tectonic incorporation of the upper part of oceanic crust to overriding plate of a convergent margin an example from the cretaceous early tertiary mugi melange the shimanto belt japan abstract a tectonic melange exposed on land is examined to reveal relationships between melange formation underplating and deformation mechanisms focusing on the deformation of basaltic rocks the studied mugi melange of the shimanto belt is composed of a shale matrix surrounding various blocks of sandstone pelagic sediments and basalts the melange was formed during late cretaceous to early tertiary times in a subduction zone under p t conditions of 150 200 c and 6 7 km depth as estimated from vitrinite reflectance and quartz veins fluid inclusions the melange represents a range of deformation mechanisms pressure solution with micro scale cataclasis in the shale matrix brittle tension cracking in the blocks and ubiquitous strong cataclasis in the basal portion of basaltic layers the cataclastic deformation in the basalts suggests a breakage of a topographic high in the seismogenic depth

for how long are pseudotachylytes strong rapid alteration of basalt hosted pseudotachylytes from a shallow subduction complex abstract basalt is one of the main components of megathrust faults in subduction zones where the world s largest earthquakes are generated paradoxically pseudotachylytes have never been reported from basaltic rocks deformed at conditions compatible with the thermally defined seismogenic zone we report the first discovery of pseudotachylyte from oceanic crustal basalt identified by microstructural criteria the fault is located within a late cretaceous subduction complex the mugi melange and either formed along the plate interface during subduction or within the upper plate during underplating after solidifying the pseudotachylytes were fragmented by cataclasis and subsequently partially hydrated to produce phyllosilicates previous experiments using dry felsic lithologies as starting material have shown that pseudotachylytes can be as strong as their host rock deterring re activation and favoring their preservation over geologic time however we show that where fluid is present pseudotachylyte can be replaced by phyllosilicate rich layers with a low frictional strength the rate of dissolution is dependent on the bulk composition of the pseudotachylyte with dissolution of mafic glasses occurring at least three orders of magnitude faster than felsic glasses under hydrothermal conditions the replacement of pseudotachylytes by layers of frictionally weak phyllosilicates is predicted to occur over time intervals shorter than the megathrust earthquake cycle this process likely reduces fault strength and promotes reactivation

progress of illitization along an imbricate frontal thrust at shallow depths in an accretionary prism abstract fossil imbricate thrusts branching from a decollement in an ancient accretionary prism the miura boso accretionary prism are exposed in the southern parts of the miura and boso peninsulas in central japan an analysis of the clay mineralogy of fault rocks along one of the imbricate thrust faults the shirako fault revealed local illitization of mixed layer illite smectite i s and the partial breakdown of kaolinite the shape of the i 001 s 001 reflection in the x ray diffraction pattern suggests that the illite fraction in i s crystallites within the fault gouge is 9 more than in the surrounding rocks these results imply that there has been a local temperature anomaly within the slip zone attributable to frictional heating induced by high velocity slip a thermal model coupled with a kinetic simulation of illitization in i s suggests that the reaction was probably facilitated by multiple high velocity slips at a peak temperature of 450 c suggesting repeated seismic rupture propagations to the prism toe as also inferred from the modern accretionary prism in the nankai trough

reaction pathways and reaction progress for the smectite to chlorite transformation evidence from hydrothermally altered metabasites the transformation from smectite to chlorite has been interpreted as involving either a disequilibrium chlorite smectite mixed layering sequence or an equilibrated discontinuous sequence involving smectite corrensite chlorite here analysis of the smectite to chlorite transition in different geothermal systems leads us to propose that the transformation proceeds via three contrasting reaction pathways involving i a continuous mixed layer chlorite smectite series ii a discontinuous smectite corrensite chlorite series and iii a direct smectite to chlorite transition such contrasting pathways are not in accord with an equilibrium mineral reaction series suggesting that these pathways record kinetically controlled reaction progress in the geothermal systems reviewed the style of reaction pathway and degree of reaction progress is closely correlated with intensity of recrystallization and not to differences in thermal gradients or clay grain size this suggests a kinetic effect linked to variation in fluid rock ratios and or a contrast between advective or diffusive fluid transport the mode of fluid transport provides a means by which the rates of dissolution nucleation growth can control the reaction style and the reaction progress of the smectite to chlorite transition slow rates of growth are linked to the first reaction pathway involving mixed layering while increasing rates of growth relative to nucleation promote the generation of more ordered structures and ultimately lead to the direct smectite to chlorite transition representative of the third pathway

coseismic fluid rock interactions at high temperatures in the chelungpu fault chemical and isotopic variations in crushed material along the chelungpu fault in taiwan are suggestive of interactions at high temperatures with coseismically generated aqueous fluids high fluid pressures along the fault zone during the magnitude 7 6 chi chi earthquake in 1999 could have reduced friction and fault strength aqueous fluids are thought to have an essential role in faulting and the dynamic propagation of earthquake rupture fluid overpressure can affect earthquake nucleation1 2 and in a process termed thermal pressurization pore fluid pressure produced by frictional heating can reduce the effective normal stress acting on the fault surface3 4 5 this may lead to a marked reduction in fault strength during slip however the coseismic presence of fluids within slip zones and the role of fluids in dynamic fault weakening is still a matter of debate here we present compositions of major and trace elements as well as isotope ratios of core samples representing relatively undamaged as well as very fine grained deformed material from three active zones of the chelungpu fault taiwan depth profiles across the most intensely sheared bands that range in thickness from 2 15 cm exhibit sharp compositional peaks of fluid mobile elements and of strontium isotopes we suggest that high temperature fluids 350 c derived from heating of sediment pore fluids during the earthquake interacted with material within the fault zone and mobilized the elements the coseismic presence of high temperature fluids under conditions of low hydraulic diffusivity6 within the fault zone is favourable for thermal pressurization this effect may have caused a dynamic decrease of friction along the chelungpu fault during the 1999 magnitude 7 6 chi chi earthquake

depth of oceanic crust underplating in a subduction zone inferences from fluid inclusion analyses of crack seal veins fluid inclusions in crack seal veins are analyzed in accreted melange now on land the vein i inclusions are observed in the necked parts of sandstone blocks in melange and the vein ii inclusions developed in shale below the thrust fault which cuts the melanges the pressure and temperature estimations from the inclusions within vein i show that the cracks were sealed at 125 195 8c under 92 144 mpa of fluid pressure vein ii formed in cracks that might have opened in a damage zone caused by the thrust fault as it broke through oceanic crust and into the melange these veins contain fluid inclusions trapped at 135 245 8c under 107 149 mpa of fluid pressure the depth 4 6 km below the seafloor and temperature estimates are consistent with the conditions where an aseismic decollement within sedimentary rocks steps down into the oceanic basement so that a thin section of oceanic crust underplates in the hanging wall such a step down site is the updip limit of the seismogenic zone in the modern nankai trough

experimental investigation of frictional melting of argillite at high slip rates implications for seismic slip in subduction accretion complexes 1 discovery of pseudotachylytes from exhumed accretionary complexes indicates that frictional melting occurred along illite rich argillite derived slip zones during subduction earthquakes we conducted high velocity friction experiments on argillite at a slip rate of 1 13 m s and normal stresses of 2 67 13 33 mpa experiments show slip weakening followed by slip strengthening slip weakening is associated with the formation and shearing of low viscosity melt patches the subsequent slip strengthening occurred despite the reduction in shear strain rate due to the growth thickening of melt layer suggesting that the viscosity of melt layer increased with slip microstructural and chemical analyses suggest that the viscosity increase during the slip strengthening is not due to an increase in the volume fraction of solid grains and bubbles in the melt layer but could be caused primarily by dehydration of the melt layer our experimental results suggest that viscous braking can be efficient at shallow depths of subduction accretion complexes if substantial melt dehydration occurs on a timescale of seismic slip melt lubrication can possibly occur at greater depths within subduction accretion complexes because the ratio of viscous shear to normal stress decreases with depth argillite derived natural pseudotachylytes formed at seismogenic depths in subduction accretion complexes are more hydrous than the experimentally generated pseudotachylytes and may be evidence of nearly complete stress drop

clay mineral reactions caused by frictional heating during an earthquake an example from the taiwan chelungpu fault 1 to understand the chemical reactions of clay minerals in a fault zone during an earthquake we analyzed the clay minerals in the chelungpu fault which slipped during the 1999 chi chi earthquake x ray diffraction spectroscopy showed that kaolinite and smectite contents were lower in the black gouge zone than in the surrounding gray gouge breccia or fracture damaged zones we applied a chemical kinetics approach to examine whether dehydroxylation of kaolinite and dehydration of interlayer water dehydroxylation and illitization of smectite occurred during coseismic frictional heating and found that the first two reactions could complete under the temperature time profile of the chi chi earthquake reconstructed by a previous study because dehydration of smectite interlayer water and dehydroxylation of kaolinite would have completed 3 6 and 8 2 s after the beginning of slip the resulting release of water might have affected the frictional mechanism during the earthquake

fluidization of granular material in a subduction thrust at seismogenic depths abstract subduction thrusts exhumed from seismogenic depths may record the dynamic slip processes during subduction zone earthquakes the thrust faults in the shimanto accretionary complex of southwest japan imbricate the melange derived from sedimentary rocks and basalt which represent a duplex underplating associated with the downward step of the subduction thrust at seismogenic depths 4 6 km in depth temperature 130 150 c one well exposed duplex fault zone consists mainly of foliated cataclasites and ultracataclasites derived from basalt the fault zone structure suggests slip localization along the 2 20 cm thick ultracataclasite layer at the boundary between different lithologies the common features observed along the ultracataclasite layer are the injection of granular material into the melange without the sorting of fine grained particles along with a small detection probability of the fragmented counterparts in the injected materials which suggests a rapid injection of fluidized granular material during faulting the ultracataclasite layer is marked by fluid related processes as indicated by the alteration and precipitation of amorphous silica gel along the ultracataclasite and the concentration of veins near the ultracataclasite the fluidization during localized slip under fluid infiltrated conditions could be due to thermal pressurization which causes the fluid pressure to approach lithostatic values the injection of fluidized granular material may result from hydraulic fracturing in response to an increase in the fluid pressure associated with thermal pressurization the plate boundary subduction thrust could be lubricated when the granular material fluidizes due to thermal pressurization during earthquakes

thermal history estimation of the taiwan chelungpu fault using rock magnetic methods 1 to investigate the cause of high magnetic susceptibility in disk shaped black materials bm disks within core samples of hole b the taiwan chelungpu fault drilling project we carried out magnetic analyses of samples from the bm disks and surrounding gouge zones frequency dependence of low temperature magnetic susceptibility and thermal demagnetization of low temperature remanent magnetization revealed lower amounts of superparamagnetic grains in the bm disks than in the surrounding gouges magnetic grain size reduction by shearing is therefore not a plausible explanation for the high magnetic susceptibility of the bm disks thermomagnetic analyses of the gouge samples showed that above 400 c magnetization could be increased by thermal decomposition of paramagnetic minerals whereas analyses of the bm disks showed a much smaller increase in magnetization thus formation of ferrimagnetic magnetite or maghemite by thermal decomposition of paramagnetic minerals was inferred to be the cause of the high magnetic susceptibility of the bm disks indicating that the bm disks but not the gouges have experienced temperatures of at least 400 c

mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks mineralogical and isotopic variations observed in altered glassy and crystalline rocksfrom the east pacific rise and the mid atlantic ridge provide information about the temperatures of alteration and seawater rock ratios for various hydrothermal regimes within the oceanic crust a systematic increase in alteration temperature is evident for the glassy rocksin the sequence 1 nontronite and celadonite vesicle fillings 35 c 2 saponite rich pillow breccias 130 170 c 3 calcite rich greenstone breccias and epidote rich greenstone 200 350 c theseresults include the highest temperatures thus far reported for saponite formation the seawater dominated hydrothermal alteration process that formed the saponite rich pillow breccias is characterized by high water rock ratios 0 1 low to moderate temperatures a seawater origin of most of the carbon in vein calcites 13 c 0 and the predominance of fe rich saponite and calcite as secondary phases greenstones chlorite quartz epidote and greenstone breccias chlorite quartz albite calcite are altered in a rock dominated system with lower water rock ratios 50 1 to 13 c 4 the crystalline rocks diabase gabbro and metagabbro are affected to varying degrees by pervasive high temperature seawater interactions that commence soon after solidification producing varying proportions of fine grained secondary minerals including talc smectite chlorite vermiculite actinolite and sodicplagioclase hydrothermal solutions derived from alteration of the crystalline rocks are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal rich deposits associated with the oceanic spreading centers

a new source of water in seismogenic subduction zones 1 seismogenic plate boundary faults at accretionary margins e g the nankai margin southwest japan may occur where the uppermost part of subducting oceanic crust composed of basaltic rocks is in contact with the overriding plate of a lithified accretionary prism the plate boundary faults in ancient accretionary complexes typically record high velocity slip under fluid rich conditions although previous studies have emphasized the mechanical significance of fluids in terms of dynamic slip weakening the source of fluid in seismogenic subduction zones remains poorly constrained in this work we focus on the hydrous smectite in the uppermost oceanic crust an alteration product of intact basalt before arrival at the trench axis a comparison between 1 new mineralogical data on basalt drillcore recovered by integrated ocean drilling program iodp expedition 322 at site c0012 a reference site for subduction input to the nankai trough and 2 mineralogical data on basalt within ancient oceanic crust embedded in a fossil accretionary complex of the shimanto belt southwest japan suggests that progressive smectite chlorite conversion would liberate bound fluids at a rate of 0 34 to 0 65 10 14 s 1 along the plate interface this rate of fluid production appears to be more than an order of magnitude greater than that from other possible sources including from overlying sediments via smectite illite conversion and the expulsion of pore fluids and may facilitate seismic slip along plate boundary faults

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

paleo stress estimates on ancient seismogenic faults based on frictional heating of coal 1 faulted coals from eastern kentucky and montana usa and the south wales coalfield uk show fault related vitrinite reflectance anomalies interpreted as due to frictional heating during seismic slip the vitrinite reflectance anomalies are converted to temperature using kinetic based software easy r for post seismic cooling rates shear stresses are calculated using lachenbruch s 1986 piezometer which depends only on the area under the thermal anomaly and fault displacement for maximum displacements of 1 3 meters the minimum shear stresses are 13 64 mpa and overlap with seismological estimates of stress drops during modern earthquakes the calculated local mean normal stress is 100 mpa resulting in coefficients of friction of 0 1 0 6 thrust and 0 2 0 4 normal faults which are lower than laboratory based values

pseudotachylytes in an ancient accretionary complex and implications for melt lubrication during subduction zone earthquakes abstract pseudotachylyte bearing fault zones found in the shimanto accretionary complex southwest japan developed during subduction or underplating at seismogenic depths the pseudotachylytes occur in narrow dark veins less than a few millimeters thick that are sharply bounded by foliated cataclasites that originated from a melange the microstructures of pseudotachylytes are represented by a fragment laden glass supported texture resulting from the rapid cooling of the frictional melt transmission electron microscopy reveals the presence of glass in which euhedral microcrystals of mullite are locally developed the compositions of the pseudotachylyte matrix and the characteristics of the unmelted grains and microlites in the matrix suggest that frictional melting occurred in an illite rich slip zone with a minimum melting temperature of 1100 c the viscosities of the frictional melt were calculated from the pseudotachylyte matrix composition as well as from the volume fraction and aspect ratio of the unmelted grains the viscosities at 1100 c range from 85 to 290 pa s and the corresponding shear resistance along a 1 mm thick melt layer at a slip rate of 1 m s was 0 1 0 3 mpa the formation of a melt layer in an illite rich slip zone can possibly induce large stress drops increase the slip rate and enhance rupture propagation which together could affect the earthquake magnitude in a subduction zone

canadian cordilleran tectonics from geosynclines to crustal collage the major contributions by the geological survey of canada in the canadian cordillera systematic mapping and definition of the regional geological framework led directly to tectonic syntheses that attempted to explain its origin from the late 1800 s until the 1960 s cordilleran mountain building was viewed as the end result of geosynclinal deposition early workers felt that a connection existed between mountain building and the pacific basin but its nature was never clear because little was known about ocean basins and their relationships to continental margins in the 1950 s the nature of the oceanic lithosphere and ocean continent relationships became better known the knowledge led to formulation of the plate tectonic hypothesis in the 1960 s a time fortuitously coinciding with completion by the survey of most of the regional geological mapping scale 1 250 000 geosynclinal rock units were reinterpreted in terms of their possible modern analogues oceanic island arc continental shelf slo

corrensite and mixed layer chlorite corrensite in metabasalt from northern taiwan tem aem empa xrd and optical studies many chloritic minerals in low grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties expand slightly upon glycolation expandable chlorite and or have excess alvi relative to aliv as well as significant ca k and na contents chloritic minerals with these properties fill vesicles and interstitial void space in low grade metabasalt from northern taiwan and have been studied with a combination of tem aem empa xrd and optical microscopy the chloritic minerals include corrensite which is an ordered 1 1 mixed layer chlorite smectite and expandable chlorite which is shown to be a mixed layer chlorite corrensite corrensite and some mixed layer chlorite corrensite occur as rims of vesicles and other cavities while later formed mixed layer chlorite corrensite occupies the vesicle cores the tem observations show that the mixed layer chlorite corrensite has ca 20 and the corrensite has ca 50 expandable smectite like layers consistent with xrd observations and with their abnormal optical properties the aem analyses show that high si and ca contents high alvi aliv and low fevi fe mg vi ratios of chlorites are correlated with interstratification of corrensite or smectite like layers in chlorite the aem analyses obtained from 200 500 a thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low aliv siiv and low fevi fe mg vi while chlorite has high aliv siiv and high fevi fe mg vi this implies that the trioctahedral smectite like component of corrensite has significantly lower aliv siiv and fevi fe mg vi the ratios of fevi fe mg vi and aliv siiv thus decrease in the order chlorite corrensite smectite the proportions of corrensite or smectite like layers relative to chlorite layers in low grade rocks are inferred to be controlled principally by fe mg ratio in the fluid or the bulk rock and by temperature compositional variations of chlorites in low grade rocks which appear to correlate with temperature or metamorphic grade more likely reflect variable proportions of mixed layered components the assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases such as chlorite corrensite corrensite smectite or chlorite corrensite smectite a model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1 1 ordered mixed layer chlorite smectite

milankovitch 41000 year cycles in lithofacies and molluscan content in the tropical middle miocene nyalindung formation jawa indonesia abstract nine cyclothems based on changes in sedimentary facies and molluscan fossil associations are identified in the middle miocene 12 ma lower part of nyalindung formation cijarian river section sukabumi west jawa province indonesia molluscan associations were studied in 75 blocks collected through the succession 47 species of autochthonous molluscs belonging to 38 genera were separated from the blocks five molluscan associations were recognized through comparison of these species with their closest living analogues a sedimentary cycle consists of two conformable lithologic units in ascending order a gravelly shellbed or gravelly conglomeratic sandstone and a muddy fine to medium grained sandstone the exception is the basal cycle which has an intercalation of limestone the systematic change in the molluscan fossil associations within individual cycles indicates that lithological changes correspond to changes in water depth with an amplitude of about 30 m the short time period represented by the section and the thin units many not more than 2 m thick indicates that the main cause of the cyclicity was orbitally induced climate change representing milankovitch scale cycles of 41 000 years this appears to be the first time milankovitch sea level cycles have been reported from the tropical regions of the earth

characterization of slip zone associated with the 1999 taiwan chi chi earthquake x ray ct image analyses and microstructural observations of the taiwan chelungpu fault abstract to characterize the fault related rocks within the chelungpu fault we performed x ray computed tomography ct image analyses and microstructural observations of hole b core samples from the taiwan chelungpu fault drilling project we identified the slip zone associated with the 1999 chi chi earthquake within the black gouge zone in the shallowest major fault zone by comparison with previous reports the slip zone was characterized by low ct number cataclastic or ultracataclastic texture and high possibility to have experienced a mechanically fluidized state taking these characteristics and previous reports of frictional heating in the slip zone into consideration we suggested that thermal pressurization was the most likely dynamic weakening mechanism during the earthquake

ferrimagnetic resonance signal produced by frictional heating a new indicator of paleoseismicity 1 high speed fault slips during earthquakes may generate sufficient frictional heat to produce fused fault rocks such as pseudotachylyte we have carried out high speed slip tests using natural fault gouge to judge whether or not frictional heating universally occurs during seismic fault slips in our shearing tests natural fault gouge is put between two cylindrical silica glasses and sheared under a fixed axial stress of 0 61 mpa despite such a low stress near the earth s surface a darkened cohesive material resembling pseudotachylyte is made from the fault gouge along the edge of a circular shear plane when shearing at a high speed of 1500 rpm the maximum slip rate reaches 1 96 m s at the edge electron spin resonance measurements reveal that the darkened cohesive material has a strong ferrimagnetic resonance fmr signal which is derived from bulky trivalent iron ions in ferrimagnetic iron oxides fe2o3 the fmr signal is produced by the thermal dehydration of antiferromagnetic iron oxides feooh in the fault gouge this may be applicable to the detection of past heating during seismic fault slip we thus attempt to reconstruct the temperature of frictional heat generated on the nojima fault plane in the 1995 kobe earthquake m 7 3 by inversion using the fmr signal the computer simulation indicates that the frictional heat generated on the nojima fault plane at 390 m depth may have attained 390 c during the 1995 kobe earthquake the temperature in the fault plane may have returned to its initial state after 1 year this result suggests that a heat flow anomaly generated by faulting may be difficult to detect

smectite to chlorite conversion by frictional heating along a subduction thrust abstract an ancient subduction thrust developed at the top of oceanic basaltic crust is exposed in the shimanto accretionary complex of eastern shikoku southwest japan the fault zone structure indicates that slip was localized along a few centimeters thick layer in which fluidization of comminuted material is recorded to identify possible clay mineral reactions during frictional heating along subduction thrusts we examined the clay mineralogy of the basalt derived fault zone rocks including ultracataclasite altered basalt foliated cataclasite and massive basalt all samples include chlorite mixed layer chlorite smectite c s and corrensite among the samples the highest chlorite content in the c s is found in the ultracataclasite the significant chloritization in the ultracataclasite is unlikely to reflect hydrothermal alteration and regional very low grade metamorphism during subduction down to seismogenic depths instead it is interpreted to have resulted from frictional heating associated with localized slip based on chlorite geothermometry and the presence of small quantities of corrensite we estimate the temperatures during this frictional heating to have been in the range of 185 260 c which is 35 130 c higher than the ambient temperature this difference of 35 130 c is consistent with a temperature rise of 50 150 c indicated by the stretching of fluid inclusions in calcite therefore the crystallographic and chemical properties of c s are potentially useful in detecting small temperature rises associated with frictional heating and the method could be widely applicable to c s bearing faults

the smectite to chlorite transition in a fossil seamount hydrothermal system the basement complex of la palma canary islands the hydrothermal metamorphism of a sequence of pliocene aged seamount extrusive and volcanoclastic rocks on la palma includes a relatively complete low p t facies series encompassing the zeolite prehnite pumpellyite and greenschist facies the observed mineral zonations imply metamorphic gradients of 200 300 c km 1 the transition from smectite to chlorite in the la palma seamount series is characterized by discontinuous steps between discrete smectite corrensite and chlorite which occur ubiquitously as vesicles and to a much lesser extent vein in fillings trioctahedral smectites mg fe mg 0 4 0 75 occur with palagonite and na ca zeolites such as analcime and a thompsonite natrolite solid solution corrensite mg fe mg 0 5 0 65 first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite discrete chlorite mg fe mg 0 4 0 6 becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases although random interstratifications of these phases have not been observed although smectite occurs as both low and high charge forms the la palma corrensite is a compositionally restricted 1 1 mixture of low charge trioctahedral smectite and chlorite electron microprobe analyses of coarse grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations calcium average 0 20 cations formula unit is the dominant interlayer cation with lesser mg k and na the absence of randomly interlayered chlorite smectite in the la palma seamount series may reflect high time integrated fluid fluxes through the seamount sequence this is consistent with the ubiquity of high variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples

chlorite chemistry of tongshankou porphyry related cu mo w skarn deposit eastern china implications for hydrothermal fluid evolution and exploration vectoring to concealed orebodies abstract recent years the depletion of shallow mineral resources has drawn increasing attention to the exploration of hidden ore bodies in deep of skarn type deposits chemical composition of chlorite is an effective tool for tracing the hydrothermal fluid evolution and has been increasingly used for deep level exploration of porphyry cu au deposits pcds however the technique was rarely applied onto porphyry related skarn deposits the tongshankou cu mo w deposit 0 55 mt cu 0 86 0 01 mt mo 0 10 and 0 12 mt wo3 0 19 is one of the largest skarn porphyry deposits in the middle lower yangtze river metallogenic belt mlyrb in eastern china in this study new petrographic and trace element data of the hydrothermal chlorites from tongshankou were presented to constrain the ore fluid evolution and to explore the vectoring potential of the concealed orebodies at tongshankou four types of chlorite have been identified i e g type chlorite that replaced the original magmatic biotite or hornblende v type chlorite in chlorite quartz sulfides veins in the granodiorite porphyry alteration zones i and ii s type chlorite that replaced garnet in the intensive skarn alteration zone iii and m type chlorite quartz calcite sulfides veins that cut the dolomitic marble in the distal alteration zones iv and v all the four types of chlorites are typically trioctahedral chlorite the fe mg tschermark and di trioctahedral substitution mechanisms likely control the geochemical variations of the tongshankou chlorites empirical thermometer indicates that the tongshankou chlorites were crystallized at 169 322 compared with typical metamorphic chlorites the higher zn and sr contents but lower al content in the tongshankou chlorites can potentially distinguish the skarn type hydrothermal chlorites from typical metamorphic ones compared with the chlorites in the typical pcds the tongshankou g type chlorite has higher fe zn as and sn contents but lower al mg co and cu contents which likely reflect its protolithic and or fluid geochemical inheritance the tongshankou v m and s type chlorites have high contents of mobile elements such as sr ca sn and b and metals such as fe cu as zn and pb indicating that they were directly precipitated from the hydrothermal fluids from the granodiorite porphyry to the marble wallrocks the spatial chlorite geochemical variations at tongshankou indicate that the increasing zn mn ga ge and pb contents and decreasing v sc and ti contents are potential vectors toward concealed mineralized porphyries at tongshankou our study highlights that the chlorite geochemistry is a potential tool for ore fluid tracer and vectoring tool toward concealed skarn porphyry orebodies in the mlyrb

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

stretching of fluid inclusions in calcite as an indicator of frictional heating on faults fluid inclusions trapped in calcite tend to increase in volume i e stretching when heated to temperatures higher than those of the initial entrapment at the entrapment pressure and the result is an increase in the homogenization temperature we examined whether the stretching of fluid inclusions in calcite occurred by frictional heating on the subduction thrust exhumed from seismogenic depths 4 6 km at which the slip is localized along the few centimeters thick ultracataclasite layer the results indicate that the histograms of the homogenization temperatures of the fluid inclusions in the ultracata clasite are marked by the pronounced skewness with the frequency mode near the low temperature end of the range and a tapering tail toward higher temperatures these skewed frequency distributions are absent in the surrounding rocks and are best explained by the stretching of the fluid inclusions by the frictional heating associated with the localized slip experimental stretching of fluid inclusions in calcite demonstrated that the tapering tail toward high temperatures in the histograms of the homogenization temperatures from the ultra cataclasite can be reproduced by a 50 150 c temperature rise along the ultracataclasite with respect to the ambient temperature stretching of fluid inclusions in calcite could record a small temperature rise during frictional heating on faults and is potentially useful in identifying the restraint of the temperature rise by fluid pressurization during an earthquake

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity