chlorine stable isotopes and halogen concentrations in convergent margins with implications for the cl isotopes cycle in the ocean abstract chlorine stable isotopes 37cl and halogen concentrations e g br cl in 168 pore fluids and 23 serpentines and other solids from three subduction zones the nankai trough costa rica and mariana forearc provide critical information on fluid sources flow paths and reaction conditions the 37cl values of pore fluids at the nankai and costa rica subduction zones are significantly more negative minimum 7 8 2 0 3 than seawater value 0 at nankai trough the minimum 37cl value is situated below the decollement and evolves laterally from 7 8 at the most arcward odp site 808 to 7 1 at site 1174 2 km seaward from site 808 and to 5 8 at the reference site 1173 at costa rica along the decollement the minimum 37cl value evolves from 5 5 at the most arcward odp site 1040 1254 to 3 2 at site 1043 1255 1 km seaward and to 0 at the reference site 1039 1253 at both subduction zones the br cl ratios are higher than the seawater value 1 5 10 3 and also show seaward evolutions these pore fluids originate from greater depth arcward at 250 c from hydrous mineral formation that preferentially incorporates 37cl and excludes br in contrast the 37cl values in the pore fluids at the mariana serpentine mud volcanoes are higher than the seawater value 0 3 to 1 8 and the br cl ratios are lower these pore fluid values and the high cl concentrations with positive 37cl values 1 2 to 6 0 in the serpentines support that the upwelling pore fluid originates from dehydration of the subducting slab that releases water enriched in 37cl into the fluid phase the constancy of the ocean 37cl over the past 200 ma suggests that the isotopically fractionated chlorine in serpentinites and the cl exchanged in subduction zones are efficiently recycled back into seawater if the efficiency is

chlorine isotopic compositions of high temperature hydrothermal vent fluids over ridge axes abstract we present chlorine stable isotope compositions of high temperature hydrothermal vent fluids from two mid oceanic ridges the six hydrothermal fluids come from sites along the slow spreading mid atlantic ridge menez gwen at 37 50 n lucky strike at 37 17 n and rainbow at 36 14 n and the ultrafast spreading east pacific rise from three contiguous segments centered respectively at 17 25 s 18 15 s and 18 26 s these samples exhibit a large range in temperature ph chlorinity and mg content reflecting various geological settings and substrata nature basaltic or ultramafic although showing a large range of chlorinity from 251 to 821 mmol kg the fluids display homogeneous chlorine isotope signatures 37 cl smoc 0 03 0 06 indistinguishable from that of seawater this homogeneity contrasts with the large range of 37 cl previously observed in continental or off axis oceanic fluids this study explores possible processes that may change cl concentration during fluid genesis and discusses their theoretical isotopic effects the 37 cl homogeneity implies that at the p t conditions of the ridge axis the process of phase separation at sub or super critical conditions that explains most of chlorinity variations does not significantly fractionate chlorine isotopes this study shows that the physical and chemical processes that likely alter cl concentrations in ridge axis systems i e transport processes mixing or water rock interaction contribute to minimize the range of 37 cl around the seawater 37 cl value

salinization processes in paleowaters in coastal sediments of suriname evidence from δ37cl analysis and diffusion modelling in the coastal plain of suriname a stagnant body of fresh 250 mg l cl and moderately brackish 250 1000 mg l cl groundwater of meteoric origin is found in permeable tertiary formations this groundwater body formed during the last wisconsin regression extends offshore into deposits on the continental shelf the authors found that this paleowater is slowly being salinized by downward solute transport from overlying holocene marine clays and upward transport from saline cretaceous sediments the downward transport has been studied at two sites by relating analyses of chloride contents and 37cl 35cl isotope ratios in pore water with computer simulations of diffusive transport optimization of process parameters yielded an effective diffusion coefficient of and a fractionation factor of 1 0027 which agrees well with earlier studies with the computer model the following periods of marine influence were found 6000 4 100 yr bp and 10 000 500 yr bp at the sites located 20 and 3 km from the coastline respectively according to the diffusion model the downward flux of salts has not penetrated deeper than 100 m salts below this depth are thought to originate from the cretaceous sediments however groundwater chloride concentration and chlorine isotope data are scarce below this depth while uncertainty regarding the various regressions and transgressions precludes solute transport modelling clay layers at the base of the tertiary appear to inhibit the upward transport by lateral dispersive mixing at the tertiary cretaceous boundary oil reservoirs are also related to these clay seals the presence of the seal and perhaps the oil below can therefore be predicted by the chloride profile in the upper 250 m

chlorine isotopic composition in seafloor serpentinites and high pressure metaperidotites insights into oceanic serpentinization and subduction processes bulk rock chlorine content and isotopic composition 37 cl were determined in oceanic serpentinites high pressure metaperidotites and metasediments in order to gain constraints on the global chlorine cycle associated with hydrothermal alteration and subduction of oceanic lithosphere the distribution of insoluble chlorine in oceanic serpentinites was also investigated by electron microprobe the hydrothermally altered ultramafic samples were dredged along the south west indian ridge and the mid atlantic ridge the high pressure metamorphic samples were collected in the western alps metaperidotites in the erro tobbio unit and metasediments in the schistes lustres nappe oceanic serpentinites show relatively large variations of bulk rock cl contents and 37 cl values with mean values of 1105 596 ppm and 0 7 0 4 o respectively n 8 1 serpentines formed after olivine meshes show lower cl content than those formed after orthopyroxene bastites in bastites of two different samples cl is positively correlated with al 2 o 3 and negatively correlated with sio 2 these relationships are interpreted as reflecting preferential cl incorporation into the bastite structure distorted by al substituted for si rather than different alteration conditions between olivine and orthopyroxene minerals high pressure metaperidotites display relatively homogeneous cl contents and 37 cl values with mean values of 467 88 ppm and 1 4 0 1 respectively n 7 1 a macroscopic high pressure olivine bearing vein formed from partial devolatilization of serpentinites at 2 5 gpa and 500 600 c shows a cl content and a 37 cl value of 603 ppm and 1 6 o respectively metasediments n 2 show low whole rock cl contents 15 ppm cl that did not allow cl isotope analyses to be obtained the range of negative 37 cl values observed in oceanic serpentinites is likely to result from water rock interaction with fluids that have negative 37 cl values the homogeneity of 37 cl values from the high pressure olivine bearing vein and the metaperidotite samples implies that progressive loss of cl inherited from oceanic alteration throughout subduction did not significantly fractionate cl isotopes chlorine recycled in subduction zones via metaperidotites should thus show a range of 37 cl values similar to the range found in oceanic serpentinized peridotites

chlorine isotope residual salt analysis a new tool to investigate formation waters from core analyses this article presents the first results of chlorine residual salt analysis cl rsa a new technique that allows investigation of the isotopic composition of chlorine in oil field waters from core analysis as water evaporates the residual salts precipitate in the pores of a core unlike the routinely used strontium isotope residual salt analysis sr rsa technique which determines the composition of a trace element strontium the cl rsa technique allows the determination of the isotopic composition and origin of one of the most abundant anions in natural waters the results show that combining the 37cl of two successive leachates of a core sample leads to an isotopic composition that is representative of pore water the reproducibility of the method applied to sandstone samples is considered to be 0 05 the cl rsa technique was tested on two wells from the elgin area north sea united kingdom the 37cl results in formation waters range from 1 03 to 0 57 with an overall increase with depth these results have been compared to the 87sr 86sr ratios of pore waters determined in the same wells using the sr rsa technique the similarity of form between the 37cl and 87sr 86sr profiles with depth confirms that residual salts permit a reliable investigation of the chlorine isotopic composition from core analysis as with the sr rsa technique cl rsa could be used to test the isotopic homogeneity of a sample and to assess the compartmentalization of oil fields and reservoirs this technique could provide key information regarding the origin of the salinity and its evolution during the reservoirs filling as well as help in the monitoring during field production

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

a technique for quantifying groundwater pumping and land subsidence using a nonlinear stochastic poroelastic model subsidence in yunlin county taiwan is serious and continuous the taiwan high speed rail thsr route crosses the subsidence area and might be affected by differential settlements it is important to evaluate the pumping quantity for water resource management and to predict the subsidence for land resource management to mitigate the subsidence problem in taiwan this study combines first order second moment fosm stochastic poroelastic theory with nonlinear parameters to develop a fosm nonlinear stochastic poroelastic model and applies it to quantify groundwater pumping and future subsidence with uncertainty the additional loading and discharge are evaluated by fitting the subsidence historical data to the numerical model the results show that the proposed model well describes the subsidence behavior and quantifies groundwater pumping however the numerical results are larger than the monitoring data at various depths which might be due to the different compaction situations in individual formations of the aquifer system the predicted subsidence at the yuanchang monitoring well is the largest 0 32 0 52 m in 2020 with consideration of the climate change effects achieved by adding an additional discharge of 31 7 the large uncertainty is caused by the large variation of hydraulic conductivity caused by the heterogeneity of the aquifer system which could be improved by doing more experiments or using a conditioned model the information provided in this study is useful for the safety of thsr and for land and groundwater resource management in yunlin county taiwan

elemental and isotopic chloride geochemistry and fluid flow in the nankai trough 1 the first transect of pore fluid cl profiles across the deformation front of an accretionary prism and underthrust section nankai trough and the first cl isotopic profile in this environment are presented these demonstrate that there is channelized horizontal episodic flow through most of the section arcward of the deformation front and in the lowermost section seaward of the deformation front in the underthrust sediments channels appear to be continuous fluid velocities within the channels based on cl gradients are 13 5cm year the near balance of depth integrated flow and the subduction of pore fluid indicates that flow episodes are frequent 37cl values are lower than seawater throughout the section averaging 6 1 per mil this demonstrates fluid mineral exchange of cl and suggests that subducted solids carry enriched 37cl that is efficiently recycled from deeper levels in the subduction zone back into seawater and may be responsible for the seawater mantle 37cl fractionation

chlorine stable isotope studies of old groundwater southwestern great artesian basin australia abstract stable cl isotope ratios 37 cl 35 cl were measured in groundwater samples from the southwestern flow system of the great artesian basin australia to gain a better understanding of the cl sources and transport mechanisms 37 cl values range from 0 to 2 5 smoc and are inversely correlated with cl concentration along the inferred flow direction the cl isotopic compositions in conjunction with other geochemical parameters suggest that cl in groundwaters is not derived from salt dissolution mixing of the recharge water with saline groundwater cannot explain the relationship between 37 cl and cl concentration measured marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the cl concentrations observed in wells that are close to the recharge area and in groundwaters sampled along the southern transect 37 cl values measured in the leachate of the bulldog shale suggest that the aquitard is the subsurface source of cl for the majority of groundwater samples studied diffusion is likely the mechanism through which cl is transported from the pore water of the bulldog shale to the aquifer however a more detailed study of the aquitard rocks is required to verify this hypothesis

chlorine isotope distribution in formation waters texas and louisiana theoretically the chlorine isotope ratio 37cl 35cl can aid in identifying chloride sources and in distinguishing chloride transport mechanisms among formation waters if ratio differences exist among samples we measured the chlorine ratios of 18 formation water samples from oil fields along the texas louisiana gulf coast representing depths between 2 016 and 4 267 m chloride concentrations of samples ranged from 4 to 94 874 g l the chlorine ratios ranged from 1 24 to 0 58 pmil with respect to standard mean ocean chloride or smoc precision 0 12 pmil and enrichment of 37cl correlates with increasing concentration we also compared the isotope ratios of samples from within the weeks island salt dome with adjacent formation waters in louisiana all ratio measurements on the salt are between 0 1 and 0 3 pmil and for the formation waters are between 0 0 and 0 22 pmil the probability that the salt measurements differ from the waters is 99 we conclude that significant chlorine isotope ratio differences exist among formation waters and between the waters and potential sources in the gulf coast region and that the chlorine ratio will be a valuable tool in interpreting chloride geochemistry in this region

a cross calibration of chlorine isotopic measurements and suitability of seawater as the international reference material abstract a collection of 24 seawaters from various worldwide locations and differing depth was culled to measure their chlorine isotopic composition 37cl these samples cover all the oceans and large seas atlantic pacific indian and antarctic oceans mediterranean and red seas this collection includes nine seawaters from three depth profiles down to 4560 mbsl the standard deviation 2 of the 37cl of this collection is 0 08 which is in fact as large as our precision of measurement 0 10 thus within error oceanic waters seem to be an homogeneous reservoir according to our results any seawater could be representative of standard mean ocean chloride smoc and could be used as a reference standard an extended international cross calibration over a large range of 37cl has been completed for this purpose 13 geological fluid samples of various chemical compositions and a manufactured ch3cl gas sample with 37cl from about 6 to 6 have been compared data were collected by gas source isotope ratio mass spectrometry irms at the paris reading and utrecht laboratories and by thermal ionization mass spectrometry tims at the leeds laboratory comparison of irms values over the range 5 3 to 1 4 plots on the y x line showing a very good agreement between the three laboratories on 11 samples the trend line between paris and reading universities is 37clreading 1 007 0 009 37clparis 0 040 0 025 with a correlation coefficient r2 0 999 tims values from leeds university have been compared to irms values from paris university over the range 3 0 to 6 0 on six samples the agreement between these two laboratories using different techniques is good 37clleeds 1 052 0 038 37clparis 0 058 0 099 with a correlation coefficient r2 0 995 the present study completes a previous cross calibration between the leeds and reading laboratories to compare tims and irms results anal chem 72 2000 2261 both studies allow a comparison of irms and tims techniques between 37cl values from 4 4 to 6 0 and show a good agreement 37cltims 1 039 0 023 37clirms 0 059 0 056 with a correlation coefficient r2 0 996 our study shows that for fluid samples if chlorine isotopic compositions are near 0 their measurements either by irms or tims will give comparable results within less than 0 10 while for 37cl values as far as 10 either positive or negative from smoc both techniques will agree within less than 0 30

palaeohydrodynamics of fluids in the brent group oseberg field norwegian north sea from chemical and isotopic compositions of formation waters generally the history of past sub surface fluid movements is difficult to reconstruct however the composition of oil field waters characterizes the origins and mixing processes that allow such a reconstruction we have investigated present day formation waters from brent group sedimentary rocks of the oseberg field in order to assess both their geochemical variations and their origin s water samples sampled at the separator produced from immediately above the oil water contact and from the aquifer water saturated zone below the oil water contact were taken from 11 wells across the field in addition 3 trace water samples were extracted from oil produced from higher up in the oil column the water samples were analysed for their chemical components and isotopic compositions conservative tracers such as cl br deltad and delta o 18 were used to evaluate the origin of the waters all formation waters can be characterised as na cl brines the separator samples are of aquifer origin indicating that aquifer water drawn up by the pressure reduction near the well is produced from the lower few tens of metres of the oil zone by defining plausible endmembers the waters can be described as mixtures of seawater 60 90 meteoric water 10 30 evaporated seawater primary brines 3 5 and possibly waters which have dissolved evaporites secondary brines alternatively using multidimensional scaling the waters can be described as mixtures of only 3 endmembers without presupposing their compositions in fact they are seawater very dilute brine and a secondary brine confirming the power of this approach meteoric water was introduced into the reservoir during the end brent and early cretaceous periods of emergence and erosion and partially replaced the marine pore fluids lateral chemical variations across the oseberg field are extremely small the waters from closer to the erosion surfaces show slightly stronger meteoric water isotopic signatures the primary and secondary brines are believed to come from permian and triassic evaporitic rocks in the deeply buried viking graben to the west and to have been modified by water rock interactions along their migration path these primary basinal brines have not been detected in the oil zone waters suggesting that the brines entered the reservoir after the main phase of oil migration there are indications that these external fluids were introduced into the reservoir along faults present day aquifer waters are mixtures of waters from different origins and hardly vary at a field scale they are different in composition to the water trapped in the present oil zone one of the oil zone samples is a very dilute brine it is thought to represent a simple mixture of seawater and meteoric water due to oil emplacement this geochemical signature was preserved in the waters trapped within the oil zone another oil zone water shows a very similar chemical signature to the aquifer waters but the chlorine isotopic signature is similar to that of the dilute oil zone water this water is interpreted to represent a palaeo aquifer water that is it was within the aquifer zone in the past but was trapped by subsequent emplacement of more oil these vertical differences can be explained by two features i emergence of the brent group sedimentary rocks in the early cretaceous allowed ingress of meteoric water ii subsequent rapid burial of viking graben rocks caused migration of petroleum and aqueous fluids into the adjacent less deeply buried oseberg field c 2001 elsevier science ltd all rights reserved

preferential diffusion of 35cl relative to 37cl in sediments of kau bay halmahera indonesia kau bay a 470 m deep basin is separated from the pacific ocean by a shallow 40 m deep sill during the last glaciation this sill was above sea level and the bay turned into a freshwater lake after glaciation the sea level rose and the bay turned saline again since then chloride from the newly formed saline sediments diffused into the freshwater sediments as the sedimentation rate was constant throughout the holocene it is relatively easy to model the chloride concentration in the sediment pore water the diffusion coefficient of 35cl is slightly higher than the diffusion coefficient of 37cl thus variations in 37cl were expected in the pore water because the pore water history of kau bay is well known it was possible to use 37cl variations to determine the diffusion coefficient ratio d35d37 for the two stable isotopes of chlorine it was found that this ratio is 1 0023 in the pore water from sediments in this bay

origin and evolution of fluids from mud volcanoes in the barbados accretionary complex a large collection of fluids 54 interstitial fluids and four expelled fluids were sampled at the manon site at the outer edge of the barbados accretionary complex these warm fluids up to 20 c are expelled by sub marine 5000 mbsl mud volcanoes consisting of diapirs unchanneled flow and diatremes channeled chlorine stable isotope ratios of these fluids were measured by irms with a reproducibility of 0 05 1 versus smoc standard mean ocean chloride a large range of 37cl between 5 3 and 0 1 is observed data from each volcanic structure describe a mixing between seawater and a low 37cl fluid the whole set of data is interpreted as the result of a mixing between two deep components and seawater the two deep fluids are chemically distinct e g in ca mg k li sr and br contents and br cl ratio they display low and significantly different 87sr 86sr ratios 0 707790 and 0 707892 respectively and 37cl values 4 51 and 5 24 respectively physicochemical processes such as mineralogical transformation diffusion compaction or ion filtration are known to fractionate chlorine stable isotopes and can produce fluids with negative 37cl values ion filtration due to sediment compaction appears to be the more likely process to explain the negative 37cl values observed at the manon site a model for the generation of these signatures is proposed where a residual negative 37cl fluid reservoir is created at the bottom of the prism or the sediment pile further compaction fracturing and or dewatering of the slab may flush out these fluids and focus them towards the decollement zone mixing between the fluids and ultimately with seawater and water released during gas hydrate destabilizations may explain the data set within the individual cores and between the different structures

major and trace element and sr isotope constraints on fluid circulations in the barbados accretionary complex part 1 fluid origin abstract we measured the chemical and sr isotope compositions of vent and pore fluids and associated sediments from a diapiric field located near 13 5 n east of the deformation front of the barbados accretionary complex the two diapiric structures with the largest thermal anomalies and characterized by active fluid conduits exhibit the strongest chemical and 87 sr 86 sr variations these two diatremes atalante and cyclope also have low chloride contents and non radiogenic 87 sr 86 sr which may be explained by interaction between seawater and volcanic ash or with underlying oceanic crust in the central zone of the two structures 87 sr 86 sr varies little with depth which implies that fluid expulsion is at such a high rate that it is not affected by seawater 87 sr 86 sr the expelled fluids probably circulate along the decollement zone and ascend along faults which act as channels a deep component is probably located in the decollement zone whereas another component may be recirculated seawater the ascending fluid interacted with numerous materials causing dehydration of clay minerals and alteration of volcanic ash and or underlying oceanic crust to explain the low chloride contents of the atalante fluids gas hydrate decomposition yielding dilution of the fluid without modifying its sr isotope ratio needs to be superimposed on the mixing between seawater and the deep component the occurrence of gypsum in these two diatremes implies higher fluid temperatures and more intense activity at least temporarily to allow the deposition of such a mineral

smectite and fluid budget at nankai odp sites derived from cation exchange capacity abstract pore fluid chlorinity lower than seawater is often observed in accretionary wedges and one of the possible causes of pore water freshening is the smectite to illite reaction this reaction occurs during diagenesis in the 80 150 c temperature range low chlorinity anomalies observed at the toe of accretionary wedges have thus been interpreted as evidence for lateral fluid migration from inner parts of the wedge and the seismogenic zone however temperature conditions in nankai trough are locally high enough for the smectite to illite transition to occur in situ cation exchange capacity is here used as a proxy for smectite content in the sediment and the amount of interlayer water released during the smectite to illite reaction represents in average 12 water molecules per cation charge water and chloride budget calculations show that there is enough smectite to explain the chlorinity anomalies by in situ reactions the shape of the pore fluid chlorinity profiles can be explained if compaction is also taken into account in the model lateral flow is not needed this argument based solely on chloride concentration does not imply that lateral flow is absent however previous estimations of lateral fluid fluxes and of the duration of transient flow events along the decollement should be reconsidered

chlorine isotope constraints on fluid rock interactions during subduction and exhumation of the zermatt saas ophiolite 1 chlorine isotope compositions of high pressure 2 3 gpa serpentinite rodingite and hydrothermally altered oceanic crust aoc differ significantly from high and ultrahigh pressure 3 2 gpa metasedimentary rocks in the aosta region italy texturally early serpentinites rodingites and aoc have bulk 37cl values indistinguishable from those of modern seafloor analogues 37cl 1 0 to 1 0 in contrast serpentinites and aoc samples that recrystallized during exhumation have low 37cl values 2 7 to 0 5 37cl depletion correlates with progressive changes in bulk chemistry hp uhp metasediments have low 37cl values median 2 5 that differ statistically from modern marine sediments median 0 6 cl in metasedimentary rocks is concentrated in texturally early minerals indicating modification of seafloor compositions early in the subduction history the data constrain fluid sources during both subduction and exhumation related phases of fluid rock interaction 1 marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction 2 no pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial 3 localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel most samples however preserved protolith signatures during subduction to near arc depths

chloride and chlorine isotopes 36cl and δ37cl as tracers of solute migration in a thick clay rich aquitard system detailed vertical profiles of dissolved cl and its isotopes 36cl and 37cl provided new information on the origin and systematics of this conservative tracer in pore waters of a thick aquitard system the aquitard system consists of surficial quaternary clay rich till 80 m thick deposited 30 20 kyr b p overlying cretaceous marine clay 76 m thick deposited 71 ma the distribution of cl 37cl and br showed the presence of five distinct end members for cl the top of the unoxidized till a regional aquifer underlying the cretaceous clay two localized geological heterogeneities sand streaks in the till and glacial meltwater emplaced with the till and still present at depths of between 36 and 60 m numerical simulations of the transport of cl from the sand streaks indicated that this geochemical profile has been developing throughout most of the holocene the 36cl measurements showed that the age of the dissolved cl in the upper cretaceous clay is likely between 0 75 and 1 9 myr the 36cl measurements further suggested that the dissolved cl in the till was not directly derived from the underlying cretaceous clay finally it was not possible to quantify the effects of isotopic fractionation of 37cl relative to 35cl because of diffusion in this aquitard system

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

chlorine transfer out of a very low permeability clay sequence paris basin france 35cl and 37cl evidence abstract the marine callovo oxfordian clay formation is found at a depth around 410m in the eastern part of the paris basin france it is a very low permeability formation investigated by the french agency for nuclear waste management andra to study the feasibility of a radioactive waste disposal examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation this study uses chlorine isotopes to investigate long term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks detailed chlorine concentration and 37cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers the dogger at the bottom and the oxfordian kimmeridgian tithonian unit at the top they are discussed in terms of chlorine budget and hydrogeological processes clay pore waters and aquifer waters show strong chlorine concentration depletion a steep cl concentration gradient from the dogger at 500m in depth 2500 mg l to the oxfordian kimmeridgian tithonian aquifer near the surface 10 mg l is associated to a v shaped profile of the 37cl values modelling cl transport shows that a hydrodynamic dispersion process explains cl concentration and 37cl profiles in oxfordian limestone this process implies a mean upward flux of chloride in the 2 6 10 8 8 2 10 8 mole m2 yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride the modelling and knowledge of underground water transfer suggest a maximum effective cl hydrodynamic vertical dispersion coefficient vertical cl transport coefficient of 7 6 10 10 m2 s chlorine transfer through the callovo oxfordian clay since deposition 160my ago can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events such as early diffusion ion filtration etc

strontium isotopic characteristics of arc volcanic rocks at the initial stage of subduction in western japan abstract in western japan the philippine sea plate subducts northwestward from the ryukyu trench and the nankai trough to form two volcanic arcs the ryukyu and southwest japan arcs respectively these arcs are thought to be in the initial stage of subduction because microearthquake data show that the subducting slab extends only a short distance from the trenches in the southwest japan arc volcanoes are aligned parallel to the nankai trough although the leading edge of the subducted slab does not reach under the volcanic arc to the south the subducted slab reaches just under the ryukyu volcanic arc we determined 87sr 86sr ratios and rb and sr contents for 39 volcanic rock samples from 14 quaternary volcanoes of both arcs and summarized the spatial distribution of the ratios the ranges of 87sr 86sr ratios of volcanic rocks from the ryukyu and southwest japan arcs are 0 7040 0 7069 and 0 7035 0 7066 respectively in the ryukyu arc the regional variation in 87sr 86sr ratios of volcanic rocks is hidden under the wide scatter of ratios of different volcanic rocks from each one volcano in the southwest japan arc the ratios of volcanic rocks from volcanoes on the volcanic front vary in the along arc direction 0 7040 0 7048 for the western part 0 7035 0 7039 for the central part and 0 7048 0 7066 for the eastern part the across arc variations in the ratios are different from place to place these isotopic features suggest the absence of slab derived components in the source mantle and reflect the heterogeneous nature of 87sr 86sr ratios in the upper mantle modified by crustal processes this coincides with the seismological observation that the subducting philippine sea slab does not reach under the volcanic arc at all

contemporaneous deposition of phyllosilicates and sulfates using australian acidic saline lake deposits to describe geochemical variability on mars 1 studies of the origin of the martian sulfate and phyllosilicate deposits have led to the hypothesis that there was a marked global scale change in the mars environment from circum neutral ph aqueous alteration in the noachian to an acidic evaporitic system in the late noachian to hesperian however terrestrial studies suggest that two different geochemical systems need not be invoked to explain such geochemical variation western australian acidic playa lakes have large ph differences separated vertically and laterally by only a few tens of meters demonstrating how highly variable chemistries can coexist over short distances in natural environments we suggest diverse and variable martian aqueous environments where the coetaneous formation of phyllosilicates and sulfates at the australian sites are analogs for regions where phyllosilicates and sulfates coexist on mars in these systems fe and alkali earth phyllosilicates represent deep facies associated with upwelling neutral to alkaline groundwater whereas aluminous phyllosilicates and sulfates represent near surface evaporitic facies formed from more acidic brines

stable cl isotopes in subduction zone pore waters implications for fluid rock reactions and the cycling of chlorine stable cl isotope ratios measured in marine pore waters associated with the barbados and nankai subduction zones extend significantly to 8 the range of 37 cl values reported for natural waters these relatively large negative values together with geologic and chemical evidence from barbados and nankai and recent laboratory data showing that hydrous silicate minerals i e those with structural oh sites are enriched up to 7 5 in 37 cl relative to seawater strongly suggest that the isotopic composition of cl in pore waters from subduction zones reflects diagenetic and metamorphic dehydration and transformation reactions these reactions involve clays and or other hydrous silicate phases at depth in the fluid source regions chlorine therefore cannot be considered geochemically conservative in these systems the uptake of cl by hydrous phases provides a mechanism by which cl can be cycled into the mantle through subduction zones thus stable cl isotopes should help in determining the extent to which cl and companion excess volatiles like h 2 o and co 2 cycle between the crust and mantle

establishing constraints on groundwater ages with 36cl 14c 3h and noble gases a case study in the eastern paris basin france abstract groundwaters from the tithonian kimmeridgian oxfordian and upper dogger aquifers within the eastern part of the paris basin france were characterised using 3 h 14 c and 36 cl and noble gases tracers to evaluate their residence times and determine their recharge period this information is an important prerequisite to evaluating the confinement properties of the callovo oxfordian clay formation sandwiched between the oxfordian aquifer and the dogger aquifer currently being investigated by the french nuclear waste management agency andra for radioactive waste disposal data presented in this paper are used to test 4 hypotheses 1 the oxfordian limestone is isolated from the overlying tithonian kimmeridgian surface aquifer this first hypothesis is supported by the presence of measurable 3 h activities in groundwaters from the surface aquifer 6 11 tu and by its absence in groundwaters derived from deeper aquifers 2 the callovo oxfordian clay sequence in the vicinity of the url serves as an effective barrier to advective flow and transport between the underlying upper dogger aquifer and the overlying oxfordian limestone aquifer this second hypothesis is supported by relatively low concentrations of cl 3 5 78 mg l 1 na 15 145 mg l 1 br 0 08 0 4 mg l 1 and 4 he rad 0 2 2 3 ccstp g 1 and slightly higher 36 cl cl ratios 2 7 59 10 15 at at 1 in groundwaters from the oxfordian aquifer compared to those from the upper dogger aquifer 345 4027 mgcl l 1 402 2390 mgna l 1 1 8 22 2 mgbr l 1 1 6 37 2 ccstp he g 1 1 5 10 15 at 36 cl at 1 cl 3 groundwaters from the oxfordian aquifer in the vicinity of url are pre holocene with residence times exceeding 10 ka geochemical and isotopic lines of evidence for this hypothesis include a 13 c values measured on oxfordian aquifer waters that are close to 13 c of the aquifer matrix reflecting strong isotopic exchange over several thousand years b noble gas temperatures that indicate recharge temperatures between 3 and 8 6 c lower by 2 7 c than the modern average temperature in this area c radiogenic 4 he concentrations between 0 16 10 5 and 2 3 10 5 ccstp g 1 of water about 2 3 orders of magnitude greater than the 4 he concentration of air equilibrated water 4 groundwater residence time for the upper dogger aquifer in the vicinity of the url probably exceed several hundred thousand years such long residence times are indicated by the accumulation of radiogenic he up to 37 10 5 ccstp g 1 assuming a closed system primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of well defined 36 cl cl input ratio knowledge about the 4 he rad sources for oxfordian and dogger aquifers knowledge about transport processes occurring through the dogger aquifer and the extensive dilution of initial 14 c activities by dissolution exchange with aquifer matrix overall however although the data presented in this paper remain semi quantitative due to inevitable intrinsic limitations of the methods none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the url

37cl 35cl variations in a diffusion controlled groundwater system abstract groundwaters in the low permeability quaternary glacial deposits of southwestern ontario commonly exhibit increasing cl concentrations with depth because these deposits were formed in a freshwater glacial environment and because cl is not derived from weathering of these deposits previous investigations hypothesized that upward diffusion of saline formation waters from the shallow bedrock caused this cl trend this hypothesis was tested by measuring 37 cl 35 cl ratios in the groundwaters from two typical sites and comparing the results with theoretically derived isotopic distributions produced by diffusion 37cl measurements expressed relative to standard mean ocean chloride smoc ranged from 0 8 to 2 2 and vertical profiles showed a gradual enrichment in 35cl relative to 37cl with increasing distance upward from the bedrock till interface 537cl distributions were simulated with a mathematical solute transport model incorporating the effects of kinetic isotopic partitioning a sensitivity analysis indicated that the model results were affected by the groundwater velocity the isotope enrichment factor and diffusion times agreement between the simulated and observed cl isotope profiles was obtained using a groundwater velocity of 0 an isotopic enrichment factor of 1 0012 and diffusion times ranging from 14 000 to 16 000 years based on these results we conclude that the isotopic enrichment in 35cl was caused by upward diffusion over a period of about 15 000 years this diffusion period is consistent with what is known about the quaternary history of the area

the effects of sedimentation and compaction on oceanic heat flow summary the estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements in particular the perturbations associated with sedimentation and surface temperature changes must be taken into account analytical solutions can be obtained only for individual simplified versions of these problems whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth a physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment basement system these values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time in addition to variations in sedimentation rate sediment type radioactive heat production and surface temperature changes are considered heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent the results also indicate that alterations determined from simple analytical models tend to over estimate the true perturbation to the flux

stable chlorine isotopes in halite and brine from the gulf coast basin brine genesis and evolution stable chlorine isotope data used in conjunction with other geochemical parameters are useful in determining the origin of solute in formation waters with salinity different from that of seawater jurassic salt in the gulf coast basin has 37cl ranges of 0 5 to 0 3 bedded and 0 0 to 0 5 diapiric the values for bedded salt are consistent with a 37cl value of 0 0 for jurassic seawater chloride as in modern oceans the slightly higher values for diapiric salt are possibly caused by incongruent solution of halite formation waters have a 37cl range of 1 9 to 0 7 waters with 37cl 0 2 low salinity water from geopressured aquifers appears to have resulted from shale dewatering low 37cl values in such water are related to low mcl mna a parameter indicating dewatering but show no general relationship to cl br they are consistent with diffusion of chloride from allochthonous brine diffusion can generate domains of water with negative 37cl on a scale of hundreds of meters in 104 106 years and may also generate positive 37cl chloride in residual source brine

chlorine stable isotopic composition of basement fluids of the eastern flank of the juan de fuca ridge odp leg 168 abstract this paper presents chlorine stable isotope compositions 37cl of sediment pore waters collected by squeezing sediment cores from the sediment basement interface along an east west transect through the eastern flank of the juan de fuca ridge odp leg 168 these near basement fluids nbf are generally thought to be representative of low temperature fluids circulating in the off axis basaltic crust the 37cl value of the fluid directly sampled from a flow at the base of site 1026 wstp1026 is also reported nbf display 37cl values between 2 09 and 0 12 relative to the standard mean ocean chloride smoc defined as 0 and small variations in chlorinity 4 these data contrast with the homogeneity of 37cl values associated with highly variable chlorinities observed in high temperature on axis fluids m bonifacie j l charlou n jendrzejewski p agrinier j p donval chlorine isotopic compositions of ridge axis high temperature hydrothermal vent fluids chem geol 221 2005 279 288 the nbf 37cl values show a general decreasing trend with distance from the ridge axis except for two fluids when plotted against 18o values the 37cl of the nbf show two different trends this paper discusses the possible contributions on nbf 37cl values of fluid mixing water rock interactions and transport processes diffusion ion membrane filtration that can occur in the igneous basement however as none of these processes can fully explain the observed 37cl variations the potential effect of the sediment cover is also investigated at site 1026 the interstitial pore fluid displays a 37cl signature significantly lower than that of the fluid discharge sample 1 90 and 0 28 respectively this difference demonstrated here cannot be an artifact of the sampling method rather indicates the influence of the sediment cover on nbf 37cl values the potential contributions of physical processes associated with transport compaction e g diffusion ion membrane filtration adsorption ion exchange on nbf 37cl values are qualitatively discussed here but require additional studies for further insights however this study indicates that near basement fluids nbf are not at least for cl isotopic compositions necessarily as representative of fluids circulating in the basaltic crust as initially thought these results add new constraints on cl geodynamics and show that cl isotopes fractionate during low temperature circulation of fluids in off axis and off margin flow contexts but not to the extent observed for active margins fluids circulating at low temperature in the magmatic and or the sedimentary part of the oceanic crust might have played a major role on the 37cl evolution of seawater over geologic time

major and trace element and sr isotope constraints on fluid circulation in the barbados accretionary complex part ii circulation rates and fluxes abstract 87 sr 86 sr ratios of pore fluids recovered from diapiric structures east of the deformation front of the barbados accretionary prism remain quasi constant from the surface to depths of 8 m the sr isotopic ratios are non radiogenic compared with seawater which implies that non local fluid was expelled at such a high rate that its sr isotopic composition was dominated by the source fluid and not by pore fluid or seawater chloride depletion recorded in the fluids corresponds to a five fold dilution in the deepest sample from the atalante diatreme this also strongly suggests upward flow the comparison of measured chloride contents and sr isotope depth profiles with theoretical values obtained using a steady state advection diffusive model gives some constraints on the fluid circulation rate in the two diatremes atalante and cyclope and in one mud diapir c the velocities are variable but the diatremes which have the largest thermal and chemical anomalies yield the highest estimated advection rates the fluid circulation rate in the centre part of the largest diatreme atalante 0 47 km 2 total surface is estimated at about 1 m yr the fluid flux from the deepest to shallowest levels of the atalante diatreme was estimated on the basis of the fluid circulation rate calculations fluid release is clearly favoured if active conduits are present as they are in the diatremes but not in the mud diapirs however even though this steady state advection diffusion model provides a rough estimation of flow rates modification of the fluid pressure and therefore fluid volume during earthquakes may superimpose large but transient fluid expulsions

strong impact of ion filtration on the isotopic composition of chlorine in young clay rich oceanic sediment pore fluids abstract a collection of 34 pore fluids from young clay rich sedimentary piles of the shikoku basin on the philippine oceanic plate at the front of the nankai subduction zone southeast of japan were analyzed for their chloride content and chlorine stable isotope composition 35cl and 37cl reported as 37cl these pore fluids are samples from iodp sites c0011 and c0012 which penetrate deeper than 500 meters below the seafloor at both sites the 37cl values display a regular decrease with depth from about 0 seawater value at the seafloor to 8 5 and 6 5 respectively in hydrogeologically isolated low permeability sediment levels at some depths local deviations of up to 6 in 37cl interrupt the overall decreasing trends they may be interpreted as the injection of external fluids into the sedimentary piles as a result of sedimentary levels with higher permeability at the bottom of the sedimentary piles the injected fluids probably originating from the altered oceanic crust systematically have 37cl values closer to seawater literature data indicate the display of downward trends of decreasing 37cl values of the pore fluids in many other young clay rich sedimentary piles nankai trough and the japan trench accretionary prisms black ridge and juan de fuca ridge flank here we use conservation equations to demonstrate that these 37cl depth profiles can be modeled using the effect of the compaction of growing clay rich sedimentary piles on the water and chlorides including 35cl and 37cl isotopes this modeling shows that a small isotope fractionation of chlorine isotopes 37cl 35clexpulsed fluid residual fluid in the range of 1 006 to 1 001 may explain the observed negative 37cl chlorides at the bottom of the sedimentary piles the complementary positive 37cl chlorides must accumulate at the top but are very likely erased by dilution with seawater chlorides across the seafloor interface this range of chlorine isotope fractionation values is in agreement with the theory of ion filtration of phillips and bentley 1987 in which the mobility of chlorides through semi permeable clay membrane is determined by ion repulsion based on this study we show that young pore fluids in clay rich sediments of the oceanic crust are 37cl depleted chloride reservoirs they might be the source of 37cl depleted chloride fluids advected at mud volcanoes on the seafloor but do not seem to contribute largely to subduction zone magmatic tectonic metamorphic products where no such 37cl depleted chlorine is documented this in turn is a strong argument to propose that most of the clay rich sediment s pore waters are released back into the ocean rather than subducted

chlorine isotope variations across the izu bonin mariana arc chlorine isotope ratios were determined for volcanic gas geothermal well ash and lava samples along the izu bonin mariana volcanic front serpentinite clasts and muds from serpentine seamounts conical south chamorro torishima basalts from the guguan cross chain and sediments from ocean drilling program odp sites 800 801 802 and 1149 there is no systematic variation in 37 cl values along the volcanic front in either gas or ash samples in contrast distinct variations occur across the arc implying variations in the fluid source at different depths within the subduction zone serpentinite clasts and serpentine muds from the seamounts tap a source of 30 km depth and have 37 cl values of structurally bound chloride of 0 4 0 4 n 24 identical to most seafloor serpentinites suggesting a serpentinite chrysotile and or lizardite to antigorite transition fluid source tapping deeper levels of the subduction zone 115 130 km depth volcanic gases and ashes have 37 cl values averaging 1 1 1 0 n 29 precisely overlapping the range measured in sediments from odp cores 1 1 0 7 n 11 and limited altered oceanic crust aoc both sediments and aoc are possible cl sources in the volcanic front the guguan cross chain basalts come from the greatest depths and have an average 37 cl value of 0 2 0 2 n 3 suggesting a second serpentine derived source in this case from antigorite breakdown at 200 km depth

a chlorine isotope study of dsdp odp serpentinized ultramafic rocks insights into the serpentinization process abstract eight dsdp odp cores were analyzed for major ion concentrations and 37cl values of water soluble chloride 37clwsc and structurally bound chloride 37clsbc in serpentinized ultramafic rocks this diverse set of cores spans a wide range in age temperature of serpentinization tectonic setting and geographic location of drilled serpentinized oceanic crust three of the cores were sampled at closely spaced intervals to investigate downhole variation in cl concentration and chlorine isotope composition the average total cl content of all 86 samples is 0 26 0 16 wt 0 19 0 10 wt as water soluble cl xwsc and 0 09 0 09 wt as structurally bound cl xsbc structurally bound cl concentration nearly doubles with depth in all cores there is no consistent trend in water soluble cl content among the cores chlorine isotope fractionation between the structurally bound cl site and the water soluble cl site varies from 1 08 to 1 16 averaging to 0 21 samples with negative fractionations may be related to reequilibration of the water soluble chloride with seawater post serpentinite formation six of the cores have positive bulk 37cl values 0 05 to 0 36 the other two cores 173 1068a leg hole and 84 570 have negative bulk 37cl values 1 26 and 0 54 the cores with negative 37cl values also have variable cl so42 ratios in contrast to all other cores the isotopically positive cores 153 920d and 147 895e show no isotopic variation with depth the isotopically negative core 173 1068a decreases by 1 with depth for both the water soluble and structurally bound cl fractions non zero bulk 37cl values indicate cl in serpentinites was incorporated during original hydration and is not an artifact of seawater infiltration during drilling cores with positive 37cl values are most likely explained by open system fractionation during hydrothermal alteration with preferential incorporation of 37cl from seawater into the serpentinite and loss of residual light cl back to the ocean fluid rock ratios were probably low as evidenced by the presence of water soluble salts the two isotopically negative cores are characterized by a thick overlying sedimentary package that was in place prior to serpentinization we believe the low 37cl values of these cores are a result of hydration of ultramafic rock by infiltrating aqueous pore fluids from the overlying sediments the resulting serpentinites inherit the characteristic negative 37cl values of the pore waters chlorine stable isotopes can be used to identify the source of the serpentinizing fluid and ultimately discern chemical and tectonic processes involved in serpentinization