transient features of the erosion of shales in the mackenzie basin canada evidences from boron isotopes abstract in order to refine our knowledge of the mechanisms that drive the weathering reactions and the rate at which elements are exported out of a shale basin we have analyzed the boron concentrations and isotopic compositions of 24 rivers contributing to the mackenzie basin canada boron has been chosen to conduct this study because of the relatively high sensitivity of its isotopic system to water rock interactions after examination of the chemical composition of the mackenzie river samples boron appears to be regulated in the largest part by reactions involving silicate rocks the other contributions of rainwaters and the dissolution of carbonate and evaporite rocks can locally control the b budget but they remain of second importance at the regional to continental scales it also appears that dissolved b in rivers is regulated by input of groundwaters the comparison between the isotopic composition of the b being exported by rivers soluble and particulates and of its bulk source indicates that it is behaving out of steady state in most of the mackenzie tributaries and particularly in rivers draining the plain a model of transport reaction is proposed in this study which demonstrates that b is controlled by rapid ion exchanges at the mineral water interface and by long term dissolution of shales the responses of the model to tested conditions reveal that the b isotopic ratio of river waters is highly sensitive to hydrological conditions and to changes of the weathering rate of shales of its partition coefficient with adsorbing surface and of the water velocity the departure of the b geochemical cycle from a steady state is interpreted as the record of changes in the weathering regime in the mackenzie basin the temporal evolution of the b cycle modeled here implies an increase of the weathering rate of shales in the mackenzie basin and or an increase of the partition coefficient between soluble b and adsorbing surfaces it also appears that these changes are consistent with timescales of the recent deglaciation of the basin this study demonstrates that the present b fluxes are actually responding to past changes of the water rock interactions and that the weathering history is a key parameter to interpret the modern geochemical fluxes this conclusion is valid for any other element that has similar chemical properties with solid surfaces

probing silicate weathering reactions in soils with b isotopes abstract the determination of the mechanisms and extent of soil mineral weathering can be challenging and the caveats reside in 1 difficulty identifying minerals that are actually involved in weathering reactions 2 non stoichiometric release of cations during weathering processes due to coupled dissolution precipitation and transformation reactions and 3 impact of vegetation activity on elemental cycles in upper soil horizons to better characterize mechanisms controlling mineral weathering in soils and trace the evolution of b concentration and isotope ratios during chemical weathering quantitative mineralogical analyses were coupled to b isotopes in a group of minerals biotite muscovite k feldspar and albite samples were selected along an alocrisol alumic cambisol wrb fao soil profile from the bedrock at 130 cm depth up to 20 cm depth developed on granitic bedrock in the breuil chenue forest france the samples consist of residual primary minerals associated with weathering secondary phases vermiculite kaolinite in varying proportions the b isotopic compositions of the most pristine minerals span a very narrow range of values around 31 whereas all secondary phases point to a much heavier value around 16 regardless of mineralogy our results also show a mineral dependent evolution of b concentration or isotopic composition as weathering progresses no variation is observed during dissolution of k feldspars b behaves like a very mobile element in micas biotite and muscovite whereas it concentrates in weathered products derived from albite however rates of b concentrations and changes in isotopic compositions appear to be much faster than those inferred from mineralogy or major element concentrations determined by xrd and bulk chemical analyses respectively these results indicate that b is involved in very early weathering reactions and raises the question of its actual location in the structure of the various soil minerals as well as its pathway to solution

lithosphere of indus block in the northwest indian subcontinent through genetic algorithm inversion of surface wave dispersion the indus block in the northwest indian subcontinent is a continental area lying between the chaman fault in the west the aravalli range in the east and the main boundary fault of himalaya in the north we evaluate the lithospheric structure of this crustal block through inversion of love and rayleigh wave group velocities obtained using broadband records at bhuj from the kashmir earthquake of 8 october 2005 and its aftershocks the recording station lies in the southern edge and epicenters lie in the northern edge of this block the wave paths are mostly in the study area in a direction parallel to the aravalli trend the period of the group velocity data ranges from 5 4 to 74 1 sec and the inversion of these data resolves the structure down to the lithosphere asthenosphere boundary lab a nonlinear inversion has been carried out through a genetic algorithm with a wide solution space some new concepts of solution space of a layered structure and of a misfit function are used the mean and standard deviation of the 50 accepted solutions with low misfit give the structure ib11 for the indus block the standard deviation gives the estimation of the uncertainty and the resolution of the corresponding parameter in ib11 the sedimentary thickness is 5 6 km within two layers the total thickness of the crust is 44 2 km the s wave velocity below the crust is 4 393 km sec while this velocity is 4 603 km sec in the indian region to the east of the aravalli range in ib11 the lab is at a depth of 79 km which is much shallower than the corresponding depth of 120 km in the indian region on the other hand the s wave velocities below the crust as well as the depth of the lab are similar to those of the arabian shield these similarities support the hypothesis that the indus block is a detachment of the arabian nubian shield

boron rich groundwater in central eastern italy a hydrogeochemical and statistical approach to define origin and distribution analysis of boron within groundwater was undertaken for an area of central eastern italy although boron is a minor analyte in groundwater concentrations can often be above limits set by legislation a hydrogeochemical study supported by a statistical multifactorial analysis was undertaken to investigate the most likely origin of the boron within the groundwater it was possible to distinguish contamination caused by anthropogenic activities from natural pollution within the study hydrochemical analysis has highlighted that anomalous concentrations of boron are only seen in groundwater from the alluvial valley deposits a strong correlation between high boron concentrations and groundwater with chloride sodium facies was also identified the principal components analysis has confirmed the results from the assessment undertaken with hydrochemical analysis the most important component is characterised by high loading of boron sodium chloride and electrical conductivity the most likely origin of the boron within the hydrogeochemical context of the area appears to be connected to the uprise of chloride sodium connate groundwaters naturally enriched in boron

geochemical and boron strontium and oxygen isotopic constraints on the origin of the salinity in groundwater from the mediterranean coast of israel in order to identify the origin of the salinity and formation of saline plumes in the central part of the mediterranean coastal aquifer of israel we determined the elemental and boron strontium and oxygen isotopic compositions of fresh and brackish groundwater cl up to 1500 mg l we distinguish between two key anthropogenic sources 1 sewage effluents used for irrigation with high na cl so4 cl and b c1 ratios and low br cl ratios relative to seawater ratios low 11b values 0 10 and high 18o values 4 and 2 imported water from the sea of galilee that is artificially recharged to the aquifer with high br cl 3 10 3 and 18o values 1 and a low 87sr 86sr ratio of 0 70753 the brackish groundwater from the saline plumes have relatively low na cl ratios 0 5 0 8 and high ca mg mg cl and ca so4 hco3 1 ratios relative to seawater ratios marine so4 cl and br cl ratios 11b values of 24 8 49 9 18o of 2 95 to 4 73 and 87sr 86sr ratios of 0 708275 0 708532 the composition of most of the investigated groundwater from the saline plumes differs from those of the anthropogenic sources imported water fresh uncontaminated groundwater 87sr 86sr of 0 70866 11b of 20 30 and saline water from the adjacent eocene aquitard only in areas of artificial recharge does local groundwater have high br cl and 18o values that are typical to the sea of galilee the linear relationships between chloride and most of the ions including b and sr the relatively high 11b 30 and low 18 o 4 values and the chemical signature of the saline plumes e g marine br cl and so4 cl ratios suggest that 1 mixing processes control the chemical composition of the brackish water within the aquifer and 2 the saline postulated end member has a chemical composition that resembles modified seawater with a marine and higher 11b values and a 87sr 86sr ratio of 0 7083 we propose that most of the salinization phenomena and the formation of saline plumes in the inner parts of the coastal aquifer are derived from upconing of underlying natural saline water bodies and enhanced by overexploitation and draw down of the overlying fresh groundwater

a multi isotope b sr o h and c and age dating 3h 3he and 14c study of groundwater from salinas valley california hydrochemistry dynamics and contamination processes 1 the chemical and isotope 11b 10b 87sr 86sr 18o 16o 2h h 13c 12c 14c and 3he 3h compositions of groundwater from the upper aquifer system of the salinas valley in coastal central california were investigated in order to delineate the origin and processes of groundwater contamination in this complex system the salinas valley has a relatively deep confined 400 foot aquifer overlain by a 180 foot aquifer and a shallower perched aquifer all made up of alluvial sand gravel and clay deposits groundwater from the aquifers have different 14c ages fossil 14c 21 3 percent modern carbon pmc for the 400 foot aquifer and modern 14c 72 2 98 2 pmc for the 180 foot aquifer fresh groundwater in all aquifers is recharged naturally and artificially through the salinas river the two modes of recharge can be distinguished chemically we identified several different saline components with distinguishable chemical and isotopic fingerprints 1 saltwater intrusion in the northern basin has c1 concentrations up to 1700 mg l a na cl ratio less than seawater a marine br cl ratio a ca cl ratio greater than seawater 11b between 17 and 38 and 87sr 86sr between 0 7088 and 0 7096 excess dissolved ca relative to the expected concentration for simple dilution of seawater correlates with 87sr 86sr ratios suggesting base exchange reaction with clay materials 2 agriculture return flow is high in no3 and so4 with a 87sr 86sr 0 7082 11b 19 and 13c between 23 and 17 the 3h 3he ages 5 17 years and 14c data suggest vertical infiltration rates of irrigation water of 3 10 m yr 3 nonmarine saline water in the southern part of the valley has high total dissolved solids up to 3800 mg l high so4 na cl ratio 1 11b between 24 and 30 and 87sr 86sr 0 70852 this groundwater may have acquired its geochemical signature from leaching of sedimentary rocks associated with the coast range marine deposits of mesozoic to early cenozoic age the combination of different geochemical and isotopic fingerprints enables us to delineate the impact of salt sources in different areas of the valley and to reconstruct the origin of the so4 enriched no3 depleted saline plume that is located west of the city of salinas we suggest that the latter is derived from a mixture of different natural saline waters rather than from anthropogenic contamination

marine geochemical cycles of the alkali elements and boron the role of sediments abstract we have analysed the concentrations of li k rb cs and b and the isotopic ratios of li and b of a suite of pore fluids recovered from odp sites 1037 leg 169 escanaba trough and 1034 leg 169s saanich inlet in addition we have analysed dissolved k rb and cs concentrations for estuarine mixing of the ganges brahmaputra river system together these data sets have been used to assess the role of sediments in the marine geochemical cycles of the alkali elements and boron uptake onto clay minerals during estuarine mixing removes 20 30 of the riverine input of dissolved cs and rb to the oceans prior to this study the only other recognised sink of rb and cs was uptake during low temperature alteration of the oceanic crust even with this additional sink there is an excess of inputs over outputs in their modern oceanic mass balance pore fluid data show that li and rb are transferred into marine sediments during early diagenesis however modeling of the li isotope systematics of the pore fluids from site 1037 shows that seawater li taken up during marine sedimentation can be readily returned to solution in the presence of less hydrated cations such as nh4 this process also appears to result in high concentrations of pore fluid cs relative to local seawater due to expulsion of adsorbed cs from cation exchange sites flux calculations based on pore fluid data for a series of odp sites indicate that early diagenesis of clay sediments removes around 8 of the modern riverine input of dissolved li although nh4 rich fluids do result in a flux of cs to the oceans on the global scale this input only augments the modern riverine cs flux by 3 nevertheless this may have implications for the fate of radioactive cs in the natural environment and waste repositories

boron isotope geochemistry as a tracer for the evolution of brines and associated hot springs from the dead sea israel abstract a boron isotope study combined with analyses of elemental boron lithium and chlorine is used to suggest that brines from the dead sea and on shore hypersaline thermal springs hamme yesha hamme zohar and hamme mazor are the products of interaction of evaporated seawater with detrital sediments the high 11b values of the dead sea brines 55 7 to 57 4 versus nbs 951 and the hot springs 52 2 to 55 7 and low b li ratios 2 0 to 2 3 and 2 5 to 2 7 respectively relative to seawater indicate preferential removal of 10b from the brines and hence boron adsorption onto clay minerals the brackish en feshcha springs and the freshwater en dawid and nahal arugot springs yield lower b contents and 11b values 37 7 to 40 6 and 33 8 to 36 9 respectively the 11b values and b contents of diluted dead sea brines lie on calculated mixing lines between the composition of the brackish and freshwater springs with the composition of the dead sea the 11 b values of the hot springs however given their boron content are significantly lower than those of the mixing lines thus waters from the hot springs cannot be a mixing product of the dead sea brine with freshwater instead the dead sea brine has evolved from the brines of the hot springs through further isotopic fractionation and boron adsorption onto detrital sediments

the palaeoproterozoic boron deposits in eastern liaoning china a metamorphosed evaporite abstract we have carried out a field study of the palaeoproterozoic borate deposits of eastern liaoning province china the borates are hosted within mg silicate and mg carbonate rocks and have previously been interpreted as either skarns or metamorphosed volcanogenic exhalative deposits the deposits contain textures that are compatible with a sedimentary origin of the borates and there is a lack of the associated mineralization that is characteristic of magnesian skarns in addition preliminary boron isotope data indicate that the boron within the borates was not derived from the footwall rocks that have been proposed as the source of the skarn fluids a purely exhalative model can be dismissed on the basis of geochemical arguments and comparison with modern environments which show that borates are too soluble to precipitate directly from hydrothermal fluids the geology and field relationships show a number of similarities with recent non marine evaporite settings and young continental rifts in arid environments we conclude therefore that the liaoning deposits are metamorphosed evaporites in which the boron was originally present as primary evaporite borate minerals this model places the liaoning borates in the same category as the majority of other economic borate deposits in the world

hydrothermal alteration of hemi pelagic sediments experimental evaluation of geochemical processes in shallow subduction zones abstract laboratory hydrothermal experiments provide unique information regarding the fate of volatile and or incompatibles e g b li and as during oceanic crust subduction examination of chemical redistribution between the subducted slab mantle wedge arc volcanics and overlying ocean water during subduction is critical to gain further insight into arc volcanism and chemical oceanic budgets for instance efficient mobilization of b at shallow depths may be a key aspect of its oceanic budget and can help to explain the systematics of b 11b and b 10be in arc lavas fluid rock interactions at elevated temperatures and pressures in accretionary prisms were studied using a rocking autoclave hydrothermal apparatus to monitor sediment porewater interaction over the range of 25 to 350 c at 800 bars clay rich hemi pelagic sediments from the decollement zone of ocean drilling program site 808 nankai trough were reacted with nacl cacl2 solutions at water rock ratios of 3 5 to 1 5 w w to mimic alteration processes in the shallow subduction zone fluids were extracted at 25 50 c intervals and were analyzed for major and trace chemical constituents the fluid chemistry changed significantly during the course of these experiments but there was generally only minor modification of the solid phase only b li as br and pb are significantly depleted during the heating cycle dissolved na mg and so4 decreased sharply and nh4 sio2 k b and li increased at t 300 c calcium drops gradually at low temperatures but concentrations rise sharply at t 300 c decomposition of organic matter so42 depletion and mg fixation dominate at low temperatures however albitization of calcic plagioclase leads to marked na depletions and ca enrichments at t 300 c dissolved sio2 remained below saturation with respect to quartz and amorphous silica throughout the entire experiment b and li mobilization with large isotopic fractionations occurred at low temperature exchangeable b 11b 15 is completely leached before reaching 150 c substantial o2 exchange between fluids and the solid phase occurred at t 200 c in the spiked experiment where 18o varies more than 100 in the fluids during retrograde cooling dissolved mg so4 ca si k and sr are released as a result of carbonate or anhydrite dissolution and marked b re adsorption occurred at temperatures below 60 c

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

the boron isotope systematics of the yellowstone national park wyoming hydrothermal system a reconnaissance abstract boron concentrations and isotope compositions have been measured in fourteen hot spring waters two drill hole waters an unaltered rhyolite flow and hydrothermally altered rhyolite from the geothermal system in yellowstone national park wyoming the samples are representative of the major thermal areas within the park and span the range of fluid types for the fluids the b concentrations range from 0 043 2 69 mm kg and the 11 b values range from 9 3 to 4 4 there is no relationship between the dissolved b concentrations or isotope compositions with the concentration of any major element other than cl or physical property each basin is characterized by a restricted range in b cl ratios and 11 b values hot spring waters from the morris basin upper geyser basin calcite springs and clearwater have 11 b values close to that of unaltered rhyolite 5 2 and are interpreted to have derived their b from this source waters from mammoth hot springs sheepeater and rainbow springs have lower 11 b values close to 8 these lower values may reflect leaching of b from sedimentary rocks outside the yellowstone caldera but they are similar to the 11 b value of hydrothermally altered rhyolite 9 7 hence the light boron isotope compositions recorded in these hot spring waters may reflect leaching of previously deposited hydrothermal minerals cooler springs along the yellowstone river just outside the park boundary have lower b concentrations and higher 11 b values that may reflect mixing with shallow meteoric water

boron isotopic compositions of brine sediments and source water in da qaidam lake qinghai china abstract the isotopic compositions of boron in da qaidam lake quinghai have been determined by using the technique of thermal ionization mass spectrometry of cesium tetraborate the brines are enriched in 11b with an average 11b of 5 49 2 34 compared with those of lake sediments and boron minerals produced by the lake the apparent isotopic fractionation factors between brine and lake sediments as well as boron minerals are 0 988 0 001 and 0 986 0 001 respectively source water 11b values range from 11 72 to 16 69 depending on their origin

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

boron and oxygen isotope systematics for a complete section of oceanic crustal rocks in the oman ophiolite abstract boron content and the isotopic composition of boron and oxygen were determined for a complete 5 3 km thick oceanic crust in the wadi fizh area of the oman ophiolite a fragment of cretaceous oceanic lithosphere obducted onto the arabian shield the depth profiles of the 18 o values and the secondary mineral assemblages are consistent with successively higher temperature hydrothermal alterations occurring with increasing depth the upper pillow basalts underwent low temperature alteration 18 o 10 the lower pillow basalts and upper sheeted dikes 18 o 6 to 10 the lowermost sheeted dike complex and upper gabbros underwent high temperature alteration at 300 450 c 18 o 450 c 18 o 18 o values compared with the adjacent rocks suggesting the production of 18 o enriched melt the boron content of the rocks in the oceanic crust decreases in both abundance and range with increasing stratigraphic depth 1 4 29 1 g g in pillow lava 7 9 g g on average 1 5 11 6 g g in sheeted dike complex 5 3 g g on average 1 6 5 0 g g in dolerite dike in gabbro 2 9 g g on average 0 25 3 8 g g in gabbro 1 3 g g on average considering an original boron content of 0 72 0 47 g g for basalt and 0 06 0 09 g g for gabbro boron from seawater was incorporated into the rocks through hydrothermal alteration even at temperatures higher than 300 c the 11 b values systematically increase with stratigraphic depth 1 1 to 11 9 in pillow lava 5 5 on average 1 1 to 17 5 in sheeted dike complex 6 3 on average 8 3 to 18 6 in dolerite dike in gabbro 13 9 on average 7 3 to 17 7 in gabbro 12 0 on average the whole rock 11 b values negatively correlate with the 18 o values suggesting that the 11 b values of altered rocks are essentially controlled by isotopic equilibrium with hydrothermal fluids and the increase in the 11 b values is caused by a decrease in the rock fluid boron isotopic fractionation factor with increasing alteration temperatures the 11 b values estimated for hydrothermal fluids from rocks completely altered at 300 450 c range from 28 to 33 values indistinguishable from those of vent fluids observed at modern mid ocean ridges the boron content of the bulk oceanic crust of the oman ophiolite is estimated to be 3 6 g g and the 11 b value is estimated at 7 9 in contrast to previous views the hydrothermally altered gabbro section is a large boron sink accounting for 30 of the total boron in the oceanic crust with a high 11 b value of 13 this boron enriched high 11 b lower oceanic crust may impact estimates of the 11 b value of fluid liberated from the subducted oceanic slab which is believed to largely control the 11 b value of arc magma generated in the mantle wedge

a critical evaluation of the available measurements for the stable isotopes of boron abstract the reported measurements for the stable isotopes of b 11b and 10b in natural materials are compiled critically reviewed and evaluated the selected values along with a discussion of the error indicate the potential exists for using b isotopes in interpreting geochemical environments the isotopic values for 11b range from 31 0 for terrestrial rocks to 40 0 for sea water relative to nbs srm 951 which has a reported 11b 10b ratio of 4 04362 0 00137 2 furtherm the isotope ratios generally form a narrow cluster of values for specific rock types in some instances the reported 11b may be shifted substantially from the mean of unaltered rock as a result of weathering or reaction such as the progressive enrichment of 11b in marine sediments over time due to reaction with sea water an application of widespread interest is the use of b isotopes in environmental studies boron is a contaminant derived from numerous sources such as municipal and industrial waste the 11b in these wastes or processed waters is often significantly different from the 11b of the local ground water which will likely reflect the 11b values of the nearby rocks this modification by contaminated water can be 20 0 different from the 11b of the unaffected water providing a useful tool in delineating the source of contamination and the direction of migration

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

chemical and boron isotope compositions of non marine brines from the qaidam basin qinghai china the general chemistry and boron isotope composition were investigated in fresh waters and hypersaline brines from the qaidam basin northern qinghai xizang tibet plateau china this basin is a large tectonically active system isolated from the ocean and composed of thick clastic and evaporite sediments the modern playas are subject to intense evaporation and are characterized by hypersaline brines as well as potash and borate evaporites the chemical composition of the dissolved solutes in the modern brines and waters reveals three main sources 1 inflow of hot springs enriched in sodium sulphate and boron evaporation of these waters leads to a high na cl ratio 1 a na cl so4 brine and an evaporite mineral assemblage of halite mirabilite borate lakes daqaidam and xiaoqaidam 2 inflow surface river waters which are modified by preferential dissolution of halite and potassium and magnesium salts characterized by a na mg cl solute type with low na cl 1 brcl licl and bcl ratios and 3 ca chloridic subsurface brines which are controlled by both salt dissolution and dolomitization processes evaporation and salt crystallization of mixtures of the latter two types leads to a marine like brine e g na mg cl type nacl ratio 1 and mineral assemblages similar to that predicted for progressive evaporation of seawater e g qarhan playa halite sylvite carnallite bischofite the 11 b values of the input waters to the qaidam basin range of 0 7 to 10 9 vs nbs 951 and brines from salt lakes 0 5 to 15 0 are similar to those of associated granitic rocks 11b 2 3 to 3 7 n 3 and hence indicate the non marine origin of these fluids the highest 11b values are associated with fluids with low bli ratios indicating selective removal of elemental boron and 10b by adsorption onto clay minerals the magnitude of 11b enrichment due to adsorption is 15 20 and thus non marine brines are well distinguished from marine derived brines 11b of 39 to 59 preserving the large isotopic difference 40 of their source waters it is proposed to use this distinctive isotopic signature for tracing the origin of ancient evaporite environments

isotope and minor element geochemistry of high arsenic groundwater from hangjinhouqi the hetao plain inner mongolia abstract high as groundwater is widely distributed in the northwestern hetao plain an arid region with slow groundwater flow arsenic concentration in groundwater ranges from 1 to 1000 g l most water samples have elevated salinities with cl and or hco 3 as the dominant anions and na as the dominant cation high concentrations of as in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic c doc nh 4 dissolved sulfide arsenite and dissolved ch 4 and relatively low concentrations of no 3 and so 4 2 results of the hydrochemical and h and o isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b f and br in groundwater in na hco 3 dominated groundwaters as b and f were enriched decades of irrigation using yellow river water has resulted in elevation of the groundwater level which has accelerated salt accumulation in shallow groundwater and surface soil in addition irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters as indicated by minor element and isotope geochemical data used to trace groundwater flow paths sr isotope composition also indicates that bedrock weathering is one of the primary sources of as in groundwater in the study area

boron isotopes in tourmaline as a tracer of metasomatic processes in the bamble sector of southern norway the bamble sector of southern norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the sveconorwegian orogeny 1 06 ga the infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of fe ti oxides typical secondary mineral assemblages include either scapolite apatite amphibole phlogopite tourmaline or albite epidote calcite chlorite white mica indicating that the fluids introduced large amounts of na cl mg ca k p and b to the system metasomatic tourmalines associated with different alteration stages as identified by variations in major element composition and initial 87sr 86sr were analyzed for b isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid s measured 11b values range from 5 to 27 relative to srm 951 suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible b source reservoir the influence of a seawater derived component is clearly indicated by the heavy b isotope signature of tourmaline related to al mg rich metapelites in contrast negative 11b values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites on a regional scale i e several km 11b values in tourmaline vary widely whereas variations within a single outcrop tens of m are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses

strong b enrichment and anomalous δ11b in pore fluids from the japan trench forearc abstract interstitial pore waters from ocean drilling program odp sites 1150 and 1151 both penetrating 1200 m of sub seafloor sediment from the upper japan trench forearc were analyzed for b concentrations and 11 b isotopes b concentrations cover a wide range from 329 to 3920 m 0 8 9 3 seawater and vary isotopically from 20 to 46 relative to srm 951 in general b concentrations increase more or less steadily with depth at both sites the b enrichment and isotopic changes seem to be related to a deep fluid influence possibly coupled with alteration of volcanic products silica diagenesis does not affect the b geochemistry of the waters as is evident from intact diatom tests and high opal a contents throughout the holes the b enrichment is more pronounced at site 1150 in the seismic portion of the forearc here a large positive anomaly in 11 b values is observed which corresponds with abundant fracturing and two prominent shear zones at about the same depth range at site 1151 the 11 b values show a negative shift attesting to an enrichment in 10 b in the fluid as a result of b desorption from clay due to burial and tectonic stress we conclude that b release from clay minerals is the major contributor to pore fluid anomalies and that fluid flow through permeable out of sequence thrust like the shear zones at site 1150 may be an efficient mechanism for b backflux from the forearc into the hydrosphere

elemental dispersion and stable isotope fractionation during reactive fluid flow and fluid immiscibility in the bufa del diente aureole ne mexico evidence from radiographies and li b sr nd and pb isotope systematics the 31 6 0 3 ma old bufa del diente alkali syenite ne mexico intruded a sequence of cretaceous limestones with intercalated sub horizontal chert layers the cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow level 1 kbar contact metamorphic aureole fluid driven reactions between chert and marble wallrock and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid driven reaction aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers wollastonite formation occurred at the expense of limestone and chert and generated co2 this co2 induced fluid unmixing into an aqueous brine and a low density co2 rich fluid which was lost to the overlying marble where it oxidized organic matter and caused 13c and 18o shifts in a zone some 5 10 cm wide after wollastonite formation the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar quartz aegirine augite eudialyte zircon and apatite aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross fractures and migrated along the inner and outer borders of the wollastonite margins chemical dispersion patterns of u al na k p s fe and ree across the chert to marble boundary and its metasomatic rims are shown by autoradiography and neutron induced radiography scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale isotopic data for pb and sr across a simple metachert marble boundary and for pb sr nd b and li across a metachert pegmatite marble sequence demonstrate the following 1 the pb and sr isotopic signature of early fluids was buffered by the carbonate wallrock only late fluids shielded from wallrock interaction by a wollastonite mantle variably preserved a memory of their initial magmatic signature 2 since the nd isotope signature of marble and chert is bound to calcite and clay minerals systematic shifts to unradiogenic nd in marble reflect loss of carbonate bound nd as the wollastonite margin is approached nd in the wollastonite margin is dominated by nd originally bound to clay minerals the later emplacement of the pegmatite which carried the nd isotope signature of its alkali syenite source had little effect on the nd isotopic composition of the wollastonite rim 3 although the li and b isotopic compositions reflect the alkali syenite source they are also affected by isotopic fractionation and partitioning between melt fluid and solids

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

fractionation of boron isotopes during erosion processes the example of himalayan rivers abstract the boron isotopic composition of 5 rain waters and 35 river waters running from the high himalayas 5050 m down to the bay of bengal were measured by ion microprobe to make a first survey of the boron isotopic fractionations present in a major erosion system the rains have rather homogeneous b concentrations and isotopic compositions 0 09 0 09 mol l and 5 4 1 7 at the exception of the two kathmandu samples which probably reflect a significant anthropic contamination the river waters show a large range of b concentrations from 0 09 to 28 68 mol l and of b isotopic compositions 11b values ranging from 7 0 to 29 4 no systematic correlation between the 11b values and the major ion chemistry of the river waters is present at the exception of the most b and cl rich rivers which have systematically the highest 11b values likely controlled by evaporite dissolution after correction for the evaporite contribution from 9 4 to 64 4 of dissolved b with a systematic decrease southwards the riverine b concentrations and 11b values are still highly variable from 0 10 to 5 83 mol l and from 5 8 to 24 1 respectively this variation reflects mostly different conditions of silicate weathering congruent and incongruent silicate dissolution the contribution from the dissolution of carbonates being quite negligible 5 of the dissolved b on the river b budget at variance with congruent silicate dissolution incongruent dissolution occurs with a large b isotope fractionation which depends on ph clay water 31 2 at acidic ph and 5 8 at higher ph the b systematic suggests strongly that these fractionations are produced over a wide range of ph from 7 to 9 5 in soils and don t result from reactions between the dissolved and suspended load in rivers the net result of himalayan erosion for the global b cycle is the input to the sea of waters with highly variable b concentrations and isotopic compositions 0 67 and 0 29 mol l 5 0 and 21 0 for the ganga and the brahmaputra during the monsoon period respectively

rb sr evidence for punctuated illite smectite diagenesis in the oligocene frio formation texas gulf coast the size fractions of a suite of upper oligocene frio formation shale samples taken from below 10 500 ft in a well on the texas gulf coast fall on a rb sr isochron corresponding to an age of 23 6 0 8 m y the isochron shows an initial 87 sr 86 sr ratio of 0 7088 0 0004 this suggests that regularly interstratified illite smectite simultaneously equilibrated soon after burial over a range of burial depths at 7 000 8 000 ft shallower than at present oxygen isotope values for these clays are also consistent with equilibration under shallower burial conditions such a pattern conflicts with the prevailing idea of a gradual illitization of smectite with progressive burial a new model of episodic or punctuated diagenesis is proposed whereby sudden diagenesis is initiated by a change in pore water chemistry clay reaction occurs over a range of temperature at this time such that the deeper clays are transformed completely to 80 illite and the shallow clays are transformed less completely subsequent pore water chemical changes inhibit further clay reaction and the mineralogic gradient and the isotopic signature formed at 23 6 m y b p are frozen in seven to eight thousand feet of additional post oligocene burial has not resulted in the creation of younger illite smectite consequently there is no evidence that illite smectite diagenesis is currently taking place in the frio formation

the fate of subducted oceanic slabs in the shallow mantle insights from boron isotopes and light element composition of metasomatized blueschists from the mariana forearc abstract serpentine muds from south chamorro seamount scs drilled during odp leg 195 at site 1200 contain metamafic clasts that experienced blueschist facies metamorphism including the critical mineral assemblage pumpellyite na amphibole epidote these schists represent fragments from the actual slab mantle interface at 27 km depth their heterogeneous lithology with a metasomatic character indicates significant mobility of major elements in the mariana forearc a region of melange formation as it can also be observed in onland exposures such as the catalina schist as the mariana forearc blueschists show no late stage alteration they permit the direct study of material transfer during the subduction processes at an active convergent margin this study presents the first data of detailed b isotope 11 b and light element variations in blueschist facies minerals from the mariana arc system the primary foci are b and li concentrations and 11 b values analyzed by sims and tof sims techniques minerals such as na rich amphibole phengite and chlorite are found to be strongly enriched in li up to 70 g g be up to 8 g g and b up to 35 g g and with 11 b values of 6 4 these new data are consistent with isotopically heavy b being released into the mariana forearc mantle wedge serpentinization of dry mantle peridotite after interaction with b rich slab released high ph fluids and confirm models of significant b loss and b isotope fractionation during forearc shallow slab dehydration the elevated li be and b concentrations in minerals that comprise the bulk of the rocks namely amphibole phengite and chlorite bear a strong potential to further transport li and b as well as the isotopically light component of b to greater depths in the mantle where ongoing metamorphism is responsible for further isotope and elemental fractionation and the formation of distinct mantle reservoirs e g volcanic arc and oceanic intra plate oib magmas

the boron isotopic composition of altered oceanic crust samples of drilled oceanic crust from dsdp holes 417a 417d and 418a and odp hole 735b and oceanic crust from the oman and cyprus ophiolites were analyzed for b contents and 11b composite samples from dsdp holes 417a 417d and 418a were used to represent the upper 550 m of altered oceanic crustal layer 2a whole rock samples from the troodos ophiolite cyprus and the oman ophiolite wer selected to represent crustal layer 2b dikes composite samples from odp hole 735b were used to represent crustal layer 3 the b content of the dsdp composites ranges from 7 2 ppm to 104 ppm and correlates with both 18o and k showing that it is a good indicator of the extent of low temperature alteration the 11b of the dsdp composites varies between 2 5 and 5 4 the b content of the samples from the troodos ophiolite ranges from 2 4 ppm to 8 1 ppm 11b varies from 0 9 to 7 8 the b content of the oman ophiolite samples ranges from 5 0 ppm to 11 1 ppm 11b varies from 1 6 to 16 9 the b content of the samples from odp hole 735b ranges from 1 1 ppm to 7 1 ppm 11b varies from 4 3 to 24 9 the general pattern displayed by these samples is one of greatest and most variable b enrichment at the top of the crust and least enrichment at the bottom of the section all of these samples are enriched compared to unaltered morb which is believed to have a b content of approximately 0 5 ppm the 11b values of deeper samples from layers 2b and 3 are more variable and generally higher than those from layer 2a boron contents and 11b are not correlated the data from the dsdp site 417418 composites indicate that the 11b of fluid circulating in the upper crust changes only slightly during alteration increasing by an average of 5 1 with an accompanying decrease in b concentration of 7 low temperature alteration appears to be a water dominated process resulting in minor modification of circulating seawater a minimum water rock ratio of 400 is calculated for these samples implying a minimum low temperature seawater flux through the upper oceanic crust of 3 4 1014 l y the average b content of altered oceanic crust as represented by these samples is 5 2 1 7 ppm and the average 11b is 3 4 1 1 this average isotopic composition is measurably different from the apparent average of oceanic sediments supporting the idea that 11b could be useful for identifying the source s of b in island arcs

boron isotope systematics of marine sediments abstract boron contents and boron isotopic compositions were determined for modern and ancient permian to miocene marine sediments including pelagic clay calcareous ooze siliceous ooze and neritic clay sediments 11b values of modern marine sediments range from 6 6 to 4 8 isotopic variation is controlled by the simple mixing of four major constituents detritus of continental origin marine smectite biogenic carbonates and biogenic silica detritus of continental origin with an average 11b value of 13 to 8 is the low 11b end member constituent of marine sediments and its boron is largely controlled by the concentration of illite which originates from wind or fluvial transport marine smectite biogenic carbonate and biogenic silica on the other hand represent the high 11b end members with 11b values of 2 3 to 9 2 8 0 to 26 2 and 2 1 to 4 5 respectively these high 11b values are the result of the equilibrium uptake of boron from seawater spatial variations in boron isotopes in the pacific sediments are essentially due to the distribution of the above four constituents although ancient argillaceous sediments shale and slate have boron contents that are identical with those of modern equivalents boron contents of limestone and chert are distinctly lower than those of modern calcareous and siliceous oozes ancient marine sediments have systematically lower 11b values 17 0 to 5 6 than those of the modern sediments the lower 11b values can be caused by diagenesis which induces 1 preferential removal of high 11b boron in calcium carbonate and silica during recrystallization and 2 boron isotopic exchange in the course of the smectite illite transition the observed boron isotopic compositions of ancient argillaceous sediments are distinctly different from those of fresh and altered morb therefore boron isotope systematics will be useful in identifying components from the descending oceanic slab involved in the formation of island arc magma and in investigating mantle crust recycling through subduction processes

detrital metamorphic and metasomatic tourmaline in high pressure metasediments from syros greece intra grain boron isotope patterns determined by secondary ion mass spectrometry the boron isotopic composition of zoned tourmaline in two metasediments from the island of syros determined by secondary ion mass spectrometry sims reflects the sedimentary and metamorphic record of the rocks tourmaline from a silicate bearing marble contains small 20 m detrital cores with highly variable 11b values 10 7 to 3 6 pointing to a heterogeneous protolith derived from multiple sources the sedimentary b isotopic record survived the entire metamorphic cycle with peak temperatures of 500 c prograde to peak metamorphic rims are homogeneous and similar among all analysed grains 11b 0 9 the varying 11b values of detrital cores in the siliceous marble demonstrate that in situ b isotope analysis of tourmaline by sims is a potentially powerful tool for provenance studies not only in sediments but also in metasediments a meta tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin 11b 3 3 and prograde to peak metamorphic overgrowth zones 1 6 fe rich rims formed during influx of b bearing fluids under retrograde conditions show strongly increasing 11b values up to 7 7 towards the margins of the grains the 11b values of metamorphic tourmaline from syros formed in mixed terrigenous marine sediments reflect the b signal blended from these two different sources and was probably not altered by dehydration during subduction

how surface complexes impact boron isotope fractionation evidence from fe and mn oxides sorption experiments abstract although the ph dependence of boron isotope fractionation between solution and precipitating minerals has been widely used in earth sciences especially for reconstructing ancient seawater ph the mechanisms by which boron adsorbs on solids or coprecipitates in minerals are still poorly known here we have investigated boron isotopic fractionation during its adsorption on goethite feooh and birnessite k0 1mno2 2 0 9h2o as a function of solution ph at t 25 c and i 0 1 m maximum partition coefficients kd between adsorbed and aqueous boron equal to 39 and 34 for goethite and birnessite respectively are observed at ph 8 9 b adsorption at the surface of goethite induces its strong ph dependent isotopic fractionation ranging from 40 10b enrichment on goethite at ph 10 during adsorption on birnessite at acid and neutral ph boron isotopic fractionation is lower than during its sorption on goethite 15 decreases increases with increasing ph above ph 8 and reverses at ph 9 11b enrichment 23 at ph 10 8 is observed at birnessite surface based on combined infrared drift spectroscopic analysis and modeling of b speciation at oxides solution interfaces the observed isotopic fractionations can be rationalized by the formation of trigonal and tetrahedral boron inner sphere complexes on goethite surface and tetrahedral inner sphere and trigonal outer sphere and inner sphere complexes on birnessite surface b isotopic fractionation is strongly dependent on the structure of surface complexes formed the high steric strain induced by the formation of trigonal boron bidendate binuclear complexes at goethite surface leads to a much higher isotopic fractionation isotopically lighter sorbed boron than that following the formation of tetrahedral bidendate binuclear complexes conversely the formation at birnessite surface of trigonal complexes having almost the same isotopic composition than aqueous boric acid accounts for the heavier isotopic composition of birnessite than goethite boron both at acid and alkaline ph these results show that in nature 11b enrichment is expected in waters in equilibrium with iron or manganese oxides and that this enrichment is a function of ph that changes boron speciation in solution and at solid surfaces this is typically the case for soil solution in fe and mn rich environments and in seawater in addition the markedly different isotopic fractionation factor at the same ph of boron sorbed on goethite and birnessite at ph 8 2 is equal to 0 967 and 0 986 for goethite and birnessite respectively may be used to determine past ocean ph values without requiring knowledge of past isotopic composition

tourmaline in a mesoarchean pelagic hydrothermal system implications for the habitat of early life abstract the rna world hypothesis requires the synthesis of rna to allow the emergence of life on earth hydrothermal systems have been proposed as potential candidates for constructing complex biomolecules however in order to successfully form rna it is necessary to stabilize ribose a rna carbohydrate component borate has been found to stabilize ribose therefore boron rich hydrothermal systems are important environments concerning the origin of life on earth the 3 2 ga dixon island formation of the west pilbara superterrane western australia is a volcano sedimentary sequence the formation represents a mesoarchean pelagic hydrothermal system which formed adjacent to an immature island arc fine grained tourmaline in addition to biogenic carbonaceous matter and spherulitic and tubular bacteriomorphs are found in black chert a boron rich environment was responsible for the formation of these deposits to explore the implications of such a boron enriched environment on microbial activity modes of occurrence and chemical compositions of the tourmaline were examined the tourmaline is schorl or dravite of the alkali tourmaline group and the boron isotope compositions range in 11b from 7 3 to 2 6 the tourmaline occurs in microcrystalline quartz matrix of black chert veins that cross cut a volcanic unit and also in a bedded black chert which overlays the volcanic unit the volcanic unit contains highly altered zones with hydrothermal veins the associated lithologic and stratigraphic features suggest that the black chert veins were the conduits for upward moving hydrothermal fluids which reached the sea floor subsequently the volcanic unit was covered by organic matter rich cherty sediments that in part were fed and or altered by the hydrothermal fluids these results suggest that the origin of boron enrichment to form dixon island tourmaline is not the associated sedimentary mineral assemblage which includes diagenetic clay low grade metamorphic mica and organic matter instead the tourmaline was directly precipitated from hydrothermal fluid enriched in boron furthermore the hydrothermal fluids had already concentrated the boron in the mesoarchean pelagic system prior to the apex of organic matter production and microbial activity our findings support a hypothesis that the boron enriched hydrothermal environment aided the survival and evolution of early life

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

insight into diagenetic processes from authigenic tourmaline an example from carboniferous and permian siliciclastic rocks of western poland abstract authigenic tourmaline is a rare and minor component of siliciclastic rocks however once it occurs it can be used to interpret a number of subsurface parameters and processes such as fluid composition redox state salinity ph and fluid migration paths notwithstanding the conditions of tourmaline authigenesis still need to be recognize with greater clarity carboniferous and permian siliciclastic rocks in the subsurface of western poland in the vicinity of the dolsk fault show unusually high boron contents at places surpassing 1000 g g which are associated with the presence of authigenic tourmaline the mineral forms fine elongated crystals of nano to micrometer width grouped in radiating or semi parallel aggregates which are dispersed in the clay matrix of shales and graywackes coat grain surfaces and line secondary pores in porous sandstones replace some grains in volcaniclastic breccia and overgrow detrital tourmalines in quartzarenites regardless of host rock compositions the tourmaline is si deficient moderately al rich and shows significant x site vacancies and highly variable mg mg fetot ratios in rare zoned tourmaline the mg mg fetot ratios distinctly decrease and vacancies slightly increase towards the growth direction the results suggest that the tourmaline nucleated rapidly under a strong driving force at high boron concentration and high temperature the fluids which enabled the process were acidic reducing b and mg bearing and of low na and ca contents the tourmaline grew primarily at the expense of kaolinite possibly of other clay minerals and k feldspar in the temperature range 150 200 c its crystallization was a short episode in the diagenetic history of the host rocks tourmaline authigenesis across the carboniferous permian unconformity in the proximity of a prominent fault zone is evidence for fluid and heat migration along faults and for temporarily open geochemical system during late diagenesis the source of boron has been unproven yet the circulation of bitterns originated from upper permian evaporites was highly probable

boron isotopic composition of fumarolic condensates from some volcanoes in japanese island arcs boron samples from 40 fumarolic condensates from volcanoes in the ryukyu arc satsuma iwo jima and shiratori iwo yama and the north east japan arc usu shinzan showa shinzan esan and issaikyo yama all have 11b10b ratios close to 4 07 higher values from 4 09 to 4 13 were only observed in condensates from volcanoes in the southernmost end of the north east japan arc nasu dake the northern part of the izu bonin arc hakone and the north mariana arc ogasawara iwo jima these higher values suggest geological interaction of the magmas with sea water enriched in 11b

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

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

b o th isotope systematics in icelandic tephra abstract we report new boron concentrations and isotope compositions measured by ion microprobe on holocene tephra samples from 6 icelandic volcanoes the b concentrations range over almost a factor of 10 from 1 50 0 10 to 13 10 0 10 ppm in basalt and obsidian respectively the highest 11b 16 9 2 2 and 6 1 1 6 measured in rhyolites from the rift related askja and krafla volcanoes in contrast the lowest 11b values 5 3 and 5 2 observed in samples with the some of the highest 18o 4 92 and 5 18 respectively and 230th 232th 1 067 and 1 030 respectively correspond to a normal mantle signature the variations of boron isotope compositions in the icelandic tephra and their negative correlations with both 18o and 230th 232th strongly support the mixing between mantle derived basalts and crustal rhyolites produced from anatexis of hydrothermally altered basaltic crust the low 18o in combination with high 11b values in rhyolite is best explained by the presence of seawater derived b in a hydrothermal fluid that is mostly of meteoric origin

a reconnaissance of the boron isotopic composition of tourmaline abstract a preliminary investigation of the boron isotopic composition of tourmaline from some boron rich associations has been made the results for tourmaline from metasedimentary parageneses n 12 range from 11b 22 to 22 per mil these data mainly fall between the boron isotopic compositions of normal marine sediments with 11b 2 to 5 per mil and seawater with 11b 39 5 per mil tourmaline samples from granitic pegmatites n 6 on the other hand range from 11b 12 to 5 per mil the data provide a rudimentary indication of the range of boron isotopic variation in tourmaline some of the processes leading to this range and some possible geochemical tracer applications

saline groundwater in israel its bearing on the water crisis in the country abstract one of the major causes for the deterioration of water quality bearing heavily on the water crisis in israel is the ongoing contamination of its water resources by saline water bodies the present paper reviews the geochemical processes forming saline water lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country s various aquifers deterioration of groundwater in israel is caused by numerous natural processes such as encroachment of sea water migration of connate highly pressurized brines penetrating into fresh groundwater by subsurface dissolution of soluble salts originating in surrounding country rocks and by water rock interaction in addition to sea water two saline water bodies were identified as the main factors causing salinization of fresh groundwater a ca chloride brines encountered in the jordan dead sea rift valley in various parts of the negev and of the coastal plain and b na chloride saline water identified in the subsurface of the negev and in the southern part of the coastal plain intensive exploitation of groundwater in israel has disturbed the natural equilibrium which prevailed between fresh and saline water the newly established groundwater flow regimes have facilitated the migration of saline water bodies their participation in the active hydrological cycle and the progressive contamination of fresh groundwater these processes which were not anticipated by planners and water resources managers emphasize that large scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

boron isotope geochemistry during diagenesis part ii applications to organic rich sediments the measured clay water isotope fractionation for boron was applied to natural organic rich sediments undergoing illitization two field areas were chosen that show illitization occurring over a range of temperatures 80 500 c samples representing diagenetic temperatures of illitization 80 200 c are from the gulf of mexico sedimentary basin at 4 to 6 km depth in the eocene wilcox fm and jurassic norphlet fm the higher temperatures of illitization 200 500 c occur in a contact metamorphic aureole of the cretaceous pierre shale near walsenburg colorado here the kinetics of the illitization reaction are more rapid than in a slowly subsiding sedimentary basin but the chemical and mineralogical variations are minimized as complete illitization occurs over a small lateral distance in a single bentonite layer these studies indicate that b isotopes provide a more sensitive indicator of fluid variations in sedimentary basins than o isotopes and that b isotope analyses of authigenic illite can be a valuable geochemical tracer of fluid rock interactions boron isotope ratios in authigenic illite pore filling and muscovite stylolites from reservoir sandstones in the gulf of mexico are distinct from adjacent illitic mudstones whereas the oxygen isotopic ratios show little variation fluids in equilibrium with the mudstones cannot precipitate the authigenic clays with higher d 11 b values measured in the hydrocarbon reservoirs this suggests that the reservoir fluids were not in communication with the adjacent mudstone pore fluids but were introduced from another source area perhaps carrying a b isotopic label derived from the hydrocarbon source region authigenic illite formed in the pierre shale meta bentonite shows large isotopic fractionations of boron 20 during illitization at high temperatures incorporation of 500 ppm b in illite formed at 500 c shows that illite is a host for b even at metamorphic temperatures by using the experimentally derived b isotope fractionation data for silicates the measured d 11 b values of i s could be predicted by using a rayleigh fractionation model oxygen isotopic variations were negligible over this temperature range and thus provide little information on the mechanism of illitization copyright 2001 elsevier science ltd

fluid composition of the sediment influenced loki s castle vent field at the ultra slow spreading arctic mid ocean ridge the hydrothermal vent field loki s castle is located in the mohns knipovich bend 73 n of the ultraslow spreading arctic mid ocean ridge amor close to the bear island sediment fan the hydrothermal field is venting up to 320 c hot black smoker fluids near the summit of an axial volcanic ridge even though the active chimneys have grown on a basaltic ridge geochemical fluid data show a strong sedimentary influence into the hydrothermal circulation at loki s castle compelling evidence for a sediment input is given by high alkalinity high concentrations of nh4 h2 ch4 c2 hydrocarbons as well as low mn and fe contents the low 13c values of co2 and ch4 and the thermogenic isotopic pattern of the c2 hydrocarbons in the high temperature vent fluids clearly point to thermal degradation of sedimentary organic matter and illustrate diminution of the natural carbon sequestration in sediments by hydrothermal circulation thus carbon release to the hydrosphere in arctic regions is especially relevant in areas where the active arctic mid ocean ridge system is in contact with the organic matter rich detrital sediment fans

modeling novel stable isotope ratios in the weathering zone when rock is converted to weathering products the involved processes can be fingerprinted using the stable isotope ratios of metals for example li mg ca fe sr and metalloids b si here we construct a framework for interpreting these novel stable isotope ratios quantitatively in the compartments of the weathering zone in a geomorphic context the approach is applicable to any novel stable isotope system and is based on a simple steady state mass balance model that represents the weathering zone from the scale of a soil column to that of entire continents our model is based on the assumption that the two main processes associated with isotope fractionation are formation of secondary precipitates such as clays and uptake of nutrients by plants the model results show that the isotope composition of a given element in the weathering zone compartments depends on 1 the ratio between the release flux to water through primary mineral dissolution and the erosion flux of isotopically fractionated solid material consisting of secondary precipitates and organic matter 2 the isotope fractionation factors associated with secondary mineral precipitation and uptake by plants a relationship is established between isotope ratios isotope fractionation factors and indexes for chemical weathering such as chemical depletion fractions cdf and elemental mass transfer coefficients derived from simple elemental concentration measurements from this relationship isotope fractionation factors can be calibrated from chemical and isotope data measured on field material furthermore we show how the ratio of solid export to dissolved export of a given element from the weathering system can be estimated from the comparison of the isotope composition between bedrock water and sediment this calculation can be applied to samples from soils from rivers and from the sedimentary record and does not require knowing the isotope fractionation factors involved in the reactions finally we apply the model to the oceanic li isotope record reconstructed from marine carbonate sediments in order to discuss changes in global geomorphic regimes through the cenozoic

geochemical and boron oxygen and hydrogen isotopic constraints on the origin of salinity in groundwaters from the crystalline basement of the alpine foreland abstract the b isotopic composition in combination with o and h isotopes and hydrochemical tracers is utilized to constrain the evolution of basement hosted groundwaters via water rock interactions and fluid infiltration from external sedimentary reservoirs two distinct groundwater types have been identified in the central european crystalline basement n switzerland sw germany 1 fresh groundwaters characterized by low values of 11b 3 5 to 0 6 18o 12 0 to 10 0 and d 86 8 to 71 9 and 2 brackish groundwaters with distinctly heavier b o and h isotopic compositions 11b 6 4 to 17 6 18o 9 4 to 5 6 d 67 6 to 60 8 fresh groundwaters show a systematic decrease in 11b related to an increase in b concentrations and degree of total mineralization along the pathway of groundwater migration which can only be interpreted in terms of leaching of crystalline host rocks a 11b value of 3 3 is inferred for the crustal b source mainly hercynian granites involved in the leaching process in agreement with the known 11b range of granitic rocks the evolution of brackish groundwaters derived from crystalline basement reservoirs with little water circulation is more complex as indicated by b o h stable isotope and hydrochemical e g b cl na cl and br cl constraints brackish groundwaters from the study area are influenced by admixture of sediment derived fluids which infiltrated from late paleozoic permo carboniferous and early mesozoic lower triassic sedimentary strata the data presented show that b isotopes are sensitive to mixing processes of fluids derived from different crustal reservoirs and hence may be utilized as a tracer for constraining the internal autochthonous vs external allochthonous origin of salinity in basement hosted groundwaters

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

processes controlling the distribution of boron and chlorine in natural waters in iceland abstract the concentrations of b and cl in natural waters in iceland lie in the range 0 001 10 and 1 20 000 ppm respectively lowest concentrations occur in surface and groundwaters in the central highlands highest cl concentrations are found in high temperature waters on the reykjanes peninsula and highest b concentrations in well waters from high temperature geothermal systems in the axial zones of the active volcanic belts the b and cl contents of icelandic basalts are 0 1 6 6 and 75 750 ppm respectively these large variations are considered to result from variable degassing during consolidation as well as concentration variations in the initial magma tholeftes are lowest in both elements av 1 2 ppm b and 170 ppm ci transitional basalts intermediate av 2 1 ppm b and 240 ppm ci and alkali basalts highest av 3 8 ppm b and 340 ppm cl cl b ratios in tholeiites are most often within 25 50 but somewhat lower in alkali basalts most geothermal waters contain b and cl within 0 05 1 and 10 100 ppm respectively these rather low values are attributed to the low content of b and cl in the basaltic rock the b and cl distribution in the icelandic natural waters indicate that these elements act as essentially incompatible their sources of supply include 1 the atmosphere seawater spray and aerosols 2 the rock with which the water interacts 3 seawater groundwater and 4 magma intrusions in surface water and nonthermal groundwater the dominant source of supply of cl is seawater spray and aerosols but the soil and rock contribute often significantly to the b in these waters their cl b ratio is similar to that of seawater 1330 or somewhat lower boron and cl concentrations generally increase with water temperature warm waters cl b ratios intermediate between those of seawater and basalt with increasing temperature this ratio decreases and gradually approaches that of the rock some high temperature geothermal waters have as low cl b ratios as 1 and b concentrations as high as 10 ppm the cause is either b degassing of the magmatic intrusive heat source or phase separation in the producing aquifer some low temperature waters

boron content and isotopic composition of tektites and impact glasses constraints on source regions abstract abundances of li be and b as well as boron isotopic compositions were determined in twenty seven tektite and impact glass samples using an ion microprobe samples included tektites from the australasian north american and ivory coast strewn fields and aouelloul and darwin impact glasses variations of b abundance and isotopic composition in a flanged australite were also studied 11 b variations of only a few permil were found within the australite flange the isotopic composition shows no correlation with the b contents or with the distance from the rim of the flange the mean 11 b value for the flanged australite is very similar to that of muong nong type tektites 1 9 1 9 thus vapor fractionation has been unimportant during tektite formation this is supported by the observation that b contents and the 11 b values of the different samples from the australasian tektite strewn field are not correlated with each other most tektites show a rather limited range of 11 b values 9 3 1 5 to 2 7 1 5 o which is small compared to the range observed for common terrestrial rocks 30 to 40 the b abundance and isotopic data can be used to place constraints on the tektite source rocks australasian tektites have high b and li abundances only clay rich sediments such as pelagic and neritic sediments as well as river and deltaic sediments have b contents up to 100 ppm and 11 b values that are in agreement with the range shown by australasian tektites 4 9 to 1 4 10 be and rb sr data indicate continental crustal source rocks and exclude pelagic and neritic sediments however deltaic sediments e g from the mekong river which are of continental crustal origin agree with 10 be rb sr and b data and support a possible source locality close to the coast of se indochina in the south china sea on the other hand one bediasite sample has a very high 11 b value of 15 1 2 1 requiring the presence of marine carbonates or evaporites among the source rocks this finding supports an offshore locality for the north american tektite source crater

boron isotope geochemistry of paleozoic brachiopod calcite implications for a secular change in the boron isotope geochemistry of seawater over the phanerozoic abstract boron isotope composition of marine carbonates has been proposed as a paleo ph proxy and potential tool to reconstruct atmospheric pco2 the precise knowledge of the boron isotopic composition of ancient seawater represents the fundamental prerequisite for any paleo ph reconstruction this contribution presents boron isotope values for silurian to permian brachiopod calcite that might be used to reconstruct ph or boron isotope composition of past oceans all brachiopod shells were screened for diagenetic recrystallization by means of cathodoluminescence microscopy trace element geochemistry b fe mn sr as well as sem only nonluminescent shells revealing well preserved microstructures high strontium and boron concentrations as well as low iron and manganese contents were accepted for boron isotope analysis the boron isotope ratios of silurian devonian pennsylvanian and permian brachiopod calcite range from 6 8 to 11 0 7 3 to 14 9 12 4 to 15 8 and 10 1 to 11 7 respectively these 11b values are significantly lower in comparison to 11b values of modern biogenic carbonates and indicate that the paleozoic oceans were depleted in 11b by up to 10 box modeling of the boron geochemical cycle suggests that the significant depletion of 11b in the oceanic reservoir may have been initiated by an enhanced continental boron discharge our data support the earlier made conclusion that boron isotopes may not be used in the geological past as reliable paleo ph proxy unless the boron isotopic composition of ancient oceans can be constrained by further studies

channel response to increased and decreased bedload supply from land use change contrasts between two catchments abstract the catchments of pine creek idaho usa 200 km 2 and the drome river in the drome department france 1640 km 2 illustrate contrasting changes in land use bedload sediment production and channel response hard rock mining began in the catchment of pine creek near the end of the 19th century and together with road construction timber harvest and historically heavy grazing of uplands resulted in increased tributary bedload yield increased bedload migrating to the channel combined with removal of large cedar trees on the floodplain resulted in channel instability which propagated downstream over a period of decades on many reaches of pine creek active channel width has increased by over 50 since 1933 over roughly the same time period the drome river catchment was extensively reforested after at least one century of denudation and heavy grazing and numerous check dams were constructed on torrents to reduce erosion as a result the drome river has experienced a reduction in bedload sediment supply since the late 19th century in addition gravel has been extracted from some reaches consequently the channel has degraded and gravel bars have been colonized with woody riparian vegetation channel widths in wide braided reaches decreased from 1947 to 1970 by 60 on pine creek channel instability has resulted in bank erosion exposing contaminated mine tailings and increased flood hazard on the drome river degradation has undermined bridges and embankments and lowered the water table in areas dependent on groundwater for irrigation resulting in loss of 6 million m 3 of groundwater storage since 1960 though they differ in drainage area by nearly an order of magnitude pine creek and the drome river provide an excellent contrast in that they represent two sides of an epicycle of alluvial sedimentation set off in each case by land disturbance in both cases the most recent channel changes though in opposite directions were viewed as negative by river managers on pine creek managers have removed or protected from erosion mine tailings and have attempted to train the stream into a more stable channel and most rock waste piles the principal sediment sources have recently been controlled on the drome river managers have prohibited gravel mining and adopted new policies to permit coarse sediment to migrate through the river system

intracrystalline boron isotope partitioning in illite smectite testing the geothermometer intracrystalline b isotope differences of 40 are observed between the interlayer and tetrahedral crystallographic sites of interstratified illite smectite i s we tested the hypothesis that partitioning of b isotopes between these sites could provide a low temperature single mineral geothermometer samples studied include a metabentonite transected by a dike in the cretaceous pierre shale 200 500 c buried mudstones from the eocene wilcox formation 60 125 c and i s products from hydrothermal experiments 300 350 c different reaction kinetics are represented by these different sample sets therefore results test the equilibrium partitioning of b in the interlayer vs tetrahedral sites in all samples interlayer 11 b values are isotopically heavier than the tetrahedral 11 b because 11 b prefers trigonal coordination we infer that b oh 3 dominates the interlayer sites within each sample set the intracrystalline differences are greatest 20 40 in the most expanded i s i e smectite rich and approach 0 as illitization increases there is good correlation r 0 84 between the interlayer 11 b calculated by mass balance and water 11 b indicated by the established maximum temperature of each sample these results suggest that the interlayer sites of i s preserve the b isotopic composition of water at the temperature that produced the authigenic illite direct measurements of interlayer 11 b equilibrated with water of known 11 b are needed to refine the relationship with temperature but the existing data indicate the following temperature dependent relationship t c 11 b tetrahedral 11 b interlayer 30 0 05

chemistry of hot springs along the eastern lau spreading center abstract the eastern lau spreading center elsc is the southernmost part of the back arc spreading axis in the lau basin west of the tonga trench and the active tofua volcanic arc over its 397 km length it exhibits large and systematic changes in spreading rate magmatic tectonic processes and proximity to the volcanic arc in 2005 we collected 81 samples of vent water from six hydrothermal fields along the elsc the chemistry of these waters varies both within and between vent fields in response to changes in substrate composition temperature and pressure ph water rock ratio and input from magmatic gases and subducted sediment hot spring temperatures range from 229 to 363 c at the five northernmost fields with a general decrease to the south that is reversed at the mariner field the southernmost field vai lili emitted water at up to 334 c in 1989 but had a maximum venting temperature of only 121 c in 2005 due to waning activity and admixture of bottom seawater into the subseafloor plumbing system chloride varies both within fields and from one field to another from a low of 528 mmol kg to a high of 656 mmol kg and may be enriched by phase separation and or leaching of cl from the rock concentrations of the soluble elements k rb cs and b likewise increase southward as the volcanic substrate becomes more silica rich especially on the valu fa ridge iodine and 7li increase southward and 11b decreases as b increases apparently in response to increased input from subducted sediment as the arc is approached species that decrease southward as temperature falls are si h2s li na cl fe mn and 87sr 86sr whereas ph alkalinity ca and sr increase oxygen isotopes indicate a higher water rock ratio in the three systems on valu fa ridge consistent with higher porosity in more felsic volcanic rocks vent waters at the mariner vent field on the valu fa ridge are significantly hotter more acid and metal rich less saline and richer in dissolved gases and other volatiles including h2s co2 and f than the other vent fields consistent with input of magmatic gases the large variations in geologic and geophysical parameters produced by back arc spreading along the elsc which exceed those along mid ocean ridge spreading axes produce similar large variations in the composition of vent waters and thus provide new insights into the processes that control the chemistry of submarine hot springs