intraplate shortening and underthrusting of a large basement ridge in the eastern nankai subduction zone abstract due to the collision of the izu bonin arc with central japan the subducting philippine sea oceanic plate is affected by lithospheric shortening seaward of the eastern nankai trough in the zenisu ridge area seismic reflection and refraction profiles across the ridge show a series of low angle thrusts cutting through the entire oceanic crust they also indicate that the formation of this ridge is related to a single lithospheric thrust with 10 km throw that inserts a corner of upper mantle within the lower crust we propose that the serpentinized mantle crust transition acts as a decoupling level above which distributed shortening results in the formation of a crustal prism although the amount of deformation is much smaller than in a mountain belt such as the pyrenees a parallelism can be proposed between both systems that correspond to intraplate shortening and have in common a single mantle shear zone and overlying distributed crustal deformation the underthrusting below the eastern nankai accretionary prism of a similar and now inactive tectonic structure the paleo zenisu ridge is evidenced by the deformation pattern of the margin this ridge is probably detached on top of the subduction decollement at least where volcanoes are impinging the continental margin part of the ridge may thus be accreted to the prism backstop we show that both zenisu and paleo zenisu systems accommodate the same n s compression related to convergence partitioning process this subduction kinematics can be understood in terms of a steady state model partially constrained by the trails of volcanoes that have impinged the margin n s shortening is accommodated by the thrusts seaward of the trough and right lateral motion is prevalent along the subduction system based on these kinematics we propose that the formation of the paleo zenisu and zenisu ridges are related to the successive collisions of volcanic massifs of the izu bonin arc with the japanese arc the zenisu system is a result of the collision of the izu block since 2 ma while the paleo zenisu system was the result of the earlier collision of the tanzawa massif between 5 and 3 ma

seabeam and seismic reflection imaging of the tectonic regime of the andean continental margin off peru 4 s to 10 s abstract marine geophysical surveys employing seabeam multi and single channel seismic reflection gravity and magnetic instruments were conducted at two locations along the continental slope of the peru trench during the seaperc cruise of the r v jean charcot in july 1986 these areas are centered around 5 30 s and 9 30 s off the coastal towns of paita and chimbote respectively these data indicate that 1 the continental slope off peru consists of three distinct morpho structural domains from west to east are the lower middle and upper slopes instead of just two as previously reported 2 the middle slope has the characteristics of a zone of tectonic collapse at the front of a gently flexured upper slope 3 the upper half of the lower slope appears to represent the product of mass wasting 4 thrusting at the foot of the margin produces a continuous morphologic feature representing a deformation front where the products of mass wasting are overprinted by a compressional tectonic fabric 5 a change in the tectonic regime from tensional to compressional occurs at the mid slope lower slope boundary the accretionary prism being restricted to the very base of the lower slope in the paita area the andean margin off peru is an extensional active margin or a collapsing active margin developing a subordinated accretionary complex induced by massive collapse of the middle slope area

rare earth element mobility during prograde granulite facies metamorphism significance of fluorine mafic gneisses occur as lenses or thin layers in spatial association with tonalitic leucosomes in a granulite zone of the quetico subprovince of the superior province ontario canada and exhibit concentric zoning with a biotite rich margin orthopyroxene rich outer zone clinopyroxene rich central zone and occasionally patches of relict amphibolites within the clinopyroxene rich zone the granulites biotite orthopyroxene and clinopyroxene rich zones in the mafic gneisses are characterized by significant amounts of rare earth element ree bearing fluorapatite 1 10 vol and other ree rich minerals allanite monazite and zircon fluorapatite shows an increase in modal abundance from the biotite and orthopyroxene rich zones to the clinopyroxene rich zone but is rare in the relict amphibolites textural evidence and element partitioning indicate that fluorapatite and other ree rich minerals was part of the peak metamorphic assemblages whole rock geochemical analyses confirm that the granulites in the mafic gneisses contain anomalously high contents of ree and high field strength elements hfse whereas the relict amphibolites are geochemically typical of tholeiitic basalts mass balance calculations reveal that ree and hfse were introduced into the mafic gneisses during the prograde granulite facies metamorphism pointing to ree mobility under granulite facies metamorphic conditions the presence of high f contents in the ree rich minerals and their associated minerals e g biotite and hornblende suggests that ree and hfse may have been transported as fluoride complexes during the granulite facies metamorphism this conclusion is supported by previously published results of hydrothermal experiments on the partitioning of ree between fluorapatite and f rich fluids at 700 c and 2 kbar

seismotectonics at the trench trench trench triple junction off central honshu we study earthquakes in and near the ttt type triple junction off boso peninsula central honshu to elucidate the plate interaction in this area the pacific north america northeast japan and philippine sea plates meet at the junction of the japan and izu bonin trenches and the sagami trough we determine focal mechanisms using wwssn data we also determine accurate focal depths by modeling body waves there is no serious trade off between focal depth and source time function for the events treated in this study

halogen bearing minerals in syenites and high grade marbles of dronning maud land antarctica monitors of fluid compositional changes during late magmatic fluid rock interaction processes meta sedimentary rocks including marbles and calcsilicates in central dronning maud land cdml in east antarctica experienced a pan african granulite facies metamorphism with peak metamorphic conditions around 830 20 c at 6 8 0 5 kbar which was accompanied by the post kinematic intrusion of huge amounts of syenitic charnockitic magmas at 4 5 0 7 kbar the marbles and calcsilicates may represent meta evaporites as indicated by the occurrence of metamorphic gypsum anhydrite and cl rich scapolite that formed in the presence of saline fluids with x nacl in the range 0 15 0 27 the marbles and calcsilicates bear biotite tremolite and or hornblende and humite group minerals clinohumite chondrodite and humite which are inferred to have crystallized at about 650 c and 4 5 kbar the syenitic intrusives contain late magmatic biotite and amphibole formed between 750 and 800 c as well as relictic magmatic fayalite orthopyroxene and clinopyroxene two syenite and two calcsilicate samples contain fluorite corona textures in the marbles and calcsilicates suggest very low fluid rock ratios during the formation of the retrograde 650 c assemblages biotite in all but two syenite samples crystallized at log f h 2 o f hf ratios of 2 9 0 4 while in the calcsilicates both biotite and humite group minerals indicate generally higher log f h 2 o f hf values of up to 5 2 a few samples though overlap with the syenite values log f h 2 o f hcl derived from biotite covers the range 0 5 2 6 in all rock types within a single sample the calculated values for both parameters vary typically by 0 1 to 0 8 log units water and halogen acid fugacities calculated from biotite olivine orthopyroxene feldspar quartz equilibria and the above fugacity ratios are 1510 2790 bars for h2o 1 3 5 3 bars for hf and 7 600 bars for hcl the results are interpreted to reflect the reaction of relatively homogeneous magmatic fluids in terms of log f h 2 o f hf derived from the late magmatic stages of the syenites with both earlier crystallized still hotter parts of the syenites and with adjacent country rocks during down temperature fluid flow fluorine is successively removed from the fluid and incorporated into f bearing minerals close to the syenite into metamorphic fluorite in the course of this process log f h 2 o f hf increases significantly chlorine preferably partitions into the fluid and hence log f h 2 o f hcl does not change markedly during fluid rock interaction

helium isotopes as geochemical indicators of a serpentinized fore arc mantle wedge new helium isotope data from hot springs on eastern kyushu island were obtained in order to elucidate the geographic distribution of 3 he 4 he ratios in the fore arc regions of southwest japan systematic regional variations in 3 he 4 he ratios are clearly distinguished across the fore arc from kyushu island 0 093 0 79 r a where r a denotes the atmospheric 3 he 4 he ratio of 1 4 x 10 6 to shikoku island 0 17 3 6 r a and to the kii peninsula 0 24 7 4 r a the distribution of mantle helium relative to total helium reveals a close association with the geophysical evidence of a serpentinized fore arc mantle wedge including the occurrence of deep nonvolcanic low frequency tremors lfts believed to be caused by upwardly mobile aqueous fluids derived from slab dehydration flux of mantle helium carried by aqueous fluids via a non serpentinized fore arc mantle wedge is very low on kyushu island where lfts have not been detected and 3 he 4 he ratios are lower than the atmospheric ratio on the other hand hot springs above the regions where lfts occur in the kii peninsula and northern shikoku island have high 3 he 4 he ratios indicating a significant contribution of mantle helium carried by aqueous fluids via a serpentinized fore arc mantle wedge the helium isotopes in hot and natural spring gases may be a useful geochemical indicator of a serpentinized fore arc mantle wedge especially in areas with sparse seismic station coverage

kinematics of the philippine sea plate in this study new instantaneous rotation vectors describing the motion of the philippine sea plate relative to surrounding plates are determined that most nearly satisfy all available geological geophysical and seismological observations along the plate margins pacific philippine and caroline pacific poles are generated from a set of trial eurasia philippine poles of rotation using published determinations of the eurasia pacific and caroline philippine poles the pacific philippine caroline pacific and eurasia philippine poles are then checked for agreement with 1 slip vectors determined from focal mechanisms of earthquakes along the ryukyu trench and the nankai trough 2 convergence at the sagami trough 3 extension in the mariana trough 4 extension behind the bonin trench 5 extension in the western sorol trough and 6 convergence at the mussau trench trial eurasia philippine poles are eliminated if predicted plate motions do not match observed plate motions the locations and rotation rates of the three best fitting poles are eurasia philippine 37 0 n 141 0 e 1 60 ma pacific philippine 3 8 n 130 4 e 1 68 ma caroline pacific 16 9 n 141 4 e 0 54 ma the plate motions predicted by these new poles are compared with the spatial distribution of earthquakes and new focal mechanism solutions in the complex region where the philippine pacific and caroline plates intersect intermediate and deep focus earthquake hypocenters along the southern mariana arc show a southward decrease in the length of the seismic zone which qualitatively agrees with the predicted convergence rate as the pole of rotation is approached and as the effect of back arc spreading in the mariana trough disappears the absence of volcanism and intermediate depth seismicity along the southernmost mariana yap and palau sections of the plate boundary is attributed to very low convergence rates a new focal mechanism solution along the trench south of guam is the first clear underthrusting solution found along the mariana trench and agrees with the convergence direction implied by the pacific philippine pole of rotation no clear underthrusting focal mechanism solutions were found along the yap and palau trenches although three high angle thrust solutions demonstrate that compression is occurring in the upper plate perpendicular to the plate boundary

the multiple inverse method applied to meso scale faults in mid quaternary fore arc sediments near the triple trench junction off central japan the multiple inverse method for fault slip data is applied to meso scale faults observed in mid quaternary fore arc sediments near the triple trench junction oa the boso peninsula japan data from the otadai umegase and kokumoto formations were processed and three stresses were obtained as significant solutions vertical axial compression and triaxial stresses with the s3 axis in wnw ese and nne ssw directions the triaxial stresses were determined from the otadai and umegase data however the wnw ese tensile stress is not detected from the youngest kokumoto suggesting that the stress is older than the formation the area was subject to a wnw ese tensile stress 01 2 1 0 ma but tensile direction changed to a ne sw trend thereafter the succession was simultaneous with a tectonic event in the landward slope of the sagami trough suggesting that the subduction of the philippine sea plate aaected the stresses in the overriding plate the older tensile stress was probably a manifestation of the gravitational collapse of the hayama mineoka ridge which was growing parallel to the trough the inferred stress history is concordant with the variation of plate convergence at the trough 2000 elsevier science ltd all rights reserved

multiple indicator study of groundwater flow and chemistry and the impacts of river and paddy water on groundwater in the alluvial fan of the tedori river japan to investigate the source flow paths and chemistry of rich resources of high quality shallow groundwater in the alluvial fan between the tedori and sai rivers in central japan we analysed stable isotope ratios of h o and sr and concentrations of major dissolved ions and trace elements in groundwater river water and paddy water the sr 87 sr 86 ratios of the groundwater are related to near surface geology groundwater in sediment from the tedori river has high sr 87 sr 86 ratios 0 711 whereas that from the sai river in the north of the fan has low sr 87 sr 86 ratios 0 711 h 2 and o 18 values and sr 87 sr 86 ratios indicate that groundwater in the central and southern fans is recharged by the tedori river whereas recharge in the north is from the sai river mg2 ca2 sr2 hco3 and so42 concentrations and h 2 and o 18 values in the groundwater are high in the central fan and except for the northern area tend to increase with distance from the tedori river there are linear relationships between sr 87 sr 86 ratio and the reciprocal concentrations of sr2 mg2 and ca2 these geochemical characteristics suggest that as groundwater recharged from the tedori river flows towards the central fan it mixes with waters derived from precipitation and paddy water that have become enriched in these components during downward infiltration these results are consistent with our hydrological analysis and numerical simulation of groundwater flow thus verifying the validity of the model we used in our simulation of groundwater flow copyright c 2016 john wiley sons ltd

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

quaternary geomorphic trends within southwest japan extensive wrench deformation related to transcurrent motions of the median tectonic line abstract large scale transcurrent faults contribute to anelastic deformations along convergent plate boundaries the inner zone of southwest japan has been subjected to shearing deformations during the quaternary associated with dextral motions of the median tectonic line which was activated as a right lateral fault by oblique subduction of the philippine sea plate considering the neotectonic framework the continental crust of the chugoku block in the western part of the inner zone is simplified as a granitic test piece under a simple shear geological and geographical data in the block are incorporated to produce a quantitative analysis of the deformation mode together with an empirical model of the rheology of an orogenic crust the present results indicate that the chugoku block behaves as a newtonian fluid and flows with a strain rate of about 10 14 s 1 under a tectonic stress of 10 mpa the mode of wrenching of the study area is compared with confined deformations of other plate margins in the same tectonic regime unique extensive wrench deformation as wide as 150 km along the median tectonic line is attributed to the absence of weak zones in the continental crust such as ductile melange belt or arc volcanism which is a common phenomenon in the area of active convergence the inner zone of southwest japan is immune from these major factors reducing the shearing strength of the crust because of the intensive intrusions of cretaceous granites and the regional quaternary thermal event

intracontinental rift related deposits a review of key models abstract mineral systems associated with extensional fault systems in continental environments and not related to magmatic activity involve various deposit models that can be grouped into a single system which would plausibly explain the source and chemical composition of fluids the formation depth the source of heat and the structural history within a common geologic setting mineral deposits related to this tectonic setting are those described within the detachment related model including massive replacements stockworks and veins of cu and fe oxides with or without au polymetallic sulfide veins barite and or fluorite veins and stratabound and vein mn deposits this paper reviews the abovementioned deposits as well as others related to this tectonic setting such as se rich polymetallic deposits almaden type hg deposits u ni co as ag polymetallic deposits with subordinated bi cu pb zn five element deposits simple polymetallic pb ag zn deposits and the members of the iocg clan including the au ag detachment related deposits involved in the cu fe au model deposits all these mineral deposits are the result of fluid motion unrelated to magmatism in areas of thermal anomalies these fluids collect certain elements producing a district mineralogical specialization with inhomogeneities in the distribution of mineralization types along the region affected by rifting fluid homogenization temperatures and salinities range between 60 and 430 c and 0 and 27 equivalent wt nacl respectively the o s and d isotope composition is consistent with basinal poral fluids derived from meteoric waters under different p t conditions in an active faults environment pb isotopes suggest that pb derives from a mixture of rocks with a long period of residence in the upper crust and rocks deformed along repeated orogenic cycles with a contribution of pb from the lower crust and even the mantle fluid flow along fault planes leads to different types of hydrothermal alterations depending on p t conditions particularly propylitization and low temperature potassium metasomatism all such deposits can be found in two different geotectonic environments of metallogenic interest involving extensional faults associated with detachment zones in depth i e 1 continental extension in a back arc environment and 2 extension with rift development and generation of oceanic crust in a passive continental margin although the economic importance of this group of deposits is mainly related to industrial minerals non magmatic iocg deposits could significantly augment the economic potential of this setting the rift setting itself without relation to detachments is favorable for concentrating metals in stratabound deposits such as sedex ores additionally the development of deposits directly related to magmatic activity contributes to the economic interest of this environment

strontium isotope geochemistry of groundwater affected by human activities in nandong underground river system china abstract the nandong underground river system nurs is located in a typical karst area dominated by agriculture in se yunnan province china groundwater plays an important role in the social and economical development in the area the effects of human activities agriculture and sewage effluents on the sr isotope geochemistry were investigated in the nurs seventy two representative groundwater samples which were collected from different aquifers calcite and dolomite under varying land use types both in summer and winter showed significant spatial differences and slight seasonal variations in sr concentrations and 87sr 86sr ratios agricultural fertilizers and sewage effluents significantly modified the natural 87sr 86sr ratios signature of groundwater that was otherwise dominated by water rock interaction three major sources of sr could be distinguished by 87sr 86sr ratios and sr concentrations in karst groundwater two sources of sr are the triassic calcite and dolomite aquifers where waters have low sr concentrations 0 1 0 2 mg l and low 87sr 86sr ratios 0 7075 0 7080 and 0 7080 0 7100 respectively the third source is anthropogenic sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic 87sr 86sr ratios 0 7080 0 8352 for agricultural fertilizers and 0 7080 0 7200 for sewage effluents respectively with higher sr concentrations 0 24 0 51 mg l due to the overlapping 87sr 86sr ratios it is difficult to distinguish the sources of sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their 87sr 86sr ratios however 87sr 86sr ratios do provide key information for natural and anthropogenic sources in karst groundwater

fluorian garnets from the host rocks of the skaergaard intrusion implications for metamorphic fluid composition zoned silica deficient calcic garnets containing up to 5 mol f substitution for 0 formed during contact metamorphism of basalts by the skaergaard intrusion in east greenland fluorian calcic garnets occur as a retrograde alteration of prograde wollastonite and clinopyroxene that fills vesicles and vugs in lavas 30 70 m from the intrusion paragenetically equivalent phases include fluorite wollastonite calcic clinopyroxene prehnite quartz and calcite electron microprobe analysis shows that the garnets are 93mol grossular andradite grandite solid solutions and that the f content does not fully compensate for the silica deficiency suggesting the presence of a hydrous component in the garnets the garnets display discontinuous zoning with respect to al and fe and increases in f calculated oh and the si deficiency with increasing al concentration are observed the garnets formed at temperatures between 200 and 420 c based on the coexisting mineral assemblage and stratigraphic reconstructions indicate pressures of 1 kbar assessment of isobaric isothermal phase relations in the system cao a1203 si02 h20hf allows estimation of fluid characteristics in equilibrium with fluorian grandite bearing assemblages the presence of fluorite wollastonite quartz and calcite with these garnets combined with fluid inclusion data require that the activity a of h20 was 1 and that ah af was 10 105 to 10 10 0in the coexisting hydrothermal solutions at 200 420 c and 1 kbar if ph was neutral at these pressure and temperature conditions 5 3 0 1 the value of af associated with fluorian garnet formation was 10 4 7to 10 52 the f content of garnet is extremely sensitive to minor changes in fluid composition the calculations show that a decrease in ph or an increase in log af of 0 3 at constant pressure and temperature will decrease the f concentration in garnet from 5 to 0 mol the results of this study show that fluorian hydrous grandites provide a mineralogical record of the activities off species in coexisting metamorphic and hydrothermal fluids

influence of upwelling on the shallow water chemistry in a small wetland riparian zone basque country abstract many hydrologic conceptual models in riparian areas assume that the alluvial deposits zone is hydraulically more active than the fractured bedrock below therefore these models undervalue the possible contribution of deeper groundwater from the fractured bedrock system a hydrochemical study under various hydrological conditions has been carried out in a small riparian zone of the salburua wetland basque country in order to highlight the conceptual model this wetland is included in a wide quaternary aquifer which has been declared a nitrate vulnerable zone the results of this study suggest that the fractured bedrock is at least as dynamic as the upper clayey deposits the presence of more fractured zones which act as hydraulic windows allow the upwelling of deeper groundwater and consequently make the upper alluvial deposits and the fractured bedrock water systems to be cross connected nevertheless this upwelling is limited to some small areas in the riparian zone as a result of this local interaction several chemical reactions have been observed and the hydrochemical characteristics of shallow groundwater undergo seasonal variations the study shows that a hydrologic conceptual model which does not consider the hydraulic activity of the fractured bedrock can be too simplistic the presence of hydraulic windows could be considered throughout the entire quaternary aquifer knowledge of which could help the managers of the vulnerable zone and the wetland to take more effective measures for regulation and conservation

project kaiko introduction the kaiko project was a french japanese cooperative scientific effort to investigate the structures and geodynamic processes in the deep trenches surrounding the japanese islands seabeam mapping as well as detailed geophysical investigation of eight selected areas in the nankai suruga and sagami troughs and in the japan trench including the trench triple junction were performed in 1984 twenty seven manned dives to a maximum depth of 6000 m were made over five of these areas at carefully selected sites in 1985 the main results of the project are presented in this special issue together with a set of coloured bathymetric maps and block diagrams they illustrate a great diversity of tectonic styles from the turbidite filled trenches of the shikoku basin with a well developed accretionary prism to the much deeper japan trench with widespread evidence for large scale slumping and erosion over the inner wall special insight has been gained into the processes involved in the subduction of seamounts and of volcanic ridges benthic communities associated with chemosynthetic processes were discovered at several locations during manned dives in the nankai trough as well as in the japan trench they thus appear to be a common feature of deep sea trenches thermal geochemical and biogeochemical measurements coupled with tectonic observations indicate that they are related to overpressure fluid advections along zones of active surface deformation

a trench fan in the izu ogasawara trench on the boso trench triple junction japan soh w taira a and tokuyama h 1988 a trench fan in the izu ogasawara trench on the boso trench triple junction japan mar geol 82 235 249 the mogi trench fan 18 km in diameter is located in the 9 1 km deep izu ogasawara trench analysis of the morphology and internal structure of the mogi fan was based on 3 5 khz records seismic reflection profiles and seabeam bathymetry the mogi fan was fed from a point source and displays an even shaped partial cone morphology which can be divided into upper middle and lower fans the upper fan is defined as an apparent topographic mound having a large scale single channel with well defined levees that appear to be composed mainly of coarse grained turbidites the middle fan is characterized by divergent channels and lobes the lower fan is a smooth mound with no channel features it is postulated that the lower fan is constructed chiefly by turbidity currents that reflected back from the higher outer slope seismic reflection records across the fan show deformation resulting from plate subduction in the upper fan this deformation can be traced laterally to the lower bulge of the inner slope neighbouring the mogi fan several characteristics of the morphology of the mogi fan indicate that it is presently inactive the fan development is interpreted to have formed and prograded in the trench during a period of lowering sea level during rising sea level the sediment supply to the trench abruptly decreased and the tectonic deformation of the fan morphology was correspondingly enhanced

central japan triple junction a three dimensional compression model abstract we present a new interpretation of the tectonics of the trench trench trench triple junction off central japan using more specifically data obtained during the french japanese kaiko cruise in 1984 data analysis and consideration on the three dimensional geometry of the junction and its kinematics lead to the conclusion that the whole area undergoes large scale compressional intraplate deformation this is caused by the subduction of the philippine sea plate in the restricted space between the pacific and northern honshu plates we then apply the same analysis to the whole central japan area for which we consider the role of the interaction of the three plates at depth as a basis for tectonic reconstructions since the miocene

petrology of phlogopite sapphirine bearing al mg granulites from ihouhaouene in ouzzal hoggar algeria an example of phlogopite stability at high temperature al mg granulites with cordierite garnet sapphirine orthopyroxene sillimanite spinel phlogopite k feldspar plagioclase and variable quartz from ihouhaouene in ouzzal algeria display a range of decompression textures involving the breakdown of orthopyroxene and sillimanite and of garnet the succession of parageneses suggests that the p t t evolution corresponds to decompression with cooling from peak conditions of about 950 c and 10 kbar this decompression path is obtained from the paragenetic analysis in the fmas system however according to current kfmash grids this p t t evolution should take place outside the stability field of phlogopite quartz yet this assemblage is probably stable during most of the p t evolution notably during peak metamorphism this discrepancy is interpreted as the effect of the high content of f in phlogopite which should shift its stability limit towards higher temperature the consequences of this shift on the phase relationships in the kfemash system are investigated and it is concluded that a topological inversion could exist in the f bearing system

stability of high al titanite from low pressure calcsilicates in light of fluid and host rock composition titanite of variable al and f content was found in granulite to amphibolite facies calcsilicates in central dronning maud land antarctica the highest observed al content corresponds to an xal 5 al al 1 ti of 0 53 previously such high values of xal were reported from high pressure rocks but the titanite of this study is from a lowpressure terrain the compositional variations in titanite can be described for all samples by a set of three linearly independent exchange vectors added to the catisio5 endmember titanite in most rocks these vectors are al 1f1ti21o21 t i 20 25m0 25o21oh1 and oh1f21 in one sample the ti20 25m0 25o21oh1 vector is replaced by a si20 25m0 25o21oh1 vector the actual amount of exchange along these vectors and therefore the amount of al in titanite depends on p and t on the composition of the coexisting fluid phase in terms of its h2o hf fugacity ratio and on host rock composition in terms of al2o3 tio2 activity ratio it is inferred that in suitable chemical environments high al titanite is stable over a wide p t range therefore the al content of titanite should not be used in geothermobarometry even qualitatively additionally because of the coupled substitutions al1f1ti21o21 and al1oh1ti21o21 the concentration of f in titanite is strongly dependent on the host rock chemistry this rules out the easy use of titanite as a monitor of fluid composition

rapid quench hydrothermal experiments at mantle pressures and temperatures new experimental methods for the encapsulation extraction and analysis of large volumes of aqueous fluids enable studies of mineral solubilities and dissolution kinetics with the piston cylinder apparatus quench rates and volumes of experimental fluids with these methods are comparable with those used in modern hydrothermal experiments employing cold seal vessels analyses of fluid compositions are reproducible and consistent with independent results the techniques permit experimental investigations that will better characterize fluid rock interaction in such environments as subducting slabs the mantle wedge barrovian metamorphic belts and middle to lower crustal granulites

interaction between different water bodies in a small catchment in the paris basin brevilles france tracing of multiple sr sources through sr isotopes coupled with mg sr and ca sr ratios abstract intensive monitoring of the cuise sands aquifer in a small agricultural catchment 3 km2 where agricultural practices are well documented over nearly 5 a showed significant disparities for major element concentrations sr concentrations isotopic compositions and 3h values depending on the groundwater sampling locations lower 87sr 86sr values 0 7079 0 7085 associated with low no 3 concentrations low mg sr molar ratios 0 7085 and higher mg sr molar ratios 250 suggest a contribution of sr from anthropogenic sources strontium isotopes coupled with mg sr and ca sr ratios of groundwater in this catchment successfully demonstrated the capacity to trace fertilizer contributions which significantly modify the natural sr isotopic signature of groundwater the specific geochemical signature of groundwater revealed by sr isotopes in addition to major and trace element concentrations in particular mg sr and ca sr molar ratios demonstrated the partial isolation of groundwater bodies in this catchment compartmentalisation of the aquifer is compatible with fault distribution as defined by geological and geophysical investigations thus the sr isotopic tool coupled with mg sr and ca sr ratios has been applied with success to trace water pathways and recharge and to provide scenarios for the hydrological functioning of the system

strontium isotopes as tracers of groundwater induced floods the somme case study france major ions trace elements and o h and sr isotopes have been determined for surface water and groundwater in the somme catchment northern france the present study using a coupled hydrological and geochemical stable and sr isotopes approach focuses on the interactions between ground and surface water stable water isotopes 18o 2h show that all waters have a purely local origin from precipitation without significant evaporation or water rock interaction as all points plot close to the general meteoric water line water chemistry in the different catchments shows large variations in major element contents plotting na vs cl contents and mg2 no3 k so42 sr2 concentrations reveals a slight variations in groundwater composition b agricultural input into surface waters and c some similarities between ground and surface waters suggesting the former to be responsible for the chemical signature of the dissolved river load strontium isotope ratios measured in groundwater range from 0 70769 to 0 70808 clearly higher than that of chalk matrix water 0 707337 variations of sr isotope signatures in groundwater from the chalk aquifer are significant and help identifying different groundwater bodies the different signatures in groundwater are better explained by matrix heterogeneity which can present lateral facies variations than by a strong anthropogenic influence the sr isotope compositional range in surface waters is very wide varying from 0 70775 to 0 70816 and defining a trend towards a more radiogenic sr isotope signature with high sr contents and high mg sr ratios the relationship between 87sr 86sr and the mg sr ratios allows different end members to be defined the rivers are influenced by anthropogenic disturbance even during flood periods and river water has geochemical characteristics very similar to those of groundwater indicating a strong influence from groundwater feeding the rivers

morphology and development of a deep sea meandering canyon boso canyon on an active plate margin sagami trough japan abstract the 100 km long boso canyon is located on a plate boundary in the sagami trough off boso peninsula central japan large volumes of sediment from the izu collision zone and adjacent volcanoes have been transported to the sagami trough and the izu ogasawara trench through the boso canyon boso canyon displays a channel morphology ranging from low straight to high sinuosity meandering in the midstream an abandoned channel is preserved on the bench along the downstream high sinuosity channel quantitative analyses of the canyon morphology demonstrate that the boso canyon has definite similarities with meandering subaerial rivers especially with entrenched meanders three morphological parameters sinuosity channel gradients and canyon gradients suggest that the canyon slope appears to be compensated by an increase in sinuosity to maintain an optimum channel profile three morphological stages for the canyon development can be recognized pre abandonment channel abandonment and post abandonment assuming that the tectonic framework of the region in transtension has not changed significantly since 0 5 ma these stages would be formed corresponding to sea level changes during the preabandonment stage low sea level phase the boso canyon was straight and large amounts of detritus flowed down as turbidity currents to the katsuura basin slope and the mogi trench fan on the izu ogasawara trench floor the sediment supply rates were sufficient to mask the tectonic modification in channel morphology sediment supply rates to the boso canyon decreased abruptly as sea level rose and the channel sinuosity increased to maintain optimum channel slope gradient the building of the small confined boso submarine fan probably began at the mouth of boso canyon which masked the basin topography of the katsuura basin at highstand the channel became least active and differential tectonic subsidence led to enhanced channel entrenchment the boso canyon is a good example suggesting that tectonic and sea level changes are important in the origin and development of deep sea channels on an active plate margin

the combined use of 87sr 86sr and carbon and water isotopes to study the hydrochemical interaction between groundwater and lakewater in mantled karst abstract the hydrochemical interaction between groundwater and lakewater influences the composition of water that percolates downward from the surficial aquifer system through the underlying intermediate confining unit and recharges the upper floridan aquifer along highlands in florida the 87sr 86sr ratio along with the stable isotopes d 18o and 13c were used as tracers to study the interaction between groundwater lakewater and aquifer minerals near lake barco a seepage lake in the mantled karst terrane of northern florida upgradient from the lake the 87sr 86sr ratio of groundwater decreases with depth mean values of 0 71004 0 70890 and 0 70852 for water from the surficial aquifer system intermediate confining unit and upper floridan aquifer respectively resulting from the interaction of dilute oxygenated recharge water with aquifer minerals that are less radiogenic with depth the concentrations of sr2 generally increase with depth and higher concentrations of sr2 in water from the upper floridan aquifer 20 35 g l relative to water from the surficial aquifer system and the intermediate confining unit result from the dissolution of sr bearing calcite and dolomite in the eocene limestone dissolution of calcite 13c 1 6permil is also indicated by an enriched 13cdic 8 8 to 11 4 in water from the upper floridan aquifer relative to the overlying hydrogeologic units 13cdic groundwater downgradient from lake barco was enriched in18o and d relative to groundwater upgradient from the lake indicating mixing of lakewater leakage and groundwater downgradient from the lake the 87sr 86sr ratio of groundwater and aquifer material become less radiogenic and the sr2 concentrations generally increase with depth however sr2 concentrations are substantially less than in upgradient groundwaters at similar depths the lower sr2 concentrations result from the influence of anoxic lakewater leakage on the mobility of sr2 from clays based on results from mass balance modeling it is probable that cation exchange plays the dominant role in controlling the 87sr 86sr ratio of groundwater both upgradient and downgradient from lake barco even though groundwater from the three distinct hydrogeologic units displays considerable variability in sr concentration and isotopic composition the dominant processes associated with the mixing of lakewater leakage with groundwater as well as the effects of mineral water interaction can be ascertained by integrating the use of stable and radiogenic isotopic measurements of groundwater lakewater and aquifer minerals

geohazards in coastal areas near the northernmost sagami trough central japan review of neotectonic activity in onshore and offshore areas of the izu island arc collision subduction zone

shear partitioning near the central japan triple junction the 1923 great kanto earthquake revisited i summary we propose the existence of a major right lateral transform fault which we call the boso transform fault it is related to the sagami trough a portion of the philippine sea plate boundary south of the kanto area central japan this boso transform fault is the result of shear partitioning due to oblique subduction and has delimited a boso sliver for 2 myr the rate of motion is estimated at 16 mm yr and the total offset at 30 km the fault cuts through the miura and boso peninsulas onland where it has a multiple surface expression roughly along the limit of a steeply dipping miocene ophiolitic body these subaerial faults have been identified as active and their cumulated rate of slip across the miura peninsula can be estimated to be greater than 12 mm yr in reasonable agreement with the above estimate we propose that the slip on the boso transform fault was responsible for two large m 7 0 and 7 5 aftershocks which occurred on the second day after the 1923 great kanto earthquake this explains the unusual duration of the aftershock sequence and the large magnitudes of some of the aftershocks

aluminous titanite sphene from the eclogite zone south central tauern window austria abstract highly aluminous titanite with al 2 o 3 contents up to 14 wt 50 of the caalsio 4 f oh end member occurs in siliceous dolomites from the eclogite zone south central tauern window austria 140 chemical analyses of titanites from 13 samples from the eclogite zone and adjacent tectonic units reveal that al is incorporated into titanite primarily by the mechanism ti o al f oh there is also a strong positive correlation between al and f content of these titanites indicating that the combined substitution is enhanced by the presence of f al contents of titanite vary between tectonic units with the most aluminous varieties occurring in the high pressure eclogite zone variations also occur from sample to sample within a single tectonic unit and both between and within individual grains in a single sample complex zoning with sharp chemical and optical discontinuities is observed with al 2 o 3 variations of up to 6 wt within a single sample individual grains generally have low al cores mantled by high al zones and rimmed by low al edges it is suggested that the incorporation of al into titanite is favoured by high p low t and high f activity

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

the eastern and western ends of nankai trough results of box 5 and box 7 kaiko survey abstract seabeam mapping and detailed geophysical surveying have been conducted over the eastern and western ends of the nankai trough the eastern survey covers the transition between the large izu bonin izu ogasawara ridge collision with honshu and the nankai trough subduction it includes a northeast trending basement ridge the zenisu ridge to the southeast of nankai trough as well as two large channel systems one following the trench the nankai channel and the other coming from the north the tenryu canyon the zenisu ridge is a zone of recent intra plate shortening consisting of three distinct segments with an increasing deformation from southwest to northeast we interpret this gradient of deformation as a way to absorb the kinematic discontinuity between the diffuse shortening prevailing over the izu bonin ridge and the concentrated shortening along the nankai trough the shortening axis appears to change from north south along the zenisu ridge to northwest southeast along the nankai trough and finally to east west within honshu the western survey covers the junction between the nankai and ryukyu trenches and the kyushu palau ridge which is subducted without major internal deformation the ridge appears to act as an indenter upon the margin the tip of the indenter is presently situated under the upper accretionary prism

oblique and near collision subduction sagami and suruga troughs preliminary results of the french japanese 1984 kaiko cruise leg 2 abstract leg 2 of the french japanese 1984 kaiko cruise has surveyed the suruga and the sagami troughs which lie on both sides of the northwestward moving and colliding izu bonin ridge the northernmost part of the philippine sea plate the transition from the nankai trough to the suruga trough is characterized by northward decrease in width of the accretionary prism in good agreement with the increasing obliquity between the through axis and the direction of the convergence as the strike of the convergent boundary changes from ene nne to south north south of the area the southern margin of the zenisu ridge shows contractional deformations this supports the interpretation made by the team of leg 1 who studied the western extension of the area we studied that it is an intra oceanic thrusting of the ridge over the shikoku basin in the sagami trough where the relative motion is highly oblique to the plate boundary active subduction is mostly confined in the east west trending portions of the trough located south of the boso peninsula and along the lower boso canyon near the ttt triple junction in between the present motion is mainly right lateral along the northwest trending boso escarpment however an inactive but recent pliocene to lower pleistocene accretionary prism exists south of the boso escarpment which suggests that the relative motion was more northerly than at present before about 1 ma ago

tracing the sources of strontium in karst groundwater in chongqing china a combined hydrogeochemical approach and strontium isotope groundwater quality in karst regions is largely controlled by natural processes and anthropogenic activities over the past 10 years dissolved sr and its radiogenic isotope 87sr 86sr were widely used to trace the sources of solutes in groundwater however there is little research about hydrogeochemistry and sr isotopic compositions of the karst groundwater in chongqing karst area in this paper thirty five representative karst groundwater samples were collected from different aquifers limestone and dolomite and various land use types hydrochemical types of karst groundwater in chongqing were mainly of the ca hco3 type or ca mg hco3 type the dissolved sr concentrations of the studied groundwater ranged from 0 57 to 15 06 mmol l and the 87sr 86sr varied from 0 70751 to 0 71627 the groundwater samples from different aquifers and land use types showed distinctive dissolved sr concentrations and 87sr 86sr the very positive relationship between ca sr and mg sr in dolomite and limestone aquifers suggests that ca mg and sr element come mainly from the release of carbonate rock under the groundwater rock co2 gas interaction according to the 87sr 86sr ratio the sr element in karst groundwater in chongqing was controlled by the weathering of limestone dolomite and silicate rock allogenic water in a non karst area the relationship 87sr 86sr versus sr2 k na shows that the anthropogenic inputs also obviously contribute to the sr contents the research results show that the karst groundwater in chongqing is facing serious crisis of water quality and needs to be protected further

fluid absent melting of f rich phlogopite rutile quartz fluid absent melting is believed to be an important process in the generation of melts m the lower crust and upper mantle breakdown of phlogopite makes h 0 available and thus controls the conditions at which fluid absent melting occurs both f2andti in biotite ha e been shown to affect strongly the thermal stability of biotite to model better the fluid absenti eltmg of a ssemblagescontaining phlogopite the reaction f phlogopite quartz rutile enstatite melt has been studied experimentally experiments were pe o med at 7 10 and 15 kbar using a natural f rich phlogopite with a starting com os tion off f oh 0 43 and mg mg fe in molar proportions 0 94 results mdlcate that the therma l stability of f rich phlogopite quartz rutile is extended by as much as 450 c relative to the kmash system and by 300 c relative to the ti free f kmash system approach to equilibrium in the experiments was assessed by convergence of results of melting and crystallization experiments phlogopite compositions from e penmental products show that although f rich phlogopite incorporates relatively little ti 3 wt i02 the combination of f and ti increases the stability of phlogopite to considerably higher temperatures 300 0c than that of either component alone melts formed by the fluid absent melting off rich phlogopite quartz rutile at temperatures 1000 care anitic and stro g1yperaluminous the compositions of these melts suggest that the formationofmetalummous to peralkaline a type granites by fluid absent melting of halogen enriched sources is unlikely

very low solubility of rutile in h2o at high pressure and temperature and its implications for ti mobility in subduction zones the solubility of rutile in h2o has been measured at 1000 1100 c 1 2 gpa the data indicate that solubility is very low over the investigated range with a maximum of 4 7 millimol kg h2o at 1100 c 2 gpa the data were fit with the equation log m ti 4 892 10470 t 0 1923 p where m ti is ti molality t is in kelvins and p in gpa when compared to previous results the new data indicate substantially lower solubility opposite pressure dependence and thermodynamic properties of the reaction rutile tio2 aq that are now consistent with other oxide hydrolysis reactions calculations of ti transport during mantle metasomatism by h2o in subduction zone environments predict much lower ti mobility at all conditions these results offer strong support for models of ti retention in eclogites during slab devolatilization and require that examples of significant ti mass transfer be explained by complexing agents in solution most likely aluminosilicate complexes

thermodynamics of sio2 h2o fluid near the upper critical end point from quartz solubility measurements at 10 kbar abstract quartz solubility in sio 2 h 2 o fluid was measured at 10 kbar and 750 1130 c in a piston cylinder apparatus at 1035 c solubility was determined by weight loss of single crystals equilibrated with h 2 o rich fluid at higher temperature t the fluid phase coexisting with quartz quenched to a glass and solubility was determined by phase assemblage bracketing quartz present or absent with glass in quenched charges at 700 to 1000 c quartz solubility increases at an accelerating rate from 1 2 mol to 8 9 mol sio 2 above 1000 c there is a sharp increase to nearly equimolar fluids in equilibrium with quartz at 1080 c at t 1080 c sio 2 concentration increases less strongly the data confirm the existence of a critical end point on the hydrous melting curve of quartz and imply it lies at 1080 c and 9 5 10 kbar two independent approaches to calculating sio 2 activity at 1080 c from a mixing model for aqueous sio 2 extrapolated from lower temperatures and from depression of the melting temperature of quartz by h 2 o indicate nearly constant values over the wide compositional range of 20 60 mol sio 2 the activity of h 2 o a h at the same conditions calculated by integration of the gibbs duhem relation shows a plateau of very high a h 0 93 in the same broad composition range at 60 mol there is an abrupt change in h 2 o dissolution mechanism as sio 2 activity becomes proportional to its mole fraction at high silica concentration the activity concentration relations at 1080 c and 10 kbar were fitted to a subregular solution model giving interchange energies for sio 2 and h 2 o of respectively 25 3 and 14 3 kj mol roughly constant sio 2 activity of the near critical fluid despite a factor of 3 increase in x h2o can be explained by progressively greater amounts of hydrogen bonding of h 2 o molecules to polymerized silica units so that the effective concentration of these units remains nearly constant as h 2 o increases the sudden onset of critical phenomena in the system sio 2 h 2 o as temperature and pressure increase over narrow intervals approaching 1080 c and 10 kbar is thus explained as mainly a convergent or cooperative compositional effect in which polymerization and hydrogen bonding both play important roles

unstable forearc stress in the eastern nankai subduction zone for the last 2 million years abstract transpressional tectonics characterizes the sw japan arc however we will show in this article that offshore seismic profiles and onshore mesoscale faults indicate that the eastern part of the forearc was subject to transtensional tectonics since ca 2 0 ma offshore normal faults imaged on the profiles run parallel to the nankai trough and started activity at 1 0 ma but transtensional tectonics commenced the onshore area earlier in order to understand the stress history in the forearc region we collected fault slip data from onshore mesoscale faults in plio pleistocene sedimentary rocks in the kakegawa area at the northeastern extension of the offshore normal faults most of the mesoscale faults are oblique normal indicating that the area was subject to transtensional tectonics the faults suggest that the compressional tectonic regime was followed by the transtensional one at 2 0 ma in agreement with regional tectonostratigraphic data which indicate that folding ceased at that time present compressional stress followed the transtensional tectonic regime sometime in the late pleistocene transtensional or extensional tectonic zone shifted from the kakegawa area to the offshore region these observations indicate that the state of stress just behind the accretionary prism of the eastern nankai subduction zone has been unstable in the last 2 million years suggesting that the forearc wedge has been at critical state in that gravitational force and basal shear traction on the wedge have been balanced but the forearc tectonics has been susceptible to small perturbations possible factors compatible with the observed stress history include the change of subduction direction of the plate at 1 0 ma and the rapid uplift of central japan thereafter

structure and development of the sagami trough and the boso triple junction abstract the sagami trough is located at the particular plate margin where the izu forearc is subducted underneath the honshu forearc at its southeastern end the world s only known ttt type triple junction boso triple junction has developed several different kinds of basins occur in different segments along the sagami trough and at the triple junction the bathymetric geologic and geophysical data obtained during the kaiko project and from additional studies are summarized together with our onland studies we suggest that the right lateral oblique plate motion formed an eduction margin in the sagami basin while a normal subduction margin and an oblique subduction margin have been formed in the middle sagami trough basin these tectonic phenomena resulted from the long lasting compressional covergence between the philippine sea plate and eurasian plate since the early or middle miocene the north basin on the northeasternmost margin of the philippine sea plate near the boso triple junction has developed as a stretched basin due to the westward motion of the philippine sea plate with respect to the eurasian plate

strontium isotope geochemistry of groundwaters and streams affected by agriculture locust grove md the effects of agriculture on the isotope geochemistry of sr were investigated in two small watersheds in the atlantic coastal plain of maryland stratified shallow oxic groundwaters in both watersheds contained a retrievable record of increasing recharge rates of chemicals including no3 cl mg ca and sr that were correlated with increasing fertilizer use between about 1940 and 1990 the component of sr associated with recent agricultural recharge was relatively radiogenic 87sr 86sr 0 715 and it was overwhelming with respect to sr acquired naturally by water rock interactions in the oxidized non calcareous portion of the saturated zone agricultural groundwaters that penetrated relatively unoxidized calcareous glauconitic sediments at depth acquired an additional component of sr from dissolution of early tertiary marine caco3 87sr 86sr 0 708 while undergoing o2 reduction and denitrification ground water discharge contained mixtures of waters of various ages and redox states two streams draining the area are considered to have higher 87sr 86sr ratios and no3 concentrations than they would in the absence of agriculture however the streams have consistently different 87sr 86sr ratios and no3 concentrations because the average depth to calcareous reducing denitrifying sediments in the local groundwater flow system was different in the two watersheds the results of this study indicate that agriculture can alter significantly the isotope geochemistry of sr in aquifers and streams and that the effects could vary depending on the types sources and amounts of fertilizers added the history of fertilizer use and groundwater residence times

the mississippi valley type fluorite ore at jebel stah zaghouan district north eastern tunisia contribution of ree and sr isotope geochemistries to the genetic model abstract the fluorite district of zaghouan north eastern tunisia is characterized by f ba pb zn ore deposits mineralization occurs within stratabound to stratiform bodies either within jurassic back reef limestone uplifted blocks or along unconformity surfaces that separate them from the overlying sequence fluorite mineralization also occurs within fractures crosscutting the uplifted limestone blocks and their overburden despite the similarity of the liassic series throughout the major part of the district stratabound fluorite deposits formed subsequent to a strong epigenetic dolomitization souissi et al 1998 and occurring along the lower middle liassic unconformity are known only at jebel stah and at the adjacent jebel kohol four petrographic types of fluorite are recognized the finely laminated karst deposits fl1a the macrogranular fluorite fl1b resulting from the recrystallization of fl1a and the megacrystalline fluorite fl2 associated to calcite in lodes and fluorite in geodes fl3 this study gives new arguments in terms of the genetic model of the fluorite ore of jebel stah and by using trace metal elements mte rare earth elements ree and sr isotope geochemistry the mte geochemistry shows that the epigenetic dolomites and the fluorite fl1a bear higher concentrations in mn and zn with respect to the fluorites fl1b fl2 and fl3 while the latter are depleted in all mte but enriched in co the similarity of their ree patterns indicates that the latter are coeval and that fl1a fluorite may be considered as the early ore generation the same argument confirms that this geochemical imprint has been inherited from a hydrothermal fluid that had remained in equilibrium with shales at depth fluorite deposition appears related to an oxidized fluid derived from a sedimentary basin fluid circulation may have been triggered in response to hydraulic fracturing within a high geothermal gradient setting especially along the major structural trends fl1b fl2 and fl3 fluorites have been generated from the residual fraction of the ore fluid at later stages of mineralization and in a closed system both mineralization and the epigenetic dolomites are characterized by sr isotope ratios that are higher than the barren lower middle liassic rocks indicating that the sr cannot be derived from the wallrocks however these ratios are higher than the triassic seawater yet consistent with those of the paleozoic period thus the fluorite ore of jebel stah is believed to be remobilized from primary ore deposits which are suspected to be hosted in the late series within this period

philippine sea and east asian plate tectonics since 52 ma constrained by new subducted slab reconstruction methods we reconstructed philippine sea and east asian plate tectonics since 52 ma from 28 slabs mapped in 3 d from global tomography with a subducted area of 25 of present day global oceanic lithosphere slab constraints include subducted parts of existing pacific indian and philippine sea oceans plus wholly subducted proto south china sea and newly discovered east asian sea mapped slabs were unfolded and restored to the earth surface using three methodologies and input to globally consistent plate reconstructions important constraints include the following 1 the ryukyu slab is 1000 km n s too short to account for 20 philippine sea northward motion from paleolatitudes 2 the marianas pacific subduction zone was at its present location 200 km since 48 10 ma based on a 1000 km deep slab wall 3 the 8000 2500 km east asian sea existed between the pacific and indian oceans at 52 ma based on lower mantle flat slabs 4 the caroline back arc basin moved with the pacific based on the overlapping coeval caroline hot spot track these new constraints allow two classes of philippine sea plate models which we compared to paleomagnetic and geologic data our preferred model involves philippine sea nucleation above the manus plume 0 150 e near the pacific east asian sea plate boundary large philippine sea westward motion and post 40 ma maximum 80 clockwise rotation accompanied late eocene oligocene collision with the caroline pacific plate the philippine sea moved northward post 25 ma over the northern east asian sea forming a northern philippine sea arc that collided with the sw japan ryukyu margin in the miocene 20 14 ma

the solubility of apatite in h 2 o kcl h 2 o nacl h 2 o at 800 c and 1 0 gpa implications for ree mobility in high grade saline brines abstract apatite is an important host for lree f and cl and thus can be used to monitor elemental mass transfer in high p t settings in this investigation the solubilities of synthetic fluor and chlorapatite and natural durango fluorapatite were measured in h2o kcl h2o and nacl h2o fluids at 800 c and 1 0 gpa using the piston cylinder apparatus the solubility of apatite is reported in parts million by weight ppm and is calculated via the formula map map h2o kcl or nacl map 106 where map map in map out the experimental results indicate a strong increase in apatite solubility in aqueous fluids with moderate kcl and nacl mole fractions xkcl and xnacl under all conditions synthetic fluorapatite and synthetic chlorapatite dissolve congruently the solubility of synthetic fluorapatite increases from 19 ppm in pure h2o to 2123 ppm at xkcl 0 52 the solubility of synthetic chlorapatite rises from 37 ppm in pure h2o to 2590 ppm at xkcl 0 50 at xkcl 0 5 the solubility of synthetic fluorapatite decreases to 1691 xkcl 0 72 and the solubility of synthetic chlorapatite decreases to 2284 ppm xkcl 0 65 in contrast natural durango fluorapatite dissolves incongruently at xkcl 0 2 the solubility of natural durango fluorapatite increases from 70 ppm in pure h2o to 2073 ppm at xkcl 0 50 respectively in contrast to the kcl h2o system apatite solubilities are considerably higher in the nacl h2o system the solubility of synthetic fluorapatite increases to 4909 ppm at xnacl 0 51 and the solubility of synthetic chlorapatite rises to 5144 ppm at xnacl 0 50 compared to fluorite calcite and anhydrite apatite solubility is significantly lower in h2o nacl h2o and kcl h2o after completion of each experiment the ph was measured and a comprehensive step by step procedure limiting reactant concept was used to model the observed quench ph in the system apatite kcl h2o

tectonic evolution of the japanese islands as reflected in modal compositions of cenozoic forearc and backarc sand and sandstone cenozoic tectonic evolution of the japanese rifted continental arc trench system is reflected in the detrital modes of sand and sandstone deposited in forearc and backarc basins sampled by the deep sea drilling project at present the japan arc is divided into two segments along a complex plate boundary where the izu bonin ridge intersects the japan arc creating two triple junctions in front of and behind the ridge southwest of the izu bonin ridge quartzofeldspathic cretaceous forearc sediments were uplifted and recycled into tertiary forearc deposits in response to strike slip movement associated with backarc spreading in the shikoku basin quaternary forearc sections record the first major influx of volcanic detritus to southwest japan sites triple junction related deformation in central honshu has produced sand of mixed volcanic sedimentary provenance which is funneled by the suruga canyon into the nankai trough along the southwest japan margin north of the triple junction oligo miocene forearc sand compositions indicate oligocene forearc uplift and volcanism possibly related to initial backarc rifting and formation of the japan sea and subsequent miocene exposure of arc basement in contrast pliocene and quaternary forearc sand from northeast japan is primarily volcaniclastic and documents uninterrupted arc volcanism within the backarc region sand compositions vary from east to west across the japan sea the asian rifted continental margin and submerged remnants shed quartzofeldspathic sand into the western side of the basin whereas the japan arc sheds volcaniclastic sand into the eastern side of the basin

origin and age of rift related fluorite and manganese deposits from the san rafael massif argentina abstract the san rafael massif is characterized by widespread fluorite and manganese epithermal ore deposits whose origin has been under debate to the present isotopic sm nd and k ar and geochemical trace elements and ree data of fluorite and manganese ore allowed to establish the age and genesis of the deposits and to propose a regional genetic model the fluorite deposits were formed during the upper triassic lower jurassic as a result of the triassic rifting that launched a hydrothermal activity at regional scale the hydrothermal fluids had low t and high fo2 with fluorine probably derived from a mantle source and ree scavenged from the volcanics of the gondwanan choiyoi magmatic cycle upper section the manganese deposits were formed by oxidizing hydrothermal fluids that collected mn from deep sources and also leached ree from the upper section of the choiyoi magmatic cycle during two mineralization episodes one episode was linked to the rift tectonic setting that remained active up to the upper cretaceous and the other was related to an early miocene back arc extensional geodynamic setting both manganese and fluorite deposits were formed in extensional tectonic settings within an epithermal environment near the surface and can be ascribed to the general model of detachment related deposits

the use of strontium and lead isotopes to identify sources of water beneath the fresh kills landfill staten island new york usa abstract a study was undertaken to explore whether the isotopic compositions of pb and sr are useful to distinguish mixtures of uncontaminated groundwater seawater and landfill leachate at the fresh kills landfill staten island new york ratios of 87sr 86sr ranged from 0 7088 to 0 7137 and could be used to distinguish sr that was derived from seawater from that in uncontaminated groundwater lead isotopic abundances did not vary systematically among the different water sources plots of 87sr 86sr versus dissolved organic c b and nh4 defined perpendicular trends documenting where leachate or sea water mixed with uncontaminated groundwater and demonstrating that leachate has not contaminated groundwater in aquifers beneath the landfill

solubility of anhydrite caso4 in nacl h2o solutions at high pressures and temperatures applications to fluid rock interaction anhydrite solubility in h2o nacl solutions was measured at 6 14 kbar 600 800 c and nacl mole fractions xnacl of 0 0 3 in piston cylinder apparatus solubilities were determined by weight changes of natural anhydrite in perforated pt envelopes confined with fluid in larger pt capsules in initially pure h2o at 10 kbar and 800 c caso4 concentration is low 0 03molal though much larger than at the same temperature and 1 kbar hematite buffered experiments showed slightly lower solubilities than unbuffered runs caso4 solubility increases enormously with nacl activity at 800 c and 10 kbar and xnacl of 0 3 caso4 molality is 200 times higher than with pure h2o whereas caso4 solubility in pure h2o decreases with rising t at low t and p the high p results show that anhydrite solubility increases with t at constant p at all xnacl investigated the effects of salinity and temperature are so great at 10 kbar that critical mixing between sulfate rich hydrosaline melts and aqueous salt solutions is probable at 900 c at xnacl 0 3 recent experimental evidence that volatile laden magmas crystallizing in the deep crust may evolve concentrated salt solutions could in light of the present work have important implications regarding such diverse processes as mount pinatubo type s rich volcanism high fo2 regional metamorphism and emplacement of porphyry cu mo ore bodies where anhydrite hematite alteration and fluid inclusions reveal the action of very oxidized saline solutions rich in sulfur

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

strontium isotope geochemistry of groundwater in the central part of the dakota great plains aquifer usa abstract the dakota aquifer of the central and eastern great plains of the united states is an important source of water for municipal supplies irrigation and industrial use although the regional flow system can be characterized generally as east to northeasterly from the rocky mountains towards the missouri river locally the flow systems are hydrologically complex this study uses sr isotopic data from groundwater and leached aquifer samples to document the complex subsystems within the dakota aquifer in nebraska and kansas the interaction of groundwater with the geologic material through which it flows has created spatial patterns in the isotopic measurements that are related to long term water rock interaction during which varying degrees of isotopic equilibrium between water and rock has been achieved and the alteration of nacl fluids by water rock interaction specifically sr isotopic data distinguish brines from kansas and western nebraska from those in eastern nebraska the former are interpreted to reflect interaction with permian rocks whereas the latter record interaction with pennsylvanian rocks the sr isotopic composition of groundwater from other parts of nebraska and kansas are a function of the dynamic interaction between groundwater and unlithified sediments e g glacial till and loess followed by interaction with oxidized and unoxidized sediments within the dakota formation this study illustrates the power of combining sr chemistry with more conventional geochemical data to obtain a more complete understanding of groundwater flow systems within regional aquifer systems where extensive monitoring networks do not exist

tectonic evolution of the triple junction off central honshu for the past 1 million years seno t ogawa y tokuyama h nishiyama e and taira a 1989 tectonic evolution of the triple junction off central honshu for the past 1 million years in j p cadet and s uyeda editors subduction zones the kaiko project tectonophysics 160 91 116 we discuss several models of the evolution of the trench trench trench triple junction off central honshu during the past 1 m y on the basis of plate kinematics morphology gravity and seismic reflection profile data available for the area the study area is characterized by large basins 7 8 km deep on the inner lower trench slope on the philippine sea side and the deep 9 km izu bonin trench to the east between the basins and the trench there are 6 7 km deep basement highs the triple junction is unstable due to the movement of the philippine sea plate at a velocity of 3 cm yr in wnw direction with respect to eurasia northeast japan subparallel to the strike of the sagami trough generally we can expect the boundary area between the philippine sea and pacific plates to be extended because the pacific plate is unlikely to follow the retreating philippine sea plate due to the obstruction of the southeastern comer of eurasia the above peculiar morphology of the junction area could have resulted from this lack of stability however there are several possible ways to explain the above morphology our gravity model across the trench basement high basin area shows that the basement highs are made of low density materials 1 8 2 g cm3 thus we reject the mantle diapir model which proposes that the basement highs have been formed by diapiric injection of serpentinites between the retreating philippine sea plate and the pacific plate the stretched basin model proposes that the basins have been formed by stretching of the philippine sea plate wedge we estimated the extension to be about 10 km at the largest basin we reconstructed the morphology at 1 ma by moving the philippine sea plate 20 km farther to the east after closing the basins and thus obtained 8 km depth of the 1 ma trench which is similar to that of the present japan trench to the north although this stretched basin model can explain the formation of the basins and the deep trench other models are equally possible for instance the eduction model explains the origin of the basin by the eduction of the philippine sea basement from beneath the basement high while the accretion model explains the basement highs by the accretion of the in bonin trench wedge sediments in both of these models we can reconstruct the 1 ma trench depth as about 8 km similar to that of the stretched basin model the deformation of the basement of the basins constitutes the best criterion to differentiate between these models the multi channel seismic reflection profiles show that the basement of the largest basin is cut by normal faults in particular at its eastern edge this suggests that the stretched basin model is most likely however the upper part of the sediments shows that the basement high to the east has been recently uplifted this uplift is probably due to the recent 0 5 ma start of accretion of the trench wedge sediments beneath this basement high

active right lateral strike slip fault zone along the southern margin of the japan sea abstract we describe an active right lateral strike slip fault zone along the southern margin of the japan sea named the southern japan sea fault zone sjsfz onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features whereas the offshore parts are interpreted from single multichannel seismic data combined with borehole information in an effort to evaluate late quaternary activity along the fault zone four active segments separated by uplifting structures are identified in this study the east northeast trending sjsfz constitutes paired arc parallel strike slip faults together with the median tectonic line mtl both of which have been activated by oblique subduction of the philippine sea plate during the quaternary they act as the boundaries of three neotectonic stress domains around the eastern margin of the eurasian plate the near trench outer zone and nw se compressive inner zone of southwest japan arc and the southern japan sea deformed under e w compression from south to north

petroleum migration fluid mixing and halokinesis as the main ore forming processes at the peridiapiric jbel tirremi fluorite barite hydrothermal deposit northeastern morocco the jbel tirremi fluorite barite sulfide deposit in northeastern morocco is hosted in a jurassic aged structurally high carbonate platform known as the jbel tirremi dome the host rocks consist of unmetamorphosed flat lying early jurassic dolomitized limestones locally intruded by eocene lamprophyre dikes the orebodies consist mostly of fluorite and barite and occur as open space fillings and partial to massive replacement of the enclosing medium to coarse grained dolomitized limestones the ore mineralogy is dominated by fluorite of different colors and habits barite and to a lesser extent sulfides rare earth element compositions along with fluid inclusion halogen and isotopic data suggest that the fluorite barite mineralization and the spatially associated eocene alkaline magmatism are petrogenetically unrelated pointing instead to the regional circulation of hydrothermal basinal brines mixed to various degrees with meteoric water in a dominantly closed rock buffered system at progressively higher temperatures and fluid rock ratios in this respect fluid inclusion microthermometric measurements show that the ore bearing hydrothermal system developed in two separate stages of fluorite barite mineralization as also revealed by isotopic data both stages precipitated from saline fluids at shallow crustal levels i e 82 degrees c and possibly up to 218 degrees c whereas in the second stage the mineralizing fluid had a similar temperature range but lower salinities similar to 20 10 wt nacl equiv the recorded high salinities are interpreted to represent the involvement of a mixture of halite dissolution water and evaporated seawater component oxygen delta o 18 21 7 to 29 6 0 v smow and carbon delta c 13 7 9 to 0 2 0 v pdb isotope data along with strontium sr 87 sr 86 0 70300 070789 and lead pb 206 pb 204 17 961 20 96 pb 207 pb 204 15 511 15 697 pb 208 pb 204 37 784 39 993 isotope ratios suggest the involvement of a mixture of oil bearing fluids basinal brines and meteoric fluids that interacted extensively with the early jurassic host carbonates the underlying triassic salt bearing diapir associated siliciclastic rocks and the highly fractionated and greisenized hercynian granitic crystalline basement resulting in the release of fluoride metals and other constituents to form the jbel tirremi deposit petroleum bearing fluid released from overpressured portions of the guercif basin at lithostatic pressures and bittern brines dominated the first stage of mineralization mixing of saline oxidized cacl2 and sulfate rich bittern brine with oil bearing fluid resulted in fluorite precipitation of stage i conversely during the second stage of mineralization the hydrothermal system was open to the influx of oxidized meteoric water as a consequence of the upward migration of the triassic salt bearing diapir and associated pressure decrease the shift from stage i to stage ii is associated with the evolution of the system from lithostatic to mostly hydrostatic pressure conditions stage i mineralization is thought to have occurred during the late miocene in response to rapid sedimentation and high subsidence rates and subsequent hydrocarbon migration associated with the outward migration of the rif thrust front conversely stage ii mineralization occurred coevally with the uplift phase during tortonian time

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

the solubility of cepo4 monazite and ypo4 xenotime in kcl h2o fluids at 800 c and 1 0 gpa implications for ree transport in high grade crustal fluids

the solubility of fluorite in h2o and h2o nacl at high pressure and temperature abstract the solubility of fluorite in h2o and h2o nacl has been measured at 600 1000 c 0 5 2 0 gpa in a piston cylinder apparatus fluorite dissolves congruently at all conditions investigated the data indicate that the concentration of fluorite dissolved in h2o is low at 600 c and 0 5 gpa 0 0014 mol kg h2o but increases strongly with temperature t and pressure p to 0 247 mol kg h2o at 1000 c 2 gpa the data were fit with the equation log mcaf2 6 587 2 774p1 2 2 266 10 3 4 699 10 4p t where mcaf2 is molality of caf2 t is in kelvin and p is in gpa fluorite solubility was also measured in h2o nacl fluids at 800 c and 1 0 gpa results indicate a strong increase in dissolved fluorite concentration with increasing nacl content from 0 028 mol kg h2o at xnacl 0 to 1 673 mol kg h2o at xnacl 0 486 where xnacl is the mole fraction of nacl in the fluid the data were fit to mcaf2 0 01035 1 141xnacl 4 694xnacl2 the results indicate that f mobility will be further enhanced by saline brines in high p t igneous and metamorphic environments high f solubility in h2o and h2o nacl in the deep crust and upper mantle can promote mobilization of high field strength elements rare earth elements u and th through transport as f bearing complexes

halogen chemistry as an indicator of metamorphic fluid interaction with the ponder pluton coast plutonic complex british columbia canada during hydrothermal fluid activity associated with the intrusion of the ponder pluton coast plutonic complex british columbia canada the halogen composition of biotite amphibole and apatite is controlled by the composition of the metamorphic fluid the core of the pluton was not affected by infiltrating fluids and the fluorine composition of biotite was controlled by the biotite fe mg ratio the edge of the cooling crystallized pluton interacted with a chlorine rich fluorine poor fluid which changed the halogen composition of biotite and amphibole the composition of the metamorphic fluid derived from biotite and apatite compositions was relatively high in chlorine and low in fluorine the concentration of chlorine in the metamorphic fluid increases towards the pluton whereas fluorine remains constant this suggests that the metamorphic fluid near the pluton had the greatest potential for masstransfer of metals

tectonic record of convergence changes in a collision area the boso and miura peninsulas central japan abstract late cenozoic formations in boso and miura have been affected by several tectonic events tectonic analysis enables us to reconstruct six different paleostress types 1 early extension affecting the oligocene early miocene mineoka group 2 and 3 relatively minor compressional and extensional events probably early pliocene in age 4 major nne ssw compression dominating prior to 2 or 3 ma ago and 5 and 6 more recent major nnw sse compression to the west and wnw ese extension to the east both types affecting the pleistocene and prevailing since 1 2 ma ago the counterclockwise change from nne ssw to nnw sse compression is not accurately dated but very likely occurred between 2 and 3 ma ago it is compared to similar evolutions in other areas of the izu collision zone we conclude that it corresponds to a major counterclockwise change in the direction of plate convergence from sse nnw to se nw the relationships between the directions of convergence and the distributions of plio quaternary compressional paleostresses in and around the collision zone are described through a simple analogy for the two stages of plio quaternary collision this counterclockwise change in stress fields and relative motions also described in the taiwan collision zone along the same philippine sea plate eurasia boundary is interpreted as a major event at the scale of the plate the possible significances of the other paleostress types identified in boso are discussed we conclude that tectonic analysis in and along collision boundaries provides a key for understanding kinematic evolution

subduction process of the philippine sea plate off the kanto district central japan as revealed by plate structure and repeating earthquakes abstract the structure of the philippine sea plate in the offshore region adjacent to the boso peninsula in central japan is resolved by comparison of recent oceanic seismic survey data with natural repeating earthquake data this region is characterized by a range of seismic and aseismic phenomena associated with subduction motion of the philippine sea plate including slow slip events sses large backslip events and repeating earthquakes this offshore region is also the site of the largest aftershock of the 1923 kanto earthquake m7 9 the detailed structure of the philippine sea plate is successfully resolved and the upper boundary of plate is clearly traceable to depths of 20 km the reflection intensity of the upper boundary varies spatially in accordance with the depth of the reflector the upper boundary continues smoothly with a line of repeating earthquake hypocenters regarded as an indicator of subduction shear a continuous model extending into the offshore region can thus be proposed the variation in reflection intensity on the upper boundary of the philippine sea plate also correlates well with variation in event types a weak reflection zone overlaps the area of large backslip while a moderately strong reflection zone encroaches into the large slip area of the boso sse the reflectivity of the upper boundary is thus considered to be dependent on the physical properties and conditions of the reflector which in turn affect the event types on the plate boundary a source fault model is proposed for the largest aftershock of the 1923 kanto earthquake based on geodetic data the source fault is located eastward of the mainshock with dimensions of 40 50 km and moment magnitude of 7 5 the source fault lies within the region of large backslip and the large slip area of the boso sse

collision of the izu block with central japan during the quaternary and geological evolution of the ashigara area abstract the ashigara area is located in the northern part of the izu collision zone and has been suspected as a possible location of the boundary between the eurasian and the philippine sea plates in order to analyse its evolution during the collision we have determined the age of the ashigara group and studied its depositional environments and its deformation the age of the ashigara group is early to middle pleistocene the lower part was deposited in a 1000 2000 m deep trough which lay between the izu peninsula and central japan at that time the sedimentary facies show subsequent upward coarsening and shallowing the beginning of the collision resulted in the uplift of the tanzawa mountains which are the source of the voluminous conglomerates deposited in this area soon after the deposition of the upper part of the ashigara group this area was over thrust by the tunzawa mountains along the kannawa fault and strongly folded under a nw se compressional stress field then about 0 3 ma ago the direction of compression drastically changed to n s or ne sw when the colliding izu peninsula was finally locked against central japan

continental margin tectonics forearc processes recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of u s research from the period 1987 1990 topics addressed include the geometry of accretionary prisms coulomb wedge taper and vertical motion in response to tectonic processes offscraping vs underplating or subduction the response to oblique convergence fluids in forearc settings the thermal framework and the effects of fluid advection and serpentinite seamounts also included is a comprehensive bibliography for the period

sources of sulfur in the nandong underground river system southwest china a chemical and isotopic reconnaissance abstract sulfur isotopic compositions 34s and major ions were measured in groundwater and surface waters in order to elucidate the source s of elevated so 4 2 content in some of these waters in the nandong underground river system nurs located in an agricultural and urbanization dominated area in sw china the major chemical composition of analyzed groundwater and surface water from nurs was characterized by ca hco3 or ca mg hco3 type in forested and grass land areas and ca cl no3 so4 or ca mg cl no3 so4 type in urban and agricultural areas respectively the anomalously high so 4 2 concentrations in waters collected from urban and agricultural areas indicated a likely anthropogenic origin for so 4 2 the groundwater collected from forested and grass land areas was characterized by relatively low 34 s so 4 2 from 1 7 to 4 3 and low so 4 2 concentrations of less than 10 mg l 1 consistent with an origin for so 4 2 in these waters from a mixture of rainfall derived so 4 2 and so 4 2 from oxidation of bedrock sulfide high so 4 2 groundwater and surface water 20 mg l 1 collected from urban areas was characterized by elevated 34 s so 4 2 from 8 3 to 12 1 compared to lower 34 s so 4 2 in samples from cultivated land areas 3 7 to 6 4 indicating that the so 4 2 in these two groups of waters resulted from different anthropogenic sources the s isotopic composition of so 4 2 in urban areas is consistent with addition of so 4 2 from detergent sewage whilst in cultivated land areas isotope composition indicates that additional so 4 2 could be derived from fertilizers and or increased oxidation of sulfide

solubility of cepo4 monazite and ypo4 xenotime in h2o and h2o nacl at 800 c and 1 gpa implications for ree and y transport during high grade metamorphism abstract monazite and xenotime are important accessory minerals in metasediments because they host ree and are useful for geochronology and geothermometry it is therefore essential to understand their behavior during metasomatic processes that attend metamorphism and subduction in order to constrain the solubility of monazite and ypo 4 xenotime at high pressure and temperature we carried out weight loss experiments on synthetic single crystals of cepo 4 monazite and ypo 4 xenotime using hydrothermal piston cylinder methods at 800 c and 1 gpa in h 2 o and h 2 o nacl fluids results indicate that cepo 4 and ypo 4 dissolved congruently and that their solubilities in pure h 2 o are very low 0 04 0 04 and 0 25 millimolal respectively the solubility of cepo 4 rises to an increasing extent with added nacl to 7 94 0 07 millimolal at 50 mol nacl in contrast the solubility of ypo 4 rises to a decreasing degree with increasing nacl to 4 36 0 08 millimolal at 50 mol nacl best fit equations for the solubilities of the two phases are m cepo 4 3 56 10 5 5 82 10 3 x nacl 1 97 10 2 x 2 nacl and m ypo 4 2 48 10 4 1 26 10 2 x nacl 8 89 10 3 x 2 nacl the solubility of ypo 4 is greater than that of cepo 4 at nacl mole fractions x nacl of 0 00 0 27 the solubility enhancement behavior implies that ce dissolves as anhydrous chloride complexes whereas y forms mixed cl oh solutes the results provide a simple mechanism for redistributing ree and y in deep crustal and upper mantle environments the h 2 o ce ratio inferred for subduction zone melts and silicate rich fluids can also be produced by a cepo 4 saturated fluid with x nacl 0 1 in addition neutral ph h 2 o nacl fluids can transport substantial ree and y obviating the need to invoke highly acid solutions in environments where they are unlikely

earthquake doublet in an active shear zone southwest japan constraints from geophysical and geochemical findings abstract in 1997 the kagoshima earthquake doublet consisting of two closely associated mw 6 strike slip events five km and 48 days apart has occurred in southwest japan the location is where an e w trending discontinuity along 32 n latitude on southern kyushu island is clearly defined in gps velocities indicating the presence of a highly active left lateral shear zone however there have not been any obvious indications of active faulting at the surface prior to the earthquake doublet which could be associated with this shear zone three dimensional inversion of magnetotelluric sounding data obtained in the source region of the earthquake doublet reveals a near vertical conductive zone with a width of 20 km extending down to the base of the crust and perhaps into the upper mantle toward the okinawa trough the prominent conductor corresponds to the western part of the active shear zone elevated 3 he 4 he ratios in groundwaters sampled from hot spring and drinking water wells suggest the emission of mantle derived helium from the seismic source region the geophysical and geochemical observations are significant indications that the invasion of mantle fluids into the crust driven by upwelling asthenosphere from the okinawa trough triggers the notable left lateral shearing in the zone in the present day subduction system in addition the existence of aqueous fluids in and below the seismogenic layer could change the strength of the zones and alter the local stress regime resulting in the occurrence of the 1997 earthquake doublet

sources of sr and implications for weathering of limestone under tallgrass prairie northeastern kansas abstract grasslands of north central kansas are underlain by carbonate aquifers and shale aquitards chemical weathering rates in carbonates are poorly known and because large areas are underlain by these rocks solute fluxes are important to estimating global weathering rates grasslands exist where the amount of precipitation is extremely variable both within and between years so studies in grasslands must account for changes in weathering that accompany changes in precipitation this study 1 identifies phases that dominate chemical fluxes at konza prairie biological station kpbs and long term ecological research site and 2 addresses the impact of variable precipitation on mineral weathering the study site is a remnant tallgrass prairie in the central usa representing baseline weathering in a mid temperate climate grassland groundwater chemistry and hydrology in the 1 2 km 2 watershed used for this study suggest close connections between groundwater and surface water water levels fluctuate seasonally high water levels coincide with periods of precipitation plus low evapotranspiration rather than during precipitation peaks during the growing season precipitation is concentrated before recharging aquifers suggesting an as yet unquantified residence time in the thin soils groundwater and surface water are oversaturated with respect to calcite within limitations of available data water is more dilute in more permeable aquifers and water from one aquifer morrill is indistinguishable from surface water cations other than ca co vary with each other especially sr and mg potassium and si co vary in all aquifers and surface water and increases in concentrations of these elements are the best indicators of silicate weathering at this study site silicate weathering indices correlate inversely to aquifer hydraulic conductivity 87 sr 86 sr in water ranges from 0 70838 to 0 70901 and it decreases with increasing sr concentration and with increasing silicate weathering index carbonate extracted from aquifer materials shales soil and tufa has sr ranging from about 240 soil to 880 ppm paleozoic limestone 87 sr 86 sr ranges from 0 70834 0 00006 limestone to 0 70904 0 00019 soil in all cases 87 sr 86 sr of aquifer limestone is lower than 87 sr 86 sr of groundwater indicating a phase in addition to aquifer carbonate is contributing solutes to water aquifer recharge controls weathering during periods of reduced recharge increased residence time increases the total amount of all phases dissolved mixing analysis using 87 sr 86 sr shows that two end members are sufficient to explain sources of dissolved sr it is proposed that the less radiogenic end member is a solution derived from dissolving aquifer material longer residence time increases its contribution the more radiogenic end member solution probably results from reaction with soil carbonate or eolian dust this solution dominates solute flux in all but the least permeable aquifer and demonstrates the importance that land surface and soil zone reactions have on groundwater chemistry in a carbonate terrain

trench triple junction off central japan preliminary results of french japanese 1984 kaiko cruise leg 2 abstract leg 2 of the french japanese 1984 kaiko cruise has surveyed the trench triple junction off central japan where the japan izu bonin and sagami trenches intersect the izu bonin trench is deeper than the japan trench and filled by a thick turbiditic series its anomalous depth is explained by the westward retreat of the edge of the northwestward moving philippine sea plate on the contrary to what happens in the japan trench horst and graben structures of the pacific plate obliquely enters the izu bonin trench suggesting that the actual boundary between these two trenches is located to the north of the triple junction the inner wall of the izu bonin trench is characterized in the triple junction area by a series of slope basins whose occurrence is related to the dynamics of this area the northernmost basin is overthrust by the edge of the fore arc area of the northeast japan plate the plate boundary is hardly discernible further east which makes it impossible to locate precisely the triple junction itself these features suggest that large intra plate deformation occurs there due to the interaction of the plates involved in the triple junction and the weak mechanical strength of the wedge shaped margin of the overriding plates

release of uranium from highly radiogenic zircon through metamictization the source of orogenic uranium ores although circumstantial evidence from ore deposit mineralogy and geochemistry can imply potential sources for fluids and metals rarely is direct evidence for metal leaching from source rocks seen in the vicinity of deposits here we investigate the source of metals for a series of fault zone and shear zone hosted uranium occurrences in the mount isa inlier australia as well as containing uranium these deposits are enriched in zr and rare earth elements rees requiring that unusual fluids were responsible for addition of these typically immobile elements during the isan orogeny highly saline metamorphic fluids infiltrated the sheared margin of a highly evolved granite intrusion which contains elevated u th f zr and rees synchrotron x ray fluorescence spectroscopy and high resolution electron microprobe mineral mapping show that this radioactive element rich characteristic caused zircon crystals to become highly metamict allowing the elements therein to become mobile thus when orogenic fluids pervasively infiltrated along shear zones 100 m y after granite intrusion their unusually saline character allowed enhanced dissolution of regional carbonates and fluorite from the granite providing the ligands needed for transport of uranium and the normally immobile elements from the metamict zircons

slab rollback suggested by latest miocene to pliocene forearc stress and migration of volcanic front in southern kyushu northern ryukyu arc abstract the northern ryukyu arc has active backarc rift neutral stress forearc and active accretionary prism the okinawa trough has been shaped by the episodic rifting in the backarc paleostresses were inferred in this study from mesoscale faults in neogene forearc sediments called the miyazaki group southeast kyushu in the northern ryukyu arc the forearc stress changed from compressional to extensional from the latest miocene through early pliocene time the stress history is concordant with the transition in tectonic regime from folding to rifting in the backarc the transition in the stress state occurred simultaneously also with trenchward movement of the volcanic front these phenomena suggest that the subducting slab under southern kyushu became steeper in the early pliocene extensional tectonics ceased sometime in the late pliocene or early to mid pleistocene concordant with the counterclockwise change of subducting direction of the philippine sea plate

diamond inclusions in garnets from metamorphic rocks a new environment for diamond formation diamonds commonly occur in kimberlites lamproites and alluvial sediments derived from these rocks more recently diamonds or their graphite pseudomorphs have been discovered in ultramafic massifs1 and picrites2 here we report the occurrence of diamonds in situ in crustal rocks highly retrograded high pressure metamorphic garnet pyroxene and pyroxene carbonate garnet rocks biotite gneisses and schists from the kokchetav massif northern kazakhstan ussr the diamonds are cubo octahedral averaging 12 m in size and occur in zircons and with euhedral graphite as inclusions in unzoned garnets we believe that the zircon and garnet matrices protected these diamonds from retrogressive transformation to graphite mica rutile titanite clinopyroxene kyanite and zircon also occur as inclusions in garnet often intergrown with the diamonds equilibration relations of inclusions and host garnets indicate that both diamonds and graphite crystallized from a fluid phase under static conditions at pressures of 40 kbar and temperatures 900 1 000 c

dissolution rates and vadose zone drainage from strontium isotope measurements of groundwater in the pasco basin wa unconfined aquifer abstract strontium isotope ratios 87sr 86sr measured in groundwater samples from 273 wells in the pasco basin unconfined aquifer below the us department of energy hanford site show large and systematic variations that provide constraints on groundwater recharge weathering rates for saturated zone dissolution of the aquifer host rocks communication between unconfined and deeper confined aquifers and vadose zone groundwater interaction the impact of millions of cubic meters of wastewater discharged to the vadose zone 103 105 times higher than ambient drainage shows up strikingly on maps of groundwater 87sr 86sr extensive access through the many groundwater monitoring wells at the site allows for an unprecedented opportunity to evaluate the strontium geochemistry of a major aquifer hosted primarily in unconsolidated sediments and relate it to both long term properties and recent disturbances groundwater 87sr 86sr increases systematically from 0 707 to 0 712 from west to east across the hanford site in the general direction of groundwater flow as a result of addition of sr from the weathering of aquifer sediments and from diffuse drainage through the pasco basin vadose zone the lower 87sr 86sr groundwater reflects recharge waters that have acquired sr from columbia river basalts based on a steady state model of sr reactive transport and drainage there is an average natural drainage flux of 0 1 4 mm yr near the western margin of the hanford site and ambient drainage may be up to 30 mm yr in the center of the site assuming an average bulk rock weathering rate of 10 7 5 g g yr the weathering rates cannot be higher than those assumed by more than a factor of 2 3 in order to match sr isotope data

geochemical and isotopic characteristics of shallow groundwater within the lake qinghai catchment ne tibetan plateau abstract major ions isotopic ratios of strontium 87 sr 86 sr hydrogen d and oxygen 18 o of groundwater samples were analyzed to decipher spatial variation controlling factors solute sources and the recharge source of shallow groundwaters within the lake qinghai catchment shallow groundwaters in this area are slightly alkaline with 97 being fresh water of good quality though there are high concentrations of nitrate and sulfide in buha and lakeside groundwaters most of the shallow groundwaters are of the ca 2 hco 3 type whereas part of groundwaters surrounding the lake ls belongs to the na cl type as lake water qhl groundwater geochemistry is controlled by regional lithological association ion exchange and mineral precipitation the dissolved sr concentrations and 87 sr 86 sr ratios vary from 1 0 to 15 6 mol l and from 0 709859 to 0 715779 respectively the first quantitative calculation in groundwater using a forward model shows that 40 of dissolved sr is from carbonate weathering 33 from evaporite dissolution 17 from silicate weathering and the remainder from atmospheric input for the whole catchment carbonate weathering dominates groundwater geochemistry in shaliu sl hargai hg and buha bh samples while evaporite dissolution dominates ls and daotang dt samples d and 18 o data show that rain water is the major recharge source of both river water and shallow groundwater within the lake qinghai catchment qinghai lake water is characterized by buha type water but its sr geochemistry is different from the shallow groundwater due to carbonate precipitation although shallow groundwater contributes 5 of the dissolved sr to the qhl groundwater must be taken into account when the chemistry and budget of lake water are characterized

element and sr isotope signatures of titanite as indicator of variable fluid composition in hydrated eclogite abstract the trace element signature sr common pb u th ree and hfse of titanite gives important information about the formation process of metamorphic titanite we investigated titanite from different textural positions of a strongly retrogressed eclogite from the tromso norway high p area it shows characteristic titanite rims around partially absorbed rutile interpreted as grown during retrogression and hydration of the high p assemblage the titanite rims around rutile are polycrystalline and in contact with the plagioclase amphibole matrix large idioblastic single crystal titanite grew in veins without relics of precursor rutile compositional zoning of al ti f in titanite of both textural positions is irregular and not related to core or rim position in the crystals there is no evidence for systematic growth sequences or diffusion reflecting changing p t conditions or systematic changes of fluid composition trace element patterns of titanite la icp ms data however show systematic variations in the coupling and decoupling behaviour of strongly fluid mobile sr u moderately fluid mobile ree and little fluid mobile nb ta zr hf elements the trace element signatures of titanite from the two different fabric positions reflect contrasting characteristic fluid compositions single crystal titanite equilibrated with fluid that was channelled in the vein polycrystalline titanite on rutile records the composition of a fluid that had migrated along grain boundaries in the amphibole plagioclase matrix fluid from the matrix also contributed to the geochemical signature of vein titanite whereas influence of fluid from the vein on the composition of polycrystalline titanite in the matrix is not evident 87sr 86sr isotope ratios of the different titanite types support the inference from trace elements of spatially and temporally variable fluid sources

ti al zoning of experimentally grown titanite in the system cao al2o3 tio2 sio2 nacl h2o f evidence for small scale fluid heterogeneity chemical zoning according to the substitution al oh f ti o is a common phenomenon in natural titanite and can be used to reconstruct its growth conditions we synthesized titanite which has a zoning pattern similar to that found in natural titanite that grew at the expense of rutile visible in element distribution maps as a patchy irregular pattern run conditions in the system cao al 2 o 3 tio 2 sio 2 nacl h 2 o caf 2 were 600 c 0 4 gpa 1 to 107 days duration natural rutile crystals were placed in a perforated pt tube within an outer au capsule containing wollastonite al 2 o 3 optionally powdered caf 2 and a nacl brine to simulate conditions where rutile is transformed into titanite by a hydrous ca si al f fluid driven by a chemical potential gradient between inner and outer capsule spontaneous nucleation of titanite is restricted to a small number of crystals on the rutile surface in the inner capsule growth proceeds from sparse isolated titanite crystals after 1 day to assemblages of several 100 m large crystals in a reaction rim in the long time runs titanite is strongly zoned in al ti and shows up to 0 5 al per formula unit pfu in experiments containing f without f substitution is limited to 0 25 al pfu the range of the ti al exchange is already large in short run times and the same heterogeneity is observed in long time runs the al ti distribution with and without f in compositional domains up to several tens of micrometers is patchy and irregular no relation of the zoning with time core rim or preferred growth directions was observed in the case of fluid mediated growth mineral growth zoning represents a disequilibrium at supersaturated conditions the concentration of ti in the fluid is likely the limiting factor for titanite growth considering the low solubility compared to that of al ca and si titanium is not transported in significant amounts into the outer capsule indicating low mobility in contrast to al ca and si which are transported into the inner capsule assuming buffered al concentration from dissolution of the al source we speculate that the ti al of the fluid at the precipitation site was controlled by the local ti concentration which varies over the distance from the rutile surface to the growing titanite crystal and produces the irregular patchy zoning

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

element mobility patterns in magnetite group iocg systems the fab iocg system northwest territories canada this paper documents element mobility patterns from a magnetite group iron oxide copper gold iocg prospect in the northwest territories of canada and explores implications for space time chemical evolution of metasomatic systems hosting iocg deposits the fab system located in the great bear magmatic zone gbmz of the northwest territories canada contains numerous fe cu u showings associated with high temperature ht potassic iron alteration overprinting extensive zones of sodic to ht calcic iron alteration each hydrothermal alteration assemblage is associated with distinct element mobility patterns that record evolving physico chemical properties of the hydrothermal fluids new geochronological data constrain the alteration and iocg mineralization in the fab system to a 3 m y window between 1870 1867 ma which is broadly contemporaneous with extensive high level intrusive activity across the gbmz regional to local scale element mobility patterns characteristic of the sodic and sodic calcic iron alteration type record leaching combined with weak to strong mass losses pure sodic alteration depleted the rocks in ca co cu fe mg th u and v conversely sodic calcic iron alteration records significant depletions of nb ree ta ti th and u these element mobility patterns differ from intense ht calcic iron alteration that is enriched in ca co f fe mg mn ni and v with modest enrichments to locally significant mineralization in th u and ree ht calcic iron alteration is also characterized by substantial mass gains that translate into volume gains in stockwork zones and mass volume gains in zones of intense host rock replacement ht potassic iron alteration is characterized by enrichments in ba k ni u and v along with locally co and cu the temporal and spatial association of the fab system alteration and the emplacement of the porphyritic dacite are indicative of the predominant involvement of magmatic hydrothermal fluids the high f and cl contents of the porphyritic dacite and of the ht calcic iron alteration zones as well as nb ree ta th and ti mobility provide strong evidences of high halogen activities f and cl in the hydrothermal fluids high f and cl activities in the hydrothermal fluid are interpreted to have facilitated the mobilization of normally immobile nb ta ti th or weakly mobile elements as well as some metals e g v ni co the formation of ree fluorocarbonates and calcite in the early and incipient ht calcic iron alteration zones indicates the presence of co2 in the hydrothermal fluids weaker hfse hree and ti mobility during later ht potassic iron alteration is interpreted to reflect decreasing temperatures pressures f activities and increasing fo2 as the fluids evolved and interacted with the host rocks