sediment dewatering in the makran accretionary prism abstract sediments within the makran accretionary prism are considerably more compacted than the material entering the subduction zone due to the additional tectonic stresses resulting from plate convergence and accretionary processes tectonic compaction of the offscraped sediments has been documented by deriving in situ porosities in the upper 4 km from their seismic velocities wide angle seismic reflection refraction profiles were analysed from a transect crossing both the makran accretionary prism and the undeformed abyssal plain sediments to the south the 6 7 km thick abyssal plain sediments exhibit normal compaction with depth the sediments incorporated into the accretionary prism have higher seismic velocities at all depths corresponding to reductions in porosity of 30 40 mapping the porosity depth gradient across the prism shows that there is a marked change in porosity at the seaward toe of the prism the frontal fold there is then little further change until further folding begins to occur 70 km landward of the toe the dewatering and consolidation of the sediments is an important control on deformation occurring within the sedimentary prism

quartz vein fabrics coupled to elevated fluid pressures in the stawell gold deposit south eastern australia shear and extensional veins formed during the reactivation of the magdala shear system at stawell in western victoria australia contribute to the formation of the auriferous central and basalt contact lodes within this shear system is a range of fault rocks accompanied by steep dipping 65 quartz rich laminated shear veins and relatively flat lying extensional veins both vein sets appear to have been a primary source for the host rock permeability during fluid flow in a regime of significant deviatoric stresses the macro and microstructures suggest that the dilatancy that produced mineralized veins formed under conditions of overpressure generated by fluid infiltration late in a tectonic regime a new microfabric analysis technique is used to investigate the quartz rich veins which allows rapid integration of the microstructure with the crystallographic preferred orientations cpos both the shear and extensional quartz veins have a random cpo with 120 dihedral angles between the quartz quartz grains which is typical of a metamorphic equilibrium microfabric the microstructures indicate that the quartz has undergone extensive grain adjustment in the solid state with grain shape and size affected by interfacial solution pressure solution effects these features are consistent with inferences from experimental rock deformation studies where grain boundary migration is enhanced in a water rich environment the onset of solution transfer processes pressure solution developed as the quartz microfabric stabilized and continued to modify the cpo and microstructure significantly it is concluded that grain growth and pressure solution are coupled diffusive mass transfer processes related to fluctuations in pore fluid pressures in a region undergoing deformation at near lithostatic pressures

transient creep of a composite lower crust 1 constitutive theory a composite model is proposed to describe the time dependent response of the earth s lower crust the motivation for such a model is twofold first new observations of widespread postseismic deformation indicate that the deep continental crust responds viscoelastically having both long and short term decay times second by any number of observationally based rationales the lower crust is compositionally and structurally heterogeneous over many length scales for heterogeneities that have much smaller characteristic lengths than the minimum deformation wavelength of interest the aggregate rheology can be described by composite media theory for wavelengths of the order of the thickness of the lower crust 25 40 km and larger composite theory may be applied to heterogeneities that are smaller than about several hundred meters or equivalent to the vertical extent of a thick lower crustal mylonitic shear zone the composite media theory developed here is constructed using both eshelby mori tanaka theory for aligned generalized spheroidal inclusions and a generalized self consistent method the inclusions and matrix are considered to be maxwellian viscoelastic a rheology that is consistent with past homogeneous models of postseismic stress relaxation the composite theory presented here introduces a transient response to a suddenly imposed stress field which does not appear in homogeneous maxwell models analytic expressions for the amplitude and duration of the transient and for the effective long and short term viscosities of the composite are given which describe the sensitivity to inclusion concentration to shape and to ratio of inclusion to matrix viscosity r

diagenetic history of cambrian quartzarenites ras dib zeit bay area gulf of suez eastern desert egypt abstract in the northern corner of the el zeit range 370 m of sandstone overlie precambrian granite and underlie cretaceous marine strata the sandstones include the marine lower cambrian araba formation and the overlying dominantly fluvial upper cambrian naqus formation the framework compositions of both sandstones are almost entirely quartz with trace amounts of muscovite k feldspar and heavy minerals up to 21 oversize pores some filled with younger cements attest to extensive dissolution loss of detrital grains because the final mineralogical maturation of these quartzarenites reflects diagenesis they are diagenetic quartzarenites during burial diagenesis the introduction of up to 8 quartz cement inhomogeneously distributed mean 3 was followed by local pore occluding calcite cement which halted compaction sandstones without calcite cement underwent additional mechanical and chemical compaction sufficient to develop sutured quartz grain contacts and reduce porosity 27 these events were followed by 1 extensive dissolution loss of carbonate cement detrital feldspars micas and heavy minerals 2 formation of local patches of kaolinite mean 3 and 3 formation of extensive iron oxide cements including specular hematite these features suggest extensive invasion by oxidizing meteoric water the timing of this event can only be dated as post cambrian and pre cenomanian some outcrop samples contain pore occluding gypsum cement or mixtures of gypsum and halite sr87 sr86 ratios of four samples of gypsum cement have values 0 7079 and 0 7085 that indicate miocene and slightly younger seawater evaporites were evidently leached by modern meteoric water from nearby outcrops of miocene and younger marine evaporite bearing strata transported in surface and ground water to the topographically low terrain where the cambrian sandstones crop out and reprecipitated by evaporation initial primary porosity 45 was reduced to 27 by compaction in sands with minor quartz cement compaction ceased where calcite was precipitated subsequent dissolution of some calcite cement and unstable detrital grains generated considerable secondary porosity

changes in quartz solubility and porosity due to effective stress an experimental investigation of pressure solution experimental compaction of quartz sand was conducted in semistatic flow through systems at 150c to examine the chemical and physical processes associated with pressure solution pore fluid chemistry and porosity were monitored through time to investigate the role of effective stress on silica solubility and compaction rate the concentration of silica in the pore fluid varied directly with effective stress at constant pore fluid pressure but not in a linear fashion increases in silica were not transient and could be partially reversed by removal of the effective stress porosity decreased steadily under constant nonzero effective stress at 150c but remained essentially constant under identical loading conditions at room temperature initial compaction rates increased linearly with effective stress deformed samples show indented contacts with fractures and dissolution features healed microfractures and a decrease in average grain size multiple mechanisms pressure solution subcritical crack growth crack healing appear to operate at grain contacts during compaction the authors interpret long term time dependent compaction accompanied by stress induced changes in fluid chemistry as evidence for pressure solution

pressure solution in sedimentary basins effect of temperature gradient abstract pressure solution is an important process in sedimentary basins and its behaviour depends mainly on the sediment rheology and temperature distribution the compaction relation of pressure solution is typically assumed to be a viscous one and is often written as a relationship between effective stress and strain rate a new derivation of viscous compaction relation is formulated based on more realistic boundary conditions at grain contacts a non linear diffusion problem with a moving boundary is solved numerically and a simple asymptotic solution is given to compare with numerical simulations pressure solution is significantly influenced by the temperature gradient porosity reduction due to pressure solution is enhanced in an environment with a higher thermal gradient while porosity decreases much slowly in the region where the thermal gradient is small pressure solution tends to complete more quickly at shallower depths and earlier time in higher temperature environment than that in a low one these features of pressure solution in porous sediments are analysed using a perturbation method to get a solution for the steady state comparison with real data shows a reasonably very good agreement

on the leading negative phase of major 2010 2014 tsunamis time series observations from instruments sited in the deep ocean and along coastal margins of the pacific during major tsunami events in the years since 2010 were systematically processed examination of these records during four events 2010 chile maule 2011 east japan tohoku 2012 haida gwaii and 2014 chile iquique show the prevalence of a small negative phase leading the first major positive tsunami wave a phase that is not typically reproduced by current modelling approaches we present leading negative phase signatures in examples from the more than 40 deep ocean bottom pressure and approximately 200 tide gauge records investigated for this study high sampling rate time series 15 s were given greater weight in our investigation than the more readily available 1 min series careful investigation of tsunami arrival at each deep ocean site highlights the role filtering techniques may play in misleading researchers or masking specific tsunami features such as the leading negative phase that is the basis of this study the main focus of this investigation is to characterise the scale and repeatability of the phenomenon in support of recent similar findings rather than to provide a definitive explanation as to the cause in general our findings are in good agreement with and support the theoretical results of watada et al j geophys res solid earth 119 4287 4310 2014

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

kinetics of pressure solution at halite silica interfaces and intergranular clay films pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during aliagenesis yet the mechanisms and kinetics of this process remain highly controversial to better understand the fundamental factors controwing the rates of pressure solution at the grain to grain scale we conducted experiments in which convex halite lenses were pressed against fiats of fused silica in brine fluid pressures were maintained at 0 1 mpa temperatures and mean contact normal stresses ranged from 8 3 o to 90 2oc and 0 5 to 13 5 mpa respectively the geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another convergence were monitored using reflected light interferometry and transmitted light photomicrography convergence occurred when halite and silica lenses were pressed together in brine halite silica experiments no undercutting was observed and dry control experiments indicated negligible dislocation creep convergence rates in experiments at 50 2oc ranged from 0 01 to 0 05 m d depending on mean normal stress and contact spot radius the data are consistent with intergranular pressure solution ips rate limited by diffusion through an intergranular film with a very high diffusion coefficient 10 5 10 7 cm2 s the data further suggest that the diffusion coefficient and or thickness of this film increases with decreasing normal stresses at least for normal stresses less than about 4 mpa as no island channel boundary structures were observed we propose that this film consists of a continuous layer of strongly adsorbed i e structured water that is maintained between the halite and silica lenses during deformation convergence rates in similar experiments conducted at a constant load of 0 11 n but at 8 3 o 50 2 o and 90 2oc were approximately constant at a given normal stress and contact spot size the cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation an experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0 8 m thick film of na montmorillonite in brine this clay film produced an approximately fivefold increase in convergence rates over those observed in a halite silica experiment conducted without clay at the same load and temperature the strong sensitivity of ips rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine grained clay rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust

pressure solution and viscous compaction in sedimentary basins mathematical models of compaction in sedimentary basins typically assume a relationship between effective pressure pand porosity which is of a non linear type that is p p d however at depths greater than a kilometer pressure solution becomes important and this relationship approaches a viscous one we derive a mathematical model for viscous compaction in sedimentary basins and show how the model suggests different styles of behavior in the limits of slow nd fst compaction the initial pore pressure will be lithostatic over time the sediments compact and the resultant expulsion of pore water allows the pore pressure to approach a hy drostatic limit and in so doing the porosity is reduced at depths up to about a kilometer this compaction is elastic and due to the rearrangement of sediment particles at greater depths cementation and pressure solution occur and the latter causes further compac tion we call compaction by pressure solution viscous compaction and it forms the subject of the present pa per one of the interesting features of overpressuring is that it typically occurs suddenly at depths in excess of 3000 meters hunt 1990 and is often associated

the development of structural geology and the historical context of the journal of structural geology a reflection by bruce hobbs abstract this paper sets the historical context for the journal of structural geology when it was first published in 1979 the major advances in structural geology over the past 40 years are then highlighted finally ten grand challenges for the next decade are nominated

venture gas field offshore nova scotia case study of overpressuring in region of low sedimentation rate the venture gas field is a deep overpressured gas reservoir on the scotian shelf off eastern canada overpressuring occurs at depths below 4 5 km and is associated with significant quantities of gaseous hydrocarbons the overpressured zone is composed of high porosity sandstones interbedded with low porosity low permeability shales which have nearly normal levels of compaction pore pressures in this zone show a step wise increase with depth where pressure jumps correlate with low permeability 10 20m2 where 10 12m2 1 01 d shale beds petrophysical and lithological data for sandstones and shales in the overpressured zone are used to constrain a one dimensional single phase model of pore pressure development the con ersion of kerogen to hydrocarbons is simulated by simple kinetic reaction theory estimates of the effects on overpressuring of sediment compaction temperature changes and hydrocarbon generation were obtained from this model using the above data 2 disequilibrium compaction apparently is responsible for much of the overpressuring in the venture gas field in our simple single phase model the contribution of hydrocarbon generation to overpressuring was slight

porosity reduction by pressure solution a theoretical model for quartz arenites pressure solution and the subsequent precipitation of the dissolved material may play an important role in the lithification of sandstones and limestones this paper presents a one dimensional model for a well sorted quartz arenite sequence undergoing diagenesis the sedimentary sequence is treated as a saturated porous medium in which pressure solution occurs at individual grain contacts quartz dissolved at grain contacts precipitates on free surfaces of adjacent grains this solution and precipitation process reduces porosity and forces the migration of pore fluid permeability decreases with porosity hindering fluid migration and excess fluid pressures are generated distributions of porosity pore pressure and fluid flow rates are given for several sedimentation rates and thermal gradients complete reduction of the primary intergranular porosity was accomplished in all cases examined by a depth of 3 5 km

thermal conductivity of unconsolidated sediments with geophysical applications a theoretical model for the prediction of the thermal conductivity of unconsolidated granular sediments with application to sand shale mixtures is presented the sediment is modeled as an assemblage of grains of thermal conductivity s immersed in a pore fluid of thermal conductivity in order to take into account for the thermal interactions between the grains a differential effective medium approach is used to provide a relationship between the effective thermal conductivity of the isotropic mixtures of grains saturated by the pore fluid the porosity and the thermal conductivities of the grains and pore fluid the influence of the topology of the interconnected pore space is accounted for through the use of the electrical cementation exponent m which is related to the electrical formation factor f by f m where is the interconnected porosity the main assumption of the model lies in the small contiguity between the grains this assumption holds well for unconsolidated sand shale mixture sediments as demonstrated by comparing the model to available experimental data the model offers the possibility to derive thermal conductivity profiles from downholes measurements of natural radioactivity electrical resistivity and bulk density

rheological characterization of a sedimentary formation from a stress profile inversion summary detailed stress measurements have been carried out within a sedimentary sequence composed of a hard clay formation laying horizontally between two limestone units in the eastern paris basin france orientations of the minor and major horizontal principal stresses are found to be in good agreement with the direction of major shortening that prevailed during the last tectonic stage however their magnitudes exhibit an intriguing evolution with depth while the magnitude of the maximum horizontal stress slowly but regularly increases with depth the magnitude of the minimum horizontal one is larger in the hard clay formation than in the surrounding limestone units contrary to expectation from simple elastic considerations an analytical calculation demonstrates that the genesis of the current stress state may be reproduced by taking into account horizontal strains in two different directions and simulating erosion of part of the overburden with a viscoelastic model for the hard clay and an elastic behaviour for the limestone however the elastic constants that are derived for the limestone in order to fit the measured stress field correspond to a material that is more deformable and has a lower poisson s ratio than predicted by laboratory tests this discrepancy may be explained by a slow long term deformation process in the limestone possibly associated with pressure solution

elastic strain energy as a control in the evolution of asymmetric pressure solution contacts subjecting a water rock system to load can enhance the rock solubility by 1 increasing normal pressure at the dissolving surface and 2 raising the elastic energy of the rock for pressure solution surfaces such as grain contacts solution seams and stylolites the pressure term in the chemical potential equation is orders of magnitude larger than the strain energy term thus the contribution of the strain energy to the overall solubility of the system is very small and it is most often ignored we show that the elastic strain energy at a pressure solution interface can have a profound effect on the manner in which it evolves the mechanism we propose is the following inducing a discontinuity in elastic strain energy across a pressure solution interface e g by changing its curvature can cause one side to become slightly more soluble than the other part of the material that is dissolved may diffuse the short distance across the fluid layer and raise the saturation in the vicinity of the less soluble surface if the fluid layer was already close to saturation the dissolution at the less soluble surface may be severely slowed down or even halted therefore although the strain energy difference across the interface has a negligible effect on the total amount of material that is dissolved there it may cause only one side to dissolve in this way the formation of stylolites can be facilitated by heterogeneities in the elastic strain energy difference along a pressure solution interface

rate laws for water assisted compaction and stress induced water rock interaction in sandstones mineral water interactions under conditions of nonhydrostatic stress play a role in subjects as diverse as ductile creep in fault zones phase relations in metamorphic rocks mass redistribution and replacement reactions during diagenesis and loss of porosity in deep sedimentary basins as a step toward understanding the fundamental geochemical processes involved using naturally rounded st peter sand we have investigated the kinetics of pore volume loss and quartz water reactions under nonhydrostatic hydrothermal conditions in flow through reactors rate laws for creep and mineral water reaction are derived from the time rate of change of pore volume sand water dissolution kinetics and flow rate independent steady state silica concentrations and reveal functional dependencies of rates on grain size volume strain temperature effective pressure confining minus pore pressure and specific surface areas together the mechanical and chemical rate laws form a self consistent model for coupled deformation and water rock interaction of porous sands under nonhydrostatic conditions microstructural evidence shows a progressive widening of nominally circular and nominally flat grain grain contacts with increasing strain or equivalently porosity loss and small quartz overgrowths occurring at grain contact peripheries the mechanical and chemical data suggest that the dominant creep mechanism is due to removal of mass from grain contacts termed pressure solution or solution transfer with a lesser component of time dependent crack growth and healing the magnitude of a stress dependent concentration increase is too large to be accounted for by elastic or dislocation strain energy induced supersaturations favoring instead the normal stress dependence of molar gibbs free energy associated with grain grain interfaces

rheology of the plate interface dissolution precipitation creep in high pressure metamorphic rocks abstract subduction zone models invoke deformation to be concentrated along the plate interface in a region of particularly low temperature geophysical observations do not provide constraints on temperature stress and deformation patterns with desired resolution in contrast the record of high pressure metamorphic rocks exhumed from subduction zones provides details on p t history deformation mechanisms and stress state albeit not readily correlated with the former dynamic situation on larger scale here we review available information on dissolution precipitation creep dpc in high pressure metamorphic rocks which if representative for subduction zones in general can pose constraints on conditions rheology and flow patterns along the plate interface the key observations and conclusions are that 1 deformation is typically highly inhomogeneous and localized into shear zones 2 stresses are generally too low to drive crystal plastic deformation 3 microfabrics suggest dissolution precipitation creep to be the predominant deformation mechanism 4 an aqueous fluid at quasi lithostatic pressure is available throughout allowing for tensile fracturing and crack healing or sealing 5 low stress combined with high strain rates required for localized deformation at typical subduction rates implies low viscosity and 6 contribution of shear heating to the thermal budget of subduction zones should be moderate the dominant deformation mechanism dpc is reviewed in some detail including experimental and theoretical approaches various examples of dpc in high pressure metamorphic rocks are illustrated emphasizing the role of interphase boundaries as sites of dissolution rheology governed by dpc is proposed to control interplate coupling and development of a subduction channel with return flow being a likely candidate for rapid exhumation of high pressure metamorphic rocks

modeling of porosity loss during compaction and cementation of sandstones irreversible inelastic processes are responsible for mechanical and chemical compaction of sedimentary rocks at the time of burying our purpose is to describe the inelastic response of the rock at large time scales in order to do this we build a model that describes how porosity progressively decreases at depth we use a previous geometrical model for the compaction process of a sandstone by grain interpenetration that is restricted to the case of mass conservation in addition we introduce a compaction equilibrium concept solid grains can support stresses up to a critical effective stress c before plastic flow occurs this critical stress depends on temperature and is derived from the pressure solution deformation law pressure solution is the plastic deformation mechanism implemented during compaction our model predicts a porosity destruction at a depth of about 3 km this model has the property to define a range of compaction curves we investigate the sensitivity of the model to the main input parameters liquid film thickness grain size temperature gradient and activation energy

intergranular pressure solution in four quartzose sandstones abstract cathodoluminescence petrography and scanning electron microscopy reveal that several geologic variables significantly influenced intergranular pressure solution and quartz cementation in the bromide ordovician oklahoma upper minnelusa permian wyoming nugget jurassic utah and tuscarora silurian pennsylvania sandstones a linear relationship exists between mean grain size and intergranular pressure solution with finer grained samples having experienced more intergranular pressure solution than coarser grained ones samples that display pervasive illite grain coatings have also experienced more intergranular pressure solution than those with no or poorly developed grain coatings sorting and limited framework grain compositional variability have exerted little influence o intergranular pressure solution silica budgets indicate that in the bromide upper minnelusa and nugget sandstones more quartz has been dissolved by intergranular pressure solution than is present as cement these sandstones have exported silica during burial diagenesis in the tuscarora the amount of quartz dissolved by intergranular pressure solution is about equal to the amount of quartz cement present implying approximate mass balance however petrographic evidence suggests that most of the quartz cement in at least three of these sandstones predates most intergranular pressure solution implying that they acted as silica importers during shallow diagenesis and silica exporters during deeper diagenesis intergranular pressure solution has played varying roles in determining the ultimate porosity of these four sandstones in the nugget intergranular pressure solution was the single most important diagenetic process that influenced porosity evolution in the bromide intergranular pressure solution was slightly more important than mechanical compaction and considerably more important than cementation in the tuscarora intergranular pressure solution was slightly more important than mechanical compaction and of about equal importance to quartz cementation in the upper minnelusa intergranular pressure solution was less important than both mechanical compaction and gypsum anhydrite cementation

effects of dissolution precipitation processes on the strength and mechanical behavior of quartz gouge at high temperature hydrothermal conditions laboratory experiments on simulated quartz gouges at a temperature of 927 c a confining pressure of 300 mpa and a pore water pressure of 200 mpa demonstrate the interactions between cataclastic and dissolution precipitation processes and their effects on the strength and mechanical behavior significant porosity reduction and microstructures including grain interlocking grain interpenetration and widespread growth of euhedral shaped grains indicate the operation of dissolution precipitation processes under conditions which favor the activity of dissolution precipitation processes i e for small grain size or at slow displacement rates deformation is distributed across the whole gouge layer and strength increases continuously with increasing displacement so that coefficients of friction reach to 0 7 in contrast for specimens with large grain size sheared at fast displacement rates deformation is localized along a gouge forcing block interface after a small amount of displacement and results in slip softening and subsequent quasi stable sliding with coefficients of friction as low as 0 45 analysis of our results indicates that where the kinetics of dissolution precipitation is sufficiently fast to partly accommodate shear strain the mechanical behavior and strength of quartz gouge can be characterized by slip hardening and high strength with velocity strengthening in contrast where cataclastic processes predominantly accommodate shear strain the mechanical behavior and strength can be characterized by slip softening and subsequent localized sliding with low strength and velocity strengthening

calibration of water granite interaction with pressure solution in a flow through fracture under confining pressure fluid mineral interaction has an irreversible impact on the fracture permeability evolution in the life span of deep geological reservoirs to investigate the impact a preliminary study on water granite interaction in an undeformable fracture under confining pressure is conducted a 1 d flow and reactive transport model is therefore developed and validated against the experimental data in yasuhara et al appl geochem 26 12 2074 2088 2011 the model takes free face dissolution on pore walls as well as enhanced dissolution at asperity contacts into account together with a nested well equipped geochemical system the simulation is implemented by fem based simulator opengeosys with a plugin module of iphreeqc for speciation calculation after calibration the predictions of effluent element concentrations are in good agreement with the measurements the study indicates the high effluent concentrations arise from enhanced mineral dissolution at asperity contacts pressure solution at anorthite contacts may not take effect under experimental conditions because of the high level energy barrier to interpenetration and al bearing secondary minerals such as gibbsite may be formed in the current near equilibrium aqueous system the sensitivity analysis suggests that contact area ratio is a paramount parameter in determining the surface reactivity and reactive surface area at contacts

experimental pressure solution deposition on quartz grains the crucial effect of the nature of the fluid abstract experimental deformation by pressure solution was performed on an aggregate of small grains subjected to deviatoric stress 50 mpa for a long time several weeks or months at relatively high temperature and pressure in contact with various fluids air water 0 1 to 1 n naoh for quartz water and 5 nh 4 cl for calcite the change in shape of the grains by solution deposition depended on the duration of the experiment with the same fluid and on the concentration of the solid in solution with the same duration but various fluids significant shape changes were obtained for quartz grains but only with both long duration and very good solvents 1 n naoh by comparison with previously obtained results on the change of shape of fluid inclusions where the kinetics of dissolution was the rate controlling process the limiting process of the deformation of the quartz grains was inferred to be the rate of diffusion along grain boundaries saturated with trapped fluid

the effect of oil saturation on the mechanism of compaction in granular materials higher oil saturations lead to more grain fracturing and less pressure solution abstract whether addition of oil to sandstones slows stops or has no influence upon pressure solution and quartz cementation has long been disputed despite having major implications for petroleum exploration and appraisal strategies to elucidate the effect of addition of oil to compaction pressure solution and cementation processes this study utilizes an experimental approach simulating isochemical volumetric compaction using granular halite in the presence of variable brine oil mixtures each experiment at 500 kpa effective stress lasted 48 hours and involved repeated measurements of volumetric strain the lithified products of experiments were examined using sem techniques after 30 hours approximately 4 volumetric strain occurs when the brine oil ratio is 100 0 pure brine fractures are rare in samples from experiments undertaken with pure brine so that pressure solution and concomitant cementation must be the compaction mechanism when the brine oil ratio is decreased from 100 0 to 40 60 the volumetric strain remains about 4 but there are more fractures as quantified from sem image analysis these observations suggest that although pressure solution has occurred some of the volumetric strain is the result of fracturing implying that pressure solution has been less effective in the presence of some oil than it is in the presence of pure brine when the brine oil ratio is decreased further from 40 60 to 5 95 the volumetric strain increases up to 7 3 sem image analysis reveals that the strain is predominantly due to grain fracturing this change from pressure solution to grain fracturing is likely due to heterogeneous pressure solution resulting from heterogeneous distribution of stresses brine coated grain contacts undergo pressure solution but oil coated grain contacts experience increasing stress up to the point of failure as the surrounding grain pack compacts when the brine oil ratio is decreased to less than 5 95 volumetric strain decreased to about 1 with few induced fractures and little pressure solution compaction is negligible when the brine oil ratio is 0 100 only oil in the pores and fractures are negligible halite is more water soluble and more hygroscopic than quartz so that water will cling to halite surfaces more tenaciously than to quartz since even halite has its mechanism of volumetric strain affected when the brine oil ratio is less than 40 60 quartz pressure solution and subsequent cementation is even more likely to be affected by oil filling this experimental study suggests that the mechanism and extent of compaction and subsequent cementation in sandstones is strongly affected by the addition of oil

the rheological transition in plagioclase bearing magmas 1 volcanological processes such as melt segregation ascent and eruption are directly dependent on the rheological behavior of magmatic suspensions an increase of the crystal fraction of the suspension leads to the formation of a solid particle network which abruptly increases magma viscosity the crystal fraction at which this rheological transition occurs depends on parameters such as the strain rate and the size shape and sorting of particles to determine the influence of the crystal shape on the rheological transition suspensions of plagioclase a representative anisometric crystal have been investigated at high temperatures and pressures synthetic suspensions with crystal fractions s ranging from 0 38 to 0 75 were deformed both in compression and torsion in a paterson apparatus at 300 mpa 900 c and 800 c and for strain rates between 1 0 10 5 and 1 0 10 3 s 1 all suspensions exhibit a non newtonian shear thinning rheological behavior the experimental results coupled with existing data and models at low crystal fractions s 0 3 allow several rheological domains to be identified from steady state flow to strain weakening each characterized by a specific microstructure in particular a progressive evolution from a pervasive to a strain partitioning fabric is found when increasing the crystal fraction our results highlight the influence of both the strain rate and the shape of crystals on the rheological behavior of magmas during crystallization magmatic suspensions of anisometric minerals such as plagioclase would develop a solid particle network earlier s 0 3 than suspensions of isometric minerals s 0 5 our study shows that localization of strain early in the crystallization history of mushy zones in the magma chamber near the conduit margins and at the base of lava flows would facilitate the mobilization the transfer and the final emplacement at the surface of highly viscous feldspar rich magmas

effects of interfacial energy on compaction creep by intergranular pressure solution theory versus experiments on a rock analog nano3 groundwater systems are increasingly used for seasonal aquifer thermal energy storage sates for periodic heating and cooling of buildings its use is hampered in contaminated aquifers because of the potential environmental risks associated with the spreading of contaminated groundwater but positive side effects such as enhanced contaminant remediation might also occur a first reactive transport study is presented to assess the effect of sates on the fate of chlorinated solvents by means of scenario modeling with emphasis on the effects of transient sates pumping and applicable kinetic degradation regime temperature effects on physical chemical and biological reactions were excluded as calculations and initial simulations showed that the small temperature range commonly involved t 15 c only caused minor effects the results show that a significant decrease of the contaminant mass and eventually plume volume occurs when degradation is described as sediment limited with a constant rate in space and time provided that dense non aqueous phase liquid dnapl is absent however in the presence of dnapl dissolution particularly when the dissolved contaminant reaches sates wells a considerably larger contaminant plume is created depending on the balance between dnapl dissolution and mass removal by degradation under conditions where degradation is contaminant limited and degradation rates depend on contaminant concentrations in the aquifer a sates system does not result in enhanced remediation of a contaminant plume although field data are lacking and existing regulatory constraints do not yet permit the application of sates in contaminated aquifers reactive transport modeling provides a means of assessing the risks of sates application in contaminated aquifers the results from this study are considered to be a first step in identifying the subsurface conditions under which sates can be applied in a safe or even beneficial manner

ductile creep and compaction a mechanism for transiently increasing fluid pressure in mostly sealed fault zones a simple cyclic process is proposed to explain why major strike slip fault zones including the san andreas are weak field and laboratory studies suggest that the fluid within fault zones is often mostly sealed from that in the surrounding country rock ductile creep driven by the difference between fluid pressure and lithostatic pressure within a fault zone leads to compaction that increases fluid pressure the increased fluid pressure allows frictional failure in earthquakes at shear tractions far below those required when fluid pressure is hydrostatic the frictional slip associated with earthquakes creates porosity in the fault zone the cycle adjusts so that no net porosity is created if the fault zone remains constant width the fluid pressure within the fault zone reaches long term dynamic equilibrium with the hydrostatic pressure in the country rock one dimensional models of this process lead to repeatable and predictable earthquake cycles however even modest complexity such as two parallel fault splays with different pressure histories will lead to complicated earthquake cycles two dimensional calculations allowed computation of stress and fluid pressure as a function of depth but had complicated behavior with the unacceptable feature that numerical nodes failed one at a time rather than in large earthquakes a possible way to remove this unphysical feature from the models would be to include a failure law in which the coefficient of friction increases at first with frictional slip stabilizing the fault and then decreases with further slip destabilizing it

a model for sandstone compaction by grain interpenetration abstract the compaction of an idealized sandstone is described quantitatively in terms of its stress temperature history and the microstructure of its monomineralic load bearing grain cement framework the model relationship is developed from simple energy and volume balance considerations although chemistry mineral pore fluid and transport diffusion fluid flow play major roles in most diagenetic processes they do not appear explicitly in this mechanical model for grain interpenetration in sandstones for a model sandstone at compaction equilibrium the only quantity determined uniquely by the ambient stress and temperature is its burial constant equal to the ratio of its grain cement contact diameter to the separation of its grain centers the burial constant determines what the maximum porosity can be whether primary or secondary sandstones with identical burial constants may have very different grain interpenetrations and minus cement porosities depending on the amount of supporting cement and the time of its emplacement supporting load bearing cement increases the effective intergrain contact area thereby increasing a sandstone s resistance to compaction supporting cement usually preserves more pore space than it occupies this is in direr contrast to passive non lo d bearing cement which may destroy even more effective pore space than its solids occupy the removal of passive cement increases porosity but the removal of supporting cement initiates further compaction and causes porosity to decrease with sufficient supporting cement primary porosity can retain economic values to great depths model predictions are uniformly consistent with available observational data on quartzose sandstones agreement among data from geographically diverse sandstone reservoirs ranging in age from jurassic to pleistocene suggests that compaction equilibrium is reached in times that are short on the geological time scale and that age is not a factor in the compaction of sandstones

pervasive pressure solution transfer in a quartz sand the kinetics of deformation of a quartz aggregate by pervasive pressure solution can be under certain conditions of temperature and grain size strongly dependent upon the diffusivity of silica into the grain to grain contacts an analysis of the factors affecting this key parameter and less well constrained in the analysis of the problem of rock deformation by pressure solution is presented this analysis is based on recent advances on studying silica surfaces and particularly on the existence of a silica gel layer on the silica surfaces undergoing dissolution by reinvestigating the electroviscous effect occurring at the grain to grain contact the present analysis shows that the diffusivity of silica at the grain to grain contacts is likely to be relatively similar to that in the bulk pore water maybe 1 order of magnitude smaller but not more this contradicts the previous work by rutter 1976 which has been the key reference used in many subsequent papers to justify an extremely low value for the diffusivity of silica at the grain to grain contacts 5 orders of magnitude smaller than the diffusivity of silica in free water this finding has dramatic implications concerning the deformation rate of quartz sands and sandstones by pressure solution in sedimentary basins with regard to 1 the limiting step affecting the kinetics of the process diffusion of the solute or dissolution precipitation chemistry and 2 the existence of a thermodynamic equilibrium state when deformation by pressure solution occurs over geological timescales a poroviscoplastic model is used to describe deformation associated with pervasive pressure solution transfer in quartz sands this model is shown to be consistent with the current state of knowledge of the surface chemistry of silica in addition the comparison between this model and both laboratory and field data is rather good