a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

origin of the muguayuan veinlet disseminated tungsten deposit south china constraints from in situ trace element analyses of scheelite abstract the late triassic muguayuan w deposit is located in the middle of the jiangnan orogen south china this deposit is characterized by veinlet disseminated w mineralization that developed in the sanxianba granitic porphyry stock the ore minerals are mainly scheelite with minor molybdenite and wolframite scheelite mineralization was closely related to greisenization and phyllic alteration and took place in two stages stage i involved scheelite wolframite molybdenite quartz veinlet and disseminated mineralization whereas stage ii resulted in scheelite quartz sericite veinlet mineralization sulfide and quartz calcite pyrite veinlets formed during the post ore stage scheelites from the two mineralization stages have different textures and compositions cathodoluminescence cl images of stage i scheelites reveal two generations of growth i a and i b stage i a scheelite is dark under cl with oscillatory zoning and has light rare earth element lree enriched chondrite normalized patterns negative eu anomalies and high total ree contents stage i b scheelite forms rim overgrowths on stage i a scheelite is bright under cl and shows positive eu anomalies and relatively low ree contents although stage ii scheelites are nearly uniform under cl they can be subdivided into two generations according to their ree systematics stage ii a scheelite yields middle ree mree enriched chondrite normalized patterns with negative eu anomalies whereas stage ii b scheelite has mree depleted patterns with positive eu anomalies minor amounts of apatite formed in both stages of mineralization stage i apatite contains 1370 1930 ppm mn and 97 7 127 ppm sr whereas stage ii apatite has lower mn 111 158 ppm and higher sr 2170 4690 ppm concentrations the distinct trace elements compositions of the scheelite and apatite from the two stages identify two ore forming fluids that had different origins and compositions the ore forming fluids in stage i a were relatively reduced magma derived fluids with high mo mn nb and ta and low sr fluid modeling shows that the initial fluids of stage i a were lree enriched with negative eu anomalies similar to the sanxianba granitic porphyry precipitation of early apatite and scheelite as well as plagioclase decomposition altered the fluid composition and led to relative depletions in ree nb and ta and increases of eu and sr in the stage i b fluids cooling of these fluids and the addition of recycled meteoric water led the fluids to become relatively oxidized and sr rich stage ii scheelite precipitated from these fluids precipitation of stage ii a scheelite resulted in the stage ii b fluids becoming progressively mree depleted extensive alteration especially greisenization and phyllic alteration led to plagioclase decomposition which provided the ca necessary for scheelite mineralization this process was important in generating the w mineralization in the muguayuan deposit and perhaps for other granite hosted veinlet disseminated scheelite deposits in the jiangnan orogen

evidence for melt lubrication during large earthquakes 1 rotary friction experiments have been performed on westerly granite at start velocities of 2 0 4 0 m s 1 under loads of 250 500 n until the system stalls up to 4 s interface temperature velocity and force were measured at intervals of 0 2 milliseconds the results show that kinetic friction increases in direct proportion to temperature up to a critical value tcr whereupon the system changes from boundary lubrication slip strengthening to hydrodynamic lubrication slip weakening with an associated decrease in friction and temperature for westerly granite tcr is 1150 c this corresponds to the melting point of feldspar which constitutes 50 of the rock if tcr is exceeded in natural slip systems which will depend on rock type this can result in the generation of friction melt melt lubrication can explain the scaled energy of large earthquakes being 10 to 100 times more than that of small earthquakes

evidence for paleoseismic slip on a continental low angle normal fault tectonic pseudotachylyte from the west salton detachment fault ca usa abstract the potential of continental low angle normal faults lanf to nucleate large 6 0 m w earthquakes at low angles remains unclear despite much focused research we document evidence for ancient seismicity along a continental lanf detachment fault that formed and slipped at low angles and produced tectonic pseudotachylyte these thick and laterally persistent pseudotachylyte accumulations along the west salton detachment fault wsdf salton trough usa preserve convincing evidence for a frictional melt origin including spherulitic microlites ductile flow structures preservation of high temperature phases as clasts and injection veins cumulative thickness of pseudotachylyte along the fault ranges from 0 1 to 1 5 m and pseudotachylyte cataclasite in the fault core and damage zone are exposed along 2 6 km length of the fault reworked fragments of pseudotachylyte in cataclasites and multiple generations of cataclasites provide evidence for the preservation of multiple earthquake cycles the limited exposure

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

frictional melting of gabbro under extreme experimental conditions of normal stress acceleration and sliding velocity 1 with the advent of high velocity shear apparatus several experimental studies have been performed in recent years improving our understanding of the evolution of fault strength during seismic slip however these experiments were conducted under relatively low normal stress 20 mpa and using small cylindrical samples where a large gradient in slip velocity exists across the sliding surface given the above limitations the extrapolation of these experimental results to natural conditions is not trivial here we present results from an experimental study on gabbroic rocks using a newly developed rotary shear apparatus capable of reaching higher normal stress up to 50 mpa on ring shaped samples 30 50 mm internal external diameter and allowing precise control of the imposed slip velocity function the results confirm that steady state shear stress during the melt lubricated phase of the experiment depends on normal stress in the form of a power law equation as predicted by theoretical models however the exponent appears closer to 0 5 contrary to the theoretical prediction of 0 25 we observe no systematic dependence of shear stress on acceleration but increasing deceleration drastically decreases the recovery of friction during final slip we find that the slip weakening distance decreases inversely with increasing normal stress in agreement with theoretical considerations and decreases with increasing slip rate extrapolation of the slip weakening distance to natural conditions predicts a slip velocity for ancient seismic events of 0 3 1 m s when compared with field estimates these values compare well with seismological estimates

fractal dimension of molten surfaces as a possible parameter to infer the slip weakening distance of faults from natural pseudotachylytes high velocity friction experiments on gabbro and monzodiorite using a rotary shear high velocity friction apparatus have revealed that frictional melting and progressive growth of a molten layer along a fault cause slip weakening eventually reaching a nearly steady state the melting surface at the host rock molten layer interface is initially very flat but it becomes more complex and rounded in shape towards the steady state owing to the selective melting of minerals with lower melting points and the gibbs thomson effect this change in the melting surface topography can be quantitatively expressed by the fractal dimension d as determined by the divider method from about 1 0 near the peak friction to around 1 1 near the steady state friction the ultimate fractal dimension at steady state friction tends to decrease with increasing heat production rate presumably due to more rapid and uniform melting a systematic correlation of d with mechanical behavior of the fault during frictional melting may provide a way of estimating slip weakening distance and heat production rate at steady state friction by measuring d for natural pseudotachylytes on slip surfaces with different displacements the weakening distance is of vital significance in relation to fault instability and the heat production rate is related to the fault strength the experimental studies point to ways to estimate these difficult quantities for natural faults

thermal decomposition of carbonates in fault zones slip weakening and temperature limiting effects 1 during an earthquake the heat generated by fault friction may be large enough to activate the devolatilization of minerals forming the fault rocks in this paper we model the mechanical effects of calcite thermal decomposition on the slip behavior of a fault zone during an earthquake to do so we introduce the coupled effects of calcite volume loss heat consumption and co2 production in the theoretical analysis of shear heating and thermal pressurization of pore fluids we consider a rapidly deforming shear band consisting of a fluid saturated carbonate rock the equations that govern the evolution of pore pressure and temperature inside the band and the mass of emitted co2 are deduced from the mass and energy balance of the multiphase saturated medium and from the kinetics of the chemical decomposition of calcite numerical simulation of seismic slip at depths of 5 to 8 km show that decarbonation has two critical consequences on fault slip first the endothermic reaction of calcite decomposition limits the coseismic temperature increase to less than 800 c corresponding to the initiation of the chemical reaction inside the shear band second the rapid emission of co2 by decarbonation significantly increases the slip weakening effect of thermal pressurization the pore pressure reaches a maximum and then decreases due to the reduction of solid volume causing a restrengthening of shear stress our theoretical study shows on the example of decarbonation that the thermal decomposition of minerals is an important slip weakening process and that a large part of the frictional heat of earthquakes may go into endothermic devolatilization reactions

a fluid inclusion investigation of ore formation in a tin mineralized granite new england new south wales primary fluid inclusions have filling temperatures from 550 degrees to more than 620 degrees c and salt contents of 54 to 65 wt percent daughter crystals in multiphase inclusions were mostly halite and other chlorides above a temperature of 400 degrees c the hydrothermal solutions were two phase fluid inclusion measurements and chemical analyses indicate two stages of hydrothermal activity in stage one in which heat was dispersed but not dissolved salts the temperature decreased by 200 degrees c while the salt content increased in stage two dissolved salts were dispersed more rapidly than heat and fluid inclusion evidence indicates a decreasing incidence of vapor in the hydrothermal system formation of major fractures occurred at the transition from stage one to stage two of hydrothermal activity fracturing accelerated condensation of vapor and mixing of magmatic brine and ground water most of the tin and tungsten ores were precipitated during the decrease in salt content of the concentrated brine modified journal abstract

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

fusion by earthquake fault friction stick or slip field observations of pseudotachylites and experimental studies of high speed friction indicate that melting on a slipping interface may sig nificantly affect the magnitude of shear stresses resisting slip we investigate the effects of rock melting on the dynamic friction using theoretical models of shear heating that couple heat transfer thermodynamics of phase transitions and fluid mechanics results of laboratory experiments conducted at high order of m s slip velocities but low order of mpa normal stresses suggest that the onset of frictional melting may give rise to substantial increases in the effective fault strength presumably due to viscous effects however extrapolation of the modeling results to in situ conditions suggests that the efficiency of viscous braking is significantly reduced under high normal and shear stresses when transient increases in the dynamic fault strength due to fusion are not sufficient to inhibit slip decreases in the effective melt viscosity due to shear heating and melting of clasts drastically decrease the dynamic friction resulting in a nearly complete stress drop thermal runaway the amount of energy dissipation associated with the formation of pseudo tachylites is governed by the temperature dependence of melt viscosity and the average clast size in the fault gouge prior to melting clasts from a coarse grained gouge have lower chances of survival in a pseudotachylite due to a higher likelihood of non equilibrium overheating the maximum temperature and energy dissipation attainable on the fault surface are ultimately limited by either the rock solidus via viscous braking and slip arrest or liquidus via thermal runaway and vanishing resistance to sliding our modeling results indicate that the thermally activated fault strengthening and rupture arrest are unlikely to occur in most mafic protoliths but might be relevant for quartz rich rocks especially at shallow 5 7 km depths where the driving shear stress is relatively low

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

evolution of high temperature hydrothermal fluids associated with greisenization and feldspathic alteration of a tin mineralized granite northeast queensland greisenization albitization and k feldspathization occur as pervasive background alteration and fracture controlled selvage style alteration in the go sam granite in the herberton mount garnet tin fields of northeast queensland optical sem and microthermometric investigations of fluid inclusions principally from vug filling minerals in selvage style alteration permit interpretation of the nature and evolution of hydrothermal fluids responsible for alteration of the granite saline hydrothermal fluids are dominated by na k ca fe chloride solutions with mg mn zn si al th ce and la relatively minor but important components salinities of up to 70 wt percent total dissolved salts have been calculated using the phase volume method indicated trapping temperatures of 600 degrees to 650 degrees c for many saline inclusions in vug filling minerals from feldspathic rocks record minimum temperatures for feldspathic alteration inferred temperatures for greisenization are similar and slightly lower 450 degrees 525 degrees c trapping temperatures and the composition of fluids in saline inclusions suggest late magmatic to early postmagmatic alteration of the granite by predominantly magmatic fluids inclusions containing relatively dilute fluids of possible meteoric origin homogenize between 100 degrees and 400 degrees c salinities as low as 2 equiv wt percent nacl are indicated and significant co super 2 3 hco super 3 or so super 2 4 may be present associated vapor rich inclusions indicate that the dilute fluids were probably boiling between 300 degrees and 400 degrees c a continuous range of salinities from dilute fluids to saline fluids has been found in the inclusions investigated dilution of very saline high temperature fluids could have occurred by separation of dissolved components as the fluid cooled and by mixing with dilute fluids below 400 degrees c data from fluid inclusions in magmatic quartz from the go sam granite are similar to those obtained from vug filling minerals in fracture controlled metasomatic rocks they suggest that pervasive alteration and fracture controlled alteration occurred contemporaneously and as a result of interaction with the same fluids consistently high temperatures inferred for the formation of all feldspathic rocks and associated greisens do not fit an established soviet model which emphasizes falling temperatures for the origin of comparable rocks a tentative model which emphasizes high temperature evolution of hydrothermal fluids due to changes in chemical parameters ph salinity na k f sub f 2 and confining pressures is discussed

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

origin of the atypical puy les vignes w breccia pipe massif central france constrained by trace element and boron isotopic composition of tourmaline abstract the puy les vignes w deposit is an atypical wolframite bearing hydrothermal breccia pipe hosted in migmatitic biotite sillimanite gneisses in the northwestern french massif central the deposit is characterized by volumetrically important tourmaline alteration allowing to investigate the fluid evolution of the ore forming hydrothermal system four generations of hydrothermal tourmaline tur 1 tur 4 formed during pre syn and post mineralization stages were identified based on detailed petrographic observations and were analyzed in situ for their chemical and boron isotopic compositions at the grain scale tourmaline commonly shows oscillatory zoning and dissolution textures resulting from a multi stage crystallization in a fluid dominated system the different generations of hydrothermal tourmaline have dravite schorl compositions and show similar major and trace element contents falling into the field of metamorphic rocks high concentrations of v cr sr and low concentrations of li sn in tourmaline suggest a metamorphic dominated origin of these elements the boron isotopic compositions of tourmaline range between 13 3 and 7 8 and cannot unambiguously distinguish between a magmatic and a metamorphic fluid origin our data indicate that the chemical and boron isotopic composition of tourmaline was dominantly controlled by high temperature fluid rock interactions between the metamorphic basement and boron rich reduced and low salinity hydrothermal fluids based on these results we propose a fluid evolution scenario for the puy les vignes ore forming hydrothermal system release of magmatic hydrothermal fluids from an unexposed peraluminous leucogranite at ca 324 ma is proposed as the main mechanism responsible for early greisenization and formation of disseminated tur 1 this episode was followed by massive tourmalinization and hydraulic brecciation of the overlying gneisses producing a tourmaline rich tur 2 crackle breccia by interactions with boron rich hydrothermal fluids fluid assisted reopening and collapse of the former tourmalinite at ca 318 ma yielded a matrix supported quartz tourmaline breccia pipe and formation of wolframite bearing quartz veins accompanied by deposition of tur 3 finally post ore hydraulic fracturing at ca 300 ma led to formation of tourmaline rich microbreccias tur 4 possibly from metamorphic fluids

on the transient behavior of frictional melt during seismic slip s n and g d t were supported by a european research council starting grant project acronym usems and by a progetti di eccellenza fondazione cassa di risparmio di padova e rovigo we are grateful to nick beeler and to an anonymous referee for their constructive reviews and their help to improve the clarity of the manuscript

mineral systems approach applied to gis based 2d prospectivity modelling of geological regions insights from western australia abstract gis based 2d prospectivity modelling of three greenfield geological regions of western australia namely the west arunta orogen west musgrave orogen and gascoyne province was implemented for a range of deposit types including orogenic and intrusion related gold volcanic sediment hosted base metal sulfides magmatic nickel copper and magmatic platinum group element sulfides iron oxide copper gold tin tungsten igneous and metamorphic related rare earth elements surficial uranium and unconformity related uranium conceptual mineral systems models were generated to identify the targeting criteria the inputs to the models were the spatial proxies derived from 1 100 000 to 1 500 000 scale public domain data the results showed similar prospectivity patterns for all of the targeted deposit types except sediment hosted uranium and surficial uranium deposit types once a favourable geodynamic architecture is established it can sustain different mineral systems and produce diverse deposit types depending on the nature of ligands in the source regions and physical chemical environment in the trap regions through repeated reactivation in the subsequent geological history a model is proposed to explain the formation of different deposit types at different stages of tectonic evolution of a province the implication for gis based 2d prospectivity modelling at the scale of geological region is that the prospectivity model may not be deposit type specific further prospectivity modelling should be carried out sequentially at progressively finer scales regional to district to camp scale using only the targeting criteria that are relevant at the specific scale to delineate targets for specific deposit types

friction and roughness of a melting rock surface we acknowledge takehiro hirose for providing sample hvr 687 stefan nielsen was granted by the miur project fumo and giulio di toro and stefan nielsen were granted by the european research council starting grant project 205175 usems and ca ri pa ro we thank leonardo tauro for thin section preparation luca peruzzo steven smith and piergiorgio scarlato for sem facilities and toshi shimamoto for his constant support finally we are grateful to nick beeler and chris marone for their constructive reviews

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

the nature and significance of pseudotachylite from the nason terrane north cascade mountains washington abstract pseudotachylite has been recently discovered at numerous localities in the nason terrane of the north cascade mountains washington the pseudotachylite is widespread not associated with any single major fault or shear zone and tends to occur in narrow foliation parallel zones single pseudotachylite veins range in thickness from less than 0 1 to 10 cm veins and networks of veins occur in six distinct types and these form the basis of a suggested classification scheme multiple generations of pseudotachylite are present in some samples host lithologies include quartz diorite semipelitic schist tonalite amphibolite and especially graphitic pelitic schist glassy veins are rare most pseudotachylite is apparently holocrystalline spherulites vesicles and dendritic microphenocrysts are present and indicate a frictional melt origin the ubiquitous occurrence of cataclasite xenoliths within the pseudotachylite along with other textural observations indicates that in the nason terrane the development of cataclasite zones was the precursor to pseudotachylite generation it is inferred that cataclastic deformation of the schist provided the strain softening which resulted in faulting and pseudotachylite generation the water rich and ultra fine grained matrix of the cataclasite was an ideal starting material for pseudotachylite generation based upon bulk chemistry of host lithologies and microprobe analyses of the pseudotachylite it appears that the pseudotachylite formed as a result of a virtually complete melting of the pelitic i e non quartz vein component of the schist where pseudotachylite occurs within pelitic schist alone the composition of the pseudotachylite is very similar to the pelitic component of the schist while the composition of veins cutting tonalite gneiss in addition to pelitic schist appears to define a mixing line between these two lithologies this suggests either participation of the tonalite during initial melting or subsequent assimilation of gneiss into the melt

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

effect of water and rock composition on re strengthening of cohesive faults during the deceleration phase of seismic slip pulses abstract the elastic strain energy release rate and seismic waves emitted during earthquakes are controlled by the on fault temporal evolution of the shear stress during rupture propagation high velocity friction experiments highlighted that shear stress on the fault surface evolves rapidly during seismic slip pulses this temporal evolution of shear stress is controlled by both fault weakening at seismic slip initiation and re strengthening rate towards the end of slip while numerous studies focused on fault weakening less attention was given to co seismic re strengthening processes here we performed 53 friction experiments normal stress 30 mpa slip rate 6 5 m s 1 imposing constant slip acceleration and deceleration 7 8 m s 2 on cohesive carrara marble 99 calcite and micro gabbro silicate built rock under dry vacuum and water pressurized conditions microstructural observations showed that micro gabbro accommodated seismic slip by bulk melting of the sliding surfaces whereas carrara marble by coupled decarbonation and grain size dependent crystal plastic processes under room humidity conditions and low imposed power density i e product of normal stress per slip rate re strengthening rate during the deceleration stage was up to 17 times faster in marble than in micrograbbro in the latter the re strengthening rate increased slightly with the power density the presence of water enhanced further this trend on the contrary in marbles the re strengthening rate decreased drastically with power density and in the presence of water our experimental observations highlighted the first order importance of the mineralogy and rheology of the slip zone materials and to a second order of the presence of water in controlling co seismic re strengthening of faults during seismic slip deceleration

subtropical sea surface warming and increased salinity during eocene thermal maximum 2 eocene thermal maximum 2 etm 2 ca 54 2 ma represents the second largest of the major eocene hyperthermals yet comparatively little is known about the scale and rate of climatic change for key regions here we provide the first detailed records of subtropical sea surface warming and salinization for etm 2 at two subtropical locations ocean drilling program sites 1209 north pacific and 1265 south atlantic coupled planktic foraminiferal mg ca and 18o indicate 2 4 c of rapid warming and local salinization of 1 2 ppt at both sites the increase in sea surface temperature is equivalent to anomalies reported from higher latitude sites and is consistent with theory on the expected pattern of spatial temperature response to greenhouse gas forcing in an ice free world i e no ice albedo feedback similarly the observed salinization is consistent with the hypothesis of enhanced meridional vapor transport and increased subtropical aridity in a warmer world

frictional melt homogenisation during fault slip geochemical textural and rheological fingerprints abstract volcanic environments often represent structurally active settings where strain localisation can promote faulting frictional deformation and subsequent melting along fault planes such frictional melting is thermodynamically a disequilibrium process initiated by selective melting of individual mineral phases and softening of volcanic glass at its glass transition as a response to rapid frictional heating the formation of a thin melt layer on a fault plane surface can drastically accelerate or terminate slip during fault motion a comprehensive understanding of the physical and chemical properties of the frictional melt is required for a full assessment of slip mechanisms as frictional rheology depends on the contributions from selectively melted mineral and glass phases as well as the physical effects of restite fragments suspended in the frictional melt here we experimentally investigate the impact of host rock mineralogy on the compositional and textural evolution of a frictional melt during slip high velocity rotary shear hvr experiments were performed under controlled volcanically relevant coseismic conditions 1 m s 1 slip rate and 1 mpa normal stress using three intermediate dome lavas with contrasting mineral assemblages sampled from volcanic systems where fault friction is evident 1 an amphibole bearing andesite soufriere hills volcano montserrat 2 an amphibole poor dacite santiaguito dome complex guatemala and 3 an amphibole free andesite volcan de colima mexico for each sample five hvr experiments were terminated at different stages of frictional melt evolution namely 1 at the onset of melting 2 upon formation of a steady state melt layer and 3 after 5 m 4 10 m and 5 15 m of slip at steady state conditions progressive mixing and homogenisation of selective single phase melts within the frictional melt layer through double diffusion convection demonstrates the control of melt composition on slip behaviour amphiboles melted preferentially leading to consistently lower shear stress 1 mpa less than amphibole poor samples and pronounced shear weakening during the frictional melting of amphibole bearing lavas the results highlight the implications of mineral assemblages on fault slip including conduit flow processes which may influence the style of eruptions and run out distances of rapid granular flows

oxygen isotope evidence for the mixing of magmatic and meteoric waters during tin mineralization in the mole granite new south wales australia oxygen isotope measurements of quartz in the tin mineralized permian mole granite new south wales support a model of progressive mixing of magmatic water and surface derived water of meteoric origin in mineralizing hydrothermal circulation systems the magmatic water observed as multiphase fluid inclusions in hydrothermal quartz biotite orthoclase topaz bearing pegmatites had a high temperature 550 degrees c high salinity 55 75 wt and a delta 18 o smow value of about 8 7 per mil the initial magmatic delta 18 o smow value of the granite is estimated to be about 9 per mil the meteoric water observed as liquid rich fluid inclusions in quartz from late veins of quartz sphalerite galena had a low temperature 250 degrees c low salinity 3 5 wt and a delta 18 o smow value of 15 per mil permian meteoric water is expected to be light isotopically owing to a near polar 70 degrees palcolatitude for the new england fold belt quartz from cassiterite quartz chlorite sericite ores has a wide range of delta 18 o values from 2 8 to 6 7 per mil this is intermediate between the values for quartz deposited from magmatic and from meteoric waters the fluid inclusions in these samples have homogenization temperatures of about 300 degrees c and a wide range of salinities 25 35 wt the variation in isotopic composition observed for quartz is attributed to a fluctuating isotopic composition of the hydrothermal solutions resulting from variable degrees of mixing of magmatic and meteoric water cassiterite has a narrow range of delta 18 o 5 9 7 2ppm which suggests precipitation of cassiterite over a narrow range of mixing of the hydrothermal fluids three cassiterite quartz mineral pairs with textures indicating synchronous crystallization imply cassiterite water fractionations of 2 2 per mil at 300 degrees c and 4 1 per mil at 370 degrees c hydrogen isotope data are less systematic due to postcrystallization isotopic exchange of hydrous minerals and the presence of younger fluids in secondary fluid inclusions in quartz

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

the interplay of groundwater and magmatic fluids in the formation of the cassiterite sulfide deposits of western tasmania abstract the cassiterite sulfide deposits of western tasmania are spatially and temporally related to devonian granitoids the stable isotope and fluid inclusion data of these deposits are best explained by a genetic model in which sn is leached from the granites by reduced non magmatic fluids mixed with late stage magmatic fluids these fluids mineralize the overlying dolomite horizons and subjacent faults by a combination of wallrock and boiling induced reactions the model requires co incidental release of volatiles and ingress of groundwaters to sustain the leach mechanism this implies some specific structural deformational controls on the process and an intimate association between cassiterite sulfide deposits and volatile rich granites the sulfur isotope data show a wide range in values from about 2 to 20 per mil and are explained in terms of a near zero magmatic component and three heavier country rock sources the precambrian oonah formation the crimson creek formation and the mount read volcanics following this interpretation the heavy sulfur isotope values from the heemskirk granite hajitaheri 1985 and the federal bassett fault at renison kitto 1994 indicate ingress of groundwater into the granites salinities of fluid inclusions from the deposits show a restricted range around 5 to 15 weight percent nacl equivalent compared with the range shown by inclusions from alteration zones within the granites around 5 to 40 weight percent nacl equivalent it is suggested that the wide range of salinities in the granites is generated in the critical region of the nacl h 2 o system at temperatures around 400 to 500 c and pressures around 400 to 500 bars the limited range of salinities in the deposits reflects cooling to sub critical conditions cooling through the critical region promotes homogenization of groundwater and magmatic vapor and brine condensation of magmatic volatiles within this zone of mixing maintains acidity and promotes fluid rock reaction the geochemistry of the granites underlying the renison bell area bajwah et al 1995 is interpreted in terms of two granites the geological relationships indicate the more mafic phase the renison granite was intruded by the more fractionated pine hill granite fluids from the pine hill granite sericitised and tourmalinized both the renison granite and pine hill granite along their mutual contact generating a broad north east trending zone of alteration this contact may have been offset by the federal bassett fault before the renison deposit was formed it is suggested that groundwater flow was essentially constrained within this nw se trending structure and subsidiary structures magmatic volatiles emanating from deep within the pine hill granite acidified the reduced groundwater and promoted leaching of the granite the siting of the renison deposit on the margin of the pine hill granite is consistent with a strong up flow zone on the margin of a cooling pluton the very constant s isotope signature in the deposit is consistent with a large scale homogenization process operating over a sustained period the very large size of the renison deposit is accounted for by a long lived groundwater system maintained by the high heat flow from a fractionated granite

coseismic damage and softening of fault rocks at seismogenic depths abstract elastic stiffness a critical property for stress orientation propagation of earthquake ruptures and associated seismic waves and the capability of crustal rocks to store strain energy is expected to be highly variable throughout the seismic cycle due to complex sequences of damage and healing post seismic healing and exhumation related alteration render it impossible to assess how well rock stiffness as measured in the laboratory on samples collected from fault zones represents in situ coseismic rock stiffness at seismogenic depths here we estimate the in situ coseismic stiffness of fault rocks from the pseudotachylyte bearing gole larghe fault zone italian southern alps using aspect ratio measurements of pseudotachylyte injection veins and numerical simulations aspect ratios of injection veins cutting across tonalite and cataclasite exhibit a maximum vein aperture positively correlating with vein length to model vein opening fault and injection veins are assumed to be filled with pressurized melt consistent with recent results from studies of melt lubrication we assume that the magnitude of the melt pressure is in equilibrium with the fault normal stress and the fault vein approximately maintains constant thickness during slip the numerical simulations of injection vein opening due to pressurized frictional melt indicate that the average in situ coseismic stiffness of the wall rocks is 5 50 times smaller than the stiffness obtained from laboratory measurements on the same rocks in their present day state the disagreement between laboratory measurements and simulations brings into question the appropriateness of using laboratory derived values for rock stiffness to model coseismic processes at depth

garnetization as a ground preparation process for copper mineralization evidence from the mazraeh skarn deposit iran the mazraeh cu fe skarn deposit nw iran is the result of the intrusion of an oligocene miocene granitic pluton into cretaceous calcareous rocks the pluton ranges in composition from monzonite to quartz monzonite monzogranite tonalite and granodiorite with i type calc alkaline and weakly peraluminous characteristics the mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of 8 km pyroxene skarn garnet skarn and epidote skarn zones were formed during the intrusive phase the garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton respectively prior to mineralization garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies mass balance calculation of garnet skarn in the endoskarn zone indicates that hydrothermal fluids originating from the cooling magma introduced si fe mn ca mg p ag cu zn la pb cd mo and y the main mass loss in the garnet skarn was due to destruction of feldspars in the mazraeh plutonic rocks and leaching of k2o and na2o released ca has been fixed in the andraditic garnet garnetization of the mazraeh pluton was accompanied by mass and volume increase the magnitude of these changes depends mainly on the degree of alteration and composition of the precursor the brittle behavior of the endoskarn zone was increased due to formation of massive garnet which subsequently fractured these fractures not only facilitated movement of hydrothermal fluids but also provided new locations for cu mineralization therefore locating strongly garnetized zones may be a vector to ore in skarn deposits

effects of lithology cataclasis and melting on the composition of fault generated pseudotachylytes in lewisian gneiss scotland abstract petrological studies of fault generated pseudotachylytes formed during coseismic slip need to consider cataclastic processes as well as rapid closed system melting and freezing in order to account for the observed similarities and the variations between the chemical compositions of pseudotachylytes and their host rocks whole rock analyses of pseudotachylytes and their gneissic host rocks from the lewisian complex of northwest scotland indicate that the composition of the pseudotachylyte is sensitive not only to the bulk host rock composition but also to its mineralogy and fabric in anisotropic e g gneissic rocks selective cataclastic and melting effects may both contribute to determining the whole rock composition of pseudotachylytes electron microprobe analyses of pseudotachylyte matrices indicate more rapid decomposition and fusion of hydrous ferromagnesian phases such as biotite and amphibole and to a lesser extent feldspar relative to quartz the pseudotachylytes of this study appear to have formed neither by ultracataclasis alone nor by classical equilibrium partial melting or total fusion but through the interaction of selective cataclastic and melting processes controlled by the lithological layering and mineralogical heterogeneity in their host rocks this interpretation may be widely applicable to pseudotachylytes generated by faulting in foliated host rocks

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

hydrothermal alteration and mineralisation of the glen eden mo w sn deposit a leucogranite related hydrothermal system southern new england orogen nsw australia the glen eden mo sn w deposit in north eastern new south wales australia is an example of a leucogranite related low grade large tonnage hydrothermal system it occurs in the southern part of the new england orogen and is hosted within permian felsic volcanic rocks intruded at depth by dykes of porphyritic microleucogranite glen eden granite the deposit is hosted within a pipe like quartz rich greisen breccia body about 500 m in diameter surrounded by a greisen zone several hundred metres across zoning out into altered volcanic rocks the dominant ore minerals largely hosted as open space fillings and disseminations in quartz and quartz rich greisen are molybdenite wolframite and cassiterite they are accompanied by minor to trace amounts of muscovite fluorite topaz siderite pyrrhotite arsenopyrite chalcopyrite sphalerite bismuth bismuthinite joseite a cosalite galenobismutite beryl anatase and late stage dickite and kaolinite two types of breccia are recognised 1 greisenised volcanic rock fragments quartz muscovite cemented by hydrothermal quartz k feldspar ore minerals and 2 fragments of hydrothermal quartz cassiterite wolframite enclosed in quartz clay in both types of breccia and in stockwork veins there is evidence of early precipitation of mo sn w phases followed by bi minerals and base metal sulfides fluorite siderite

energy taken up by co seismic chemical reactions during a large earthquake an example from the 1999 taiwan chi chi earthquake 1 frictional heat in a fault zone during earthquake slip transiently induces chemical reactions that may use energy released during the earthquake we estimated the energy used by such reactions ec by a numerical analysis incorporating frictional heat thermal diffusion chemical kinetics and energy conservation and found that ec has an auto feedback effect that inhibits temperature rise in fault zone during the 1999 taiwan chi chi earthquake estimated ec was 0 43 mj m2 corresponding to 0 79 of the frictional heat generated this low percentage probably reflects the low initial concentrations of reactive materials however in the case of a fault with abundant reactive materials ec could reach 50 of the frictional heat and the auto feedback effect could be large at this case ec is a nonnegligible component on earthquake energy budget and can affect fault mechanics

biomarker thermal maturity experiments at earthquake slip rates abstract evidence of temperature rise is useful for identifying where within a fault zone earthquake slip has occurred as well as some attributes of the earthquake such as energy output biomarker thermal maturity can elucidate structures within a fault zone that were hotter than surrounding rock and therefore likely to have hosted earthquakes we performed a series of friction experiments on thin gouge layers of woodford shale at slip rates of 1 m s our results show that biomarker thermal maturity can clearly delineate zones of slip that are as thin as 150 m we establish that the kinetics of methylphenanthrene reaction previously determined at longer durations and lower temperatures are applicable at seismic slip rates and timescales temperature estimates show that once the slipping zone reached 500 c biomarker reaction was significant as predicted by the reaction kinetics our results demonstrate that temperature rise in fault zones is a function of both the work density and power density during the earthquake biomarker reactions along with other arrhenius style reactions such as those that lead to dynamic shear weakening are both a function of slip speed and frictional work

causes for large scale metal zonation around mineralized plutons fluid inclusion la icp ms evidence from the mole granite australia detailed reconstruction of the fluid evolution in several ore deposits associated with the sn w and base metal mineralized mole granite shows that multiple factors contributed to the zonal metal distribution around this intrusion information about the mechanism of ore formation was obtained from field relationships detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry la icp ms microanalysis of single fluid inclusions premineralization fluid inclusions in sn deposits are characterized by high sn w ratios whereas early fluid inclusions from w deposits contain higher w concentrations and comparatively low sn w ratios this indicates that the metal ratio in these deposits already was predefined by the composition of the magmatic input fluid however in both types of deposits the input fluid actually contained much higher concentrations of base metals pb zn cu etc than sn and w demonstrating that metal precipitation was highly selective the metal zonation around the mole granite therefore reflects both a compositional variation of the source fluid as well as sequential metal precipitation from it an additional process contributing to metal fractionation occurred by phase separation of the hydrothermal fluid into saline brine and low density vapor whereby cu b li as s ag la preferentially partitioned into the vapor phase analyses on six assemblages of unambiguously coexisting vapor and brine inclusions allowed direct determination of vapor brine distribution coefficients for 24 elements

fluid inclusion and stable isotope evidence for interaction between granites and magmatic hydrothermal fluids during formation of disseminated and pipe style mineralization at the zaaiplaats tin mine tin tungsten rare earth element mineralization at zaaiplaats is hosted by the lease and bobbejaankop granites miarolitic alkali feldspar granites which form part of the lebowa granite suite of the bushveld complex pervasive hydrothermal alteration of the granites resulted in replacement of original biotite by chlorite sericite carbonate and ti oxides development of coarse vein and patch perthite and antiperthite in alkali feldspar and precipitation of hydrothermal minerals in miarolitic cavities cassiterite occurs as a cavity infill and replacement mineral in tabular subhorizontal zones within the lease and bobbejaankop granites and in shallowly plunging and branching pipe systems in the granites disseminated mineralization exhibits no relationship to fracture systems and hydrothermal fluids appear to have evolved essentially in situ during crystallization to produce miarolitic cavities minor subvertical veins containing fluorite calcite quartz and sulfides crosscut the granites and pipes three major types of fluid inclusions have been identified in granite quartz and hydrothermal minerals from pipes and cavities high salinity inclusions characterized by the presence of solid phases such as halite sylvite and fe chloride occur as primary inclusions in 1 granite quartz 2 cavity filling quartz fluorite and scheelite and 3 cassiterite from the iota pipe these inclusions homogenize by dissolution of solid phases in the temperature range 160 degrees to 600 degrees c liquid vapor inclusions occur in 1 late quartz from cavities 2 quartz fluorite and calcite from cavities in the marginal pegmatite and 3 late quartz and calcite infill from the iota pipe these inclusions homogenize to the liquid phase between 88 degrees and 240 degrees c while ice melting temperatures range from 11 degrees to 30 degrees c h 2 o nacl co 2 inclusions occur as secondary inclusions in granite quartz and early cavity filling quartz and primary inclusions in quartz from the quartz tourmaline zone of the bobbejaankop pipe the compositional range and homogenization behavior of these inclusions is consistent with immiscibility around 350 degrees c and 1 000 bars the oxygen isotope composition of granite whole rocks ranges from 9 2 to 9 9 per mil two samples of low grade ore 8 4 and 9 0ppm are depleted relative to the granites possibly reflecting higher abundances of alteration and infill chlorite sericite and cassiterite the delta 18 o values of quartz from granites and the marginal pegmatite range from 7 3 to 9 4 per mil whereas those of quartz from cavities low grade orebodies pipes and veins range from 7 8 to 13 5 per mil most granite and cavity samples have quartz feldspar fractionations less than 0 per mil vein and pipe samples tend to have higher delta 18 o feldspar and much higher delta 18 o quartz compared to granites with quartz feldspar fractionations of 0 6 to 1 2 per mil the disequilibrium quartz feldspar fractionations observed in granites and cavities reflect pervasive hydrothermal fluid rock interaction at subsolidus temperatures modeling isotopic exchange between granites and a magmatic fluid phase in isotopic equilibrium with average bobbejaankop granite quartz at 600 degrees c indicates that whole rock compositions result from final exchange at temperatures less than 400 degrees c with fluid compositions in the range 4 2 to 5 2 per mil at 300 degrees c and 0 8 to 1 8 per mil at 200 degrees c these results are consistent with fluid compositions calculated from delta 18 o quartz and pressure corrected fluid inclusion homogenization temperatures and indicate that oxygen isotope variation at zaaiplaats reflects exchange between the granite and the magmatic fluid phase at temperatures down to 200 degrees c

high velocity frictional properties of a clay bearing fault gouge and implications for earthquake mechanics 1 frictional properties of natural kaolinite bearing gouge samples from the median tectonic line sw japan have been studied using a high velocity rotary shear apparatus and deformed samples have been observed with optical and electron scanning and transmission microscopy for a slip velocity of 1 m s 1 and normal stresses from 0 3 to 1 3 mpa a dramatic slip weakening behavior was observed x ray diffraction analysis of deformed samples and additional high velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip the critical slip weakening distance dc is of the order of 1 to 10 m these values are extrapolated to higher normal stresses assuming that dc is rather a thermal parameter than a parameter related to a true characteristic length the calculation shows that dimensionally dc 1 n2 where n is the normal stress applied on the fault the inferred dc values range from a few centimeters at 10 mpa normal stress to a few hundreds of microns at 100 mpa normal stress microscopic observations show partial amorphization and dramatic grain size reduction down to the nanometer scale localized in a narrow zone of about 1 to 10 m thickness fracture energy gc is calculated from the mechanical curves and compared to surface energy due to grain size reduction and energies of mineralogic transformations we show that most of the fracture energy is either converted into heat or radiated energy the geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust

a chemical kinetic approach to estimate dynamic shear stress during the 1999 taiwan chi chi earthquake 1 estimation of the dynamic shear stress on a fault during an earthquake is important for understanding the earthquake itself using a chemical kinetic approach we examined the thermal decomposition of carbonate minerals to estimate the shear stress on the taiwan chelungpu fault which slipped during the 1999 chi chi earthquake the reaction rate of the decomposition was related to temperature by using the arrhenius equation and the chemical kinetics taking into account the temperature change over time caused by frictional heating and heat conduction was solved by the finite difference method the dynamic shear stress during the chi chi earthquake was deduced to be 1 31 mpa and the frictional coefficient to be 0 04 0 05 this estimated value agrees with the hypothesis that friction along the chelungpu fault was low

superheated friction induced melts in zoned pseudotachylytes within the adamello tonalites italian southern alps pseudotachylytes and cataclasites are present along a strike slip fault zone in the tonalites of the adamello intrusion italian southern alps ambient conditions during faulting were 0 25 0 3 gpa and 250 300 c pseudotachylyte veins thicker than 6 mm are zoned and consist of two symmetric microlitic domains towards the vein walls and a central spherulitic domain the thickness of the microlitic domains x increases linearly with the half total thickness a of the pseudotachylyte vein commonly 2 cm according to the relation x 0 29 0 12 a the spherulitic and microlitic domains have similar chemical composition but the microlitic domain has a lower amount of plagioclase clasts a numerical model explains zoning as the result of the different cooling rates and clast melt interactions at the center and periphery of thick veins zoning is compatible with the injection of a single pulse of superheated friction induced melt tmelt 1450 c melt temperatures estimated by the clast matrix ratio o hara 2001 are considerably lower 316 577 c it is suggested that the difference in the temperature estimates reflects a more complex slip history than a single seismic slip event along the fault during production of cataclasites pseudotachylytes

earthquake rupture dynamics frozen in exhumed ancient faults just by looking at the traces of solidified friction induced melt produced by ancient earthquakes it is possible to learn about fractures that lasted a few seconds during seismic events that took place millions of years ago in the italian alps large sections of an ancient fault have been uprooted by tectonic movements brought to the surface almost intact and polished by the abrasion of a glacier secondary fractures created during the earthquakes tend to lie to one side of the fault in a particular direction suggesting that rupture propagated in the same direction during repeated earthquakes most of our knowledge about co seismic rupture propagation is derived from inversion and interpretation of strong ground motion seismograms1 2 3 laboratory experiments on rock4 5 and rock analogue material6 or inferred from theoretical and numerical elastodynamic models7 8 9 however additional information on dynamic rupture processes can be provided by direct observation of faults exhumed at the earth s surface10 pseudotachylytes solidified friction induced melts11 12 are the most certain fault rock indicator of seismicity on ancient faults13 here we show how the asymmetry in distribution and the orientation of pseudotachylyte filled secondary fractures around an exhumed fault can be used to reconstruct the earthquake rupture directivity rupture velocity and fracture energy by comparison with the theoretical dynamic stress field computed around propagating fractures in particular the studied natural network of pseudotachylytes is consistent with a dominant propagation direction during repeated seismic events and subsonic rupture propagation close to the rayleigh wave velocity

marcasite inversion and the petrographic determination of pyrite ancestry pyrite formed by the inversion of marcasite or by oxidative leaching of pyrrhotite can be recognized in polished sections by the following characteristics compiled from synthetic pyrite after marcasite and natural samples of pyrite after marcasite and after pyrrhotite pyrite formed by inversion from marcasite is characterized by approximately 2 modal percent pore space no by products filling the pores optical anisotropy dark green to dark red anhedral shape and polycrystalline daughter pyrite domains in two orientations relative to the marcasite parent crystal pyrite or marcasite formed by oxidative dissolution as opposed to leaching of pyrrhotite exhibits up to 32 modal percent pore space gaps between the pyrite and parent pyrrhotite pores and gaps filled with by product siderite magnetite hisingerite or other fe bearing phase optically isotropic character for pyrite development of crystal faces and random orientation relative to the parent pyrrhotite marcasite formed by oxidative leaching of fe as opposed to complete dissolution from pyrrhotite also exhibits a large amount of pore space but has preferred orientation relative to the parent pyrrhotite pyrite after marcasite may be used as an indicator of ph 5 and t ca 240 degrees c during deposition of the parent marcasite marcasite precipitated following dissolution of pyrrhotite is also indicative of those conditions during alteration marcasite formed by oxidative leaching of pyrrhotite cannot be used as evidence of those conditions however

unusual ruby sapphire transition in alluvial megacrysts cenozoic basaltic gem field new england new south wales australia abstract rare ruby crystals appear among prevailing sapphire crystals mined from placers within basaltic areas in the new england gem field new south wales australia new england ruby ner has distinctive trace element features compared to those from ruby elsewhere in australia and indeed most ruby from across the world the ner suite includes ruby up to 3370 ppm cr pink sapphire up to 1520 ppm cr white sapphire up to 910 ppm and violet mauve purple or bluish sapphire up to 1410 ppm cr some crystals show outward growth banding in this respective colour sequence all four colour zones are notably high in ga up to 310 ppm and si up to 1820 ppm high ga and ga mg values are unusual in ruby and its trace element plots laser ablation inductively coupled plasma mass spectrometry and suggests that magmatic metasomatic inputs were involved in the ner suite genesis in situ oxygen isotope analyses secondary ion mass spectrometry across the ner suite colour range showed little variation n 22 18 o 4 4 0 4 2 error and are values typical for corundum associated with ultramafic mafic rocks the isolated ner xenocryst suite corroded by basalt transport and with few internal inclusions presents a challenge in deciphering its exact origin detailed consideration of its high ga chemistry in relation to the known geology of the surrounding region was used to narrow down potential sources these include late palaeozoic triassic fractionated i type granitoid magmas or mesozoic cenozoic felsic fractionates from basaltic magmas that interacted with early palaeozoic cr bearing ophiolite bodies in the new england orogen other potential sources may lie deeper within lower crust mantle metamorphic assemblages but need to match the anomalous high ga geochemistry of the new england ruby suite

frictional melting of peridotite and seismic slip 1 the evolution of the frictional strength along a fault at seismic slip rates about 1 m s is a key factor controlling earthquake mechanics at mantle depths friction induced melting and melt lubrication may influence earthquake slip and seismological data we report on laboratory experiments designed to investigate dynamic fault strength and frictional melting processes in mantle rocks we performed 20 experiments with balmuccia peridotite in a high velocity rotary shear apparatus and cylindrical samples 21 8 mm in diameter over a wide range of normal stresses 5 4 16 1 mpa slip rates 0 23 1 14 m s and displacements 1 5 71 m during the experiments shear stress evolved with cumulative displacement in five main stages stages 1 5 in stage 1 first strengthening the coefficient of friction increased up to 0 4 0 7 first peak in friction in stage 2 abrupt first weakening decreased to about 0 25 0 40 in stage 3 gradual second strengthening shear stress increased toward a second peak in friction 0 30 0 40 in stage 4 gradual second weakening the shear stress decreased toward a steady state value stage 5 with 0 15 stages 1 and 2 are of too short duration to be investigated in detail with the current experimental configuration by interrupting the experiments during stages 3 4 and 5 microstructural field emission scanning electron microscope and geochemical electron probe micro analyzer and energy dispersive x ray spectroscopy analysis of the slipping zone suggest that second strengthening stage 3 is associated with the production of a grain supported melt poor layer while second weakening stage 4 and steady state stage 5 are associated with the formation of a continuous melt rich layer with an estimated temperature up to 1780 c microstructures formed during the experiments were very similar to those found in natural ultramafic pseudotachylytes by performing experiments at different normal stresses and slip rates 1 the thermal as it includes the thermally activated first and second weakening slip distance to achieve steady state from the first peak in strength decreased with increasing normal stress and slip rate and 2 the steady state shear stress slightly increased with increasing normal stress and for a given normal stress decreased with increasing slip rate the ratio of shear stress versus normal stress was about 0 15 well below the typical friction coefficient of rocks 0 6 0 8 the dependence of steady state shear stress with normal stress was described by means of a constitutive equation for melt lubrication the presence of microstructures similar to those found in natural pseudotachylytes and the determination of a constitutive equation that describes the experimental data allows extrapolation of the experimental observations to natural conditions and to the study of rupture dynamics in mantle rocks

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths