lead and bromine enrichment in eclogite facies fluids extreme fractionation during lower crustal hydration hydration reactions associated with eclogite facies metamorphism of granulites in the norwegian caledonides led to the formation of saline brines with exceptional compositions primary omphacite and garnet hosted fluid inclusions from norwegian eclogites formed by hydration of granulites contain a plethora of solid phases a total of 18 different minerals have been identified in multiphase brines and 12 of these occur at the badsholmen locality in sunnfjord fluid inclusions from this locality are characterized by a high br cl mass ratio 0 03 and extreme pb enrichment as demonstrated by the presence of pb bearing daughter minerals including galena a pb cl bearing phase and a pb cl br bearing phase the fluid compositions may reflect enrichment of elements incompatible with the silicate structure during consumption of h 2 o by eclogite forming hydration reactions pb is believed to have been scavenged from the parent granulite by the increasingly saline brine during k feldspar breakdown

the relationship between riverine lithium isotope composition and silicate weathering rates in iceland abstract this study presents lithium isotope and elemental data for the dissolved phase and suspended and bedload sediments of the major icelandic rivers for the dissolved phase 7li values range between 10 1 and 23 8 while river sediments display lower and much more homogeneous values 7li 3 1 4 8 close to the composition of unweathered mid ocean ridge basalt morb high 7li values are associated with high k li na li and mg li ratios in waters draining mainly old and weathered basalt catchments whereas low 7li rivers are located in younger parts of the island simple mixing between precipitation li rich hydrothermal springs and basalt weathering is unable to explain the entire range of 7li values instead a simple model of li uptake by secondary minerals associated with clay water li isotope fractionation 7li ranging from 1 to 7 5 can explain both water and sediment 7li values a negative correlation is observed between basalt chemical erosion rates and 7li measured in icelandic rivers and an empirical law is inferred comparison with literature data suggests that this relationship may be applicable at a more global scale and if confirmed could be of particular use for estimating the evolution of continental weathering preserved in marine sedimentary records however more data are now needed for rivers draining silicates typical of the continental crust in order to refine large scale modelling

halogen contents of eclogite facies fluid inclusions and minerals caledonides western norway primary multiphase brine fluid inclusions in omphacite and garnet from low to medium temperature eclogites have been analysed for cl br i f li and so4 halogen contents and ratios provide information about trapped lower crustal fluids even though the major element na k ca contents of inclusion fluids have been modified by fluid mineral interactions and step daughter crystal formation after trapping halogens in the inclusion fluids were analysed with crush leach techniques cl br and cl i mass ratios of eclogite fluids are in the range 31 395 and 5000 33 000 respectively most fluids have a cl br ratio lower than modern seawater and a cl i ratio one order of magnitude lower than modern seawater fluids with the lowest cl br and highest cl i ratios come from an eclogite that formed by hydration of granulite facies rocks and may indicate that br and i are fractionated into hydrous minerals reconstructions indicate that the inclusion fluids originally contained 500 4000 ppm br 1 14 ppm i and 33 438 ppm li electron microprobe analyses of eclogite facies amphibole biotite phengite and apatite indicate that f and cl fractionate most strongly between phengite f cl mass ratio of 1469i1048 and fluid f cl mass ratio of 0 008 and the least between amphibole and fluid the chemical evolution of cl and br in pore fluids during hydration reactions is in many ways analogous to cl and br in seawater during evaporation the cl br ratio remains constant until the ah2o value is sufficiently lowered for cl to be removed from solution by incorporation into hydrous minerals

configuration of subducting philippine sea plate and crustal structure in the central japan region a seismic experiment with six explosive sources and 391 seismic stations was conducted in august 2001 in the central japan region the crustal velocity structure for the central part of japan and configuration of the subducting philippine sea plate were revealed a large lateral variation of the thickness of the sedimentary layer was observed and the p wave velocity values below the sedimentary layer obtained were 5 3 5 8 km s p wave velocity values for the lower part of upper crust and lower crust were estimated to be 6 0 6 4 and 6 6 6 8 km s respectively the reflected wave from the upper boundary of the subducting philippine sea plate was observed on the record sections of several shots the configuration of the subducting philippine sea slab was revealed for depths of 20 35 km the dip angle of the philippine sea plate was estimated to be 268 for a depth range of about 20 26 km below this depth the upper boundary of the subducting philippine sea plate is distorted over a depth range of 26 33 km a large variation of the reflected wave amplitude with depth along the subducting plate was observed at a depth of about 20 26 km the amplitude of the reflected wave is not large and is explained by the reflected wave at the upper boundary of the subducting oceanic crust however the reflected wave from reflection points deeper than 26 km showed a large amplitude that cannot be explained by several reliable velocity models some unique seismic structures have to be considered to explain the observed data such unique structures will provide important information to know the mechanism of inter plate earthquakes d 2004 elsevier b v all rights reserved

source mechanism of a very long period event at mt ontake central japan response of a hydrothermal system to magma intrusion beneath the summit abstract a very long period vlp volcanic event which occurred on 25 january 2007 beneath mt ontake central japan was recorded by nearby broadband seismometers as well as the japanese nationwide hi net and f net seismic networks the vlp waveforms show a pulse like shape with a duration of approximately 1 min the vlp event was accompanied by a burst sequence of long period lp events we carried out waveform inversion to determine the source mechanism and location of the vlp event our analysis indicates volumetric changes in an inclined crack seismic moment of 10 14 nm at the vlp source which is located at 0 6 km above sea level beneath the summit of mt ontake and above dikes determined from gps data the source time functions of the vlp event showed a pulse like triangular shape indicating inflation followed by deflation of the crack at the source we interpreted the result of the waveform inversion as follows gases released from the intruded magma heated an aquifer system beneath the summit of mt ontake a break of unstable superheated water in a hydrothermal crack in the system caused vaporization of water and associated crack inflation which was followed by discharge of steam from the crack resulting in its collapse these processes caused the vlp event which may have been a precursor of a small phreatic eruption that occurred in late march 2007

helium 3 emission related to volcanic activity the helium 3 helium 4 ratio in bubbling gases from ten hot springs located around mount ontake an active volcano in central japan ranges from 1 71 r sub atm 1 71 times the atmospheric ratio of 1 40 x 10 sup 6 to 6 15 r sub atm the value of the ratio decreases with distance from the central cone of the volcano such a tendency may be a characteristic of helium 3 emission in volcanic areas and suggests more primitive helium 3 is carried with fluid flowing through a conduit during volcanic activity 6 references 1 figure 1 table

an experimental study of alteration of oceanic crust and terrigenous sediments at moderate temperatures 51 to 350 c insights as to chemical processes in near shore ridge flank hydrothermal systems studies of hydrothermal circulation within partly buried basement on the eastern flank of the juan de fuca ridge jfr have shown that ridge flank geochemical fluxes are potentially important for the global budgets of some elements there are major uncertainties in these flux calculations however because the composition of these basement fluids is strongly dependent on temperature and because they may be modified by interaction with the overlying terrigenous sediments either by diffusive exchange with basement or during upwelling to the seafloor to better understand the nature and temperature control of basalt fluid and sediment fluid reactions at the jfr flank we have conducted laboratory experiments between 51 and 350 c and at 400 bars pressure k rb and si are leached from basalt between 150 and 351 c and sr and u are taken up the direction of exchange of li and ca with basalt varies with temperature li and sr are removed from fluid at 150 c but isotope studies show that there is simultaneous release of both elements from basalt indicating that uptake is controlled by the formation of secondary minerals moreover our experiments confirm that sr isotope exchange with oceanic crust occurs at moderate temperature and is not confined to high temperature axial hydrothermal systems our data and field data from the jdr flank indicate that uptake of u into basalt at moderate temperature could remove between 9 9 and 15 106 mol u yr 1 from the oceans this is higher than a recent estimate based on measurements of u in altered ocean crust 5 7 3 3 106 mol yr 1 which concords with arguments that the element heat ratios of jdr flank fluids are too large to be representative of average global flank fluids k ca sr ba li si and b are leached from terrigenous sediments between 51 and 350 c and u is taken up cs and rb are removed from the fluid below 100 c and leached from the sediment at higher temperature sr isotope data show that sr is preferentially mobilised from volcanic components within terrigenous sediments which may lead to an overestimation of the ridge flank sr isotope flux at the jdr if there is exchange of sediment pore fluids with basement

lithium and strontium isotopic systematics of waters around ontake volcano japan implications for deep seated fluids and earthquake swarms abstract since 1976 earthquake swarms have occurred beneath the southeast flank of ontake volcano in central japan electrical conductivity surveys have shown that these earthquake swarms are associated with the upwelling of deep seated fluid to investigate the nature of the deep seated fluid we analyzed 7 li 6 li and 87 sr 86 sr ratios of water samples collected from springs and wells around ontake volcano in 2000 2003 2005 2007 and 2009 the li and sr isotopic compositions of these water samples are largely explained by binary component mixing between near surface meteoric water and non surface fluid at each sampling site on the basis of their cl li and cl sr ratios we singled out water samples whose li and sr isotopic ratios were minimally affected by meteoric water contamination to represent non surface fluids the li and sr isotopic compositions of most ontake non surface fluids except for samples from the earthquake swarm region can be explained as the result of volcanic fluids reacting with basement rocks where they acquired upper crustal signatures we attribute the fluid associated with the region of earthquake swarms to the lower crust beneath the study area

composition of fluids in the lower crust inferred from metamorphic salt in lower crustal rocks knowledge of the rheological properties of the lower crust and the metamorphic processes that operate there is important for our understanding of orogenic processes and granite genesis the rheological properties critically depend on whether fluids are present in the lower crust1 2 and if present on their composition3 4 5 6 fluid inclusion7 8 9 and phase equilibria4 10 studies of lower crustal granulites have shown that fluids with low water activities due to the presence of dissolved components such as ch4 n2 co co2 and chlorides 11 are present at least episodically in the lower crust here we report the occurrence of a solid salt solution nacl kcl found together with chlorine rich amphibole and biotite in lower crustal granulites a desiccation mechanism explains how salt and chlorine rich minerals formed from an originally water rich fluid through a short lived series of hydration reactions in the granulites during which chlorine was progressively enriched in the fluid consequently it would appear that fluid was present in the lower crust in only small amounts and was not stable over geologically long periods of time leading to the conclusion that the lower crust is devoid of a free fluid phase during most of its history

the lithium isotopic composition of waters of the mono basin california mono lake a major closed basin alkaline salt lake in eastern california derives its water from a mixture of creeks and springs with the former providing in excess of 75 of the total the li isotopic composition of lake water has not varied significantly over a 4 year meromictic period 7li 19 5 springs are isotopically distinct groundwater springs and seeps carry water enriched in isotopically heavy li whereas thermal springs supply isotopically light 7li 50 of the li to the lake 2 the li budget is sensitively balanced on small thermal spring contributions 3 of the total spring inflow and 3 the residence time of li in the lake is 28 ka other great basin closed lakes have variable li isotopic compositions 7li from 16 7 to 23 7 all of which differ significantly from those of several major lakes and seawater homogeneously 32

temperature dependent isotopic fractionation of lithium between clinopyroxene and high pressure hydrous fluids the fractionation of lithium isotopes between synthetic spodumene as representative of li bearing clinopyroxene and cl and oh bearing aqueous fluids was experimentally determined between 500 and 900 c at 2 0 gpa in all the experiments 7li was preferentially partitioned into the fluid the fractionation is temperature dependent and approximated by the equation 7li clinopyroxene fluid 4 61 1 000 t k 2 48 r 2 0 86 significant li isotopic fractionation of about 1 0 exists even at high temperatures of 900 c using neutral and weakly basic fluids revealed that the amount of fractionation is not different the li isotopic fractionation between altered basalt and hot spring water 350 c in natural samples is in good agreement with our experimentally determined fractionation curve the data confirm earlier speculations drawn from the li isotopic record of dehydrated metamorphic rocks that fluids expelled from a dehydrating slab carry heavier li into the mantle wedge and that a light li component is introduced into the deeper mantle li and li isotopes are redistributed among wedge minerals as fluids travel across the wedge into hotter regions of arc magma production this modifies the li isotopic characteristics of slab derived fluids erasing their source memory and explains the absence of cross arc variations of li isotopes in arc basalts

seismic velocity structure of the crust beneath the japan islands abstract more than 13 000 arrival times of 562 local shallow earthquakes selected from the japan university network earthquake catalog are used to investigate the seismic velocity structure of the crust beneath the japan islands we simultaneously determined the hypocenter parameters p and s wave station corrections and depth distributions of the conrad and moho discontinuities beneath the whole of the japan islands by applying an inversion method the p and s wave station corrections show similar distribution patterns they are negative relatively late arrivals of seismic waves in hokkaido and positive relatively early arrivals of seismic waves in western japan in eastern honshu they are positive along the coast of the pacific ocean and negative in the land area and along the coast of the japan sea the conrad discontinuity is located at a depth range from 12 to 22 km in hokkaido the conrad is shallow in the eastern pan and becomes deep toward the west in ne honshu the conrad is deep beneath the land area and becomes shallow toward the surrounding seas in western japan the conrad is shallow in the northern part and becomes deep toward the south the moho is located in a depth range from 25 to 40 km in hokkaido the moho has the shape of a circular cone with a maximum depth of 36 km in most parts of the japan islands the moho is deep beneath the land area and becomes shallow toward the surrounding seas the moho is deepest up to 40 km beneath the central part of the chubu district

lithium isotope fractionation between li bearing staurolite li mica and aqueous fluids an experimental study abstract we determined the lithium isotope fractionation between synthetic li staurolite and aqueous fluids containing excess licl or lioh at 3 5 gpa between 670 and 880 c and between li mica and similar fluids at 2 0 gpa and 300 to 500 c in all experiments for the system li staurolite fluid 7 li was weakly partitioned into li staurolite whereas for li mica fluid 7 li preferentially fractionated into the fluid the difference in the li isotope fractionation behaviour results from different li coordination in staurolite li 4 and mica li 6 for the system li mica fluid fractionation is about half as large along the same t range as for spodumene fluid wunder b meixner a romer r l heinrich w 2006 t dependent isotopic fractionation of lithium between clinopyroxene and high pressure hydrous fluids contrib mineral petrol 151 112 120 this behaviour is consistent with differences in the bonding strengths of the li octahedra in li mica and spodumene subduction and concomitant dehydration of metabasic oceanic crust containing chlorite and clinopyroxene with li in six fold coordination releases fluids enriched in li and 7 li into the fore arc and arc mantle and thus introduces a light li component into the deeper mantle ongoing dehydration and li loss along the subduction path produces fluids with increasingly lower li concentrations and lighter lithium isotope compositions however as staurolite is the most important carrier of li in metapelitic assemblages the inverse fractionation of li isotopes relative to fluids enables staurolite to transport high li concentrations in combination with an isotopic composition enriched in 7 li into the mantle thus depending on the li contents and li isotope signature of the protolite breakdown of li bearing staurolite at high p and t can release fluids with high li contents and isotopically heavy li into the deep mantle wedge

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

dominant simple shear deformation during peak metamorphism for the lower portion of the greater himalayan sequence in west nepal new implications for hybrid channel flow type mechanisms in the dolpo region abstract i conducted new vorticity and deformation temperatures studies to test competing models of the exhumation of the mid crustal rocks exposed in the dolpo region west nepal my results indicate that the main central thrust is located 5 km structurally below the previous mapped locations deformation temperature increasing up structural section from 450 c to 650 c and overlap with peak metamorphic temperature indicating that penetrative shearing was responsible for the exhumation of the ghs occurred at close to peak metamorphic conditions i interpreted the telescoping and the inversion of the paleo isotherms at the base of the ghs as produced mainly by a sub simple shearing wm 0 88 1 pervasively distributed through the lower portion of the ghs my results are consistent with hybrid channel flow type models where the boundary between lower and upper portions of the ghs broadly corresponding to the tectonometamorphic discontinuity recently documented in west nepal represents the limit between buried material affected by dominant simple shearing and exhumed material affected by a general flow dominates by pure shearing this interpretation is consistent with the recent models suggesting the simultaneous operation of channel flow and critical wedge type processes at different structural depth

subduction of the philippine sea plate beneath southwestern japan slab geometry and its relationship to arc magmatism 1 we carry out high resolution three dimensional seismic tomography of the crust and upper mantle beneath southwestern sw japan using arrival time data obtained from the nationwide seismograph network the tomographic images provide new insights into the configuration of the philippine sea slab and arc magmatism the results confirm the existence of an aseismic portion of the philippine sea slab at greater depths beyond the seismic portion the philippine sea slab is subducting aseismically down to at least a depth of 200 km in chubu 60 80 km in kinki and 60 km in chugoku and is subducting seismically to depths of 150 200 km in kyushu in the chubu district it is subducting seismically at a shallow dip and then bends downward beneath the volcanic area whereas in the kinki district it is subducting subhorizontally as far as the japan sea the differences in the slab geometry between adjacent regions correlate with the differences in volcanic activity suggesting the importance of the geometry of the philippine sea slab on arc magmatism our tomographic images further imply subduction of the philippine sea slab down to a depth of around 70 km northwest of the izu peninsula the philippine sea slab in that region might have split into western and eastern parts separated by a slab tear and collided with the pacific slab at depths of 150 200 km

flowpath and retention of snowmelt in an ice covered arctic lake the extent to which snowmelt flowing into ice covered lakes spreads horizontally and mixes vertically influences retention of solutes derived from the landscape to quantify these transport processes and retention we combine time series temperature and specific conductance measurements in toolik lake alaska and its major inflow with measurements of discharge and meteorology and profiles of specific conductance temperature fluorescence chlorophyll a and dissolved organic carbon doc in spring of 3 yr during early snowmelt the concentration of doc in the stream was 750 m twice that in the lake during slow melt discharge q 6 m3 s 1 the incoming water partially flushed the inlet basin and the more dilute water flowed over the original intrusion with a preferential flowpath to the outlet penetrative convection was restricted by the increased density gradients from the incoming plume and initially constrained to shallow mixing zones associated with the step changes in density as ice thickness decreased to less than 1 m heating caused density instabilities at the base of the intrusions that mixed solutes 10 m vertically contributing to retention near surface layers enriched with doc persisted for 10 d during a rapid melt and for over 3 weeks when the melt was slow retention of order 10 20 also depended on the rapidity of melt and magnitude of discharge

kar age determination of late quaternary volcanic rocks using the mass fractionation correction procedure application to the younger ontake volcano central japan abstract we propose an age derivation procedure for the k ar dating method to be applied to late quaternary volcanic rocks of low to medium k 2 o content whose k ar ages calculated by the conventional derivation procedure provide insufficient age information in this procedure which we call the mass fractionation correction procedure mfcp the initial 40 ar 36 ar ratios of the samples are estimated from the stable 38 ar 36 ar ratios determined by the unspiked technique assuming that the initial argon isotope ratios of all the samples should lie on a theoretical mass fractionation line of argon in the atmosphere to examine the usefulness of the mfcp systematic k ar age determinations using this procedure were made on volcanic rocks from the stratigraphically well known younger ontake volcano in central japan which has erupted repeatedly over the past 100 ka the k ar ages determined for these volcanics by this procedure generally have analytical uncertainties within 25 1 level and are consistent with the volcanostratigraphy exceptions were the large phenocrysts in pumice fall deposits these may contain significant amounts of excess 40 ar and we considered them to be unsuitable for accurate k ar age determinations of young volcanic rocks in the cases of lava flows which underlie a widespread fallout tephra the k ar ages determined by the mfcp were consistent with the 14 c age of the tephra 21 22 ka

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

application of sr isotopes to geochemical mapping and provenance analysis the case of aichi prefecture central japan abstract geochemical maps expressing areal distributions of chemical elements in the earth s land surface have been published in several countries in relation to various global environment issues the authors have applied a radiogenic isotope ratio 87 sr 86 sr to geochemical mapping in order to understand the geological origin transportation and dispersion system of chemical elements in the earth s land surface the sr isotope ratio is a useful tracer for distinguishing the geological origin of surficial deposits especially in areas where surface exposure of bedrocks is low because it is not significantly altered by the processes of weathering and transportation most bedrocks in the japanese islands are covered by plants soils and urban areas in this study 142 of 1219 stream sediments 87 sr 86 sr values and the above average presence of granitic rocks in the study area compared with the surface exposure of the japan arc the first factor controlling the distribution of sr isotope ratios is the bedrock distributed around the sampling points regional variation in the 87 sr 86 sr value shows that it is higher in the western and southeastern parts where sedimentary rocks and metamorphic rocks are distributed and that it is lower mainly in the central part where granitic rocks are distributed the 87 rb 86 sr 87 sr 86 sr plot for stream sediments more clearly reveals the differences and similarities of bedrocks in some locations the distribution of sr isotope ratios does not correspond to that of bedrocks on the geological map one reason is the existence of unmapped bedrock for example small intrusive masses of granite the other is fluvial transportation and dispersion the distribution of the isotope ratios suggests that some stream sediments include surficial deposits from a few km upstream application of the sr isotope ratio to geochemical mapping is useful for revealing both the distribution of unexposed bedrocks and the transportation of surficial deposits information on unexposed bedrocks will be expected to contribute to the improvement of geological mapping

downstream and seasonal changes of lithium isotope ratios in the ganges brahmaputra river system the li isotope ratio 7li is expected to be a useful tracer of silicate weathering in river and groundwater systems which is an important contributor to the seawater compositional changes that accompany the evolution of the earth s surface environment to obtain accurate estimates of continental li fluxes to the ocean we determined 7li values of dissolved li in the lower ganges brahmaputra river system in both the dry and rainy seasons and in deep groundwater in the bengal basin dissolved li and 7li values in the lower reaches of the rivers 0 04 0 66 mol kg 1 and 19 1 to 34 2 respectively were predominantly derived from silicate weathering as is the case in the upper parts of these rivers we observed large changes in 7li over a distance of more than 1000 km downstream that were due mainly to rayleigh type removal of li from river water extremely high li concentrations 1 15 1 67 mol kg 1 and low 7li values 5 1 to 11 6 in groundwater samples indicate congruent isotope leaching and dissolution of silicate minerals in the deep aquifer where the water residence time is long in the rainy season li concentrations and 7li values were lower than in the dry season owing to the shorter residence time of river water and the substantial input of local subsurface flow through lowland alluvium these results suggest that accurate estimation of continental li fluxes to the ocean should take account of downstream and seasonal changes as well as aquifer depth variations in 7li values

origins of lithium in submarine mud volcano fluid in the nankai accretionary wedge abstract to investigate fluid regimes in the nankai accretionary wedge we estimated the temperatures of lithium li reservoirs from the li isotope ratio 7li 6li in fluids recovered from kumano mud volcano no 5 kmv 5 in the nankai forearc basin the 7li 6li ratios in the kmv 5 fluids are among the lightest reported from submarine mud volcanoes the estimated li reservoir temperatures 310 c at maximum were significantly higher than the smectite to illite conversion temperature 60 150 c whereas the temperature of fluid from the deeper nankai decollement was estimated to be 150 c at maximum data obtained from previous conductivity surveys across the trench suggest that there are two fluid reservoirs associated with distinct dehydration processes in the nankai subduction zone from these results we inferred that the discontinuous mud diapirism in the kumano forearc basin results from the periodic injection of deep seated fluid accumulated in the corner of the serpentinized forearc mantle wedge that travels upward via a thrust fault the intermittent upwelling of deep seated fluid from the nankai accretionary wedge due to periodic breaches of a low permeability barrier above the fluid reservoir may be associated with seismogenic fault activity

effects of pore fluid pressure and tectonic stress on diverse seismic activities around the mt ontake volcano central japan abstract to understand the effects of pore fluid pressure and tectonic stress in generating diverse seismicity we deployed 11 temporary seismic stations around an active volcano mt ontake in central japan during the summers of 2009 2011 we obtained well constrained focal mechanism solutions from the seismic data recorded at the temporary stations and permanent stations located within 50 km around mt ontake we estimated the 3 d pore fluid pressure field taking into consideration spatial changes in the tectonic stress pattern by applying the method of focal mechanism tomography to the dataset we found overpressurized fluid reservoirs with a peak of 100 150 mpa at depths between 5 and 12 km in the southeast and east flanks of mt ontake this region has experienced earthquake swarm activity since 1976 many seismic events concentrated at the edge of the overpressurized fluid reservoirs where pore fluid pressure gradients are steep this indicates that a large amount of fluid flow would trigger seismic events by decreasing fault strength caused by an increase in pore fluid pressures many small events m

helium and carbon isotope systematics at ontake volcano japan we have measured chemical compositions he ne ratios and he and c isotopic compositions of 47 gas samples collected from crater fumaroles and hot springs associated with ontake volcano japan geographical and temporal variations of chemical compositions 3he 4he ratios and 13c values of co2 are reported here between 1981 and 1993 3he 4he ratios decreased with increasing distance from the central cone of the volcano while 13c values increased with the distance magmatic he and co2 are probably carried by a fluid flowing through the volcanic edifice and are diluted by crustal he and co2 a negative correlation of 3he 4he ratios and 13c values suggests two component mixing between magmatic and crustal end members at the sampling sites close to the fault formed by a m6 8 earthquake that occurred in september 1984 3he 4he ratios have increased significantly with time from 1984 to 1993 while except for three sites close to the fault no systematic change of 13c values is found on the other hand he and c isotopes have been constant at the sites distant from the fault the temporal variations of 3he 4he ratios may be related to the recent reactivation of ontake volcano