hydrothermal alteration as a trigger mechanism for earthquake swarms the vogtland nw bohemia region as a case study summary earthquake swarms occur mostly in regions with co2 enriched pore fluids it is generally accepted that both geodynamic stress accumulation and critical pore fluid pressures act as a triggering mechanism for most seismic events the new thesis presented here is that hydrothermal alteration processes in fault zones help facilitate the shear failure propagation due to mechanical weakening and dissolution of the wall rock in addition to the normal shear stress and fluid overpressure the basic idea that stress corrosion cracking results from chemical weakening and comminution has been discussed for many years however it has not yet been applied to explain the earthquake swarm phenomenon studies of extensive alteration as well as the latest investigations of co2 sequestration give evidence that these high dissolution rates of wall rock in contact with an acid fluid phase exist in seismogenic fault zones several indications support the assumption that in the vogtland nw bohemia region the weakening of stressed fault zones by hydrothermal alteration could take place at seismogenic depths and could generate earthquake swarms investigations of quartz samples from the fracture zones by means of cathodoluminescence as well as spatiotemporal analysis of seismicity and numerical modelling of alteration induced earthquake swarms support this hypothesis

mechano chemical interactions in sedimentary rocks in the context of co2 storage weak acid weak effects abstract due to the corrosive nature of dissolved co2 the potential short or long term alteration of rock properties represents a major issue in several sites where natural co2 circulation is observed as well as in reservoirs targeted for storage of anthropogenic co2 to date this has been primarily studied from a transport chemical perspective with laboratory evidence of microstructural modifications together with the consequences for flow properties compared to the transport chemical aspects the mechanical chemical aspects have been less investigated though it is to be expected that mechanical properties e g elastic properties failure parameters and time dependent mechanical behaviour could potentially be affected in a similar manner to hydraulic parameters yet since co2 is a weak acid the ph drop is expected to be moderate with a likely lower limit close to 4 0 the buffering of ph by calcite minerals present in most reservoirs targeted for storage may further limit the ph drop as well as confining it to a localized rock volume around the injection well this leads to the question of the magnitude and time spatial scales of chemically mediated mechanical processes during co2 sequestration the authors propose to address this issue by reviewing recent laboratory based studies restricted to sedimentary rocks namely reservoir rocks carbonate or sandstone intact or fractured caprocks and fault rocks key findings include the following 1 the short term impact on the elastic and inelastic behaviour of intact caprocks remains limited 2 shear strength weakening is likely to be respectively low and low to moderate for shale clay rich and anhydrite rich faults but without modifying slip stability in either case 3 the largest impact is located within carbonate reservoirs but with a broad range of reported responses depending on hydrodynamic conditions closed or open and on dissolution regime uniform or channelling and 4 creep experiments confirm that co2 induced dissolution may enhance long term compaction of carbonate reservoirs but the magnitude of acceleration varying from non significant to 50 times depends to a large extent on site specific conditions grain size ph temperature effective stress state etc which renders any direct extrapolation from laboratory to reservoir scale difficult finally some directions for future research studies are discussed

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

fracture mechanical properties of carbonate and evaporite caprocks in sichuan basin china with implications for reservoir seal integrity abstract fracture development in reservoir rocks enhances the flow and transport properties of the petroleum system yet fracture in caprocks can significantly risk reservoir seal integrity over geological time scales the slow subcritical fracture propagation can contribute considerably to the fracture system development especially under reactive fluid environments during petroleum migration and accumulation using the double torsion technique we measure the subcritical fracture growth properties of carbonate and anhydrite caprock core samples in sichuan basin china under different environments of ambient air de ionized water and formation water experimental results show that the aqueous fluids significantly promote subcritical fracture growth 1 compared to ambient air the presence of aqueous fluids dramatically reduces both the fracture toughness kic and subcritical fracture growth index sci of the caprocks 2 the kic reduction is more prominent for the anhydrite 50 caprock than the carbonate 30 caprock which suggest that mineral solubility is responsible for the fluid weakening effect 3 a systematic change of sci with varying fluid conditions is observed sci is the largest in air smallest in formation water and intermediate in de ionized water microstructural analysis suggests a predominantly opening mode for both the natural fractures and induced fractures during fracture mechanical testing our results further demonstrate that subcritical fracture growth process is also strongly related to rock composition and stress conditions these observations provide insights into the mechanisms controlling fracture growth in carbonate and evaporite caprocks which could extend to brittle failure and fluid rock interactions occurring during the seismic cycle in the upper crust

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

influence of surrounding environment on subcritical crack growth in marble abstract understanding subcritical crack growth in rock is essential for determining appropriate measures to ensure the long term integrity of rock masses surrounding structures and for construction from rock material in this study subcritical crack growth in marble was investigated experimentally focusing on the influence of the surrounding environment on the relationship between the crack velocity and stress intensity factor the crack velocity increased with increasing temperature and or relative humidity in all cases the crack velocity increased with increasing stress intensity factor however for carrara marble cm in air we observed a region in which the crack velocity still increased with temperature but the increase in the crack velocity with increasing stress intensity factor was not significant this is similar to region ii of subcritical crack growth observed in glass in air region ii in glass is controlled by mass transport to the crack tip in the case of rock the transport of water to the crack tip is important in general region ii is not observed for subcritical crack growth in rock materials because rocks contain water because the porosity of cm is very low the amount of water contained in the marble is also very small therefore our results imply that we observed region ii in cm because the crack velocity increased in both water and air with increasing temperature and humidity we concluded that dry conditions at low temperature are desirable for the long term integrity of a carbonate rock mass additionally mass transport to the crack tip is an important process for subcritical crack growth in rock with low porosity

subcritical crack growth and other time and environment dependent behavior in crustal rocks stable crack growth strongly influences both the fracture strength of brittle rocks and some of the phenomena precursory to catastrophic failure quantification of the time and environment dependence of fracture propagation is attempted with the use of a fracture mechanics technique we examine some of the difficulties encountered when applying techniques originally developed for simple synthetic materials to complex materials like rocks a picture of subcritical fracture propagation is developed that embraces the essential ingredients of the microstructure a microcrack process zone and the different roles that the environment plays to do this we examine the results of 1 fracture mechanics experiments on five rock types 2 optical and scanning electron microscopy 3 studies of microstructural aspects of fracture in ceramics and 4 exploratory tests examining the time dependent response of rock to the application of water

the effect of fluid composition salinity and acidity on subcritical crack growth in calcite crystals chemically activated processes of subcritical cracking in calcite control the time dependent strength of this mineral which is a major constituent of the earth s brittle upper crust here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid ph range 5 7 5 and ionic strength and species na2so4 nacl mgso4 and mgcl2 on the propagation of microcracks in calcite single crystals the effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close all solutions were saturated with caco3 the crack velocities reached during the experiments are in the range 10 9 10 2 m s and cover the range of subcritical to close to dynamic rupture propagation velocities results show that for calcite saturated solutions the energy necessary to fracture calcite is independent of ph as a consequence the effects of fluid salinity measured through its ionic strength or the variation of water activity have stronger effects on subcritical crack propagation in calcite than ph consequently when considering the geological sequestration of co2 into carbonate reservoirs the decrease of ph within the range of 5 7 5 due to co2 dissolution into water should not significantly alter the rate of fracturing of calcite increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep the healing of cracks is found to vary with the specific ions present

comparison of elemental distribution in fresh and weathered samples of selected coals in the jurassic cretaceous kootenay group british columbia canada abstract the concentration of 52 elements in a suite of fresh coal seams and their weathered outcrops was determined using inaa the concentration of organically bound elements such as br cl and s in samples from weathered outcrops was lower than their fresh samples in contrast the concentration of inorganically bound elements such as al ga and fe in fresh samples was lower than their weathered outcrops the concentration or depletion of elements with intermediate bonding such as s in weathered samples was dependent on its affinity towards the organic or inorganic fraction of coal

time dependent brittle creep in darley dale sandstone 1 the characterization of time dependent brittle rock deformation is fundamental to understanding the long term evolution and dynamics of the earth s crust the chemical influence of pore water promotes time dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short term failure strength here we report results from a study of time dependent brittle creep in water saturated samples of darley dale sandstone initial porosity 13 under triaxial stress conditions results from conventional creep experiments show that axial strain rate is heavily dependent on the applied differential stress a reduction of only 10 in differential stress results in a decrease in strain rate of more than two orders of magnitude however natural sample variability means that multiple experiments must be performed to yield consistent results hence we also demonstrate that the use of stress stepping creep experiments can successfully overcome this issue we have used the stress stepping technique to investigate the influence of confining pressure at effective confining pressures of 10 30 and 50 mpa while maintaining a constant 20 mpa pore fluid pressure our results demonstrate that the stress corrosion process appears to be significantly inhibited at higher effective pressures with the creep strain rate reduced by multiple orders of magnitude the influence of doubling the pore fluid pressure however while maintaining a constant effective confining pressure is shown to influence the rate of stress corrosion within the range expected from sample variability we discuss these results in the context of microstructural analysis acoustic emission hypocenter locations and fits to proposed macroscopic creep laws

time dependent cracking and brittle creep in crustal rocks a review abstract rock fracture under upper crustal conditions is driven not only by applied stresses but also by time dependent chemically activated subcritical cracking processes these subcritical processes are of great importance for the understanding of the mechanical behaviour of rocks over geological timescales a macroscopic manifestation of time dependency in the brittle field is the observation that rocks can deform and fail at constant applied stresses a phenomenon known as brittle creep here we review the available experimental evidence for brittle creep in crustal rocks and the various models developed to explain the observations laboratory experiments have shown that brittle creep occurs in all major rock types and that creep strain rates are extremely sensitive to the environmental conditions differential stress confining pressure temperature and pore fluid composition even small changes in any of these parameters produce order of magnitude changes in creep strain rates and times to failure three main classes of brittle creep model have been proposed to explain these observations phenomenological statistical and micromechanical statistical and micromechanical models explain qualitatively how the increasing influence of microcrack interactions and or the increasing accumulated damage produces the observed evolution of macroscopic deformation during brittle creep however no current model can predict quantitatively all of the observed features of brittle creep experimental data are limited by the timescale over which experiments are realistically feasible clearly an extension of the range of available laboratory data to lower strain rates and the development of new modelling approaches are needed to further improve our current understanding of time dependent brittle deformation in rocks

microfracturing and microporosity in shales shales are ubiquitous rocks in sedimentary basins where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories waste waters co2 nuclear fuels moreover when they contain organic matter they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial a process referred to as primary migration and when the hydrocarbons cannot escape these rocks can be exploited as oil or shale gas reservoirs while the presence of fractures at the outcrop scale has been described the existence of fractures at smaller scales their link with microporosity the mechanisms that created them their persistence over geological times and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data here we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability one question is whether such microfractures when observed in outcrops or in drilled core samples extracted from boreholes are related to decompaction and do not exist at depth another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation the mechanisms of microfracture development are described some have an internal origin fracturing by maturation of organic matter dehydration of clays while others are caused by external factors tectonic loading importantly the amount of microfracturing in shales is shown to depend strongly on the content in 1 organic matter and 2 strong minerals the nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso to macro scales such percolating microfracture networks could control both the long term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks finally possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed

the use of sequential extraction to determine the distribution and modes of occurrence of mercury in permian huaibei coal anhui province china sequential extraction tests using a flow injection mercury system fims were done on 34 samples collected from the number 3 4 5 7 and 10 coal seams in the huaibei coalfield average total mercury hg concentrations for the seams were 0 13 0 18 0 54 0 34 and 0 19 mg kg respectively the average value for all of the coal samples was 0 26 mg kg which is higher than most chinese and u s coals six modes of hg occurrence were recognized including water leachable ion exchangeable organic bound carbonate bound silicate bound and sulfide bound hg with rare exception little hg was found in water soluble ion exchangeable or carbonate bound forms sulfide bound hg and organic bound hg dominated seams 3 4 and 10 whereas silicate bound hg dominated seams 5 and 7 the relatively high hg values observed in seams 5 and 7 especially in parting samples are attributed to hg enrichment by magmatic intrusions

physical and chemical controls on the composition of waters in sedimentary basins abstract the composition of subsurface waters is determined not only by diagenetic reactions but also by physical processes of fluid convection and hydrodynamic dispersion the south west louisiana gulf coast provides an instructive field example of the net effects of diagenetic reaction and solute transport on pore water compositions in a regional siliciclastic sequence most formation waters here have compositions totally unlike the compositions of the connate meteoric and marine fluids that were buried with their host sediments at the time of deposition dissolved chloride has been generated by the subsurface dissolution of salt domes and has been pervasively transported by fluid flow throughout most of the upper 3 km of the sedimentary section the simultaneous systematic variation in dissolved na k mg ca and alkalinity with chloride in these waters supports the hypothesis that metastable thermodynamic buffering by silicate carbonate mineral assemblages is a first order control on fluid compositions the chemical potential of chloride or alternatively total anionic charge appears to be a master variable which ranks in importance with such other variables as pressure and temperature in driving diagenesis in this region this variable is controlled largely by physical processes of advection and dispersion in the upper 3 km of the section and by dehydration reactions in deeper mudstone dominated sediments where the composition of the fluid is largely rock buffered the ultimate origin of the fluid and its pathway of chemical evolution may be obscured at least in terms of major solute composition non buffered components such as cl and br or isotopic compositions are more likely to retain information on original end member fluid compositions and reaction pathways

chalcophile elements in western canadian coals abstract concentrations of chalcophile elements as co cu hg mo ni pb sb and zn in western canadian coals were determined using inaa and aas the concentrations of these elements in western canadian coals are within the range for most world coals however there are some high values for coals from outcrops and from areas which are not currently being mined arsenic content in the majority of western canadian coals particularly those currently being mined is low 0 2 3 ppm however there are coals with high arsenic content for example lignites from hat creek a zone contain between 4 0 and 14 0 ppm as in some samples from comox and suquash the as concentration is as high as 240 ppm and 1400 ppm respectively the enrichment of as in high arsenic coals is related to the geology and nature of country rocks associated with the coal seams the concentration of other elements for most western canadian coals particularly those being mined are within the range for most world coals in these coals the concentration ranges in ppm of chalcophile elements are 0 3 3 6 for sb 0 8 4 6 for co 7 35 for cu

influence of pore fluid salt content on compaction creep of calcite aggregates in the presence of supercritical co2 abstract we have performed uniaxial compaction experiments on simulated porous carbonate rocks crushed and sieved carrara marble using pore fluids of varying salinity saturated with co2 in order to investigate the long term chemically coupled effects of co2 on creep of such rock materials experiments were performed at reservoir conditions equivalent to 3 km depth which is up to 30 mpa effective pressure and a temperature of 80 c on samples with mean grain sizes of 28 37 50 and 106 m the tests were carried out using saline pore fluid solutions containing 0 0 6 1 2 and 3 m nacl or 0 1 and 2 m mgcl2 with and without supercritical co2 at a pressure of 10 mpa addition of either salt nacl or mgcl2 to the pore fluid in samples compacted with co2 caused a reduction in compaction creep rate at low salt concentrations 0 6 1 m as salt concentration was increased to values of 2 3 m creep rates increased to approach or exceed values obtained in salt free experiments by comparison of our data on the compaction creep of carbonate aggregates in the presence of added salts and supercritical co2 with microphysical models and previous work on fluid enhanced deformation mechanisms we suggest that the effect of increasing salt concentration in samples tested with supercritical co2 is the net result of progressive inhibition of pressure solution and enhancement of the role of subcritical crack growth the present results imply that storage of co2 in highly porous carbonate formations increases creep rates by up to ten times depending on the salt concentration however it remains difficult to quantify the rate of compaction creep of specific carbonate reservoirs in the context of co2 storage as compaction behaviour is strongly influenced by porosity and other microstructural and compositional factors as well as by salinity

brittle creep in basalt and its application to time dependent volcano deformation time dependent brittle deformation is a fundamental and pervasive process operating in the earth s upper crust its characterization is a pre requisite to understanding and unraveling the complexities of crustal evolution and dynamics the preferential chemical interaction between pore fluids and strained atomic bonds at crack tips a mechanism known as stress corrosion allows rock to fail under a constant stress that is well below its short term strength over an extended period of time a process known as brittle creep here we present the first experimental measurements of brittle creep in a basic igneous rock a basalt from mt etna volcano under triaxial stress conditions results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress and can be equally well fit by a power law or an exponential law with a 20 increase in stress producing close to three orders of magnitude increase in creep strain rate results from stress stepping creep experiments show that creep strain rates are also influenced by the imposed effective confining pressure we show that only part of this change can be attributed to the purely mechanical influence of an increase in effective pressure with the remainder interpreted as due to a reduction in stress corrosion reactions the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips overall our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure regardless of the level of applied stress and the time taken to reach this point the experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law and compared with the observed deformation history at mt etna volcano c 2011 elsevier b v all rights reserved

mercury content of the springfield coal indiana and kentucky abstract with pending regulation of mercury emissions in united states power plants its control at every step of the combustion process is important an understanding of the amount of mercury in coal at the mine is the first step in this process the springfield coal middle pennsylvanian is one of the most important coal resources in the illinois basin in indiana and western kentucky hg contents range from 0 02 to 0 55 ppm the variation within small areas is comparable to the variation on a basin basis considerable variation also exists within the coal column ranging from 0 04 to 0 224 ppm at one kentucky site larger variations likely exist since that site does not represent the highest whole seam hg nor was the collection of samples done with optimization of trace element variations in mind estimates of hg capture by currently installed pollution control equipment range from 9 53 capture by cold side electrostatic precipitators esp and 47 81 hg capture for esp flue gas desulfurization fgd the high cl content of many illinois basin coals and the installation of selective catalytic reduction of no x enhances the oxidation of hg species improving the ability of esps and fgds to capture hg

scale dependence of textural alignment in shales quantified using electron microscopy abstract textural alignment is the primary cause of anisotropy associated with the permeability and mechanical and acoustic properties of rocks although particle alignment in shales is known to be influenced by burial depth mineralogical composition and diagenetic history understanding how these influence image based measures of compaction at the micrometer to nanometer scale is not well understood here we use a novel method which combines scanning electron microscopy and image analysis algorithms to quantify clay alignment in sedimentary rocks for a given field of view the alignment intensity in shales from the podhale basin in poland is positively correlated with clay content based on image analysis however our analysis also shows that the intensity is strongly dependent on the spatial scale of imaging as magnification increases and the field of view in the sem images decreases the alignment intensity drops therefore in images with small fields of view clay alignment is determined by the presence of localized equant silicate mineral grains which effectively hinder the alignment process at the micrometer scale by contrast in images with larger fields of view alignment intensity is determined by the overall compaction state we also show that when the field of view is constant alignment intensity decreases with pixel density and we suggest a range of operating parameters required for obtaining optimum values for alignment intensity from sem images of shales

influence of co2 on the long term chemomechanical behavior of an oolitic limestone 1 in order to study the long term mechanical and petrographical evolutions of a carbonate rock oolitic limestone during storage of co2 co2 injection tests were performed in triaxial cells at temperature and mechanical stresses isotropic and deviatoric corresponding to the depth of the dogger carbonate reservoirs of the paris basin 800 m we used a specific flow through triaxial cell which allowed us to measure very low strain rates in both axial and lateral directions while ensuring the sealing of the samples during the injection of co2 under isotropic loading neither the dynamic percolation i e flow through tests of dry supercritical gaseous co2 nor the diffusion of co2 into initially saturated samples was shown to produce significant axial compaction and calcite dissolution indeed even though the interstitial aqueous fluid becomes acidic the progressive increase in dissolved species induces the h2o co2 calcite re equilibrium the dynamic injection of co2 saturated solution induced significant axial compaction due to the dissolution of calcite at the sample piston interface only under open flow conditions i e the injected acidic solution is continuously renewed under closed flow conditions i e acidic solution recirculation or no flow conditions which reproduce the physicochemical conditions of co2 storage at the field scale better the rapid h2o co2 calcite re equilibrium inhibits calcite dissolution under deviatoric loading and closed conditions the diffusion of co2 induced a very small increase in the psc pressure solution creep process which was stopped by the h2o co2 calcite re equilibrium inside the sample therefore a significant compaction of limestone samples was obtained only under open conditions and is mainly due to a purely chemical mechanism calcite dissolution while the contribution of the chemo mechanical mechanism psc was found to not be of any great importance in the context of massive injection of co2 at the field scale if the reservoir can be considered as a closed system from a hydrodynamic point of view i e the brine circulates in the aquifer but is not renewed by any groundwater co2 will not play a significant role in the chemistry of carbonate reservoirs due to the h2o co2 calcite re equilibrium and will not induce reservoir compaction and affect its long term storage capacity whatever the stress state isotropic or deviatoric

influence of temperature on brittle creep in sandstones the characterization of time dependent brittle creep promoted by chemically active pore fluids is fundamental to our understanding of the long term evolution and dynamics of the earth s crust here we report results from a study of the influence of temperature on both short term strength and time dependent brittle creep in three sandstones under triaxial stress conditions we show that an increase in temperature from 20 degrees to 75 degrees c significantly enhances stress corrosion cracking in all three sandstones leading to 1 a systematic reduction in strength during constant strain rate experiments and 2 an increase by several orders of magnitude in brittle creep strain rates during stress stepping creep experiments we also show that a conventional creep experiment performed at 75 degrees c exhibits a qualitatively similar three stage brittle creep curve as that observed at ambient temperature extrapolation of our results suggests that temperature is likely to be the dominant influence on the evolution of creep strain rate with depth in the shallow crust citation heap m j p baud and p g meredith 2009 influence of temperature on brittle creep in sandstones geophys res lett 36 l19305 doi 10 1029 2009gl039373

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

effects of chemical environment on dislocation creep of quartzite the water related chemical parameter that affects dislocation creep in quartzite has been determined from variations in sample strength and microstructure with chemical environment in buffered deformation and hydrostatic annealing experiments samples were weld sealed in double capsules and were buffered using solid oxygen buffers agcl or co2 black hills quartzite was deformed at 900 c and 1 5 10 5s 1 two samples were deformed at 1700 mpa confining pressure at constant and with and varying over 8 and 15 orders of magnitude respectively both samples deformed by climb accommodated dislocation creep with flow stresses of 300 mpa two additional samples were deformed at 700 mpa at constant lower than for the 1700 mpa samples with varying over 2 orders of magnitude both samples faulted with a peak strength of 800 mpa these four experiments suggest no dependence of dislocation creep strength on or instead a strong dependence of strength on is inferred previously deformed samples of heavitree quartzite were hydrostatically annealed for 4 days at 800 c and 1200 or 500 mpa confining pressure varying and over 2 5 and 1 order of magnitude respectively the microstructures of these samples show increased rates of dislocation climb and grain boundary migration with increasing but no dependence on these buffered experiments indicate that dislocation creep is affected by alone and suggest that the exponent for the term in the power law creep flow law is 2

geology and geochemistry of the mammoth breccia pipe copper creek mining district southeastern arizona evidence for a magmatic hydrothermal origin the copper creek mining district southeastern arizona contains more than 500 mineralized breccia pipes buried porphyry style copper bearing stockworks and distal lead silver veins the breccia pipes are hosted by the copper creek granodiorite and the glory hole volcanic rocks the unexposed mammoth breccia pipe solely recognized by drilling has a vertical extent of 800 m and a maximum width of 180 m the pipe consists of angular clasts of granodiorite cemented by quartz chalcopyrite bornite anhydrite and calcite biotite 40ar 39ar dates suggest a minimum age of 61 5 0 7 ma for the host copper creek granodiorite and 40ar 39ar dates on hydrothermal sericite indicate an age of 61 0 0 5 ma for copper mineralization fluid inclusion studies suggest that a supercritical fluid with a salinity of approximately 10 wt nacl equiv condensed to a dilute aqueous vapor 1 2 8 wt nacl equiv and a hypersaline brine 33 4 35 1 wt nacl equiv minimum trapping temperatures are 375 c and trapping depths are estimated at 2 km sulfur isotope fractionation of cogenetic anhydrite and chalcopyrite yields a temperature of mineralization of 469 25 c calculated oxygen and hydrogen isotope values for fluids in equilibrium with quartz and sericite range from 10 2 to 13 4 and 60 to 39 respectively suggesting that the mineralizing fluid was dominantly magmatic evidence from the stable isotope and fluid inclusion analyses suggests that the fluids responsible for cu mineralization within the mammoth breccia pipe exsolved from a gray porphyry phase found at the base of the breccia pipe

stress corrosion cracking of quartz a note on the influence of chemical environment abstract tensile mode i stress corrosion growth of cracks on the a plane of quartz in a direction normal to z has been studied in de ionized water in 2n hcl and in 2n naoh solutions at 20 c the double torsion testing method was used to obtain crack velocity v stress intensity factor ki curves the stress corrosion index n where v kin was 19 3 for 2n hcl 12 8 for deionized water and 9 5 for 2n naoh the degree of influence of reagent chemistry on crack velocity was most marked at low ki values at 0 5 kic 3 orders of magnitude increase in crack velocity results from substituting 2n naoh for 2n hcl as the corrosive medium but decreased monotonically on raising ki so that close to kic there was no clearly discernible influence on crack growth rates ca 10 3 m s 1 these observations are explained in terms of a model of crack propagation in which at low ki values the chemistry of the bulk fluid environment controls the corrosion reaction the rate of crack growth is enhanced by increasing environmental oh concentration at high ki or velocity however the chemical composition of the quartz surface may control crack propagation rates through its influence on the chemistry of the crack tip fluid as the ph of natural pore fluids is likely to vary widely in different geological environments these results should be noted when invoking stress corrosion to explain geophysical phenomena

vertical variations of mercury in pennsylvanian coal beds from indiana abstract twenty three in situ coal sections were sampled in indiana mines to investigate mercury hg concentrations with a special reference to in seam vertical variations in hg distribution in addition to raw coal corresponding float fractions were also analyzed to evaluate the effectiveness of hg reduction during conventional pre combustion washing hg content in indiana coals in the locations studied averages 0 11 mg kg which after recalculation into equal energy units corresponds to 9 2 lb hg 1012 btu 39 5 kg hg 1010 mj hg content is reduced after washing to 0 07 mg kg on average corresponding to an equal energy hg loading of 5 2 lb hg 1012 btu 22 3 kg hg 1010 mj a large portion of hg appears to be associated with pyrite as in the springfield coal member of the petersburg formation pennsylvanian in the samples from the danville coal member of the dugger formation pennsylvanian hg is associated to a larger extent with organic matter large differences in hg content may exist between different portions of a coal bed in a single location indicating that very careful complete sampling is necessary to get representative hg concentration data

mercury in western canadian subbituminous coal a weighted average study to evaluate potential mercury reduction by selective mining abstract western canadian subbituminous coal is mined using strip mining methods the coal is used to feed coal fired power plants for electricity generation parameters that influence the mercury content of these coals include the occurrence and frequency of partings in the seam weathering and epigenetic mineralization most partings have higher mercury content than the coal layers in the same seam with the single bentonite bed having the highest hg content however some high ash components such as sandy siltstone do not follow this trend the incorporation of the high mercury partings into the as mined coal may increase the hg content in the feed coal epigenetic mineralization may also increase the mercury content of coal depending on the nature of the mineralization calculation of the weighted mean of mercury content for various combination of lithological components of a seam illustrates how these components influence the total mercury content of the seam this approach also suggests how selective mining might be used to reduce mercury in as mined coal results of weighted average calculations of mercury indicate that the thin lithological units with moderate mercury may not necessarily influence that overall weighted average of hg for a seam however there can be exception such as presence of thin 3 5 cm bentonite parting with high mercury in a 94 5 cm seam that increased the mercury content of seam by 83 4

effect of fluid salinity on subcritical crack propagation in calcite abstract the slow propagation of cracks also called subcritical crack growth is a mechanism of fracturing responsible for a ductile deformation of rocks under crustal conditions in the present study the double torsion technique was used to measure the effect of fluid chemistry on the slow propagation of cracks in calcite single crystals at room temperature time lapse images and measurements of force and load point displacement allowed accurate characterization of crack velocities in a range of 10 8 to 10 4 m s velocity curves as a function of energy release rates were obtained for different fluid compositions varying nh 4 cl and nacl concentrations our results show the presence of a threshold in fluid composition separating two regimes weakening conditions where the crack propagation is favored and strengthening conditions where crack propagation slows down we suggest that electrostatic surface forces that modify the repulsion forces between the two surfaces of the crack may be responsible for this behavior

time dependent recovery of microcrack damage and seismic wave speeds in deformed limestone limestone samples were deformed up to 5 inelastic axial strain at an effective confining pressure peff 50 mpa in the cataclastic flow regime and subsequently maintained under constant static stress conditions either isostatic of triaxial for extended periods of time while elastic wave speeds and permeability were continuously monitored during deformation both seismic wave speeds and permeability decrease with increasing strain due to the growth of subvertical microcracks and inelastic porosity reduction during the static hold period under water saturated conditions the seismic wave speeds recovered gradually typically by around 5 relative to their initial value after 2 days while permeability remained constant the recovery in wave speed increases with increasing confining pressure but decreases with increasing applied differential stress the recovery is markedly lower when the samples are saturated with an inert fluid as opposed to water the evolution in wave speed is interpreted quantitatively in terms of microcrack density which shows that the post deformation recovery is associated with a decrease in effective microcrack length typically of the order to 10 after 2 days the proposed mechanism for the observed damage recovery is microcrack closure due to a combination of backsliding on wing cracks driven by time dependent friction and closure due to pressure solution at contacts between propping particles or asperities and microcrack walls the recovery rates observed in the experiments and the proposed underlying mechanisms are compatible with seismological observations of seismic wave speed recovery along faults following earthquakes

tracking mercury from the mine to the power plant geochemistry of the manchester coal bed clay county kentucky abstract the high volatile a bituminous manchester coal bed was sampled at five mine sites in central clay county southeastern kentucky the coal bed has a high mercury concentration at certain sites particularly in the high sulfur uppermost lithology whole coal hg contents range up to 0 52 ppm in a sample with 3 36 pyritic sulfur hg is enriched in the upper lithotype at several of the sites arsenic content exceeds 700 ppm ash basis for all of the whole channel samples and exceeds 1000 ppm for several of the lithotype samples regional geochemical trends from an area of approximately 75 60 km were determined using data from this study in combination with data published by the u s geological survey hg as pb and cl contents exhibit highs in the northwestern portion of the region within the smaller area covered by the detailed mine study the two western sites both have a high sulfur upper lithotype containing high levels of as and hg basement structures previously described in the study area could have influenced the regional coal rank and geochemistry possibly acting as conduits for mineralizing fluids

how precisely can the temperature of a fluid event be constrained using fluid inclusions u s national science foundation ear 1624589 chemical sciences geosciences and biosciences division office of basic energy sciences office of science u s department of energy de fg02 03er15430 bureau of economic geology jackson school of geosciences university of texas austin

partitioning of elements and macerals during preparation of antaibao coal abstract analyses of the macerals ash sulfur and 43 major and trace elements were performed on samples of feed coal cleaned coal middlings and slime collected from the antaibao coal preparation plant china and also on samples from coal preparation experiments this study is focused on the partitioning of elements and macerals during coal preparation and potential environment aspects of the elements the conclusions are as follows 1 in comparison with the feed coal the cleaned coal has a higher vitrinite content and relatively lower inertinite and exinite contents whereas the middlings and slime have lower vitrinite and exinite contents and relatively higher inertinite contents the vitrinite contents in the size segregated cleaned coals were observed to show a slightly increasing tendency with increasing particle size while the inertinite contents decreased 2 physical coal cleaning is not only effective for removal of ash and sulfur but also in reducing the concentration of most elements as cd co cs hg fe k mg nb and ni are observed to show a high degree of removal while br be cu u mn zn and organic sulfur are enriched in the cleaned coal and show a lower degree of removal the large sized cleaned coal is cleaner than the smaller sized fractions 3 the middlings especially the slime are enriched in s hg cr v zn etc so that these fractions should not be directly used as fuel in addition the concentration of pb and v in the process water exceeds the limit of relevant environmental water quality standard consequently it is necessary to develop new processes to remove ash sulfur and hazardous trace elements to the maximum extent further studies on deep processing of the middlings and slime and cleaning of the process water should also be performed

rhenium osmium evidence for regional mineralization in southwestern north america more than 40 base metal porphyry ore deposits in southwestern north america are associated with the laramide orogeny about 90 million to 50 million years ago rhenium osmium dates on molybdenite a rhenium enriched sulfide common in many of the deposits reveal that in individual deposits mineralization occurs near the final stages of magmatic activity irrespective of the time of inception magnitude or duration of magmatism deposits that differ widely in location and in the extent and timing of magmatism have nearly identical ages for mineralization rhenium osmium ages suggest that mineralization occurred during two distinct intervals from about 74 million to 70 million years ago and from 60 million to 55 million years ago most deposits that formed in the oldest interval are within the older precambrian basement of northwestern arizona whereas the younger deposits are restricted to the younger precambrian basement in southern arizona and northern mexico synchronous widespread mineralization indicates that similar crust mantle interaction occurred on a regional scale for ore deposits once thought to be the product of localized processes

parameters influencing the variation in mercury emissions from an alberta power plant burning high inertinite coal over thirty eight weeks period feed coals and fly ashes from a coal fired power station burning alberta subbituminous coal were examined for a period of thirty eight weeks to determine the variation in emitted mercury feed coal samples were analyzed for proximate calorific value and hg content while fly ash samples were examined for c and hg contents the maceral content of the feed coal was also determined the emitted mercury was calculated and compared to mercury emitted from the stack according to a mass balance calculation from a previous study for the same station mercury contents ranged from 0 029 to 0 066 mg kg for feed coal and from 0 069 to 0 112 mg kg for fly ash the carbon char in fly ash was separated into reactive vitrinitic bimacerate and less reactive inertinitic chars using znbr2 at specific gravities of 1 7 2 0 and 2 25 to 2 4 the result shows that there is a positive correlation between the carbon and mercury content of the fly ash the reactive char particles in the fly ash may be responsible for the capture mercury in fly ash the percentage of estimated captured mercury by fly ash increases with increasing carbon content in fly ash the percentage of emitted mercury for the period of 38 weeks is estimated to be within the range of 49 to 76 of the total input of mercury

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

quantifying micron scale grain detachment during weathering experiments on limestone weathering in carbonate rocks is often assumed to be governed by chemical dissolution nevertheless chemical processes can be coupled to mechanical mechanisms with small grains undergoing partial dissolution along grain boundaries followed by detachment from the rock surface crucially this process can even extend down to the micron scale although chemo mechanical detachment could be critical for the understanding of carbonate weathering at the global scale the role it plays has not been directly quantified to calculate the contribution of grain detachment to surface retreat rates and to determine the impact of the flow regime we carried out a series of flow through weathering experiments on micritic limestone using atomic force microscopy we obtained high resolution in situ data of surface topography for reacting rock surfaces in all the experiments both grain detachment and chemical dissolution were observed under the laminar flow conditions we explored we found no clear correlation between flow rate and the size of detached grains or between the flow rate and the frequency of grain detachment events importantly our results establish that grain detachment contributes significantly to the overall surface retreat on average accelerating mass loss by 38 in addition to speeding up weathering this micron scale mechanism could also influence the evolution of porosity in aquifers and hydrocarbon reservoirs and provide a natural flux of colloids that could transport heavy metals or radionuclides in groundwater

formation of oreshoots in mesothermal gold quartz vein deposits examples from queensland australia abstract mesothermal gold quartz vein deposits in granitoid hosted and melange sediment hosted goldfields contain oreshoots in areas of structural dilation the environment of formation is localized at depths of 2 5 km in brittle to brittle ductile shear zones which have stick slip seismic movement lithologic contacts and fissure intersections affect the shape and geometry of the oreshoots mineralizing fluids in these shear zones range between 3 and 10 wt nacl equiv with 18 o values of about 5 8 fluids are locally co 2 bearing with formation temperatures of between 220 and 350 c fluid source is either of deep magmatic or metamorphic origin and can rarely be correlated directly with nearby plutonism fluid transport is via single pass flow in high permeability conduits such as mylonites in granitoids or melange cleavage in sediments complex mixtures of mineralized quartz gouge fault rocks and altered wall rock reflect the environment of formation comb ribbon buck and breccia quartz and microscopic textures indicate different processes and stages of oreshoot formation quartz deposition is due to changes in silica solubility resulting from temperature and pressure fluctuations local pressure changes are due to reduced velocity of the fluid in dilated zones according to bernoulli s equation at restricted or dilated portions of the fissure throttling and adiabatic cooling are common and result in quartz deposition and channel choking which lead to pressure and temperature build ups and faulting the long dip lengths in many mesothermal oreshoots may also account for substantial pressure and temperature reductions in the fluid from bottom to top the venturi effect in connecting fissures may also affect quartz deposition microscopic textures indicate that multiple generations of quartz have been involved in cracking stress corrosion and dissolution due to porosity changes and dilation prior to and during faulting gouge and clay seams stabilize fault movement and may have acted as impermeable barriers and pressure seals which channelled fluid flow and if hydrated may have expelled concentrated brines when compressed by faulting hydrothermal alteration indicates early diffusive transport and chemical and ph gradients away from the oreshoots four main stages of oreshoot formation occur from the outside to the inside of oreshoots as 1 ground preparation and nucleation 2 reinjection and sheeting 3 major fault movement channeling of fluid flow local dissolution and cracking and 4 consolidation and oreshoot growth including fluid stagnation and ponding

subcritical creep compaction of quartz sand at diagenetic conditions effects of water and grain size 1 compactional creep was measured for aggregates of quartz sand that were subjected to an effective pressure of 34 5 mpa and temperature of 150 c for times up to 6 months the effects of grain size and water on creep were determined by loading quartz aggregates of 255 60 130 18 and 35 12 m grain size under nominally dry water vapor static liquid water and flowing water conditions all aggregates displayed transient decelerating creep volume strain rates as low as 2 10 10 s 1 were achieved volume strain rate increases systematically with decrease in grain size and increase in exposure to water at comparable strain or time despite the fact that the effective pressure applied was far less than the critical pressures for short term cataclastic compaction of the quartz aggregates grain scale microstructures indicate that the underlying mechanism of creep is crack growth creep rates are explained by subcritical crack growth as governed by water silicate reactions at crack tips controlled by access of water at dry and vapor conditions and solute chemistry under static and flowing liquid water conditions extrapolation of the experimental results to natural compaction of quartz sand during burial and diagenesis over times of tens of millions of years indicates that porosity loss through subcritical cracking and grain rearrangement of medium grained porous wet quartz sands can reach 10

experimental evidence for rock layering development by pressure solution natural deformation of rocks is commonly associated with development of mineralogical layering leading to irreversible transformations of their microstructure the mechanisms of such chemical differentiation processes during diagenesis tectonics metamorphism or fault differentiation remain poorly understood as they are difficult to reproduce experimentally due to the very slow kinetics involved this paper shows that development of differentiated layering similar to that observed in natural deformation is stress driven and can be obtained from indenter experiments samples of 1 gypsum plaster mixed with clay and 2 natural diatomite loosely interbedded with volcanic ash saturated with aqueous solutions in equilibrium were subjected to loading for several months at 40 c and 150 c respectively x ray microtomography and scanning electron microscopy observations show that layering develops by a self organized pressure solution process stress driven dissolution of the soluble minerals either gypsum or silica is initiated in the areas initially richer in insoluble species clay or volcanic ash as diffusive mass transfer along the interface between soluble and insoluble minerals is much faster than along the healed boundaries of the soluble minerals the passive concentration of the insoluble minerals amplifies the dissolution along layers oriented perpendicularly to the maximum compressive stress conversely in areas with an initial low content of insoluble minerals and clustered soluble minerals dissolution is slower consequently these areas are less deformed they host the re deposition of the soluble species and act as rigid objects that concentrate both stress and dissolution near their boundaries thus amplifying the differentiation and the development of layered microstructures

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form