

16

1.50

0.

85

0.61

18

.60

1.06

1.

96

N14

-100

-6

291.

22

0.20

0.

09

0.23

0.

01

0.00

5.

53

0.08

0.

22

N14

-100

-7

452.

73

0.84

0.

87

0.83

0.

52

0.37

5.

34

0.70

0.

95

N14

-100

-9

460.

76

1.07

0.

73

1.05

0.

55

0.39

6.

12

0.79

0.

82

N14

-100

-10

471.

83

1.04

0.

79

1.08

0.

57

0.40

16

.12

0.75

0.

83

N14

-100

-12

353.

52

0.56

0.

45

0.49

0.

41

0.29

0.

71

0.49

0.

74

N14

-100

-13

389.

34

0.63

0.

51

0.61

0.

47

0.34

2.

38

0.58

1.

10


6.4 Results A noticeable increase in element concentration at the very beginning of the

tests is observable for room temperature tests as well as for heated tests between

1*10-5 and 1*10-6 MPa (Fig. 3A,B). After this early peak in solutes, the concentrations

drop down and remain fairly constant until at least �e=10 MPa. This is particularly

obvious for the 100 °C temperature test of the smectite-rich sample N13 (e.g. K, Na,

Ba, Sr, S, Si), because of the larger number of measured samples in the low stress

range. Single elevated concentrations for the illite-rich sample may hint to a similar

trend for these experiments. However, for room temperature tests most solutes return

to seawater composition with increasing stress. Exceptions are enriched

concentrations of Na, Ba and Mn for the illite-rich and Na, Sr, Si and Mn for the

smectite-rich sample with solute concentration higher than the seawater concentration.

The most notable observation is the temperature-related change in solute

concentrations. It is marked by an offset compared to the room temperature tests

which develops immediately after heating started (Fig. 3C-F). Although there are

common elements for both lithologies showing the offset, there are slightly more

affected solutes for the illitic sample. The enrichment of the very same element can be

quite ambiguous with different lithology (e.g. Rb; Fig. 3E,F). However, the observed

offsets towards enrichment with increasing temperature from 20 °C and 100 °C tests

are observable for the smectite-rich sample N13 for K, Ba, Rb and Si. The step

between the 100 °C test and the 150 °C test for these elements is quite ambiguous.

Some elements are further enriched (K, Ba, Si) while Rb shows no difference between

the 100 °C and 150 °C tests (cp. Fig. 3C-F). For the illitic sample it is pronounced for

the elements K, Ba, Ca, Rb, Si and, less explicitly, for Mn due to larger scatter.

Instead, Mg solely decreases with increasing temperature. It is observable for both

lithologies in N13 and N14, with a stronger depletion for the smectite sample (Fig.

3G,H).

The smectite-rich sample N13 reveals some unique characteristics. Most

notable is the decrease in solute concentration beyond a threshold of ~10 MPa (Fig.

3I). For the room temperature test these are Na, K, Ca, Sr and S. The Na depletion

might be also allusively displayed for the illitic sample. The depletion is for the

100 °C run less obvious because fewer fluids have been sampled at stresses higher

than 10 MPa (Fig. 3I). Thus, a similar trend than that of the room temperature tests


may also be assumed. The 150 °C test follows this trend clearly for the elements Ca,

Sr and S, but indicates gentle enrichment for Na and K (Fig. 3A,D). Most strikingly,

however, are a strong decrease in sulphur and the total loss of sulphate (Fig. 3J).

Fig. 3: Pore water concentrations for selected elements vs logarithm of

effective stress. (A,B) Note the peaks for the smectite (N13) as well as the illitic (N14) sample at the beginning of consolidation. (C,D) K shows a clear enrichment with temperature which increases for the 150 °C test of the smectite sample at the end of the test. (E,F) Average value for Rb at 20 °C and 100 °C (dotted line) and shaded areas as standard deviation to highlight the temperature dependent offset. (G,H) The depletion is more enhanced for the smectite than for the illite sample and shows a larger offset between the 100 °C and 150 C test. (I) Besides Ca, also Na, K, Ca, Sr and S show a significant depletion beyond an effective stress of 10 MPa. (J) Note the strong depletion in S for the 150 °C test which may hint to the precipitation of sulphate.


There are also some less pronounced trends, associated to a small number of

elements or related to a specific lithology. Heavy rare elements (Yb, Lu), for example,

are depleted only for smectite tests (N13). The same can be observed for Pb in all

experiments conducted. U takes the role of an outlier because the room temperature

tests show enrichment for both lithologies (N13, N14). Light rare earth elements (e.g.

La, Ce and Y) do not display a variation between different temperatures, stresses or

lithologies at all and trends remain ambiguous due to large scattering for Al and Fe.

6.5 Discussion In the following the possible processes, which are responsible for the observed

changes in element concentrations during hydrothermal oedometer testing are

discussed. The influence of increasing effective stress and temperature is separately

addressed in subchapters. The identified processes are then examined for their

geological relevance and their significance for pore water sampling.

6.5.1 Primary results from hydrothermal oedometer tests

From the results several major trends can be distinguished for the illite- and

the smectite-rich samples. One is the offset in solute concentration between 20 °C,

100 °C and 150 °C test, which is observable for both lithologies. This observation is

discussed in the light of temperature dependencies since they seem unrelated to

increasing stress.

The observed early peaks in solute concentrations for room temperature and

high-temperature tests appear to be independent of temperature and were observed for

both specimens tested (cf. K, Ba). The significant depletion of solutes beyond

�e=10 MPa is observed only for the smectite-rich sample, but is noticeable at the three

temperatures tested.

6.5.1.1 Temperature

Temperature increase leads to an almost instantaneous increase in K, Ba and

Si as well as to a depletion of Mg for both tested lithologies. This is quite similar to

the observation from hydrothermal tests of marine sediments in rocking autoclaves

(e.g. Thornton and Seyfried, 1985; You et al., 1996). The average concentrations

between 1 and 10 MPa document a total exchange of solutes of 564.1 mg/l (N13) and


1015.5 mg/l (N14) between the 20 °C and 100 °C runs with net differences

accounting for a small enrichment of 8.8 mg/l and 40.9 mg/l, respectively. This

residual surplus may be accounted to the depletion of solutes, which have not been

measured yet (e.g. NH4).

Results of rocking autoclave testing have been mainly interpreted in terms of

thermal alteration of the sediment and most of the proposed diagenetic reactions occur

>> 150 °C (cp. You and Gieskes, 2001). The interpretation is supported by the fact

that boron isotope measurements suggest that efficient release of lattice bound B starts

not until T 300 °C in these experiments (You and Gieskes, 2001). The rapid

release/depletion of solutes in our experiments, the lower temperature and the

consistency of released elements despite the different initial compositions argue for

the absence of such a thermally driven diagenetic reaction in our experiments.

Considering that an ion can be found in three sites within the sediment, namely the

interstitial solution, the exchangeable sites and integrated in the lattice (Murthy and

Ferrell, 1972), we propose that the observed change in element concentrations is

merely due to the interaction of the pore water with exchangeable sites at the charged

surface of clay minerals. Additionally, the ion exchange reactions with clay minerals

have been proposed to be rather fast (Masuzawa et al., 1980). Results from Bischoff et

al. (1970) and Masuzawa et al. (1980) corroborate our hypothesis. These authors

analyzed temperature effects while squeezing pore waters from marine sediments.

Although these experiments were conducted at significant lower temperatures (2-

25 °C), these researchers found enrichment in K and Si. Also, the observed depletion

of Mg is strikingly similar to our results. Collectively, these experiments suggest that

the ion exchange capacity of clay minerals is a function of temperature, but also

depends on variables such as the type of clay mineral, crystal size and the clay-water

ratio (Bischoff et al., 1970). These processes may explain the differences in

magnitude of enrichment and depletion of single elements (e.g. Ca). However, we can

conclude that the ion affinity for K decreases with increasing temperature and leads to

its release into the solution whereas the capacity increases for e.g. Mg and causes an

uptake of that element. Thus, the heating changes the replaceability sequence of

cations and generates the early offset of solute concentrations. According to the

enrichment/depletion in the solution (Fig. 4A,B) we propose the following retention

sequence with increasing temperature of Mg>Ca for divalent cations and Na>K for


monovalent cations. Unless there is no decomposition of clay minerals, this

phenomenon is reversible (Masuzawa et al., 1980).

Fig. 4: (A,B) Mg/Ca and Na/K concentration ratios in the expelled pore water

at 55% porosity for both lithologies vs temperature. Decreasing ratios indicate that the clay surface attraction is Mg>Ca for divalent ions and Na>K for monovalent ions with increasing temperature.

The 150°C test of the smectite-rich sample (N13) follows the temperature-

dependent trend described above, and shows an immediate depletion of S (Fig. 3J).

The strong deviation from the 100 °C test and the late enrichment suggest another

phenomenon than the above proposed ion exchange reaction. The decrease of SO4 and

S strongly hints to the precipitation of sulphates such as gypsum or anhydrite.

Experimental data by Bischoff and Seyfried (1978) on seawater geochemistry suggest

that anhydrite reaches saturation between 150 and 200 °C. Although the determined

amount is close to the detection limit, XRD analyses show a notable fraction of

anhydrite in the 150 °C test, but not in the 100 °C test. Thus, it may support the

precipitation of small amounts of this mineral. Another possibility for the decreased

sulphate concentration is the formation of kieserite, which forms upon evaporation of

seawater (Matthes, 1987). In addition, the formation of a Mg-hydroxysulphate hydrate

(caminite) may be possible. This phase has been reported to precipitate in laboratory

hydrothermal testing of seawater and marine sediment by Thornton and Seyfried


(1985), although at slightly higher temperatures (200 °C) than our tests. Precipitation

of a Mg-sulphate salt may be suggested by the similarity in the development of both

Mg and SO4 concentrations (e.g., sinoidal patterns with a minimum at 0.01 MPa and

similar relative concentration differences between the 100 °C and 150 °C

experiments; Figures 3G and 3J), whereas Ca does not display a close similarity with

SO4, which would be expected if anhydrite was the sole sulphate phase precipitated.

Thus, we propose that the Mg and sulphate depletions are the result of precipitation of

a Mg-sulphate phase.

6.5.1.2 Effective stress

It is well known that the negative charge of the surface of the clay particles

attracts cations from the surrounding solution while anions are repelled. This is

counteracted by diffusion, which tends to balance the unequal charge distribution. A

double layer is formed by the diffusive layer, which is characterized by exponential

increasing cation concentrations and inversely increasing anion concentrations to the

clay surface (Kharaka and Berry, 1973; Meunier, 2005). Thus it can be distinguished

between the free pore water and the water of the diffusive layer (Baldi et al., 1988;

Henry 1997; Fig 5).

With the onset of consolidation the steady state of the resting sediment

seawater slurry is disturbed by the spatial convergence of the sediment particles and

the change of the pore water from a static to a flowing state with the onset of pore

water expulsion. Upon the initiation of fluid flow the water movement deforms the

double-layer (Hanshaw and Coplen, 1973). During the manifestation of this process

weakly associated cations in the vicinity of the double layer may be dragged with the

effluent until a new equilibrium is established. Similar observations have been made

by Tang et al. (2006) for the Pb distribution in expelled fluids during consolidation

tests. These authors propose that the high seepage velocity at the beginning of their

tests may change the adsorption-desorption equilibrium near the drainage surface.

Considering that the deformation of the double layer is a function of the flow velocity

(Kharaka and Berry, 1973) this assumption would be consistent with our

interpretation.

Another likely explanation might be that element exchange between

seawater and clay surfaces was incomplete after re-hydration. Thus, the peak in

concentrations at the beginning of the deformation experiments results from the


transitional condition until the exchange is completed, which is than represented by

the constant element concentrations afterwards. However, a definitive answer is not

possible under these circumstances and stresses the importance for a better control of

the re-hydration process by geochemical measurements of fluids sampled during the

procedure.

Fig. 5: (A) Schematic distribution of particles and pore water in a clayey sediment (modified after Kharaka and Berry, 1973; Baldi et al., 1988; Henry, 1997). The total pore water can be distinguished into free pore (dotted) and double layer water (grey shaded) associated to the clay particles. (B) The accentuation in the upper right shows that the anions (as Cl-) are restricted mainly to the free pore water. (C) Where the double layer is overlapping the ion concentration of interstitial water is dominated by cations.

With increasing stress the pore space decreases and the double layers of

opposite clay particles will eventually overlap (Fig. 5). Several authors demonstrated

that such highly compacted clays function as filtration membranes for cations (e.g.

McKelvey and Milne, 1962; Hanshaw and Coplen, 1973; Kharaka and Berry, 1973).

Kharaka and Smalley (1976) propose a retention sequences for monovalent ions of

Cs>Rb>K>Na>Li and Ba>Sr>Ca>Mg for divalent cations where the replacing power

is greater for ions with higher charges and hydrated radii. Comparing the major cation

concentrations before and after the threshold effective pressure of 10 MPa is reached

for the 20°C test of this study we can propose an equivalent retention sequence with

K>Na and Ca>Mg (Fig. 6). These sequences are opposite to the thermally driven

retention, which may explain the observed weakening of filtration at higher

temperatures by Kharaka and Berry (1973). Nonetheless, the assumption of


membrane filtration is supported by the fact that the illite-rich sample does not reveal

the depletion effect because of phyllosilicates are less abundant and a considerable

amount of quartz and feldspar is at hand to separate the clay particles.

Fig. 6: A,B) Mg/Ca and Na/K concentration ratios in the pore water vs effective stress for smectite-rich sample (N13) at 20 °C. The linear fit increases at an effective stress > 10 MPa. This indicates that the clay surface attraction is Ca>Mg for divalent ions and K>Na for monovalent ions. The solid line suggests a good linear fit. In general, the filtration efficiency increases with compaction and ion

exchange capacity of the sediment (Kharaka and Berry, 1973). The flow of ions

through the membrane may be further influenced by the concentration of the solute,

the velocity of the flowing pore water, the electrical interaction of the ion with the

negative sites of the clay particle and the interaction with the streaming potential

(Hanshaw and Coplen, 1973; Kharaka and Berry, 1973). The streaming potential is

the electrical potential gradient across the membrane formed by the deformation of

the double layer. The outflow side of the membrane becomes positively charged, this

way accelerating anions relatively to flow of the pore water. This hydraulic drag of

the anions is larger on divalent than on monovalent cations according to the Stokes

equation (Kharaka and Berry, 1973; Sacchi et al., 2001).

Another explanation might be that the free pore water will be pushed out

first and the anions are to a large extent expelled with it (Sacchi et al., 2001 and


references therein). Once the free pore water is gone, the solutes from the double layer

will start to be released. Because of electrical neutrality the loss of cations is

dependent on the anions which are depleted in the remaining solution. Thus, the

expelled fluid should have a lower salinity, which is consistently true with our results.

Similar observations were made by von Engelhardt and Gaida (1963) with starting

depletion between 3 and 81 MPa for montmorillonite clay. Although both

explanations are feasible, membrane filtration refers to flow through experiments

while latter one was established by compaction testing (von Engelhardt and Gaida,

1963; Chiligarian et al., 1973) and seems more suitable to explain the observed

depletion for the smectite sample beyond �e=10 MPa (Fig. 4).

6.5.2 Geological relevance of hydrothermal experiments

Our experiments show that temperature and increasing effective stress can

modify the composition of pore fluid that is expelled from the sediment during

consolidation and that these changes are independent of diagenetic processes. The

compaction driven retention is detectable only for the smectite-rich sample above a

threshold of �e=10 MPa. In contrast, the T-induced enrichment/depletion seems less

dependent on the nature of the lithologies tested. For natural conditions it can be

assumed that the thermally driven release/retention increases with depth as a function

of the regional geothermal gradient. Considering the low temperatures along the

subduction thrusts, this process may be rather relevant for deeper portion of the

subduction zone. Accordingly increasing effective stress and temperature may be

important for pore water geochemistry at burial depths >>1 km.

It remains difficult to quantify the significance of the identified processes for

their geologic consequences at convergent margins. Although increasing effective

stress is supposed to be analogous to the natural process of consolidation,

experimental pore water release is rather high because of rapid loading under

laboratory conditions. Accordingly advection has a higher impact than under natural

conditions and diffusion is underestimated.

The influence of membrane filtration at convergent margins was discussed by

Martin et al. (1995). These authors suggested that it is negligible although fluid

pressures are sufficiently high to favour fluid flow through highly compacted clays.

Its significance is supposed to be small because of the complex geochemical effects as

a result of dilution through mineral dehydration, fluid-mineral exchange reactions,


diffusion-advection and mixing with external (e.g. meteoric water) or internal sources

(e.g. deep-seated fluids). Further, focused fluid flow along permeable faults at

convergent margins would allow circumventing clay membranes and only sediments

with high smectite contents can produce a significant filtration effect.

On the other hand, it can be argued that highly permeable faults may also act

as drainage for compacting sediments (Carson and Screaton, 1998). In this case the

permeable conduit is at least partially fed by the pore water expulsion from the

surrounding sediment. Depending on the consolidation state, the sediment will

eventually release low salinity pore water after the free pore water is expelled. The

extensive testing of Kharaka and Berry (1973) and results from this study suggest that

high clay contents and especially smectite must be present in the sediment to produce

considerable effects of membrane filtration or consecutive release of free and

adsorbed pore water. Further, high fluid pressures determined for the accretionary

Nankai margin and other subduction zone sediments may delay consolidation and thus

closer packing of clay minerals (Saffer, 2007; Fig. 7). Eventually smectite-rich

sediments will loose their retention efficiency with the transition of smectite-to-illite.

Kharaka and Berry (1973) suggest a low retention capacity for illite of less than 10 %

below of 70 MPa. In summary, it can be suggested that the subsequent release of pore

water constituents due to overlapping double layer is negligible.

Fig. 7: Cross section of the Nankai margin (modified after Morgan et al., 2007). Shaded areas indicate excess pore pressure with 90 %, 80 %, 70 %, and 60 % of the lithostatic stress. The outtake shows fluid flow at toe of the prism with localised fluid flow along faults (solid arrows) and diffusive fluid flow between (dotted arrows) (modified after Yamano et al., 1992).


Although the amount and the number of elements changes with sediment

composition, end member lithologies suggest the release of K, Ca and Si and the

removal of Mg from the pore water with increasing temperature at the Nankai margin.

Even if the impact of this process is small the increased availability of released

elements may facilitate diagenetical processes and lithification at depth, making the

sediment prone to unstable failure (Moore et al., 2007). The temperature-related

release of K may facilitate the smectite-illite conversion, which is important for the

hydrology and stress regime at convergent margins (Brown et al., 2003; Saffer et al.,

2008). The transition starts at 60 °C and is virtually completed at 150 °C under natural

conditions (e.g. Colten-Bradley, 1987). The reaction equation is given by:

clay (kaolinite, smectite) + cations (K+) = aluminosilicate (illite) + quartz + water

following Bjorlykke (1998).

The greater desorption of Ca and Si with increasing temperature may facilitate

the precipitation of quartz and carbonate cements and veins. This would be in

accordance with the observation that cementation and veining by carbonates becomes

common above 125 °C and quartz veining by 200 °C (Moore et al., 2007) and can be

associated with enhanced mobility of Si, Na, K, Ca and trace elements (Bebout and

Barton, 1989). This correlation suggests that the observed desorption/adsorption

processes may be more important for water-rock interaction in the shallow subduction

zone than previously believed by other workers (e.g. Kastner et al., 1991).

Heat flow distribution on the Nankai trough seafloor suggests that warm fluids

flow to the ocean along the decollement or fault zones (Yamano et al., 1992, Fig. 8).

Thus, the released elements may also be expelled to the ocean unless they are

consumed by diagenetical reactions. It may be assumed that fixed elements to the clay

surface will be dragged further down-slab. The release of HFSE, REE and volatile

elements during hydrothermal uniaxial deformation testing was suggested to have

implications on HFSE enrichment in magmas as proxy for sediment consumption

(Kopf et al., 2002). You et al. (1996) proposed from hydrothermal rocking autoclave

experiments that the released elements are partially taken up by newly metamorphic

minerals and thus being further dragged down. Observed hydrothermal fractionation

of Pb/Ce, La/Ba, Rb/Cs, B/Nb and B/Be are supposed to explain ratios in arcs.

However, it can only be speculated that the observed retardation and release of


elements with increasing temperature and effective stress from our experiments may

foster the enrichment of large-ion-lithophile elements (e.g. Mg, K, Ca, Sr) in arc

magmas relative to high-field-strength elements (e.g. Ti, Th, Hf, Nb, Zr).

6.5.3 Significance of results for laboratory pore water sampling

While the thermal and stress induced impact on pore water geochemistry

under natural conditions may be preliminary and highly variable depending on the

location, its significance for laboratory conditions is important and has been

established before (e.g. McKelvey and Milne, 1962; Bischoff et al., 1970; Hanshaw

and Coplen, 1973; Kharaka and Berry, 1973; Masuzawa et al., 1980; Sacchi et al.,

2001). Especially the pore fluid sampling may suffer from their influence. In the

following we will focus the discussion on pore fluid sampling by squeezing which is

the present standard sampling procedure within the IODP (Integrated Ocean Drilling

Program). A broader overview of pore water sampling artefacts is given by Sacchi et

al. (2001).

Fitts and Brown (1999) have shown that interstitial water studies of marine

sediments may be substantially affected by stress-induced smectite dehydration from

squeezing. Under certain circumstances the observed compactive fluid filtration from

this study may also affect sampled fluids. However, besides smectite content the

effective stress must be >10 MPa to have a significant influence. The study by Fitts

and Brown (1999) demonstrated that under rapid loading rates the effective stress

remains rather low because of the time-dependent dissipation of the pore water.

Considering that sample squeezing is a very fast process we propose that compactive

filtration should be negligible.

The temperature dependence of ion exchange capacity is long known (e.g.

Bischoff et al., 1970; Masuzawa et al., 1980) and its impact can be prevented by

squeezing at in-situ temperatures. While near seafloor surface temperatures (~ 4 °C)

are in most cases slightly lower than at laboratory conditions deep drilling is

occasionally related to areas with high thermal gradients. The central part of Nankai

margin is such an area. Relating to the enrichment found for particular elements, it

can be assumed that the core recovery in areas with high in-situ temperatures leads to

an underestimation of e.g K and Si while Mg will be overestimated because of the

reversibility of ion exchange (Masuzawa et al., 1980). A quantitative correction of the

effect afterwards, however, is difficult because of the complexity owing to various


parameters such as type, size and abundance of clay minerals (Bischoff et al., 1970).

Thus, squeezing at in-situ temperatures may be necessary to accurately address pore

water geochemistry for samples with very different in-situ temperatures or from large

subseafloor depth.

6.6 ConclusionsThe pore waters expelled from hydrothermal laboratory consolidation of

sediments from the Nankai margin bear some similarity with data from previous

rocking autoclave testing (e.g. You et al. 1996). However, due to lower temperatures

we found our results especially influenced by ion-exchange behaviour of clays. The

ion-exchange capacity may be a function of parameters such as clay mineralogy,

temperature, fluid content or fluid flow velocity. A significant difference is the

consecutive release of free pore water followed by double layer water which led to a

significant depletion effect. This feature is neglected in rocking autoclaves where

effective stresses remain low due to high fluid pressures. The potential impact of the

observed ion exchange suggests that their relevance might be more important at burial

depth of several kilometres. The observed change in pore water geochemistry may

foster diagenetic processes at convergent margin but their geological relevance

remains rather small because the footprint of diagenetical processes is supposed to be

more evident. Nonetheless, the observed processes are relevant for pore water

sampling by squeezing.

Acknowledgments

We appreciate the assistance of Jill Weinberger for some of these tests and

Kevin Brown for providing laboratory space. Christoph Vogt is thanked for XRD

analyses. Samples and data used in this study have been provided by the Ocean

Drilling Program (ODP). We also thank Silvana Pape, Pat Castillo and Heike Anders

for assisting with pore water analyses.

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Chapter 7: Conclusions and outlook A novel laboratory approach has been conducted to simulate underthrusting of

sediments at convergent margins to understand their response to increasing PT

conditions on their way from aseismic sliding to seismic stick-slip behaviour. The

main conclusions of all three manuscripts as well as the wealth of unpublished results

(see appendices) are highlighted in the following as bullet points with consequences

for future perspectives:

� Tested end member samples reveal contraction behaviour with increasing

temperature regardless of the lithological composition. This observation can be

related to a decrease in intergranular friction. While the induced weakening may be

compensated by compressive strain under normally consolidated, drained

conditions, underthrust sediments are characterized by high excess pore pressures

suggesting that the compressive strain cannot keep pace with thermal weakening.

The test results may have implications for frictional behaviour, which could not

appropriately studied due to large temperature and effective stress differences

between hydrothermal consolidation tests and shear test. Future work by heated

friction experiments has to be conducted to shed light on the two competing

effects.

� Inferred from the hydrothermal consolidation tests the consolidation state of a

specific sediment is dependent on effective stress, time and temperature.

Knowledge of in-situ temperature can provide better description of the

consolidation state as shown for the central portion of the Nankai margin. The

inferred excess pore pressure estimates for the toe of the accretionary prism of the

Nankai margin are found to be smaller than previously believed. Thus, temperature

may have a veritable impact on the consolidation behaviour within deeper parts of

the subduction zone and, therefore, on excess pore pressure generation.

Temperature-controlled permeability tests could help to refine previous estimates.

� The different consolidation behaviour of the smectite and illite end members

suggest that the compositional transition during illitisation decreases the

compressibility with increasing illite. The associated cementation of by-products

such as quartz may facilitate this process and reduce the pore space. The decrease

in permeability may have severe implications for excess pore pressure generation.

Consolidation tests of different smectite-illite mixtures could help to shed light on


the changing consolidation behaviour during the smectite-to-illite transition. Also,

temperature tests at higher temperatures to facilitate smectite-illite transition within

the experimental time would be possible. However, the results of this research

study and of other workers show that mechanical behaviour of underthrust

sediments is subjected to a complex pattern of effective stress, time, temperature

and diagenetic change. All these parameters vary from margin to margin and their

specific impact has to be determined for each margin anew.

� The outlined influence on temperature underlines the importance of temperature

controlled laboratory testing, because major differences between in-situ and

laboratory data exist. The thermal hardening, which happens during cooling of

samples when they are removed from “hot” in-situ conditions may have severe

implications for the interpretation of the data. The application of a thermo-

mechanical model to quantify the thermal hardening enabled the re-interpretation

of available consolidation data of samples from the Nankai margin: The

temperature-corrected data is in better agreement with the general notion of a

normally consolidated stratum seaward of the deformation front of the accretionary

prism. Thus, the effect of cementation to explain overconsolidation may be less

important than previously believed. As a consequence a model was put forward

where decollement formation at the central portion of the Nankai margin is

consistent with additional physical properties data. The study shows that heated

tests are an inevitable tool to avoid thermal artefacts. This may be especially

important for the upcoming deep drilling at the Nankai margin with the riser vessel

Chikyu in the near future, when cores from deep and hot in-situ conditions will be

recovered.

� Geochemical analyses of expelled pore waters suggest that water-rock interaction

occurs mainly as desorption and adsorption processes at the stress and temperature

range regarded. It is astonishing that especially elements such as K and Si are

released from the clay mineral surface, which may directly facilitate smectite-to-

illite transition and quartz cementation. However, the experimental approach has

also shown that studying natural processes is difficult due to slow kinetic reactions

of diagenetic reactions. Experimental temperatures well above 150 °C may

enhance such diagenetic reactions tremendously, resulting eventually in enhanced

progress of diagenesis within the 3-5 month duration of the experiments.

ACKNOWLEDGEMENTS 99

Acknowledgements This PhD thesis was conducted within the framework of the ROME (Research

on Ocean Margins Earthquakes) project. I am very grateful to my supervisor Prof. Dr.

Achim Kopf for providing me with the chance to participate in this exciting

interdisciplinary research at the intersection of soil mechanics, structural geology,

hydrology and geochemistry. I especially valued his insightful input and constructive

criticism during the progress of this work. Particularly his patience during the

development of a heated oedometer, a trying task where I faced many obstacles, was

much appreciated.

I would furthermore like to thank Prof Dr. Tobias Mörz of the engineering

geology group for being co-referee. I am much obliged for the excellent cooperation,

e.g. when it came to sharing standard soil mechanical equipment.

Initial oedometer tests were conducted at SCRIPPS Institution of

Oceanography. Prof. Dr. Kevin Brown and Dr. Jill Weinberger provided laboratory

space and help with these tests, and I am grateful to both of them.

The setup of the heated oedometer devices at the University of Bremen would

have been unimaginable without the help of Matthias Lange. His assistance and

Labview experience definitely proved to be indispensable. The help of Wolfgang

Schunn with assembling electrical equipment of the oedometer device is also much

acknowledged.

I also thank Dr. Stefan Kreiter for his valuable advice concerning soil

mechanical problems. His help was of great benefit. I am also much obliged to Prof.

Dr. Wolfgang Bach and PD Dr. Matthias Zabel who provided helpful comments for

the interpretation of the pore water geochemistry data. Pore water analyses were

conducted by Heike Anders, Pat Castillio and Silvana Pape – I express my gratitude.

I want to give another big ‘Thank you’ to all my co-workers of the marine

geotechnics and the engineering geology group. Their warm welcome made it easy to

start my position at the University of Bremen in the first place, and we shared a

fantastic time in the following years. I very much enjoyed our daily trips to the

canteen and our after work arrangements. Special thanks go to my current and former

roommates Annedore Seifert, Hendrik Hanff and Annika Förster for the occasional

off-topic distraction. Annika needs to be mentioned in particular for babysitting my

ACKNOWLEDGEMENTS 100

oedometer tests at the weekend numerous times, and Katja Zimmerman conducted

some of the direct and ring shear tests.

Last but not least, I want to express my deep gratitude to my parents for their

support during my university studies. They always gave me the freedom to find my

own way. Finally, I want to thank my fiancée Bettina Unger for everything.


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APPENDIX 110

APPENDIXThe PhD project can be separated into two individual parts: (1) Mechanical,

geochemical and mineralogical analysis and interpretation of the large number of

samples from the pilot study conducted at the SCRIPPS Institution of Oceanography

and (2) the development and implementation of a heated uniaxial consolidation

apparatus (oedometer) at the MARUM, University of Bremen. The two thematically

blocks are dived into appendix A and appendix B, respectively.

Outline of Appendix A

There remains a tremendous data set from the post analyses of the pilot study,

which were collected or processed by the PhD candidate and are presented within the

appendix for the sake of completeness.

The focus of the PhD thesis was on samples from the projected underthrust

sequence at DSDP Site 297. However, additional samples were taken around the

future plate boundary thrust, which had also undergone consolidation tests and were

processed by the PhD candidate. Provisional analysis of the data promises a good data

basis for publication. These tests are presented in appendix A1.

In appendix A2 additionally geochemical data is shown. These data could not

be considered for manuscript 3, because of the vast data basis. Thus, it was planned to

split the data into major and trace element geochemistry. The latter is planned for

future publication.

SEM investigations on compacted samples from the oedometer tests were

conducted to shed light on water-rock interaction and textural changes with

deformation. Selected images are presented in appendix A3. They may complement

geochemical data for publication.

The compacted samples from the heated and room temperature tests

underwent mechanical testing at the MARUM soil mechanical laboratory. The

samples were tested for their peak and residual strength as well as rate dependent

friction behaviour. Selected results of direct and ring shear tests are presented in

appendix A4.

APPENDIX 111

Outline of Appendix B

In the appendix B the development and implementation of the heated uniaxial

consolidation apparatuses are described. The general capabilities of the new systems

are shortly outlined and initial results from mono-mineral standards are presented.

Due to the long term tests of 3-5 month, time was too short to accumulate sufficient

data for publication within the PhD project.

APPENDIX 112

APPENDIX A1 As part of the pilot work at SCRIPPS Institution of Oceanography, a number

of room temperature consolidation tests were carried out in addition to the heated

tests, which represent the heart of this PhD thesis. These tests were run on samples

from DSDP Site 297 and sampled the interval in the incoming sedimentary succession

most likely to become the future plate boundary thrust.

At present, the data was reprocessed by the PhD candidate and discussed with the

investigators involved. A publication is planned in the near future focussing on

consolidation behaviour and permeability studies. Owing to the fact that a broad suite

of fine- to coarse-grained specimens was tested, this work expands the understanding

of the overall hydrogeologic behaviour of clay-rich marine sediments during

subduction.

The results of the consolidation studies are shown in Figure 1-7. The majority

of the samples display a similar void ratio vs. effective stress relationship. Typical

values for the compression indices from the log-linear fit line range from 0.43-0.24.

Changes in lithology can alter this relationship and likely account for some of the

variability in the data (cf. Tab. 1). The hydraulic conductivity vs. void ratio

relationship for all the samples is also shown in the figures.

Table 1: XRD results of samples which under went high stress consolidation.

(Sm=Smectite, Qtz=quartz, Plg=plagioclase, Chl=Chlorite, Il=illite,

Musc=muscovite)

Core Name Depth (mbsf) Lithology Sm

(wt-%) Qtz

(wt-%) Plg

(wt-%) Chl

(wt-%) Il

(wt-%)

23-3-102-107 Nan1 594.02 Ash-Rich-silty Claystone 39.37 19.78 10.53 6.69 7.03

26-2-105-108 Nan2 668.55 Volcanic Ash 54.02 36.08 2.81 1.03 39.78 25-3-121-127 Nan3 651.21 Volcanic Ash 33.19 10.78 15.94 6.44 10 24-3-18-26 Nan4 621.68 Silty Claystone 20.2 30.5 17.2 6.6 25.5

23-4-0-6 Nan5 594.5 Ash-Rich-silty Claystone 13.26 18.86 14.18 13.92 43.3

25-6-73-78 Nan9 655.23 Volcanic Ash 51 13 15 4 23.62

APPENDIX 113

Fig 1: Preliminary results of the consolidation test of sample Nan1 at room temperature. (A) Settlement of the sample presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.

APPENDIX 114


APPENDIX 115


APPENDIX 116


APPENDIX 117


APPENDIX 118


APPENDIX 119


APPENDIX 120


APPENDIX 121

APPENDIX A2 To understand the transfer of geochemical tracers within the shallow subduction

zone, trace elements (table 1-3) and boron isotopes (Fig. 1) were determined. Trace

elements compositions of sampled fluids from hydrothermal tests were partly measured

at SCRIPPS Institution of Oceanography as well as by the PhD candidate at the

University of Bremen. The latter can be recognized in table 1-3 where the full set of trace

elements is shown. Preliminary results were presented by the PhD candidate at the ICDP-

IODP Kolloquium 2007 in Potsdam, Germany (see next page). Data analyses and

manuscript preparation by the PhD candidate is underway to complete the geochemical

investigation of fluid-rock investigation of the Nankai end member samples.

Fig. 1: Overview of boron systematic in the expelled fluids. (A) Boron enrichment with increasing temperature and effective stress and (B) �11B data plotted against boron content in the fluids. Note that the majority of the data lies between the typical values for seawater and exchangeable boron attached to the clay surface.

APPENDIX 122

Hüpers, A., Kopf, A.J., 2007. Consolidation experiments of marine sediments under hydrothermal conditions: implications for water-rock interaction in the shallow subduction zone, in: IODP-ICDP Kolloquium 2007, Potsdam.

Consolidation experiments of marine sediments under hydrothermal conditions: implications for water-rock interaction in the shallow subduction

zone

A. Hüpers, A.J. Kopf Research Center Ocean Margins, Bremen University, P.O. Box 330440, 28334 Bremen,

Germany ([email protected], [email protected])

Fluids play a critical role to understand key mechanisms in the subduction factory. Hence, it is necessary to reconstruct and quantify the transfer of geochemical tracers from the subducted slab to the overlying lithosphere, hydrosphere and atmosphere. At shallow levels diagenetic and low-grade metamorphic reactions are important processes. They may cause expulsion of large volumes of fluids from hydrous minerals, but also fault seal by precipitation of authigenic phases from interstitial, supersaturated fluids. Both mechanisms can produce pore pressure transients which influence the thermal and rheological development of the accretionary prism. Due to the lack of natural samples from deeper sites, hydrothermal experimental techniques provide the possibility to simulate shallow subduction processes. Previous studies demonstrated the mobilization of large ion lithophile elements relative to high field strength and rare earth elements. Furthermore, they described enrichments in water-soluble elements, as well as on ratios of key trace elements (e.g., B, Ba, Th, Nb).

To characterize the water- rock interaction of marine sediments and seawater, long-term compaction tests were conducted up to PT conditions similar to the upper seismogenic zone. Remoulded samples of the main lithologies (smectite-, illite- and quartz-rich) in the Nankai Trough (Japan) were loaded in an uniaxial apparatus up to 70MPa at 20°C, 100°C and 150°C. Fluids were continuously extracted and analyzed for major and trace elements. As a main result, smectite- and illite-rich samples show a similar distribution of element concentrations with almost constant concentrations of rare earth element during the tests. Fluids of quartz-rich samples show at least twice the threshold for these elements which are already released at low effective normal stresses of < 1MPa. Other elements (e.g. Sr) decrease with increasing pressure towards the end of the tests, while some major elements concentrations (e.g. Mg, Ca) are slightly increasing throughout heated and also room temperature tests. We conclude that some elements may be mobilized throughout our low T hydrothermal experiments (e.g. Rb, K, Ba), although they were previously believed to represent the "slab component" in arc magmas. Thus, such elements are may be less powerful to identify sedimentary input to volcanics than previously assumed. More testing from marine sediments of other convergent margins, possibly at temperatures up to 200-250°C, is necessary to verify these results.

APP

END

IX

12

3

Tab.

1: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of e

xpel

led

fluid

s dur

ing

the

room

tem

pera

ture

con

solid

atio

n te

st o

f the

smec

tite-

rich

sam

ple

(N13

). Th

e as

soci

ated

eff

ectiv

e st

ress

for

the

rele

ased

por

e w

ater

is g

iven

as

aver

age

effe

ctiv

e st

ress

bet

wee

n at

tach

ing

and

rem

ovin

g th

e sa

mpl

ing

flask

.

Sea

- w

ater

N

13-

20_1

N

13-

20_3

N13

-20

_5N

13-

20_7

N13

-20

_9N

13-

20_1

2 N

13-

20_1

5N

13-

20_1

8N

13-

20_2

1N

13-

20_2

4N

13-

20_2

7N

13-

20_2

9 N

13-

20_3

0N

13-

20_3

1N

13-

20_3

2 A

vera

ge

effe

ctiv

e st

ress

(M

Pa)

6.

4011

5E-0

5 0.

0001

9 0.

0005

6 0.

0014

0.

0034

0.

01

0.06

0.

25

0.99

2.

62

6.83

13

.22

18.8

6 27

.85

40.9

7

Ele

men

t

Li

_7(n

g/m

L)

36

1.22

91

4.57

1449

.79

Rb_

85(n

g/m

L)

123.

49

168.

56

248.

20

228.

69

307.

64

27

9.01

26

7.20

28

2.30

27

7.86

26

7.09

24

4.40

20

8.67

16

2.66

12

0.87

66

.27

Y_89

(n

g/m

L)

0.41

37

.29

276.

43

131.

75

16.2

9 94

.99

2.94

2.

60

2.52

1.

07

1.08

0.

99

1.03

1.

26

1.25

1.

55

Zr_9

0(n

g/m

L)

2.

67

31.8

6

5.70

Nb_

93(n

g/m

L)

0.

14

2.59

0.91

Cs_

133

(ng/

mL)

2.85

1.

45

1.

89

La_1

39

(ng/

mL)

0.

54

28.1

1 13

3.60

62

.60

9.79

13

0.67

1.

59

1.35

1.

34

0.97

1.

13

0.95

0.

97

1.19

1.

26

1.05

Ce_

140

(ng/

mL)

0.

63

82.9

0 31

2.55

11

2.72

10

.82

148.

64

1.83

1.

58

1.50

1.

24

1.31

1.

22

1.27

1.

57

1.65

1.

36

Pr_

141

(ng/

mL)

0.

48

6.12

28

.10

10.7

3 0.

87

20.8

7 1.

01

0.95

0.

94

0.92

0.

96

0.94

0.

93

0.92

1.

00

0.95

Nd_

146

(ng/

mL)

0.

43

22.1

7 10

5.43

39

.79

3.26

10

.95

0.94

0.

85

0.84

0.

63

0.65

0.

60

0.63

0.

80

0.86

0.

71

Ta_1

81

(ng/

mL)

0.03

0.

96

0.

20

Pb_2

08

(ng/

mL)

13

.88

568.

56

1425

.97

179.

61

12.3

9

6.15

3.

90

2.87

2.

21

3.62

2.

31

11.3

2 22

.01

5.15

3.

56

Th_2

32

(ng/

mL)

0.

59

4.80

29

.63

13.9

6 3.

17

6.85

1.

88

1.63

1.

57

1.46

1.

51

1.48

1.

49

1.48

1.

60

1.73

U_2

38(n

g/m

L)

0.79

15

.45

19.9

8 1.

20

6.97

146.

13

166.

15

175.

23

86.5

8 11

4.30

87

.84

121.

72

91.4

2 74

.95

77.2

7

Sc_4

5 (n

g/m

L)

0.

26

0.53

0.08

V_51

(n

g/m

L)

24

0.83

13

4.53

20.8

1

Cr_

52(n

g/m

L)

87

50.4

2 22

334.

48

34

0.08

APP

END

IX

12

4

Tab.

1: c

ontin

ued.

Sea

-w

ater

N

13-

20_1

N

13-

20_3

N

13-

20_5

N

13-

20_7

N

13-

20_9

N13

-20

_12

N13

-20

_15

N13

-20

_18

N13

-20

_21

N13

-20

_24

N13

-20

_27

N13

-20

_29

N13

-20

_30

N13

-20

_31

N13

-20

_32

aver

age

effe

ctiv

e st

ress

(M

Pa)

6.

4E-0

5 0.

0001

9 0.

0005

6 0.

0014

0.

0034

0.

01

0.06

0.

25

0.99

2.

62

6.83

13

.22

18.8

6 27

.85

40.9

7

Elem

ent

Co_

59

(ng/

mL)

29.8

4 57

.96

26

.03

Ni_

60

(ng/

mL)

1689

7.8

3560

9.24

1935

0.13

Cu_

63

(ng/

mL)

612.

70

171.

94

16

.92

Zn_6

6 (n

g/m

L)

12

31.3

2 21

65.2

2

350.

85

Ga_

69

(ng/

mL)

0.95

0.

26

0.

02

Sm_1

47

(ng/

mL)

0.

53

6.20

30

.16

9.54

0.

83

27.8

9 0.

98

0.83

0.

85

0.84

0.

90

0.89

0.

84

0.80

0.

76

0.77

Eu_

151

(ng/

mL)

0.

37

0.57

3.

83

1.64

0.

10

11.1

3 0.

46

0.44

0.

43

0.44

0.

44

0.43

0.

42

0.41

0.

45

0.44

Gd_

157

(ng/

mL)

6.25

34

.07

1.

10

Tb_1

59

(ng/

mL)

0.

39

0.97

5.

43

2.30

0.

19

1.27

0.

47

0.45

0.

45

0.45

0.

47

0.46

0.

46

0.44

0.

47

0.46

Dy_

163

(ng/

mL)

0.

28

5.39

31

.99

14.4

3 0.

98

1.07

0.

61

0.57

0.

56

0.48

0.

50

0.48

0.

49

0.51

0.

54

0.53

Ho_

165

(ng/

mL)

0.

49

1.03

6.

71

4.21

0.

26

1.

43

1.33

1.

26

1.40

1.

39

1.41

1.

32

1.22

1.

26

1.24

Er_

166

(ng/

mL)

0.

37

2.94

19

.53

10.4

6 0.

59

10.6

2 1.

00

0.94

0.

89

0.86

0.

88

0.90

0.

84

0.82

0.

90

0.91

Tm_1

69

(ng/

mL)

0.

36

0.36

2.

58

1.66

0.

07

0.82

0.

62

0.60

0.

59

0.60

0.

62

0.61

0.

60

0.57

0.

63

0.62

Yb_1

72

(ng/

mL)

0.

46

3.31

23

.53

8.15

0.

61

1.02

0.

65

0.60

0.

58

0.53

0.

55

0.54

0.

54

0.53

0.

57

0.58

Lu_1

75

(ng/

mL)

0.

34

0.49

3.

57

1.42

0.

10

0.26

0.

29

0.28

0.

27

0.27

0.

28

0.27

0.

27

0.26

0.

28

0.28

Hf_

178

(ng/

mL)

0.09

0.

55

0.

08

APP

END

IX

12

5

Tab.

2: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of

expe

lled

fluid

s du

ring

the

heat

ed c

onso

lidat

ion

test

of

the

smec

tite-

rich

sam

ple

(N13

) at 1

00 °C

. The

ass

ocia

ted

effe

ctiv

e str

ess

for t

he re

leas

ed p

ore

wat

er is

giv

en a

s av

erag

e ef

fect

ive

stre

ss b

etw

een

atta

chin

g an

d re

mov

ing

the

sam

plin

g fla

sk.

S

ea-

wat

er

N13

-100

_1

N13

-100

_3

N13

-100

_5

N13

-100

_5

N13

-100

_7

N13

-100

_9

N13

-10

0_13

N13

-10

0_17

N13

-10

0_21

N13

-10

0_25

av

erag

e ef

fect

ive

stre

ssM

Pa

2.

9E-0

6 6.

02E

-06

4.8E

-06

3.08

E-0

5 4.

7E-0

5 4.

7E-0

5 0.

0003

4 0.

0017

0.

0092

0.

090

Elem

ent

Li

_7(n

g/m

L)

63

1.02

20

61.3

3

3519

.48

4629

.13

Rb_

85

(ng/

mL)

12

3.49

27

9.88

53

6.01

56

9.86

69

6.61

76

3.86

63

1.20

62

5.44

66

9.27

66

4.35

70

7.71

Y_89

(n

g/m

L)

0.41

10

4.35

59

.89

1.11

2.

06

0.71

1.

03

1.14

1.

05

0.99

1.

29

Zr_9

0 (n

g/m

L)

40

.98

7.53

0.52

0.

76

Nb_

93

(ng/

mL)

2.75

2.

14

0.

28

0.17

Cs_

133

(ng/

mL)

3.65

7.

93

10

.18

11.0

8

La_1

39(n

g/m

L)

0.54

48

.74

28.0

8 1.

06

0.83

0.

17

1.10

0.

97

0.94

1.

00

1.45

Ce_

140

(ng/

mL)

0.

63

127.

22

68.0

2 1.

42

1.46

0.

48

1.34

1.

31

1.23

1.

25

1.14

Pr_1

41

(ng/

mL)

0.

48

10.7

6 5.

48

0.95

0.

10

0.04

0.

97

0.90

0.

94

0.93

1.

00

Nd_

146

(ng/

mL)

0.

43

41.4

0 21

.04

0.62

0.

39

0.19

0.

73

0.58

0.

63

0.58

0.

81

Ta_1

81(n

g/m

L)

1.

16

0.46

0.03

0.

02

Pb_

208

(ng/

mL)

13

.88

1009

.96

2799

.63

8.10

48

.67

11.2

4 8.

61

6.59

2.

75

3.96

0.

88

Th_2

32(n

g/m

L)

0.59

24

.81

4.37

1.

51

0.19

0.

07

1.53

1.

45

1.52

1.

47

1.01

U_2

38

(ng/

mL)

0.

79

15.9

7 5.

80

1.60

0.

71

1.20

3.

15

6.81

11

.11

10.3

1 10

.33

Sc_

45(n

g/m

L)

3.

00

1.32

0.08

0.

10

V_5

1(n

g/m

L)

24

9.53

22

6.44

26.9

6 43

.97

Cr_

52(n

g/m

L)

51

245.

09

9877

.75

49

.08

16.4

5

APP

END

IX

12

6

Tab.

2: c

ontin

ued.

Sea-

wat

er

N13

-100

_1

N13

-100

_3

N13

-100

_5

N13

-100

_5

N13

-100

_7

N13

-100

_9

N13

-10

0_13

N13

-10

0_17

N13

-10

0_21

N13

-10

0_25

aver

age

effe

ctiv

e st

ress

M

Pa

2.

9E-0

6 6.

0E-0

6 4.

8E-0

6 3.

0E-0

5 4.

7E-0

5 4.

7E-0

5 0.

0003

4 0.

0017

0.

0092

0.

090

Ele

men

t

Co_

59(n

g/m

L)

11

9.70

55

.51

18

.37

18.3

6

Ni_

60(n

g/m

L)

74

257.

99

3149

8.11

7067

.90

4007

.00

Cu_

63(n

g/m

L)

34

90.4

6 36

08.0

2

3506

.75

4348

.94

Zn_6

6 (n

g/m

L)

21

73.1

5 40

972.

22

11

21.8

5 84

9.08

Ga_

69

(ng/

mL)

0.51

0.

65

0.

03

0.03

Sm

_147

(n

g/m

L)

0.53

11

.97

6.32

0.

87

0.12

0.

10

0.89

0.

63

0.79

0.

92

1.08

Eu_1

51

(ng/

mL)

0.

37

1.39

0.

66

0.51

0.

02

0.01

0.

51

0.46

0.

49

0.48

0.

75

Gd_

157

(ng/

mL)

13.1

5 6.

68

0.

19

0.03

Tb_1

59

(ng/

mL)

0.

39

2.10

1.

05

0.46

0.

01

0.00

0.

47

0.44

0.

46

0.45

0.

34

Dy_

163

(ng/

mL)

0.

28

12.3

7 6.

14

0.50

0.

10

0.07

0.

51

0.47

0.

49

0.48

0.

71

Ho_

165

(ng/

mL)

0.

49

2.60

1.

35

1.33

0.

11

0.11

1.

45

1.04

1.

34

1.39

1.

30

Er_1

66

(ng/

mL)

0.

37

7.43

3.

88

0.88

0.

05

0.01

0.

92

0.81

0.

88

0.87

0.

96

Tm_1

69(n

g/m

L)

0.36

1.

01

0.51

0.

62

0.00

0.

00

0.63

0.

59

0.62

0.

61

0.60

Yb_1

72

(ng/

mL)

0.

46

9.11

4.

43

0.55

0.

11

0.04

0.

56

0.53

0.

55

0.53

0.

84

Lu_1

75

(ng/

mL)

0.

34

1.34

0.

71

0.28

0.

02

0.01

0.

28

0.26

0.

27

0.27

0.

60

Hf_

178

(ng/

mL)

0.88

0.

15

0.

02

0.01

APP

END

IX

12

7

Tab.

2: c

ontin

ued.

Sea-

wat

er

N13

-10

0_28

N13

-10

0_30

N13

-10

0_32

N13

-10

0_34

N13

-10

0_35

N13

-10

0_36

N13

-10

0_37

N

13-

100_

38N

13-

100_

39N

13-

100_

41N

13-

100_

42av

erag

eef

fect

ive

stre

ssM

Pa

0.

27

0.68

1.

24

4.29

5.

65

7.73

10

.33

14.3

0 19

.91

27.

41.3

9

Ele

men

t

C

o_59

(ng/

mL)

Ni_

60

(ng/

mL)

Cu_

63(n

g/m

L)

Zn_6

6 (n

g/m

L)

Ga_

69

(ng/

mL)

Sm

_147

(n

g/m

L)

0.53

0.

96

0.93

1.

03

1.04

1.

01

0.95

1.

13

0.90

1.

04

0.94

1.

77

Eu_1

51

(ng/

mL)

0.

37

0.74

0.

77

0.74

0.

73

0.73

0.

72

0.78

0.

74

0.76

0.

80

0.90

Gd_

157

(ng/

mL)

Tb_1

59

(ng/

mL)

0.

39

0.34

0.

35

0.35

0.

34

0.34

0.

33

0.36

0.

33

0.34

0.

35

0.42

Dy_

163

(ng/

mL)

0.

28

0.71

0.

72

0.73

0.

72

0.70

0.

70

0.85

0.

71

0.72

0.

74

1.34

Ho_

165

(ng/

mL)

0.

49

1.15

1.

24

1.26

1.

30

1.32

1.

37

1.36

1.

30

1.31

1.

31

1.46

Er_

166

(ng/

mL)

0.

37

1.61

0.

96

1.00

0.

94

0.97

0.

95

1.06

0.

96

0.96

0.

97

1.32

Tm_1

69(n

g/m

L)

0.36

0.

81

0.60

0.

61

0.60

0.

59

0.59

0.

62

0.58

0.

59

0.61

0.

64

Yb_1

72

(ng/

mL)

0.

46

0.96

0.

84

0.86

0.

84

0.83

0.

83

0.90

0.

82

0.83

0.

86

1.14

Lu_1

75(n

g/m

L)

0.34

0.

65

0.61

0.

62

0.60

0.

59

0.59

0.

62

0.59

0.

60

0.62

0.

65

Hf_

178

(ng/

mL)

APP

END

IX

12

8

Tab.

3: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of

expe

lled

fluid

s du

ring

the

heat

ed c

onso

lidat

ion

test

of

the

smec

tite-

rich

sam

ple

(N13

) at 1

50 °C

. The

ass

ocia

ted

effe

ctiv

e str

ess

for t

he re

leas

ed p

ore

wat

er is

giv

en a

s av

erag

e ef

fect

ive

stre

ss b

etw

een

atta

chin

g an

d re

mov

ing

the

sam

plin

g fla

sk.

Se

a-w

ater

N

13-

150_

5 N

13-

150_

7 N

13-

150_

9N

13-

150_

10N

13-

150_

11

N13

-15

0_13

N13

-15

0_14

N13

-15

0_15

N

13-

150_

16N

13-

150_

17

N13

-15

0_18

N13

-15

0_19

N13

-15

0_20

aver

age

effe

ctiv

e st

ress

M

Pa

0.

020

0.43

0.

87

1.24

1.

88

3.96

8.

45

12.3

3 15

.87

21.2

4 25

.00

40.6

5 61

.47

Ele

men

t

Li

_7(n

g/m

L)

75

49.9

9 88

70.7

2 11

922.

9 10

974.

31

2529

.87

1156

7.95

13

373.

1 12

741.

25

1088

5.43

19

55.7

23

0.66

21

2.64

28

52.7

6

Rb_

85(n

g/m

L)

123.

49

800.

66

883.

77

1001

.21

892.

45

218.

39

880.

43

977.

34

914.

59

730.

52

145.

25

21.0

6 25

.66

375.

70

Y_89

(n

g/m

L)

0.41

8.

38

1.15

0.

87

2.35

0.

54

0.88

0.

95

1.03

0.

97

0.22

0.

08

0.14

4.

36

Zr_9

0(n

g/m

L)

8.

62

0.38

0.

29

1.74

0.

54

0.33

0.

34

0.38

0.

69

0.27

0.

19

0.20

5.

51

Nb_

93(n

g/m

L)

0.

48

0.02

0.

02

0.10

0.

03

0.02

0.

03

0.03

0.

03

0.02

0.

00

0.00

0.

04

Cs_

133

(ng/

mL)

16.0

3 17

.75

19.4

7 17

.45

4.32

16

.75

18.4

9 16

.91

12.7

9 2.

48

0.46

0.

66

13.5

4

La_1

39

(ng/

mL)

0.

54

10.8

8 2.

10

1.20

2.

65

0.51

0.

93

1.00

0.

97

0.80

0.

22

0.08

0.

17

5.33

Ce_

140

(ng/

mL)

0.

63

24.3

2 4.

43

2.78

6.

53

1.27

2.

40

2.57

2.

55

2.08

0.

47

0.13

0.

25

8.39

Pr_1

41

(ng/

mL)

0.

48

1.93

0.

20

0.12

0.

43

0.08

0.

12

0.12

0.

12

0.11

0.

03

0.01

0.

01

0.39

Nd_

146

(ng/

mL)

0.

43

6.33

0.

63

0.39

1.

37

0.31

0.

40

0.40

0.

40

0.38

0.

10

0.04

0.

04

1.06

Ta_1

81

(ng/

mL)

0.15

0.

02

0.01

0.

02

0.00

0.

01

0.01

0.

01

0.01

0.

00

0.00

0.

00

0.00

Pb_2

08

(ng/

mL)

13

.88

364.

99

143.

23

305.

81

795.

79

192.

30

611.

67

930.

14

922.

61

630.

82

208.

65

65.1

9 66

.72

1488

.67

Th_2

32

(ng/

mL)

0.

59

6.45

0.

11

0.05

1.

18

0.15

0.

07

0.07

0.

07

0.11

0.

05

0.01

0.

01

0.19

U_2

38(n

g/m

L)

0.79

2.

20

0.18

0.

07

0.44

0.

11

0.11

0.

10

0.09

0.

12

0.17

0.

10

0.08

2.

25

Sc_4

5 (n

g/m

L)

0.

93

0.78

0.

36

0.47

0.

18

0.30

0.

34

0.41

0.

84

0.24

0.

07

0.06

2.

34

V_51

(n

g/m

L)

11

.43

0.62

0.

28

9.34

3.

23

0.66

0.

87

0.82

0.

98

0.56

0.

31

0.33

10

.33

Cr_

52(n

g/m

L)

82

.54

21.3

7 27

.44

79.3

9 21

.99

36.8

4 46

.94

52.9

6 64

.64

27.0

5 13

.19

14.6

2 34

5.52

APP

END

IX

12

9

Tab.

3: c

ontin

ued.

Sea

-w

ater

N

13-

150_

5 N

13-

150_

7 N

13-

150_

9 N

13-

150_

10

N13

-15

0_11

N

13-

150_

13

N13

-15

0_14

N

13-

150_

15

N13

-15

0_16

N

13-

150_

17

N13

-15

0_18

N

13-

150_

19

N13

-15

0_20

av

erag

e ef

fect

ive

stre

ss

MP

a

0.

020

0.43

0.

87

1.24

1.

88

3.96

8.

45

12.3

3 15

.87

21.2

4 25

.00

40.6

5 61

.47

Ele

men

t

C

o_59

(n

g/m

L)

4.

28

4.08

5.

55

7.21

3.

70

6.49

5.

65

4.95

5.

73

2.26

1.

51

5.63

98

.74

Ni_

60

(ng/

mL)

554.

05

407.

47

689.

83

1027

.95

479.

32

1505

.94

1352

.7

1141

.0

1348

.55

469.

26

196.

05

531.

59

8484

.87

Cu_

63

(ng/

mL)

456.

70

80.8

5 17

.31

120.

63

47.2

1 31

.06

18.9

9 16

.87

54.2

5 13

1.65

49

.20

96.6

7 22

53.4

9

Zn_6

6 (n

g/m

L)

63

96.4

0 57

5.69

61

5.85

24

449.

13

2910

8.54

73

3.55

65

0.80

99

4.74

24

78.0

9 40

00.0

2 13

245.

42

8657

5.7

1553

849.

57

Ga_

69

(ng/

mL)

7.67

0.

28

0.11

1.

62

0.41

0.

11

0.13

0.

12

0.11

0.

08

0.10

0.

64

11.8

8

Sm

_147

(n

g/m

L)

0.53

1.

51

0.14

0.

06

0.42

0.

06

0.03

0.

09

0.12

0.

09

0.03

0.

01

0.01

0.

31

Eu_1

51

(ng/

mL)

0.

37

0.05

0.

02

0.01

0.

03

0.01

0.

01

0.01

0.

01

0.01

0.

00

0.00

0.

00

0.04

Gd_

157

(ng/

mL)

1.50

0.

20

0.07

0.

35

0.05

0.

10

0.10

0.

08

0.09

0.

04

0.00

0.

03

0.23

Tb_1

59

(ng/

mL)

0.

39

0.20

0.

02

0.01

0.

05

0.01

0.

01

0.01

0.

01

0.02

0.

00

0.00

0.

00

0.05

Dy_

163

(ng/

mL)

0.

28

1.16

0.

09

0.08

0.

20

0.06

0.

07

0.06

0.

06

0.08

0.

02

0.00

0.

01

0.30

Ho_

165

(ng/

mL)

0.

49

0.24

0.

06

0.12

0.

17

0.04

0.

17

0.18

0.

16

0.08

0.

01

0.01

0.

01

0.30

Er_

166

(ng/

mL)

0.

37

0.52

0.

07

0.03

0.

11

0.02

0.

02

0.05

0.

04

0.04

0.

01

0.00

0.

01

0.46

Tm_1

69

(ng/

mL)

0.

36

0.07

0.

01

0.00

0.

01

0.00

0.

01

0.01

0.

01

0.01

0.

00

0.00

0.

00

0.07

Yb_1

72

(ng/

mL)

0.

46

0.54

0.

08

0.05

0.

16

0.03

0.

09

0.05

0.

07

0.09

0.

01

0.00

0.

01

0.34

Lu_1

75

(ng/

mL)

0.

34

0.07

0.

01

0.00

0.

02

0.01

0.

01

0.01

0.

01

0.01

0.

00

0.00

0.

00

0.03

Hf_

178

(ng/

mL)

0.27

0.

00

0.00

0.

03

0.03

0.

02

0.00

0.

01

0.02

0.

02

0.00

0.

01

0.14

APP

END

IX

13

0

Tab.

4: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of e

xpel

led

fluid

s dur

ing

the

room

tem

pera

ture

con

solid

atio

n te

st o

f the

illit

ic sa

mpl

e (N

14).

The

asso

ciat

ed e

ffec

tive

stre

ss fo

r the

rele

ased

por

e w

ater

is g

iven

as

aver

age

effe

ctiv

e st

ress

bet

wee

n at

tach

ing

and

rem

ovin

g th

e sa

mpl

ing

flask

.

Sea-

wat

er

N14

-20

_1N

14-

20_4

N14

-20

_6N

14-

20_8

N14

-20

_10

N14

-20

_12

N14

-20

_13

N14

-20

_14

N14

-20

_15

N14

-20

_16

N14

-20

_17

Ave

rage

ef

fect

ive

stre

ss M

Pa

0.

46

2.29

3.

37

4.89

8.

42

9.27

11

.23

13.0

3 14

.23

26.7

0 56

.15

Ele

men

t

Li

_7(n

g/m

L)

31

7.95

Rb_

85

(ng/

mL)

12

3.4

159.

56

150.

94

153.

85

149.

19

270.

90

155.

22

153.

32

147.

20

138.

33

130.

24

270.

90

Y_89

(n

g/m

L)

0.41

3.

51

0.87

1.

07

0.84

3.

14

0.82

0.

82

0.92

0.

80

0.82

3.

14

Zr_9

0 (n

g/m

L)

0.

04

Nb_

93

(ng/

mL)

0.01

Cs_

133

(ng/

mL)

0.89

La_1

39(n

g/m

L)

0.54

6.

26

1.05

1.

02

0.91

1.

34

1.19

0.

95

1.04

1.

09

1.02

1.

34

Ce_

140

(ng/

mL)

0.

63

15.7

8 1.

52

1.40

1.

21

1.55

1.

62

1.26

1.

32

1.38

1.

27

1.62

Pr_1

41

(ng/

mL)

0.

48

1.27

0.

94

0.97

0.

92

0.97

0.

95

0.92

0.

94

0.95

0.

93

0.97

Nd_

146

(ng/

mL)

0.

43

4.27

0.

66

0.66

0.

57

0.78

0.

67

0.60

0.

59

0.61

0.

61

0.78

Ta_1

81(n

g/m

L)

0.

00

Pb_

208

(ng/

mL)

13

.88

10.9

3 12

.40

4.56

2.

27

5.46

47

.00

6.50

6.

54

8.38

6.

68

47.0

0

Th_2

32(n

g/m

L)

0.59

0.

02

1.48

1.

81

1.54

1.

67

1.45

1.

47

1.49

1.

48

1.48

1.

81

U_2

38

(ng/

mL)

0.

79

8.02

11

.50

12.9

0 14

.53

92.6

9 17

.75

19.4

5 21

.14

24.2

2 27

.77

92.6

9

Sc_

45(n

g/m

L)

0.

03

V_5

1 (n

g/m

L)

9.

32

Cr_

52(n

g/m

L)

83

.45

APP

END

IX

13

1

Tab.

4: c

ontin

ued.

Sea-

wat

er

N14

-20

_1N

14-

20_4

N14

-20

_6N

14-

20_8

N14

-20

_10

N14

-20

_12

N14

-20

_13

N14

-20

_14

N14

-20

_15

N14

-20

_16

N14

-20

_17

aver

age

effe

ctiv

e st

ress

M

Pa

0.

46

2.29

3.

37

4.89

8.

42

9.27

11

.23

13.0

3 14

.23

26.7

0 56

.15

Ele

men

t

C

o_59

(ng/

mL)

5.41

Ni_

60(n

g/m

L)

10

19.6

4

Cu_

63(n

g/m

L)

44

.36

Zn_6

6 (n

g/m

L)

10

94.2

7

Ga_

69

(ng/

mL)

0.01

Sm

_147

(n

g/m

L)

0.53

1.

15

0.78

0.

74

0.67

0.

92

0.61

0.

66

0.64

0.

65

0.67

0.

92

Eu_1

51

(ng/

mL)

0.

37

0.07

0.

43

0.44

0.

44

0.44

0.

43

0.44

0.

44

0.44

0.

44

0.44

Gd_

157

(ng/

mL)

0.87

Tb_1

59

(ng/

mL)

0.

39

0.10

0.

50

0.47

0.

45

0.47

0.

44

0.45

0.

46

0.46

0.

45

0.50

Dy_

163

(ng/

mL)

0.

28

0.55

0.

51

0.50

0.

48

0.56

0.

47

0.48

0.

49

0.49

0.

48

0.56

Ho_

165

(ng/

mL)

0.

49

0.12

1.

13

1.14

1.

05

1.38

1.

00

1.03

1.

06

1.01

1.

02

1.38

Er_

166

(ng/

mL)

0.

37

0.22

0.

84

0.87

0.

82

0.96

0.

82

0.85

0.

86

0.85

0.

84

0.96

Tm_1

69(n

g/m

L)

0.36

0.

02

0.60

0.

62

0.61

0.

62

0.59

0.

60

0.62

0.

61

0.61

0.

62

Yb_1

72

(ng/

mL)

0.

46

0.20

0.

54

0.56

0.

54

0.62

0.

53

0.54

0.

60

0.54

0.

54

0.62

Lu_1

75

(ng/

mL)

0.

34

0.03

0.

27

0.28

0.

27

0.29

0.

27

0.27

0.

29

0.27

0.

27

0.29

Hf_

178

(ng/

mL)

0.00

APP

END

IX

13

2

Tab.

5: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of e

xpel

led

fluid

s du

ring

the

heat

ed c

onso

lidat

ion

test

of t

he il

litic

sam

ple

(N14

) at

100

°C. T

he a

ssoc

iate

d ef

fect

ive

stre

ss fo

r the

rele

ased

por

e w

ater

is g

iven

as a

vera

ge e

ffec

tive

stre

ss b

etw

een

atta

chin

g an

d re

mov

ing

the

sam

plin

g fla

sk.

Se

a-w

ater

N

14-

100_

1 N

14-

100_

4N

14-

100_

6N

14-

100_

7N

14-

100_

8N

14-

100_

9 N

14-

100_

10N

14-

100_

11

N14

-10

0_12

N14

-10

0_13

N14

-10

0_14

av

erag

e ef

fect

ive

stre

ss M

Pa

8.

0E-0

6 0.

0042

0.

035

0.09

0.

26

0.69

2.

37

5.82

12

.89

37.0

9 61

.00

Ele

men

t

Li

_7(n

g/m

L)

39

97.4

3

Rb_

85(n

g/m

L)

123.

49

249.

99

450.

93

750.

83

709.

49

711.

87

722.

61

738.

81

707.

25

742.

82

670.

26

620.

76

Y_89

(n

g/m

L)

0.41

0.

97

1.12

0.

51

1.32

1.

45

1.68

1.

62

1.19

1.

17

1.09

1.

09

Zr_9

0(n

g/m

L)

0.

42

Nb_

93(n

g/m

L)

0.

11

Cs_

133

(ng/

mL)

17.1

6

La_1

39

(ng/

mL)

0.

54

1.40

1.

16

0.22

1.

36

1.09

1.

14

1.24

0.

94

0.94

0.

88

0.99

Ce_

140

(ng/

mL)

0.

63

1.29

1.

50

0.60

1.

31

1.34

1.

65

1.69

1.

14

1.03

1.

04

1.11

Pr_

141

(ng/

mL)

0.

48

1.02

1.

02

0.05

0.

96

0.97

1.

01

1.04

0.

96

0.98

0.

93

0.95

Nd_

146

(ng/

mL)

0.

43

0.88

0.

93

0.16

0.

85

0.89

0.

94

1.03

0.

80

0.85

0.

79

0.79

Ta_1

81

(ng/

mL)

0.01

Pb_2

08

(ng/

mL)

13

.88

8.54

18

.55

14.2

6 8.

38

6.77

9.

60

25.2

3 3.

00

1.50

4.

09

2.68

Th_2

32

(ng/

mL)

0.

59

1.02

1.

06

0.20

1.

10

1.09

1.

23

1.18

1.

01

1.04

1.

00

1.00

U_2

38(n

g/m

L)

0.79

1.

43

1.95

0.

57

1.49

1.

40

1.29

1.

29

1.55

1.

55

1.90

2.

27

Sc_4

5 (n

g/m

L)

0.

08

V_51

(n

g/m

L)

10

.77

Cr_

52(n

g/m

L)

79

.36

APP

END

IX

13

3

Tab.

5: c

ontin

ued.

Sea-

wat

er

N14

-10

0_1

N14

-10

0_4

N14

-10

0_6

N14

-10

0_7

N14

-10

0_8

N14

-10

0_9

N14

-10

0_10

N14

-10

0_11

N

14-

100_

12N

14-

100_

13N

14-

100_

14

aver

age

effe

ctiv

e st

ress

M

Pa

8.

0E-0

6 0.

0042

0.

035

0.09

0.

26

0.69

2.

37

5.82

12

.89

37.0

9 61

.00

Ele

men

t

C

o_59

(ng/

mL)

15.2

0

Ni_

60(n

g/m

L)

14

84.1

1

Cu_

63(n

g/m

L)

61

27.8

9

Zn_6

6 (n

g/m

L)

17

6.09

Ga_

69

(ng/

mL)

0.01

Sm

_147

(n

g/m

L)

0.53

0.

77

0.83

0.

06

0.82

0.

90

0.92

0.

96

0.86

0.

90

0.91

0.

90

Eu_1

51

(ng/

mL)

0.

37

0.73

0.

74

0.01

0.

74

0.73

0.

73

0.79

0.

77

0.80

0.

79

0.81

Gd_

157

(ng/

mL)

0.03

Tb_1

59

(ng/

mL)

0.

39

0.33

0.

34

0.01

0.

32

0.33

0.

34

0.35

0.

33

0.34

0.

32

0.33

Dy_

163

(ng/

mL)

0.

28

0.70

0.

74

0.02

0.

70

0.77

0.

77

0.77

0.

72

0.72

0.

68

0.70

Ho_

165

(ng/

mL)

0.

49

0.67

0.

75

0.04

0.

84

0.92

0.

92

1.04

0.

99

1.06

1.

05

1.13

Er_

166

(ng/

mL)

0.

37

0.87

0.

91

0.03

0.

88

0.95

0.

98

0.97

0.

92

0.96

0.

91

0.94

Tm_1

69(n

g/m

L)

0.36

0.

58

0.60

0.

00

0.58

0.

59

0.60

0.

62

0.59

0.

61

0.57

0.

59

Yb_1

72

(ng/

mL)

0.

46

0.82

0.

85

0.02

0.

82

0.85

0.

87

0.90

0.

83

0.86

0.

80

0.82

Lu_1

75

(ng/

mL)

0.

34

0.59

0.

61

0.00

0.

58

0.60

0.

60

0.63

0.

60

0.61

0.

58

0.59

Hf_

178

(ng/

mL)

0.07

APP

END

IX

13

4

Tab.

6: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of e

xpel

led

fluid

s du

ring

the

heat

ed c

onso

lidat

ion

test

of t

he il

litic

sam

ple

(N14

) at

150

°C. T

he a

ssoc

iate

d ef

fect

ive

stre

ss fo

r the

rele

ased

por

e w

ater

is g

iven

as a

vera

ge e

ffec

tive

stre

ss b

etw

een

atta

chin

g an

d re

mov

ing

the

sam

plin

g fla

sk.

S

ea-

wat

er

N14

-150

_1

N14

-150

_2

N14

-150

_4

N14

-150

_6

N14

-150

_8

N14

-150

_10

N14

-150

_12

aver

age

effe

ctiv

e st

ress

MP

a

2.9E

-10

2.8E

-09

1.2E

-08

1.2E

-08

1.0E

-08

3.9E

-08

11.0

5

Elem

ent

Li_7

(ng/

mL)

14.4

2 3.

59

17.7

9 5.

24

3.34

8.

90

25.2

4

Rb_

85

(ng/

mL)

12

3.49

6.

09

3.20

5.

72

2.29

1.

68

3.03

7.

94

Y_89

(n

g/m

L)

0.41

2.

24

0.76

1.

70

0.62

0.

60

0.88

1.

63

Zr_9

0 (n

g/m

L)

0.

80

0.33

0.

54

0.28

0.

38

0.58

0.

77

Nb_

93

(ng/

mL)

0.15

0.

07

0.16

0.

07

0.09

0.

08

0.19

Cs_

133

(ng/

mL)

0.18

0.

10

0.21

0.

12

0.13

0.

11

0.35

La_1

39(n

g/m

L)

0.54

0.

13

0.05

0.

19

0.07

0.

06

2.77

0.

41

Ce_

140

(ng/

mL)

0.

63

0.53

0.

20

0.68

0.

25

0.23

11

.11

1.28

Pr_1

41

(ng/

mL)

0.

48

0.09

0.

03

0.10

0.

04

0.04

0.

67

0.17

Nd_

146

(ng/

mL)

0.

43

0.52

0.

18

0.51

0.

22

0.21

2.

05

0.82

Ta_1

81(n

g/m

L)

0.

00

0.00

0.

01

0.00

0.

00

0.00

0.

00

Pb_

208

(ng/

mL)

13

.88

36.5

0 17

.36

27.0

2 17

.61

19.5

6 19

.59

33.6

5

Th_2

32(n

g/m

L)

0.59

0.

01

0.02

0.

06

0.04

0.

04

0.09

0.

23

U_2

38

(ng/

mL)

0.

79

7.34

2.

92

3.40

1.

27

1.22

0.

96

1.67

Sc_

45(n

g/m

L)

0.

10

0.11

0.

24

0.12

0.

13

0.18

0.

39

V_5

1(n

g/m

L)

15

.00

8.19

14

.23

9.01

12

.13

22.2

0 13

.69

Cr_

52(n

g/m

L)

30

51.1

8 16

50.5

4 30

69.1

0 13

61.5

9 14

02.8

6 31

78.8

7 52

39.0

8

APP

END

IX

13

5

Tab.

6: c

ontin

ued.

Sea

-w

ater

N

an14

-150

_1

Nan

14-1

50_2

N

an14

-150

_4

Nan

14-1

50_6

N

an14

-150

_8

Nan

14-1

50_1

0 N

an14

-150

_12

aver

age

effe

ctiv

est

ress

MPa

2.

9E-1

0 2.

8E-0

9 1.

2E-0

8 1.

2E-0

8 1.

0E-0

8 3.

9E-0

8 11

.05

Elem

ent

Co_

59(n

g/m

L)

5.

29

2.76

7.

49

3.57

3.

17

5.13

13

.19

Ni_

60(n

g/m

L)

46

17.1

1 37

77.0

2 37

63.8

6 40

58.8

4 38

62.3

5 33

66.9

3 37

18.6

1

Cu_

63(n

g/m

L)

92

2.56

21

4.12

37

69.5

4 54

9.52

75

9.47

20

63.6

7 88

38.5

0

Zn_6

6(n

g/m

L)

45

21.0

0 24

71.4

9 84

59.0

6 39

13.1

7 29

66.7

5 59

60.7

3 17

102.

47

Ga_

69(n

g/m

L)

0.

14

0.07

0.

16

0.06

0.

07

0.12

0.

41

Sm

_147

(n

g/m

L)

0.53

0.

19

0.13

0.

14

0.09

0.

07

0.10

0.

30

Eu_

151

(ng/

mL)

0.

37

0.07

0.

02

0.04

0.

02

0.02

0.

03

0.07

Gd_

157

(ng/

mL)

0.32

0.

11

0.24

0.

12

0.09

0.

21

0.40

Tb_1

59(n

g/m

L)

0.39

0.

06

0.02

0.

04

0.03

0.

01

0.03

0.

05

Dy_

163

(ng/

mL)

0.

28

0.32

0.

12

0.26

0.

14

0.12

0.

17

0.32

Ho_

165

(ng/

mL)

0.

49

0.07

0.

03

0.06

0.

02

0.02

0.

03

0.06

Er_1

66

(ng/

mL)

0.

37

0.17

0.

07

0.12

0.

06

0.06

0.

09

0.15

Tm_1

69

(ng/

mL)

0.

36

0.04

0.

01

0.02

0.

01

0.01

0.

01

0.02

Yb_1

72

(ng/

mL)

0.

46

0.19

0.

09

0.19

0.

06

0.05

0.

11

0.20

Lu_1

75(n

g/m

L)

0.34

0.

03

0.00

0.

02

0.01

0.

01

0.01

0.

02

Hf_

178

(ng/

mL)

0.02

0.

03

0.01

0.

01

0.02

0.

03

0.02

APP

END

IX

13

6

Tab.

7: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of

expe

lled

fluid

s du

ring

the

room

tem

pera

ture

con

solid

atio

n te

st o

f th

e tu

rbid

itic

sam

ple

(N18

). Th

e as

soci

ated

eff

ectiv

e st

ress

for

the

rele

ased

por

e w

ater

is g

iven

as

aver

age

effe

ctiv

e st

ress

bet

wee

n at

tach

ing

and

rem

ovin

g th

e sa

mpl

ing

flask

.

Sea

-w

ater

N

18-2

0_1

N18

-20

_3N

18-

20_5

N18

-20

_7N

18-

20_9

N

18-

20_1

1N

18-

20_1

8N

18-

20_1

4N

18-

20_1

5N

18-

20_1

6N

18-

20_1

8N

18-

20_1

9av

erag

e ef

fect

ive

stre

ss M

Pa

1.33

145E

-05

0.00

237

217

0.03

754

748

0.11

829

973

0.43

860

086

1.38

391

623.

2150

058

95.

9918

579

39.

9063

251

414

.574

038

232

.062

003

51.0

931

485

Elem

ent

Li

_7(n

g/m

L)

4370

.01

4423

.17

43

90.6

7

Rb_

85(n

g/m

L)

123.

49

253.

53

370.

81

388.

46

392.

79

408.

42

404.

27

396.

86

609.

63

556.

55

355.

89

425.

28

218.

90

Y_89

(n

g/m

L)

0.41

16

9.90

49

1.69

70

3.72

75

1.64

80

5.21

80

5.27

80

8.86

10

44.7

6 99

3.87

81

4.70

10

18.8

2 83

6.73

Zr

_90

(ng/

mL)

10

5.03

12

1.95

132.

24

N

b_93

(ng/

mL)

1.

45

1.72

1.92

Cs_

133

(ng/

mL)

8.

43

7.48

5.29

La_1

39(n

g/m

L)

0.54

90

.56

289.

37

413.

84

440.

45

472.

69

477.

14

473.

86

787.

51

757.

07

483.

48

766.

95

490.

88

Ce_

140

(ng/

mL)

0.

63

230.

36

772.

53

1106

.65

1171

.24

1250

.67

1255

.08

1247

.38

1887

.68

1821

.06

1264

.80

1820

.78

1251

.08

Pr_

141

(ng/

mL)

0.

48

25.0

6 87

.45

124.

21

131.

66

140.

92

141.

09

141.

21

183.

97

176.

28

139.

36

172.

01

136.

23

Nd_

146

(ng/

mL)

0.

43

104.

69

373.

08

532.

56

565.

37

602.

78

602.

89

600.

38

670.

28

645.

90

597.

78

624.

65

576.

06

Ta_1

81(n

g/m

L)

1.51

1.

84

2.

27

P

b_20

8 (n

g/m

L)

13.8

8 94

8.79

33

9.92

19

3.38

14

9.87

11

7.55

12

2.40

14

3.15

78

.00

127.

20

138.

56

32.1

0 10

8.98

Th

_232

(ng/

mL)

0.

59

0.82

2.

61

2.93

3.

93

4.82

5.

60

5.96

8.

19

8.82

6.

46

9.27

7.

16

U_2

38(n

g/m

L)

0.79

7.

71

21.2

5 30

.31

31.0

9 32

.67

31.9

4 31

.32

39.2

0 38

.54

29.0

1 34

.82

27.4

9 S

c_45

(ng/

mL)

17

.32

15.3

5

16.7

1

V_5

1(n

g/m

L)

1099

.74

1183

.10

11

73.0

6

Cr_

52

(ng/

mL)

26

94.4

3 28

98.4

3

4658

.82

APP

END

IX

13

7

Tab.

7: c

ontin

ued.

Sea

-w

ater

N

18-2

0_1

N18

-20

_3N

18-

20_5

N18

-20

_7N

18-

20_9

N

18-

20_1

1N

18-

20_1

8N

18-

20_1

4N

18-

20_1

5N

18-

20_1

6N

18-

20_1

8N

18-

20_1

9av

erag

eef

fect

ive

stre

ssM

Pa

1.

33E

-05

0.00

23

0.03

7 0.

11

0.43

1.

38

3.21

5.

99

9.90

14

.57

32.0

6 51

.09

Elem

ent

C

o_59

(ng/

mL)

12

57.5

8 12

12.1

5

1321

.71

N

i_60

(ng/

mL)

79

80.5

5 80

22.7

1

1237

7.5

5C

u_63

(ng/

mL)

64

2.54

47

2.43

349.

73

Zn

_66

(ng/

mL)

73

93.4

1 71

68.9

1

8117

.64

G

a_69

(n

g/m

L)

4.01

4.

22

4.

23

S

m_1

47

(ng/

mL)

0.

53

22.8

1 84

.31

120.

79

129.

12

136.

92

137.

32

136.

52

170.

75

161.

16

133.

25

159.

98

129.

35

Eu_

151

(ng/

mL)

0.

37

4.79

16

.56

23.7

3 24

.95

26.5

9 26

.54

26.5

4 29

.25

27.8

5 25

.71

27.4

0 25

.01

Gd_

157

(ng/

mL)

16

0.99

15

4.55

155.

85

Tb

_159

(ng/

mL)

0.

39

4.83

15

.88

22.7

5 23

.80

25.8

8 25

.70

25.7

5 23

.40

22.7

4 25

.34

22.6

1 24

.73

Dy_

163

(ng/

mL)

0.

28

26.2

4 85

.52

124.

87

132.

33

141.

58

142.

30

140.

67

125.

95

120.

69

139.

24

122.

19

137.

56

Ho_

165

(ng/

mL)

0.

49

5.57

15

.55

21.9

9 23

.05

24.7

3 25

.00

24.7

3 23

.38

22.2

7 24

.22

22.5

0 24

.14

Er_

166

(ng/

mL)

0.

37

15.2

3 44

.43

63.6

1 67

.78

71.4

4 72

.27

71.7

2 63

.00

60.5

8 71

.80

61.1

6 70

.78

Tm_1

69

(ng/

mL)

0.

36

2.48

5.

30

7.24

7.

57

8.09

8.

16

7.97

7.

90

7.62

7.

95

7.58

7.

90

Yb_1

72

(ng/

mL)

0.

46

13.6

3 39

.97

56.1

4 59

.41

63.5

3 63

.72

62.7

0 71

.57

69.9

5 61

.76

67.4

8 61

.55

Lu_1

75(n

g/m

L)

0.34

2.

15

5.09

6.

99

7.42

7.

88

7.81

7.

89

10.4

1 9.

88

7.60

9.

67

7.66

H

f_17

8(n

g/m

L)

1.80

2.

17

2.

51

APP

END

IX

13

8

Tab.

8: R

aw d

ata

of tr

ace

elem

ent m

easu

rem

ents

of e

xpel

led

fluid

s du

ring

the

heat

ed c

onso

lidat

ion

test

s of

the

turb

iditc

sam

ple

(N18

) at

100

°C a

nd 1

50 °C

. The

ass

ocia

ted

effe

ctiv

e st

ress

for t

he re

leas

ed p

ore

wat

er is

giv

en a

s ave

rage

eff

ectiv

e st

ress

bet

wee

n at

tach

ing

and

rem

ovin

g th

e sa

mpl

ing

flask

.

Se

awat

er N

18-1

00_1

N18

-100

_2N

18-1

00_3

N18

-100

_4N

18-1

00_5

N18

-100

_6 N

18-1

00_7

N18

-100

_8N

18-1

00_9

N18

-150

_1N

18-1

50_6

aver

age

effe

ctiv

e st

ress

MPa

0.00

038

0.01

2 1.

47

3.66

7.

10

14.0

4 21

.49

31.8

21

49.7

9 0.

0003

164

0.01

5295

2

Ele

men

t

Li

_7(n

g/m

L)

31

20.0

3

34

8.84

10

.60

Rb_

85(n

g/m

L)

123.

49

664.

91

908.

62

1202

.20

1229

.58

1439

.77

1158

.43

812.

14

551.

80

538.

08

116.

97

5.15

Y_89

(n

g/m

L)

0.41

47

9.68

58

9.03

90

7.27

92

0.86

10

85.0

7 10

31.8

4 85

6.77

88

3.68

73

5.13

72

.18

0.42

Zr_9

0(n

g/m

L)

23

.01

0.69

0.

29

Nb_

93(n

g/m

L)

0.

23

0.02

0.

01

Cs_

133

(ng/

mL)

14.1

8

10

.20

1.17

La_1

39(n

g/m

L)

0.54

36

2.64

36

5.74

52

5.34

48

0.51

47

0.23

38

9.18

31

8.38

24

2.26

18

7.85

31

.62

0.11

Ce_

140

(ng/

mL)

0.

63

863.

99

1043

.01

1500

.71

1440

.47

1574

.93

1434

.87

1195

.39

1057

.98

793.

81

99.3

5 0.

43

Pr_

141

(ng/

mL)

0.

48

84.0

3 12

7.97

19

0.32

18

7.47

21

3.70

19

2.45

16

1.28

15

1.40

11

5.14

12

.60

0.07

Nd_

146

(ng/

mL)

0.

43

307.

60

507.

89

764.

31

764.

57

863.

33

792.

34

664.

52

626.

22

477.

96

53.3

5 0.

37

Ta_1

81

(ng/

mL)

0.15

0.

03

0.00

Pb_2

08

(ng/

mL)

13

.88

2924

.27

2264

.39

2279

.49

1199

8.09

502.

83

226.

95

1187

1.91

401.

31

1096

0.36

590.

89

45.2

9

Th_2

32

(ng/

mL)

0.

59

1.72

11

.30

29.4

0 27

.11

28.6

6 24

.54

21.4

6 16

.72

8.48

0.

03

0.08

U_2

38(n

g/m

L)

0.79

24

.44

85.3

3 13

2.41

12

4.07

13

7.49

12

2.39

94

.99

91.7

2 52

.65

3.28

1.

60

Sc_4

5 (n

g/m

L)

2.

26

0.28

0.

44

V_51

(n

g/m

L)

51

3.25

42

.11

18.6

4

Cr_

52

(ng/

mL)

1063

.79

205.

48

66.9

5

APP

END

IX

13

9

Tab.

8: c

ontin

ued.

S

eaw

ater

N18

-100

_1N

18-1

00_2

N18

-100

_3N

18-1

00_4

N18

-100

_5N

18-1

00_6

N18

-100

_7N

18-1

00_8

N18

-100

_9N

18-1

50_1

N18

-150

_6av

erag

eef

fect

ive

stre

ss M

Pa

0.

0003

8 0.

012

1.47

3.

66

7.10

14

.04

21.4

9 31

.82

49.7

9 0.

0003

1 0.

015

Ele

men

t

C

o_59

(ng/

mL)

627.

54

140.

14

4.37

Ni_

60

(ng/

mL)

5729

.33

2841

.35

257.

82

Cu_

63(n

g/m

L)

13

50.8

4

14

82.2

9 20

.36

Zn_6

6(n

g/m

L)

18

976.

07

22

04.8

8 17

3.86

Ga_

69

(ng/

mL)

0.60

0.

10

0.04

Sm

_147

(n

g/m

L)

0.53

77

.04

117.

87

180.

91

179.

90

204.

29

185.

70

154.

99

146.

55

110.

54

13.8

6 0.

10

Eu_1

51

(ng/

mL)

0.

37

13.3

4 21

.09

31.7

1 32

.08

36.5

9 32

.43

27.1

7 25

.72

19.5

2 2.

60

0.03

Gd_

157

(ng/

mL)

73.1

8

15

.81

0.12

Tb_1

59

(ng/

mL)

0.

39

10.4

6 19

.15

29.1

8 29

.52

34.1

0 31

.61

26.1

5 25

.75

20.6

9 2.

04

0.02

Dy_

163

(ng/

mL)

0.

28

56.4

9 10

2.63

15

4.44

15

5.78

17

8.56

16

4.90

13

8.14

13

5.73

11

0.43

11

.23

0.11

Ho_

165

(ng/

mL)

0.

49

10.6

8 18

.59

27.2

6 27

.69

31.8

3 29

.29

24.8

4 24

.47

20.4

7 1.

97

0.02

Er_

166

(ng/

mL)

0.

37

28.4

4 51

.57

75.1

6 75

.46

87.0

7 80

.52

67.1

5 67

.43

56.4

3 4.

97

0.04

Tm_1

69(n

g/m

L)

0.36

3.

60

7.91

11

.64

11.6

1 13

.43

12.2

1 10

.23

10.4

7 8.

64

0.56

0.

01

Yb_1

72

(ng/

mL)

0.

46

32.9

2 45

.75

64.5

6 64

.60

73.7

2 67

.44

56.4

6 55

.92

47.7

1 3.

65

0.04

Lu_1

75(n

g/m

L)

0.34

4.

74

6.52

9.

14

9.17

10

.33

9.55

8.

03

8.29

6.

88

0.50

0.

01

Hf_

178

(ng/

mL)

0.45

0.

02

0.00

APPENDIX 140

APPENDIX A3The compacted samples underwent SEM investigation to document water-rock

interaction and microstructural features developed during the deformation. As

described in manuscript 1 and 3 no significant mineral alteration took place. Thus, no

mineral surface alteration or new mineral formations were detected. High resolution

pictures of samples after the direct shear tests show distinct slickensides and lineation

on the shear surfaces. Microcracks of coarser grains in samples N14 and N18 suggest

grain crushing either during the consolidation test or the direct shear experiments. All

samples reveal low porosity, which can be related to the high consolidation stresses

the sediment samples experienced. Further, the SEM pictures give evidence for grain

size description outlined in manuscript 1. The selected samples end member samples

are a smectite-rich clay (sample N13; Fig. 1-3), an illite-rich silty clay (N14; Fig. 4-6)

and a clayey silty to fine sand-grained quartz/feldspar-rich sample (N18; Fig. 7-9

Fig. 1: SEM image with diagonal view on a fragment surface of the smectite-rich sample N13-100 after the consolidation. The sample shows an uniform grain size of flaky clay particles.

APPENDIX 141

Fig. 2: SEM overview image with view on a fragment of the sample N13-100 after the consolidation. The view is parallel to the applied load in the consolidation tests. The flaky arrangement of the particles led to a dense surface.

Fig. 3: SEM overview image with vertical view on the shear plane after the compact of N13-100 underwent direct shear testing. The shear surface is characterised by slickensides and lineation.

APPENDIX 142

Fig. 4: SEM image with view on a fragment of the illitic sample N14-100 after the consolidation. The mineral skeleton of the sample shows flaky clay and silty quartz particles. The latter is recognisable by the conchoidal fracture of the grain in the right corner of the picture.

Fig. 5: SEM image with view on a fragment of the illitic sample N14-100 after the consolidation. In the middle of the picture is a silty grained quartz mineral with typical conchoidal fracture. Microcracks of the grain in the lower left corner suggest grain crushing either during the consolidation test or the direct shear experiment.

APPENDIX 143

Fig. 6: SEM overview image with vertical view on the shear plane after the compact of N14-100 underwent direct shear testing. The shear surface is characterised by slickensides and lineation similar to the smectite-rich sample.

Fig. 7: SEM image with view on a fragment of the relative coarser grained turbiditic sample (N18-100). In the middle can be seen a sandy grained quartz mineral and surrounded by silty grains in the lower left and upper left corner and some clayey fraction between.

APPENDIX 144

Fig. 8: SEM image with view on a fragment of the turbiditic sample (N18-100). In the middle can be seen a fractured silty to sandy grained quartz mineral. Microcracks suggest grain crushing either during the consolidation test or the direct shear experiment.

Fig. 9: SEM overview image with vertical view on the shear surface after the compact of N18-20 underwent direct shear testing. The shear surface is characterised by slickensides and lineation similar to the other samples.

APPENDIX 145

APPENDIX A4 Direct shear experiments

The compacted samples from the heated and room temperature tests were

tested for their peak and residual strengths to determine the impact of the alteration on

mechanical behaviour. The residual geometry of the pucks was not feasible to cut an

annular sample for the planned ring shear tests because some material was cut from

the pucks after the oedometer tests to determine the water content. Thus, subsamples

were tested with the direct shear apparatus at the MARUM geotechnical laboratory.

The direct shear device was originally able of 3 MPa given a cell dimension of

100x100 mm and three experiment rigs combined. The PhD candidate modified the

shear apparatus under his own direction to allow a theoretical normal stress of

40 MPa. This corresponds to a force of 30 kN on a sample geometry of 25x30 mm,

which was accomplished by a custom-built spacer (Fig. 1). However, the

experimental setup did not allow shear forces greater 4500N to pull the upper half of

the shear box. This force was found to be not sufficient to shear the samples at the

proposed high stresses. Thus, a normal load of 4 MPa was used for direct shear testing

despite the fact that samples were highly overconsolidated under these conditions.

Further, a re-hydration of the samples for the tests was not possible, because initial

tests showed that the samples disintegrated during the swelling process. The actual

experiments were conducted in collaboration with a master student who was

supervised by the PhD candidate for the tests. The results (Fig. 2-4) were presented in

combination with ring shear data on disintegrated samples during the IODP/ICDP

colloquium 2008 in Hannover. The abstract is attached to the end of this section.

Fig. 1: Photograph of the modified direct shear cell (25 x 30 mm) and spacer.

APPENDIX 146

Fig. 2: Direct shear test results of the smectite-rich sample (N13).

Fig. 3: Direct shear test results of the illitic sample (N14).

Fig. 4: Direct shear test results of the turbiditic sample (N18).

APPENDIX 147

Ring shear experiments

To determine rate-dependence of frictional behaviour and residual shear

strength, ring shear tests were conducted with the heated and non-heated samples

from the oedometer tests. To perform these experiments the samples were remoulded

and placed in the annular sample chamber. The tests were performed at normal

stresses of 0.9, 3.8, 7.6 and 15.2 MPa. Tested velocities were 0.0005, 0.001, 0.01 and

0.1 mm/s. The total duration of an experiment is 2 weeks to test the complete set of

normal stresses and velocities.

The PhD candidate also modified the ring shear apparatus to allow heated ring

shear tests. Heat-sensitive components of the ring shear device were replaced and the

sample chamber was heated by a small heating blanket (McMaster-Carr), capable of

ca. 170 °C maximum temperature. Pilot tests reached ~50 °C within the sample

chamber, which could be enhanced by additional insulation to a maximum

temperature of ~80°C. The majority of the tests were conducted within a period of

24h at a temperature of 80±5°C and a normal stress of 7.6 MPa. Evaporation was

compensated with tempered water. Thus, the fully saturation was ensured throughout

a test. The majority of the tests were conducted by the PhD candidate and some tests

were conducted by a master student. Preliminary results were presented during the

IODP/ICDP Kolloquium 2008 in Hannover and selected plots are presented for room

temperature and heated tests runs at 7.6 MPa in figures 6-16. The abstract is attached

to the end of this section. A publication of the shear test results is planned under the

lead of the PhD candidate.

Fig. 5: Photograph of the ring shear apparatus with the heating unit surrounding the annular sample cell.

APPENDIX 148

Fig. 6: Rate dependent friction behaviour of remoulded material from the puck of the room temperature consolidation test of the smectite-rich sample (N13-20).

Fig. 7: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the smectite-rich sample (N13-20).

APPENDIX 149

Fig. 8: Rate dependent friction behaviour of remoulded material from the puck of the heated consolidation test of the smectite-rich sample (N13-150).

APPENDIX 150

Fig. 9: Rate dependent friction behaviour of remoulded material from the puck of the room temperature consolidation test of the illitic sample (N14-20).

Fig. 10: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the illitic sample (N14-20).

APPENDIX 151

Fig. 11: Rate dependent friction behaviour of remoulded material from the puck of the heated consolidation test of the illitic sample (N14-150).

Fig. 12: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the heated consolidation test of the illitic sample (N14-150).

APPENDIX 152

Fig. 13: Rate dependent friction behaviour of remoulded material from the puck of the room temperature consolidation test of the turbiditic sample (N18-20).

Fig. 14: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the turbiditic sample (N18-20).

APPENDIX 153

Fig. 15: Rate dependent friction behaviour of remoulded material from the puck of the heated consolidation test of the turbiditic sample (N18-150).

Fig. 16: Rate dependent friction behaviour at elevated temperatures (80±5 °C) of remoulded material from the puck of the room temperature consolidation test of the turbiditic sample (N18-20).

APPENDIX 154

Zimmermann, K., Hüpers, A. Kopf, A.J., 2008. Physical Properties of Marine Sediments Undergoing Subduction – Results from Heated Shear Experiments at the Nankai Convergent Margin, in: IODP-ICDP Kolloquium, 2008, Hannover.

Physical Properties of Marine Sediments Undergoing Subduction – Results from Heated Shear Experiments at the Nankai Convergent

Margin

K. Zimmermann, A. Hüpers, A. Kopf MARUM, Bremen University, P.O. Box 330440, 28334 Bremen, Germany

Subduction zones produce frequently earthquakes of magnitude M8 or larger.

These events occur along the subduction plate boundary thrust within a temperature range of 100-150°C to 350-450°C, known as the seismogenic zone. The reason for the onset of coseimic behaviour of the sediments is still unknown. Diagenetic and consolidation processes are supposed to alter the mechanical properties of the initially weak sediments, which may lead to the onset of unstable sliding behaviour. However, effects of PT conditions equivalent to the updip limit on mechanical properties of marine sediments are still poorly understood. Since natural samples from these depths are not available, we conducted isothermal compaction test equivalent to the updip limit to overcome this shortcoming. For this, we focused on end member lithologies from underthrust section of the incoming plate at the Nankai margin (Japan), where the Phillippine Plate subducts under the Eurasian Plate with a velocity of ~4cm/yr. Three samples of marine sediments with different grain sizes (clay - silt) were compacted up to 70 MPa at different temperatures (20°C, 100°C, 150°C) in a hydrothermal oedometer apparatus to simulate subduction down the slab. Afterwards these compacted samples were sheared in a direct shear box at a normal load of 3.8 MPa, room temperature conditions up to a displacement of 8 mm with a velocity of 3 x 10-3mm/s. Furthermore, remoulded aliquots of the same samples of compacted clay- (smectite and illite) and quartz-rich sediments were sheared at up to 16 MPa normal stress to high displacement rate using a ring shear device. Those tests were carried out at four shear velocities and both at room temperature under seawater saturated conditions, and were then subsequently heated to >80°C seawater saturated under drained conditions. As a main result from the direct shear experiments, the clay-rich sediments show the most pronounced strain softening with high peak strength and very low residual coefficient of friction. In contrast, the silty samples show little strain softening. Additionally, the discrepancy between peak and residual is largest for the smectite clay compared to the silty specimens. This increase in peak relative to residual strength may be explained by the higher effective surface area in the samples poor in quartz content. Within all tests conducted so far, the samples compacted at 20°C seem slightly stronger than those which got thermally altered. At high displacements during the ring shear experiments, the friction coefficient of clay minerals (�n~2 MPa) show similar values and are much smaller than the quartz rich sample (ca. residual of 0.13-0.23). At higher normal stresses (up to ~16 MPa) and room temperature, the friction coefficients almost double. When the same samples are heated to >80°C, more pore water as well as clay mineral-bound water is released so that the specimens show a strain hardening behaviour and approach friction coefficients of >0.4. The data correlate well with friction values estimated for plat boundary faults with increasing depth.

APPENDIX 155

APPENDIX B To accomplish the proposed goals of the research project ROME, two heated

deformation apparatuses have been developed at the soil mechanical laboratory at

MARUM (Fig. 1). The main objective of the new devices is to study water-saturated

sediment samples of differing compositions over an extensive PT range. The neat

design of the apparatuses allows investigating both, physical and chemical processes,

in long-term experiments. Basically, an apparatus consists of two principal parts: a

hydraulic system and an uniaxial consolidation cell.

A special hydraulic system setup has been adjusted for each apparatus to create

the required vertical forces, consisting of a load frame, a high tonnage cylinder

(HZB), and a power unit. The power units in use are an ISCO 500D and an ISCO

100DX high precision syringe pump. The unique feature of these pumps is the

extremely slow flow rate. The 500D pump is able to generate forces up to 343kN and

flow rates down to 0.001ml/min. Combined with the HZB hydraulic cylinder this

arrangement generates particularly small vertical displacements down to 4.33*10-

2 mm/day, which are needed for long term testing. The 100DX is capable of forces up

to 915 kN and even smaller flow rates down to 0.00001 ml/min creating

displacements down to 4.33*10-4 mm/day. The load frames are also especially

adapted to provide the necessary access to the consolidation cell from all sides.

Fig. 1: Photograph of one (of the two) computer-controlled oedometer frame with titanium sample cell and ISCO high-precision syringe pump.

APPENDIX 156

The actual deformation of the specimen occurs in the uniaxial consolidation

cell. The cell consists of two pistons at either end of the sample. The lower piston is

arrested at the base plate of the load frame, while the upper piston is steadily moving

downward to apply increasing normal loads onto the sample (Fig. 2). This rather

simple design is particularly useful to remove the compacted sediment pucks in a non-

destructional way after the tests by pushing the pistons through the entire length of the

cylinder. The inner diameter of the cell is 63 mm and the cell can be loaded with

initial sample heights of 100 mm. With these sample dimensions we are able to

produce maximum stresses of 110 MPa (equivalent to depths of ~7 km) and strain

rates down to 1.25*10-8 s-1 in case of the 500D-based system. Maximum stresses for

the 100DX system are 293 MPa and strain rates down to 1.25*10-10 s-1. For heated

tests, the consolidation cell is additionally equipped with a band heater which is

wrapped around the cell (Fig. 3). The heater is capable of maximum temperatures of

200 °C with a regulation of the temperature by an external controller that also

measures the temperature in the cell.

Fig. 2: Schematic diagram of the sample cylinder with two pistons, band heater, pore pressure control (bottom), and fluid collection system (left). (B) Photograph of one computer-controlled oedometer frame during a heated test.

APPENDIX 157

For the proposed investigation of the physical and chemical processes in the

specimen, both pistons are equipped with boreholes to get access to the sample.

Stainless steel filter slabs between sample and piston prevent solids to get into the

bores. To get aliquots of pore water throughout the experiment for geochemical

testing, the upper sample access is drained. With increasing stress the pore fluid will

be squeezed out of the system and collected in attached flasks. Thus, we get pore

water samples for different stages of consolidation (i.e. different effective normal

stress ranges). A back-pressure regulator for drainage ensures that the pore water does

not evaporate in case of heated tests, and that accidentally trapped air remains

dissolved in the pore water. The seals in use allow us to increase the back pressure up

to 30 MPa. To minimise interaction of the saturated sample with the equipment, the

consolidation cell was made of titanium (grade 2). Other components such as tubing

and fittings also consist of non-corrosive materials like high-grade stainless steel,

PTFE, or PP.

Fig. 3: Photograph of one computer-controlled oedometer frame during a heated test.

The alteration of mechanical properties such as permeability, void ratio and

porosity can be determined by the change of deformation and pore water pressure

throughout the tests. The deformation is measured by a displacement transducer. Two

pressure transducers, mounted to the bottom and the top of the cell, measure the pore

water pressure gradient in the cell.

APPENDIX 158

Calibration of the heated uniaxial consolidation devices

All data are logged by a self-adjusted computer program (Fig. 4), which also

functions as a control unit for the pump. Therefore, various types of consolidation

tests such as constant-rate of strain (CRS), constant-rate of loading (CRL), or

incremental loading (IL) experiments can be automatically performed. Measured data

of the hydraulic pump, pressure transducers, displacement transducer and temperature

are immediately displayed in a diagram by the graphical user interface of the program.

The system was thoroughly calibrated before the heated consolidation tests.

The calibration included the displacement transducer, the hydraulic pump, pressure

transducers attached to the consolidation cell and the temperature probe (Fig. 5).

Calibration factors can be inserted into the program, which allows the immediate

display of the data (Fig. 4). Further, the systems were loaded to pressures and

temperatures without sample material in the consolidation cell to determine the

compressibility, the heat loss and the thermal expansion of the systems (Fig. 5).

Especially the implications of compressibility and thermal expansion on sample

deformation have to be regarded in the post-processing of the data.

Fig. 4: Screenshot of the user interface of the LabView™ program, which controls the hydraulic system and logs the different parameter. The view shows the logged temperature with time.

APPENDIX 159

Fig. 5: Example of the calibration procedure showing (A) calibration line of the displacement transducer, (B) the hydraulic pump, (C) the temperature transducer, (D) the pressure transducer attached to the bottom of the consolidation cell, (E) pressure transducer attached to the top of the consolidation cell, (F) the compressibility of the load frame, (G) the heat loss between bandheater and consolidation cell, and the thermal expansion of the consolidation cell.

APPENDIX 160

Preliminary results of heated consolidation tests of end member mineral

standards and testing experiences

The first experimental phase of the new heated consolidation apparatuses

focus on pure mono-mineral standards. These mono-mineral standards represent the

pure end members of the tested samples from DSDP Site 297, namely smectite, illite

and quartz. The testing of mono-mineral standards is underway since early 2007 at

MARUM, after setup of the system, extensive calibration of the hydraulic systems

and some preliminary consolidation experiments for testing purposes were finished.

Five tests have been conducted so far with good quality results (Fig. 6-9). The

geochemical analysis will be conducted soon to complete these experiments and to

prepare the data for publication.

Testing began with quartz-seawater slurries at room temperature and 100 °C.

However, high sidewall friction led to severe damage of the cells and some delay

occurred until the consolidation cells were repaired. Thereafter, the consolidation of

the smectite standards at 20 °C and 60 °C went smoothly. After the successful

experiments the consecutive experiments at 100 °C were influenced by severe water

loss along the gap between piston and cell wall. Therefore, the sealing system of the

pistons was re-engineered and the new system prevents the pressing of the sediment

into the gap between cell and piston and thus damaging the sealing. This latest design

seems to satisfy the requirements of temperature of up to 200 °C and 110 MPa

effective stress.

On the strength of the past experiences initial heights of 30 mm or rather

diameter:height ratios of 2:1 are recommended. Thus, sidewall friction is negligible

and does not influence the loading of the specimen in the cell. Starting strain rates of

0.06 % or 0.018 mm/h are adaptable to a wide range of sediments including low

permeable clays. These values are suitable for the proposed testing interval of ~3

month and fulfil ASTM experimental requirements for CRS consolidation tests.

However, despite some initial difficulties, the new systems are ready and provide

several improvements compared to the devices, which were used for the pilot study.

These are amongst others the higher logging resolution, immediate display of logged

parameters and the possibility to apply different methods of consolidation techniques.

APPENDIX 161

Fig 6: Preliminary results of the consolidation test of quartz at room temperature. (A) Settlement of quartz presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.

APPENDIX 162

Fig 7: Preliminary results of the consolidation test of quartz at 100 °C. (A) Settlement of quartz presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.

APPENDIX 163

Fig 8: Preliminary results of the consolidation test of smectite at room temperature. (A) Settlement of smectite presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.

APPENDIX 164

Fig 9: Preliminary results of the consolidation test of smectite at 60 °C. (A) Settlement of smectite presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell.

APPENDIX 165

Fig 10: Preliminary results of the consolidation test of smectite at 100 °C. (A) Settlement of smectite presented as void ratio vs logarithm of effective stress. (B) Logarithm of the hydraulic conductivity plotted against the void ratio. The hydraulic conductivity was inferred from the measured excess pore pressure at the undrained bottom of the cell. Note that the hydraulic conductivity could be calculated only to a void ratio of 1.1 because of seal breakage.

ERKLÄRUNG 166

Erklärung Hiermit versichere ich, dass ich

1. die Arbeit ohne unerlaubte fremde Hilfe angefertigt habe, 2. keine anderen als die von mir angegebenen Quellen und Hilfsmittel benutzt habe und 3. die den benutzten Werken wörtlich oder inhaltlich entnommenen Stellen als solche kenntlich gemacht habe.

Bremen, den 18.05.2009 ………………………..

(Unterschrift)

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Physico-chemical processes in seawater-saturated ...elib.suub.uni-bremen.de/diss/docs/00011513.pdfreduced and compensated by irreversible strain. This phenomenon reveals that the consolidation