aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

magmatism and metamorphism in the lhasa block tibet a geochronological study u pb systematics in small fractions of zircon monazite and sphene 5 to 20 grains each have been analyzed in order to decipher the age and origin of magmatism in the lhasa block and to date the tectono metamorphic events additionally we analyzed a few minerals for rb sr the results show that the granites and an ignimbrite were formed essentially through anatexis of continental crust the magma source regions of which consisted of palaeozoic to precambrian materials up to 2 b y in age the following episodes can be distinguished 1 an early tertiary plutonism volcanism in the southern lhasa block yangbajing region strongly related to intracontinental tectono metamorphism 2 a late jurassic to early cretaceous plutonism in the central and northern lhasa block and 3 a middle jurassic low grade metamorphism affecting the basement at the northern margin 171 6 m y ago the early tertiary magmatism and metamorphism in the south are probably a direct result of tethys subduction indian plate

40ar 39ar thermochronological evidence for formation and mesozoic evolution of the northern central segment of the altyn tagh fault system in the northern tibetan plateau to better constrain the probable timing of formation and evolution of the altyn tagh sinistral strike slip system in the mesozoic a 40ar 39ar thermochronological study has been carried out in the north central segment of the altyn tagh fault system the northern margin of the qaidam basin and the eastern kunlun orogenic belt muscovite biotite and k feldspar separated from mylonite granite pegmatite and metamorphic rocks have been analyzed the range of 40ar 39ar data and structural evidence indicate that a peak metamorphic event in terranes bordering the altyn tagh fault system occurred between 450 and 420 ma at ca 250 230 ma there is evidence for initial sinistral strike slip shearing sinistral strike slip deformation occurred later along the altyn tagh fault system at 165 160 ma and 100 89 ma respectively cooling histories in the northern margin of the qaidam basin and the eastern kunlun orogenic belt show that these areas also experienced rapid cooling ca 250 230 ma as was the case for the early altyn tagh fault system this regional tectonic and cooling process indicates that the initial formation of the altyn tagh sinistral slip fault system occurred in latest permian early triassic time and was coupled with or related to suturing in the northern margin of the qaidam basin and the kunlun orogenic belt cooling events along the altyn tagh fault system between 165 and 160 ma and 100 89 ma were accompanied by differential closure along the bangong lake nujiang suture zone in its eastern and western sectors during the middle late jurassic and early cretaceous respectively zhao et al 2001 1 wang et al 2002 2 1 ref 48 2 ref 41

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

cooling history and tectonic exhumation stages of the south central tibetan plateau china constrained by 40ar 39ar and apatite fission track thermochronology between the qiangtang block and yalung zangpo suture zone in the south central tibetan plateau the following geological units and suture zones have been identified from south to north the gangdese granitic belt the lhasa block the nyainqentanghla shear zone the dangxiong sangxiong tectono granitic belt and the bangong nujiang suture zone to better constrain the tectonic evolution and cooling histories of these units 40 ar 39 ar muscovite biotite and k feldspar as well as apatite fission track dating and thermochronological analysis have been carried out the analytical results indicate that the south central tibetan plateau with the exception of the nyainqentanghla shear zone provides a record of three cooling stages at 165 150 130 110 and 45 35 ma fission track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks very different cooling phases occurred in the south central tibetan plateau compared with southern tibet as well as along the yalung zangpo suture zone there is no thermochronological evidence to indicate that the south central part of tibetan plateau was influenced by the underthrusting of indian plate the three stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the bangong nujiang suture zone along its eastern segment during middle late jurassic 165 150 ma and its western segment in the early late cretaceous 130 110 ma as well as by the collision between the indian and asian plates in the paleogene 45 35 ma 2005 elsevier ltd all rights reserved

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

an early unroofing in northeastern tibet constraints from 40ar 39ar thermochronology on granitoids from the eastern kunlun range qianghai nw china abstract in order to better constrain the mechanisms accommodating the india asia collision along the whole kunlun range northern tibet which is essential to better understand the evolution of the entire deformations area a 40 ar 39 ar thermochronological study has been carried out on a suite of granitoids collected in the vicinity of golmud eastern kunlun range biotite and k feldspar have been analysed and the cooling histories of the latter have been modelled the ranges of 40 ar 39 ar data bt 128 257 ma kf 102 228 ma are similar to previous rb sr and k ar data indicating both a middle paleozoic unit and a mesozoic unit including a triassic series and a jurassic cretaceous series this suggests that the two geological units previously reported in the western kunlun are also present in the eastern part of the range suggesting that eastern and western kunlun ranges might have been left laterally offset by as much as 500 km along a strike slip fault presently parallel to the altyn tagh fault the cooling histories based upon k feldspar modelling show that samples from the southern part of the range recorded an important cooling event 9 15 myr around 30 ma which is thought to reflect an increasing rate of denudation related to the tectonic activity in this area minimum denudation rates of 0 2 0 3 km ma have been estimated in contrast samples from the northern part of the range did not record any variation in their cooling history this heterogeneous denudation across the range is thought to be related to ramp stacking and normal faulting with associated uplift mainly affecting the southern part of the range suggesting that the eastern kunlun underwent an important crustal thickening period 30 ma ago this crustal thickening event is suggested to be related to the motion along the great asian strike slip faults in a way which remains problematic but possibly associated to the cenozoic propagation of the altyn tagh fault finally unroofing in the eastern kunlun range appears to predate that in the western kunlun range where it is suggested to have started around 20 ma ago this diachronous denudation could be related to a higher denudation rate in western kunlun range and it is thus highly probable that the important unroofing event outlined around 20 ma ago in the western kunlun has also affected the eastern part of the range even though the signature is not available at the moment

vent activity in a subduction area nankai wedge the foraminiferal test records we have collected 41 sediment samples from the depths of about 2000 m and 4000 m in the nankai trough area using the submersiblenautile study of these samples has enabled recognition of two main preservation states of planktonic and benthic foraminiferal tests dissolution in all the samples and superimposed encrustation in some of them the distributional pattern of planktonic foraminifera reveals a strong rate of dissolution of the tests among the benthic foraminifers the aragonitic specieshoeglundina elegans shows below 2000 m a corrosion of test surfaces removing parts of growth layers and breakage of last chambers on the basis of pore water chemistry the high rates of dissolution are related to unusual aragonite undersaturation in pore water at the sediment water interface and to expulsion of pore water in open sea water furthermore a peculiar etching of the whole test ofh elegans and encrusted calcitic tests are observed but only in the samples collected near fluid venting manifestations clams worms and shell concretions suggesting a possible relationship between diagenesis and fluids

the spatial footprint of injection wells in a global compilation of induced earthquake sequences fluid injection can cause extensive earthquake activity sometimes at unexpectedly large distances appropriately mitigating associated seismic hazards requires a better understanding of the zone of influence of injection we analyze spatial seismicity decay in a global dataset of 18 induced cases with clear association between isolated wells and earthquakes we distinguish two populations the first is characterized by near well seismicity density plateaus and abrupt decay dominated by square root space time migration and pressure diffusion injection at these sites occurs within the crystalline basement the second population exhibits larger spatial footprints and magnitudes as well as a power law like steady spatial decay over more than 10 kilometers potentially caused by poroelastic effects far reaching spatial effects during injection may increase event magnitudes and seismic hazard beyond expectations based on purely pressure driven seismicity

planktonic foraminifera of the northern indian ocean distribution and preservation in surface sediments in the northern indian ocean planktonic foraminiferal tests accumulate in a wide variety of surface water environments and depositional settings this variability enables us to isolate the effects that surface water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples foraminiferal abundance varies from 0 to 104 whole foraminifera in the greater than 150 m fraction per gram dry sediment values 10 characterize the three deep basins of the equatorial indian ocean and the western bay of bengal foraminiferal tests are most abundant on carbonate covered ninety east and carlsberg ridges absolute abundance patterns are mainly controlled by non ecological processes variations in dissolution resistant species rsp with water depth reveal that the foraminiferal lysocline fl varies regionally the fl is deepest 3 800 m in the equatorial region rises abruptly to 3 300 m in the arabian sea and varies from 2 600 m to near 2 000 m moving northward in the bay of bengal deep samples with anomalously low rsp 30 suggest redeposition systematic geographic and depth related variation is observed for the 17 most abundant foraminiferal species dissolution resistant species g menardii g tumida g dutertrei p obliquiloculata generally exhibit a rapid and continuous increase in relative abundance at and below the fl susceptible species g ruber g bulloides g glutinata for example exhibit a rapid and continuous decrease in relative abundance at and below the fl moderately susceptible species g conglobatus g aequilateralis g conglomerata for example rapidly increase in abundance at the fl and systematically decrease with depth below the fl principal components analysis pca of faunal data from minimally dissolved 30 rsp samples reveals important ecologically related species intercorrelations the major biogeographic gradient is the negative covarying relationship between ag bulloides g glutinata species pair and a grouping ofg sacculifer g conglobatus g aequilateralis andg ruber pca of all samples demonstrates how differential dissolution alters this and other species relationships species groupings that incorporateg ruber g menardii andg dutertrei are particularly affected by dissolution comparison of average faunal data from minimally dissolved samples in the northern indian ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean for example g bulloides g falconensis andg hexagona are significantly more abundant in northern indian ocean surface sediments while such species asg ruber g sacculifer g dutertrei andp obliquiloculata dominate in other tropical regions

evidence for mesozoic shear along the western kunlun and altyn tagh fault northern tibet china the strike slip faults of north tibet accommodate part of the cenozoic convergence between india and asia along the karakax valley south of yecheng and near the xidatan trough south of golmud the active traces of the altyn tagh and kunlun faults follow narrow belts of metamorphic rocks the deformation recorded in those mylonites is sinistral strike slip rb sr and 40ar 39ar ages of deformation from syntectonic fabrics formed at 350 400 c 120 ma argon loss suggests that deformation was associated to a 250 300 c thermal pulse that lasted 5 20 ma after the onset of movement unroofing occurred much later around 25 ma when sudden cooling suggests a component of thrusting or more likely normal faulting the cretaceous shear may be related to collision between the qiantang and the lhasa blocks the karakax and xidatan shear zones may have formed a unique continuous boundary in the cretaceous which was later reused by the tertiary strike slip faults leading to potentially calculable offsets along the altyn tagh fault

physics based seismic evaluation method evaluating possible seismic moment based on microseismic information due to fluid stimulation abstractthe forecasting and risk assessment of induced seismicity associated with fluid injection have considerable importance for subsurface energy development we have developed a seismic evaluation method called the possible seismic moment posemo model to assess the potential seismic moment that could be released in the future based on current seismic activity the posemo model assumes the existence of a representative parameter that can describe the seismic characteristics of a given field this parameter is defined as the seismic moment density which quantifies the seismic moment able to be released per rock volume the rock volume presumed to be in critical condition because of stimulation is defined as the stimulated rock volume the current stimulation condition for the posemo model can be estimated from the product of these two parameters the difference between the output of the posemo model and the observed cumulative seismic moment corresponds to the cumulative seismic moment that could be

scaling of seismicity induced by nonlinear fluid rock interaction 1 fluid injections into geothermal systems sometimes can produce significant seismic events with magnitudes of up to 4 however in the case of hydraulic fracturing of hydrocarbon reservoirs such events occur extremely seldom in the last case in contrast to the former one the structure of rocks is being actively destroyed e g opening of tensile fractures and the fluid rock interaction is strongly nonlinear e g a strong increase of permeability what is the role of this nonlinearity we consider nonlinear pore pressure diffusion to explain features of seismicity we formulate seismicity triggering front its propagation is sensitive to a grade of nonlinearity to spatial dimension of diffusion and to the injection rate we show that a probability of an event with a magnitude larger than a given one increases proportionally to the injected mass an increase of this probability with time is insensitive to the nonlinearity we compare different borehole experiments in some cases the injection produces clearly nonlinear impact on rocks in others this impact is approximately linear we find a well agreement with our theory we observe an insensitivity of temporal increments of magnitude probability to the grade of nonlinearity these increments are controlled by injection rate increments in contrast nonlinear fluid rock interactions are characterized by a strong dominance of small earthquakes defects activated by a nonlinear diffusion possibly obey gutenberg richter statistics with anomalous high b values in the case of a linear diffusion magnitude distributions of events are probably inherited from pre existing fracture systems

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

an experimental investigation of hydraulic behaviour of fractures and joints in granitic rock a method of measuring mean mechanical aperture of fractures based on gas volume balance is introduced the effects of shear displacement and normal stress on mechanical and hydraulic behaviour of fractures are also investigated the results obtained from tests conducted on granite samples from olympic dam central australia are compared with those calculated from existing shear dilation theories it is found that hydraulic aperture is considerably narrower than the measured mean mechanical aperture this highlights the need to consider tortuosity and surface roughness of fractures in the calculation of hydraulic aperture it is also found that shear dilation angle decreases linearly with increases in confining pressure as opposed to more rapid decreases predicted by existing empirical models from the results of this study a range of data describing the relationships between confining pressure shear displacements hydraulic aperture and permeability are presented which could help to develop stimulation programs for geothermal reservoirs

microseismicity and permeability enhancement of hydrogeologic structures during massive fluid injections into granite at 3 km depth at the soultz hdr site summary a high rate injection of 20 000 m3 of water into granite between 2 8 and 3 4 km depth at the soultz hot dry rock hdr test site in france in 1993 september led to a 200 fold increase in borehole transmissivity and produced a subvertical cloud of microseismicity of dimensions 0 5 km wide 1 2 km long 1 5 km high and oriented 25 nw the resulting data set is unusually complete and well suited to studying permeability creation enhancement processes in crystalline rock and the utility of microseismic data for revealing them although the microseismic cloud defined using joint hypocentre determination jhd locations was diffuse and showed little structure application of the collapsing method showed it to be composed largely of discrete tubes and planes that propagated coherently one prominent structure that extended 350 m downwards from the vicinity of a flow inlet early in the injection and that appears to contain a major flow path was subjected to detailed investigation to establish its hydrogeologic nature and the mechanisms underpinning its inferred permeability enhancement high resolution microseismic mapping techniques i e multiplets and clustering showed it to be a subvertical nnw sse striking fracture zone of width 10 20 m the strike and scale of the structure identifies it as a member of a family of hydrothermally altered cataclastic shear structures that constitute the primary permeable paths for fluid migration within the rock mass both under ambient and forced fluid flow conditions the microseismicity occurred on subvertical small scale fractures within the cataclastic shear zone whose azimuths scatter within 22 of parallel to the parent structure although the structure is likely to have been naturally permeable to some degree its permeability appears to have been significantly enhanced as a consequence of the injection the most likely mechanism of permeability enhancement which is in accord with the strong preference for the microseismicity to grow downwards involves strike slip shearing which produced the opening of vertical tubes at along strike jogs in the fault the so called hill mesh seismic moment release averaged over the structure suggests shear displacements of at least 0 3 mm occurred which are sufficient to generate aperture changes that are hydraulically significant the preponderance of discrete structures within the microseismic cloud after collapsing suggests that significant flow and permeability enhancement i e stimulation within the rock mass is largely confined to the interiors of shear zones that appear to have a spacing of approximately 100 m

permeability creation and damage due to massive fluid injections into granite at 3 5 km at soultz 2 critical stress and fracture strength 1 the stress acting on fractures in a 3 5 km deep borehole in granite is examined to place constraints on fracture strength and to evaluate whether permeable fractures tended to be critically stressed two data sets consisting of some 500 fractures are analyzed the first considers the permeable impermeable fracture populations in their natural state the second considers the populations after the hole had been subject to a prolonged 9 mpa overpressure in two major injections which increased the number of permeable fractures from 18 to more than 95 for both data sets it is found that permeable fractures are critically stressed inasmuch as they support levels of shear stress that would be verging on failure if their strength were governed by a coulomb friction law with a coefficient of 0 6 1 0 however the vast majority of impermeable fractures are also critically stressed implying that critical stressing is a necessary but not a sufficient condition for permeability to develop most permeable fractures showed evidence of shear failure after the injections and tended to occur in hydrothermally altered cataclastic shear zones suggesting that they may have been relatively weak because of the presence of illite to prevent failure of the impermeable fractures during the injections requires a cohesion of at least 6 5 mpa to augment a maximum allowable friction coefficient of 1 0 these are probably early mode 1 fractures that are sealed primarily with calcite the strength of the shear zones appears to be significantly greater than the illite rich fractures from which they are composed this imposes constraints on their internal architecture

diversity of channeling flow in heterogeneous aperture distribution inferred from integrated experimental numerical analysis on flow through shear fracture in granite 1 shear mode ii fractures with shear displacements of 1 and 5 mm were generated by direct shear on granite under normal stresses of 1 20 and 60 mpa fracture surface mapping showed that the surface roughnesses of the shear fractures decreased with increasing shear displacement and normal stress and were smaller than those of tensile fractures reported in our previous study fluid flow experiments on the shear fractures provided fracture permeabilities at a wide range of confining pressures of 10 100 mpa nonmonotonic permeability was usually observed to decrease with increasing confining pressure however the permeability changes were different between the shear fractures generated at the normal stress of 20 and 60 mpa in addition obvious permeability changes with shear displacement were observed for 60 mpa whereas no significant difference was observed for 20 mpa comparing the shear fractures with the tensile fractures having shear displacements revealed clear differences even for equivalent shear displacements numerical models that were constructed using the data of the fracture surface mapping by matching their permeabilities with the experimentally evaluated fracture permeabilities revealed the development of preferential flow paths i e channeling flows for the shear fractures providing a diversity of channeling flow in heterogeneous aperture distributions of rock fractures in the earth s crust

pore pressure migration during hydraulic stimulation due to permeability enhancement by low pressure subcritical fracture slip understanding the details of pressure migration during hydraulic stimulation is important for the design of an energy extraction system and reservoir management as well as for the mitigation of hazardous induced seismicity based on microseismic and regional stress information we estimated the pore pressure increase required to generate shear slip on an existing fracture during stimulation spatiotemporal analysis of pore pressure migration revealed that lower pore pressure migrates further and faster and that higher pore pressure migrates more slowly these phenomena can be explained by the relationship between fracture permeability and stress state criticality subcritical fractures experience shear slip following smaller increases of pore pressure and promote migration of pore pressure because of their enhanced permeability the difference in migration rates between lower and higher pore pressures suggests that the optimum wellhead pressure is the one that can stimulate relatively permeable fractures selectively its selection optimizes economic benefits and minimizes seismic risk

nankai trough japan trench and kuril trench geochemistry of fluids sampled by submersible nautile abstract deep water samples collected during the kaiko project are often associated with biological communities located on geological structures favorable to fluid venting the evidence of fluid venting are the temperature anomalies the decrease in sulfate concentrations the content in methane and the lowc 1 c 2 c 3 ratio of light hydrocarbons because of large dilution by ambiant seawater during sampling it is difficult to compute the composition of the advected end member pore fluid part of this fluid should originate in the petroleum window i e at temperature about 60 c modeling the upward flow of water taking into account the anomalies of temperature measured on the seafloor and the geochemical anomalies leads to non steady state advection of the pore fluid the occurrence of a deep component in the fluid has implications for the geological and tectonic models of the subduction zones off japan

maximum magnitude of injection induced earthquakes a criterion to assess the influence of pressure migration along faults abstract the maximum expected earthquake magnitude is an important parameter in seismic hazard and risk analysis because of its strong influence on ground motion in the context of injection induced seismicity the processes that control how large an earthquake will grow may be influenced by operational factors under engineering control as well as natural tectonic factors determining the relative influence of these effects on maximum magnitude will impact the design and implementation of induced seismicity management strategies in this work we apply a numerical model that considers the coupled interactions of fluid flow in faulted porous media and quasidynamic elasticity to investigate the earthquake nucleation rupture and arrest processes for cases of induced seismicity we find that under certain conditions earthquake ruptures are confined to a pressurized region along the fault with a length scale that is set by injection operations however earthquakes are sometimes able to propagate as sustained ruptures outside of the zone that experienced a pressure perturbation we propose a faulting criterion that depends primarily on the state of stress and the earthquake stress drop to characterize the transition between pressure constrained and runaway rupture behavior

geochemistry of the tenryu canyon deep sea fan biological community kaiko abstract the tenryu canyon deep sea fan biological community is characterized by both reduced and oxidized sediments in the immediate vicinity of the pore water vents the upper sediments in contact with the clams are reduced the organic matter is enriched in sulfur and inorganic sulfides fe cu zn are forming towards the outer fringes of the communities the sediment is oxidized and metals generally associated with ferro manganese oxides are concentrated several metals cd pb mo show distributions which are strongly influenced by the metabolism of the clam colony comparison of water and sediment geochemistry leads to the conclusion that there should be a downward flux of oxygenated seawater on the boundaries of the colony and an upward flux of chemically more reduced deep pore water at the location of the colony trace metals anomalies as well as 15n anomalies of organic matter may be useful to prospect for extinct venting areas in ancient subduction zones

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

multiplet clustering analysis reveals structural details within the seismic cloud at the soultz geothermal field france multiplet clustering analysis is a method for precise determination of microseismic event locations and is used to identify subsurface fractures and fracture networks a multiplet is a group of microseismic events with very similar waveforms despite different origin times and it is likely the expression of stress release on the same structure the relative source locations of similar events can be determined with high resolution and accuracy by using the moving window cross spectrum analysis technique deduced seismic clusters called multiplet clusters are indicative of seismically activated structures and the orientations of these structures can be estimated using the seismic clusters even though the absolute locations of the multiplet clusters cannot themselves be determined we examine methods of determining the relative locations of multiplet clusters and introduce the concept of clustering analysis the clustering analysis method is used to estimate the relative location of multiplet clusters by detecting phase differences between similar stacked events we describe the procedure for multiplet clustering analysis estimate relative locations of multiplet clusters and apply the method to induced microseismic data from the soultz hot dry rock field france we show that a fracture network can be delineated through multiplet clustering analysis whereas it is difficult to identify detailed structures on the basis of source locations estimated by the joint hypocenter determination method manuscript received 1 march 2002

tectonic context of fluid venting at the toe of the eastern nankai accretionary prism evidence for a shallow detachment fault during the kaiko nankai diving cruise the peak of the venting activity was located near the top of the very first anticline the most prominent morphological feature between the mid slope 3870 m and the apex of the fold 3770 m is a 20 m high cliff cutting through subhorizontal massive mudstones affected by numerous joints the trend of this scarp is oblique to the fold axis and structurally controlled along two sharply defined nne sse and e w directions fresh talus and blocks found locally suggest active tectonics and recent erosion intense deformation is evident from strongly tilted strata restricted to the base of the cliff that we interpret as an upslope thrust at the scale of seabeam mapping this thrust can be followed eastward for more than 5 km along the 3820 m isobath two seismic lines recorded during one of the pre site surveys show deformation at shallow depth including small scale folding and thrusting affecting only the wedge shaped top sequence deeper layers can be traced continuously below this sequence we conclude that the boundary between the piggy back basin and the frontal fold turbidites acts as a shallow detachment fault and interpret the base of the cliff as the outcrop of the fault dense colonies ofcalyptogena clams and strongly nonlinear thermal gradients locate the major peak of fluid activity at the edge of the plateau above the main cliff scattered biological colonies as well as white bacterial mats and cemented chimneys were also found in a narrow belt along the base of the cliff fluid activity is thus closely related to the shallow detachment fault fluid being expelled both at the outcrop of the fault and above it through the overlying strata possibly using the very dense joint network

seafloor manifestations of fluid seepage at the top of a 2000 metre deep ridge in the eastern nankai accretionary wedge long lived venting and tectonic implications abstract the results of the 1989 kaiko nankai diving cruise to the eastern nankai accretionary wedge show that a narrow corridor on the top of a 2000 m deep ridge is characterized by concentrated surface manifestations of fluid seepage and chaotic outcrop orientations suggesting active faulting along a right lateral shear zone modern biological indicators of fluid venting include bivalve vesicomyid species and vestimentiferan tube worms ancient manifestations of fluid venting consist of similar vesicomyid species found in 20 and 150 ka concretions this suggests relatively constant biotypes carbonate deposits including fossil cemented shells were observed near active sites either as paving stones diffuse seepage and cementation cut by channels or as pinnacles local seepage and cementation despite its proximity less than 15 km a nearby 3800 m deep site where substantial fluid discharge occurs seems to be completely separate from the 2000 m deep ridge site the 3800 m deep site differs from its shallower counterpart in terms of its seafloor manifestations and the composition of its fluids the sediment at the top of the ridge ranges in age around 500 300 ka which attests that the transition from a depositional to an erosional stage was younger than 800 ka but older than 200 ka this transition can be due to either the incorporation of this unit from the trench fill into the accretionary wedge front or the uplift of a slope basin the first hypothesis leads to a 2 5 cm yr minimum progradation rate associated with a 2 5 mm yr minimum uplift rate from the paleotrench to the present ridge the second hypothesis implies a recent uplift of a piggy back basin at a minimum rate of 1 mm yr

activation of the nyainqentanghla shear zone implications for uplift of the southern tibetan plateau neogene extension of the tibetan plateau is manifested as a series of north south trending graben the most prominent of which is the yadong gulu rift the nyainqen tanghla shan a ne sw trending mountain range 100 km nw of lhasa bounds the western margin of the yangbajian graben the central segment of the yadong gulu rift the eastern edge of the nyainqentanghla massif is marked by a low angle 25 o detachment fault shear zone of amphibolite grade mylonites the noar 3 ar thermal history results from samples collected along two deeply incised valleys within the massif reveal that a rapid cooling event propagated from 8 ma in the core of the range to 4 ma within the high strain zone at the eastern boundary assuming that faulting initiated at high angle 60o thermal histories were fit to a numerical simulation of slip on a normal fault to yield estimates of both the age of fault initiation and the slip rate history the form of the isotopically derived thermal histories are similar to general form predicted by the thermal model and suggests that significant movement began at 8 1 ma in the southern valley goring la and proceeded at an average slip rate of 3 mm yr between 8 and 3 ma a more complex history is required to fit the data from the northern valley balum chun but the timing of initiation and average slip rate are similar to the goring la result numerical simulations in which the fault angle is varied indicate that the isotopically derived temperature histories are inconsistent with slip occurring at low angle 40o because the extension direction of the yangbajian graben is representative of most rifts on the southern tibetan plateau our data suggest that crustal thickness and elevation reached close to their present values by 8 1 ma a carbon isotopic shift in pedogenic carbonates from the siwalik formation at about 7 5 ma appears to reflect intensification of the asian monsoon and by inference that the plateau had attained an important threshold elevation by that time formation of a diffuse plate boundary in the indian oceanic lithosphere beginning at 7 5 8 0 ma is also consistent with this history we suggest that the plateau had attained a threshold area and elevation by 8 1 ma sufficient to trigger these three independent manifestations

tertiary structural evolution of the gangdese thrust system southeastern tibet structural and thermochronological investigations of southern tibet xizang suggest that intracontinental thrusting has been the dominant cause for formation of thickened crust in the southernmost tibetan plateau since late oligocene two thrust systems are documented in this study the north dipping gangdese system gts and the younger south dipping renbu zedong system rzt west of lhasa the gangdese thrust juxtaposes the late cretaceous forearc basin deposits of the lhasa block the xigaze group over the tethyan sedimentary rocks of the indian plate whereas east of lhasa the fault juxtaposes the late cretaceous eocene andean type arc the gangdese batholith over tethyan sedimentary rocks near zedong 150 km southeast of lhasa the gangdese thrust is marked by a 200 m thick mylonitic shear zone that consists of deformed granite and metasedimentary rocks a major south dipping backthrust in the hanging wall of the gangdese thrust puts the xigaze group over tertiary conglomerates and the gangdese plutonics north of xigaze and west of lhasa a lower age bound for the gangdese thrust of 18 3 0 5 ma is given by crosscutting relationships the timing of slip on the gangdese thrust is estimated to be 27 23 ma from 40 ar 39 ar thermochronology and a displacement of at least 46 9 km is indicated near zedong the age of the gangdese thrust gt is consistent with an upper age limit of 24 ma for the initiation of movement on the main central thrust in places the younger renbu zedong fault is thrust over the trace of the gt obscuring its exposure the rzt appears to have been active at circa 18 ma but had ceased movement by 8 1 ma the suture between india and asia has been complexly modified by development of the gts rzt and locally strike slip and normal fault systems

investigation of injection induced seismicity using a coupled fluid flow and rate state friction model we describe a numerical investigation of seismicity induced by injection into a single isolated fracture injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems egs during which water is injected into fractured low permeability rock triggering slip on preexisting large scale fracture zones a model was developed and used that couples 1 fluid flow 2 rate and state friction and 3 mechanical stress interaction between fracture elements based on the results of this model we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation which we refer to as the sequential stimulation ss mechanism if the ss mechanism is realistic it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity we investigated the effect of injection pressure on induced seismicity for injection at constant pressure there was not a signifi

the tectonic evolution of the kohistan karakoram collision belt along the karakoram highway transect north pakistan the kohistan arc terrane comprises an intra oceanic island arc of cretaceous age separating the indian plate to the south from the karakoram asian plate to the north within the indus suture zone of north pakistan the intra oceanic arc volcanics chalt dras group were built on a foundation of dominantly mid ocean ridge basalt morb related amphibolites of the kamila group the subarc magma chamber is represented by multiple intrusions of a huge gabbro norite complex chilas complex which includes some ultramafic assemblages of residual mantle harzburgite and dunite layered cumulates and hornblendites cut by late stage dikes of hornblende plagioclase pegmatites the chilas complex norites intrude the gilgit metasediments of lower amphibolite and greenschist facies in northern kohistan which also form xenolithic roof pendants within the top of the chilas complex along the southern margin of kohistan jijal and sapat complex ultramafics dunites harzburgites and websterites form remnant suprasubduction zone ophiolitic mantle rocks along the hanging wall of the main mantle thrust the cretaceous obduction plane along which kohistan was emplaced onto indian plate rocks garnet granulites of the jijal complex formed at 12 14 kbars represent original magmatic lower crustal rocks subducted to depths of at least 45 km and metamorphosed during high pressure and high temperature subduction of earlier arc related rocks obduction of the sapat ophiolite and kohistan arc occurred between 75 and 55 ma the closure of the shyok suture zone separating kohistan from the karakoram plate must have occurred prior to 75 ma the age of the jutal basic dikes which crosscut the closure related fabrics mainly late north directed backthrusting in the lower hunza valley andean type granitoid gabbrodiorite granodiorite granite emplacement along the kohistan ladakh batholith ended at the time of india asia collision 60 50 myr ago postcollisional crustal thickening along the karakoram led to multiple episodes of metamorphism from latest cretaceous and throughout the tertiary sillimanite grade metamorphism in hunza was actually pre india asia collision and may have resulted from the earlier kohistan collision localized and sporadic crustal melting episodes across northern kohistan indus confluence and parri granite sheets and the southern karakoram hunza dikes and sumayar and mango gusar leucogranites occurred from 51 to 9 ma and culminated in the huge baltoro monzogranite leucogranite intrusion 25 21 myr ago a vast network of leucogranitic and pegmatitite dikes containing gem quality aquamarine muscovite tourmaline garnet biotite quartz are younger than 5 ma and form the final phase of intrusion in the haramosh area and parts of the southern karakoram area

tectonic significance of the cold seepage zones in the eastern nankai accretionary wedge an outcome of the 15 years kaiko projects abstract the tectonic significance of the cold fluid venting in the eastern nankai accretionary wedge has been elucidated based upon results of precise mapping and submersible observation executed since 1984 under the french japanese cooperative projects kaiko i ii kaiko nankai and kaiko tokai in conjunction with studies of the japan trench sagami bay and other regions the very sharp boundary of benthic communities associated with temperature anomalies indicates the occurrence of focused upflow of nutrient rich fluids through cracks in the carbonate crust existing on a near surface horizon of permeable sediment the linear alignment of venting zones is a surface expression of the shallow detachment faults methane rich fluids expelled from the conduit along a fault migrate in the overlying permeable sediment and react with circulating sea water containing sulfate to produce hydrogen sulfide and carbonate precipitate en echelon or zigzag patterns of the cracks are developed in the carbonate crust under the influence of tectonic shear stress it has been concluded that bivalve communities grow on a thin veneer of sediment above the cracks of carbonate through which fluid containing hydrogen sulfide diluted with sea water flows out on the other hand bacterial mats seem to flourish either on thin sediment overlying the fault conduit or over a thick cover of sediment without carbonate crust in the former case bivalves cannot grow because venting fluids are too dense with methane and hydrogen sulfide to maintain the oxygen rich condition of the bottom water in the western nankai trough fine grained less permeable sediment cover seems to prevent circulation of fluids whereas methane appears to be widespread in the deeper sedimentary layer there major distinctions in modes of seepage among sites are presumed to be caused by 1 the tectonic regime causing channels of upward fluid venting 2 rates and composition of venting fluids affected by mixing rates of sea water and 3 the permeability and thickness of the near bottom sediment

nyainqentanglha shear zone a late miocene extensional detachment in the southern tibetan plateau a major low angle ductile shear zone containing s c mylonites involves metamorphosed granitic rocks at the southeastern edge of the nyainqentanglha mountain range southern tibet prominent triangular facet geomorphology is developed by valley erosion of the detachment surface defined by the top of the southeast dipping mylonitec shear zone kinematic criteria consistently indicate a top to southeast sense of shear the ductile shearing deformation is inferred from isotopic cooling ages to have occurred during the interval 11 5 ma late miocene we interpret the shear zone as a regional extensional detachment its development indicates when the extensional tectonics in this area started which in turn may mark the time when the maximum sustainable surface elevation and perhaps crustal thickness was reached in southern tibet

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data