the effects of rupture and diffusion on the salinity of fault related fluid inclusions abstract the combined effects of fault rupture and diffusive transport on the salinity of fault related fluids are addressed in the case of both an external solute source and that of rock buffered fluid compositions the effects of injection of a dilute and a saline fluid into a fault zone followed by diffusion are examined in the case of both periodic and random fault rupture events the models reproduce the large salinity variations characteristic of fault related secondary fluid inclusions and suggest that correlation of salinity variations may allow reconstruction of rupture events in the case of rock buffered fluid compositions the hydration of periclase to form brucite is used as a simple petrological model for increasing salinity in fault zones an episodic hydration reaction both with and without dilution effects is capable of increasing the salinity of small volumes of fluid along microfractures and also of producing large salinity variations these considerations suggest that large salinity variations and high fluid concentrations common in secondary fluid inclusions associated with retrograde shear zones may be due to the combined effects of diffusion and rock buffering reactions in the fault zone the concentration spikes produced during rupture are damped by diffusion with increasing distance from the site of rupture concentration peaks and troughs coincide in time at different distances from the source suggesting the possibility of correlating salinity variations in the vicinity of a fault zone

petrology and shock metamorphism of pampa del infierno chondrite abstract pampa del infierno an l6 chondrite displays strong evidence of impact metamorphism rare chondrules and two types of dark colored clasts occur in a light colored matrix granular clasts are similar in mineralogy and chemistry to the host meteorite but display shock metamorphic features produced mainly by deformation such as mosaicism undulatory extinction and fracturing partial melting in the granular clasts is manifested by the presence of selvages of mafic glass with troilite iron eutectic intergrowths around remnants of low ca pyroxene and plagioclase glass with skeletal poikilitic inclusions of olivine clasts with spinifex texture are believed to have crystallized from a supercooled impact generated ultramafic melt of the host chondrite or a chondritic source of similar composition the light colored matrix mainly displays evidence of shock metamorphism under subsolidus conditions as manifested by kinking and deformation twinning in pyroxene high pressure phase transitions of olivine and low ca pyroxene to ringwoodite and majorite respectively and lineation that still preserves the deformation features in the different mineral phases pertinent shock wave data used to interpret the metamorphic history of the pampa del infierno chondrite suggest metamorphism by impact at a minimum peak pressure greater than 300 kbar

development of a shear flow test apparatus and determination of coupled properties for a single rock joint abstract a new laboratory technique for coupled shear flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints this technique was used to carry out coupled shear flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm the hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law the shear flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint the hydraulic conductivity increases rapidly by about 1 2 1 6 orders of magnitude for the first 5 mm of shear displacement after passing the residual shear stress the hydraulic conductivity becomes gradually a constant value with increasing shear displacement on the other hand the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing shear flow coupling characteristics obtained from these tests have a consistent trend with barton s model prediction during the initial shear process however increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement

sediment dispersal in the argentine basin evidence from visible light spectra abstract visible light reflectance spectra were determined for each of 236 core top samples from the argentine basin and surrounding areas the spectra were analyzed by taking the first derivative of the raw spectral curves and factor analyzing the first derivative values using wavelengths as variables we used a four factor solution that explains about 90 of the cumulative variance factors were evaluated by comparing factor loadings to first derivative curves from known minerals and mineral combinations by the mapped distributions of the factor scores and by comparison to factors from other areas the four factors represent in order of decreasing variance goethite terrigenous vs pelagic sedimentation organic matter and chlorite the goethite and chlorite factors are useful for interpreting sediment influx and dispersal goethitecomes from the falkland plateau and the argentine continental margin once introduce to the deep ocean goethite appears to be transported primarily by isobath parallel currents chlorite on the other hand is transported into the argentine basin by antarctic bottom water aabw and from the falkland plateau however along the falkland plateau chlorite is transported normal to the slope probably by gravitational processes

organic walled microfossils and geochemical tracers sedimentary indicators of productivity changes in the north water and northern baffin bay during the last centuries analyses performed on 26 surface sediment samples collected with a box corer at 17 stations throughout the north water and northern baffin bay 75 791n 68 801w revealed abundantorganic walled microfossils most ly dinoflagellate cysts 10 3 10 4 cysts g 1 and organic linings of benthic foraminifers 10 2 10 3 ol g 1 as well as high organic carbon concentrations 0 87 2 81 dry weight these data indicate high productivity in both the pelagic and benthic environments of the north water and slightly lower productivity in northern baffin bay the data also showed calcium carbonate and biogenic silica dissolution throughout the study area the dinocyst assemblages were relatively uniform in the north water and dominated by heterotrophic taxa algidasphaeridium minutum and brigantedinium spp whereas northern baffin bay assemblages were dominated by autotrophic taxa notably operculodinium centrocarpum and spiniferites elongatus the difference between these two assemblages may be related to higher diatomaceous primary production in the north water than in northern baffin bay since diatoms constitute the principal food source of heterotrophic dinoflagellates the biogeographical boundary between the north water and northern baffin bay has been maintained for at least the last few centuries as shown by analyses of microfossils and geochemical tracers in two sediment cores one taken in the southeastern part of the north water 76117 0 n 72102 0 w and the other in northeastern baffin bay 75135 0 n 70148 0 w the analyses of the north water core revealed relatively uniform microfossil assemblages and organic carbon fluxes ranging from 1 1 to 1 5 mg corg cm 2 yr 1 for the last few centuries which corresponded to 4 6 of the present annual primary production in the euphotic zone these data suggest high productivity and relatively stable conditions in the polynya on a decadal time scale in the northeastern baffin bay core the analyses indicated generally lower organic carbon fluxes ranging from 0 3 to 0 6 mg corg cm 2 yr 1 and from the microfossil data significant variations in sea surface conditions at this lower latitude over the last centuries r 2002 elsevier science ltd all rights reserved

importance of stress effects on inputs to fracture network models used for subsurface flow and transport studies importance of stress effects on inputs to fracture network models used for subsurface flow and transport studies

hydromechanical behavior of a deformable rock fracture subject to normal stress lbl 12297 preprint to be published in the journal of geophysical research hydromechanical behavior of a deformable rock fracture subject to normal stress y w tsang and p a witherspoon january 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info diu is ion ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

elastic wave velocities of forsterite and its β spinel form and chemical boundary hypothesis for the 410 km discontinuity a method for measuring elastic wave velocities at pressures up to 15 gpa has been developed velocities of forsterite and spinel were measured using a piston cylinder apparatus with a pulse echo overlap method for pressures up to 4 gpa and using a split sphere apparatus with a pulse transmission technique for higher pressures to validate the results volume compression incompressibility and rigidity were estimated from measured travel times and comparison was made between the present estimates and data from x ray brillouin and acoustic measurements the v p and k values for spinet are 3 and 8 higher than previous measurements at 10 gpa respectively velocity jumps in v p and v s due to olivine to spinel transition were about 1 34 and 0 80 km s 1 respectively very different from seismological observations of velocity jumps at the 410 km discontinuity which were concentrated around 0 45 km s 1 for the p wave and 0 22 km s 1 for the s wave velocity jumps in mantle peridotite were calculated using the experimental results and comparison was made between these estimates and seismological observations at the 410 km discontinuity the evidence does not support the phase change hypothesis and a chemical boundary was proposed as the origin of the 410 km discontinuity an eclogitic mineral assemblage might be an alternative for the composition of the transition layer

ultrahigh pressure phase relations in the system mg4si4o12mg3al2si3o12 high pressure phase relations in the system mg4si4o12 mg3al2si3o12 were investigated at pressures from 10 to 22 gpa and at a temperature of 1000 c the experimental results indicate that the maximum solubility of enstatite mg4si4o12 in pyrope mg3al2si3o12 is 80 mol enstatite at 15 gpa at pressures between 15 and 19 gpa the solubility is insensitive to pressure at 19 gpa garnet ilmenite transformation first occurs in enstatite composition at pressures above 19 gpa the compositional range of the ilmenite solid solution expands toward pyrope composition with increasing pressure based on the present experiments if pyrolite mantle is assumed the pyroxene garnet transformation appears at 350 400 km depth and garnet modified spinel and garnet spinel phase assemblages become stable successively up to 580 km depth at greater depths garnet decomposes to ilmenite garnet and hence the pyrolite mantle consists of ilmenite garnet spinel assemblage

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

formation of compound strike slip fault zones mount abbot quadrangle california abstract numerous strike slip fault zones in granitic rocks of the mount abbot quadrangle california developed from steeply dipping subparallel joints these joints generally were less than 50 m long and were spaced several centimeters to several meters apart some joints subsequently slipped and became small faults simple fault zones formed as oblique dilatant fractures splay fractures linked non coplanar faults side to side and end to end these simple fault zones are as much as 1 km long and accommodated displacements as great as 10 m compound fault zones formed as splay fractures linked small faults and simple fault zones they are as much as several kilometers long and accommodated displacements as great as 100 m these zones are distinctly different from riedel shear zones and the mechanics of their formation are unlikely to be described well by mohr coulomb mechanisms simple and compound fault zones are composed of non coplanar segments that join at steps or bends splay fracture length determines step widths the longest splay fractures occur along the longest fault zones allowing step widths to increase as the length and displacement across the zones increase these findings are consistent with the structure of some active seismogenic faults and they provide a mechanically consistent field based conceptual model for fault zones that grow in basement rocks from a preexisting set of joints

the plio pleistocene glaciation of the barents sea svalbard region a new model based on revised chronostratigraphy based on a revised chronostratigraphy and compilation of borehole data from the barents sea continental margin a coherent glaciation model is proposed for the barents sea ice sheet over the past 3 5 million years ma three phases of ice growth are suggested 1 the initial build up phase covering mountainous regions and reaching the coastline shelf edge in the northern barents sea during short term glacial intensification is concomitant with the onset of the northern hemisphere glaciation 3 6 2 4 ma 2 a transitional growth phase 2 4 1 0 ma during which the ice sheet expanded towards the southern barents sea and reached the northwestern kara sea this is inferred from step wise decrease of siberian river supplied smectite rich sediments likely caused by ice sheet blockade and possibly reduced sea ice formation in the kara sea as well as glacigenic wedge growth along the northwestern barents sea margin hampering entrainment and transport of sea ice sediments to the arctic atlantic gateway 3 finally large scale glaciation in the barents sea occurred after 1 ma with repeated advances to the shelf edge the timing is inferred from ice grounding on the yermak plateau at about 0 95 ma and higher frequencies of gravity driven mass movements along the western barents sea margin associated with expansive glacial growth

climatic dependence of the organic matter contributions in the north eastern norwegian sea over the last 15 000 years abstract lipids are used for the evaluation of the different organic matter contributions in the north eastern norwegian sea m23258 site 75 n 14 e over the last 15 000 years development of a mass balance model based on the down core quantification of the c 37 alkenones the odd carbon numbered n alkanes a odd and the unresolved complex mixture of hydrocarbons ucm has allowed three main organic matter inputs involving marine continental and ancient reworked organic matter to be recognized the model shows good agreement between measured and reconstructed toc values similarly a strong parallelism is observed between predicted components such as marine toc and carbonate content which was determined independently representation of the model results within a time scale based on 15 ams 14 c measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15 000 years thus the predominance of reworked organic matter is characteristic of termination ia up to 70 continental organic matter was dominant during the bolling allerod b a and younger dryas yd periods about 85 and a strong increase of marine organic matter occurred in the holocene between 50 and 75 this agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka ice rafted detritus from the barents continental platform ice melting waters from the arctic fluvial system discharging into the barents sea and dominance of north atlantic currents respectively in this respect the high resolution down core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the barents ice sheet at the end of the deglaciation period termination ib

a 20 ma pollen record of east asian summer monsoon evolution from guyuan ningxia china abstract pollen analysis was conducted on the fluviolacustrine sediments from the east side of the liupan mountains a relatively monsoon sensitive region and provided for the first time a continuous evolutionary history of vegetation and climate in east china during the neogene the pollen record spanning the last 20 ma indicates that the vegetation and thus east asian summer monsoon evolution can be divided into three stages 20 13 14 25 ma 14 25 11 35 ma and 11 35 0 08 ma in spite of general dominance of steppe throughout the neogene during the period 20 13 14 25 ma the pollen assemblage was characterized by high abundance of artemisia and small amounts of temperate to subtropical deciduous broad leafed trees such as juglans carya quercus and betula suggesting that the east asian summer monsoon was generally strong the interval from 14 25 to 11 35 ma was marked by a significant decline in the east asian summer monsoon as indicated by artemisia gradually replaced by humulus and halophytic chenopodiaceae nitraria and ephedra also reached high values in this period since 11 35 ma ago percentages of halophytes dominated by chenopodiaceae and tamaricaceae maintained a high mean value of about 40 revealing a weak intensity of east asian summer monsoon the general weakening of the monsoon circulation during the neogene and the significant monsoon decline during the late middle miocene in particular might link with the global cooling trend probably through two mechanisms cooling and ice sheet expansion over the polar region caused an increase in meridional temperature gradients leading to the southward retreat of the monsoon circulation the global cooling may have also reduced the amount of water vapor held in the atmosphere and led to both additional cooling and further weakening of the east asian summer monsoon the cause for a short lived resumption during the period 1 0 0 8 ma is under investigation

modelling storage behaviour in a fractured rock mass abstract a transient model was used to represent single borehole injection tests in fractured rock masses on the basis of a three dimensional stochastic description of the fracture network and of the mechanical behaviour of the fractures the rock matrix remains impervious and storage occurs in the fractures with a nonlinear compliance effect depending on both fluid pressure and normal closure stress acting on the joints the aim of the study is to show how the shortest weakly connected joints can be removed and replaced in the system by an equivalent parameter these efforts can save computer time or enlarge the modelled rock volume moreover this approach may be helpful in addressing the troublesome up scaling problem in discontinuous media

hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses the experiments consist of hydraulic loading unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes hydromechanical response of the reservoir was measured using six pressure normal displacement sensors located on discontinuities and two surface tiltmeters a dual hydraulic behavior was characterized for low permeability bedding planes well connected to highpermeability faults displacement responses show high variability nonlinear changes sometimes with high frequency oscillations and a large scattering of magnitudes initial normal stiffnesses and effective normal stresses along fault planes were estimated in the field by interpreting pressure normal displacement relations with a nonlinear function between effective normal stress and normal displacement two dimensional discontinuum modeling with transient fluid flow was performed to fit measurements during hydraulic loading tests results show that the hydromechanical behavior of the reservoir is restored if a high stiffness contrast is allocated between low and high permeability discontinuities thus a dual permeability network of discontinuities will likely also be a contrasting stiffness network in which the deformation of major flow conducting discontinuities is significantly influenced by the stiffness of the surrounding less permeable discontinuities

single crystal elasticity of iron bearing majorite to 26 gpa implications for seismic velocity structure of the mantle transition zone abstract single crystal elastic moduli of synthetic iron bearing majoritic garnet were measured using brillouin spectroscopy up to a pressure of 26 gpa we found that the iron bearing majoritic garnet mg 0 79 fe 0 08 al 0 30 si 0 84 o 3 remains elastically isotropic throughout the pressure range of this study the shear and adiabatic bulk moduli and their pressure derivatives at zero pressure were determined to be 0 88 7 7 gpa k s0 166 2 gpa p 0 1 28 8 k p 0 4 2 2 these values are almost indistinguishable within the experimental uncertainties from those obtained in previous studies of pure mgsio 3 majorite and other solid solutions of the majorite pyrope join our direct acoustic velocity measurements of iron bearing majorite indicate that the incorporation of iron into majoritic garnet does not drastically affect its elastic moduli and their pressure derivatives the measured pressure derivatives of iron bearing majorite are about 3 6 times lower than required to account for the high seismic velocity gradients observed in the mantle transition zone

garnet and pyroxenes in the mantle a test of the majorite fractionation hypothesis experimental data are reported for the compositions of garnets and pyroxenes that coexist with liquid in the system cao mgo al2o3 sio2 cmas at 80 160 kbar all experiments were run using the uniaxial split sphere apparatus at stony brook our data have permitted a refinement of gasparik s 1990a thermodynamic analysis of garnets and pyroxenes that occur at arid below the solidus our results should provide precise estimates of the temperature pressure conditions at which peridotite and garnet xenoliths equilibrated in the mantle an examination is also made of the composition of garnet that crystallizes as a liquidus phase it is demonstrated to be a function of both composition and pressure pressure has the effect of changing the composition of garnet from pyropic at around 80 kilobars to pyroxene like majorite at pressures in excess of 140 kbar changes that mirror those seen for garnets in the subsolidus failure to consider the effects of pressure on the composition of liquidus garnet can result in an erroneous test of the hypothesis that garnet fractionation occurred in early earth history it is shown that primitive mantle peridotite could have formed as a liquid by 35 majorite garnet fractionation from a cv chondrite like allende at 200 260 kbar these results support the hypothesis that extensive or possibly total melting occurred during the growth of the earth by accretion of planetesimals e g davies 1985 abe and matsui 1985 stevenson 1987 wetherill 1990 and that majorite fractionation could have occurred during this time ohtani and sawamoto 1987 removal of majorite to the lower mantle during the crystallization of a magma ocean is a successful way of explaining differences in mgo sio2 and cao al2o3 between mantle peridotite and chondrite

akimotoite mg fe sio3 a new silicate mineral of the ilmenite group in the tenham chondrite akimotoite mg fe sio 3 a new silicate mineral of the ilmenite group was found in the shock metamorphosed tenham chondrite it occurs as aggregates adjacent to clinoenstatite in fragments within shock induced melt veins chemical analyses show the simplified formula to be mg sub 0 79 fe sub 0 21 sio 3 the same as for clinoenstatite selected area electron diffraction saed patterns correspond to the synthetic mg fe sio 3 ilmenite phase with space group r3 lattice parameters derived from saed patterns are a 0 478 5 nm c 1 36 1 nm and v 0 269 8 nm 3 in the hexagonal setting the calculated density is 4 0 1 g cm 3 akimotoite in this occurrence is thought to have been transformed from original orthoenstatite in a solid state reaction produced by a shock event peak pressure and temperature generated by shock events in tenham are estimated to be 22 gpa max max 2000 degrees c assuming that equilibrium crystallization of aluminous majorite occurred in the melt veins this new mineral was named after syun iti akimoto

numerical simulation of shear induced flow anisotropy and scale dependent aperture and transmissivity evolution of rock fracture replicas fluid flow anisotropy in a single rock fracture during a shear process is an important issue in rock mechanics and is investigated in this paper using fem modelling considering evolutions of apert

the role of iron partitioning in mantle composition evolution and scale of convection the effect on composition and evolution of the mantle of the recently observed strong concentration of iron in mg fe o magnesiowustite mw at the expense of mg fe sio 3 perovskite pv structure is studied by calculating a temperature and pressure dependent iron partitioning coefficient for the lower mantle the value of the standard entropy for mgsio 3 perovskite is found to be 69 4 10 3 j mole deg from the recently determined phase diagram of forsterite iron remains concentrated in mg fe o throughout the entire lower mantle if account is taken of an feo phase change with the partitioning coefficient x pv fe x pv mg x mw fe x mw mg increasing from 0 04 to 0 8 between 670 km a the core mantle boundary partitioning has negligible effect on gross density and elastic properties of the lower mantle by using recent shock wave and static compression results for feo and mgsio 3 perovskite we find that the lower mantle is more pyroxene rich than the upper mantle and as iron rich or somewhat less so than the upper mantle mg mg fe 0 93 0 95 for the lower mantle compared with 0 85 0 90 for the uppermost mantle the lower mantle mg si ratio is closer to chondritic values 0 99 0 03 1 5 for a peridotite with px ol 0 4 molar thus supporting the idea of a chemically layered mantle with implications for the style of mantle convection while partitioning of iron has no significant effect on gross lower mantle density we find that the mg fe o and perovskite components of the lower mantle have essentially the same densities mantles with higher bulk iron contents have mg fe o denser than the perovskite component for a bulk magnesium mole fraction of 0 80 the density difference is 0 7 0 8 g cm 3 we investigate the feasibility of the mao bell and yagi gravitational separation hypothesis of mantle evolution in which a mantle more iron rich than present loses iron through gravitational sinking of the denser mg fe o and we conclude that the process cannot successfully compete with solid state convection unless implausibly large grain sizes or unacceptably low viscosities are invoked a likely explanation for removal of iron from an initially iron rich lower mantle is upward extraction of feo enriched basalts or picrites and concentration of iron in upper mantle garnets during accretion of the earth or subsequent convection with the entire mantle passing through the partial melt zone thus the lower mantle was depleted of iron relative to both the upper mantle and the mantles of the small terrestrial planets and satellites which do not have mantle pressures sufficient to form perovskite structure silicates or which had lower accretional temperatures and less extensive melting on this basis venus would be expected to have a mantle similarly depleted in iron

structural localization and origin of compartmentalized fluid flow comstock lode virginia city nevada bonanza grade orebodies in epithermal style mineral deposits characteristically occur as discrete zones within spatially more extensive fault and or fracture systems empirically the segregation of such systems into compartments of higher and lower permeability appears to be a key process necessary for high grade ore formation and most commonly it is such concentrations of metals that make an epithermal vein district world class in the world class silver and gold producing comstock mining district nevada several lines of evidence lead to the conclusion that the comstock lode is localized in an extensional stepover between right lateral fault zones this evidence includes fault geometries kinematic indicators of slip the hydraulic connectivity of faults as demonstrated by veins and dikes along faults and the opening of a normal fault bounded asymmetric basin between two parallel and overlapping northwest striking lateral to lateral oblique slip fault zones during basin opening thick generally subeconomic banded quartz adularia veins were deposited in the normal fault zone the comstock fault and along one of the bounding lateral fault zones the silver city fault as deformation continued the intrusion of dikes and small plugs into the hanging wall of the comstock fault zone may have impeded the ability of the stepover to accommodate displacement on the bounding strike slip faults through extension within the stepover a transient period of transpressional deformation of the comstock fault zone ensued and the early stage veins were deformed through boudinaging and hydraulic fragmentation fault motion inversion and high and low angle axial rotations of segments of the fault planes and some fault bounded wedges this deformation led to the formation of spatially restricted compartments of high vertical permeability and hydraulic connectivity and low lateral hydraulic connectivity bonanza orebodies were formed in the compartmentalized zones of high permeability and hydraulic connectivity as heat flow and related hydrothermal activity waned along the comstock fault zone extension was reactivated in the stepover along the occidental zone of normal faults east of the comstock fault zone volcanic and related intrusive activity in this part of the stepover led to a new episode of hydrothermal activity and formation of the occidental lodes

burial rates of organic matter along the eastern canadian margin and stable isotope constraints on its origin and diagenetic evolution abstract organic carbon oc and nitrogen n contents and 13 c and 15 n values in total organic matter om were measured in sub surface sediments 0 30 cm sub bottom from 21 cores raised from the laurentian channel of the gulf of st lawrence and the labrador sea to document om fluxes and storage along the eastern canadian margin storage rates as high as 2 5 g m 2 yr 1 for oc and 0 2 g m 2 yr 1 for n are observed in the laurentian channel suggesting that the shelf plays a significant role in terms of om storage from 1 to 2 of the primary production based on the isotopic composition of the essentially marine om of the labrador sea 13 c v pdb 21 9 0 4 15 n air 7 6 0 6 n 12 there is no isotopic evidence for a significant relative input of terrestrial om along the laurentian channel 13 c v pdb 21 9 0 4 15 n air 8 0 0 9 n 10 either due to high relative fluxes of marine om and or to the trapping of continental om in the estuary and upstream high storage rates of om are also observed on the continental rise of the labrador sea as high as 1 1 g c m 2 yr 1 and 0 09 g n m 2 yr 1 they contrast with one order of magnitude lower rates on the slope due to low sedimentation rates sr and sediment winnowing by the western boundary undercurrent wbuc reduced early diagenetic alteration of om is observed particularly in the laurentian channel it results in discrete i losses of oc and n ii shifts in c n ratios suggesting preferential removal of n bearing om also highlighted by losses in total hydrolysable amino acids haa in the labrador sea slope records due to low sr om concentration changes linked to long term temporal variations may superimpose on these diagenetic trends and some influence of the wbuc is noticeable

organic carbon distribution in the north atlantic ocean during the last glacial maximum abstract the organic carbon content of eighty two last glacial maximum lgm sediment samples from the north atlantic ocean was determined with a coulometer organic carbon in these sediments averaged about 0 5 by weight slightly higher than in modern sediments factors that control organic carbon distribution were examined in two ways by mapping the spatial distribution of organic carbon during the lgm and by comparing organic carbon content to sediment characteristics in general sediment organic content increases with increasing sedimentation rate increasing clay content and decreasing carbonate content the spatial distribution of lgm organic content is similar in most respects to the mapped modern distribution the primary exception being areas of high organic content one area of high organic content off nortwest africa is situated in the same area geographically but is larger than its modern counterpart perhaps indicating that wind driven upwelling was more intense and or widespread during the lgm the two other areas of high organic carbon content the north american margin and west of the mid atlantic ridge mar at about 40 n have no modern counterpart on the north american margin south of cape cod organic carbon content is generally 0 6 and in several samples is 0 9 the increased organic carbon content of sediment in this area appears to be related to an increase in sedimentation rate and the concomitant increase in inorganic nutrients the area west of the mar is more perplexing and appears to be related to changes in lgm surface circulation

on fluid reserves and the production of superheated steam from fractured vapor dominated geothermal reservoirs vapor dominated geothermal reservoirs produce saturated or superheated steam and vertical pressure gradients are close to vapor static these observations have been generally accepted as providing conclusive evidence that the liquid saturation must be rather small 50 in order that liquid may be nearly immobile this conclusion ignores the crucial role of conductive heat transfer mechanisms in fractured reservoirs for vaporizing liquid flowing under two phase conditions we have developed a multiple interacting continuum method minc for numerically simulating two phase flow of a homogeneous fluid in a fractured porous medium application of this method to reservoir conditions representative of the geysers california and results from an analytical approximation show that for matrix permeability less than a critical value 2 5 to 5 microdarcies the mass flux of water from the matrix to the fractures will be continuously vaporized by heat transported due to conduction this gives rise to production of superheated steam even when the matrix has nearly full liquid saturation simple estimates also show that heat driven steam water counterflow can maintain a nearly vapor static vertical pressure profile in the presence of mobile liquid water in a reservoir with low vertical matrix permeability the implication of these findings is that the fluid reserves of vapor dominated geothermal reservoirs may be larger by a factor of about 2 than has generally been believed in the past

coupled hydromechanical thermochemical processes in rock fractures the behavior of rock fractures under various coupled processes is reviewed under seven broad categories 1 hydromechanical processes 2 thermohydrologic processes 3 hydrochemical processes 4 thermohydromechanical processes 5 thermohydrochemical processes 6 hydromechanical chemical processes and 7 thermomechanical hydrochemical processes the state of the art and possible directions of further research in these coupled processes are discussed rock fracture behaviors considered include not only dilation closure shear and joint propagation but also changes in flow permeability and chemical sorption and retardation capabilities these properties are of critical concern in practical considerations of the rock mass as a medium to store and isolate chemical and radioactive wastes investigations of coupled processes in two fracture systems and multifracture systems are identified as important areas for future research the need to consider coupled processes in borehole testing procedures involving rock fractures is emphasized

seismic architecture and evolution of the disko bay trough mouth fan central west greenland margin abstract the present study is the first to document the large scale glacigenic evolution of a west greenland trough mouth fan tmf system i e the disko bay tmf from onset of shelf based glaciation to present we have constrained the paleo ice sheet configuration in the disko bay region and determine the controlling factors of ice stream development using 2d and 3d seismic reflection data seabed bathymetry and stratigraphic information from two exploration wells this has revealed three stages of the disko bay tmf development the early stage probably of pliocene early pleistocene age marks the onset of a central depocentre located below the modern mid shelf and constructed by sediment progradation delivered through at least two erosive pathways related to fast flowing grounded ice at that time ice stream routing in the disko bay shelf region was strongly controlled by the pre glacial topography and structural boundaries associated with fracture zones and deep seated faults during the middle evolutionary stage the focus of deposition shifted from the mid shelf to two elongate areas fringing the outer margin the marginal depocentres were not only related to glacial processes but also alongslope deposition by contour currents which may have developed as a consequence of basin subsidence surrounding the davis strait high and the kangerluk structure the late stage of tmf development presumably representing the late pleistocene to holocene is characterized by the marginal depocentres becoming less significant and sediment aggradation occurring over wide parts of the mid outer shelf while features of subglacial erosion are generally absent in contrast to the inferred fast flowing ice streams of the early middle evolutionary stages this points to the existence of a rather thin and lightly grounded ice sheet i e at the threshold of floatation the lightly grounded ice sheet scenario applying to the late pleistocene interval of the disko bay tmf was possibly associated with floating ice shelves during periods of maximum cooling while intermittent and short lived advances of grounded ice streams may have occurred during interstadial stadial climate transitions a controlling factor for the development of the aggradational stage may relate to the prominent basement ridge that separates the disko trough from the egedesminde dyb depression we suggest that a neotectonic emergence of the ridge gradually restricted the flow of ice through the central disko trough forcing glaciers to diverge along the entire length of the ridge and find complementary drainage routes

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

late cretaceous to early quaternary organic sedimentation in the eastern equatorial atlantic abstract reconstructing the long term evolution of organic sedimentation in the eastern equatorial atlantic odp leg 159 provides information about the history of the climate ocean system sediment accumulation and deposition of hydrocarbon prone rocks the recovery of a continuous 1200 m long sequence at odp site 959 covering sediments from albian to the present day about 120 ma makes this position a key location to study these aspects in a tropical oceanic setting new high resolution carbon and pyrolysis records identify three main periods of enhanced organic carbon accumulation in the eastern tropical atlantic i e the late cretaceous the eocene oligocene and the pliocene pleistocene formation of upper cretaceous black shales off west africa was closely related to the tectono sedimentary evolution of the semi isolated deep ivorian basin north of the cote d ivoire ghana transform margin their deposition was confined to certain intervals of the last two cretaceous anoxic events the early turonian oae2 and the coniacian santonian oae3 organic geochemical characteristics of laminated coniacian santonian shales reveal peak organic carbon concentrations of up to 17 and kerogen type i ii organic matter which qualify them as excellent hydrocarbon source rocks similar to those reported from other marginal and deep sea basins a middle to late eocene high productivity period occurred off equatorial west africa porcellanites deposited during that interval show enhanced total organic carbon toc accumulation and a good hydrocarbon potential associated with oil prone kerogen deposition of these toc rich beds was likely related to a reversal in the deep water circulation in the adjacent sierra leone basin accordingly outflow of old deep waters of southern ocean origin from the sierra leone basin into the northern gulf of guinea favored upwelling of nutrient enriched waters and simultaneously enhanced the preservation potential of sedimentary organic matter along the west african continental margin a pronounced cyclicity in the carbon record of oligocene lower miocene diatomite chalk interbeds indicates orbital forcing of paleoceanographic conditions in the eastern equatorial atlantic since the oligocene miocene transition a similar control may date back to the early oligocene but has to be confirmed by further studies latest miocene early pliocene organic carbon deposition was closely linked to the evolution of the african trade winds continental upwelling in the eastern equatorial atlantic ocean chemistry and eustatic sea level fluctuations reduction in carbonate carbon preservation associated with enhanced carbon dissolution is recorded in the uppermost miocene 5 82 5 2 ma section and suggests that the latest miocene carbon record of site 959 documents the influence of corrosive deep waters which formed in response to the messinian salinity crisis furthermore sea level related displacement of higher productive areas towards the west african shelf edge is indicated at 5 65 5 6 5 55 5 2 4 8 ma in view of humid conditions in tropical africa and a strong west african monsoonal system around the miocene pliocene transition the onset of pronounced toc cycles at about 5 6 ma marks the first establishment of upwelling cycles in the northern gulf of guinea an amplification in organic carbon deposition at 3 3 ma and 2 45 ma links organic sedimentation in the tropical eastern equatorial atlantic to the main steps of northern hemisphere glaciation and testifies to the late pliocene transition from humid to arid conditions in central and western african climate aridification of central africa around 2 8 ma is not clearly recorded at site 959 however decreased and highly fluctuating carbonate carbon concentrations are observed from 2 85 ma on that may relate to enhanced terrigenous eolian dilution from africa

use of in situ fiber optic sensors to characterize highly heterogeneous elastic displacement fields in fractured rocks fractured and porous rock masses undergo complex deformations relating to geological mechanical and hydrological processes such as plate tectonics earthquakes earth tides and the engineering design of structures in and on rock masses the distribution of stresses in the earth s crust governs the deformation field within and on the surface of geological systems in turn the rock stiffness the presence of faults and others discontinuities the topographical variations the pore pressures body forces and tectonic forces affect the stresses distribution in the earth 1 under basic loading or unloading such as overburden loads tectonics forces underground excavation fractured rock masses generally deform according to a complex mechanical or hydromechanical behavior 1 2 displacements are first localized along pre existing discontinuities and then propagate within the porous rock matrix 2 3 along discontinuity planes the displacements are generally of high magnitude and instantaneous while displacements of the rock matrix are generally of lesser magnitude and slower thus in active zones deformation changes within fractured rocks present a large frequency range and can be both static and dynamic static changes involve static deformations that can be produced by volcanoes tectonic sources hydrologic effects while dynamic changes are best represented by seismic waves produced by earthquake sources 4 geodesy has been the classical field measurements method for static changes and seismology for

multiphysics processes in partially saturated fractured rock experiments and models from yucca mountain 1 the site investigations at yucca mountain nevada have provided us with an outstanding data set one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media such advancement was made possible foremost by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale the development of coupled process models within the project have resulted in a number of new advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications using such models the potential impact of thermal hydrological mechanical thm multiphysics processes over the long term e g 10 000 years could be predicted and bounded with some degree of confidence the fact that the rock mass at yucca mountain is intensively fractured enabled continuum models to be used although discontinuum models were also applied and are better suited for analyzing some issues especially those related to predictions of rockfall within open excavations the work showed that in situ tests rather than small scale laboratory experiments alone are essential for determining appropriate input parameters for multiphysics models of fractured rocks especially related to parameters defining how permeability might evolve under changing stress and temperature a significant laboratory test program at yucca mountain also made important contributions to the field of rock mechanics showing a unique relation between porosity and mechanical properties a time dependency of strength that is significant for long term excavation stability a decreasing rock strength with sample size using very large core experiments and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200 c the analysis of in situ heater experiments showed that fracture closure opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating cooling and that fracture shear dilation appears to be less significant significant effort was devoted to predicting the long term stability of underground excavations under mechanical strength degradation and seismic loading perhaps one of the most challenging tasks within the project we note that such long term strength degradation is actually an example of a chemically mediated process governed by underlying microscopic stress corrosion and chemical diffusion processes in the yucca mountain project such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock a possible future research direction would be to simulate such processes mechanistically in a complete coupled thmc framework where c denotes chemical processes

elasticity of a majorite pyrope solid solution the elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 mg sub 4 si sub 4 o sub 12 majorite a high pressure form of pyroxene have been measured by brillouin spectroscopy under ambient conditions values of the adiabatic bulk modulus k sub s 164 plus minus 15 gpa and shear modulus g 89 4 plus minus 3 7 gpa are similar to those for low pressure aluminosilicate garnets the enstatite majorite reaction is characterized by a large 49 increase in k sub s and a much smaller 13 increase in g the properties of low pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in ca rich systems taken at face value the stp properties of these phases imply that large quantities of ca rich clinopyroxene are needed in order to satisfy seismologically determined shear modulus gradients in the transition zone this suggestion is however subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals and the velocity structure of the transition zone

tracer movement in a single fissure in granitic rock some experimental results and their interpretation radionuclide migration was studied in a natural fissure in a granite core the fissure was oriented parallel to the axis in a cylindrical core 30 cm long and 20 cm in diameter the traced solution was injected at one end of the core and collected at the other breakthrough curves were obtained for the nonsorbing tracers tritiated water and a large molecular weight lignosulphonate molecule and for the sorbing tracers cesium and strontium from the breakthrough curves for the nonsorbing tracers it could be concluded that channeling occurs in the single fissure a dispersion model based on channeling is presented the results from the sorbing tracers indicate that there is substantial diffusion into and sorption in the rock matrix sorption on the surface of the fissure also accounts for a part of the retardation effect of the sorbing species a model which includes the mechanisms of channeling surface sorption matrix diffusion and matrix sorption is presented the experimental breakthrough curves can be fitted fairly well by this model by use of independently obtained data on diffusivities and matrix sorption

depositional environment and source rock potential of miocene strata from the central fram strait introduction of a new computing tool for simulating organic facies variations abstract organic rich sediments were recognized in early miocene strata from the norwegian greenland sea during odp leg 151 three organic geochemical subunits were distinguished in hole 909c using detailed organic geochemical and microscopic analyses toc up to 3 wt hi up to 200 mg hc g toc and 13corg values 24 26 indicate the predominance of terrestrial type iii organic matter in subunit 3 18 16 2 ma biomarker and vitrinite reflectance values r0 0 5 point to rather fresh immature terrestrial organic matter supplied by river discharge from adjacent vegetated coastal areas although the sediments of subunit 3 have a fair to good source rock potential they are insufficiently mature to generate significant amounts of oil or gas to test if the moderate generation potential and source rock quality of subunit 3 are applicable to the entire area the computer software of mod was applied several modelling runs testing the most probable depositional scenarios result even under conservative assumptions in the formation of good to excellent source rocks towards the basin margins

effects of local rock heterogeneities on the hydromechanics of fractured rocks using a digital image based technique a digital image based dib finite element approach is developed based on the numerical code rock failure process analysis rfpa to characterize micro scale rock heterogeneity and to understand the impact of micro scale rock heterogeneity on the macro scale hydromechanical response of rocks the dib technique incorporates small scale spatial variability of initial deformation modulus strength and permeability directly into a coupled hydromechanical model variability in young s modulus strength and permeability is applied by a property map defined from the pixel scale of a digital image in the rfpa mechanical deformation is followed including the accumulation of damage applied in individual elements which modifies modulus strength and permeability with the intensity of damage the rfpa simulates progressive failure in fractured rocks representing both the growth of existing fractures and the formation of new fractures without having to identify crack tips and their interaction explicitly in this dib simulation approach image voxels are used to give equivalent mechanical and flow properties these property maps are ported to the model capable of solving directly for the evolving deformation and fluid flow fields the model is validated through comparisons of the simulated results with phenomenological observations documented in previous studies the validated model is then applied to investigate the hydromechanical response of fractured rock characterized by digital image the model is able to reproduce the spatial evolution of damage in the sample the coalescence of existing cracks and the formation of new cracks

analysis of some laboratory tracer runs in natural fissures tracer tests in natural fissures performed in the laboratory are analyzed by means of fitting two different models in the experiments sorbing and nonsorbing tracers were injected into a natural fissure running parallel to the axis of a drill core the models take into account advection dispersion diffusion into the rock matrix and sorption onto the surface of the fissure and on the microfissures inside the matrix for the second mechanism one of the models considers hydrodynamic dispersion while the other model assumes channeling dispersion the models take into account time delays in the inlet and outlet channels the dispersion characteristics and water residence time were determined from the experiments with nonsorbing tracers surface and volume sorption coefficients and data on diffusion into the rock matrix were determined for the sorbing tracers the results are compared with values independently determined in the laboratory good agreement was obtained using either model when these models are used for prediction of tracer transport over larger distances the results will depend on the model the model with channeling dispersion will show a greater dispersion than the model with hydrodynamic dispersion assuming constant dispersivity

organic carbon accumulation in baffin bay and paleoenvironment in high northern latitudes during the past 20 m y the results of the investigation of organic carbon deposition in baffin bay provide important information about paleoenvironmental evolution in high northern latitudes during cenozoic time during miocene to quaternary time organic carbon enrichment of up to 3 insediments sampled at ocean drilling program site 645 was controlled mainly by increased supply of terrigenous organic matter two distinct maxima were identified 1 a middle miocene maximum possibly reflecting a dense vegetation cover and fluvial sediment supply from adjacent islands which decreased during late miocene and early pliocene time because of expansion of tundra vegetation due to global climatic deterioration 2 a late pliocene pleistocene maximum probably caused by glacial erosion and meltwater outwash significant amounts of marine organic carbon were deposited in baffin bay during middle miocene time suggesting higher surface water productivity triggered by the inflow of cold and nutrient rich arctic water masses the decrease in average surface water productivity to values similar to those of modern baffin bay occurred during the late miocene and were probably caused by development of a seasonal sea ice cover reaching maximum expansion during the past 3 4 m y

self ordering and complexity in epizonal mineral deposits epizonal base and precious metal deposits makeup a range of familiar deposit styles including porphyry copper gold epithermal veins and stockworks carbonate replacement deposits and polymetallic volcanic rock hosted vhms deposits they occur along convergent plate margins and are invariably associated directly with active faults and volcanism they are complex in form variable in their characteristics at all scales and highly localized in the earth s crust more than a century of detailed research has provided an extensive base of obser vational data characterizing these deposits from their regional setting to the fluid and isotope chemistry of mineral deposition this has led to a broad understanding of the large scale hydrothermal systems within which they form low salinity vapor released by magma crystallization and dispersed into vigorously convecting ground water systems is recognized as a principal source of metals and the gases that control redox conditions within systems the temperature and pressure of the ambient fluid anywhere within these systems is close to its vapor liquid phase boundary and mineral deposition is a consequence of short timescale perturbations generated by localized release of crustal stress however a review of occurrence data raises questions about ore formation that are not addressed by traditional genetic models for example what are the origins of banding in epithermal veins and what controls the frequency of oscillatory lamina tion what controls where the phenomenon of mineralization occurs and why are some porphyry deposits for example so much larger than others the distinctive self organized characteristics of epizonal deposits are shown to be the result of repetitive coupling of fracture dilation consequent on brittle failure phase separation boiling and heat transfer between fluid and host rock process cou pling substantially increases solute concentrations and triggers fast far from equilib rium depositional processes since these coupled processes lead to localized transient changes in fluid characteristics paragenetic isotope and fluid inclusion data relate to conditions at the site of deposition and only indirectly to the characteristics of the larger scale hydrothermal system and its longer term behavior the metal concentra 1 the us government has the right to retain a nonexclusive royalty free license in and to any copyright covering this paper

energy extraction from fractured geothermal reservoirs in low permeability crystalline rock two hot dry rock geothermal energy reservoirs were created by hydraulic fracturing of precambrian granitic rock on the west flank of the valles caldera a dormant volcanic complex in the jemez mountains of northern new mexico heat was extracted in a closed loop mode of operation injecting water into one well and extracting the heated water from a separate production well the first reservoir was produced by fracturing the injection well at a depth of 2 75 km where the indigenous rock temperature was 185 c the relatively rapid decline in temperature of the water produced from the first reservoir 100 c in 74 days indicated an effective fracture radius of about 60 m with an average thermal power extracted of 4 mw a second larger reservoir was created by refracturing the injection well 180 m deeper downhole measurements of water temperature at the reservoir outlet as well as temperatures inferred from chemical geothermometry showed that the thermal decline of this reservoir was negligible the effective heat transfer area of the new reservoir must be at least 45 000 m2 nearly 6 times larger than the first reservoir in addition reservoir residence time studies employing visible dye tracers indicated that the mean volume of the second reservoir is 9 times larger other measurements showed that flow impedances were low and that downhole water losses from these reservoirs should be manageable the geochemistry of the produced water was essentially benign with no scaling problems apparent moreover the level of induced seismic activity was insignificantly small

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

the origin of tensile fracture lineaments abstract fracture controlled lineaments commonly seen where brittle basement is exposed at the earth s surface are generally restricted to a small number of sets with angles of 45 90 between sets the length frequency distribution of lineaments in each set follows a truncated poisson function such lineaments usually show almost no shearing offset suggesting a tensile origin a simple mechanical model of tensile fracturing is used to explain the spacing directions and length of lineaments as well as their depth frequency distribution results suggest that the penetration depth of tensile fractures which produce lineaments at the earth s surface is directly related to their length and that the fracture density is inversely proportional to fracture depth finally the angles between lineament sets may be controlled by the ratio of strength of unfractured rock to that of pre existing fractures which might heal with time the most likely source of tension is tectonic uplift fractures due to typical uplifts of 0 5 1 km over distances of 10 100 km may penetrate as brittle fractures to several kilometres into the crust perhaps to the depth at which seismic activity ceases

deformation phenomena in jointed rock the role of rock joints in rock mass deformation phenomena is described individually joints display concave shaped stress closure curves under normal loading and convex shaped stress displacement curves under shear usually accompanied by dilation the deformation behaviour of rock masses depends on the relative magnitudes of these components of closure shear and dilation the deformation of a rock mass may result in dramatic changes in the joint apertures and conductivities conversely changes in joint water pressure cause changes in joint aperture which affect the overall deformation of the rock mass examples of compaction in jointed reservoirs and leakage phenomena in pressure tunnels are cited each of which may be caused by changes in effective stress the presence of rock joints is seen to affect stress slabbing phenomena in tunnels and is the suspected cause of depth dependent contrasts of stress in sedimentary rocks the phenomenon of hydraulic shearing of joints is discussed with particular

the state of the art of numerical modeling of thermohydrologic flow in fractured rock masses the state of the art of numerical modeling of thermohydrologic flow in fractured rock masses is reviewed and a comparative study is made of several models which have been developed in nuclear waste isolation geothermal energy ground water hydrology petroleum engineering and other geologic fields the general review is followed by individual summaries of each model and the main characteristics of its governing equations numerical solutions computer codes validations and applications

clinopyroxenite from the sulu ultrahigh pressure terrane eastern china origin and evolution of garnet exsolution in clinopyroxene the rizhao garnet clinopyroxenite occurs as small mantle slices faulted into subducted continental crust in the sulu ultrahigh pressure uhp terrane china two representative garnet clinopyroxenites with exsolution microstructures were studied 1 a massive ilmenite rich specimen composed of coarse grained clinopyroxene containing abundant exsolution rods of grossular rich garnet 20 vol ilmenite 3 4 vol in a fine grained matrix of clinopyroxene garnet ilmenite and 2 megacrystic garnet bearing sample characterized by garnet containing inclusions of clinopyroxene and ilmenite the clinopyroxene inclusions show exsolution rods and blebs with variable amounts of garnet 1 15 vol and minor ilmenite both exsolved and matrix garnets have similar grossular rich compositions the aggregate composition of clinopyroxene garnet ilmenite intergrowth is similar to the whole rock composition we propose that the parental phase of exsolved garnet ilmenite lamellae and clinopyroxene host was either a homogeneous clinopyroxene hypothesis a or a majoritic garnet hypothesis b that experienced three discrete evolution stages if the parental phase was clinopyroxene abo3 with an si deficiency in the b site the rizhao garnet clinopyroxenite could have an initial assemblage clinopyroxene grt ilm formed at near solidus conditions 1400 c at 5 gpa in the upper mantle the second stage is defined by garnet exsolution from the primary clinopyroxene involving decreasing temperature and or increasing pressure related to continental subduction coexisting clinopyroxene host and garnet exsolution grtexs recrystallized at temperatures of 900 c at an assumed minimum p of 5 gpa the third stage is represented by recrystallization of exsolution phases to form the fine grained matrix of cpx grt ilm at 700 c and 3 gpa during the early exhumation of the uhp terrane the speculative hypothesis b implies that the proposed majoritic garnet was from the mantle transition zone 450 km depth this suggestion remains to be tested

mesoscale characterization of coupled hydromechanical behavior of a fractured porous slope in response to free water surface movement mesoscale characterization of coupled hydromechanical behavior of a fractured porous slope in response to free water surface movement y guglielmi a f cappa a b j rutqvist b c f tsang b and a thoraval c b geosciences azur cnrs unsa ird upmc sophia antipolis france lawrence berkeley national laboratory earth sciences division berkeley usa c ineris ecole des mines de nancy nancy france a corresponding author fax 33 4 92 94 26 10 e mail address guglielmi geoazur unice fr y guglielmi abstract to better understand the role of groundwater level changes on rock slope deformation and damage a carbonate rock slope 30 m 30 m 15 m was extensively instrumented for mesoscale hydraulic and mechanical measurements during water level changes the slope is naturally drained by a spring that can be artificially closed or opened by a water gate in this study a 2 hour slope dewatering experiment was analyzed changes in fluid pressure and deformation were simultaneously monitored both at discontinuities and in the intact rock using short base extensometers and pressure gauges as well as tiltmeters fixed at the slope surface field data were analyzed with different coupled hydromechanical hm codes rocmas flac 3d and udec field data indicate that in the faults a 40 kpa pressure fall occurs in 2 minutes and induces a 0 5 to 31 10 6 m normal closure pressure fall is slower in the bedding planes lasting 120 minutes with no normal deformation no pressure change or deformation is observed in the intact rock the slope surface displays a complex tilt towards the interior of the slope with magnitudes ranging from 0 6 to 15 10 6 rad close agreement with model for both slope surface and internal measurements is obtained when a high variability in slope element properties is introduced into the models with normal stiffnesses of k n faults 10 3 k n bedding planes and permeabilities of k h faults 10 3 k h bedding planes a nonlinear correlation between hydraulic and mechanical discontinuity properties is proposed and related to discontinuity damage a parametric study shows that 90 of slope deformation depends on hm effects in a few highly permeable and highly deformable discontinuities located in the basal saturated part of the slope while the remaining 10 are related to elasto plastic deformations in the low permeability discontinuities induced by complex stress strain transfers from the high permeability zones the periodicity and magnitude of free water surface movements cause 10 to 20 variations in those local stress strain accumulations related to the contrasting hm behavior for high and low permeable elements of the slope finally surface tilt monitoring coupled with internal localized pressure deformation measurements appears to be a promising method for characterizing the hm properties and behavior of a slope and for detecting its progressive destabilization key words fracture rock slope mesoscale in situ poroelastic measurements hydromechanics numerical modeling tiltmeter monitoring damage 1 introduction understanding coupled groundwater and mechanical processes in complex fractured porous rocks is essential for the safety and efficiency of subsurface and slope stability engineering and thus for the security and economic well being of the general public although poorly documented water is often mentioned as a triggering mechanism for failure of rocks with well developed pre existing fractures networks and thus the cause for rock

strike slip fault bridge fluid pumping mechanism insights from field based palaeostress analysis and numerical modelling abstract we present a finite element study of stress perturbation in evolving compressive and extensional strike slip fault bridges the results are compared with a fracture study of a compressive bridge at st donats uk horizontally interbedded calcareous mudstone and bioclastic calcilutite at st donats have a distinct vertical permeability anisotropy this sedimentary sequence behaves as a set of horizontal aquifers the fluid flow in these aquifers is sensitive to mean stress gradients paleostress analysis of field fracture data verified by finite element modelling indicates a rotation of 1 towards parallelism with boundary faults inside the growing compressive bridge boundary faults and bridge faults recorded numerous fluid flow events the modelled mean stress pattern shows a regional maximum within the bridge and local maxima minima pairs at boundary fault tips finite element modelling of an extensional bridge indicates that 3 rotates towards parallelism with boundary faults the mean stress pattern is similar to the pattern in compressive bridge but with maxima and minima locations interchanged the stress patterns are reestablished by each stress build up preceding the rupturation of the boundary faults throughout the development stages of strike slip fault bridges mean stress gradients developed pre failure control the fluid flow in fractures of the strike slip fault system at and after the end of each stress build up and the fluid flow in boundary faults post failure fracture reactivation and new fracture generation within an evolving bridge is a process consisting of multiple successive events that retain the storage capacity of the bridge rupture and sealing of the main bounding faults is a step wise process that opens and closes fluid conduits between areas with different pressures

burial of different types of organic carbon in core 17962 from south china sea since the last glacial period abstract total organic carbon toc black carbon bc and land derived organic carbon loc extracted from marine sediment core 17962 from the southern south china sea and analyzed by pyrolysis gas chromatography elemental analyzers and mass spectroscopy can be interpreted in terms of regional land biomass burning climatic conditions vegetation cover and ocean paleoproductivity carbon from terrestrial sources including bc and loc appears to be a significant component of toc 3 1 39 3 range 16 5 average for bc 4 4 56 6 range 14 6 average for loc the production of bc and loc was only slightly higher during the last maximum glaciation lgm than during the holocene therefore dramatic changes in climate and vegetation cover do not seem to have occurred at the pleistocene holocene boundary paleoproductivity data calculated from marine organic carbon proved to be more accurate than those calculated from toc and exhibit the same pattern of temporal variation however the glacial interglacial contrast in the refined palaeoproductivity is less evident than that calculated from toc

linking thermal hydrological and mechanical processes in fractured rocks abstract in this paper an overview is presented of coupled processes linking thermo hydro mechanical thm effects in fractured rocks a formulation is first presented to show the linkage mathematically which can be used as a basis for numerical solutions and for further developments two simple examples of hydromechanical hm and thermo hydro mechanical thm coupled processes are discussed to convey physical insight into such couplings finally three large scale long term experiments currently under way are described these are being conducted specifically to study coupled processes in situ

application of the geomechanical facies approach and comparison of exploration and evaluation methods used at soultz sous forets france and spa urach germany geothermal sites earth reservoirs are increasingly exploited today with the extraction of resources such as heat and hydrocarbons and the large scale emplacement of waste such as co2 sequestration the characterization site investigation predictive modeling and long term monitoring are dependent on the processes being investigated and modeled in most cases complex coupled processes have to be addressed in a geologically complex rock mass system in this paper we present a conceptual holistic framework known as geomechanical facies linking all the scales of investigation characterization and reservoir development methods we demonstrate this concept on the work undertaken during the design and development of the enhanced geothermal systems egs systems at the forefront of european hot dry rock hdr technology soultz sous forets france and spa urach germany soultz sous forets is situated within granitic rocks and an active tectonic graben system in the central part of the rhine graben it presents conditions of lithology temperature stress hydraulics and geochemistry that are very different from those at spa urach located in a very dense gneiss formation in the south german crystalline complex spa urach exhibits more elastic behavior and is set tectonically within an almost inactive strike slip stress field described in more detail in sects drill core analysis and hydraulic stimulation at spa urach this paper compares the exploration and field development methods used at these two sites against the back drop of the geomechanical facies concept issues addressed include the key parameters for flow and heat transport properties coupled hydro mechanical process identification the success of the hdr reservoir as a heat exchanger and exploration techniques applicable to the different facies identification of the key geomechanical facies gives an indication as to which technologies will prove more efficient in the application of hdr technology the results of this study will hopefully help in developing heat recovery schemes for the long term economical operation of future hdr plants and egs as well as assist in the understanding of engineered geosystems

interior structure of terrestrial planets modeling mars mantle and its electromagnetic geodetic and seismic properties 1 we present a new procedure to describe the one dimensional thermodynamical state and mineralogy of any earth like planetary mantle with mars as an example the model parameters are directly related to expected results from a geophysical network mission in this case electromagnetic geodetic and seismological processed observations supplemented with laboratory measurements we describe the internal structure of the planet in terms of a one dimensional model depending on a set of eight parameters for the crust the thickness and the mean density for the mantle the bulk volume fraction of iron the olivine volume fraction the pressure gradient and the temperature profile and for the core its mass and radius currently available geophysical and geochemical knowledge constrains the range of the parameter values in the present paper we develop the forward problem and present the governing equations from which synthetic data are computed using a set of parameter values among all martian models fitting the currently available knowledge we select eight candidate models for which we compute synthetic network science data sets the synergy between the three geophysical experiments of electromagnetic sounding geodesy and seismology is emphasized the stochastic inversion of the synthetic data sets will be presented in a companion paper

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

measuring well hydraulic connectivity in fractured bedrock using periodic slug tests summary periodic hydraulic experiments were conducted in a five spot well cluster completed in a single bedding plane fracture tests were performed by using a winch operated slug submerged solid cylinder to create a periodic head disturbance in one well and observing the phase shift and attenuation of the head response in the remaining wells transmissivity t and storativity s were inverted independently from head response inverted t decreased and s increased with oscillation period estimated s was more variable among well pairs than t suggesting s may be a better estimator of hydraulic connectivity among closely spaced wells these estimates highlighted a zone of poor hydraulic connection that was not identified by a constant rate test conducted in the same wells periodic slug tests appear to be a practical and effective technique for establishing local scale spatial variability in hydraulic parameters

single fractures under normal stress the relation between fracture specific stiffness and fluid flow abstract fracture specific stiffness and fluid flow through a single fracture under normal stress are implicitly related through the geometry of the void space and contact area that comprise the fracture data from thirteen different rock samples each containing a single fracture show that relationships between fracture specific stiffness and fluid flow through a fracture fall into two general classes of behavior fractures either fall on a loosely defined universal curve relating fluid flow to fracture specific stiffness or else the flow is weakly dependent on fracture specific stiffness the second relationship shows that flow decreases slowly with increasing fracture specific stiffness the first relationship shows that flow decreases rapidly for increases in fracture specific stiffness to understand this behavior computer simulations on simulated single fractures were performed to calculate fluid flow fracture displacement and fracture specific stiffness as a function of normal stress simulated fractures with spatially correlated and uncorrelated aperture distributions were studied fractures with spatially uncorrelated aperture distributions tend to exhibit a weak dependence of fluid flow on fracture specific stiffness because these fractures tend to have multiple connected paths across the sample which can support flow with uniformly distributed contact area thus an increment in stress will increase the stiffness of the fracture without greatly reducing the amount of fluid flow on the other hand fractures with spatially correlated aperture distributions tend to belong to the universal relationship because correlated fractures tend to have only one or two dominant flow paths and the contact area is limited to a few regions resulting in a compliant fracture thus an increment in stress on a spatially correlated fracture will result in an increase in stiffness and rapid decrease in fluid flow these spatial correlations in fracture void geometry can be differentiated in the laboratory based on the observed fracture specific stiffness fluid flow relationship for a single fracture under normal loading

constitution of the mantle 2 petrological models of transition zone based on fms phase diagram abstract a detailed picture is presented of phase transformations in the mantle transition zone based upon the study of phase relations and topologies in the feo mgo sio2 fms system the p t x diagram for the composition close to pyrolite sio2 40 mol and fe fe mg 0 12 is used in modelling the structure of the mantle transition zone to connect phase transitions in minerals to the observed seismic discontinuities the mineralogical nature of the first seismic discontinuity at a depth of about 400 km is associated either with a univariant transformation px px or with a sharp divariant transformation px px px which should be closer to 420 km for the fixed composition close to pyrolite at a depth of about 650 km neither univariant nor invariant equilibria are observed in the fms system it has been found that in the fms system two extremely narrow 1 2 km wide stability fields of divariant mineral assemblages pv st and pv mw separated by a trivariant zone pv about 5 km wide might be responsible for the nature of the 650 km discontinuity because of the negative slope of the phase boundaries the second seismic discontinuity in the cold subducting slab is deeper than in the surrounding mantle

mgsio3 fesio3 al2o3 in the earth s lower mantle perovskite and garnet at 1200 km depth natural pyroxene and garnet starting materials are used to study the effects of joint fe and al substitution into mgsio3 perovskite at 50 gpa garnet is found to coexist with perovskite in samples containing both fe and al to pressures occurring deep into the lower mantle 1200 km depth the volume of the perovskite unit cell is vo a3 162 59 5 95xfesio3 10 80xal2o3 with aluminum causing a significant increase in the distortion from the ideal cubic cell on the basis of a proposed extension of the mgsio3 al2o3 high pressure phase diagram toward fesio3 fe is shown to partition preferentially into the garnet phase the stability of garnet deep into the lower mantle may hinder the penetration of subducted slabs below the transition zone

thermohydrological conditions and silica redistribution near high level nuclear wastes emplaced in saturated geological formations evaluation of the thermohydrological conditions near high level nuclear waste packages is needed for the design of the waste canister and for overall repository design and performance assessment most available studies in this area have assumed that the hydrologic properties of the host rock are not changed in response to the thermal mechanical or chemical effects caused by waste emplacement however the ramifications of this simplifying assumption have not been substantiated we have studied dissolution and precipitation of silica in liquid saturated hydrothermal flow systems including changes in formation porosity and permeability using numerical simulation we compare predictions of thermohydrological conditions with and without inclusion of silica redistribution effects two cases were studied namely a canister scale problem and a repository wide thermal convection problem and different pore models were employed for the permeable medium fractures with uniform or nonuniform cross sections we find that silica redistribution in water saturated conditions does not have a sizeable effect on host rock and canister temperatures pore pressures or flow velocities

titanium solubility in coexisting garnet and clinopyroxene at very high pressure the significance of exsolved rutile in garnet exsolution microstructures including ilmenite garnet in clinopyroxene and rutile in garnet are common in clinopyroxenite and eclogite from the sulu ultrahigh pressure uhp terrane in order to understand the phase relations and ti solubility in both garnet and clinopyroxene in a natural tio2 bearing system several experiments at 5 15 gpa 1000 1400 c were carried out using the multianvil high pressure apparatus the hujianlin ilmenite rich garnet clinopyroxenite showing exsolution microstructure was selected as starting material because it closely approaches a composition lying in the tio2 cao mgo feo al2o3 sio2 system except for minor melt in one experiment at 1400 c and 5 gpa other run products contain majoritic garnet clinopyroxene ilmenite or rutile and exhibit neoblastic texture with increasing pressure ti and ca mg and si contents of neoblastic garnet increase with decreasing al the principal coupled substitutions are ca2 ti4 2al3 and si4 mg2 2al3 responding to majorite component increase titanium solubility 0 8 4 5 wt as tio2 in garnet and grtti cpxti ratio have a pronounced positive correlation with pressure between 5 and 15 gpa on the other hand the coexisting clinopyroxene contains low ti 0 17 0 53 wt as tio2 and shows no significant pressure effect rutile exsolution in garnet is coupled to that of pyroxene exsolution both are exsolved from majoritic garnet on decompression therefore the amount of such exsolved lamellae is a potential indicator of high pressure metamorphism in exhumed rocks whereas the tio2 content of clinopyroxene coexisting with garnet is not sensitive to pressure change

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

an experimental study of the garnet perovskite transformation in the system mgsio3mg3al2si3o12 phase transformations in the system mgsio3 mg3al2si3o12 have been studied at pressures between 22 and 28 gpa at 1500 c using a multi anvil apparatus majorite garnet with less than about 10 wt al2o3 was found to completely transform into an orthorhombic perovskite structure over a pressure interval between 24 and 27 gpa whereas pyrope garnet disproportionated into sub aluminous perovskite plus corundum solid solutions at pressures greater than 26 5 gpa alumina contents in the perovskite structure are dependent on temperature and increase from 11 wt at 1500 c to 17 wt at 1800 c at a pressure of 27 gpa the alumina content of perovskite also in creases with increasing pressure such that aluminous perovskite with the pyrope composition 25 mol al2o3 should be formed by about 30 40 gpa these observations are consistent with our recent experimental results on a pyrolite composition which demonstrated that no separate aluminous phase exists in the upper part of the lower mantle the entire inventory of al2o3 in pyrolite can be accommodated in solid solution in magnesium silicate perovskite

a new parameter to assess hydromechanical effects in single hole hydraulic testing and grouting grouting or filling of the open voids in fractured rock is done by introducing a fluid grout through boreholes under pressure the grout may be either a newtonian fluid or a bingham fluid the penetration of the grout and the resulting pressure profile may give rise to hydromechanical effects which depend on factors such as the fracture aperture the pressure at the borehole and the rheological properties of the grout in this paper we postulate that a new parameter a which is the areal integral of the fluid pressure change over the fracture plane is an appropriate measure to describe the change in fracture aperture volume due to a change in effective stress in many cases analytic expressions are available to calculate pressure profiles and the a parameter the approach is verified using a fully coupled hydromechanical simulator for the case of a newtonian fluid results of the verification exercise show that the new approach is reasonable and that the a parameter is a good measure for the fracture volume change i e the larger the a parameter the larger the fracture volume change in an almost linear fashion to demonstrate the application of the approach short duration hydraulic tests and constant pressure grouting are studied it is concluded that using analytic expressions for penetration lengths and pressure profiles to calculate the a parameter provides a possibility to describe a complex situation and compare discuss and weigh the impact of hydromechanical couplings for different alternative grouting strategies further the analyses identify an effect of high pressure grouting that of uncontrolled grouting of larger fractures and insufficient or less than expected sealing of finer fractures under certain grouting conditions

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

some anomalous features of flow and solute transport arising from fracture aperture variability model fractures with variable apertures are generated by a statistical method and water flow and tracer transport in these fractures are calculated tracer injection and collection are simulated for parallel and convergent flow fields the impact of the use of different injection flow rates and the different locations of injection and collection points are studied the results show that the transport time dispersion and the so called mass balance fracture aperture are very sensitive to the location of the injection point and the injection flow rate these anomalous effects appear to be consistent with observations in several recent field experiments the implications of the calculated results on the analysis of tracer tests are discussed it is concluded that because of the stochastic nature of variable fracture apertures and their permeabilities a point tracer test in a fracture is not sufficient to characterize the properties of the fracture dispersivities and apertures calculated from different tracer tests in the same fracture may vary by orders of magnitude depending on the flow rate and the location of the injection however a line injection of tracer averaged over a series of adjacent points may avoid some of these problems

a biomarker approach to the organic matter deposited in the north atlantic during the last climatic cycle abstract the study of the composition of total organic carbon toc c37 alkenones and c23 c33 n alkanes in the north atlantic ocean cores su90 08 and su90 39 has allowed the development of a model for the differentiation of marine and terrigenous toc this model gives rise to results in good agreement with inorganic markers such as magnetic susceptibility ms and non carbonate content according to this model the terrigenous toc accounts for most of the organic matter in the glacial sediments thus the higher toc of the glacial periods 0 1 0 45 vs 0 05 0 15 in the interglacials is due to the increase in terrigenous toc the changes in marine toc those associated to sea surface productivity are independent of the glacial interglacial evolution the terrigenous toc is more important at higher latitudes probably due to higher terrigenous detrital inputs associated with iceberg transport in this respect the correlation between n alkanes and ms strongly suggests that the main source of these hydrocarbons are ice rafted materials and that aeolian inputs only represent minor contributions the four peaks of reworked n alkanes in the su90 08 core that are coincident with the heinrich layers h1 h2 h4 and 115 are in agreement with this hypothesis on the other hand the abrupt marine toc peaks of su90 08 show a 23 ka periodicity indicating that the marine productivity at 43 n in the north atlantic ocean was precessionally driven the productivity maxima in this core correlate with low latitude oceanographic processes such as periods of enhanced trade wind intensity and equatorial upwelling which are also tuned to precession and independent of the global glacial interglacial evolution

analysis of the hydromechanical behavior of a flat lying fracture during a slug test slug tests dilate and contract fractures in aquifers we developed a coupled hydromechanical analysis of an idealized fracture to evaluate effects of these deformations in fractured crystalline rock aquifers the analysis shows the abrupt increase in pressure at the beginning of a slug test causes a slight opening of a fracture but the fracture continues to open as the pressure falls in the wellbore this happens because the pressure increases over an ever widening area even though it decreases in the wellbore eventually decreasing pressure in the vicinity of the wellbore offsets the spreading pressure and the fracture starts to close ultimately returning to its initial aperture when the pressure equilibrates the displacement in the wellbore when the pressure head is rising is always smaller than when the head is falling and this produces a loop like hysteresis when displacement is plotted as a function of pressure a sensitivity analysis shows the displacement at the wellbore is sensitive to the magnitude and distribution of aquifer properties suggesting that the displacement signal could be combined with pressure measurements to improve the interpretation of slug tests during aquifer characterization

fractured rock hydromechanics from borehole testing to solute transport and co2 storage the paper was prepared with partial support of the us department of energy under contract no de ac02 05ch11231 with the lawrence berkeley national laboratory

thermally induced phase changes lateral heterogeneity of the mantle continental roots and deep slab anomalies pressure induced solid solid phase changes are responsible for most of the increase of density and seismic velocity with depth in the upper mantle lateral variations in temperature cause a similar effect abrupt changes of density and seismic velocity due to phase changes are superposed on smaller changes associated with thermal expansion temperature induced isobaric phase changes are as important in explaining various recent geophysical data as are the more familar pressure induced phase changes in cold slabs the equilibrium mineral assemblage contains high density high velocity phases which are not stable in hotter mantle in particular the ilmenite form of mgsio 3 and the spinel form of mg 2sio 4 have broad stability fields in cold mantle which increase the density and velocity of deep slabs to values in excess of those which have been used in geoid and seismic travel time modeling recent arguments for slab penetration into the lower mantle and whole mantle convection are based on thermal models of the slab which ignore the large density and seismic velocity anomalies associated with temperature induced phase changes when these effects are taken into account the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and layered models of mantle convection the seismicity cutoff and evidence for slab thickening at 670 km also favor this style of convection mantle seismic velocities between 200 and 400 km depth in tectonic and young oceanic regions are lower than in shield regions and this is due to the presence of a melt phase and lower velocity high temperature phase assemblages deep 200 km long lived continental roots differing in chemistry from normal mantle are not required when isobaric phase changes are taken into account high velocity subshield mantle is closer to normal subsolidus mantle than is suboceanic mantle which is affected by the presence of high temperature phase assemblages the whole mantle convection thick continental root and deep slab penetration hypotheses are not supported by seismic and geoid data when isobaric phase changes are included in the analysis phase changes are more effective in changing density and seismic velocity than are lateral variations in temperature and composition the lack of correlation of the geoid with ridges shields heat flow and upper mantle velocity variations suggests a low geoid sensitivity to the upper mantle consistent with layered convection

a study of regional temperature and thermohydrologic effects of an underground repository for nuclear wastes in hard rock heat released by the radioactive decay of nuclear wastes in an underground repository causes a long term thermal disturbance in the rock mass the nature of this disturbance for a planar repository 3000 m in diameter at a depth of 500 m below surface is investigated loaded initially with a power density of 10 w m2 of spent fuel assemblies 10 years after discharge from a reactor the maximum increase in temperature of the repository in granite is about 50 c and the epicentral thermal gradient about 70 c km different waste forms and periods before burial have significant effects on the thermal disturbance the effects of temperature changes on the groundwater flow are evaluated with simple models of a vertical fracture connected to a horizontal fracture in the rock mass the buoyancy groundwater flow through the vertical fracture is a function of both the vertical and the horizontal fracture transmissivities as well as the changes in density and viscosity of groundwater caused by the temperature changes finite hydraulic recharge from the surrounding rock mass affects the thermohydrologic disturbance

structural setting and timing of hydrothermal veins and breccias on hurd peninsula south shetland islands a possible volcanic related epithermal system in deformed turbidites quartz veins and vein breccias in a greywacke shale sequence of carboniferous triassic age were previously regarded as mesothermal silicified fault breccias and related to an adjacent eocene granodiorite pluton new mapping of vein assemblages and textures and their structural and cross cutting relationships demonstrates that the steeply dipping sheeted epithermal textured vein array was hydraulic in origin and possibly cretaceous in age the main vein and breccia swarm trends for 14 km nne along strike and 2 km across strike cutting large irregular areas of silicified and brecciated sandstone and patchy areas of pyritic propylitic and k feldspar alteration angular vein fabrics and hydraulic disruption textures indicate wedging by hydrothermal solutions hydraulic rupture brecciation and fragment transport followed by open space precipitation in veins generally 15 cm thick and breccias up to a few metres thick hydrothermal quartz chlorite calcite and chalcedony predominate with variable amounts of chalcopyrite galena sphalerite and pyrite epidote arsenopyrite k feldspar and andradite garnet are conspicuous in places breccias were pre and syn mineralization whereas mineral precipitation was pre syn and post breccia formation hydrothermal activity was simultaneous with extensional faulting striking nne and accompanied by intrusion of dacitic dykes there followed conjugate shearing on east and ese striking faults intrusion of high level tonalite stocks and several phases of basaltic andesite dyke intrusion these hypabyssal rocks were probably coeval with the antarctic peninsula volcanic group dominating livingston island dated between 130 and 75 ma minor copper and iron sulphide bearing veins occur in adjacent volcanic and hypabyssal intrusive rocks the hurd peninsula veins may therefore form part of a volcanic epithermal hydrothermal system adularia sericite quartz type of cretaceous age rather than a porphyry related system of eocene age

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

melting experiments on the enstatite pyrope join at 80 152 kbar melting temperatures of the assemblage pyroxene garnet on the enstatite pyrope join were experimentally determined at 11 different pressures between 80 and 152 kbar with a split sphere anvil apparatus ussa 2000 the compositions of pyroxene garnet and melt coexisting along the solidus were also determined comparison with previous data at lower temperatures revealed a large temperature dependence of the compositions of garnet coexisting with pyroxene it is proposed that the observed variation in the garnet composition is caused by disorder in garnet the obtained alumina contents of orthopyroxene coexisting with garnet on the solidus at 80 110 kbar contributed to an improvement of the garnet peridotite thermobarometry an internally consistent set of thermodynamic parameters was derived which allows calculation of the temperature pressure phase diagram for the enstatite pyrope join at 20 260 kbar

injection and thermal breakthrough in fractured geothermal reservoirs lbl 12698 preprint submitted to the journal of geophysical research injection and thermal breakthrough in fractured geothermal reservoirs gudmundur s bodvarsson and chin fu tsang may 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info division ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

coupled thermal hydraulic mechanical phenomena in saturated fractured porous rocks numerical approach the fundamentals of the theory of consolidation and thermoelasticity are recast into the formulation of a phenomenon called thermohydroelasticity subsequently a variational principle and galerkin formulation are combined with the finite element method to develop a new technique to investigate coupled thermal hydraulic mechanical behavior of liquid saturated fractured porous rocks a code to code verification of the method is performed finally the environment of a heater emplaced in hard rock is simulated the effects of the coupled thermal stresses in the fractured rock are evident from the dramatic reduction of permeability due to the deformation of the fractures these results can improve the understanding of observations and displacement measurements made in the in situ experiments at the stripa mine in sweden 46 references

determining the composition of late quaternary marine sediments from nuv vis and nir diffuse reflectance spectra abstract as the length of marine cores increases and sampling intervals decrease the need for rapid and inexpensive means of determining sediment composition has become apparent in this study we examine one potentially useful technique for assessing compositional changes in marine cores diffuse reflectance spectrophotometry we examined nearultraviolet visible and near infrared reflectance spectra from five data sets each data set consists of calibration samples and test samples the calibration samples spectra were related to a sediment component using multiple linear regression the resulting regression or calibration equations were then evaluated using the test samples calibration equations were written relating spectra to several sediment components including carbonate atlantic and east pacific rise odp site 847 organic carbon content atlantic and east pacific rise and opal content east pacific rise the correlation coefficients for the regression equations ranged from a high of 0 99 for carbonate and opal at odp site 847 to a low of 0 97 for atlantic carbonate indicating that spectral variations are highly correlated to sediment composition all of the equations include a substantial number of variables from shorter visible and longer near ultraviolet wavelengths suggesting that these wavelengths are especially important for devices designed specifically to scan marine cores although equations for estimating organic and carbonate content appear independent of other sediment components the opal equation is strongly dependent on carbonate content indicating that opal concentration is correlated to carbonate content tests of the calibration equations indicated that all our equations reasonably estimate the pattern of changes either down core or in surface sediments where our spectral estimates have difficulty is with absolute values frequently over or underestimating observed values by a substantial amount within these limitations diffuse reflectance spectrophotometry can be a useful tool for characterizing marine cores and as our understanding of the relationship between spectra and mineralogy improves so will estimates of absolute values

response of marine palynomorphs to neogene climate cooling in the iceland sea odp hole 907a abstract the present study on odp leg 151 hole 907a combines a detailed analysis of marine palynomorphs dinoflagellate cysts prasinophytes and acritarchs and a low resolution alkenone based sea surface temperature sst record for the interval between 14 5 and 2 5 ma and allows to investigate the relationship between palynomorph assemblages and the paleoenvironmental evolution of the iceland sea a high marine productivity is indicated in the middle miocene and palynomorphs and ssts both mirror the subsequent long term neogene climate deterioration the diverse middle miocene palynomorph assemblages clearly diminish towards the impoverished assemblages of the late pliocene parallel with a somewhat gradual decrease of ssts being as high as 20 c at 13 5 ma to around 8 c at 3 ma superimposed palynomorph assemblages not only reflect middle to late miocene climate variability partly coinciding with the short lived global miocene isotope events mi events but also the initiation of a proto thermohaline circulation across the middle miocene climate transition which led to increased meridionality in the nordic seas last occurrences of species cluster during three events in the late miocene to early pliocene and are ascribed to the progressive strengthening and freshening of the proto east greenland current towards modern conditions a significant high latitude cooling between 6 5 and 6 ma is depicted by the supraregional decahedrella event coeval with lowest miocene productivity and a sst decline in the early pliocene a transient warming is accompanied by surface water stratification and increased productivity that likely reflects a high latitude response to the global biogenic bloom the succeeding crash in palynomorph accumulation and a subsequent interval virtually barren of marine palynomorphs may be attributed to enhanced bottom water oxygenation and substantial sea ice cover and indicates that conditions seriously affecting marine productivity in the iceland sea were already established well before the marked expansion of the greenland ice sheet at 3 3 ma

estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses cappa et al modelling pressure pulses in rock fractures estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses frederic cappa 1 yves guglielmi 2 jonny rutqvist 3 chin fu tsang 3 and alain thoraval 4 geosciences azur university of nice sophia antipolis sophia antipolis france geologie des systemes et des reservoirs carbonates university of provence aix marseille france earth sciences division lawrence berkeley national laboratory berkeley usa ineris ecole national superieure des mines de nancy parc de saurupt nancy france corresponding author fax 33 4 92 94 26 10 e mail address cappa geoazur unice fr f cappa