structure and diffusive properties of fluid filled grain boundaries an in situ study using infrared micro spectroscopy the rate of numerous diagenetic deformation and metamorphic processes in crustal rock systems ultimately depends on the structure and diffusive properties of water bearing grain boundaries we present the first in situ spectroscopic study of the nature of aqueous films present in mineral interfaces undergoing stress induced dissolution or pressure solution using infrared micro spectroscopy we show that during active pressure dissolution of the 111 plane of halite nacl against a caf2 plate the confined intercrystalline liquid has an average thickness of 85 185 nm and occupies a rough non equilibrium grain boundary structure the hydrogen bonding of the water within the grain boundary film is modified due to increased polymerization towards ice like hard water simultaneous pressure solution rate measurements show that diffusion within the grain boundary fluid is about one order of magnitude slower than in bulk solution during active pressure solution of the 100 plane of halite a similar non equilibrium grain boundary structure develops but the average thickness of the confined water film is only 40 nm and no evidence is found for modification of the hydrogen bonding of the water the difference in hydrogen bonding between the two orientations studied is attributed to differences in surface charge distribution on the 111 and neutral 100 interfaces in nacl the difference in mean film thickness is attributed to differences in crystallographically controlled roughness of the dissolving nacl surface if similar grain boundary thickness and diffusivity effects occur in other rock forming minerals pressure solution in such systems will tend to be interface reaction controlled and may be capable of producing significant seismic anisotropy

ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

compositional recycling structure of an archean super plume nb th u lree systematics of archean komatiites and basalts revisited the volcanic stage of the 2 7 ga abitibi greenstone belt canada is dominated by bimodal arc magma series and komatiite basalt sequences the latter represents an aerially extensive oceanic plateau erupted from an anomalously hot super plume komatiites define a linear array of nb th vs nb u extending from nb th 8 20 and nb u 26 58 whereas basalts plot on a separate but overlapping field extending to higher th u but lower nb th values inter element ratios of th u nb and lree of komatiites and basalts plot with phanerozoic and modern ocean plateau basalts th u nb and lree are fractionated in subduction zones into low nb th nb u and nb lree arc crust and complementary high nb th nb u and nb lree residual slab accordingly the archean komatiite basalt association may be explained by a plume that likely originated from the core mantle boundary with komatiites erupted from a hot axis containing recycled oceanic crust and basalts erupted from the plume annulus that entrained upper mantle containing recycled oceanic and continental crust high nb th and nb u of plume related volcanic sequences documented in abitibi yilgarn and baltic archean greenstone belts suggest that the extraction and recycling of continental crust may have occurred early in the archean

early carbonate veining and gold mineralization in the timmins camp depositional context of the dome mine ankerite veins abstract the earliest auriferous veining event in the development of the over 16 moz gold endowment at the dome mine was an extensive set of ankerite veins over 5400 m strike length the depositional context of the dome mine ankerite veins has been historically contentious and their role in the mineralization history of the deposit not well understood we present a deposit wide geochemical study of the ankerite veins and their host rocks with observations from new underground mapping ankerite veining across the mine is almost exclusively restricted to the vipond formation which is fe rich and tholeiitic in nature metamorphic fluids and ankerite vein formation generally focused along flow boundaries in the volcanic sequence however carbonatization is ubiquitous the flows of the vipond formation maintain their protolith geochemical signatures as ree zr al2o3 tio2 and y are largely immobile during mineralization and alteration which mobilized na2o k2o and locally fe2o3 the ankerite vein structures are reactivated and overprinted by quartz and quartz tourmaline veining and gold grade is variable ranging from

quantifying damage saturation and anisotropy in cracked rocks by inverting elastic wave velocities crack damage results in a decrease of elastic wave velocities and in the development of anisotropy using non interactive crack effective medium theory as a fundamental tool we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties using this same tool we show that both the anisotropy and shear wave splitting of elastic waves can be derived two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation reaching up to 60 in the dry case comparison with experimental data on two granites a basalt and a marble shows that the range of validity of the non interactive effective medium theory model extends to a total crack density of approximately 0 5 considering symmetries up to orthorhombic in the isotropic case kachanov s 1994 non interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions inversions are stable and give coherent results in terms of crack density and aperture evolution crack density variations can be interpreted in terms of crack growth and or changes of the crack surface contact areas as cracks are being closed or opened respectively more importantly the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio and therefore aperture with pressure which has broader geophysical implications in particular on fluid flow the recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure in the anisotropic cases both transverse isotropic and orthorhombic symmetries were considered anisotropy and saturation patterns were well reproduced by the modelling and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging

experimental pressure solution in halite the effect of grain interphase boundary structure to investigate the mechanisms and kinetics of pressure solution we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50 2 0 2 c and fluid pressures of 0 1 mpa loads applied using small springs ranged from 0 1 4 2 n mean effective normal stresses within the contact zone ranged from 1 14 mpa the geometry and diametric growth rate of the contact spot neck growth and the rate at which the lenses approached one another convergence were monitored during deformation using transmitted and reflected light photomicrography time dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine convergence rates in the halite silica experiments were 0 01 0 05 m day although the initial deformation during loading involved elastic and plastic processes control experiments without brine showed no time dependent convergence indicating that dislocation creep did not contribute to the observed rates no undercutting or cataclasis was observed in any experiments residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine indicating non zero wetting angles

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

subaqueous rhyolite block lavas in the miocene ushikiri formation shimane peninsula sw japan abstract a rhyolite mass of the miocene ushikiri formation in the western part of the shimane peninsula sw japan is a small subaqueous edifice about 600 m high and 4 km wide formed at water depths between 200 and 1000 m it consists mainly of three relatively flat lava flow units 50 300 m in maximum thickness each of which includes lobes and their polyhedral fragments the lava lobes are poorly to well vesiculated glassy to microcrystalline and flow banded and folded compared with mafic pillows they are large having thick quenched and brecciated glassy crusts because of their high viscosity surface tension and thermal conductivity their surfaces disintegrate into polyhedral fragments and grade into massive volcanic breccia the massive volcanic breccia composed of the lobe fragments is poorly sorted and covered with stratified volcanic breccia of the same rock type the rhyolite lavas commonly bifurcate in a manner similar to mafic pillow lavas however they are highly silicic with 1 5 vol phenocrysts and have elongated vesicles and flow folds implying that they were visco plastic during flowage their surface features are similar to those of subaerial block lava with respect to rheological and morphological features they are subaqueous equivalents of block lava

subaqueous phreatomagmatic explosion breccias at buttercup hill noranda quebec irregular branching white fragment breccia dikes are restricted to the uppermost flows of the amulet formation where they occur within or are parallel to synvolcanic faults at buttercup hill the breccia dikes bifurcate upward and are continuous with a localized deposit of identical conformable breccia within the lowermost andesitic flows of the millenbach andesite formation the dikes are shallow poorly sorted intrusive breccias and like the overlying conformable breccia deposit are characterized by white angular fragments of variably silicified andesite derived from the immediately underlying amulet formation and to a lesser extent from the millenbach andesite formation the fragments show a complete range in size from 0 5 m to 1 cm and occur within a finer matrix that includes fine ash broken feldspar crystals and chloritized sideromelane shards sideromelane shards are foreign juvenile fragments derived from underlying andesitic magma emplaced as dikes during the onset of volcanism brec

stereology based fabric analysis of microcracks in damaged granite abstract crack related fabric analyses were carried out in terms of crack tensors using inada granite deformed inelastically in a triaxial vessel up to post failure focusing on the fabric changes during brittle failure complementarily numerical simulation tests were conducted to determine the representative volume element rve required for crack surveying numerical simulation tests show that the window size for crack surveying should be at least six times the mean trace length in order to obtain a statistically meaningful crack tensor a larger window is needed to estimate the distribution of crack radii in quartz cracks grow preferentially parallel to the major loading axis crack tensors in quartz can provide a measure of damage reflecting inelastic deformation under differential stress in past geological events during the first stage of inelastic deformation the number density of cracks decreases with a rather sharp increase in crack diameters this happens because pre existing cracks in intact rock join together to make longer cracks however the density remains almost constant during the second stage of loading from 90 to 100 of the peak stress the crack diameter gradually increases due to the stable propagation of cracks when granite is further deformed beyond the peak stress the number density decreases again while sharp increases in crack diameters appear as a result of the forking and coalescence of cracks it is also suggested that load normal grain boundary cracks are generated as a result of the rolling and sliding of disintegrated blocks in the post failure stage

the significance of europium anomalies in the ree spectra of granites and pegmatites mont laurier quebec abstract negative eu anomalies in the ree spectra of granitic rocks are usually interpreted as evidence of earlier separation of a mineral phase such as plagioclase our study of the behaviour of the ree and of u and th during late stage alteration of granites and the formation of pegmatites suggests an alternative means for producing eu anomalies albitization of earlier formed plagioclase has depleted the granites in eu and enriched the pegmatites in this element this process is linked to the mobilization of u in the granites which is dependent on the oxidation state of the fluids a systematic correlation between the ratios eu ce and u th leads us to suggest a similar explanation for irregularities in the abundances of ce and other rare earths in the ree spectra of these rocks we suggest that anomalous behavior of eu in other environments or processes such as the alteration of basalt and the formation of certain ore deposit types may be caused partly by this mechanism

a comparison of miocene and archean rhyolite hyaloclastites evidence for a hot and fluid rhyolite lava abstract in this paper we compare the geology and petrography of miocene and archean submarine rhyolite hyaloclastites the hyaloclastites are sparsely 10 or less plagioclase quartz and pyroxene phyric the hyaloclastites consist of a feeder dyke from which branch lava lobes and irregularly shaped lava pods the lava bodies consist of a holocrystalline core with microlitic texture grading outward into a flow layered rim zone and finally into obsidian the proportion of plagioclase and pyroxene microlites decreases outward some layers of the rim zone may be pumiceous vesicularity up to 50 vesicle size 1 mm or less but most of the lava has less than 5 vesicles one or a few cm long the obsidian shows perlitic fracture patterns the lava bodies grade through an in situ breccia into a hyaloclastite composed of angular obsidian granules and in many cases of fragments of lava lobes evidence for alteration at high temperature is as follows in the archean rhyolite hyaloclastites plagioclase microlites are overgrown by quartz albite spherulites furthermore parts of the miocene and archean hyaloclastite have been cemented and granules have been marginally replaced by quartz and albite hyaloclastite cemented at high temperature locally shows columnar joints at low temperatures obsidian has been hydrated and or has been replaced by clay minerals zeolites chlorite or prehnite chess board albite and fibroradial prehnite in archean hyaloclastite is possibly a pseudomorph after zeolites the sparsely porphyritic nature of the lava and the absence of microlites from the quenched glass suggests that the thyolite hyaloclastites extruded at high near liquidus temperature furthermore pumice is present only locally in the flow layered rim zone and in fragments derived from that zone these features suggest that vesiculation was inhibited by the weight of the water column high temperature and possibly the volatile h 2 o content explain the relatively low viscosity and shear strength of the lava and resulted in the flow morphology particular to this type of hyaloclastic rhyolite flows

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

rare earth element mobility at constant inter ree ratios in the alteration zone at the phelps dodge massive sulphide deposit matagami quebec rare earth elements ree from la to ho were mobile and enriched in hydrothermally altered rocks below the archean phelps dodge cu zn volcanogenic massive sulphide deposit in northwestern quebec largest net enrichment was in the moderately altered quartz chlorite zone where la concentration increased six fold and lanybn steepened from 1 9 to 13 0 the intensely altered chloritite zone had both minor net ree enrichment and depletion yb and lu were immobile throughout both zones the mobile ree were added and subtracted in constant chondrite normalized inter ree proportions 1 0 la 0 79 ce 0 57 nd 0 49 sm 0 01 eu 0 10 tb and 0 02 hb small additions of eu relative to generally larger additions of lree and tb produced enhanced negative eu anomalies the ree were mobilized at the hot 300 c core of the alteration system and deposited at the cooler periphery other sites of intense alteration and water rock interaction display similar ree changes indicating that selective ree enrichment at constant inter ree ratios is a widespread phenomenon

compaction creep of simulated anhydrite fault gouge by pressure solution theory v experiments and implications for fault sealing the sealing and healing behaviour of faults filled with anhydrite gouge by processes such as pressure solution is of interest in relation both to the integrity of faults cutting geological storage systems sealed by anhydrite caprocks and to seismic events that may nucleate in anhydrite bearing sequences such as those present in the seismogenic zone beneath the apennines we have developed a detailed series of kinetic models for pressure solution in anhydrite fault gouge allowing for dissolution diffusion and precipitation control to estimate the time scale on which such sealing and healing effects occur we compare the models obtained with previously reported experimental data on compaction creep rates in simulated anhydrite fault gouge tested under wet upper crustal conditions the results confirm earlier indications that compaction under these conditions likely occurs by diffusion controlled pressure solution applying our most rigorous model for diffusion controlled pressure solution constrained by the fit to the experimental data we infer that anhydrite fault sealing will occur in a few decades at most which is rapid compared with both co2 storage time scales and with the recurrence interval for seismicity in the apennines

compaction of granular quartz under hydrothermal conditions controlling mechanisms and grain boundary processes 1 we report isostatic compaction experiments performed on granular quartz under hydrothermal conditions 3 129 m of initial grain size 300 600 c 200 mpa of fluid pressure and 25 100 mpa of effective pressure from microstructural evidence it was determined that whereas microcracking controlled precompaction at room temperature pressure solution was the main mechanism during hydrothermal compaction although a role of microcracking could not be excluded entirely our mechanical data together with theoretical pressure solution rate models further indicated that pressure solution was controlled by interface kinetics dissolution being the most likely rate controlling mechanism an empirical relation of the form 10 7 8 0 10 0 3 4d 1 exp 105 000 rt was fitted to our data to describe experimental compaction rates electron backscatter diffraction ebsd analysis performed on one sample showed limited evidence for plastic deformation dauphine twinning and lattice bending at grain contact points under high stress contact microstructures formed during compaction were studied using quartz single crystal discs or a mica plate as reference surfaces this showed that in all contacts microstructures were rough with a micrometer scale roughness many contacts also showed internal microcracking and it is inferred that microcracking is likely an important mechanism for creating and maintaining rough contacts during quartz pressure solution at least under the present experimental conditions extrapolation of our empirical equation for compaction rates to natural conditions is consistent with previous observations that during burial and diagenesis of a sandstone pressure solution starts to operate at depths of about 1 5 2 km becoming the dominant compaction mechanism at depths greater than 2 5 3 km the extrapolation gives good agreement with porosity depth trends reported for natural arenitic sandstones

roughness of fault surfaces over nine decades of length scales 1 we report on the topographic roughness measurements of five exhumed faults and thirteen surface earthquake ruptures over a large range of scales from 50 m to 50 km we used three scanner devices lidar laser profilometer white light interferometer spanning complementary scale ranges from 50 m to 10 m to measure the 3 d topography of the same objects i e five exhumed slip surfaces vuache sillingy bolu corona heights dixie valley magnola a consistent geometrical property i e self affinity emerges as the morphology of the slip surfaces shows at first order a linear behavior on a log log plot where axes are fault roughness and spatial length scale covering five decades of length scales the observed fault roughness is scale dependent with an anisotropic self affine behavior described by four parameters two power law exponents h constant among all the faults studied but slightly anisotropic h 0 58 0 07 in the slip direction and h 0 81 0 04 perpendicular to it and two pre factors showing variability over the faults studied for larger scales between 200 m and 50 km we have analyzed the 2 d roughness of the surface rupture of thirteen major continental earthquakes these ruptures show geometrical properties consistent with the slip perpendicular behavior of the smaller scale measurements our analysis suggests that the inherent non alignment between the exposed traces and the along or normal slip direction results in sampling the slip perpendicular geometry although a data gap exists between the scanned fault scarps and rupture traces the measurements are consistent within the error bars with a single geometrical description i e consistent dimensionality over nine decades of length scales

subaqueous paleoproterozoic metarhyolite dome flow cone complex flin flon greenstone belt manitoba canada abstract two sparsely plagioclase phyric rhyolite domes 50 100 m thick and 125 250 m long as observed in 2 dimensional vertically dipping exposures are partly mantled by a rhyolite volcaniclastic complex that on the south side of the domes also forms a half cone like mound at least 60 m thick and 500 m long the domes and mantling volcaniclastic complex are overlain by three aphyric to sparsely phyric rhyolite flows that are 70 120 m thick and 550 1200 m long domes and flows have a lower columnar jointed highly fractured locally brecciated subfacies that grades upward into 40 95 crackled and disaggregated breccia crackled breccia is a highly fractured subfacies in which clast like areas are bounded by closely spaced joints and minor matrix but there is only limited rotation of clasts crackled breccia was produced by quench fracturing combined with hydraulic action of water converted to steam or supercritical fluid within the fractures overlying disaggregated breccia comprises rotated particles and 25 50 matrix it is most abundant near flow margins and is a crumble breccia produced by flow advance or expansion the volcaniclastic mound comprises lenticular interlayered facies of 1 resedimented phreatomagmatically generated heterolithic rhyolitic tuff and lapilli tuff 2 isolated to close packed rhyolite lobes that are 0 5 5 m thick and 0 5 50 m long the lobes are at least in part pillows and 3 units comprising small

microstructural insight into the nonlinear swelling of argillaceous rocks argillaceous rocks are chosen as possible host rocks for underground radioactive nuclear waste disposal these rocks exhibit complex coupled thermo hydro chemo mechanical behavior the description of which would strongly benefit from an improved experimental insight on micro scale in this work we present some recent observations of the evolution of these rocks upon swelling on the scale of their composite microstructure essentially made of a clay matrix with embedded grains of calcite and quartz with sizes ranging from a few to several hundreds of micrometers the micro scale experimental investigation was based on the combination of high definition and high resolution imaging in an environmental scanning electron microscope esem and digital image correlation techniques samples were held at a constant temperature of 2 c while the vapor pressure in the esem chamber was varied from a few to several hundreds of pascals generating a relative humidity rh ranging from about 10 up to 99 results on micro scale showed strongly heterogeneous deformation fields which result from complex hydromechanical interactions between different components of argillaceous rocks the swelling of argillaceous rocks is moderate at low rh but becomes significant at high rh the observations demonstrated that the nonlinearity is related not only to the micro cracking upon wetting but also to the nonlinear swelling of the clay matrix itself that is governed by different mechanisms

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

review of archean supracrustal assemblages of the southern abitibi greenstone belt in ontario canada products of microplate interaction within a large scale plate tectonic setting abstract previously formulated plate convergent models account for many aspects of the large scale regularity and parallelism between different subprovinces of the archean superior province such models do not however appear to adequately explain the within subprovince evolution of 2 75 2 68 ga supracrustal assemblages of the late archean southern abitibi greenstone belt principal supracrustal assemblage classes include l assemblages dominated by tholeiitic metabasalt and metakomatiite with varying amounts of tholeiitic intermediate to felsic metavolcanic rocks these assemblages probably formed in extensional settings the ratio of basalt to komatiite and the ratio of basalt komatiite to intermediate felsic metavolcanic rocks may be a function of mantle temperature and crustal thickness at the site of extension respectively 2 assemblages dominated by intermediate to felsic fragmental and or effusive rocks are generally of calcalkalic affinity and likely formed in island arc settings 3 assemblages containing a substantial component of iron formation may represent older supracrustal assemblages that form structural and or stratigraphic basement to some of the younger supracrustal assemblages 4 assemblages consisting almost wholly of turbidite facies metasedimentary rocks appear to postdate volcanic activity related to the previous assemblages deposition of these sediments broadly coincides with the onset of regional deformation these assemblages may represent distal deposits related to an emerging collisional orogen 5 assemblages consisting of alluvial fluvial metasedimentary rocks with or without spatially associated alkalic metavolcanic rocks are associated with crustal scale shear zones and are the youngest assemblages within the greenstone belt alluvial fluvial assemblages likely represent the final emergence of the consolidating orogen geochronological data and assemblage distribution suggest that the supracrustal assemblages of the southern abitibi greenstone belt may represent the amalgamation of products of diverse and intricate microplate tectonic settings repeated in time and space prior to the impingement of the large scale plate tectonic regime that dictated the final large scale configuration of the archean superior province

equilibrium halite h2o dihedral angles high rock salt permeability in the shallow crust shallow deposits of halite are well known to be impermeable to brines and hydrocarbons yet recent studies of deeply buried salt point toward considerable water halite interaction we have resolved this apparent paradox via experimental determinations of the dihedral angle for the static halite h 2 o system at temperatures of 20 to 300 c and pressures from atmospheric to 2 kbar the halite brine dihedral angle which controls pore fluid connectivity and hence permeability is found to be a sensitive function of both temperature and pressure in sedimentary basins with normal geothermal gradients halite bodies at depths exceeding 3 km will contain a stable interconnected brine filled porosity resulting in permeabilities comparable to those of sandstones our results explain recent observations of major salt fluid interactions at depth and suggest that deep rooted salt diapirs may act as conduits for basinal formation water they also have important implications for the flow of brines around heat producing canisters of high level nuclear waste buried in natural rock salt

creep burst coincident with faulting in marble observed in 4 d synchrotron x ray imaging triaxial compression experiments faults in carbonate rocks show both seismic and aseismic deformation processes leading to a wide range of slip velocities we deformed two centimeter scale cores of carrara marble at 25 c und

massive sulfide deposits of the noranda area quebec ii the aldermac mine the original aldermac mine near noranda contained several cu zn massive sulfide lenses hosted by felsic to mafic volcanic rocks of the late archean blake river group the original nos 3 6 orebodies which consisted of massive pyrite with lesser magnetite pyrrhotite chalcopyrite and sphalerite contained 1 87 mt of cu zn ore that averaged 1 47 cu zn was not recovered the orebodies occurred within felsic breccias and tuffs up to 100 m thick that are stratigraphically overlain by an extensive dome of mainly massive rhyolite and rhyodacite up to 250 m thick and at least 550 m across most of the volcanic rocks that laterally flank and overlie the felsic dome are dacitic to andesitic flows breccia and tuff with minor rhyolites and associated subvolcanic sills of quartz feldspar porphyry and gabbro the new massive sulfide deposit discovered in 1988 lies 150 200 m east of the mined out orebodies at a similar stratigraphic level within altered felsic breccia and tuff the sulfides are mainly in

fingerprinting multiple gold mineralization events at the dome mine in timmins ontario canada trace element and gold content of pyrite abstract the dome mine is host to over 16 moz of orogenic gold deposited during a period of up to 25 ma through multi stage enrichment the earliest economic stage of veining is an extensive set of ankerite veins which were historically considered barren except where overprinted by subsequent veining events gold in these veins is intimately associated with pyrite mineralization and three stages of pyrite growth have been identified py1 2 3 the trace element content of each stage of pyrite growth determined by dynamic secondary ion mass spectrometry and synchrotron radiation x ray fluorescence reveals that there were three auriferous fluid events each with a unique gold and trace element fingerprint which can be related to deposits wide mineralization events early ankerite vein forming fluids were auriferous lower temperature 200 250 c and deposited py1 enriched in gold metals and metalloids as cu ni zn py2 growth is related to deposit wide quartz tourmaline and quartz fuchsite veining based on trace element geochemistry au ag and associated mineral assemblages this deposited ni enriched pyrite tellurides galena and gold with anomalously high au ag ratios there is also evidence for remobilization of early gold and trace elements from py1 pyrite during the py2 forming event the final stage of gold endowment in the ankerite veins is related to a deposit and camp wide quartz veining event py3 growth is trace element as ni cu and au poor with respect to py1 and py2 however this veining event contributed the bulk of the ankerite vein gold endowment the remobilization of gold and trace elements from sieve textured py1 in addition to overprinting py2 and py3 and their associated gold endowments helps explain the difficulty in applying bulk rock trace element vectors to gold at the dome mine the work also provides conclusive evidence for the auriferous nature of early ankerite veining at the dome mine and reveals that the system was fertile for a period of over 7 to 25 ma a key component for the formation of a world class deposit

multiple rind structure in pillow lava as an indicator of shallow water multiple rind structure is common among shallow water pillows with diameters larger than about 1 m in oamaru new zealand on the columbia plateau usa and elsewhere a rind consists of sideromelane tachylyte and tachylytic basalt a multiple rind is a concentric set of repeated rinds in various forms e g a portion of a broken rind thrust under another part a series of short and detached subparallel rinds or a pouch shaped depression transitions and combinations of these three forms are common multiple rind structure develops at any part of the pillow perimeter but does not cover the pillow completely it is always accompanied by a rupture in the outermost rind up to 13 rinds have been observed but two to four rinds are most common the multiple rind structure is formed by implosion resulting from condensation of exsolved h2o when h2o condenses a pressure difference between the interior and exterior of a pillow is created above a certain threshold pressure difference the outer skin of a pillow is torn at weak points such as radial joints and thrusts under the neighboring skin buckles to form a pouch shaped depression or produces some variation of these one set of multiple rinds is thus formed further exsolution and condensation of h2o in solidifying pillows may cause development of additional rinds h2o exsolution and condensation and subsequent implosion are limited to low pressure environments so that multiple rind structure is characteristic of shallow water pillow lava

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

influence of stress temperature and strain on calcite twins constrained by deformation experiments abstract a series of low strain triaxial compression and high strain torsion experiments were performed on marble and limestone samples to examine the influence of stress temperature and strain on the evolution of twin density the percentage of grains with 1 2 or 3 twin sets and the twin width all parameters that have been suggested as either paleopiezometers or paleothermometers cylindrical and dog bone shaped samples were deformed in the semibrittle regime between 20 c and 350 c under confining pressures of 50 400 mpa and at strain rates of 10 4 10 6 s 1 the samples sustained shear stresses up to 280 mpa failing when deformed to shear strains 1 the mean width of calcite twins increased with both temperature and strain and thus measurement of twin width provides only a rough estimation of peak temperature unless additional constraints on deformation are known in carrara marble the twin density nl no of twins mm increased as the rock hardened with strain and was approximately related to the peak differential stress mpa by the relation 19 5 9 8 n l dislocation tangles occurred along twin boundaries resulting in a complicated cell structure which also evolved with stress as previously established the square root of dislocation density observed after quench also correlated with peak stress apparently both twin density and dislocation cell structure are important state variables for describing the strength of these rocks

the effect of fluid chemistry on quartz microcrack lifetimes abstract metamorphic porosity consists of a branching hierarchy of primary features grain boundaries secondary features 3 and 4 grain junction tubules tertiary features microcracks and higher order features fractures while some of these features are rarely open to bulk fluid flow e g boundaries higher order features are open to fluid flow for timescales which vary significantly as a function of temperature pressure and fluid and rock chemistry the kinetics of microcrack healing in quartz between 300 600 c at 200 mpa increases as a function of fluid chemistry in the following order co 2 h 2 o 2 o m nacl 2 m cacl 2 6 m nacl changes in fluid chemistry which increase quartz solubility correlate with increased rates of healing these observations suggest that local redistribution of quartz occurs by solution precipitation driven by gradients in curvature along the crack surface and is possibly rate limited by pore fluid diffusion however the effect of crack geometry is larger than the effect of fluid chemistry at elevated temperatures and pressures aqueous fluids with elevated nacl concentrations can penetrate pervasively into polycrystalline quartz along a branching hierarchy consisting of episodically open fractures connected to 3 and 4 grain junction tubule networks while pure water or h 2 o co 2 fluid can only infiltrate pervasively along episodically open fractures 1 at lower temperatures and pressures 3 and 4 grain tubule networks in polycrystalline rocks may be closed to all fluids limiting fluid infiltration to microfacture networks lifetimes of quartz microcracks in all these fluids p fluid p confining is geologically short even at temperatures as low as 200 c

experimental pressure solution compaction of synthetic halite calcite aggregates experimental observations are reported of weakening of sediment like aggregates by addition of hard particles sieved mixtures of calcite and halite grains are experimentally compacted in drained pressure cells in the presence of a saturated aqueous solution the individual halite grains deform easily by pressure solution creep whereas calcite grains act as hard objects and resist compaction the fastest rate of compaction of the mixed aggregate is not obtained for a 100 halite aggregate but for a content of halite grains between 45 and 75 we propose that this unusual compaction behavior reflects the competition between two mechanisms at the grain scale intergranular pressure solution at grain contacts and grain boundary healing between halite grains that prevent further compaction

low effective viscosity during high pressure metamorphism due to dissolution precipitation creep the record of hp lt metamorphic carbonates and siliciclastic rocks from crete the micro structural record of high pressure low temperature hp lt metamorphic rocks t 400 50 c p 10 2 kbar of the phyllite quartzite unit in western crete greece is interpreted in terms of deformation mechanisms and flow stress phyllites were deformed at low stress by dissolution precipitation creep governed by strongly enhanced dissolution along quartz mica 001 phase boundaries quartzites and quartz veins were deformed by dislocation creep at higher flow stress the contrasting effective viscosities caused stress concentration in the quartzites and quartz veins also microstructures from aragonite marbles indicate that dissolution precipitation creep was the dominant deformation mechanism and that dislocation creep has not been activated in these rocks pervasive ductile deformation was restricted to hp lt metamorphic conditions and the microstructural record of deformation at maximum depth has been preserved with all subsequent deformation localized and confined to the brittle field constraints on the timing of deformation allow an estimation of strain rates experimentally determined flow laws for dislocation creep are used to pose upper bounds on flow stress and bulk viscosities of rocks deformed by dissolution precipitation creep for the phyllites a conservative estimate is about 1019 pa s or below in contrast to 1020 pa s derived for the quartzites this compares well to the viscosity contrast of 1 2 orders of magnitude reflected by the mesoscopic structures since phyllites and carbonate rocks form large portions of the subducted sedimentary pile the low flow stress during rapid deformation of these rocks at hp lt metamorphic conditions and the lack of deformation along the burial and exhumation path imply very low strength of the plate boundary shear zones and negligible shear heating

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

extensive young silicic volcanism produces large deep submarine lava flows in the ne lau basin new field observations reveal that extensive up to 402 km2 aphyric glassy dacite lavas were erupted at multiple sites in the recent past in the ne lau basin located about 200 km southwest of samoa this discovery of volumetrically significant and widespread submarine dacite lava flows extends the domain for siliceous effusive volcanism into the deep seafloor although several lava flow fields were discovered on the flank of a large silicic seamount niuatahi two of the largest lava fields and several smaller ones northern lava flow fields were found well north of the seamount the most distal portion of the northernmost of these fields is 60 km north of the center of niuatahi caldera we estimate that lava flow lengths from probable eruptive vents to the distal ends of flows range from a few km to more than 10 km camera tows on the shallower near vent areas show complex lava morphology that includes anastomosing tube like pillow flows and ropey surfaces endogenous domes and or ridges some with crease like extrusion ridges and inflated lobes with extrusion structures a 2 1 5 km 30 m deep depression could be an eruption center for one of the lava flow fields the lau lava flow fields appear to have erupted at presumptive high effusion rates and possibly reduced viscosity induced by presumptive high magmatic water content and or a high eruption temperature consistent with both erupted composition 66 sio2 and glassy low crystallinity groundmass textures the large areal extent 236 km2 and relatively small range of compositional variation 0 60 for wt si02 within the northern lava flow fields imply the existence of large eruptible batches of differentiated melt in the upper mantle or lower crust of the ne lau basin at this site the volcanism could be controlled by deep crustal fractures caused by the long term extension in this rear arc region submarine dacite flows exhibiting similar morphology have been described in ancient sequences from the archaean through the miocene and in small batches on present day seafloor spreading centers this study shows that extensive siliceous lavas can erupt on the modern seafloor under the right conditions

pressure solution lithification as a mechanism for the stick slip behavior of faults many major faults including a large fraction of the san andreas appear to be virtually quiescent between great earthquakes the locked sections of the san andreas near san francisco and los angeles have little or no seismic activity on the primary fault trace although secondary faults may be active stick slip behavior on a fault can be explained in terms of a static coefficient of friction which is larger than the dynamic or sliding coefficient in this paper we propose a modification of the friction hypothesis in which chemical lithification cementation occurs on the fault between earthquakes as the stress on the fault increases it becomes large enough to break the cemented bonds between particles causing slip on the fault we treat this problem quantitatively assuming that pressure solution is responsible for the cementation an advantage of this model is that the hydrostatic pressure approaches the lithostatic pressure during cementation so that low fault strengths are predicted

composition volume changes during hydrothermal alteration of andesite at buttercup hill noranda district quebec abstract hydrothermally altered andesites in the upper member of the amulet formation at buttercup hill noranda quebec represent part of the aquifer and cap of a self sealing geothermal system that focussed the discharge of hydrothermal fluids during the formation of massive cu zn sulfide deposits five alteration facies are recognized 1 pervasive greenschist facies regional metamorphism least altered andesite 2 epidotization silicification 3 albitization silicification 4 chloritization 5 sericitization silicification alteration is localized on permeable zones such as amygdules fractures flow tops discordant breccia dikes and conformable breccia horizons epidotized silicified andesite is enriched in ca sr eu and depleted in mg and first transition series metals ftsm relative to least altered andesite albitized silicified andesite is significantly enriched in na and depleted in most ftsm relative to least altered andesite the abundances and inter element ratios of the rare earth elements ree and most high field strength elements hfs y zr th u hf ta are similar in least altered epidotized silicified and albitized silicified andesites the most silicified andesites are strongly enriched in na si strongly depleted in mg and divalent ftsm and slightly but systematically depleted in ree and most hfs elements serialized andesites were previously silicified they are very strongly enriched in k rb cs ba very strongly depleted in na ca sr eu and slightly depleted in light ree relative to silicified andesite chloritized andesitic rocks exhibit heavy ree and hfs element ratios similar to those of leastaltered andesite but are relatively strongly enriched in mg and divalent ftsm strongly depleted in si and large ion lithophile lil elements and slightly depleted in light ree the coupled behavior of the heavy ree and most hfs elements during epidotization albitization silicification chloritization and serialization suggests that they were inert during hydrothermal modification of the andesite mass balance calculations suggest that volume was conserved during epidotization silicification and albitization silicification but that intense silicification was accompanied by volume increases up to 30 percent

endogenous growth of a miocene submarine dacite cryptodome rebun island hokkaido japan momo iwa rebun island hokkaido japan is a dacite cryptodome 200 300 m across and 190 m high the dome is inferred to have intruded wet poorly consolidated sediment in a shallow marine environment the internal structure of the dome is concentric with a massive core banded rim and narrow brecciated border all of which are composed of compositionally uniform feldspar phyric dacite boundaries between each of the zones are distinct but gradational the massive core consists of homogeneous coherent unfractured dacite and is characterized by radial columnar joints 60 200 cm across the banded rim encircles the massive core and is 40 m wide it is characterized by large scale flow banding parallel to the dome surface the flow banding comprises alternating partly crystalline and more glassy bands 80 150 cm thick the outermost brecciated border is up to 80 cm thick and consists of in situ breccia and blocky peperite the in situ breccia comprises polyhedral dacite clasts 5 20 cm across and a cogenetic granular matrix the blocky peperite consists of polyhedral dacite clasts 0 5 2 cm across separated by the host sediment mudstone the internal structures of the dome suggest endogenous growth involving a continuous magma supply during a single intrusive phase and simple expansion from the interior although much larger the internal structures of momo iwa closely resemble those of lobes in subaqueous felsic lobe hyaloclastite lavas

facies architecture and origin of a submarine rhyolitic lava flow dome complex ponza italy the islands of ponza and gavi western pontine archipelago italy preserve parts of a subaqueously emplaced high silica 75 77 sio2 rhyolitic lava flow that overlies the margins of three older domes exposures of the lava alone cover 24 km2 and with a thickness of 150 m exposed in the cliffs the preserved volume of the lava flow is 3 6 km3 and the original volume is likely to have exceeded 7 km3 the lava flow consists of coherent obsidian and several hyaloclastite facies including in situ and clast rotated breccias and sandstones which all exhibit gradational relationships the coherent obsidian occurs as separate domains and is often flow banded although flow folds occur the banding is generally subhorizontal dipping gently to the nne the hyaloclastite representing 90 of the lava by volume has a diffuse layering varying from 0 5 to 2 m in thickness this layering also dips gently to the nne and is marked in places by alternation of some coherent horizons coarse and finely fragmented in situ hyaloclastite pumiceous hyaloclastite and clast rotated hyaloclastite the layering is laterally continuous and consistent in orientation over most of the 13 km length of ponza the subhorizontal orientation of the flow banding and presence of resedimented deposits in the upper parts of the sequence indicate that the unit is a lava flow the resedimented deposits comprise both proximal and distal deposits of debris flows and turbidity currents initiated by gravitational instability of the upper and marginal parts of the lava flow and include stratified monomictic obsidian breccias and bedded vitric siltstones and sandstones the lava flow has been intruded and crosscut by rhyolitic bodies of various ages including discordant coherent to internally fractured contemporaneous rhyolite bodies and late penecontemporaneous dikes with glassy margins and alteration haloes

laboratory study of fault healing and lithification in simulated fault gouge under hydrothermal conditions abstract seismic data geologic observations and laboratory friction studies suggest that faults lithify and strengthen heal during the interseismic period of the earthquake cycle we report on experiments to investigate the influence of healing duration and temperature on the strength and healing rate of simulated faults layers of m sized quartz powder were used to simulate granular fault gouge gouge layers were sheared within sioux quartzite in a triaxial pressure vessel at elevated pressures p c 250 mpa elevated temperatures 230 636 c and in the presence of water p h 2 o 75 mpa we performed hold slide experiments in which samples were subjected to a period of healing under hydrostatic load followed by shear deformation healing times ranged from a few hundred s to 10 5 s to isolate the effects of lithification and temperature on friction we ran two types of hold slide experiments 1 samples were subjected to healing and shear deformation at elevated temperature and 2 following healing at elevated temperature temperature was reduced prior to shear we also ran slide hold slide experiments in which samples were healed under shear load at elevated temperature 636 c experiments in which deformation was carried out at a lower temperature than healing show that both the static and sliding coefficient of friction increase with heal time samples healed and deformed at higher temperature showed lower peak strengths and within the scatter of our data did not exhibit time dependent strengthening these data are interpreted to result from enhanced lithification rates at elevated temperature samples healed under shear load exhibited a log linear decrease in friction with hold time modeling using rate and state dependent friction laws indicates velocity strengthening behavior with friction a b values of 0 05 to 0 08 our data indicate that at high temperature the effective state evolution term b is negative moreover the data indicate the rate of frictional strengthening varies significantly for hydrostatic and non hydrostatic load conditions our measurements of healing are consistent with seismic estimates of fault healing rates if stress drop is a fraction of the total shear stress and effective fault normal stress is 60 to 100 mpa

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

internal structure and emplacement of an upper pliocene dacite cryptodome milos island greece the upper pliocene kalogeros cryptodome is exposed on the northeastern part of milos greece the dacite cryptodome is 800 1300 m across and at least 120 m high it is inferred to have intruded wet unconsolidated pumiceous sediments in a shallow marine environment the kalogeros cryptodome includes five facies the coherent dacite facies 80 vol consists of massive non vesicular dacite and is characterised by radial columnar joints 20 250 cm across the banded dacite facies 15 vol encircles the coherent core and is up to 40 m thick it comprises alternating bands 0 5 4 m thick of pale grey and black dacite the fractured dacite facies less than 1 vol forms an irregular zone 1 3 m thick at the outer margin of the cryptodome the outermost massive dacite breccia facies less than 2 vol consists of blocky to polyhedral dacite clasts 1 40 cm in diameter and is characterised by domains of jigsawfit and clast rotated breccia the stratified dacite breccia 2vol is clast to matrix supported monomictic poorly sorted and composed of dacite clasts up to several metres in diameter the facies association collectively records endogenous growth of a cryptodome that involved a continuous magma supply during a single intrusive phase and simple expansion inflation during emplacement the margins of the kalogeros cryptodome were quench fragmented forming an outer domain of intrusive hyaloclastite and intensely fractured dacite the near solid outer carapace insulated the hotter less viscous interior laminar shear accompanied inflation generating large scale flow banding around the outer part of the core once stagnant concentric isotherms were established within the cryptodome and controlled the orientation of columnar joints cryptodomes are characterised by a well developed internal concentric distribution of distinctive textural domains modest autoclastic breccia and the absence of redeposited autoclastic facies

localized deformation induced by heterogeneities in porous carbonate analysed by multi scale digital image correlation abstract the understanding and the prevention of damage mechanisms which have an impact on the hydrocarbon production and recovery rates are of paramount interest for reservoir engineers the modelling of such coupled processes relies essentially on experimentally obtained data which characterize the macroscopic mechanical and transport properties this approach however cannot account for the multi scale structural heterogeneities of the considered rocks in spite of their fundamental importance the microstructural characterization of damage is usually based on post mortem observations of the samples which provide both qualitative and quantitative information about the effects of the mechanisms activated at the grain scale and at intermediate scales at a pervasive stage of damage after sample unloading new techniques provide more quantitative and direct methods to follow the deformation history and the eventual development of localization and damage in this study the 2d digital image correlation dic technique has been applied to sequences of images taken from carbonate samples during uniaxial compression tests several scales have been considered ranging from the centimetric scale of the samples to the local scale of their microstructure for this purpose both optical observations and scanning electron microscopy sem were used although the macroscopic strain at failure was very small

fluid distribution in grain boundaries of natural fine grained rock salt deformed at low differential stress qom kuh salt fountain central iran implications for rheology and transport properties we used a combination of broad ion beam cross sectioning and cryogenic sem to image polished surfaces and corresponding pairs of fractured grain boundaries in an investigation of grain boundary microstructures and fluid distribution in naturally deformed halite from the qom kuh salt glacier central iran at the scale of observations four types of fluid filled grain boundary can be distinguished by morphology from straight to wavy thickness from 5000 to 50 nm and the presence of fluid inclusions the mobility of the brine is shown after cutting the inclusions by broad ion beam bib in vacuum and fine grained halite forms efflorescence and precipitates on internal walls of inclusions at cryogenic temperature grain boundary brine is shown either as continuous film or in isolated inclusions the halite halite grain boundary between isolated fluid inclusions is interpreted to have formed by fluid assisted grain boundary healing preliminary experiments on the samples at shear stress conditions of natural salt glacier show very slow strain rates 7 4 10 10 s 1 and 1 10 9 s 1 which are less than expected for pressure solution creep both microstructures and deformation experiments suggest interfacial energy driven grain boundary healing and therefore rendering inactive the pressure solution creep in our samples this result disagrees with previous microstructural studies of the same sample which showed microstructural evidence for pressure solution and dislocation creep different explanations are discussed which imply that both healing and reactivation of grain boundaries are important in salt glaciers leading to heterogeneous distribution of deformation mechanisms and strain rates in both space and time

experimental study of the influence of stress temperature and strain on the dynamic recrystallization of carrara marble carrara marble has been deformed experimentally at temperatures ranging between 500 and 1000 c at confining pressures of 200 and 300 mpa and up to very large strains in extension and compression in order to study the microstructural and mechanical property changes associated with dynamic recrystallization microstructural studies were made by optical microscopy on ultrathin sections and automatic grain size measurement techniques were used when the temperature is sufficiently high 600 c and the stresses are high enough for deformation twinning to occur twin boundary migration is a powerful recrystallization mechanism that does not modify the grain size at stress levels too low to activate twinning recrystallization occurs in two stages the formation of nuclei by grain boundary bulging and subgrain rotation recrystallization in the grain boundary regions followed by a second stage of grain boundary migration recrystallization to a larger grain size that eventually overprints the entire rock volume the recrystallization process requires larger prestrains at the lower temperatures the size to which migration recrystallized grains grow seems to be limited by the stress and grain size dependent twinning field boundary or by the boundary between the dislocation creep and grain size sensitive flow mechanisms within the range of experimental observations dynamically recrystallized grain size does not depend on strain rate or temperature separate empirical stress versus grain size relations are presented for rotation and migration recrystallization that may be used for palaeopiezometry no unequivocal experimental evidence of weakening resulting from recrystallization to finer grain sizes at laboratory strain rates was found however extrapolation of the experimental data to low natural strain rates suggests that weakening following recrystallization may occur in nature

spherulitic aphyric pillow lobe metatholeiitic dacite lava of the timmins area ontario canada a new archean facies formed from superheated melts fragmental rocks of the v10 units of the vipond formation of the tisdale assemblage previously have been identified as pillow basalts but many samples are shown to be intermediate to felsic in character likely tholeiitic dacite in composition specifically the v10b unit is mapped as a pillow lobe dacite aside from being more geochemically evolved in terms of their immobile trace elements these rocks differ from typical pillow basalts in that they have more abundant primary breccia and hyaloclastite the pillow lobes are contorted having been folded in a plastic state and are zoned typically having a spherulite rich core moreover the flows are aphyric interpreted to mean that they were erupted in a superheated state this along with their pillow lobe nature demonstrates that they were erupted as relatively low viscosity melts for such silicic compositions interaction with water quenched the outer pillow lobe and contributed to the formation of the abundant breccia the fact that the melt was crystal and microlite free inhibited crystal growth such that the bulk of the lobes were quenched to crystal free glass nucleation occurred only in the cores where cooling rates were lower in comparison to the medial and exterior areas of the pillow lobes although in the cores crystal growth rates were high so that abundant spherulite formation took place the flows are exposed over a strike length of more than 10 km and are interpreted to be continuous and to have resulted from fissure eruptions the resulting porous permeable high fe mg high surface area glassy rocks may have been ideal for channeling and reacting with gold bearing hydrothermal solutions descriptions of most other archean subaqueous felsic lobes document that the lavas were phyric and that spherulites formed near the external lobe margin the distinctly different zoning of the v10b pillow lobes suggests that they constitute a new archean facies formed from superheated melts

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

influence of grain boundary structural evolution on pressure solution creep rates intergranular pressure solution is a well known rock deformation mechanism in wet regions of the upper crust and has been widely studied especially in the framework of compaction of granular materials such as reservoir sandstones and fault rocks several analytical models exist that describe compaction creep by stress induced mass transport and the parameters involved are relatively well constrained by laboratory experiments while these models are capable of predicting compaction behavior observed at relatively high porosities they often overestimate compaction rates at porosities below 20 by up to several orders of magnitude this suggests that the microphysical processes operating at low porosities are different and are not captured well by existing models the implication is that available models cannot be extrapolated to describe compaction of sediments and fault rocks to the low porosities often reached under natural conditions to address this problem we propose a new thermodynamic model that describes the decline of pressure solution rates within individual grain contacts as a result of time averaged growth of asperities or islands and associated constriction of the grain boundary diffusion path here termed grain boundary evolution the resulting constitutive equations for single grain grain contacts are then combined and solved semianalytically the compaction rates predicted by the model are compared with those measured in high strain compaction experiments on wet granular halite a significant reduction in compaction rate is predicted when grain boundary evolution is considered which compares favorably with the experimental compaction data

direct measurement of asperity contact growth in quartz at hydrothermal conditions earthquake recurrence requires interseismic fault restrengthening which results from solid state deformation in room temperature friction and indentation experiments in contrast exhumed fault zones show solution transport processes such as pressure solution and contact overgrowths influence fault zone properties in the absence of fluid flow overgrowths are driven by gradients in surface curvature where material is dissolved diffuses and precipitates at the contact without convergence normal to the contact to determine the rate of overgrowth for quartz we conducted single contact experiments in an externally heated pressure vessel convergence was continuously monitored using reflected light interferometry through a long working distance microscope contact normal force was constant with an initial effective normal stress of 1 7 mpa temperature was between 350 and 530 c and water pressure was constant at 150 mpa two control experiments were conducted one dry at 425 c and one bimaterial sapphire at 425 c and 150 mpa water pressure no contact growth or convergence was observed in the controls for wet single phase contacts growth was initially rapid and then decreased with time no convergence was observed fluid inclusions indicate that the contact is not uniformly wetted the contact is bounded by small regions of high aperture reflecting local free face dissolution as the source for the overgrowth the apparent activation energy is 125 kj mol extrapolation predicts rates of contact area increase orders of magnitude faster than in dry room temperature and hydrothermal friction experiments suggesting that natural strength recovery near the base of the seismogenic zone could be dominated by contact overgrowth

mass change calculations in altered rock series a technique is presented whereby precursors of altered rocks in a fractionated rock series can be identified and changes in chemical components mass and volume accurately calculated the procedure utilizes elements with high degrees of immobility in hydrothermal and associated interactive water rock systems igneous rock series and sedimentary and metamorphic rocks with primary continuity of chemical composition are amenable to this treatment in the procedure for igneous rocks best fit fractionation lines are established for an immobile igneous compatible incompatible element pair the latter element functioning as the fractionation monitor alteration paths are linear and pass through the origin intersections of the fractionation and alteration lines yield the immobile element concentrations in the precursors to the altered rocks mobile components are determined from fractionation lines and monitor values total mass changes are proportional to the displacement of altered samples from the fractionation line masses of other elements in an altered sample reconstructed values are recalculated to the concentration of the monitor element in the precursor chemical changes are the differences between the calculated precursor compositions and the reconstructed altered rock compositions errors are mainly a function of the positioning of the fractionation lines

geologic setting of pacmanus hydrothermal area high resolution mapping and in situ observations abstract this study presents a systematic analysis and interpretation of autonomous underwater vehicle based microbathymetry combined with remotely operated vehicle rov video recordings rock analyses and temperature measurements within the pacmanus hydrothermal area located on pual ridge in the bismarck sea of eastern manus basin the data obtained during research cruise magellan 06 and so 216 provides a framework for understanding the relationship between the volcanism tectonism and hydrothermal activity pacmanus is a submarine felsic vocanically hosted hydrothermal area that hosts multiple vent fields located within several hundred meters of one another but with different fluid chemistries vent temperatures and morphologies the total area of hydrothermal activity is estimated to be 20 279 m2 the microbathymetry maps combined with the rov video observations allow for precise high resolution mapping estimates of the areal extents of hydrothermal activity we find the distribution of hydrothermal fields in the pacmanus area is primarily controlled by volcanic features that include lava domes thick and massive blocky lava flows breccias and feeder dykes spatial variation in the permeability of local volcanic facies appears to control the distribution of venting within a field we define a three stage chronological sequence for the volcanic evolution of the pacmanus based on lava flow morphology sediment cover and lava sio2 concentration in stage 1 sparsely to moderately porphyritic dacite lavas 68 69 8 wt sio2 erupted to form domes or cryptodomes in stage 2 aphyric lava with slightly lower sio2 concentrations 67 2 67 9 wt sio2 formed jumbled and pillowed lava flows in the most recent phase stage 3 massive blocky lavas with 69 to 72 5 wt sio2 were erupted through multiple vents constructing a volcanic ridge identified as the pacmanus neovolcanic zone the transition between these stages may be gradual and related to progressive heating of a silicic magma following a recharge event of hot mantle derived melts

effect of water on the strength and microstructure of carrara marble axially compressed at high temperature in this study we aimed to i answer the question if water affects the strength of marble deforming at high temperature and ii establish criteria that allow assessment of the role of water in microstructure development in marble samples of carrara marble were axially compressed at temperatures ranging 600 1000 8c and strain rate w10 k5 s k1 with or without addition of 0 4 2 1 wt water water added samples were found to be slightly weaker than dry samples microstructurally all samples showed grain flattening and twinning at 600 8c and dynamic recrystallization dominated by grain boundary migration at higher temperature grain boundaries in wet samples showed isolated or semi continuous remnants of fluid pockets the average grain roundness r and fractal dimension d relating grain diameter d and grain perimeter p pfd d for wet recrystallized samples were systematically lower than for dry samples at 600 8c high pore fluid pressure probably enhanced dilatation of wet samples and helped grain boundary sliding gbs thereby lowering the strength at higher temperature fluid enhanced grain boundary migration served as a recovery process reducing the contribution of gbs to creep overall water has little effect on strength and microstructure of marble experimentally deformed at high temperature q 2005 elsevier ltd all rights reserved

host rock and structural controls on the nature and timing of gold mineralization at the holloway mine abitibi subprovince ontario the holloway mine a mesothermal gold deposit is located within the western abitibi subprovince ontario mineralized zones that contain microscopic gold within pyrite are hosted by a sequence of metakomatiites mafic to felsic metavolcanic and metasedimentary rocks there were two mineralization events however the early one was the main event in terms of the amount of gold mineralization this event was associated with albitization silicification chloritization and sericitization in addition to pyritization the later mineralization is associated with sericitization and pyritization carbonate and sericite alterations are associated with both mineralizing events results of u pb zircon age dating of rocks within the sequence constrains the main mineralization event to 2672 ma ore lenses of the holloway deposit are enveloped by 080 striking steeply south dipping zones of intense deformation and fabric development within the porcupine destor deformation zone the shear zones are characterized by a strong foliation and locally an associated extension lineation the ore lenses are interpreted to represent lithons that were formed by boudinage of the more competent mineralized zones which are pervasively albitized analysis of geochemical data demonstrates that the ree th nb hf ti fe and al were largely immobile with respect to the albite quartz chlorite sericite and hematite alterations locally preserved textures such as abundant varioles and spherulites indicate that the host metavolcanics were relatively evolved rocks geochemical data show they have an iron enrichment trend typical of tholeiitic mafic to felsic suites and that they were derived through fractional crystallization of parent basalt because of their high fe mg ratios the rocks reacted with hydrothermal solutions carrying gold presumably as thio complexes to form pyrite which scavenged the gold

near liquidus growth of feldspar spherulites in trachytic melts 3d morphologies and implications in crystallization mechanisms the nucleation and growth processes of spherulitic alkali feldspar have been investigated in this study through x ray microtomography and electron backscatter diffraction ebsd data here we present the first data on shape preferred orientation spo and crystal preferred orientation cpo of alkali feldspar within spherulites the analysis of synchrotron x ray microtomography and ebsd datasets allowed us to study the morphometric characteristics of spherulites in trachytic melts in quantitative fashion highlighting the three dimensional shape preferred orientation branching of lamellae and crystal twinning providing insights about the nucleation mechanism involved in the crystallization of the spherulites the nucleation starts with a heterogeneous nucleus pre existing crystal or bubble and subsequently it evolves forming bow tie morphologies reaching radially spherulitic shapes in few hours since each lamella within spherulite is also twinned these synthetic spherulites cannot be considered as single nuclei but crystal aggregates originated by heterogeneous nucleation a twin boundary may have a lower energy than general crystal crystal boundaries and many of the twinned grains show evidence of strong local bending which combined with twin plane creates local sites for heterogeneous nucleation this study shows that the growth rates of the lamellae 10 6 10 7 cm s in spherulites are either similar or slightly higher than that for single crystals by up to one order of magnitude furthermore the highest volumetric growth rates 10 11 10 12 cm3 s show that the alkali feldspar within spherulites can grow fast reaching a volumetric size of 10 m3 in 1 s

internal textures of rhyolite flows as revealed by research drilling recent drilling of 550 and 140 000 yr old rhyolite lava flows in the inyo dome chain california and valles caldera new mexico and field inspection of 8 ma flows in western arizona reveal a more detailed vertical zonation of lava textures in glassy rhyolite flows than has previously been recognized the upper vitrophyre of a flow can usually be subdivided into a surficial finely vesicular pumice underlain by obsidian coarsely vesicular pumice and a second obsidian layer beneath these layers is the crystalline center of the flow which in turn is underlain by a basal obsidian layer lower vitrophyre differences in lava vesicularity and crystallinity between zones in a flow result from primary effervescence devitrification lava rheology and migration of water vapor

lithogeochemical and stratigraphic controls on gold mineralization within the metavolcanic rocks of the hoyle pond mine timmins ontario the hoyle pond gold deposit is hosted in complexly deformed mafic ultramafic volcanic rocks of the hersey lake and central formations tisdale assemblage in the porcupine gold camp located approximately 15 km northeast of timmins in the abitibi greenstone belt the deposit is hosted within a homoclinal sequence of south facing stacked volcanic flows of high mg tholeiitic basalt basaltic komatiite and komatiite flows and interbedded high mg tholeiitic basalt and fe rich tholeiitic basalts the bulk of the gold mineralization was emplaced at lithologic contacts along late shear zones associated with isoclinal folding and thrusting the mineralization is characterized by micron to centimeter sized flakes of free gold or veinlets in quartz carbonate dolomite and ferroan dolomite shear and extension vein arrays at the mine scale a broad carbonate alteration is evident two alteration zones surrounding the veins were mapped at the meter scale an inner sericite alteration zone composed of sericite muscovite fuchsite cr muscovite quartz arsenopyrite pyrite ferroan dolomite dolomite and graphite plus tourmaline and an outer zone of albite alteration consisting of albite quartz ferroan dolomite and dolomite geochemical analyses of 355 samples show that the ree zr al2o3 tio2 and y were largely immobile during alteration and mineralization co2 k2o na2o cr2o3 rb as b sio2 and cao and locally fe2o3 feo and mgo were mobile during alteration and mineralization the chromium enrichment is not primary and is interpreted to have been caused by remobilization from ultramafic rocks during mineralization in addition an intense graphite alteration originally derived from organic matter probably from sedimentary rocks and now associated with mineralization is present in zones that were porous and permeable at the time of mineralization in common with other mesozonal orogenic gold deposits gold was likely transported as a thio complex the cr enrichment in the wall rock indicates that cr was mobile most likely as cr6 because species such as cr6 are transported under oxidizing conditions and carbon and au hs species are transported under reduced conditions we suggest that more than one fluid was involved in the mineralization and or alteration mixing between reducing and oxidizing fluids is thought to have reduced cr6 to cr3 oxidized the organic matter to form graphite oxidized sulfur to form sulfides and precipitated au this is consistent with the observed para genesis reducing fluids rich in boron arsenic carbon and au may have been generated from sedimentary rocks porcupine assemblage at depth and expelled during orogenesis into syndeformation structures within overlying volcanic rocks where they mixed with oxidizing fluids containing cr k2o sio2 na2o and cao

dynamics of microscale precursors during brittle compressive failure in carrara marble microscale heterogeneities influence failure mechanisms in the crust to track the microstructural changes in rock samples when loaded until failure we employed a novel experimental technique that couples dynamic x ray microtomography imaging with a triaxial deformation apparatus we studied the brittle failure of carrara marble under triaxial compression dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure we quantified the emergence of scaling relationships between microstructural parameters including total damage volume incremental damage volume the largest connected microfracture and the applied differential stress the total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase the growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure the microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure these characteristic features of brittle failure in carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition we also observed that very close to failure several power law relationships broke down which we interpret to be related to the coalescence of the largest microfractures in a finite size volume scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models our results show that precursors of macroscopic brittle failure in carrara marble follow predictable trends

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

the micromechanics of westerley granite at large compressive loads the micromechanical damage mechanics formulated by ashby and sammis pure appl geophys 133 3 489 521 1990 has been shown to give an adequate description of the triaxial failure surface for a wide variety of rocks at low confining pressure however it does not produce the large negative curvature in the failure surface observed in westerly granite at high confining pressure we show that this discrepancy between theory and data is not caused by the two most basic simplifying assumptions in the damage model 1 that all the initial flaws are the same size or 2 that they all have the same orientation relative to the largest compressive stress we also show that the stress strain curve calculated from the strain energy density significantly underestimates the nonlinear strain near failure in westerly granite both the observed curvature in the failure surface and the nonlinear strain at failure observed in westerly granite can be quantitatively fit using a simple bi mineral model in which the feldspar grains have a lower flow stress than do the quartz grains the conclusion is that nonlinearity in the failure surface and stress strain curves observed in triaxial experiments on westerly granite at low loading rates is probably due to low temperature dislocation flow and not simplifying assumptions in the damage mechanics the important implication is that discrepancies between experiment and theory should decrease with increased loading rates and therefore the micromechanical damage mechanics as formulated can be expected to give an adequate description of high strain rate phenomena like earthquake rupture underground explosions and meteorite impact

microfracturing damage and failure of brittle granites 1 the evolution of stress induced damage and the eventual brittle failure are experimentally analyzed for mount scott granite of oklahoma we quantify the damage intensity in two methods and directly compare model predictions and actual damage the 14 samples of the medium grain size granite were loaded triaxially at dry conditions room temperature and under 41 mpa confining pressure microfractures were mapped in five samples and the majority of them 80 belong to two groups tensile microfractures trending subparallel to the loading axis and shear microfractures trending 11 40 off the loading axis the tensile microfractures dominate the low stress stage and they remain intragranular with a stress increase the relative density of shear microfractures increases with increasing stresses and they formed elongated intergranular zones of coalescing microfractures we compared two independent values of damage intensity 1 the macroscopic experimentally measured reduction of the deformation modulus and 2 the expected reduction of this modulus calculated with several damage models for the density of the mapped microfractures our fracture density data best fit the model of noninteracting cracks of kachanov 1992

diffusive properties of fluid filled grain boundaries measured electrically during active pressure solution abstract diffusion through wetted grain boundaries is often the rate limiting process during rock deformation by intergranular pressure solution however the underlying processes operative within such boundaries are poorly understood in this contribution we have studied the diffusive properties of wetted grain boundaries by measuring the electrical resistivity of single annular halite glass contacts undergoing active pressure solution optical observation shows continuous growth i e widening of the annular contacts by pressure solution from the resistivity measurements and making use of the nernst einstein equation it was possible to calculate the apparent grain boundary diffusion coefficient z d c i e the product of grain boundary diffusion coefficient d grain boundary film thickness and the solubility c of the diffusing species in the grain boundary fluid during the pressure solution process the z values obtained lie in the range 3 10 20 2 10 18 m3 s show an inverse dependence on normal stress n and agree well with values inferred previously from single contact and polycrystalline compaction experiments

compaction creep of wet granular calcite by pressure solution at 28 c to 150 c 1 uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone analytical grade calcite and superpure calcite the tests were performed at 28 c 150 c effective stresses of 20 47 mpa and a pore pressure of 20 mpa using presaturated caco3 solution as the pore fluid sample grain sizes ranged from 12 to 86 m the aim was to determine if creep occurs by intergranular pressure solution ips under these conditions and to identify the rate controlling process the wet samples showed significant creep while dry and oil flooded samples did not wet samples were also characterized by microstructures such as sutured grain contacts grain indentations and overgrowths suggesting the operation of ips the behavior of the wet samples at low strains 4 5 agreed well with the predictions of standard models for diffusion controlled pressure solution however at higher strains 5 10 creep slowed down compared with the model predictions transient flow through tests performed in this regime led to an acceleration of creep consistent with models for precipitation controlled ips and demonstrated an increase in the impurity content of the pore fluid toward higher strains since some of these impurities notably mg2 retard precipitation in calcite we suggest that creep occurred by diffusion controlled ips at low strain giving way to precipitation control at larger strains as impurities accumulated fitting of the diffusion controlled ips model to the low strain data yielded values of the grain boundary diffusion product ds in calcite of 10 19 m3 s 1 at 150 c

a special issue devoted to base metal and gold metallogeny at regional camp and deposit scales in the abitibi greenstone belt preface the abitibi greenstone belt contains some of the world s largest cu zn and au deposits and significant amounts of ni cu pge mineralization discoveries early in the 20th century were made by classic prospecting with subsequent discoveries commonly resulting from diamond drilling of targets identified by electromagnetic surveys the next generation of deposits will be found at greater depth based on geological and geophysical models principally beneath the extensive overburden that covers most of the abitibi greenstone belt thus exploration will require improved knowledge of the geologic characteristics of the existing deposits particularly the relationship between deposit and regional scale features including the stratigraphic plutonic structural and metamorphic architecture of the region and will rely more heavily on expensive geophysical and geochemical techniques verified by diamond drilling the papers in this special issue are part of the discover abitibi initiative a geoscience program funded by federal provincial and municipal governments in collaboration with the mining industry many of the results reported here are from projects funded by phase ii of the discover abitibi initiative which commenced in 2003 and was focused on the timmins kirkland lake region fig 1 a high mineral potential portion of the abitibi greenstone belt that has been the source of exceptional mineral wealth as part of the discover abitibi initiative the greenstone architecture project was undertaken by the mineral exploration research center at laurentian university to bridge the gap between academic and company information at the scale of individual deposits and the broad based knowledge derived from government mapping the project was designed as a multidisciplinary approach involving faculty postdoctoral fellows and graduate students in collaboration with geoscientists from the ontario geological survey the geological survey of canada consultants and company geologists as can be seen in the papers in this special issue the program had both geological and

dynamic in situ three dimensional imaging and digital volume correlation analysis to quantify strain localization and fracture coalescence in sandstone advances in triaxial compression deformation apparatus design dynamic x ray microtomography imaging data analysis techniques and digital volume correlation analysis provide unparalleled access to the in situ four dimensional distribution of developing strain within rocks to demonstrate the power of these new techniques and acquire detailed information about the micromechanics of damage evolution deformation and failure of porous rocks we deformed 3 cm scale cylindrical specimens of low porosity fontainebleau sandstone in an x ray transparent triaxial compression apparatus and repeatedly recorded three dimensional tomograms of the specimens as the differential stress was increased until macroscopic failure occurred experiments were performed at room temperature with confining pressure in the range of 10 20 mpa distinct grayscale subsets indicative of density enabled segmentation of the three dimensional tomograms into intact rock matrix pore space and fractures digital volume correlation analysis of pairs of tomograms provided time series of three dimensional incremental strain tensor fields throughout the experiments after the yield stress was reached the samples deformed first by dilatant opening and propagation of microfractures and then by shear sliding via grain rotation and strain localization along faults for two samples damage and dilatancy occurred by grain boundary opening and then a sudden collapse of the granular rock framework at failure for the third sample a fault nucleated near the yield point and propagated in the sample through the development of transgranular microfractures the results confirm findings of previous experimental studies on the same rock and provide new detailed quantifications of 1 the proportion of shear versus dilatant strain in the sample 2 the amount of dilatancy due to microfracture opening versus pore opening when a fault develops and 3 the role of grain boundaries and pore walls in pinning microfracture propagation and slowing down the rate of damage accumulation as failure is approached our study demonstrates how the combination of high resolution in situ dynamic x ray microtomography imaging and digital volume image correlation analysis can be used to provide additional information to unravel brittle failure processes in rocks under stress conditions relevant to the upper crust

compaction creep of quartz sand at 400 600 c experimental evidence for dissolution controlled pressure solution intergranular pressure solution ips is an important compaction and deformation mechanism in quartzose rocks but the kinetics and rate controlling process remain unclear the aim of the present study is to test microphysical models for compaction creep by ips against isostatic hot pressing experiments performed on quartz sand under conditions expected to favor pressure solution confining pressure 300 mpa pore water pressure 150 250 mpa temperature 400 600 c microstructural observations revealed widespread intergranular indentation features and confirmed that intergranular pressure solution was indeed the dominant deformation mechanism under the chosen conditions for porosities down to 15 the mechanical data agree satisfactorily with a microphysical model incorporating a previously determined kinetic law for dissolution of loose granular quartz suggesting that the rate limiting mechanism of ips was dissolution the model also predicts ips rates within one order of magnitude of those measured in previous experiments at 150 350 c and thus seem robust enough to model sandstone compaction in nature such applications may not be straightforward however as the present evidence for dissolution control implies that the compositional variability of natural pore fluids may strongly influence ips rates in sandstones

spherulitic rhyolites of the archean blake river group canada implications for stratigraphic correlation and volcanogenic massive sulfide exploration based on the distinctive textural and chemical character of highly spherulitic rhyolites in the late archean volcanogenic massive sulfide rich blake river group of quebec it is proposed that they represent key beds which may be used to infer the age relationships between the three subgroups rouyn pelletier misema and noranda into which the blake river group is divided in this area these rhyolites occur as flow and fragmental volcaniclastic probably pyroclastic facies both of which contain crystallization spherulites they occur as three units a flow facies exhibiting parallel agglomerated lath shaped plagioclase crystals the fish roe rhyolite a fragmental spherulitic rhyolite which is aphyric and a second very local flow which is quartz plagioclase porphyritic chemically however the three units are identical and distinct within the blake river group stratigraphy the ti y yb and zr contents are higher in the spherulitic rhyolites than in the other rhyolites in the blake river group whereas the la content is similar between the two rhyolite populations these values translate into higher ti zr and lower zr y and la yb ratios for the spherulitic rhyolites and result in their being important stratigraphic marker units in the group in quebec statistical analyses of the geochemical data from the rhyolites in the blake river group show that there is a 95 percent probability that the spherulitic rhyolite analyses represent a single genetically related population and may in fact be a single stratigraphic unit the occurrence of the fragmental highly spherulitic rhyolite in the andesitic misema subgroup and in the bimodal andesitic rhyolitic noranda subgroup implies that these two domains formed at least in part concurrently the same conclusion can be drawn for the basaltic rouyn pelletier subgroup and the noranda subgroup as the fish roe rhyolite occurs in both these domains this in turn suggests that a complex interplay of contemporaneous magmatic systems rather than a single vertically stacked evolutionary system was responsible for the formation of the blake river group and its volcanogenic massive sulfide deposits

quantitative trace element modelling of the crystallization history of the kinojevis and blake river groups abitibi greenstone belt ontario the archean tholeiitic kinojevis suite is characterized by an iron enrichment trend and abundant fe ti oxides in its evolved basalts andesites and rhyolites the rare earth element ree patterns of the suite remain flat from the basalts through to the rhyolites with the development of small negative eu anomalies quantitative modelling of the trace elements from little altered samples is consistent with the mineralogy suggesting that the suite was produced through fractional crystallization of olivine pyroxene plagioclase and fe ti oxides the evolved rhyolites are interpreted as having developed by greater than 90 fractional crystallization in a high level magma chamber the calc alkaline blake river group conformably overlies the kinojevis rocks and is characterized by enrichment in alkalis and silica the ree patterns are light rare earth element lree enriched and the felsic rocks have prominent negative eu anomalies geochemical modelling shows that the suite could have developed either th

porosity depth trends in reservoir sandstones theoretical models related to jurassic sandstones offshore norway abstract theoretical models of compaction and porosity modification in sandstones during burial are discussed theory predicts that mechanical compaction is the dominant porosity reducing mechanism during burial from 0 to 2 5 3 km porosity depth trends are at this stage mainly controlled by the stability of the grain framework and the effective stress time and temperature also influence the porosity depth gradients at shallow to moderate depths but are probably less important than effective stress and framework grain composition at greater burial depths below 2 5 3 km chemical compaction including pressure solution can explain most of the porosity reduction in well sorted clean arenites theoretical modelling of the intergranular pressure solution suggests that sandstones may lose porosity rapidly by this mechanism below 2 5 3 km and that factors capable of retarding pressure solution and quartz cementation are required to maintain prospective porosities below 4 km this theory and comparisons with empirical data from jurassic sandstones from offshore norway indicate that high porosity is favoured by 1 overpressures approaching the lithostatic pressure gradient 2 a short residence time below 3 km burial 3 coatings on grains of clay or microcrystalline quartz which prevent quartz dissolution and precipitation and 4 a high content of feldspar and early diagenetic secondary pores early hydrocarbon emplacement may retard quartz cementation and preserve porosity but chemical compaction probably continues after oil emplacement except at very high hydrocarbon saturations

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

geochemistry of hydrothermally altered rocks at the horne mine noranda quebec low k rhyolites of the archean blake river group that host the horne volcanogenic massive sulfide deposit are altered to quartz sericite chlorite albite quartz sericite zone and chlorite or quartz chlorite zone assemblages the quartz sericite zone accounts for approximately 90 percent of the 5 km 3 of the altered hanging wall and footwall rocks chlorite zone alteration is limited to portions of the footwall and flanks of the cu rich h orebodies clusters of gold bearing chlorite quartz veinlets crosscut large volumes of the quartz sericite zone rocks alteration has added an average of 13 wt percent sio 2 2 3 wt percent k 2 o 430 ppm ba and 46 ppm rb to the system and leached 3 6 wt percent na 2 o 2 2 wt percent cao and 41 ppm sr middle and light ree were increasingly mobile from yb to la they were leached from the chlorite zone rocks and added to quartz sericite zone rocks chlorite was more fe rich fe fe mg 0 65 0 85 in the chlorite zone rocks than in other altered lithologies fe fe mg 0 2 0 5 sulfur isotope values for massive ores are in the range delta 34 s 2 1 to 1 9 per mil mineral separates from altered rocks yielded delta 18 o values of 10 2 to 12 1 per mil for quartz 7 2 to 9 5 per mil for calcite 2 2 to 3 0 per mil for chlorite and 0 1 to 1 0 per mil for magnetite oxygen and sulfur isotope fractionation between coexisting minerals suggests formation from fluids having delta 18 o 3 to 4 per mil at temperatures between 275 degrees to 380 degrees c oxygen isotope compositions of host rocks are delta 18 o 8 or 1 per mil for freshest rhyolite delta 18 o 6 6 to 11 6 per mil for quartz sericite zone rocks and delta 18 o 3 9 to 4 4 per mil for chlorite zone rocks these measured values compare closely to estimated whole rock delta 18 o values based on mass balance considerations using normative mineralogies alteration of wall rocks encompassing the massive sulfide orebodies is characterized by intense sericitization a high degree of silicification and a marked positive delta 18 o anomaly calculations based on sio 2 solubilities and probable k contents of the hydrothermal fluids suggest a water rock mass ratio of 50 to 300 during the mineralization event