mineral and gas chemistry of hydrothermal fluids on an ultrafast spreading ridge east pacific rise 17 to 19 s naudur cruise 1993 phase separation processes controlled by volcanic and tectonic activity during the naudur cruise in december 1993 23 dives using the french submersible nautile were conducted on the axis of the east pacific rise between 17 and 19 s where the spreading rate is among the fastest in the ocean 14 to 16 cm yr twenty hydrothermal fluids located at the topographic high of each segment in the axial domain were collected between 2573 and 2669 m depth on three segments centered respectively at 17 25 s 18 15 s and 18 26 s the fluids exhibit a very wide range of temperature chemical and gas compositions on the 17 25 s and 18 26 s segments fluids have quite uniform compositions low chlorinities are gas enriched and are low in dissolved metals relative to fluids from the 18 15 s segment which show high chlorinities are less gas enriched and show high metal concentrations chloride and metal depletion associated with gas enrichment is consistent with phase separation whereas ch 4 end members show large variations between sites the 13 ch 4 data are very similar with 13 c values in a narrow range 22 0 to 23 9 versus pee dee belemnite pdb 13 co 2 measured in fluids within the 18 15 s and 18 26 s segments are respectively 7 9 and 5 8 versus pdb similar to 13 c of co 2 trapped in mid oceanic ridge basalts suggesting a magmatic origin the variability in fluid composition is linked to the variability of the accretion process observed on the three segments the uniform venting of low chlorinity fluids in the 17 25 s and 18 26 s segments is connected with volcanic activity which causes boiling with preferential venting of vapor enriched fluids high salinity fluids are emitted on the 18 15 s segment where the ridge is tectonics dominated and subseafloor circulation controlled by faults phase separated effluents induced by volcanic and tectonic activity are delivered to the deep ocean in this area as previously observed on the juan de fuca ridge or in the north fiji basin ridge

investigating the role of the itoigawa shizuoka tectonic line towards the evolution of the northern fossa magna rift basin abstract the itoigawa shizuoka tectonic line istl fault system is considered to have one of the highest probabilities for a major inland earthquake occurrence in the whole of japan it is a complex fault system with the dip directions of the local fault segments changing from north to south between an east dipping low angle thrust fault a strike slip fault and a west dipping thrust fault the tectonic relations between the different parts of the fault system and the surrounding geological units are yet to be fully explained this study aims to reveal the juncture of the northern and central parts of the istl and investigate its contribution towards the shaping of the northern fossa magna rift basin we conducted 3 deployments of 1 or 2 linear arrays of seismic stations across the central and northern istl regions and observed local micro earthquakes for a period of 3 years each deployment recorded continuous waveform data for approximately 3 months using arrival times of 1193 local earthquakes we jointly determined earthquake locations and a 3d velocity model applying the tomography method we were able to image the regional crustal structures from the surface to a depth of 20 km with a spatial resolution of 5 km subsequently we used the obtained 3d velocity model to relocate the background local seismicity from 2003 to 2009 the juncture of the northern and central parts of the istl was well constrained by our results the depth extension of the northern parts of the istl fault segments follows the bottom of the miocene northern fossa magna rift basin nfm and forms an east dipping low angle fault in contrast the central parts of the istl fault segments are estimated to lie along the eastern boundary of the matsumoto basin forming an oblique strike slip fault fig 1

heat flow anomaly in the middle okinawa trough heat flow measurements in the okinawa trough were carried out on three cruises in 1984 and 48 new values were obtained non linear temperature depth profiles were obtained at some stations and interpreted as showing the results of hydrothermal circulation in the southwestern part of the trough heat flow appears to be lower in the central rift zone than in the surrounding area a high heat flow area around 126 e exists an extremely high and localized heat flow anomaly was observed in the central rift zone of the middle okinawa trough it is probably caused by present or recent igneous activity if the anomaly is due to an intrusion the maximum depth and age of the intrusive body can be assessed by the amplitude and horizontal extent of the heat flow anomaly assuming conductive cooling the age is younger than 3 105 yrs and the depth is shallower than 3 5 km when advective heat transfer is taken into account the age must be much younger

boron isotope geochemistry of vent fluids from arc back arc seafloor hydrothermal systems in the western pacific abstract boron concentrations and isotopic compositions were determined for vent fluids from 11 sites in arc back arc seafloor hydrothermal systems this new dataset allowed a systematic comparison of boron behavior during water rock interaction in different geological settings in sediment starved hydrothermal systems e g manus basin izu bonin arc mariana trough end member fluids showed large variations in boron concentration 0 53 1 52 mmol kg and 11 b value 13 5 29 7 reflecting the interaction of seawater with varied types of rock that occur in arc back arc settings based on the model calculations the boron concentration and 11 b value of the fluid are better explained by an equilibration between seawater and rock than a mixing model the chlorine depleted fluids from phase separated hydrothermal systems e g north fiji basin had low boron concentrations 0 44 0 55 mmol kg and high 11 b values 34 5 36 1 the small fractionations of boron and boron isotopes during phase separation suggest that these characteristics were acquired during water rock interaction rather than phase separation and segregation processes the fluids from sediment hosted hydrothermal systems e g okinawa trough are characterized by high boron concentrations 3 9 4 8 mmol kg and low 11 b values 2 5 2 9 these fluids also showed high cs b ratios indicating interactions with terrigenous sediments model calculations demonstrate that the combined evaluation of 11 b values and cs b ratios are useful for a quantitative estimate of sedimentary contributions in seafloor hydrothermal systems

mantle helium flux from the bottom of lake mashu japan abstract most of the 52 water samples from lake mashu hokkaido japan show large anomalies in their3he 4he ratios up to 4 6 times the atmospheric ratio and4he 20ne ratios indicating continuous injection of mantle he due to hot spring activity at the lake bottom the3he 4he ratio of the injected mantle he is estimated at3he 4he 9 43 0 17 10 6 which is close to the highest value reported for volcanic gases from the japanese islands accumulation of mantle he in the near bottom water can be reasonably explained by a diffusion process with a constant he flux from the lake bottom off4he 9 2 107 atoms cm2 s andf3he 8 7 102 atoms cm2 s the heat 3he ratio 1 7 10 7j atom falls in the range of values reported for submarine hydrothermal systems 0 4 26 10 7 j atom whereas the c3he ratio 1 8 1011 is about two orders of magnitude higher than the morb average 2 109 the mantle he injected from the lake bottom has a fairly short mean residence time in the lake water and is estimated at about 2 4 years overturn of the lake water which occurs twice a year probably plays an important role in the rapid transportation of the mantle he from the bottom to the surface

light hydrocarbon gases in guaymas basin hydrothermal fluids thermogenic versus abiogenic origin light hydrocarbon gases methane through pentane in high temperature hydrothermal fluids of the guaymas basin gulf of california are predominantly derived from thermocatalysis of organic carbon in sediments intruded by mid ocean ridge volcanic rocks the spectrum of c1 c5 gases in guaymas basin hydrothermal fluids is characterized by a preponderance of alkanes with essentially no alkenes present comparison with high temperature fluids from 21 n on the east pacific rise where geochemical evidence indicates a distinct lack of thermogenic gas and where methane is derived abiogenically from the basalts shows that the 21 n hydrocarbon gases are characterized by a prominent ethylene signature stable isotope compositions of guaymas basin m thane differ from 21 n gas guaymas basin has dgr13c values of 43 to 51 pmil vs pdb compared to 21 n where values as high as 15 pmil have been measured these differences reflect the different origins of light hydrocarbon gases in the two systems with guaymas methane being overwhelmingly of an organic thermogenic derivation and showing no evidence of the abiogenic basalt derived gas that characterizes the 21 n environment carbon isotope analyses of dissolved inorganic carbon in guaymas basin hydrothermal fluids indicate that high temperature hydrocarbon oxidation may be an important process acting in conjunction with high temperature thermocatalytic hydrocarbon generation

seeping hydrocarbons and related carbonate mineralisations in sediments south of lihir island new ireland fore arc basin papua new guinea hydrocarbon gases have been sampled from both cold seeping and heat venting areas in the new ireland fore arc basin in the vicinity of lihir island highest concentrations of up to 10 l l ch4 with a 13cch4 value of 54 9 pdb have been measured in the deep ocean water within a long and narrow deep sea basin located between edison seamount and an uplifted structure named mussel cliff surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as calyptogena species and tube worms large authigenic calcite concretions occur in the sediments between 50 and 200 cm sediment depth the carbon isotopes of the carbonates in the concretions range from 15 to 40 pdb indicating a mixture of two co2 sources normal marine inorganic carbon fixed in biogenic shells and co2 from anaerobe bacterial oxidation processes of methane accordingly 14c ams dating suggests that authigenic calcite mineralisation incorporated relatively young carbon from methane oxidation in contrast the c1 c2 ratio of 234 and the 13cch4 value of 24 1 pdb in the hot hydrothermal vent of lihir harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with lihir volcano the observed variable fluid characteristics within only 20 km distance between hot hydrothermal venting and the methane seeping deep sea area indicates highly variable heat flow situations and or sediment distributions which control the gas geochemical characteristics in the new ireland fore arc basin

paleomagnetic evidence for the miocene counter clockwise rotation of northeast japan rifting process of the japan arc paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of cretaceous to miocene age from northeast japan the remanent magnetizations of welded tuffs with age between 32 ma and 21 ma old from 17 widely distributed sampling sites in northeast japan are fairly well grouped with a mean ofd 41 2 i 56 5 95 7 2 the remanent magnetization of welded tuffs of 14 ma and 11 ma from 4 sites shows a northerly direction d 11 7 i 60 5 95 15 3 these data imply that northeast japan was apparently subjected to a counter clockwise rotation through 47 14 about a vertical axis on the representative point of northeast japan 141 e 39 n during the past 21 ma comparing with the period of the clockwise rotation of southwest japan the differential rotation between northeast japan and southwest japan is concluded to have occurred concurrently during the period between 21 ma and 12 ma a rifting model of the japan arc is proposed northeast japan rotated counter clockwise through 50 about a northern pivot at 146 e 44 n while southwest japan rotated clockwise through 54 about a southern pivot at 129 e 34 n the differential rotation about different rotation pivots gives rise to the opening of a diamond shaped back arc basin the japan sea

jurassic subsidence history in the hebrides n w scotland abstract geohistory analyses have been applied to the generally well dated triassic jurassic successions of three areas in the hebrides basin north west scotland and the importance of making corrections for decompaction palaeobathymetry and eustatic changes of sea level are assessed the thermo tectonic subsidence patterns in the skye areas north suggest a three phase history of crustal stretching though only the first phase is well developed in the mull area south episodes of relatively rapid subsidence are 1 1 late triassic c210 ma until earliest toarcian 186 ma 2 2 latest toarcian 180 ma until late bathonian c161 ma 3 3 early oxfordian 154 ma until at least early kimmeridgian incomplete these are separated by toarcian 186 180 ma and latest bathonian callovian c161 154 ma episodes of either little subsidence or of uplift but at slower rates than eustatic rise of sea level the intervals between phases at 30 ma and 26 ma are remarkably similar but the wider significance of this remains to be established

geochemical observations within the water column at the co2 rich hydrothermal systems hatoma knoll and yonaguni knoll iv in the southern okinawa trough the okinawa trough is one of three known hydrothermal sites worldwide where liquid carbon dioxide is emitted from the seafloor into the water column in march 2008 investigations were performed at two active areas yonaguni knoll iv and hatoma knoll in order to identify impacts of hydrothermal venting on the water column chemistry vertical profiles of ph and redox potential eh were recorded and discrete water samples were taken for the analysis of total carbon dioxide ct and helium 3he 4he anomalies with respect to reference stations ct ph and 3he with respect to saturation with the atmosphere 3heexcess were used to characterize the impact of hydrothermal vents these data indicate that the flux of co2 into the water column is dominated by hot hydrothermal co2 rich vents located in close proximity to the liquid co2 emission sites bubbles and droplets sampled at the cold gas outlets at hatoma knoll differed considerably from the water column regarding co2 3he ratios and thus provide additional evidence that cold liquid phase co2 is of minor importance for the total co2 flux at both hydrothermal systems although hydrothermal vents at back arc basins are known to emit large amounts of acids other than co2 the correlation between ph and ct at both research areas clearly suggests that the observed ph reduction is mainly caused by the addition of co2 deviating ct 3he and ct ph ratios and the prevailing water currents indicate a yet undiscovered vent site at the flank of a seamount in the northeast

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

intense ch4 plumes generated by serpentinization of ultramafic rocks at the intersection of the 15 20 n fracture zone and the mid atlantic ridge abstract as part of the fara french us program designed to study the mid atlantic ridge mar between 15 n and the azores twenty three dives with the submersible nautile were conducted during the french us faranaut 15n cruise on the eastern and western parts of the 15 20 n fracture zone ridge axis intersection south of the eastern ridge transform fault intersection nine nautile dives were made within the rift valley and along the western rift valley wall ch4 concentrations in the bottom waters reach 53 2 nmol kg along faulted zones on top and on the east flank of the ultramafic inner corner high 15 05 n 44 59 w where serpentinized rocks outcrop no 3he anomaly is associated with methane ruling out any primary mantle component fourteen dives were also made in the rift valley to the north close to the western intersection of the 15 20 n transform high ch4 anomalies up to 22 nmol kg are also present in the bottom waters of the rift valley northern segment on both the western and eastern valley walls and on the inner high adjacent to the eastern wall where ultramafic rocks outcrop seven vertical hydrocasts carried out in the axial valley 4500 m deep show an intense ch4 anomaly with a maximum 35 8 nmol kg at 3200 m depth this ch4 concentration is among the highest found along the mid atlantic ridge charlou and donval 1993 charlou et al 1997 ch4 concentrations of 9 9 14 9 nmol kg are also present on the western wall along the 3200 m isobath the high ch4 concentrations correspond to only weak 3he anomalies this ch4 rich plume is also associated with active fault zones that expose peridotite rocks ch4 output from ultramafic outcrops on the western and eastern intersections of the 15 20 n fracture zone with the mar is believed to reflect ongoing serpentinization these results associated with many other ch4 anomalies measured in the water column above ultramafic outcrops found between 12 n and the azores most likely reflect serpentinization processes extending along the whole slow spreading mid atlantic ridge

helium isotopes in icelandic geothermal systems ii helium heat relationships abstract a model has been developed that relates the 3he content of the reservoir fluid to the fluid enthalpy in contrast to oceanic hydrothermal systems that display a uniform 3he enthalpy ratio 0 4 14 106 atoms of 3he joule icelandic systems vary by 1000 0 4 400 106 atoms joule a process that preferentially extracts helium relative to heat from a cooling magma produces high 3he enthalpy ratios for young systems e g krafla and low 3he enthalpy ratios for aging magmatic systems e g hveragaerdi using the highest 3he heat ratios measured in the fluid estimates of initial gas concentrations in the basalt are made for 3he 5 10 10 cc g and carbon 1200 ppm low temperature wells near geysir in southwest iceland appear to result from mixing of high temperature fluid 200 c and cold groundwater along a curve of constant 3he enthalpy

changes in depositional systems and sequences in response to basin evolution in a rifted and inverted basin an example from the neogene niigata shin etsu basin northern fossa magna central japan abstract the niigata shin etsu basin which occurs along the eastern margin of the sea of japan was generated in middle miocene time as a failed rift basin in relation to the backarc opening of the japan arc and was converted to a compressional basin in late miocene time the basin filling succession can be divided into four tectonostratigraphic units stages based on characteristics of depositional systems depositional sequences tectonic subsidence rate and sediment supply these units coincide in time with major tectonic events during backarc rifting and subsequent basin inversion unit i 16 13 5 ma represents a syn rift stage characterized by rapid basin subsidence the rate of accommodation exceeded the rate of accumulation resulting in a retrogradational stacking pattern of muddy slope to basin floor systems unit ii 13 5 6 5 ma represents a post rift thermal subsidence stage the rate of accommodation nearly equaled the rate of accumulation resulting in an aggradational stacking pattern of five third order depositional sequences mainly comprising submarine fan turbidite systems affected by supply of coarse clastics unit iii 6 5 1 ma represents the basin inversion stage showing no subsidence or uplift the accumulation rate exceeded the rate of accommodation resulting in rapid progradation of depositional sequences composed of slope shelf shallow marine delta and fluvial systems unit iv 1 ma present represents an intense compressional stress field sedimentation has been restricted to a synclinal area due to syndepositional folding and uplift changes in basin subsidence rate and sediment supply resulting from tectonics and climate change in the basin and the provenance strongly affected characteristics of the depositional systems and sequences the change in basin subsidence also created a basinwide depositional cycle whereas eustasy affected relative sea level changes created higher order depositional sequences during relatively stable phases of tectonics

subcritical creep compaction of quartz sand at diagenetic conditions effects of water and grain size 1 compactional creep was measured for aggregates of quartz sand that were subjected to an effective pressure of 34 5 mpa and temperature of 150 c for times up to 6 months the effects of grain size and water on creep were determined by loading quartz aggregates of 255 60 130 18 and 35 12 m grain size under nominally dry water vapor static liquid water and flowing water conditions all aggregates displayed transient decelerating creep volume strain rates as low as 2 10 10 s 1 were achieved volume strain rate increases systematically with decrease in grain size and increase in exposure to water at comparable strain or time despite the fact that the effective pressure applied was far less than the critical pressures for short term cataclastic compaction of the quartz aggregates grain scale microstructures indicate that the underlying mechanism of creep is crack growth creep rates are explained by subcritical crack growth as governed by water silicate reactions at crack tips controlled by access of water at dry and vapor conditions and solute chemistry under static and flowing liquid water conditions extrapolation of the experimental results to natural compaction of quartz sand during burial and diagenesis over times of tens of millions of years indicates that porosity loss through subcritical cracking and grain rearrangement of medium grained porous wet quartz sands can reach 10

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

high alkalinity due to sulfate reduction in the clam hydrothermal field okinawa trough abstract high alkalinity 1 8 mmol kg 1 ph 4 7 5 3 and ammonium 5 mmol kg 1 in hydrothermal fluids from the jade and clam sites in the mid okinawa trough back arc basin demonstrate organic matter decomposition during high temperature fluid sediment interaction the endmember fluid from the jade site 320 c black smoker which is free of mg and so4 has similar chemical characteristics as those at the escanaba trough one of the representative sediment hosted ridge systems in the eastern pacific on the other hand fluid samples from the clam site 100 c show remarkably high alkalinity 10 3 mmol kg 1 comparable to the highest alkalinity of 10 6 mmol kg 1 guaymas basin yet observed in hydrothermal fluids and significantly higher 34s of so4 25 than ambient seawater 21 it is suggested that sulfate reduction plays a dominant role in decomposing organic matter to increase alkalinity in the clam site variation of the 34s values of h2s from 0 2 to 3 0 in the clam fluids taken from different vents suggests that the clam site should consist of multiple local hydrothermal systems in different evolutionary stages with regard to sulfate reduction

helium and carbon geochemistry of hydrothermal fluids from the mid okinawa trough back arc basin southwest of japan abstract hydrothermal systems located in the okinawa trough back arc basin are considered to be related to rifting activities in the continental margin hydrothermal fluids sampled from two sites jade and clam are significantly enriched in gas species compared to those from mid oceanic ridges a high temperature fluid 320 c from the jade site shows a co 2 concentration of 200 mmol kg 1 which is more than one order of magnitude higher than that of sediment starved ridge crest hydrothermal systems both helium r r a 6 1 6 5 and carbon 13 c co2 5 0 to 4 7 pdb isotopic compositions are typical of island arc magmatic gases also the abundance ratio of co 2 3 he 3 10 10 is within the range of values found in island arcs chemical and isotopic composition of the jade fluid are considered to indicate that both co 2 and helium are derived from a magmatic source beneath the hydrothermal system without significant contamination contrary to these species ch 4 is attributed to a thermogenic origin based on its isotopic composition 13 c ch 4 41 to 36 pdb and high concentration 7 1 mmol kg 1 which values are similar to those observed in sediment hosted hydrothermal systems the clam fluids show gas geochemistry much more affected by fluid sediment interaction lower 3 he 4 he ratios r r a 3 7 3 8 and higher co 2 3 he ratios 10 11 may reflect involvement of gas species introduced during secondary fluid circulation within the sedimentary pile magmatic activity is the main contributor of gas species to the hydrothermal fluids in both the jade and clam sites although fluid sediment interaction modifies their composition the relatively high abundance of co 2 in the mid okinawa trough hydrothermal systems reflects the geochemical nature of island arc magma

permeability of illite bearing shale 2 influence of fluid chemistry on flow and functionally connected pores 1 bedding parallel permeability of illite rich shale of the wilcox formation has been investigated using distilled water and 1 m solutions of nacl kcl and cacl2 as pore fluids despite low modal concentrations of swelling clays specimens expand upon fluid saturation and permeabilities depend on fluid composition permeabilities to flow of 1 m cacl2 are 3 5 times greater than values measured for the other pore fluids suggesting sensitivity to exchange of divalent cations for monovalent cations at clay mineral surfaces permeabilities of individual samples exhibit nonrecoverable changes with sequential changes in composition of incoming fluid permeabilities k at varying effective pressure pe fit a cubic law k k0 1 pe p1 m 3 where m and p1 are independent of fluid composition and k0 is greater for transport of 1 m cacl2 than that for transport of the other pore fluids assuming that fluid conduits have crack like dimensions the lack of sensitivity of m and p1 to fluid composition suggests that surface roughness and asperity stiffness of conduits are unaffected by cation exchange while changes in k0 reflect changes in the clay fluid interfaces of the connected pore space index terms 5114 physical properties of rocks permeability and porosity 5139 physical properties of rocks transport properties 1832 hydrology groundwater transport 3947 mineral physics surfaces and interfaces 1045 geochemistry low temperature geochemistry keywords permeability shale fluid chemistry citation kwon o b e herbert and a k kronenberg 2004 permeability of illite bearing shale 2 influence of fluid chemistry on flow and functionally connected pores j geophys res 109 b10206 doi 10 1029 2004jb003055

seismological evidence of an active footwall shortcut thrust in the northern itoigawa shizuoka tectonic line derived by the aftershock sequence of the 2014 m 6 7 northern nagano earthquake abstract a destructive m 6 7 earthquake struck northern nagano prefecture on november 22 2014 the main shock occurred on the kamishiro fault segment of the northern itoigawa shizuoka tectonic line istl we used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between november 18 and november 30 2014 to estimate hypocenters we assigned low vp models to stations within the northern fossa magna nfm basin thus accounting for large lateral crustal heterogeneities across the kamishiro fault in order to further improve accuracy the final hypocenter locations were recalculated inside a 3d velocity model using the double difference method we used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the kamishiro fault and dips 30 45 se while the deeper part of the source fault corresponds to the downdip portion of the otari nakayama fault a high angle fault dipping 50 65 se that formed during the opening of the nfm basin in the miocene along its surface trace the otari nakayama fault has been inactive during the late quaternary we verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half space model and comparing it to observed surface deformation from satellite interferometry assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity shallowing of the source fault from 50 65 to 30 45 in the upper 4 km in the areas where both surface fault traces are visible is a result of footwall shortcut thrusting by the kamishiro fault off the otari nakayama fault

relationship between weathering mountain uplift and climate during the cenozoic as deduced from the global carbon strontium cycle model abstract a global carbon strontium coupled model over the cenozoic is presented the carbon cycle includes improvements on the uplift parameter in the himalayan and tibetan regions and the hydrothermal flux at back arc basins from the carbon cycle model of kashiwagi and shikazono kashiwagi h shikazono n 2003 climate change during the cenozoic inferred from global carbon cycle model including igneous and hydrothermal activities palaeogeography palaeoclimatology palaeoecology 199 167 185 the strontium cycle incorporates groundwater flux basalt weathering and himalayan weathering the model result indicates that the paleocene to the late eocene is characterized by decreasing strontium weathering and gradually increasing isotopic value 87sr 86sr which is a result of the decrease in radiogenic silicate weathering and less radiogenic carbonate weathering caused by decline of the atmospheric temperature since then the 87sr 86sr continuously increases towards the present the increase in the sr isotopic value from 40 ma to 35 ma is attributed to appearance of hydrothermal calcite in the himalayan region the increasing patterns of the 87sr 86sr from that time to the early miocene roughly correspond to the continental glaciations in high latitudes such as those at the eocene oligocene boundary in the middle miocene and at the oligocene miocene boundary radiogenic weathering accelerated by physical erosion due to glaciations and the subsequent deglaciations as suggested by previous studies might be related however there are time lags between the 87sr 86sr and 18o signals which might have resulted from long residence time of sr in the ocean reactivity of minerals under such low temperature and other climatic conditions is still unclear more supportive works to assure a favourable environment for sufficient weathering and to constrain the timings and amplitudes of the glacial events during these periods would be necessary the presented model shows the increase in the sr weathering flux since the late miocene which would have induced the elevation of seawater 87sr 86sr whereas the evolution of the glaciations partially might have contributed to that some disagreement between other studies and the model is confirmed the evaluation of the palaeo sealevel variation and carbonate compensation depth might produce the uncertainties in the estimate of weathering flux moreover the basaltic province through which several major rivers drain and discrimination of these rivers and the ganges brahmaputra indus might be important for the strontium cycle because these rivers are likely to be influenced by the radiogenic upstream area and non radiogenic downstream province whose 87sr 86sr would have changed considerably during the cenozoic despite these uncertainties it is clear that we can not attribute the increase in the seawater 87sr 86sr values during the cenozoic entirely to the influence of the himalayan uplift and the seawater 87sr 86sr variation does not serve as a proxy for silicate weathering rate and atmospheric co2 consumption rate of atmospheric co2

geochemical origin of hydrothermal fluid methane in sediment associated fields and its relevance to the geographical distribution of whole hydrothermal circulation abstract we investigated the chemical composition of hydrothermal fluids and deduced the origin of hydrothermal fluid methane in a sediment associated minami ensei me hydrothermal field the okinawa trough the endmember hydrothermal fluid of the me field contained isotopically 13 c enriched methane 26 0 to 24 7 which suggested a thermogenic origin however the observed methane dominating hydrocarbon compositions c 1 c 2 10 3 suggested that biogenic methane not thermogenic hydrocarbons is predominant the conflict between these geochemical indications can be resolved by the hypothesis that the thermal reaction of sedimentary organic matter initially generates the primary source of hydrocarbons and the secondary thermal decomposition of hydrocarbons increases the c 1 c 2 ratio as high as that of biogenic methane the low molecular hydrogen concentration 0 04 mmol kg in the me fluid suggests that the thermal fluid sediment interaction occurred in the recharge stage not the discharge stage of hydrothermal circulation less biogenic methane in the me fluid implies a laterally shrunken hydrothermal fluid circulation that reduced biogenic methane incorporation at the recharge stage a comparison of hydrothermal fluid chemistry and geological geographical settings among the global sediment associated hydrothermal systems also suggests representative patterns in the geochemical origins of hydrothermal fluid methane and their relevance to hydrothermal fluid circulation as a whole

structural controls on palaeozoic basin evolution and inversion in southwest wales the tectonic evolution of sw dyfed is presented in terms of a model of basin evolution and subsequent destruction by reactivation of the basin bounding faults in contractional mode movements along long lived palaeozoic extensional faults were reversed during variscan compression with the pre existing faults accommodating the contraction in addition to the development of a thin skinned thrust and fold system basin analysis of the pre variscan extensional system uses sedimentological and stratigraphical evidence to constrain the timing of movements of the basin bounding faults thus allowing division of the stratigraphy into depositional megasequences related to these extensional movements field examples on all scales illustrate active extension during the palaeozoic structural cross sections through sw dyfed demonstrate the interrelationship of the extensional and contractional deformations with palinspastic restorations of the cross sections illustrating the complexity of the pre variscan template

hydrothermal diagenesis of paleozoic seamount carbonate components we present geochemical results of paleozoic carbonate components brachiopods biogenic low mg calcite blmc crinoids biogenic high mg calcite bhmc and whole rock admixture of aragonite and calcite wrac from open ocean permo carboniferous seamounts of japan situated in the tropical mid panthalassic ocean the diagenetic history of these and other carbonate allochems was determined by visual optical inspection of their external morphology and luminescence by evaluation of their microstructures and by assessment of their trace element and stable isotope distributions the degree and trends of the diagenetic alteration tests were then reconciled with their concomitant sr isotope values and compared to those of the established seawater sr isotope curve the altered carbonate material from three of the four time slices support the novel concept of diagenesis in the presence of marine hydrothermal fluids leading to less radiogenic sr isotope values in addition sr isotope values of unaltered blmc from three of the four time slices do not concur with the values for the concurrent time of the established seawater 87sr 86sr curve an adjustment of their stratigraphic position is untenable and unsatisfactory in light of their biostratigraphic assignment which suggests that sr isotope diagenesis is much more complex and complicated than is espoused in the literature consequently the concept of less radiogenic sr isotope values in diagenetic marine carbonates has profound implications for the veracity of the established seawater 87sr 86sr profile and curve and it needs to be re evaluated in light of the findings

geographical distribution of 3he 4he ratios in japan implications for arc tectonics and incipient magmatism the 3he 4he and 4he 20ne ratios of 115 natural gas samples including various types of gases from volcanoes hot springs mineral springs water wells petroleum fields and natural gas fields were measured using a mass spectrometer the observed 3he 4he and 4he 20ne ratios range from 7 47 10 8 to 9 65 10 6 and from 0 26 to 1100 respectively the 3he 4he ratios reflect well the geotectonic structure of the japanese islands in northeastern ne japan there is a clear geographical difference in the 3he 4he ratios between the frontal arc forearc and volcanic arc back arc regions lower ratios were found in the trench side region and higher ratios in the back arc side this result suggests that the mantle derived helium in the volcanic arc region is associated with the diapiric uprise of a magma lower 3he 4he ratios in the frontal arc region may be due to radiogenic he produced by radioactive decay of u and th in the crustal and sedimentary rocks in southwestern sw japan there is no clear geographical contrast in the 3he 4he ratios some samples in the frontal arc region show quite high 3he 4he ratios the tendency of the 3he 4he ratios agrees with the distribution of terrestrial heat flow data and reflects geotectonic structures different from ne japan the high 3he 4he ratios observed in the frontal arc region in sw japan may be indicative of renewed or incipient magmatism due to a descending young and warm slab

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

hydrothermal fluid emanations from the submarine kick em jenny volcano lesser antilles island arc abstract little is known about the role of island arcs as hydrothermal sources to the ocean when compared to the extensive research that has been carried out on hydrothermal systems at spreading ridges although increasingly more work is being done on intraoceanic arcs here we present fluid geochemistry data from the kick em jenny kej submarine volcano of the lesser antilles island arc discharge of diffuse hydrothermal fluid was discovered on the southwestern flanks of the volcano hydrothermal input into the water column was recognized from ch4 and trace metal anomalies in water column profiles in a depth range of 500 700 m samples collected directly on the seafloor also showed evidence for hydrothermal emissions where mg and cl were depleted in the fluids compared to ambient seawater while ch4 and several trace metals were enriched the chemical composition of these samples including o and h isotope data suggests that the fluids are a mixture between a condensed vapor phase derived from a phase separated hydrothermal fluid which was conductively cooled in the sub surface and seawater increased dissolved organic carbon doc concentrations of the fluids also indicate interaction with the sediment layer through which the fluids percolated although the volcanic crater could not be sampled directly due to safety concerns 3he and some trace metal values in seawater samples indicate fluid input containing a mantle component probably from a hot focused flow source in the crater region around 200 300 m depth

carbon isotopic distribution of methane in deep sea hydrothermal plume myojin knoll caldera izu bonin arc implications for microbial methane oxidation in the oceans and applications to heat flux estimation the concentration and stable carbon isotopic composition 13c of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the myojin knoll caldera izu bonin arc in the western north pacific the hydrothermal end member concentrations and 13c of methane show near homogeneity among vents 41 2 mol kg and 16 3 0 8 pdb respectively while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation 2 1 11 nmol kg and 29 0 to 11 3 pdb respectively comparison of concentration and 13c data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume assuming steady state emission of methane from the vents 1 kinetic isotope effect due to the microbial oxidation k12 k13 2 methane flux from the vents fvents 3 heat flux from the vents q and 4 average turnover time of hydrothermal methane tall are estimated to be k12 k13 1 005 0 001 fvents 90 340 mol d q 30 110 mw and tall 60 240 d respectively the estimated turnover times however are not uniform within the water column around the vents a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean while those at the distant points correspond to values more typical for deep ocean water

experimental study of the compaction of phyllosilicate bearing sand at elevated temperature and with controlled pore water pressure relative to the time dependent compaction behavior of clean quartz sands little experimental work has been carried out on phyllosilicate rich siliciclastic rocks mudstones compaction is expected to be produced by intracrystalline plastic deformation of the phyllosilicate matrix coupled with pressure solution of embedded quartz grains and with silica reprecipitation in the adjacent pore spaces or loss from the system via an advective flux of pore water time dependence of compaction also arises in nature owing to the generation of excess pore pressure which lowers effective stress and hence compaction rate until such pressure excess becomes dissipated by permeation a suite of experiments was performed on synthetic mixtures of quartz sand in a matrix of fine grained illite muscovite hydrostatically compacted at a range of effective pressures between 10 mpa and 210 mpa with a constant pore water pressure of 70 mpa and at temperatures ranging between 300 and 450 c a small adjacent volume of porous quartz sand was provided as a precipitation sink for silica dissolved from the phyllosilicate quartz mixture volume strains were measured by a direct measurement of sample length and b measurement of amount of pore water expelled at constant pore pressure and interpreted with the aid of quantitative petrography on compacted samples control experiments were performed on i dry clean sand ii dry sand phyllosilicate and iii wet clean sand dry clean sand showed almost no compaction wet clean sand showed a degree of compaction similar to dry phyllosilicate sand but wet phyllosilicate sand showed dramatically more compaction compaction rate for the wet mixed phyllosilicate sand samples is described by formula 1 in which is effective stress mpa is porosity r is the gas constant and t is temperature k petrographic study showed interpenetration of grain contacts formation of quartz overgrowths a decrease in the amount of quartz embedded in the phyllosilicate matrix and an increase in mean grain size of quartz with progressive compaction these effects are attributed to solution and redeposition of quartz the empirical compaction law was integrated over a natural burial history the porosity evolution is extremely sensitive to the evolution of pore fluid pressure and relatively less to temperature gradient and burial rate there is reasonable qualitative agreement when compared with porosity depth relations reported in the literature 1 embed graphic 1 gif

seawater carbon and strontium isotope variations through the late ediacaran to late cambrian in the tarim basin abstract the radiation of early animals during the cambrian explosion was accompanied by widespread perturbations in oceanic and atmospheric conditions however the cause effect relationships between evolutionary innovations carbon c cycling and continental weathering are still a matter of debate further paleoenvironmental reconstructions of poorly studied paleo continents covering the precambrian cambrian pc c transition may improve the correlation of the events and their impact on the earth system on a global scale the tarim basin was presumably located proximal to the well studied south china craton during the ediacaran cambrian boundary and is expected to contribute equally to our paleoenvironmental reconstructions here we apply carbon and strontium sr isotope records 13c and 87sr 86sr obtained from well preserved marine carbonates spanning the late ediacaran to the late cambrian from the keping region in the northwestern tarim basin nw china by comparison to other carbonate successions from various paleo continents our obtained seawater 87sr 86sr curve in this study shows a stepwise first order increase to more radiogenic values superimposed by second order presumably regional variations our obtained 13c variations exhibit four prominent negative and three positive excursions identical to the global 13c record based on existing paleontological evidence and our new tarim 13c and 87sr 86sr curves we propose a stratigraphic correlation from the late ediacaran to the late cambrian between the tarim basin and other paleo continents besides our paleoenvironmental reconstruction reveals both regional and global sea level changes that may have controlled the influx of radiogenic sr and presumably the influx of nutrients controlling primary production and the rate of organic carbon burial in the tarim basin at the time of deposition these feedbacks may have ultimately influenced the rapid diversification of metazoans and the oxygenation of the cambrian ocean and atmosphere approaching present po2 levels

mechanical behaviour of fine grained sediments experimental compaction and three dimensional constitutive model abstract the usual undimensional description of deformations of sediments based on a phenomenological relationship between porosity and the vertical effective stress does not give information about the horizontal stress and moreover is irrelevant for sedimentary structures in which deformation process is not only vertical modelling three dimensional deformation processes in sedimentary basins requires a three dimensional mechanical constitutive model for sediments a special dometric cell was conceived in g 3s this cell allows the measurement of the lateral stress during dometric compaction and so enables us to elaborate a three dimensional model of mechanical behaviour four varieties of fine grained sediments were studied by this cell in a large scale of strain and stresses the modified cam clay model was used for fitting the experimental data and it was shown that this model can reproduce the mechanical compaction of sediments up to 50 mpa of vertical effective stress about 3 km burial depth if its parameters are deduced from dometric zero lateral strain data

volume change during sediment diagenesis and the development of growth faults abstract the stress system induced the weight of a sediment and the pore fluid it contains termed the passive stress system is capable of deforming the sediment this volumetric deformation is examined with respect to the evolution of porosity and permeability during burial the effect of this self deformation on the shape of growth faults and normal faults in extensional terrains is considered

hydrothermal regime and constraints on reservoir depth of the jade site in the mid okinawa trough inferred from heat flow measurements detailed heat flow measurements revealed an enormous heat flow variation 102 to 105 mw m 2 in the jade hydrothermal field 27 16 n 127 05 e and water depth 1350 m located on the slope of the izena hole in the mid okinawa trough within the jade site heat flow is higher than 1000 mw m 2 and decreases to 100 mw m 2 with a 1 km horizontal scale near the jade black smoker heat flow varies from 30 000 mw m 2 at a hydrothermally altered area to 1700 mw m 2 less than 100 m from it a large scale heat flow variation suggests that the base of the escarpment near the jade site serves as a recharge area for the jade site linear geotherms indicate that the upward darcian flow within sediments is slower than 3 cm yr 1 thus the fluid circulation pathways would basically be restricted in permeable channels estimated conductive heat output rate from the jade site is 4 7 mw which is comparable to heat output by a single black smoker vent 8 mw one dimensional thermal modeling predicts the existence of a boiling zone at 200 m beneath the jade site which may be overlain by a fractured impermeable layer the normal chloride content of venting fluids from the black smoker may be explained either by upwelling of fluid which boiled at shallow depth but suffered no phase segregation or by upwelling of fluid above the boiling interface

chemical and isotopic compositions of volcanic gases from the east sunda and banda arcs indonesia the easternmost sunda arc and the banda arc represent a continent arc collision zone where magma genesis is influenced by subducted continent derived material chemical and isotopic studies of volcanic gas samples from this environment provide information on the sources of volatiles in arc magmas these volcanic gases some of which last equilibrated at magmatic temperatures are characterized by anomalous low sup 3 he sup 4 he values but by common arc values of c s approx 2 4 delta sup 13 c approx minus 3 per thousand and delta sup 34 s sub tot approx 5 per thousand abundant helium and high he ar ratios are consistent with the subduction of terrigenous components in local sediments or slivers of continental crust although individual concentration and isotope ratios of volatile components may be explicable by complex fractionation in the recycling process the combined data are in agreement with an important role of subducted sedimentary source components comparison of the authors results with volcanic gas data from other arcs indicates that the carbon and sulfur signals in arc gases are relatively insensitive to the amount and nature of sediment on the subsiding plate hence a contribution to arc volcanic gases from subducted altered oceanic crust cannot be excluded

chemical compositions of mussels and clams from the tangyin and yonaguni knoll iv hydrothermal fields in the southwestern okinawa trough abstract studies of the chemical characteristics of mussels and clams in seafloor hydrothermal fields are important for understanding mass fluxes and elemental partitioning from hydrothermal vents into the biosphere metal bioaccumulation of seafloor hydrothermal ecosystems and the sources and sinks of biogeochemical and fluid cycles we are the first to measure the mineral major trace and rare earth element and carbon and oxygen isotope compositions of mussels bathymodiolus platifrons and clams conchocele bisecta from the tangyin and yonaguni knoll iv hydrothermal fields in the southwestern okinawa trough mineralogical analysis shows that the carbonate shells of the mussel and clam samples are mainly composed of calcite and aragonite metal elements exhibit linear correlations in the shells e g v and u and tissues e g li and rb of the mussels and clams suggesting that not all positive correlations of elements in tissues are inherited by the shells v as ca sr and fe cr ratios in the mussels and clams are close to those in the seawater indicating that element ratios of seawater might be inherited by the mussels and clams in addition the fe cr ratio of the shells of both mussels and clams can be used to trace the local seawater composition the total lree concentrations of mussel and clam tissue samples are higher than those of the mussel and clam shell samples are similar to the hydrothermal fluids exhibit lree enrichment lacn ndcn ratios 1 86 32 1 and no or only slightly negative eu anomalies indicating that benthic animals are a sink of lrees from hydrothermal fluids and that the eu eu ratios of fluids change when fluids are incorporated into the tissues of the mussels and clams in addition the 13c values of mussel shell samples are heavier than those of the clam shell samples in the hydrothermal field indicating that more than one carbon source may be involved in defining the 13c compositions of the shells the majority of the 18o values of clam shell samples fall in the range of 18o values of the mussel shell samples and are close to the hydrothermal fluid 18oh2o values implying that the 18o values of mussel and clam shell carbonate is influenced by the hydrothermal environment magmatic water and fluid dilution with seawater

a multi isotope study of deep sea mussels at three different hydrothermal vent sites in the northwestern pacific abstract to investigate symbiotic bacterial ecosystems at different deep sea hydrothermal systems in the northwestern pacific compound specific carbon and hydrogen isotope analyses of lipid biomarkers have been performed in addition to bulk c h n s and o isotope analyses on bathymodiolus mussels from the hatoma seamount b platifrons the daiyon yonaguni yonaguni knoll b platifrons and the suiyo seamount b septemdierum the two b platifrons contain large amounts of diploptene while no hopanoid is detected in b septemdierum suggesting that b platifrons and b septemdierum harbors methanotrophic and thiotrophic bacteria respectively in spite of the same symbiont the large bulk 13c difference between the hatoma 44 8 and yonaguni 24 5 mussels reflects isotopically distinct hydrothermal ch4 hatoma 48 yonaguni 26 as a carbon source fatty acids of the hatoma and yonaguni mussels are more enriched in d 144 to 101 than the suiyo mussel 265 to 162 suggesting that d depleted magmatic water or d enriched hydrogen derived from ch4 could be a partial hydrogen source for methanotrophy or thiotrophy respectively apparent positive correlations are observed between 13c and d of the bulk and biomarkers for each mussel due to similar biochemical processes during de novo synthesis the compound specific 13c and d variations have provided much information on not only distinct carbon and hydrogen sources but also the lipid synthesis with respect to different symbiotic bacterial ecosystems

in situ quantitative raman detection of dissolved carbon dioxide and sulfate in deep sea high temperature hydrothermal vent fluids carbon dioxide emitted from hydrothermal vents as an important part of the global carbon cycle can directly affect hydrothermal ecosystems however traditional chemical analysis methods cannot directly measure the concentrations of dissolved co2 in high temperature hydrothermal fluids although in situ mass spectrometry has been applied to the measurements of deep sea it cannot be used to detect high temperature fluids in this study an in situ raman quantitative method for measuring dissolved co2 suitable for a hydrothermal environment is established the raman relative intensity of co2 displayed a linear relationship with increasing concentration of co2 under the investigated conditions up to 300 degrees c and 40 mpa allowing this in situ measurement method to be applied to most hydrothermal fields worldwide moreover we find that the quantitative calibration curve for so42 for high temperature and high pressure conditions is identical to that of so42 for room temperature and atmospheric pressure the concentrations of co2 in mid okinawa trough hydrothermal fluids determined by in situ raman measurement are 188 4 532 3 mmol kg which are about 3 times higher than those obtained by traditional sampling methods 59198 mmol kg however the concentrations of so42 calculated from in situ raman spectra were near zero indicating that the in situ raman measurement avoids hydrothermal fluids contaminated with seawater

formation and shortening deformation of a back arc rift basin revealed by deep seismic profiling central japan abstract the northern fossa magna nfm basin is a miocene rift system produced in the final stages of the opening of the sea of japan it divides the major structure of japan into two regions with north trending geological structures to the ne of the basin and ew trending structures to the west of the basin the itoigawa shizuoka tectonic line istl bounds the western part of the northern fossa magna and forms an active fault system that displays one of the largest slip rates 4 9 mm year in the japanese islands deep seismic reflection and refraction wide angle reflection profiling were undertaken in 2002 across the northern part of istl in order to delineate structures in the crust and the deep geometry of the active fault systems the seismic images are interpreted based on the pattern of reflectors the surface geology and velocities derived from refraction analysis the 68 km long seismic section suggests that the miocene nfm basin was formed by an east dipping normal fault with a shallow flat segment to 6 km depth and a deeper ramp penetrating to 15 km depth this low angle normal fault originated as a comparatively shallow brittle ductile detachment in a high thermal regime present in the miocene the nfm basin was filled by a thick 6 km accumulation of sediments shortening since the late neogene is accommodated along ns to ne se trending thrust faults that previously accommodated extension and produce fault related folds on their hanging wall based on our balanced geologic cross section the total amount of miocene extension is ca 42 km and the total amount of late neogene to quaternary shortening is ca 23 km

methane rich plumes in the suruga trough japan and their carbon isotopic characterization the carbon isotopic compositions 13cch4 of the methane rich buoyant plumes observed in the oxygenated hemipelagic sea waters of the suruga trough japan are discussed in relation to their sources during a survey made in may 1996 two layers of anomalous methane rich plumes both of which centred at the same station about a few tens of kilometres off the coast were found in the suruga trough the deeper plume ca 2100 m depth with a maximum methane concentration of 13 nmol kg had already been detected by a previous survey in 1986 at the same station whereas the shallower plume ca 1000 m depth with a maximum methane concentration of 10 nmol kg was newly discovered the estimated end member 13cch4 value 59 3 pdb for the deeper plume suggests a microbial origin of the methane probably derived from some shallow surface layer of sediment the plume could be supplied from a continuous cold fluid seepage on the sea floor of the suruga trough on the other hand the shallower plume is characterized by more 13c enriched end member methane 13cch4 38 2 pdb presumably produced by the thermogenic degradation of organic matter since thermogenic methane should originate from a deeper part more than 1000 m of the sedimentary layer it is unlikely that the thermogenic methane reaches the sea water by normal transport processes the shallower plume may be a result of some sudden catastrophic event on the sea floor such as earthquakes

helium isotopes in geothermal and volcanic gases of the western united states ii long valley caldera abstract systematic trends in helium isotope ratios and gas compositions in long valley caldera hot spring and fumarole gases reflect subsurface processes and conditions in the hydrothermal system high 3 he 4 he ratios to 6 5 atmospheric indicate a magmatic helium source diluted to varying degrees by crustal radiogenic helium as observed in western united states geothermal systems in general helium isotope ratios increase eastward across the caldera which we interpret as an input of magmatic helium to the hydrothermal fluid as it flows eastward over the caldera decreasing he condensible gas he co2 ratios accompanying this trend suggest that co2 addition and or preferential helium loss due to boiling are also occurring although near surface ph related co2 hco3 equilibria obscure the nature of this effect substantial changes in 3 he 4 he ratios were observed in long valley gases between 1978 and 1985 helium isotope ratios increased by 15 in the hot creek thermal vent with maximum ratios achieved in 1983 helium isotope ratios subsequently decreased in this and other hot vents in the caldera these observations indicate that substantial changes in the mixing ratio of radiogenic and magmatic helium may occur over relatively short periods of time in magmatically active systems

magnesium isotopic composition of submarine vent fluids from arc and back arc hydrothermal systems in the western pacific abstract seafloor hydrothermal systems are important sinks for mg as their concentration in high temperature hydrothermal vent fluids decreases to near zero through the formation of secondary minerals however the problem of mass balance still persists regarding the global sink for mg via sub seafloor high temperature hydrothermal reactions in this study we measured isotopic compositions of mg in high temperature hydrothermal vent fluids from 5 arc and back arc systems in the western pacific this was done to better understand mg behavior during hydrothermal circulation and to quantify the oceanic mg cycle the samples with significantly low mg concentrations showed 26mg depletion due to mg fractionation and mg fixation during hydrothermal circulation addition of mg to the permeable sub seafloor during venting is the probable reason for the isotopic variation of mg the vent fluids return flux with lighter mg isotopic compositions contain much smaller amounts of mg than seawater this confirms that the high temperature hydrothermal sinks have a less significant effect on the oceanic mg isotopic composition based on the simple steady state equations and low temperature hydrothermal sinks of 26mg 0 25 to 0 00 of 26mg 7 26 of the riverine mg input is presumed to be removed through the high temperature sink this estimate is lower than that proposed by mottl and wheat 1994 which was 10 40 thus other mg sinks such as the low temperature hydrothermal sink and or the dolomite sink need to be considered

helium isotope composition of fluid inclusions hosted in massive sulfides from modern submarine hydrothermal systems noble gas compositions of fluid inclusions hosted in sulfides from two modern submarine hydrothermal sites of contrasting tectonic settings have been analyzed the jade field central okinawa trough japan is located in an active intracontinental back arc basin whereas the so 134 field is related to the central spreading ridge of the north fiji basin which represents an active highly mature intra ocean back arc system previous conventional studies of fluid inclusions have revealed compelling evidence for subcritical phase separation of the hydrothermal fluids at both sites elemental abundances of ne ar kr and xe in fluid inclusions in all studied samples of chalcopyrite and sphalerite from both hydrothermal sites indicate that the heavier noble gases are derived from ambient seawater in contrast helium concentrations are 1 to 2 orders of magnitude higher than expected for equilibrium solution in seawater indicating that helium is predominantly derived from a magmatic source beneath the hydrothermal systems the 3 he 4 he ratios in sphalerite hosted fluid inclusions from the jade field and the so 134 field are similar to those reported from related vent fluids and show that fluid inclusions reliably record the helium isotope ratio of the original hydrothermal fluid however in the north fiji basin earlier black smoker activity and the formation of fe rich kies type sulfides seems to have been related to a more morb like volcanism whereas the younger recent white smoker hydrothermal activity in the north fiji basin can be attributed to a hot spot magmatism in the study area

on changes in porosity and volume during burial of argillaceous sediments abstract the porosity and hence volume of argillaceous sediments is determined by 1 the magnitude of the effective stress acting within the sediment 2 the previous stress history of the sediment and 3 at shallow depths of burial by features such as the mineralogy and the nature of the depositional environment stress paths and the critical state diagrams for a number of clays are used to investigate the range of porosities possible in argillaceous sediments as the effective stresses increase it is found that all porosity effective stress curves converge at large stresses the change in porosity is strongly dependent on the mean effective stress but largely independent of the deviatoric stress and thus is largely independent of the nature of the stress field acting on the basin compressional extensional etc because of the dependence of porosity on the mean effective stress no simple relationship exists between porosity and depth of burial but in the absence of overpressured pore fluids and assuming the sediment is not overconsolidated it is possible to contour the porosity effective stress diagram in terms of burial depths these data should assist in recalculating stratigraphic thicknesses for basin reconstruction and stratigraphic correlation studies

active hydrothermal mounds in the okinawa trough backarc basin japan abstract dive studies by the shinkai 2000 were made in september 1984 and july 1986 in the central axial rift of the middle okinawa trough a possible active backarc basin in a nascent stage hydrothermally active mounds were discovered on a small knoll 27 34 4 n 127 08 6 e directly south of the area where a high heat flow higher than 1 w m2 had been observed previously the largest mound 5 6 m high and 15 25 m wide has several peaks and ridges along which yellow materials are exposed shimmering water was noted at several places on the yellow materials the rest of the mound is thinly covered by brown materials the temperature of the ejecting water was higher than that of the ambient seawater by 2 3 c and a 40 cm long thermometer inserted into the mound recorded a temperature of 20 50 c analysis of the ejected water showed a methane content of about 200 nl kg it is possible that further dive studies will reveal larger scale hydrothermal activity in the area

evaluating earth degassing in subduction zones by measuring helium fluxes from the ocean floor abstract volatiles are lost from the earth s mantle to the atmosphere hydrosphere and the crust through subaerial and submarine volcanism quantifying the volatile sources bears fundamental information on a number of issues in earth sciences from the evolution of the atmosphere and oceans to the nature of chemical heterogeneity of the earth s mantle the primordial noble gas isotope 3he provides an unambiguous measure of the volatile flux from the mantle yet so far in the ocean region it has been only measured at a mid ocean ridge here we present original measurements of the 3he flux at the mid okinawa trough back arc basin the 3he flux was estimated from 3he 20ne vertical profiles measured in deep sea sediment pore water diffusive 3he fluxes vary from 1 6 3he atoms cm 2 s 1 at the hydrothermally active izena cauldron to 0 57 3he atoms cm 2 s 1 at the background site 13 km away these values are about 20 of the 3he flux measured at the east pacific rise supporting the never proven hypothesis that 3he mantle flux from subduction zones is a quarter of that at mor measured ocean floor 4he flux ranges from 3 3 105 to 4 8 105 4he atoms cm 2 s 1 higher than that measured worldwide suggesting that 4he flux at subduction zones might have been previously underestimated

helium and methane measurements in hydrothermal fluids from the mid atlantic ridge the snake pit site at 23 n methane and helium isotopes concentrations have been measured in hydrothermal fluids of black smoker vents at the snake pit area mar 23 n as part of the hydrosnake cruise with the submersible nautile the samples contain large quantities of helium and methane with endmember values of 4 6 10 5 cm3 stp g for helium and 1 38 10 3 cm3 stp g for methane the helium isotopic ratio 3he 4he is 8 4 times the atmospheric ratio these values are strikingly similar to those already obtained on the east pacific rise the ch4 3he ratio is also quite similar ch4 3he 2 6 106 suggesting a non biogenic origin of this gas in the fluids assuming that the range of variation of the 3he concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid ocean ridges the global mass flow involved in the hydrothermal circulation at the ridge s axis is estimated between 1000 and 3000 m3 of water sec leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years this estimate implies that in addition to the individual vents smokers there is an extensive diffuse circulation of hydrothermal fluids along the ridges in agreement with recent observations concerning heat budgets at hydrothermal sites in the eastern pacific

geotechnical properties of lower trench inner slope sediments abstract geotechnical property analyses on sediments recovered by dsdp drilling within select convergent margins were integrated to determine the variability in these properties along the trench inner slope and to delineate the effects of convergence on these properties consolidation states range from very underconsolidated to highly overconsolidated with preconsolidation pressures exceeding 46 000 kpa in quaternary sediments underconsolidated sediments are attributed to 1 1 high sedimentation rates 2 2 low sediment permeability relative to the length of the drainage path 3 laterally applied stresses and 4 induced pore water pressures resulting from the subduction of pelagic sediments with high water content factors contributing to the state of overconsolidation include 1 tectonically induced overpressures 2 removal of overburden by mass movement processes 3 3 low sediment accumulation rates 4 4 age vertical gradients of index properties also vary greatly with the maximum gradient associated with overconsolidated sediments values of porosity generally exceed 30 at all margins studied suggesting this porosity represents the minimum attainable solely by the effects of convergence geotechnical property results and site specific parameters suggest two end members should be considered in the general geotechnical property model for convergent margin sediments clastic dominated margins form the basis for the initial geotechnical property model these margins are characterized by thick trench sediment sequences which are folded and faulted and become progressively more deformed upslope convergence rates are low and no well developed faults or hrst and graben structures are evident on the downbending oceanic plate highly overconsolidated sediments and index property values which change rapidly with depth result from the slow progressive deformation of trench and lower slope sediments examples of clastic dominated margins include the nankai trough aleutian trench and washington continental margin pelagic dominated margins have significantly different geotechnical properties and site specific parameters these margins are characterized by thin clastic trench sediment sequences overlying pelagic sediments on a rapidly converging oceanic plate well developed faults and or hrst and graben structures are evident on the downbending oceanic plate sediment deformation along the trench and lower slope appears limited these sediments are underconsolidated and index property values change gradually but often irregularly with depth japan trench and middle america trench guatemala margins are considered pelagic dominated middle america trench mexico appears to represent an intermediate case having characteristics of both margin types

application of geometric models to inverted listric fault systems in sandbox experiments paper 2 insights for possible along strike migration of material during 3d hanging wall deformation abstract fault geometry is a primary control on hanging wall deformation in this study a series of positive inversion analogue experiments was conducted using rigid fault surfaces of true 3d geometry with consistent listric geometry along the transport direction the deformed geometry of the top horizon of the syn extension sequence on vertical serial sections was examined with a conventional 2d geometric restoration technique to calculate the inclined antithetic shear angle that best approximates the actual fault shape and to estimate the amount of apparent horizontal shortening during contraction the apparent shear inclination and the estimated apparent shortening show a systematic change along strike corresponding to the plan geometry of the master detachment surface at the hanging wall above embayments in the fault geometry the uplift is highest the apparent shear inclination is gentlest and the apparent horizontal shortening is greatest in contrast the apparent shear inclination is steepest and the estimated shortening is smallest above salients in the master detachment geometry where the uplift is lowest these changes suggest that the hanging wall displacement had an along strike component during deformation the hanging wall material moves from the regions above salients to those above embayments in the detachment surface during contraction average of the estimated apparent shortening was smaller than the actual amount of the experiments probably due to tectonic compaction this study shows that the geometry of the master detachment in plan view has the primary control on the lateral variation of the hanging wall deformation the data presented in this paper help understand 3d geometric relations between the hanging wall deformation and the underlying detachment surfaces

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

claystone porosity and mechanical behavior vs geologic burial stress abstract a dataset was assembled from studies on 35 preserved claystone cores from different locations around the world and burial depths from

variations in temperature and salinity of the surface water above the middle okinawa trough during the past 37 kyr abstract east china sea ecs is an important climate modulator of east asia in the last glacial period the global sea level the path and strength of the kuroshio current experienced great changes combined with the variable volume of fresh run off input they made the hydrographic situation in the ecs quite different from nowadays based on high resolution alkenone sea surface temperature sst and oxygen isotope composition of planktonic foraminifera globigerinoides sacculifer we reconstructed paleo sea surface salinity sss of a long piston core dgks9604 retrieved from the middle okinawa trough of the eastern ecs the 18o and sst records display significant variations with global ice volume synchrony of the millennial scale climate events like yd and heinrich events of core dgks9604 to the ice core from the northern high latitudes and the synchroneity of deglacial warming with the bolling allerod warming suggests a strong coupling of the sst variations in the marginal pacific ocean to the climate of the north atlantic most likely through the asian monsoon atmospheric circulation the ecs documents lowest sst 22 c at 26 cal kyr bp and 3 c sst difference between the full glaciation 26 to 19 cal kyr bp and mid to late holocene 6 cal kyr bp present the overall long term hydrographic variations in the middle okinawa trough are controlled by temporal and spatial variations in i the intensity and position of the kuroshio current ii intensity of the asian summer monsoon and iii sea level fluctuations coupled with ecs topography saline surface water dominated over the middle okinawa trough during early pre glaciation 37 to 31 cal kyr bp last deglaciation 19 to 11 6 cal kyr bp and mid to late holocene 6 cal kyr bp present whilst freshened surface water prevailed during the late pre glaciation 31 to 26 cal kyr bp full glaciation 26 to 19 cal kyr bp and early holocene 11 6 to 6 cal kyr bp

hydrothermal vent waters at 13 n on the east pacific rise isotopic composition and gas concentration abstract gas concentrations and isotopic compositions of water have been measured in hydrothermal waters from 13 n on the east pacific rise in the most mg depleted samples 5 10 3 moles kg the gas concentrations are 3 4 5 10 5 cm 3 stp kg helium 0 62 1 24 cm 3 stp kg ch 4 10 80 16 71 10 3 moles kg co 2 the samples contain large quantities 95 126 cm 3 kg of h 2 and some carbon monoxide 0 26 0 36 cm 3 kg which result from reaction with the titanium sampling bottles 13 c in methane and co 2 16 6 to 19 5 and 4 1 to 5 5 respectively indicate temperatures between 475 and 550 c whereas 13 c co is compatible with formation by reduction of co 2 on ti at 350 c close to the sampling temperature 3 he 4 he are very homogeneous at 7 5 0 1 r a 3 he 4 he 1 0 10 5 and very similar to already published data as well as ch 4 3 he ratios between 1 4 and 2 1 10 6 18 o and d in water show enrichments from 0 39 to 0 69 and from 0 62 to 1 49 respectively these values correspond to w r ratios of 0 4 7 the distinct 18 o enrichments indicate that the isotopic composition of the oceans is not completely buffered by the hydrothermal circulations the 3 he enthalpy relationship is discussed in terms of both hydrothermal heat flux and 3 he mantle flux

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

volume changes during diagenesis abstract the literature pertaining to volume change during diagenesis of clastic sediments is reviewed with respect to the problem of calculating pre and syn compaction thicknesses of sediments for basin reconstruction and stragraphic correlation studies four major mechanisms for volume change are identified mechanical compaction mechanical dissolution chemical dissolution and phase change the first two of these are found to be strongly dependent on the effective stress whilst the latter two show at least a pressure dependence quantification of the relationships between porosity and depth of burial of a sediment seems to be possible only for specific examples of the first of these processes at present this quantification is dealt with in the accompanying related publication

detailed volcanic and tectonic morphology of nakadomari hill in the southern okinawa trough abstract nakadomari hill is an unexplored edifice in the southern okinawa trough back arc basin where crustal extension by continental rifting occurs and few submarine eruptions associated with back arc volcanism have been mapped in detail high resolution bathymetric mapping with an autonomous underwater vehicle auv reveals that nakadomari hill is a submarine volcanic complex with recent lava flow eruptions the high resolution 2 m bathymetry shows striking contrast between rugged terrain in the central area and the adjacent smooth terrain the cone shaped features in the rugged terrain are covered by ropey fabric with high acoustic reflectivity and are devoid of tectonic deformation thus they are interpreted to be relatively younger lava domes the cone shaped features in the smooth terrain show low reflectivity and are dissected by ene wsw trending tectonic lineaments suggesting they were formed during older volcanism nakadomari hill developed through multi stage eruptions before and after back arc rifting and faulting the ropey and curtain folded morphology with high acoustic reflectivity are interpreted to be a field of lava flows and they are relatively young the area considered to be lava flows is estimated to be over 13 km2 showing that eruptions in the southern okinawa trough have been extensive an active volcanic system is supported by indicators of high temperature hydrothermal venting hydrothermal plumes with concurrent sharp temperature increases of up to 0 17 c were present even at the vehicle altitude of 100 m above the bottom the alignment of volcanic cone shaped features at nakadomari hill is in the nnw sse direction which is clearly different from the orientation of local rifting ene wsw at a larger scale the volcanic edifices west of kume island from the arc to back arc are also aligned roughly in the nnw sse direction and they are sub parallel to a major tectonic structure in the arc the kerama gap the agreement of the local volcanic and tectonic trends implies that magmatic focusing may have taken place along the tectonic structures of the kerama gap and in turn caused the extensive back arc volcanism in this area

methanogens in h2 rich hydrothermal fluids resulting from phase separation in a sediment starved basalt hosted hydrothermal system abstract we here report on specific chemical and microbial compositions observed at the archaean hydrothermal site in the southern mariana backarc spreading center which produces two remarkably different hydrothermal fluids one was black smoker hydrothermal fluid at 340 c containing a low concentration of methane with a relatively high carbon isotope ratio 13 c of methane relative to vpdb 7 8 indicating that methane originated from a magmatic source thus this is a fairly ordinary hydrothermal fluid for basalt hosted hydrothermal activity in contrast the other fluid was clear smoker hydrothermal fluid at 117 c containing a high concentration of methane with a very low carbon isotope ratio 49 7 the host rock of the archaean hydrothermal site is basalt and therefore fischer tropsch type reactions resulting from serpentinization of mantle rocks are not feasible as a source for the light carbon in methane additionally the carbon isotope ratio of carbon dioxide demonstrated that the sources of co 2 and ch 4 were not organic materials the remaining possibility biogenic methane was confirmed by cultivation of hyperthermophilic hydrogen oxidizing methanogens from both rocks covering the vent of clear smoker hydrothermal fluids and in situ cultivation systems although the dominance and abundance of methanogens were very low in this ecosystem the number was consistent with the relationship between hydrogen concentration and methanogen abundance takai et al 2015 these results suggest that phase separation led to concentration of hydrogen and subsequent persistence of a hyperthermophilic subsurface lithoautotrophic microbial ecosystem in both serpentine hosted and basalt hosted hydrothermal systems this type of ecosystem may occur in similar settings elsewhere on modern earth in addition similar communities may have existed in other types of deep sea hydrothermal systems in the geological past

mechanisms of compaction of quartz sand at diagenetic conditions the relative contribution of cracking grain rearrangement and pressure solution during experimental compaction of quartz sand at diagenetic conditions was determined through electron and optical microscopy and image analysis aggregates of st peter sand 255 60 m diameter grain size and porosity of approximately 34 were subjected to creep compaction at effective pressures of 15 34 5 70 and 105 mpa temperatures of 22 and 150 c nominally dry or water saturated pore fluid pressure of 12 5 mpa conditions and for times up to one year all aggregates displayed transient decelerating creep and volume strain rates as low as 2 10 10 s 1 were achieved the intensity of fracturing and degree of fragmentation increase with volume strain and have the same dependence on volume strain at all conditions tested indicating that impingement fracturing and grain rearrangement were the main mechanisms of compaction throughout the creep phase the increase in fracture density and decrease in acoustic emission rate at long times under wet conditions reflect an increase in the contribution of subcritical cracking no quantitative evidence of significant pressure solution was found even for long term creep at 150 c and water saturated conditions comparison of our findings to previous work suggests that pressure solution could become significant at temperatures or times somewhat greater than investigated here

he ar n and c isotope compositions in tatun volcanic group tvg taiwan evidence for an important contribution of pelagic carbonates in the magmatic source abstract the tatun volcanic group tvg northeastern taiwan is considered to be the extension of the ryukyu arc and belongs to the post collisional collapse okinawa trough strong hydrothermal activity is concentrated along the chinshan fault and da you keng dyk represents the main fumarolic area where the most primitive isotopic and chemical composition is observed in this study we present chemical and he ar c and n isotopic compositions of fumaroles bubbling gas and water from hot springs sampled in 2012 and 2013 high 3 he 4 he ratios from dyk fumaroles 6 5 ra show a typical arc like setting whereas other sampling areas show a strong dependence of 3 he 4 he and ch 4 3 he ratios with the distance from the main active hydrothermal area dyk this could mean strong crustal contamination and thermal decomposition of organic matter from local sediments carbon isotope compositions of dyk range from 6 67 to 5 85 and indicate that carbon contribution comes mainly from pelagic carbonates from the slab limestone mantle and sediment contributions are 63 19 and 18 respectively this is consistent with the negative 15 n values 1 4 0 5 observed for dyk implying a strong nitrogen mantle contribution and an absence of contribution from nitrogen pelagic carbonates these results have important consequences related to the ryukyu subducted slab in fact the ryukyu margin presents little in off scraping the sedimentary cover to the subducting plate that does not permit any nitrogen contribution in magma from tvg

peculiar features of suiyo seamount hydrothermal fluids izu bonin arc differences from subaerial volcanism abstract this is the first report of the dissolved gas composition of a deep sea venting hydrothermal system originating from arc volcanism the origin of dissolved gases in hydrothermal fluids from the suiyo seamount in the southern izu bonin ogasawara arc is discussed on the basis of chemical and isotopic compositions twelve high temperature up to 310 c fluid samples were collected from three vents of the hydrothermal system using the submersible shinkai 2000 the average 3 he 4 he ratio of the dissolved he is 8 1 r r atm which is within the range of values reported for n morb the co 2 3 he ratio is 12 109 which is within the range of arc volcanic gas values the 13c values of co2 and ch4 are 1 and 8 5 respectively which is quite high compared with other subaerial arc volcanic gases and those from mid ocean ridges these results which do not accord with those from subaerial volcanism are unlikely to result from fractionation or addition of carbon sources during the fluid circulation but are regarded as characteristic of the magma source of suiyo seamount a simple mixing of 97 morb mantle with 3 subducting slab explains well the composition of the helium and carbon in the parent magma

carbon sources in arc volcanism with implications for the carbon cycle new co2 3 he data from the east sunda arc indonesia confirm earlier observations that arc volcanic gases have higher co2 3 he ratios than mor environments on average 80 of arc volcanic co2 is recycled exogene carbon addition of a few percent of carbonate bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases but can not explain the he isotope observations the co2 3he in arc volcanoes is not strongly dependent on the composition of modem trough sediments e g deep sea clays vs carbonate rich sequences and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of arcs the sum of globally deep subducted sediment and slab carbon exceeds the estimated arc co2 flux and approximately 3 5 teramole of carbon may return annually to the mantle in convergent zones the modem combined processes of mor volcanism slab alteration and subduction volcanism do not produce a substantial carbon flux into the exosphere and rate changes in ocean floor spreading are unlikely to cause major changes in atmospheric co2 as a result of changes in the volcanic co2 fluxes intense pulses of flood basalt volcanism however may alter the co2 contents of the atmosphere over the course of a millenium or so and influence global climate

methane seepage inferred from pore water geochemistry in shallow sediments in the western slope of the mid okinawa trough abstract widely distributed cold seeps are crucial sources of carbon to the seawater whereas anaerobic oxidation of methane aom and precipitation of authigenic carbonate might change the compositions of the methane rich fluids and thus reduce the outputs of dissolved carbon to seawater in this work we analyze the pore water compositions of four gravity cores with high methane concentration abnormalities in pore water or in overlying seawater in the western slope of the mid okinawa trough for the northern research area active weak methane seepage through the seafloor is identified in the vicinity of mud volcanoes sites c01 and c10 and strong emissions of gas and fluids may occur in the central mud volcanoes in a submarine canyon at the south c23 site exhibits rarely methane seepage while high rate transportation of methane from deep sediments and associated aom are identified at site c25 where small vertical faults and gas bearing layers are developed at the surrounding aom at site c25 is indicated by 1 quasi linearly decrease of sulfate concentrations with depths 2 intense increases of dissolved inorganic carbon dic concentrations and 3 significantly negative 13c values vary from 7 2 to 26 3 of dic organoclastic degradation in the shallow sediments is not obviously recognized in the study area because of the low concentrations of nh4 as well as negligible sulfate consumption at three of the four sites our data reveal that the cold systems are one of the dic sources the fluxes are ca 11 2 mmol m2 yr to the seawater in the okinawa trough which can be tracked by high depletion of 13c 13cdic ranges from 7 2 to 26 3 vpdb

volatile element isotopes of submarine hydrothermal mineral deposits in the western pacific the abundance and isotopic compositions of volatile elements trapped in fluid inclusions of submarine hydrothermal mineral deposits in western pacific subduction zones okinawa trough izu bonin arc mariana trough and lau basin and in kuroko ores in northeastern japan are presented the helium isotopic compositions corrected for air contribution of the okinawa and mariana troughs ranging 4 49 7 68 ra are lower than those of the izu bonin and lau basin 7 62 8 91 ra this characteristic might reflect the differences in regional tectonic setting the okinawa and mariana troughs are related to back arc spreading with strong graben sedimentary signature whereas the izu bonin arc is associated with island arc magmatism the arc contribution to the lau basin volcanism is significantly strong even though it is assigned to back arc spreading nitrogen isotopes can also be explained by a similar hypothesis whereas argon and carbon isotopes cannot be used to discriminate tectonic setting 13c co2 3he and 15n n2 36ar diagrams elucidate the source of carbon and nitrogen the mor type mantle contributions to carbon are mostly smaller in the okinawa and mariana troughs ranging 0 06 8 9 with the average of 2 4 than in the izu bonin and lau basin 2 1 25 with the average of 7 7 the sedimentary contributions to nitrogen are larger in the okinawa and mariana troughs 11 65 with the average of 35 than in the izu bonin and lau basin 4 24 with the average of 15 and the kuroko samples agree well with the latter carbon and nitrogen fluxes are again higher in okinawa trough than in izu bonin arc

on the hydro mechanical behaviour of remoulded and natural opalinus clay shale the geo energy sector makes use of advanced technologies such as shale gas extraction co2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations due to the great depths involved in these applications and the difficulties in retrieving intact samples remoulded shale specimens are often adopted for hydro mechanical testing remoulded and intact shales may substantially differ in their hydro mechanical behaviour due to the particular structure of the natural material which is the result of diagenesis and burial history this paper presents an experimental campaign aimed at i characterizing the role of diagenesis and depth for opalinus clay shale and their impact on the hydro mechanical behaviour of the material and ii understanding how representative the behaviour of the remoulded material is with respect to that of the natural shale in this paper the hydro mechanical behaviour of remoulded and intact specimens from the opalinus clay shale formation is investigated by means of a comprehensive oedometric testing campaign the effects of depth and diagenesis on the material behaviour are analysed by testing intact specimens that come from two different sites and depths of the considered shale formation the results highlight a considerably greater stiffness for the natural opalinus clay with respect to the remoulded specimens when the same vertical effective stress is considered together with a significantly lower porosity for the former which is shown to be the result of diagenetic processes rather than solely mechanical compaction a lower swelling sensitivity is also manifested by the natural material with respect to the remoulded specimens as a result of the formation of bonding on the other hand the diagenetic processes do not seem to have a strong impact on the permeability of the material finally creep effects are reduced when diagenesis occurs while they become more relevant when the material is disturbed or remoulded the obtained results provide significant insight into the roles of depth diagenesis and structural disturbance on the hydro mechanical behaviour of the opalinus clay shale

helium and carbon gas geochemistry of pore fluids from the sediment rich hydrothermal system in escanaba trough abstract ocean drilling program odp leg 169 which was conducted in 1996 provided an opportunity to study the gas geochemistry in the deeper part of the sediment rich hydrothermal system in escanaba trough gas void samples obtained from the core liner were analyzed and their results were compared with analytical data of vent fluid samples collected by a submersible dive program in 1988 the gas geochemistry of the pore fluids consisted mostly of a hydrothermal component and was basically the same as that of the vent fluids the he isotope ratios r ra 5 6 6 6 indicated a significant mantle he contribution and the c isotopic compositions of the hydrocarbons 13c ch4 43 13c c2h6 20 were characterized as a thermogenic origin caused by hydrothermal activity on the other hand the pore fluids in sedimentary layers away from the hydrothermal fields showed profiles which reflected lateral migration of the hydrothermal hydrocarbons and abundant biogenic ch4 helium and c isotope systematics were shown to represent a hydrothermal component and useful as indicators for their distribution beneath the seafloor similarities in he and hydrocarbon signatures to that of the escanaba trough hydrothermal system were found in some terrestrial natural gases which suggested that seafloor hydrothermal activity in sediment rich environments would be one of the possible petroleum hydrocarbon generation scenarios in unconventional geological settings