local deformation in compacting flows development of pressure shadows abstract small scale structures produced by deformation and compaction are common in igneous metamorphic and sedimentary rocks and are often used to define foliation and lineation directions analytic solutions for models of flow round a rigid stationary sphere are obtained using the equations that describe viscous compaction the finite deformation associated with these flows shows many of the features observed in deformed rocks some of which resemble those generated when the ratio of the bulk viscosity to the shear viscosity is small under these conditions the particle paths of the matrix are almost unaffected by the presence of the sphere it is encouraging that the continuum compaction equations can describe the observed behaviour even though the length scale on which the deformation occurs is only mm to cm it is unlikely that the observations can be used to distinguish between d arcy flow of the low viscosity phase and mass transport by diffusion

hydrothermal germanium over the southern east pacific rise germanium enrichment in the oceanic water column above the southern axis of the east pacific rise results from hydrothermal solutions emanating from hot springs along the rise crest this plume signature provides a new oceanic tracer of reactions between seawater and sea floor basalts during hydrothermal alteration in contrast to the sharp plumes of 3he and manganese the germanium plume is broad and diffuse suggesting the existence of pervasive venting of low temperature solutions off the ridge axis

brittle and semibrittle creep of tavel limestone deformed at room temperature deformation and failure mode of carbonate rocks depend on the confining pressure in this study the mechanical behaviour of a limestone with an initial porosity of 14 7 is investigated at constant stress at confining pressures below 55 mpa dilatancy associated with micro fracturing occurs during constant stress steps ultimately leading to failure similar to creep in other brittle media at confining pressures higher than 55 mpa depending on applied differential stress inelastic compaction occurs accommodated by crystal plasticity and characterized by constant ultrasonic wave velocities or dilatancy resulting from nucleation and propagation of cracks due to local stress concentrations associated with dislocation pile ups ultimately causing failure strain rates during secondary creep preceding dilative brittle failure are sensitive to stress while rates during compactive creep exhibit an insensitivity to stress indicative of the operation of crystal plasticity in agreement with elastic wave velocity evolution and microstructural observations

effects of strait mixing on ocean stratification the density distribution in the abyssal atlantic ocean suggests that mixing associated with overflows across deep sills may account for substantial amounts of deep mixing estimates of the strait mixing are made from published estimates of the overflows and the difference between antarctic bottom water densities across the vema channel and the romanche fracture zone to demonstrate that the strait mixing is an order of magnitude larger than the abyssal mixing estimated for a standard diffusivity of 1 times 10 ndash 4 m2 s ndash 1

the distribution of geothermal fields on the juan de fuca ridge near bottom water temperatures were mapped along 400 km of the strike of the juan de fuca ridge as part of a combined sea marc seabeam experiment to image the variability of morphology and structure along a spreading center segment the water temperature data collected by a continuously towed thermistor chain in addition to salinity data indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the cobb propagator and one field just to the north of the propagator on the endeavor ridge segment each thermal region is located above a morphological dome on the spreading center these domes are an average of 100 200 m shallower than the rest of the axis the structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0 06 sup 0 c up to 300 m above the bottom two simple models are used to estimate the heat flux associated with these features

hydrothermal manganese plumes in the mid atlantic ridge rift valley the concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor here we present vertical profiles of seawater manganese concentrations above the rift valley of the mid atlantic ridge mar the values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley these plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins differences between them suggest that there are at least five hydrothermal sources along this 1 700 km long section of mid ocean ridge

water column anomalies associated with hydrothermal activity in the guaymas basin gulf of california abstract sea floor hydrothermal activity in the guaymas basin gulf of california is quite different from that associated with ridge crest spreading centers injection of hydrothermal fluids occurs in the bottom of a semi enclosed basin and water column anomalies produced by this activity increase to much higher values than in the open ocean in the guaymas basin the hydrothermal venting generates large clouds of fine suspended particulate matter spm 100 300 m above active mounds and chimneys these hydrothermal clouds have potential temperature anomalies of about 0 010 0 020 c are enriched in dissolved silica particulate manganese and depleted in dissolved oxygen relative to areas away from the vents the particulate manganese values increase from about 3 nmol kg at 1000 m well above the enclosing topography of the subsill basin to 100 150 nmol kg in the clouds of spm and in the bottom nepheloid layer the particulate mn in the hydrothermal clouds appears to originate from both direct precipitation of dissolved mn2 injected by the vents and entrainment of mn rich spm in the rising hydrothermal plumes injection of silica rich vent fluids into the basin bottom waters produces a silica anomaly of 10 15 mol relative to the other deep basins of the gulf of california spillover of guaymas basin deep water produces a silica plume just above the basin sill depth which is detectable to the mouth of the gulf a simple two endmember mixing model indicates that the deep waters of the guaymas basin contain approximately 0 1 hydrothermal fluid oxygen anomalies associated with the hydrothermal clouds are on the order of 5 mol relative to regions away from active vents the basin as a whole shows a depletion in oxygen of about 13 mol relative to the other deep basins of the gulf the mixing model shows that this oxygen consumption can be explained by the oxidation of dissolved sulfide and methane injected by the hydrothermal vents box models of the deep basins of the southern gulf of california indicate that the guaymas basin has a significantly higher source term for dissolved silica and sink term for dissolved oxygen than the other basins the calculated flux of hydrothermal fluids into the guaymas basin is 10 12 m3 s

an integrated chemical and stable isotope model of the origin of midocean ridge hot spring systems chemical and isotopic changes accompanying seawater basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs incorporating provision for addition and subtraction of a wide range of reactant and product minerals as well as cation and oxygen and hydrogen isotopic exchange equilibria the models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100 to 350 c with an overall water rock ratio of about 0 5 being constrained by an assumed 18 o h 2o at 350 c of 2 0 per mil h craig personal communication 1984 this is a realistic model because 1 the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust 2 the water rock ratio is high 50 at low temperatures and low 0 5 at high temperatures and 3 it allows for back reaction of earlier formed minerals during the course of reaction progress the results closely match the major element chemistry von damm et al 1985 and isotopic compositions craig et al 1980 of the hydrothermal solutions presently emanating from vents at 21 n on the east pacific rise the calculated solution chemistry for example correctly predicts complete loss of mg and so 4 and substantial increases in si and fe however discrepancies exist in the predicted ph 5 5 versus 3 5 measured and state of saturation of the solution with respect to greenschist facies minerals the calculated d h 2o is 2 6 per mil in excellent agreement with analytical determinations the calculated chemical mineralogic and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges humphris and thompson 1978 stakes and o neil 1982 as well as with data from ophiolites gregory and taylor 1981 predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite epidote chlorite tremolite greenschist assemblage at 350 c the models demand that the major portion of the water rock interaction occur at temperatures of 300 350 c interaction at temperatures below approximately 250 c results in negative 18 o h 2o shifts contrary to the observed positive 18 o values of the fluids exiting at midocean ridge vents hydrogen isotope fractionation curves by suzuoki and epstein 1976 lambert and epstein 1980 and liu and epstein 1984 among others are compatible with the model and require d h 2o to increase at all temperatures as a result of seawater basalt interaction

temperature dependent viscoelastic compaction and compartmentalization in sedimentary basins the near surface compaction regime of most sedimentary basins is characterized by hydrostatic fluid pressures and is therefore determined entirely by sediment matrix rheology within this regime compaction is initially well described by a pseudoelastic rheological model with increasing depth precipitation dissolution processes lead to thermally activated viscous deformation the steady state porosity profile of the viscous regime is a function of two length scales the viscous e fold length related to the compaction activation energy and a scale determined by the remaining parameters of the sedimentary process overpressure development is weakly dependent on the second scale for activation energies 20 kj mol application of the steady state model to pannonian basin shales and sandstones indicates a dominant role for viscous compaction in these lithologies at porosities below 10 and 25 respectively activation energies and shear viscosities derived from the profiles are 20 40 kj mol and 1020 1021 pa s at 3 km depth the analytical formulation of the compaction model provides a simple method of predicting both the depth at which permeability limits compaction resulting in top seal formation and the amount of fluid trapped beneath the top seal fluid flow during hydraulically limited compaction is unstable such that sedimentation rate perturbations or devolatilization cause nucleation of porosity waves on the viscous e fold length scale 0 5 1 5 km the porosity waves are characterized by fluid overpressure with a hydrostatic fluid pressure gradient and propagate through creation of secondary porosity in response to the mean stress gradient the waves are a mechanism of episodic fluid expulsion that can be significantly more eycient than uniform darcyian fluid flow but upward wave propagation is constrained by the compaction front so that the waves evolve into essentially static domains of high porosity following cessation of sedimentation yielding mechanisms do not appreciably alter the time and length scale of episodic fluid flow because fluid expulsion is ultimately controlled by compaction the flow instabilities inherent in viscous compaction are similar to and a possible explanation for fluid compartments 2000 elsevier science b v all rights reserved

shear enhanced compaction during non linear viscous creep of porous calcite quartz aggregates abstract in this paper we extend the previous studies of semi brittle flow of synthetic calcite quartz aggregates to a range of temperatures and effective pressures where viscous creep occurs triaxial deformation experiments were performed on hot pressed calcite quartz aggregates containing 10 20 and 30 wt quartz at confining pressure of 300 mpa pore pressures of 50 290 mpa temperatures of 673 1073 k and strain rates of 3 0 10 5 s 8 3 10 5 s and 3 0 10 4 s starting porosity varied from 5 to 9 we made axial and volumetric strain measurements during the mechanical tests pore volume change was measured by monitoring the volume of pore fluid that flows out of or into the specimen at constant pore pressure yield stress increased with decreasing porosity and showed a dependence on effective pressure thus the yield stress versus effective pressure can be described as a yield surface with negative slope that expands with decreasing porosity and increasing strain hardening gradually approaching the envelope of strength at 10 strain which has a positive slope creep of porous rock can be modeled to first order as an isolated equivalent void in an incompressible nonlinear viscous matrix an incremental method is used to calculate the stress strain curve of the porous material under a constant external strain rate the numerical simulations reproduce general trends of the deformation behavior of the porous rock such as the yield stress decreasing with increasing effective pressure and significant strain hardening at high effective pressure the drop of yield stress with increasing porosity is modeled well and so is the volumetric strain rate which increases with increasing porosity

a mid ocean ridge thermal model constraints on the volume of axial hydrothermal heat flux the depth to the axial magma chamber at three oceanic spreading centers as indicated by seismic reflection surveys is greater than that predicted by conductive cooling thermal models of ridge crests the additional cooling at the ridge axis is owed to the circulation of seawater through the shallow crust a theoretical model for the temperature distribution at spreading centers which includes distributed heat sources and sinks is presented by representing the hydrothermal heat loss as a series of heat sinks the depths to the axial magma chamber at the east pacific rise at latitude 9 n the southern juan de fuca ridge and the lau basin spreading center are modeled heat sinks are added to the input model to increase the solidus depth until the computed magma chamber depth matches the magma chamber depth determined by seismic reflection surveys the thermal modeling indicates that the axial hydrothermal heat flux is between 7 1 106 and 13 8 106 mj m2 or 10 to 20 of the total missing heat at the ridge axis requiring extensive low temperature circulation off axis high temperature vents that are spaced 1 km apart and are active between 4 and 10 of the time would account for the axial hydrothermal heat loss

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

permeability and storativity of binary mixtures of high and low permeability materials 1 as a first step toward determining the mixing laws for the transport properties of rocks we prepared binary mixtures of high and low permeability materials by isostatically hot pressing mixtures of fine powders of calcite and quartz the resulting rocks were marbles containing varying concentrations of dispersed quartz grains pores were present throughout the rock but the largest ones were preferentially associated with the quartz particles leading us to characterize the material as being composed of two phases one with high permeability and the second with low permeability we measured the permeability and storativity of these materials using the oscillating flow technique while systematically varying the effective pressure and the period and amplitude of the input fluid oscillation control measurements performed using the steady state flow and pulse decay techniques agreed well with the oscillating flow tests the hydraulic properties of the marbles were highly sensitive to the volume fraction of the high permeability phase directly related to the quartz content below a critical quartz content slightly less than 20 wt the high permeability volume elements were disconnected and the overall permeability was low above the critical quartz content the high permeability volume elements formed throughgoing paths and permeability increased sharply we numerically simulated fluid flow through binary materials and found that permeability approximately obeys a percolation based mixing law consistent with the measured permeability of the calcite quartz aggregates

evolution of dilatancy and permeability in rock salt during hydrostatic compaction and triaxial deformation combined gas permeability and p and s wave velocity measurements were carried out on rock salt samples from the gorleben salt dome and the morsleben salt mine under hydrostatic and triaxial loading condions mostly at room temperature permeabilities in the as received samples vary between 10 16 and 2x10 20 m 2 the initial permeability is primarily due to decompaction induced by drilling core retrieval and sample preparation hydrostatic loading gives rise to a marked decrease of permeability and a coeval significant increase of p and s wave velocities due to progressive closure of grain boundary cracks tending to approach the in situ matrix permeability 18 mpa differential stress at 10 mpa confining pressure to similar to 30 mpa at confining pressures above similar to 70 mpa dilatancy is due to the opening of grain boundary and 100 cleavage cracks and depends on the applied confining pressure the orientation of the open cracks is primarily controlled by the loading geometry system compression extension as a consequence permeability increases dramatically with progressive dilatancy followed by a period of plus minus constant permeability during strain hardening up to 10 axial strain or even more this suggests that the evolution of permeability is not only a function of dilatancy but also of microcrack linkage importantly the anisotropic crack array within the samples causes a strong directional dependence of permeability

permeability evolution of sandstone under short term and long term triaxial compression abstract permeability of sandstone under increasing deviatoric stress both in short term and creep compression condition are measured with pulse transient technique based on the experimental results of short term triaxial compression coupled with gas permeation the influence of confining stress on the strength and failure mode of sandstone specimen are analyzed the results show that the variation patterns of permeability under different confining stresses are similar and the pressure differential has little influence on the mechanical behavior of sandstone the crack volumetric strain is also calculated and a linear relationship between the crack volumetric strain and permeability of sandstone specimen can be concluded according to the creep test results with various loading procedures and different permeation fluids the permeability evolution of sandstone is characterized as having four stages according with the typical deformation stages in a monotonic loading creep test the failure strength of sandstone specimen under cyclic loading creep is lower and the system of cracks is more complicated than that under multi stage loading creep with the same confining stress and permeation pressure

evidence of an effect of heat flux from the east pacific rise upon the characteristics of the mid depth waters on an isopycnal surface that lies at mid depth in the south pacific ocean there is a zone of high temperature near 10 s 20 s heat flux into the water from the crest of the east pacific rise and westward flow of the heated water may account for this temperature pattern

p t x effects on equilibrium carbonate h 2 o co 2 nacl dihedral angles constraints on carbonate permeability and the role of deformation during fluid infiltration fluid solid solid dihedral angles in the nacl h2o co2 calcite dolomite magnesite system have been determined at pressures ranging from 0 5 to 7 kbar and temperatures from 450 c to 750 c at 1 kbar and 650 c both dolomite and magnesite exhibit a dihedral angle minimum for intermediate h2o co2 fluids similar to that previously determined by the present authors for calcite but the depth of the minimum is smaller being above the critical value of 60 for both dolomite and magnesite for all fluid compositions calcite calcite brine dihedral angles at 650 c have been determined in the pressure range 1 5 kbar angles decrease with increasing salt content of the fluid tending towards a constant value of about 65 for strong brines at pressures above 2 kbar there is a general increase of angle with increasing pressure which is most marked for strong brines a positive correlation of angle with pressure is also observed in calcite h2o co2 fluids the position of the minimum moving towards higher angles and towards h2o rich fluids with increasing pressure the permeability window previously observed by the present authors at 1 kbar and intermediate fluid compositions closes at about 1 5 kbar the results demonstrate that the permeability of carbonates to grain edge fluid flow is only possible at low pressures and for fluids of restricted h2o co2 nacl compositions however geochemical evidence from metamorphic terrains suggests that pervasive infiltration does occur under conditions where impermeability is predicted from examination of published studies of infiltrated carbonates we conclude that deformation plays a critical role in enhancing carbonate permeability possible mechanisms for this include shear enhanced dilatancy micro cracking fluid inclusion drag by deformation controlled grain boundary migration and dynamically maintained transient grain boundary fluid films

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

gas permeability evolution of cataclasite and fault gouge in triaxial compression and implications for changes in fault zone permeability structure through the earthquake cycle abstract we report the results of permeability measurements of fault gouge and tonalitic cataclasite from the fault zone of the median tectonic line ohshika central japan carried out during triaxial compression tests the experiments revealed marked effects of deformation on the permeability of the specimens permeability of fault gouge decreases rapidly by about two orders of magnitude during initial loading and continues to decrease slowly during further inelastic deformation the drop in permeability during initial loading is much smaller for cataclasite than for gouge followed by abrupt increase upon failure and the overall change in permeability correlates well with change in volumetric strain i e initial nearly elastic contraction followed by dilatancy upon the initiation of inelastic deformation towards specimen failure if cemented cataclasite suffers deformation prior to or during an earthquake a cataclasite zone may change into a conduit for fluid flow fault gouge zones however are unlikely to switch to very permeable zones upon the initiation of fault slip thus overall permeability structure of a fault may change abruptly prior to or during earthquakes and during the interseismic period fault gouge and cataclasite have internal angles of friction of about 36 and 45 respectively as is typical for brittle rocks

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

permeability evolution during non linear viscous creep of calcite rocks permeability storage capacity and volumetric strain were measured in situ during deformation of hot pressed calcite aggregates containing 10 20 and 30 wt quartz both isostatic and conventional triaxial loading conditions were used the tests were performed at confining pressure of 300 mpa pore pressures between 50 to 290 mpa temperatures from 673 to 873 k and strain rates of 3 10 5 s 1 argon gas was used as the pore fluid the initial porosities of the starting samples varied from 5 to 9 with higher porosity correlated to higher quartz content microstructural observations after the experiment indicate two kinds of pores are present 1 angular crack like pores along boundaries between quartz grains or between quartz and calcite grains and 2 equant and tubular voids within the calcite matrix under isostatic loading conditions the compaction rate covaries with porosity and increases with increasing effective pressure most of the permeability reduction induced during compaction is irreversible and probably owes to plastic processes as has been found in previous studies on hot pressed calcite aggregates permeability k is nonlinearly related to porosity o over small changes in porosity the two parameters are approximately related as k mathbf alpha mathbf phi n the exponent n strongly increases as porosity decreases to a finite value from about 4 to 6 depending on quartz content suggesting a porosity percolation threshold when subjected to triaxial deformation the calcite quartz aggregates exhibit shearenhanced compaction but permeability does not decrease as rapidly as it does under isostatic conditions during triaxial compaction the exponent n only varies between 2 and 3 non isostatic deformation seems to reduce the percolation threshold and in fact enhances the permeability relative to that at the same porosity during isostatic compaction our data provide constraints on the governing parameters of the compaction theory which describes fluid flow through a viscous matrix and may have important implications for expulsion of sedimentary fluids for fluid flow during deformation and metamorphism and melt extraction from partially molten rocks

mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20 600 c implications for natural faults in limestones we report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures t within the range from 20 to 600 c the experiments were performed wet using pore fluid pressures pf of 10 pf 60 mpa one series of experiments employed a constant effective normal stress neff of 50 mpa while in a second series neff was sequentially stepped from 30 to 100 mpa in all experiments sliding velocity v was stepped in the range from 0 03 to 100 m s the results showed stable velocity strengthening behavior at 20 c but velocity weakening at 100 to 550 c for all v steps to 3 m s which was frequently accompanied by stick slip at 600 c velocity strengthening occurred microstructural observations suggest increasing importance of ductile deformation with increasing temperature as reflected by a localized shear band structure at 20 c giving way to a pervasive shear plane parallel grain shape fabric at 600 c using existing flow equations for dense calcite polycrystals we show that dislocation and or diffusion creep of 10 30 m sized bulk gouge grains likely played a role in experiments performed at t 400 c we suggest that the observed velocity weakening behavior can be explained by a slip mechanism involving dilatant granular flow in competition with creep controlled compaction our results have important implications for the breadth of the seismogenic zone in limestone terrains and for the interpretation of natural fault rock microstructures specifically while samples sheared at 400 550 c exhibited essentially brittle frictional mechanical behavior stick slip the corresponding microstructures resembled that of a mylonite

the limitations of accurate thin film x ray fluorescence analysis of natural particulate matter problems and solutions abstract the limitations of thin film x ray fluorescence xrf analysis of natural particulate matter have been re examined theoretically and experimentally the degree to which elemental signal intensity is absorbed by the sample matrix far exceeds that which has been assumed in most previous field studies by means of a simplified theoretical model the magnitude of absorption effects is predicted for various elements in a variety of natural matrices the non specialist may quantify potential analytical artefacts by means of the tables graphs and equations presented here relatively simple formulae have been derived by which absorption phenomena may be calculated and corrected for even in samples characterised by a wide range of particle sizes multimodal size distributions and chemical inhomogeneity as a function of particle size the applicability of these formulae to the enhanced accuracy of coastal particulate matter analyses is discussed meaningful analyses of filtered particulate samples by xrf procedures are quite feasible the limitations of the technique however are finite and must be considered in detail matrix absorption effects although modified by various physical parameters are of sufficient magnitude to render the term thin film inappropriate to the analysis of natural particulates

active hydrothermal vents and sulfide deposits on the southern juan de fuca ridge massive sulfide deposits rich in zinc and silver were recovered from the juan de fuca ridge 500 km west of oregon in september 1981 the samples recovered are composed largely of zinc sulfide with lesser amounts of iron lead and copper sulfide most of the deposits occur at a series of hydrothermal vents within a relatively continuous depression in the center of a smooth 1 km wide valley along the ridge axis the depression appears to be formed by collapse of a lava lake possibly modified by extensional faulting the axial valley floor outside the depression is underlain by fresh glassy ferrobasalt sheet and lobate flows two types of sulfide mineral deposits were dredged from one of the hydrothermal vents 1 angular slabs of dark gray zinc sulfide and 2 subrounded fragments of porous light gray zinc sulfide the samples contain fresh sphalerite zoned wurtzite pyrite and minor amounts of marcasite galena and chalcopyrite cubanite the spreading rate of the juan de fuca ridge and the composition of the sulfide samples are generally similar to the east pacific rise lat 21 n site however the texture and geologic setting of the sulfide deposits are significantly different

correlation of microseismic and chemical properties of brittle deformation in locharbriggs sandstone constant stress rate loading the exit pore fluid was analyzed after the tests for the concentration of dissolved ions and acoustic emission was monitored in real time throughout the tests the exit pore fluid silica concentration and microcrack damage derived from the acoustic emission ae data both exhibited an exponential increase during the strain hardening phase of deformation damage parameters inferred from the ae data predict the stress strain curves adequately or at least up to the point of strong microcrack coalescence the damage parameters and silica signal were strongly correlated by a power law relationship the observed environment and strain rate dependence of mechanical properties can hence be attributed uniquely to time dependent crack growth by the stress corrosion mechanism index terms 1045 geochemistry low temperature geochemistry 5102 physical properties of rocks acoustic properties 5104 physical properties of rocks fracture and flow keywords stress corrosion acoustic emission silica dissolution subcritical crack growth deformation rate brittle fracture citation ojala i o b t ngwenya i g main and s c elphick correlation of microseismic and chemical properties of brittle deformation in locharbriggs sandstone j geophys res 108 b5 2268 doi 10 1029 2002jb002277 2003

microcrack growth and healing in deformed calcite aggregates abstract modelling of fluid flow in the earth s crust depends on our understanding of the physical processes responsible for porosity production and porosity reduction this study concerns the role of thermally activated processes on the evolution of porosity and permeability in rock samples containing microcracks experimentally deformed carrara marble and a synthetic marble were heat treated at effective pressures of 50 and 150 mpa and temperatures up to 923 k with argon as pore fluid in situ measurements of the connected porosity and the permeability during heat treatment indicate a complicated evolution of porosity and permeability during heating up to 600 700 k the porosity changes very slowly with increase in temperature and time decreasing by 0 01 0 02 while the permeability increases by an order of magnitude at higher temperatures the porosity reduction rate accelerates and both the connected porosity and the permeability decrease with increasing temperature and time the permeability is proportional to the cube of the connected porosity microstructural changes during heat treatment of carrara marble include a the replacement of the finely crushed fragments within the intergranular damage zones by rounded or polyhedral grains 5 20 m in diameter and b the partial to complete healing of twin boundary cracks and tips sub branches of transgranular cracks in the finer grain size synthetic marble heat treatment blunts the tips of grain boundary cracks partial healing of grain boundary cracks is associated with the formation of ridge channel structures on many grain interfaces the evolution of porosity permeability and microstructure points to the roles of thermal cracking plastic compaction and diffusional crack healing in controlling fluid transport properties of cracked rocks at elevated temperature significantly the porosity permeability relationships during isostatic crack healing are very different from those associated with crack growth during deformation

dehydration induced porosity waves and episodic tremor and slip episodic tremor and slip ets along the subduction interface takes place where there is abundant evidence for elevated near lithostatic pore pressures at sufficiently great depths 30 45 km that chemical dehydration reactions must act as their dominant source we simulate fluid and heat flow while tracking the location of a vertically oriented one dimensional column of material as it subducts through the slow slip and tremor zone the material in the column is transformed through a pressure dependent and temperature dependent dehydration reaction that we describe with a generalized nonlinear kinetic rate law column deformation is largely dominated by viscous creep with a closure rate that depends linearly on porosity this behavior causes the dehydration reaction to generate traveling porosity waves that transport increased fluid pressures within the slow slip region to explore the possibility that the observed periodicity of slow slip and tremor in subduction zones can be explained by the migration of such porosity waves we derive a dispersion relation that accurately describes our numerical results we also obtain an expression for how the thickness of the dehydrating layer is expected to vary as a function of the parameters in the reaction rate law although the amplitudes of pore pressure perturbations rival those that are produced by known external forcings e g tides or passing surface waves our analysis suggests that given reasonable estimates of rock viscosity permeabilities in the range 6 5 10 15 to 5 10 10 m2 are required for porosity wave trains to form at periods comparable to those of slow slip and tremor

hydrothermal particle plumes over the southern juan de fuca ridge hydrothermal particles originate in buoyant plumes emanating from seafloor thermal vents1 4 and accumulate as metalliferous sediments found along oceanic spreading centres5 7 observational evidence of the transport pathway of hydrothermal particles is scarce however and the structure extent and particle concentrations of hydrothermal plumes remain largely conjectural to evaluate the potential of hydrothermal plumes as particle transport agents we mapped their distribution along and across the 80 100 m deep axial valley of the southern juan de fuca ridge in the north east pacific ocean 44 30 n 130 w an area of known hydrothermal activity8 11 continuous light scattering measurements reported here defined numerous particle plumes centred 30 120 m above bottom m a b elemental analysis of the plume particles and the theta potential temperature s salinity signatures of the plume water verified their hydrothermal origin concentrations of hydrothermal particles remained elevated at ridge crest depths at least 100 km from the ridge indicating distant off axis dispersal of hydrothermal emissions

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

measurements of plume flow from a hydrothermal vent field simultaneous velocity temperature and conductivity data were taken in the convective flow emanating from a hydrothermal vent field located at 10 56 n 103 41 w on the east pacific rise the horizontal profiles obtained indicate that the flow field approaches an ideal plume in the temperature and velocity distribution such parameters as total heat flow and maximum plume height can be estimated using either the velocity or the temperature information the results of these independent calculations are in close agreement yielding a total heat flow from this vent site of 3 7 0 8 mw and a maximum height of 150 10 m the nonlinear effects of large temperature variations on heat capacity and volume changes slightly alter the calculations applied to obtain these values

a major helium 3 source at 15 s on the east pacific rise an extensive plume of water enriched with helium 3 has been discovered in the deep pacific ocean at latitude 15 s on the east pacific rise in the core of the plume at a depth of 2500 meters over the ridge crest the helium 3 helium 4 ratio is 50 percent higher than the ratio in atmospheric helium indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems the helium 3 plume is completely absent east of the rise but it can be traced over 2000 kilometers to the west above a newly observed physical feature a density discontinuity here caled the ridge crest front the injected plume provides a unique deep sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west the striking intensity and lateral extent of this helium 3 anomaly compared to observations at known oceanic hydrohrmal sites suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 s on the east pacific rise

the compaction of igneous and sedimentary rocks in many problems of interest to geology and soil mechanics a fluid moves through a solid matrix which is also being deformed in most cases of interest the effective viscosity of the matrix is many orders of magnitude greater than that of the percolating fluid and both form interconnected networks in three dimensions the partial differential equations governing such behaviour can now be obtained and a variety of simple model problems have been investigated some of the more surprising solutions contain solitary waves and compaction fronts some of the less exotic solutions are presently of more geological interest the mobility of volatile rich melts at melt fractions as small as 0 1 has important consequences for trace element geochemistry the geometry of layered intrusives appears to result from differential compaction of the crystal mush and the rates required can be used to estimate a viscosity of 3 x 10 18 pa s for an olivine matrix this value agrees excellently with laboratory experiments when proper account is taken of the grain size dependence compaction in sedimentary rocks results in overpressure when the porosity becomes sufficiently small and can also lead to the development of secondary porosity