the origin and evolution of canadian shield brines evaporation or freezing of seawater new lithium isotope and geochemical evidence from the slave craton abstract new chemical and isotopic data for deep seated calcium chloride brine from the miramar con gold mine yellowknife n w t strongly suggest that the brine salinity is of marine origin diagnostic marine properties include uniformly elevated br cl ratios typical of seawater concentrated beyond halite saturation and li br ratios 0 0254 0 0325 and 6 li compositions 32 1 to 36 3 similar to seawater 32 3 the mean 6 li for all mine water samples of 35 1 may reflect minor uptake of li by secondary minerals this interpretation is supported by analyses of altered metabasalt from fault zones which is enriched in li but depleted in 6 li 14 7 to 15 6 relative to the unaltered metabasalt 5 4 the mechanism responsible for concentrating the hypersaline brine end member is not unequivocal as evidence exists to support both evaporative and cryogenic processes on the one hand the devonian sedimentary record in the great slave lake region in conjunction with yellowknife brine isotopic compositions 2 h and 34 s so 4 that are similar to various devonian fluids support an evaporative origin on the other hand the na cl br cl relationship in the brine strongly suggests a cryogenic mechanism regardless of the concentrative mechanism the chemical data indicate that the yellowknife parent brine was concentrated 28 to 30 fold relative to seawater the extreme depletion of mg and enrichment of ca in the brines accompanied by sr ca ratios similar to that of seawater are accounted for by dolomitization of an aragonite rich marine sediment by the brine before infiltration into the crystalline basement rocks subsequent alteration of silicate minerals in the shield added additional ca and sr to the brine as indicated by their radiogenic 87 sr 86 sr ratios up to 0 7147 based on mineral balance calculations the major mineral products of the cryogenic and evaporitic concentration and evolution paths are significantly different the cryogenic evolution results in some 15 mirabilite 60 hydrohalite and 18 dolomite whereas the major minerals formed from the evaporitic evolutionary sequence are 36 halite 8 gypsum 17 dolomite and 30 albite the great similarity between the calcium chloride brine from yellowknife and other such canadian shield brines indicates that they may share a common marine origin

lithium isotopes in island arc geothermal systems guadeloupe martinique french west indies and experimental approach abstract we report lithium li isotopic measurements in seawater derived waters that were discharged from geothermal wells thermal springs and sub marine springs located in volcanic island arc areas in guadeloupe the bouillante geothermal field and martinique lamentin plain and the diamant areas while li isotopic signatures of the geothermal fluids collected from deep reservoirs were found to be homogeneous for a given site the 7li signatures for each of these reservoirs were significantly different the first low temperature 25 250 c experiments of li isotope exchange during seawater basalt interaction confirmed that li isotopic exchange is strongly temperature dependent as previously inferred from natural studies li isotopic fractionation ranged from 19 4 solution solid at 25 c to 6 7 at 250 c these experiments demonstrated the importance of li isotopic fractionation during the formation of li bearing secondary minerals and allowed us to determine the following empirical relationship between isotopic fractionation and temperature solution solid 7847 t 8 093 application of experimental results and literature data to the bouillante area suggested that geothermal water was in equilibrium at 250 260 c it likely has a deep and large reservoir located in the upper sheeted dike complex of the oceanic crust just below the transition zone between andesite volcanic flows and the basaltic dikes the upper dike section from which li is extracted by hydrothermal fluids was characterized by light li isotopic values in the rocks indicating retention of 6li by the altered rocks for the lamentin and diamant areas the geothermal fluids appeared to be in equilibrium with reservoir volcano sedimentary rocks at 90 120 c and 180 c respectively further evidence for this argument is provided by the fact that only the na li thermometric relationship determined for sedimentary basins yielded temperature values in agreement with those measured or estimated for the reservoir fluids this suggests the importance of a sedimentary signature in these reservoir rocks altogether this study highlights that the use of li isotopic systematics is a powerful tool for characterizing the origin of geothermal waters as well as the nature of their reservoir rocks

the behavior of lithium and its isotopes in oilfield brines evidence from the heletz kokhav field israel twenty four brine samples from the heletz kokhav oilfield israel have been analyzed for chemical composition and li isotope ratios the chemical composition of the brines together with geological evidence suggests derivation from messinian seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization the present salinity of the samples 18 47 g cl l was achieved by dilution of the original evaporitic brine by local fresh waters like brines from other sedimentary basins the li cl ratios in the heletz kokhav samples show a prominent li enrichment five fold to eight fold relative to modern seawater the isotopic ratios of li expressed in the 6 li notation vary from 26 3 to 17 9 all values being significantly higher than that of modern seawater 32 irrespective of their corresponding li concentration 1 0 2 3 mg l the isotopic composition of li and the li cl ratio in the oilfield brines were acquired in two stages a the original evaporated seawater gained isotopically light li during the diagenetic interaction between the interstitial messinian brine and the basin sediments a parent brine with an elevated li cl ratio was formed the brine was later diluted in the oilfields b the 6 li values of the final brines were determined during epigenetic interaction with the heletz kokhav aquifer rocks at the same time the li cl ratio inherited from stage a remained largely unchanged this work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins copyright 2002 elsevier science ltd

variation of lithium isotope composition in the marine environment a preliminary report the li isotopic compositions of ocean waters lake water hydrothermal solutions altered and unaltered basalts have been determined using the technique of thermal ionization mass spectrometry of lithium tetraborate seawater appears to be homogeneous in li isotopic composition the mean delta sup 6 li value is minus 32 3 plus minus 0 5 per thousand relative to an isotopic standard three lakes studied lake tanganyika caspian sea and dead sea yield delta sup 6 li similar to the seawater isotopic composition a fresh basalt glass from 21 degree n east pacific rise displays a delta sup 6 li value of minus 4 7 per thousand a hydrothermal solution from a 21 degree n vent field has delta sup 6 li of minus 10 per thousand indicating incomplete extraction of li from the igneous minerals or partial retention in secondary phases the alteration margin of a basalt from the mid atlantic ridge has delta sup 6 li of minus 8 4 per thousand the isotope data of submarine basalts suggest preferential removal of sup 6 li from seawater into alteration minerals during low temperature weathering the delta sup 6 li values of two hydrothermal solutions from guaymas basin were found to be minus 5 per thousand and minus 10 per thousand the results can be interpreted as the net effect of li addition from basalt and sediments and incorporation in hydrothermal precipitates as the hydrothermalmore fluids interact with basin sediments the observed enrichment of sup 7 li in seawater relative to submarine hydrothermal solutions its principal li input is tentatively attributed to isotopic fractionation associated with low temperature alteration of sea floor basalt and incorporation in authigenic sediments it appears that the li isotope system may have characteristics that can resolve the mass balance of li in the ocean less

redox and ph constraints in the subseafloor root zone of the tag hydrothermal system 26 n mid atlantic ridge abstract experiments were conducted at 375 400 c 500 bars to assess the role of redox and ph on fe cu and h 2 s concentrations at temperatures pressures and total dissolved chloride concentrations applicable to the trans atlantic geo traverse tag hydrothermal system at 26 n mid atlantic ridge the magnetite bornite anhydrite mineral assemblage imposed redox constraints while ph was buffered with a 0 65 molal na k cl bearing aqueous fluid coexisting with k feldspar muscovite and quartz results indicate a strong inverse correlation between dissolved cu and h 2 s aq whereas dissolved fe is more sensitive to ph magnetite bornite anhydrite fluid equilibria is characterized by unusually low mfe mcu molar ratio and low h 2 aq h 2 s aq activities to form this mineral assemblage during subseafloor hydrothermal alteration however requires elevated fluid rock mass ratios such that the ferrous iron and sulfur in the rock become sufficiently depleted to render pyrite and chalcopyrite unstable the relatively high cu concentrations the low h 2 s aq and mfe mcu ratios observed at tag vent fluids are consistent with constraints imposed by magnetite bornite anhydrite fluid equilibria at ph of approximately 4 9 available chemical data confirm that the tag hydrothermal system has experienced elevated fluid rock mass ratios in keeping with the extent of mass transfer needed to generate oxidizing low h 2 s aq conditions

an integrated chemical and stable isotope model of the origin of midocean ridge hot spring systems chemical and isotopic changes accompanying seawater basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs incorporating provision for addition and subtraction of a wide range of reactant and product minerals as well as cation and oxygen and hydrogen isotopic exchange equilibria the models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100 to 350 c with an overall water rock ratio of about 0 5 being constrained by an assumed 18 o h 2o at 350 c of 2 0 per mil h craig personal communication 1984 this is a realistic model because 1 the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust 2 the water rock ratio is high 50 at low temperatures and low 0 5 at high temperatures and 3 it allows for back reaction of earlier formed minerals during the course of reaction progress the results closely match the major element chemistry von damm et al 1985 and isotopic compositions craig et al 1980 of the hydrothermal solutions presently emanating from vents at 21 n on the east pacific rise the calculated solution chemistry for example correctly predicts complete loss of mg and so 4 and substantial increases in si and fe however discrepancies exist in the predicted ph 5 5 versus 3 5 measured and state of saturation of the solution with respect to greenschist facies minerals the calculated d h 2o is 2 6 per mil in excellent agreement with analytical determinations the calculated chemical mineralogic and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges humphris and thompson 1978 stakes and o neil 1982 as well as with data from ophiolites gregory and taylor 1981 predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite epidote chlorite tremolite greenschist assemblage at 350 c the models demand that the major portion of the water rock interaction occur at temperatures of 300 350 c interaction at temperatures below approximately 250 c results in negative 18 o h 2o shifts contrary to the observed positive 18 o values of the fluids exiting at midocean ridge vents hydrogen isotope fractionation curves by suzuoki and epstein 1976 lambert and epstein 1980 and liu and epstein 1984 among others are compatible with the model and require d h 2o to increase at all temperatures as a result of seawater basalt interaction

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

a mid ocean ridge thermal model constraints on the volume of axial hydrothermal heat flux the depth to the axial magma chamber at three oceanic spreading centers as indicated by seismic reflection surveys is greater than that predicted by conductive cooling thermal models of ridge crests the additional cooling at the ridge axis is owed to the circulation of seawater through the shallow crust a theoretical model for the temperature distribution at spreading centers which includes distributed heat sources and sinks is presented by representing the hydrothermal heat loss as a series of heat sinks the depths to the axial magma chamber at the east pacific rise at latitude 9 n the southern juan de fuca ridge and the lau basin spreading center are modeled heat sinks are added to the input model to increase the solidus depth until the computed magma chamber depth matches the magma chamber depth determined by seismic reflection surveys the thermal modeling indicates that the axial hydrothermal heat flux is between 7 1 106 and 13 8 106 mj m2 or 10 to 20 of the total missing heat at the ridge axis requiring extensive low temperature circulation off axis high temperature vents that are spaced 1 km apart and are active between 4 and 10 of the time would account for the axial hydrothermal heat loss

a time series of vent fluid compositions from 21 n east pacific rise 1979 1981 1985 and the guaymas basin gulf of california 1982 1985 a time series study of four hot spring fields at 21 n on the east pacific rise demonstrates that the solution compositions of mid ocean ridge hydrothermal vents are stable on a decadal time scale the ocean bottom seismometer obs national geographic smoker ngs and south west sw vents show no significant changes in the major element composition of their end member fluids since 1979 two of the vents obs and sw have maintained exit temperatures near 350 c since 1979 the ngs vent has remained close to 270 c since 1981 after cooling from 350 c in 1979 only one vent hanging gardens shows important changes in solution chemistry from 1981 to 1985 in 1985 this vent appears to have cooled 10 c relative to the other vents the depth of the reaction zone as determined by quartz geobarometry has increased by about 1 km at this vent the large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances rather the constancy of small interfield variations in solution composition is more consistent with control by rock buffering a 4 year time series study of hydrothermal vents in the guaymas basin also shows no significant changes in the major element composition of the end member fluids interfield differences in solution chemistry have been maintained from 1982 to 1985 this phenomenon is best explained in terms of an equilibrium model

evolution of cenozoic seawater lithium isotopes coupling of global denudation regime and shifting seawater sinks abstract the li isotopic record of seawater shows a dramatic increase of 9 over the past 60 million years here we use a model to explore what may have caused this change we focus particularly on considering how changes in the reverse weathering sinks that remove li from seawater can contribute to explain the observed increase our interpretation is based on dividing the oceanic sink which preferentially removes light li into two components i removal into marine authigenic clays in sediments at low temperatures with associated high fractionation factors and ii removal into altered oceanic basalt at higher temperatures and resulting lower fractionation factors we suggest that increases in the flux of degraded continental material delivered to the oceans over the past 60 ma could have increased removal of li into sedimentary authigenic clays versus altered basalt because altered basalt is associated with a smaller isotopic fractionation an increasing portion of the lower temperature authigenic clay associated sink could contribute to the rise of the seawater li isotope value this effect would moderate the extent to which the isotopic value of continental inputs must have changed in order to explain the seawater record over the cenozoic nonetheless unless the magnitude of fractionation during removal differs significantly from current understanding substantial change in the li 7 of inputs from continental weathering must have occurred our modeling suggests that dissolved riverine fluxes in the early eocene were characterized by li 7 of 0 to 13 with best estimates of 6 6 12 6 these values imply increases over the past 60 myrs of between 10 and 24 and we view a 13 increase as a likely scenario these changes would have been accompanied by increases in both the dissolved li flux from continental weathering and the removal flux from seawater into marine authigenic clays increases in li 7 of continental input are consistent with a change in the global denudation regime as a result of increasing continental erosion rate through the cenozoic changes in denudation may have meant increasing climate sensitivity of weathering over time but do not require globally supply limited and thus entirely climate insensitive weathering in the early cenozoic

behavior of li and its isotopes during serpentinization of oceanic peridotites analyses of li and li isotopes in serpentinized peridotites have been performed using thermo ionisation mass spectrometry tims and secondary ion mass spectrometry sims techniques on samples collected from the southwest indian ridge swir in the bulk samples li concentrations range from 0 6 to 8 2 ppm while whole rock 6li values range from 2 9 to 14 in situ analyses display a greater range in both li concentration 0 1 19 5 ppm and li isotopic composition 27 to 19 with the serpentinized portions having higher li concentrations than the associated relict phases these variations may reflect changes in li partitioning and isotopic fractionation between serpentine and fluid with temperature and water rock ratio they may also be explained by changes in the composition of the serpentinizing fluid over the course of serpentinization as the serpentine forms by interaction with a circulating fluid it preferentially removes 6li causing the li in the fluid to become isotopically heavier the isotopic composition of the initial hydrothermal fluid is dominated by basalt derived li which easily overwhelms the very low li content originally present in seawater as this fluid circulates through ultramafic rocks it induces the formation of serpentine that incorporates this mantle derived li hence li in serpentine is mainly derived from oceanic crust rather than from seawater and serpentinization involves li recycling within this crust consequently li isotopes are good tracers of the hydrothermal contribution in serpentinizing fluid these results imply that serpentinized peridotites are probably only a minor sink of oceanic li

rupture processes of the 2004 chuetsu mid niigata prefecture earthquake japan a series of events in a complex fault system 1 we relocated the hypocenters of the 2004 chuetsu earthquake sequence niigata japan using the double difference method the distribution of aftershocks reveals a complex fault system consisting of five different fault planes inversions of strong motion records for the five major events within the sequence indicate that the mainshock mw 6 6 and the largest aftershock mw 6 3 occurred on parallel wnw dipping fault planes the zones of large slip asperities of these two events are located near the hypocenters in contrast the three other large earthquakes mw 5 9 5 7 and 5 9 occurred on east dipping fault planes oriented perpendicular to the fault plane of the mainshock we used slip distributions deduced from waveform inversions to estimate the coulomb failure stress changes that occurred immediately prior to each event cff values were positive at the hypocenters and within the asperities of the major aftershocks these results suggest that stress changes resulting from individual earthquakes led directly to the occurrence of subsequent earthquakes within the complex fault system

lithium isotope geochemistry of the hawaiian plume results from the hawaii scientific drilling project and koolau volcano 1 we determined lithium isotopic compositions of mauna loa and mauna kea basalts from the 3 1 km drill hole of the hawaiian scientific drilling project hsdp for comparison li isotopic ratios were also determined for basalts from koolau volcano these two suites of samples define geochemical extremes in the range of hawaiian shield lavas the 400 ka record of mauna kea in the hsdp core shows temporal fluctuations between low 7li 4 relative to the l svec standard and high 7li 5 6 suggesting that the source components in the hawaiian plume are heterogeneous in li isotopic composition based on sio2 content and isotopic ratios of he li nd hf and pb three geochemical groups are identified in mauna kea lavas mauna kea basalts between 1900 and 2500 mbsl have relatively low 7li of about 4 they are low sio2 lavas distinguished by the highest 3he 4he and 208pb 204pb and low 176hf 177hf and 143nd 144nd like basalt from loihi seamount this mauna kea group is considered to originate from the core of the plume above 1900 mbsl high 7li lavas with high sio2 contents appear in both the submarine and subaerial sections they are marked by low 3he 4he and high 176hf 177hf the 7li rich signature of some samples 7li up to 5 7 is indicative of recycled oceanic crust in the plume this magma group defines the kea component the low sio2 lavas in the subaerial section have low 7li 4 3he 4he and 208pb 204pb their 7li values overlap the range of 7li in unaltered mid ocean ridge basalt morb and are consistent with upper mantle material entrained by the plume or contamination of plume derived magmas by the pacific lithosphere the 7li of koolau lavas mostly fall within the range of 4 5 0 3 exceptions are two samples that have 7li of 2 3 the lightest isotopic values may indicate subducted li that was isotopically fractionated during slab dehydration in contrast to other isotopic systems most koolau samples however resemble mauna kea samples in li isotopic composition mauna loa samples have 7li values of 3 5 to 4 9 within the range of the koolau and mauna kea lavas based on these data the loa trend volcanoes and kea trend volcanoes have largely overlapping li isotopic compositions in summary the hawaiian plume is not highly variable in li isotopic composition 7li is typically 4 with perturbations by subducted components to lower and higher ratios 2 5 to 5 7 the overlap of most hawaiian basalt and morb in their range of li isotopic ratios suggests minor influence of recycled oceanic crust in the plume and perhaps similar li isotopic ratios in the upper and lower mantle

east pacific rise at 21 n the volcanic tectonic and hydrothermal processes of the central axis abstract photographs obtained by the angus survey system at 21 n reveal many similarities to the geological processes delineated at other spreading centers and in particular those observed in the galapagos rift at 86 w the region of recent volcanism is restricted to a narrow zone zone 1 approximately 1 km wide this suggests that the width of the magma chamber feeding these flows is also narrow at the top variations in sediment cover are used to subdivide the flows within zone 1 into three sheet flow pillow flow pairs the youngest pair appears to have erupted form a linear fissure 8 km long running parallel to the valley axis this fissure is part of a larger en echelon pattern of eruptive fissures active hydrothermal vents associated with the youngest flows are situated directly above the apparent eruptive fissure the high 350 c temperature for some of the fluids exiting from the vents suggests a highly restricted circulation system involving at times little to no mixing with cold seawater the lava terrain in the remainder of zone 1 and bordering regions is characterized by extensive fracturing further suggesting a narrow upper dimension to the magma chamber and also that subsurface hydrothermal deposition of massive sulfides may lead to a reduction in the mixing processes

geothermal waters from the taupo volcanic zone new zealand li b and sr isotopes characterization in this study we report chemical and isotope data for 23 geothermal water samples collected in new zealand within the taupo volcanic zone tvz we analyzed major and trace elements including li b and sr and their isotopic compositions delta7li delta11b 87sr 86sr in high temperature geothermal waters collected from deep boreholes in different geothermal fields ohaaki wairakei mokai kawerau and rotokawa geothermal systems lithium concentrations are high from 4 5 to 19 9 mg l and lithium isotopic compositions delta7li are very homogeneous being comprised between 0 5 and 1 4 in particular it is noteworthy that except the samples from the kawerau geothermal field having slightly higher delta7li values 1 4 the other geothermal waters have a very constant delta7li signature around a mean value of 0 0 6 2s n 21 boron concentrations are also high and relatively homogeneous for the geothermal samples falling between 17 5 and 82 1 mg l boron isotopic compositions delta11b are all negative and display a range between 6 7 and 1 9 these b isotope compositions are in agreement with those of the ngawha geothermal field in new zealand li and b isotope signatures are in a good agreement with a fluid signature mainly derived from water rock interactions involving magmatic rocks with no evidence of seawater input on the other hand strontium concentrations are lower and more heterogeneous and fall between 2 and 165 g l 87sr 86sr ratios range from 0 70549 to 0 70961 these sr isotope compositions overlap those of the rotorua geothermal field in new zealand also confirming that some geothermal waters with more radiogenic strontium have interacted with bedrocks from the metasedimentary basement each of these isotope systems on their own reveals important information about particular aspects of either water source or water rock interaction processes but considered together provide a more integrated understanding of the geothermal systems from the tvz in new zealand

a lithium isotope study of hot springs and metabasalts from mid ocean ridge hydrothermal systems the li isotopic compositions of seawater and of fresh and altered basalts are distinct and therefore applicable to the study of the hydrothermal processes in the oceanic crust and the li balance in the ocean high temperature fluids from seven vents on the east pacific rise epr at 21 n and 11 13 n have 6li values ranging between 6 and 11 i e 3 7 heavier than fresh basalt values the intervent variations in li concentration and isotopic composition correlate well with water rock ratios no temporal change in the isotopic value was observed between 1981 and 1985 metabasalts show both li depletion and enrichment relative to fresh basalt they display light li isotopic values which reflect incorporation of li mobilized from fresh basalt from these observations we conclude that the li isotopic composition of submarine hot springs is controlled by a path dependent process involving dissolution of primary minerals and precipitation of li with alteration phases 6li values of fluids from the mid atlantic ridge 6 to 8 fall in the range of the epr indicating similar reaction controls at the two ridge systems the lack of 7li enrichment in the fluids from slower spreading ridges indicates that li is not recycled from older weathered crust thus the difference between the 3he and 87sr 86sr based hydrothermal flux and the crustal transfer rate of li cannot be reconciled by the inclusion of secondary li from older crust

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

lithium isotopes in hydrothermally altered basalts from hengill sw iceland abstract the li isotope signatures of hydrothermal fluids are remarkably constant li 7 8 0 1 9 irrespective of the water rock ratio w r permeability temperature or fluid involved seawater or meteoric high temperature hydrothermal fluids represent the second most significant source of li to the ocean yet the homogeneity of the li isotopic signatures of this source remains to be explained and in this context the lack of data for the corresponding altered phases is problematic we measured li contents and li isotope signatures as well as mineralogy composition and local fluid temperature in hyaloclastites collected from a borehole in the hellisheidi geothermal system iceland which have been altered by high temperature aqueous fluids from 170 to 300 c li is more enriched in the solid phases than the other alkali metals highlighting its greater ability to be incorporated into secondary phases especially at high temperatures 250 c mass balance calculations show that the low li concentrations in hydrothermal fluids are best explained by a high water rock ratio and a high permeability of this system the li isotopic signature of the altered hyaloclastites li 7 between 1 9 and 4 0 remains close to the fresh basalt at deep levels and high temperatures 290 300 c as measured li 7 range between 3 7 and 4 0 and decreases at shallower depths and lower temperatures 150 270 c li 7 between 1 9 and 3 1 a mass balance model involving basalt dissolution secondary phase formation and successive isotope equilibrium during the migration and the cooling of the percolating fluid was developed the corresponding apparent mineral fluid li isotope fractionation factors resulting from precipitation of secondary phases li minerals fluid 7 range between 0 at 300 c and 8 5 at 170 c and highlight a key role of chlorite applying the same approach to mid ridge oceanic hydrothermal systems allows the relatively homogeneous isotope signatures of high temperature fluids of various locations to be explained

developments in the understanding and application of lithium isotopes in the earth and planetary sciences the significant relative mass difference c 16 between the two stable isotopes of li approximately 6li 7 5 7li 92 5 coupled with broad elemental dispersion in earth and planetary materials makes this a system of considerable interest in fingerprinting geochemical processes determining mass balances and in thermometry natural mass fractionation in this system is responsible for c 6 variation among materials examined to date fig 1 although the modern era of li isotope quantification has begun there are still many questions about the li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered e g hoefs 1997 figure 1 summary of lithium isotopic compositions of earth and planetary materials filled bars are solid samples open bars are liquids see text for references and details the purpose of this chapter is to summarize the current understanding of li isotopes in geo and cosmochemical systems and to indicate 1 where li isotopes have a high probability of adding new understanding of these systems 2 where some of the more significant deficits in knowledge exist the small but burgeoning li isotope community has not yet compiled the volume of peer reviewed literature needed to adequately assess even that which has been studied to date as a result significant portions of this chapter are based on data reported in abstracts and as such are more than normally subject to revisions over time this chapter is anticipated to serve as a starting point for those interested in research incorporating li isotope geochemistry or in understanding the state of extant research experiments in li isotope fractionation knowledge of significant li isotopic fractionation during basic chemical processes is long standing the early experiments by taylor and urey 1938 in which li isotopes were fractionated by incomplete extraction of an aqueous solution from a zeolite exchange

cesium and rubidium in submarine hydrothermal fluids evidence for recycling of alkali elements abstract cs rb and k concentrations have been measured in hydrothermal fluids from the east pacific rise epr southern juan de fuca ridge and mid atlantic ridge mar the results of a time series from 21 n epr show a fall in the cs rb ratios from 1979 to 1985 together with results from other areas the data are consistent with a cracking front moving from weathered oceanic crust into fresh basalt within the magma chamber that supplies the heat for hydrothermal convection interaction of hydrothermal fluids with basalts that have undergone low temperature weathering results in recycling of the alkalis and other elements between oceanic crust and seawater these data demonstrate that the concentration of alkali elements in hydrothermal fluids do not represent a rigid constraint on the global magnitude of the circulation of seawater through axial high temperature hydrothermal systems

seawater intrusion through the oceanic crust and carbonate sediment in the equatorial pacific lithium abundance and isotopic evidence 1 large scale lateral advection of seawater within the oceanic crust is thought to be the cause of low heat flow in the equatorial pacific until now supportive evidence is limited to reversals of b and 11b ca mg so4 2 sr and 87sr 86sr in sediment pore waters here we report new evidence from a detailed study of li and its isotopes in sediment cores from odp sites 844 and 851 carbonates at these sites were significantly recrystallized leading to large variations in li and 7li in the sediments and associated pore waters in addition to diagenetic effects distinct reversals in lithium concentration and isotopic ratio toward modern seawater composition are observed in waters near the basaltic basement lending further support to the seawater intrusion hypothesis three endmembers are identified in the pore waters seawater a diagenetically altered component and evolved crustal fluid the new lithium isotopic results underscore the importance of diagenetic artifacts in carbonate sediments

behavior of li rb and cs during basalt glass and olivine dissolution and chlorite smectite and zeolite precipitation from seawater experimental investigations and modelization between 50 and 300 c abstract this study investigates experimentally the behavior of li rb and cs during the hydrothermal alteration of a basalt glass and of forsterite the behavior of trace alkalis during the dissolution of a basalt glass and forsterite has been followed between 150 and 300 c rb and cs are preferentially leached from the glass while li exhibits a stoichiometric release with respect to silica on the other hand incongruent loss of li relative to si during forsterite dissolution reflects a crystallographic site energy control of the release of trace elements from crystalline silicates the partitioning of li rb and cs between hydrothermal solutions and chlorites smectites and zeolites has been experimentally investigated between 50 and 260 c the alteration phases were synthesized by altering silicate glasses in solutions containing the trace alkalis the lower the temperature the higher the exchange capacity of the mineral or the lower the ionic hydration energy then the more the element is incorporated into the solid phases computer simulations generated with the eq3 6 software package and our experimental data on distribution coefficients account for the behavior of alkali trace elements during the alteration of basalt glasses by seawater at mid ocean ridges

trace element mobility and lithium isotope exchange during hydrothermal alteration of seafloor weathered basalt an experimental study at 350 c 500 bars abstract the relative mobility of trace incompatible elements and exchange of lithium isotopes during alteration of basalt previously altered by exposure to seawater at low temperatures seafloor weathered were experimentally determined at 350 c 500 bars these data are important as a means to test models calling for hydrothermal alteration of weathered basalt as a source of alkali elements for hot spring vent fluids at mid ocean ridges weathered basalt used for the experiment was characterized by high cs rb b k and li concentrations high cs rb and low k rb and ba rb ratios respectively relative to fresh basalt the basalt is enriched in 7li consistent with a history involving li uptake during seafloor weathering the experiment involved a na ca k cl fluid and flexible cell hydrothermal equipment which permitted periodic sampling of the fluid phase at experimental conditions the extraction efficiency of all trace incompatible elements was significant and ranged from 40 to 80 cesium rubidium lithium and boron were particularly mobile whereas ba sr and to a lesser degree k were taken up by alteration minerals early stage release of li was dominated by 7li most probably as a consequence of the dissolution of low temperature alteration phases in the weathered basalt that were rendered unstable at the elevated temperatures of the experiment subsequently however an increase in 6li in solution was observed owing to a combination of mineral dissolution from li bearing components in fresh basalt and isotopic equilibration effects owing to the mobility of li during hydrothermal alteration of weathered basalt it is unlikely that dissolution of weathered basalt components in subseafloor reaction zones 350 400 c could occur without noticeably affecting the lithium isotope composition of vent fluids as inferred previously from field studies thus the relatively high cs rb ratios of some vent fluids which were thought to be the result of hydrothermal alteration of weathered basalt may be caused by other effects such as partitioning of rb relative to cs into hydrothermal minerals at temperatures in excess of 400 c cs rb ratios in vent fluids from a wide range of pacific and atlantic ridge localities however reveal relatively large variations in space and time which suggest that a single process is unlikely to account for all of the data the relative mobility of trace alkali elements in weathered basalt not only constrains models of alkali element enrichment in hot spring vent fluids at mid ocean ridges but also provides data bearing on potential sources of alkali elements for arc magmas in subduction zones

hydrothermal lead transfer from mantle to continental crust the role of metalliferous sediments abstract the amount of lead annually transferred from oceanic crust to metalliferous sediments was estimated in order to test the hypothesis that a non magmatic flux of lead causes the pb surplus in the continental crust a pb surplus has been inferred from global crust mantle lead mass balances derived from lead concentration correlations with other trace elements and from lead isotope systematics in oceanic basalts dsdp odp data on the amount of metalliferous sediments in the pacific ocean and along a south atlantic traverse are used to calculate the mean worldwide thickness of 3 1 m for purely metalliferous sediment componens lead isotope ratios of 39 metalliferous sediments from the pacific define mixing lines between continent derived seawater and mantle derived basaltic lead with the most metal rich sediments usually having the most mantle like pb isotope composition we used this isotope correlation and the pb content of the 39 metalliferous sediments to derive an estimate of 130 70 g g for the concentration of mantle derived lead in the purely metalliferous end member mass balance calculations show that at least 12 8 of the lead annually transferred from upper mantle to oceanic crust at the ocean ridges is leached out by hydrothermal processes and re deposited in marine sediments if all of the metalliferous lead is ultimately transferred to the continental crust during subduction the annual flux of this lead from mantle to continental crust is 2 6 2 0 106 kg assuming this transfer rate to be proportional to the rate of oceanic plate production one can fit the lead transfer to models of plate production rate variations through time integrating over 4 ga hydrothermal lead transfer to the continental crust accounts for a significant portion of the pb surplus in the continental crust it therefore appears to be one of the main reasons for the anomalous behavior of lead in the global crust mantle system

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

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

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

li and li isotopic composition of hydrothermally altered sediments at middle valley juan de fuca li and li isotopes have been measured in the clay fraction of sediments recovered from the middle valley hydrothermal site on the juan de fuca ridge the li content of pure detrital clays is 51 ppm while hydrothermal clays and carbonates have lower li 22 11 ppm however there is no clear relationship between the mineralogy of the hydrothermal alteration products and their li content the 7li value of the detrital clays is 5 8 hydrothermal clays and carbonates have 7li in the range of 3 9 to 7 8 these values do not seem to be dependent on the temperature at which they formed modelling of the li and li isotope systematics indicates that the fluid from which the alteration products form is significantly enriched in li higher than 10 000 mol kg 1 relative to pore fluids recovered from within the sediments up to 589 mol kg 1 wheat c g m j mottl 1994 data report trace metal composition of pore water from sites 855 through 858 middle valley juan de fuca ridge in mottl m j davis e e fisher a t slack j f eds proc odp sci res 139 749 755 and that this li is derived from sediment thus the alteration products are not in equilibrium with their conjugate pore fluids rather the alteration minerals formed at lower water sediment ratios this suggests that fluid flow pathways at middle valley were more diffuse in the past than they are today

time series studies of vent fluids from the tag and mark sites 1986 1990 mid atlantic ridge a new solution chemistry model and a mechanism for cu zn zonation in massive sulphide orebodies

limited lithium isotopic fractionation during progressive metamorphic dehydration in metapelites a case study from the onawa contact aureole maine the major trace element and li isotopic compositions of granodiorite and metapelites from the onawa pluton and surrounding contact aureole have been measured to document the behavior of li and its isotopes during progressive metamorphic dehydration major andtraceelementconcentrationsinmetapelitesofthecontactaureolechangelittle whilelossonignition loi decreaseswithincreasing metamorphic grade which ranges from regional chlorite zone metamorphism far removed from the pluton to partially melted rocks adjacent to the pluton lithium concentrations in metapelites from all zones correlate with loi and abundances of the main li bearing minerals chlorite biotite muscovite decreasing by a factor of two from 130 ppm far removed from the pluton to 64 ppm adjacent to thepluton incontrast liisotopiccompositionsremainrelativelyunchangedacrosstheaureole 7 li 3 5to 1 0 andarecomparable to the range observed in schists and unmetamorphosed shales compared to the surrounding metasediments the granodiorite has a lower li content 45 ppm and a comparable 7 li value of 0 2 similar to those of other granites and the average upper crust 0 2 these observations are consistent with the removal of li from metapelites via rayleigh distillation during progressive metamorphic dehydration with isotopic fractionation factors between fluids and rocks ranging between 1 001 and 1 004 these values are similar to thoseofarecentexperimentalstudyandproduceisotopicfractionationthatisbarelybeyondanalyticaluncertainty 1 fortheobserved degree ofli depletion the good correlationsbetweenli concentrations and loiwithmineralogicalabundancesreflecttheimportanceof mineralogyincontrollingliconcentrationsandisotopiccompositionsofmetamorphicrocks comparisonoftheseresultswiththosefrom a study of a contact halo around the tin mountain pegmatite suggests that the nature of the intrusion plays a critical role in controlling the behavior of li in country rocks large diffusive driven isotopic fractionation over a small scale is expected to occur when rocks are infiltrated by li rich magmatic fluids while metamorphic devolatilization results in minor isotopic fractionation on the aureole scale published by elsevier b v

the effect of hydrothermal spring weathering processes and primary productivity on lithium isotopes lake myvatn iceland lithium isotopes are rapidly becoming one of the most useful tracers of silicate weathering processes but little is known on their behaviour in groundwaters and hydrothermal springs and how these sources might influence the weathering signal in surface waters this study presents lithium isotope compositions 7li for cold groundwaters 3 7 c and hydrothermal springs that were at geothermal temperatures 200 300 c but have cooled during transport 17 44 c both represent an important source of water and nutrients for lake myvatn iceland we also present a time series from the laxa river which is the single outflow from the lake the 7li values in the input springs to lake myvatn are highly variable 5 27 and correlate inversely with temperature and total dissolved solids these co variations imply that even in such waters the processes controlling 7li variations during weathering still operate that is the ratio of primary rock dissolution to secondary mineral formation where the latter preferentially incorporates 6li with a temperature dependent fractionation factor in high temperature geothermal waters 300 c secondary mineral formation is inhibited and has a low fractionation factor leading to little 7li fractionation even in waters that have cooled considerably over several months from their geothermal temperatures fractionation is still low and 7li values are similar to those reported from waters measured at 350 c in contrast cooler groundwaters promote relatively high proportions of clay formation which scavenge dissolved solids including 6li the time series on the laxa river the single outflow from lake myvatn shows little 7li variation with time over the 12 month sampling period 17 21 demonstrating that in contrast to tracers such as si isotopes li isotopes are unaffected by the significant seasonal phytoplankton blooms that occur in the lake thus these results clearly illustrate that li isotopes are ideally suited to constrain silicate weathering processes because fractionation by secondary mineral formation operates even when groundwater and hydrothermal inputs are significant and because li isotopes are demonstrably unaffected by phytoplankton or plant growth

lithium isotope geochemistry of marine pore waters insights from cold seep fluids lithium concentration and isotope data 7li are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments a sediment hosted hydrothermal system and two mediterranean brine basins the new reference data and literature data of hydrothermal fluids and pore fluids from the ocean drilling program follow an empirical relationship between li concentration and 7li 7li 6 0 0 3 ln li 51 1 2 reflecting li release from sediment or rocks and or uptake of li during mineral authigenesis cold seep fluids display 7li values between 7 5 and 45 7 mostly in agreement with this general relationship ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite illite is the major sink for light pore water li in deeply buried continental margin sediments deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport related fractionation trends pore fluids on passive margins receive disproportionally high amounts of li from intensely weathered and transported terrigenous matter by contrast on convergent margins and in other settings with strong volcanogenic input li concentrations in pore water are lower because of intense li uptake by alteration minerals and most notably adsorption of li onto smectite the latter process is not accompanied by isotope fractionation as revealed from a separate study on shallow sediments a numerical transport reaction model was applied to simulate li isotope fractionation during upwelling of pore fluids it is demonstrated that slow pore water advection order of mm a 1 suffices to convey much of the deep seated diagenetic li signal into shallow sediments if carefully applied li isotope systematics may thus provide a valuable record of fluid mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure

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

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

determination of the lithium isotopic composition of planktic foraminifera and its application as a paleo seawater proxy to investigate the potential use of li isotopes in foraminifera as a paleo lithium seawater proxy the li isotopic compositions of planktic foraminifera orbulina universa globigerinoides sacculifer globorotalia menardii a ndgloborotalia truncatulinoides were determined by thermal ionization mass spectrometry tims using phosphate as an ion source and multi collector inductively coupled plasma mass spectrometer mc icp ms rigorous cleaning procedures were employed to purify foraminiferal tests of detrital metal oxide and organic phases in single species analyses data generated using both methods reveal that d 7 li in planktic foraminifera resemble seawater such that the isotopic fractionation from the precipitation of foraminiferal calcite appears to be minimal down core measurements indicate that the d 7 li of o universa has remained constant over the last 44 ka in the north atlantic suggesting little change of li isotopic composition of ocean water during the last glaciation consistent with the long mean residence time of li results suggest that planktic foraminifera may provide a reliable record of the lithium isotopic composition of ocean water in the past the first measurements of seawater d 7 li from the indian ocean average 33 0f1 2x 2r throughout the water column this value is within error of values previously reported for the atlantic and pacific oceans as is expected based on the long mean residence time of li in the ocean there is no evidence for a significant decrease in li cl ratios as reported by some workers with indian ocean waters averaging 9 10f0 11 ag g d 2005 elsevier b v all rights reserved

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

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

downhill progressive landslides in long natural slopes triggering agents and landslide phases modeled with a finite difference method a large landslide in tuve gothenburg sweden 1977 initiated the development of a model for slope stability analysis taking the deformation softening of soft sensitive clays into consideration the model studies triggering agents and five phases in progressive slope failure are identified 1 in situ 2 disturbance 3 unstable dynamic 4 transitory or permanent equilibrium and 5 global failure the clay resistance in these phases may differ widely mostly due to different rates of loading two time dependent failure criteria are defined i the triggering load condition in the disturbance phase 2 and ii the transitory equilibrium in phase 4 indicating whether minor downhill displacements or a veritable landslide catastrophe will occur the analysis explains why downhill landslides tend to spread over vast areas of almost horizontal ground further downslope the model has been applied to landslides in scandinavia and canada three case studies are briefly discussed the model is a finite difference approach where local downhill deformations caused by normal forces is maintained compatible with deviatory shear deformations above and if relevant below the potential or the established failure surface software and an easy to use spreadsheet are introduced as well as recent developments

subseafloor phase equilibria in high temperature hydrothermal fluids of the lucky strike seamount mid atlantic ridge 37 17 n abstract as part of an integrated study conducted at the lucky strike seamount mid atlantic ridge 37 17 n in 2008 gas tight sampling devices were used to collect high temperature 300 c hydrothermal fluids issuing from sulfide structures distributed throughout the vent field located in the summit depression compared with previous observations from 1993 to 1997 the most substantial changes in vent fluid compositions are dramatically increased co2 concentrations 5 up to 133 mmol l and the observation of vent fluids enriched in dissolved chloride relative to seawater combined with an increase in 13 c co 2 values by 4 in 2008 the elevated co2 indicates replenishment of the magmatic heat source and may be indicative of a recent magmatic event the additional supporting fluid chemistry is however similar to that of the previous sampling intervals necessitating a reassessment of the subseafloor controls on vent fluid chemistry at lucky strike in the context of recently obtained geophysical data that provides the depth extent of a steady state magma chamber two phase behavior is indicated by the chloride variability in the vent fluids and comparison with experimental data for the associated chloride dependent partitioning of minor trace elements suggests the possibility of a similar source fluid for all the vent structures while limiting the likelihood of shallow phase separation and subseafloor mixing for the hydrothermal end members a recently calibrated fe mn geothermometer indicates minimum subseafloor equilibration temperatures of 350 385 c however constraints imposed by dissolved si cl in conjunction with geophysical observations are consistent with peak reaction conditions at temperatures of 430 475 c and pressures near the top of the axial magma chamber 410 480 bars where magmatic co2 becomes entrained in the circulating fluids the distance between the magma chamber and the seafloor at lucky strike is substantially greater than at most faster spreading ridges and we propose the resulting increased residence time in the up flow zone leads to the re equilibration of temperature sensitive transition metals at conditions less extreme than those associated with peak reaction agreement between experimental data thermodynamic model calculations and dissolved concentrations of fe cu zn h2 and h2s in the lucky strike fluids reinforce the hypothesis of ph redox equilibria for transition metals at relatively oxidizing conditions and temperatures predicted by the empirical fe mn geothermometer in situ ph measurements of the high temperature fluids exiting the seafloor are also consistent with the model calculations

lithium isotopic composition of central american volcanic arc lavas implications for modification of subarc mantle by slab derived fluids abstract li contents and isotopic compositions were determined for a suite of well characterized basaltic lavas from the central american volcanic arc cava variable li y 0 2 0 5 li sc 0 1 0 4 and 6 li values 2 6 to 7 7 attest to significant compositional heterogeneity in the subarc mantle within specific arc segments these parameters correlate strongly with each other and with a number of other constituents e g k rb ba b la 10 be 9 be 87 sr 86 sr u ce and 230 th 232 th among others these correlations are particularly strong for nicaragua samples coupling of this particular set of constituents is best explained in terms of addition of subduction components to the subarc mantle moreover their selective enrichment with respect to relatively fluid immobile incompatible elements signifies the dominance of fluid vs silicate melt transport of slab components to the subarc mantle several interesting nuances are revealed by the li data first although li and b are strongly correlated in both costa rica and nicaragua there are systematic along strike variations in li b that are consistent with these elements having different fluid release patterns from subducted slab segments for example li b is highest in costa rica where auxiliary evidence indicates higher subduction zone temperatures apparently b is preferentially depleted and li retained in the slab under warmer conditions the same relations are reflected in li 10 be and other subduction tracer systematics all of which point to larger subduction contributions below nicaragua yet even nicaragua lavas vary widely in levels of subduction enrichment high ti basalts from nejapa are the least enriched and have the highest 6 li 1 4 to 2 6 these values are greater than in fresh morb ca 4 and are not easily explained by additions of subducted li because most oceanic crustal rocks and marine sediments have lower 6 li than morb with typical values between 8 and 20 thus it appears the nejapa data may be representative of isotopically light mantle domains relatively light 6 li values in an undepleted spinel lherzolite 11 3 from zabargad is red sea and in primitive backarc basalts 1 6 to 0 5 from lau basin support this conclusion considering representative fluid and mantle endmember compositions the cava data are consistent with limited up to a few percent additions of slab derived fluids to a heterogeneous mantle containing variably depleted and enriched domains to form the respective magma sources in our view the subarc mantle is heterogeneous on a small scale but some arc sectors clearly received greater slab inputs than others

lithium isotope geochemistry of pore waters from ocean drilling program sites 918 and 919 irminger basin the distribution of li isotopes in pore waters to a depth of 1157 m below seafloor is presented for odp sites 918 and 919 in the irminger basin offshore greenland lithium isotope data are accompanied by strontium isotope ratios to decipher diagenetic reactions in the sediments which are characterized by the pervasive presence of volcanic material as well as by very high accumulation rates in the upper section the lowering of the 87sr 86sr ratio below contemporaneous seawater values indicates several zones of volcanic material alteration the li isotope profiles are complex suggesting a variety of exchange reactions with the solid phases these include cation exchange with nh4 and mobilization from sediments at depth in addition to the alteration of volcanic matter lithium isotopes are therefore a sensitive indicator of sediment water interaction 6li values of pore waters at these two sites vary between 42 and 25 at shallow depths 100 mbsf rapid decreases in the li concentration accompanied by a shift to heavier isotopic compositions indicate uptake of li into alteration products a positive anomaly of 6li observed at both sites is coincident with the nh4 maximum produced by organic matter decomposition and may be related to ion exchange of li from the sediments by nh4 in the lower sediment column at site 918 dissolved li increases with depth and is characterized by enrichment of 6li the li isotopic compositions of both the waters and the solid phase suggest that the enrichment of li in deep interstitial waters is a result of release from pelagic sediments the significance of sediment diagenesis and adsorption as sinks of oceanic li is evaluated the maximum diffusive flux into the sediment due to volcanic matter alteration can be no more than 5 of the combined inputs from rivers and submarine hydrothermal solutions adsorption on to sediments can only account for 5 10 of the total inputs from rivers and submarine hot springs