chemical and isotopic effects of retrogression in metamorphic fluid inclusions fluid inclusions may provide compositional and isotopic information about fluids from which the host mineral precipitated as long as the host mineral does not react with the fluid our transmission electron microscope tem investigation of grain boundaries and of fluid inclusions in zoisite and quartz of high pressure metamorphic rocks from dabie shan eastern china demonstrates daughter minerals such as margarite muscovite calcite and anhydrite their precipitation changes 1 the composition of the fluid by selective and mineral specific removal of co2 carbonates h2o sheet silicates hydration of the walls or s gypsum anhydrite sulfides 2 the concentrations and proportions of ions dissolved in the fluid and 3 the isotopic composition of the fluid because of isotopic fractionation between mineral precipitate and fluid and between unmixed fluids fluid leakage from overpressurized fluid inclusions with daughter minerals changes the overall chemical and isotopic composition of the inclusion irreversibly even when the daughter crystals later redissolve such fluid loss yields a wide range of compositionally and isotopically different fluids from a single starting fluid depending on the relation between mineral reactions in and fluid loss from the inclusion the fluid remaining in the inclusion and the fluid lost from the inclusion may appear entirely unrelated

the origin of jadeitite forming subduction zone fluids cl guided sims oxygen isotope and trace element evidence jadeitite a rare high p t rock is associated spatially with blueschist and or eclogite terranes scanning electron microscope sem and cathodoluminescence cl petrography of jadeitite samples from several major occurrences in burma myanmar guatemala japan kazakhstan and the u s a show that grains were deposited from s uids jadeite grain compositions indicate these s uid compositions changed with time cl imagery guided the acquisition of oxygen isotope and trace element analyses with the ion microprobe jadeite grains in each rock grew in cycles that began with red and or blue luminescent and ended with green luminescent zones the cl images were used to order the data into crystallization sequences these data and electron microprobe major element analyses document the association of green cl with increases in ca mg and cr 1 toward grain exteriors 2 in ne grained matrix around porphyroblasts 3 in shear zones that cut grains 4 in former open spaces now lled with jadeite or 5 in veins abundances of many trace elements are greater in green cl jadeitite compared with the red or blue cl zones some of these elements in particular li rb sr ti hf zr y and ree are unlikely to have been derived from serpentinite although crystal chemical effects may explain some of the trace element systematics e g preferential incorporation of ree into ca richer jadeite some kinetic control is suggested by sector zoned rhythmically zoned grains the oxygen isotope data suggest that jadeitite depositing s uids either had multiple sources or evolved in composition along their s ow paths or both

change in fabric of melange in the shimanto belt japan change in relative convergence systematic changes in fabrics of melanges have been detected in rocks of the shimanto belt japan several shear indicators including s c structures riedel shears and folds in the melanges indicate consistent sense of shear both in outcrop and microscopic scales the deformation mechanisms independent particulate flow and pressure solution suggest that the deformation started under unlithified conditions and progressed through lithification due to strain hardening after lithification cataclastic deformation occurred locally but most of the earlier deformation features are preserved this process appears to have taken place along the decollement beneath the off scraped accretionary prism sinistral reverse sense of shear is observed in the campanian melange whereas a dextral reverse sense of shear is preserved in the early eocene melange in the shimanto belt this change in fabric is interpreted to be linked to a change in relative convergence between the subducting and overriding plates three different plate models have been proposed for the late cretaceous to early tertiary western pacific margin 1 subduction of the kula pacific ridge along the continental margin 2 subduction of the pacific plate since 85 ma and 3 subduction of the aborted kula pacific ridge after 43 ma the observed change in fabric of melange is consistent only with the third model which predicts a change in relative convergence from sinistral to dextral at the appropriate time

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

offscraping accretion of jurassic chert clastic complexes in the mino tamba belt central japan abstract detailed structural and biostratigraphical analysis of the jurassic inuyama sequence a coherent chert clastic complex in the mino tamba belt central japan clarifies the evolution of accretionary processes at shallow structural levels the inuyama sequence is characterized by a series of stacked thrust sheets each sheet consists of an early triassic to middle jurassic oceanic plate stratigraphy composed of four lithologic units which are in ascending order siliceous claystone ribbon chert siliceous mudstone and clastic rocks the structural features of the inuyama sequence demonstrate a four stage progressive deformation 1 a decollement was initiated within the siliceous mudstone when this sequence was just seaward of the deformation front clastic dikes and sills formed at the horizon just above the decollement at this time 2 the stratigraphic section above the decollement was imbricated by in sequence thrusting in the frontal part of the wedge this initial stage of thrusting and imbrication was followed by 3 the formation of duplex structures with fault related folds within the lower stratigraphic section as the decollement stepped down section to the lowest siliceous claystone interval finally 4 these thrust packages were overprinted by secondary prism thickening in the form of out of sequence thrust faulting

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

hydration and uplift of the oceanic crust on the mid atlantic ridge associated with hydrothermal activity evidence from boron isotopes boron isotope systematics of vent fluids from the mid atlantic ridge mar and the faster spreading east pacific rise epr reveal that at the mar 50 of seawater boron is removed from circulating fluids on the downwelling limb of the hydrothermal convection cell whereas little boron is removed at epr sites geophysical and petrographic studies suggest that downwelling fluids on the mar penetrate deep in the oceanic crust and upper mantle where boron is removed during serpentinization of peridotite the associated hydration of the oceanic crust reduces its density and modelling of the data suggests that this results in uplift leading to significant elevation of the median valley walls in the vicinity of active hydrothermal systems

rb cs fractionation a link between granulite metamorphism and the s process abstract high grade metamorphism of pelitic sediments produces large cs losses with little k and rb depletion island arc volcanics contain an enhanced cs component relative to k and rb we suggest a connection between these two processes whereby fluids or melts removed from feldspar bearing subduction assemblages under high grade metamorphic conditions are enriched in cs relative to k and rb these cs enriched components infiltrate subarc mantle and lead to ubiquitous cs enrichment in arc volcanics normal oceanic magmatism is not effective in fractionating rb cs therefore the canonical oceanic basalt value of 85 for rb cs is distinctive relative to processes involving sediments recycling fluid melt metamorphism and arc volcanism

discovery of hydrothermal vent fields on alarcon rise and in southern pescadero basin gulf of california author s paduan jb zierenberg ra clague da spelz rm caress dw troni g thomas h glessner j lilley md lorenson t lupton j neumann f santa rosa del rio ma wheat cg abstract 2018 the authors hydrothermal vent fields located in the gap between known sites in guaymas basin and 21 n on the east pacific rise were discovered on the alarcon rise and in southern pescadero basin the alarcon rise spreading segment was mapped at 1 m resolution by an autonomous underwater vehicle individual chimneys were identified using the bathymetric data vent fields were interpreted as active from temperature anomalies in water column data and observed and sampled during remotely operated vehicle dives the ja sit pericu and meyibo active fields are near the eruptive fissure of an extensive young lava flow vent fluids up to 360 c from meyibo have compositions similar to northern east pacific rise vents the tzab ek field is 850 m west of the volcanic axis and active chimneys rise up to 33 m above a broad sulfide mound the inactive field is 10 km north northeast along the rift axis and most sulfide chimneys are enriched in zn and associated elements that are transported at lower temperature compared to the more cu rich active fields in southern pescadero basin the auka field is on the margin of a sediment filled graben at 3 670 m depth discharging fluids are clear contain hydrocarbons and have neutral ph elevated salinity and temperatures up to 291 c they have deposited massive mounds of calcite with minor sulfide the fluids are compositionally similar to those in guaymas basin produced by high temperature basalt seawater interaction followed by reaction with sediment the paucity of sulfide minerals suggests subsurface deposition of metals

experimental study of boron geochemistry implications for fluid processes in subduction zones a comprehensive experimental study utilizing an autoclave hydrothermal apparatus with a 10b isotopic tracer has been conducted to monitor the geochemical behavior of sediment b during early subduction zone processes the partition coefficient of exchangeable b kd was determined over a temperature range of 25 350 c at 800 bars and a water rock ratio of 3 1 5 w w these kd are shown to be a complex function of temperature ph and possibly mineralogy at low temperatures kd is significantly high at 4 in contrast to the value of essentially zero at temperatures higher than 100 c a kd of zero represents no b adsorption implying efficient mobilization of exchangeable b at shallow depths during sediment subduction our experimental results demonstrate high mobilization of bulk b in sediments both exchangeable and lattice bound at elevated temperatures 200 350 c in good agreement with previous observations of b in metasediments indicating progressive depletion during metamorphism in addition this study emphasizes the importance of a possible water rock ratio dependence of b mobilization in other words the degree of sedimentary b mobilization in subduction zones strongly depends on the local thermal structure and porosity distribution in low geothermal gradient areas large amounts of porewater are expelled before significant b mobilization has occurred so that some sedimentary b will survive and get into the deeper parts of the subduction zone our results imply that efficient mobilization of b from the subducted slab must occur and that arc magmatism recycles most of the remaining subducted b back to surface reservoirs a reconsideration of the b budget in subduction zones provides critical information with respect to b sources and sinks in the ocean

development of slaty cleavage and degree of very low grade metamorphism a review illite crystallinity ic and other indicators of the grade of very low grade metamorphism associated with the appearance of various stages of slaty cleavage in phyllosilicate rich rocks have been compiled from a wide variety of terranes ic values have been converted to a kubler equivalent standard scale but the diverse characterizations of the cleavage fabrics in published descriptions do not always allow an unequivocal identification of equivalent stages of cleavage development nevertheless there exists a distinct relationship between grade and the appearance of various stages of cleavage development 1 indications of incipient slaty cleavage such as s0 s1 pencil structure appearance of primary s1 crenulation cleavage and of closely spaced cleavage without parallel fabric in the microlithons is associated with a wide range of mostly medium and high grade diagenetic ic values 2 the appearance of smooth cleavage with a strong parallel fabric in the microlithons and or quartz mica beards and the chlorite mica stacks shortened at a high angle to 001 and of irregular cleavage in sandy beds is associated with a much narrower range of predominantly low and medium grade anchimetamorphic grades rarely high grade diagenetic the first appearance of these stages of cleavage development with higher grades can often be related to post kinematic magmatic heating polymetamorphism pre cleavage metamorphism or static recrystallization without cleavage formation for example in low strain zones there exists a relationship between finite strain fabric and metamorphic grade in mudstones and slates in coarser clastic rocks the same finite strain fabric relationship occurs at appreciably higher grades a relationship between finite strain in carbonate rocks and ic in the nearby rocks has been reported from the helvetic zone of the swiss alps the earlier stages of cleavage formation are associated with little improvement in ic the narrow range of ic associated with smooth cleavage is concluded to represent recrystallization and grain growth concurrent with cleavage formation

hydrothermal water rock interaction and the redistribution of li b and cl in the taupo volcanic zone new zealand abstract lithium b and cl occur as trace elements in the dominant protoliths rhyolite andesite and greywacke underlying high temperature hydrothermal systems in the taupo volcanic zone tvz the fluid mobility of li decreases substantially at 200 c 20 c with the pervasive deposition of quartz chlorite regardless of protolith and altering fluid compositions boron and cl are more fluid mobile than li at all temperatures with mobility affected by the rock type composition of circulating aqueous solutions and to a limited extent by incorporation of the trace elements in hydrothermal minerals uptake of b by clays decreases its mobility at 320 c occur compared to volcanic rocks the mobility of b and cl in greywackes is very low and thus the b cl signature of greywacke in hydrothermal aqueous solutions of the tvz is overwhelmed by the effects of rhyolite and andesite dissolution temperature dependent transitions from mg fe clays and phyllosilicates to k bearing illitic clays tend to decrease the mg li ratios in aqueous solutions at 200 c

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

plate reconstruction based upon age data of japanese accretionary complexes the ages of the oceanic plates for the japanese accretionary complexes are plotted against time of accretion the plots show that early cretaceous transform faulting modified the arrangement of the pre middle cretaceous accretionary complexes and that three or four mid ocean ridges have collided with the japan arc since permian time the plate configuration for the western north pacific is reconstructed

lithium behavior during cooling of a dry basalt an ion microprobe study of the lunar meteorite northwest africa 479 nwa 479 northwest africa 479 nwa 479 is a lunar meteorite recovered in 2000 from morocco this unbrecciated low ti basalt is paired with nwa 032 the texture of nwa 032 479 indicates a simple crystallization history and a fast cooling followed by an impact event the occurrence of high pressure polymorphs of olivine ringwoodite and wadsleyite in shock melt veins indicates shock pressures of at least 20 gpa

travel time of accreted igneous assemblages in western pacific orogenic belts and their associated sedimentary rocks abstract accreted igneous assemblages in orogenic belts maybe divided into three types depending on whether they derive from seamounts ocean ridges or subduction related ophiolites seamount type basalts are associated with shallow water sediments mostly reefoidal limestones ocean ridge type basalts are generally overlain by pelagic cherts subduction related ophiolitic eruptives often underlain by gabbroic and ultramafic rocks are associated with hemipelagic mudstones the age of such diverse eruptive lithologic assemblages reflects the time taken for them to have traveled from their locus of generation to their place of accretion at a continental margin this relationship has been established for each type of accretionary complex examples being taken mostly from japan and the western pacific rim in order to represent evolutionary processes at a typical active plate margin in general the seamount types are older ridge types are of intermediate age and the ophiolitic types are by far the youngest usually close to zero age seamount type basalts are accreted by shallower scraping of the seamount s sediment apron together with fragments of seamount basalt ridge type by peeling due to permeability contrast and the ophiolitic types by deeper scraping as a consequence of an inflected temperature gradient accordingly it is concluded that the ophiolitic rocks are generated close to the trench and may be accreted as a result of ridge subduction

accretionary process of the tertiary setogawa and mikasa groups southwest japan the middle eocene to lower miocene setogawa group consists of pelagic hemipelagic and terrigenous sediments with volcanic intercalations the sediments were deposited in and below the lower bathyal zone the setogawa group is a wedge shaped volcano sedimentary pile deformed by reverse faults and asymmetric folds at the landward edge and constitutes a subduction complex the reverse faulting and asymmetric folding took place abruptly accompanied by tilting uplifting and gravity sliding of strata and dewatering and consolidation of sediments this was followed by the lower miocene mikasa group which consists of in ascending order debris flow deposits terrigenous and volcano terrigenous sediments the basal debris flow deposits were mostly derived from the upper part of the setogawa group they buried the structural depressions formed by the reverse faulting and asymmetric folding and eroded the underlying strata over the short timespan included in the stichocorys delmontensis zone the mikasa g

the composition and petrogenesis of the lower crust a xenolith study granulite facies lower crustal xenoliths from a single basaltic vent hill 32 in the mcbride volcanic province north queensland australia illustrate the extreme lithologic diversity of the deep crust these xenoliths are dominantly mafic but intermediate and felsic granulites represent a significant proportion 20 of the xenolith population all xenoliths have high grade mineralogies and generally well equilibrated textures as well as decompression features which are indicative of derivation from deep crustal levels 0 7 1 0 gpa major and trace element chemistry for 12 xenoliths chosen to span the observed lithologic range are used to constrain the petrogenesis of these rocks in the smaller layered samples metamorphic differentiation may lead to nonrepresentative sampling however in most instances such secondary processes can be identified and the original chemical characteristics delineated the mafic xenoliths formed through a variety of processes including crystallization of mafic magma crystal accumulation from mafic and felsic magmas and partial melting of intermediate compositions to yield a mafic residuum the two analyzed intermediate xenoliths are metasediments based upon high alumina to alkali ratios and rare earth element patterns whereas the two felsic xenoliths have compositions similar to igneous rocks comparisons of noncumulate and or restite xenoliths with unmetamorphosed rock types show that k and rb are variably depleted whereas th and u are strongly depleted in all rock types the large ion lithophile element depletion patterns for xenoliths are similar to those of rocks from granulite facies terrains suggesting similar processes were operative suggestions of an anomalously ba and sr rich lower crust are not supported by the data by using the observed lithologic proportions of xenoliths at hill 32 and the chemical analyses presented here a weighted mean composition of the lower crust can be obtained and compared with recently proposed lower crustal compositions the weighted mean composition is mafic and formed through a combination of basaltic underplating crystal accumulation tectonic underplating and partial melting no simple model of lower crust formation through basaltic or andesitic underplating nor intracrustal melting is sufficient to explain lower crust formation in phanerozoic continental margin settings

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

lithium isotopic systematics of hydrothermal vent fluids at the main endeavour field northern juan de fuca ridge vent fluids issuing from the main endeavour field mef juan de fuca ridge were analyzed for 7li to help constrain subseafloor hydrothermal alteration and phase separation processes magmatic activity prior to sampling of the fluids in 1999 enhanced heat and mass transfer as indicated by the large scale but temporary changes in vent fluid chemistry in particular dissolved chloride concentrations indicate formation of supercritical cl poor vapors which affected alteration throughout the mef system 7li of fluids however ranges from 7 2 to 8 9 and reveals no significant correlation with dissolved chloride being consistent with results of hydrothermal experiments that show no lithium isotope fractionation during supercritical phase separation on a chloride normalized basis li concentration data indicate relatively short residence times or high fluid rock mass ratios of vent fluids most impacted by phase separation effects reaction path models involving li isotope data also show elevated fluid rock mass ratios boron data in contrast suggest direct input from degassing magma enhanced heat flow associated with magmatic injection at depth inhibits penetration of seawater derived hydrothermal fluid into fresh basalt particularly in those systems where magmatic volatile input is most active the inverse correlation between li cl and b cl in vapor rich vent fluids may be a useful indicator of recent subseafloor magmatic activity

li and δ7li in mudrocks from the british caledonides metamorphism and source influences mudrocks from three lower paleozoic basins in the british caledonides southern lake district northern lake district and southern uplands were investigated to determine the influence of sub greenschist facies metamorphism on li and the factors that control li in fine grained terrigenous sedimentary rocks metamorphic grade as determined by ki kubler index does not correlate with li content li and 7li indicating that sub greenschist facies metamorphism has negligible effect on li in these rocks collectively the data for all three basins show a negative correlation between li and 7li and a positive correlation between li and the chemical index of alteration cia suggesting that provenance exerts the greatest control on li in mudrocks samples from the northern lake district which were deposited in an extensional basin have homogeneous ree patterns similar to shale composites paas the highest cia th u and li and the lowest 7li and end consistent with their derivation from a highly weathered ancient continental source by contrast mudrocks from the southern uplands range to the lowest cia th u and li and have the highest 7li and end these samples were deposited in a forearc basin on the southern margin of the laurentian craton and contain volcanic detritus their ree patterns are the most variable ranging from average shale like patterns to less lree enriched patterns the compositional heterogeneity within the southern uplands mudrocks is consistent with a mixed provenance that includes juvenile crustal materials lower li end and th u higher 7li likely derived from the arc as well as more highly weathered continental detritus mudrocks from the southern lake district were deposited in a foreland basin and exhibit geochemical characteristics intermediate between the northern lake district and the southern uplands mudrocks indicating their derivation from a mixed source our study shows that li concentrations and 7li can provide additional information on the degree of weathering of the provenance of mudrocks

breakup of young oceanic lithosphere in the upper part of a subduction zone implications for the emplacement of ophiolites it is investigated by means of numerical modelling whether the interaction between young oceanic lithosphere and a subduction zone can lead to the breakup of a young and thin oceanic plate first a thermal model of the upper part of a subduction zone the region between the trench and the volcanic arc is presented temperatures are modelled for situations in which the age of the subducting oceanic lithosphere gradually decreases culminating in the arrival of a spreading ridge at the trench temperatures are used to infer the strength of material within the subducting plate from a pressure and temperature dependent rheology next it is investigated by means of finite element modelling whether the forces acting upon young subducting oceanic lithosphere recently created at a spreading center in the vicinity of a subduction zone can lead to its breakup our modelling results show that very young oceanic lithosphere may indeed break up during the early phase of its subduction whether breakup occurs depends upon the spreading velocity and the length of the ridge segment that interacts with the trench if breakup occurs some young oceanic lithosphere situated in the upper part of the subduction zone and in the region between the ridge and the trench will be detached from the other parts of the subducting plate the detached sheet of thin oceanic lithosphere will not be subducted to mantle depths instead subduction of the trailing plate at the opposite side of the ridge can lead to the incorporation of this sheet into the forearc region our modelling provides a mechanism to incorporate thin oceanic lithosphere into an arc trench region and eventually upon closure of the ocean basin into an orogenic belt it is shown that a large subset of ophiolites those with a harzburgite dominated mantle section has properties in good agreement with an emplacement history in which the breakup of young oceanic lithosphere in the upper part of a subduction zone is the first phase

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

arrested kinetic li isotope fractionation at the margin of the ilimaussaq complex south greenland evidence for open system processes during final cooling of peralkaline igneous rocks li contents li and isotopic composition 7 li of mafic minerals mainly amphibole and clinopyroxene from the alkaline to peralkaline ilimaussaq plutonic complex south greenland track the behavior of li and its isotopes during magmatic differentiation and final cooling of an alkaline igneous system li in amphibole increase from b10 ppm in caamphiboles of the least differentiated unit to n3000 ppm in na amphiboles of the highly evolved units in contrast li in clinopyroxene are comparatively low b85 ppm and do not vary systematically with differentiation the distribution of li between amphibole and pyroxene is controlled by the major element composition of the minerals ca rich and na rich respectively and changes in oxygen fugacity due to li incorporation via coupled substitution with ferric iron during magmatic differentiation 7 li values of all minerals span a wide range from 17 to 8 with the different intrusive units of the complex having distinct li isotopic systematics amphiboles which dominate the li budget of whole rocks from the inner part of the complex have constant 7 li of 1 8 2 2 2 n 15 this value reflects a homogeneous melt reservoir and is consistent with their mantle derivation in agreement with published o and nd isotopic data clinopyroxenes of these samples are consistently lighter with 7 liamph cpx as large as 8 and are thus not in li isotope equilibrium these low values probably reflect late stage diffusion of li into clinopyroxene during final cooling of the rocks thus enriching the clinopyroxene in 6 li at the margin of the complex 7 li in the syenites increases systematically from 2 to high values of 14 this coupled with the observed li isotope systematics of the granitic country rocks reflects post magmatic open system processes occurring during final cooling of the intrusion although the shape and magnitude of the li isotope and elemental profiles through syenite and country rock are suggestive of diffusion driven isotope fractionation they cannot be modeled by one dimensional diffusive transport and point to circulation of a fluid having a high 7 li value possibly seawater along the chilled contact in all this study

paleothermal structure of the shimanto accretionary prism shikoku japan role of an out of sequence thrust vitrinite reflectance study on the cretaceous shimanto accretionary prism of southwest japan shows that the vitrinite reflectance varies from 0 6 to 3 0 corresponding to the estimated maximum paleotemperature variation of 90 210 c the thermal structure shows a sharp discontinuity across an out of sequence thrust separating it into two thermal blocks in each block vitrinite reflectance values increase systematically toward the prism younging direction and the thermal structure is clearly overprinted on the tectonic imbrication of turbidite and melange units this provided us with a set of data to calculate the geometry and displacement of the out of sequence thrust the fission track zircon partial annealing ages indicate that this thrust was active about 43 ma probably in response to the accretion of eocene rocks this study shows that initial thickening of the accretionary prism in an order of several kilometres was mainly controlled by out of sequence thrust

two stages of granulite facies metamorphism in the eastern himalayan syntaxis south tibet petrology zircon geochronology and implications for the subduction of neo tethys and the indian continent beneath asia the eastern himalayan syntaxis in southeastern tibet consists of the lhasa terrane high himalayan rocks and indus tsangpo suture zone the lhasa terrane constitutes the hangingwall of a subduction zone whereas the high himalayan rocks represent the subducted indian continent our petrological and geochronological data reveal that the lhasa terrane has undergone two stages of medium p metamorphism an early granulite facies event at c 90 ma and a late amphibolite facies event at 36 33 ma however the high himalayan rocks experienced only a single high p granulite facies metamorphic event at 37 32 ma it is inferred that the late cretaceous c 90 ma medium p metamorphism of the southern lhasa terrane resulted from a northward subduction of the neo tethyan ocean and that the oligocene 37 32 ma high p 1 8 1 4 gpa rocks of the high himalayan and coeval medium p 0 8 1 1 gpa rocks of the lhasa terrane represent paired metamorphic belts that resulted from the northward subduction of the indian continent beneath asia our results provide robust constraints on the mesozoic and cenozoic tectonic evolution of south tibet

ridge subduction and slab windows in the central asian orogenic belt tectonic implications for the evolution of an accretionary orogen abstract cenozoic ridge subduction and the resultant slab windows have been well documented worldwide especially along the western margins of north and south america the principal characteristics of ridge subduction which can be used to recognize the process in ancient orogens include intrusion of ridge generated magmas into a forearc in a near trench position this can be regarded as the hallmark of ridge subduction the key magmatic products are adakites that include plutonic and volcanic rocks with intermediate to high sio2 high sr y and la yb ratios elevated mgo na2o k2o ni and cr contents and high lile and lree elements they range from hornblende biotite bearing high mg diorites and granodiorites to hornblende pyroxene high mg andesites they are typically associated with a wide variety of coeval and compositionally diverse volcanic and plutonic rocks such as high ca boninites tholeiitic high t basalts alkaline basalts charnockites peraluminous ttgs i type granites and mid ocean ridge mor not supra subduction ophiolites the trace element chemistry of these rocks demonstrates that they were generated by partial melting of dehydrated subducted oceanic crust and of lower continental crust contaminated and metasomatized by juvenile melts that originated by upwelling of asthenospheric mantle it is this combination of mixed sources that gives rise to the diagnostic and distinctive features of coeval and associated ridge subduction rocks in a near trench environment other important features of ridge subduction are high temperature metamorphism closely associated with near trench plutons created by heat released through a slab window and porphyry gold copper zinc mineralization associated with mor ophiolites and generated in hydrothermal vents at a mor when a ridge subducts under a continental margin the diverging plates associated with the ridge continue to separate creating a slab window that forms between the separating plates adakitic melts tend to be generated close to the hot plate margins whereas a type granites and porphyry cu au deposits form in the centre of the opening slab window most of the above features have been described and analyzed in many parts of the central asian orogenic belt caob particularly in west junggar chinese altai russian altai east junggar beishan chinese tianshan inner mongolia kyrgyzstan and at alxa prominent in one of two slab windows defined in west junggar are two swarms of late carboniferous high mg hornblende biotite diorite dykes with sanukitoid chemistry that intruded through the slab window one generation was orthogonal to an ophiolite strewn paleotrench suture and the second was parallel to a transform fault that was parallel to the paleo trench the dikes provide the best evidence so far for the orientation and opening of a slab window in the caob and for the relative movement directions of the downgoing and overriding plates during the subduction and closure of the paleo asian ocean however these are early days because most parts of the caob have yet to be investigated for evidence of ridge subduction and slab windows so the prospects are high

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

geochemistry of north cleft segment vent fluids temporal changes in chlorinity and their possible relation to recent volcanism hydrothermal vent fluids from the north cleft segment of the juan de fuca ridge between 44 54 and 45 00 n were sampled in 1988 1990 1991 and 1992 in 1988 chloride depleted relative to seawater diffuse fluids with low dissolved metal concentrations relative to other mid ocean ridge mor fluids were sampled over a distance of 10 km along axis in 1990 and 1991 both high temperature 200 c and diffuse vents were consistently metal and chloride enriched the end member compositions of high temperature vents and nearby diffuse vents were very similar there were small but significant correlated changes in diffuse and high temperature composition from 1990 to 1991 the large scale but temporary venting of low chlorinity fluids over the entire north cleft segment provides a resolution to the apparent mass imbalance implied by observations of continuous venting of chloride enriched fluids it is possible that a volcanic event along the north cleft segment prior to 1987 for which there is firm geologic evidence initially caused a boiling event which resulted in the preferential venting of vapor enriched fluids through 1988 followed by a transition to brine enriched fluids by 1990 high iron low sodium and low sr ca ratios in the high chlorinity fluids suggest that the brine phase has continued to react and approach reequilibration with an alteration mineral assemblage after the phase separation event the absence of chloride depleted fluids from 1990 onward and the systematics of lithium boron and manganese with chloride in the high temperature fluids from north cleft suggest that the evolution toward lower chlorinity at monolith vent from 1990 to 1992 is caused by progressive dilution of a brine with hydrothermal seawater

mesoarchaean aluminous rocks at storo southern west greenland new age data and evidence of premetamorphic seafloor weathering of basalts abstract metamorphosed meso to neoarchaean supracrustal rocks in the central part of the island of storo nuuk region southern west greenland show field and geochemical evidence of premetamorphic chemical alteration this alteration changed basaltic precursors into aluminous lithologies and following amphibolite grade metamorphism and penetrative ductile deformation these garnet biotite schists now resemble adjacent metapelitic schists of sedimentary origin mass balance calculations isocon method suggests that most major elements si fe mg ca na and p were leached during alteration the calculated overall net mass changes are between 18 and 45 consistent with breakdown of olivine pyroxenes plagioclase and apatite in the basaltic precursor rocks major and trace elements such as k cs rb ba pb zn la and ce were added during this alteration process whereas high field strength elements ti al zr hf and nb remained essentially immobile and were thus residually enriched interestingly th which is generally assumed to be immobile in fluids was also added during this process these chemical changes reflect interaction between a basaltic protolith and hydrous fluids that established a new equilibrium and thus a different mineral assemblage it is proposed that the premetamorphic alteration at storo was due to low temperature interaction between seawater and oceanic crust and thus essentially represents in situ submarine seafloor weathering this interpretation is consistent with the mass balances reported from well documented examples in younger settings new u pb zircon geochronology from the arc related mafic sequences at storo shows that they comprise at least two distinct age groups an older anorthosite complex dated at 3051 3 2 6 ma and a younger supracrustal sequence with age brackets between 2840 and 2710 ma the allochthonous nature of these two mafic igneous to sedimentary stacks is consistent with accretionary processes in island arc complexes and a compressional archaean tectonic setting

increasing exchanges at greenland scotland ridge and their links with the north atlantic oscillation and arctic sea ice 1 a global ice ocean model shows increasing atlantic water aw inflow at the iceland scotland ridge isr during 1953 2002 as a result the greenland iceland norwegian gin sea is gaining more heat and salt from the north atlantic ocean while the latter is being freshened mainly by exporting more salt to the gin sea the exchanges of volume heat and freshwater at the greenland scotland ridge gsr are strongly correlated with the north atlantic oscillation nao and their positive trend is closely linked to the nao elevation in recent decades the model confirms observations of decreasing dense water outflow at the faroe scotland passage since the 1950s however the simulated dense water outflow shows an increase at denmark strait at the iceland faroe ridge and at the gsr as a whole owing to an increase in aw inflow that may cause an increase in aw recirculation and deep water production in the gin sea the increase of the isr heat inflow since 1965 contributes to continued thinning of the arctic sea ice since 1966 the influence of the heat inflow on arctic sea ice lags 2 3 years which suppresses ice production even when the nao temporarily shifts to a negative mode because of this delay the decline of arctic sea ice is likely to continue if the inflow continues to increase and if the nao does not shift to a sustained negative mode

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

aerosol size confines climate response to volcanic super eruptions extremely large volcanic eruptions have been linked to global climate change biotic turnover and for the younger toba tuff ytt eruption 74 000 years ago near extinction of modern humans one of the largest uncertainties of the climate effects involves evolution and growth of aerosol particles a huge atmospheric concentration of sulfate causes higher collision rates larger particle sizes and rapid fall out which in turn greatly affects radiative feedbacks we address this key process by incorporating the effects of aerosol microphysical processes into an earth system model the temperature response is shorter 9 10 years and three times weaker 3 5 k at maximum globally than estimated before although cooling could still have reached 12 k in some midlatitude continental regions after one year the smaller response plus its geographic patchiness suggests that most biota may have escaped threshold extinction pressures from the eruption

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

relicts of an intra oceanic arc in the sapi shergol melange zone ladakh nw himalaya india implications for the closure of the neo tethys ocean in the ladakh zanskar area relicts of both ophiolites and paleo accretionary prism have been preserved in the sapi shergol me lange zone the paleo accretionary prism related to the northward subduction of the northern neo tethys beneath the ladakh asian margin mainly consists of tectonic intercalations of sedimentary and blueschist facies rocks whole rock chemical composition data provide new constraints on the origin of both the ophiolitic and the blueschist facies rocks the ophiolitic rocks are interpreted as relicts of the south ladakh intra oceanic arc that were incorporated in the accretionary prism during imbrication of the arc the blueschist facies rocks were previously interpreted as oceanic island basalts oib but our new data suggest that the protolith of some of the blueschists is a calc alkaline igneous rock that formed in an arc environment these blueschists most likely originated from the south ladakh intra oceanic arc this arc was accreted to the southern margin of asia during the late cretaceous and the buried portion was metamorphosed under blueschist facies conditions following oceanic subduction the external part of the arc was obducted to form the south ladakh ophiolites or was incorporated into the sapi shergol me lange zone the incorporation of the south ladakh arc into the accretionary prism implies that the complete closure of the neo tethys likely occurred by eocene time

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

systematics of and postulated controls on submarine hydrothermal solution chemistry the chemical compositions of seafloor hydrothermal solutions from the galapagos spreading center 21 n and 13 n on the east pacific rise the southern juan de fuca ridge and the guaymas basin gulf of california are examined for systematic variations several elemental ratios elemental products and empirical geothermometers show much consistency among the various areas in spite of large absolute differences in elemental concentrations the results suggest that most of the major cations in these solutions are solubility controlled with respect to a similar phase assemblage at all of the sites examination of the solution chemistry in conjunction with experimental results and seafloor rock alteration data permits identification of phases which may be important in controlling the solution chemistry as potassium appears to be solubility controlled its use to calculate water rock ratios is inappropriate lithium appears to be a better element to use in these calculations a model to explain the observed solution chemistries as a result of three component mixing is discussed all of the solutions are postulated to be either the result of mixing between a seawater hydrothermal solution which has not undergone a phase separation and is hence gas containing a gas rich vapor phase and a gas poor brine phase or any one of these individual components alone the vapor and brine phases are the result of phase separation which may have occurred at some time in the past essentially all of the reported data fall within the field defined by these three components the solutions apparently have had sufficient time after the mixing event s to reequilibrate with the rock this is true for quartz as well as other chemical components the best test of this model is chloride together with gas and isotropic data as the model predicts that solutions with elevated chlorinities will be depleted in gases and enriched in 18 o and low chlorinity solutions will have elevated gas contents and lower 18 o

plagioclase and epidote buffering of cation ratios in mid ocean ridge hydrothermal fluids experimental results in and near the supercritical region abstract experiments have been performed with na ca k cl fluids of seawater chlorinity and diabase basalt and plagioclase bearing mineral mixtures at 350 425 c and 250 400 bars to help constrain hydrothermal alteration processes at mid ocean ridges dissolved ca na and ph for all experiments responded systematically to differences in dissolved sio2 concentrations and the compositions of plagioclase reactants diabase alteration at low fluid rock mass ratios 0 5 to 1 produces fluids undersaturated with respect to quartz during hydration of primary olivine and orthopyroxene whereas basalt alteration under similar conditions yields fluids slightly supersaturated with respect to quartz during breakdown of glass to smectite and amphibole fluid chemistry in all experiments appears to approach a partial equilibrium state with the albite and anorthite components in plagioclase and approaches a ph consistent with plagioclase alteration to epidote trace element data from vent fluids specifically b and sr together with major element chemistry ca na sio2 ph provides evidence that the reaction zone for black smoker fluids at mid ocean ridges is composed of only slightly altered diabase and is characterized by small amounts of epidote nearly fresh plagioclase and clinopyroxene and partially to completely hydrated olivine and orthopyroxene fluids reacting with this rock may be undersaturated with respect to quartz so pressure estimates based on the quartz geobarometer should be regarded as minimums using equilibrium between plagioclase the dominant reactant and epidote the dominant reaction product in experiments we estimate that temperatures in reaction zones are in excess of 375 c for most vent systems these temperatures are higher than measured vent temperatures suggesting that hotspring fluids commonly loose heat during ascent to the seafloor

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

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

lithium abundance and isotope systematics of forearc serpentinites conical seamount mariana forearc insights into the mechanics of slab mantle exchange during subduction 1 variable lithium contents and contrasting li isotopic signatures are evident in the serpentininite muds and clasts extruded at conical seamount in the mariana forearc the muds have high li contents compared to mantle values 3 7 ppm and a mean 7li value of 6 the clasts are generally lower in li and 7li varies from 6 to 10 with higher 7li correlating broadly to higher lithium contents the diverse 7li in the serpentinite clasts suggests li exchanges between mantle rocks and evolving slab derived fluids from different depths producing a subarc mantle that is zoned in terms of li abundances and 7li mariana forearc li isotopic signatures reach values as high as those reported in mariana arc lavas but neither mariana lavas nor lavas from other mature arcs show the variability observed in the serpentinites although elevated serpentinite li contents indicate forearc releases of li large differences in 7li are not evident in the slab outputs at forearc versus arc depths in the marianas despite evidence for changes in other alkaline species e g ba sr k it is thus possible that the li sampled by mariana arc volcanoes is in large part li which was released in the forearc and transported in the mantle via convection to arc depths as has been proposed to explain b isotopic variations straub and layne 2002 the uniform 7li signatures observed in mature volcanic arcs tomascak et al 2002 are consistent with higher overall fluxes of slab fluids which generate larger melting anomalies including both modified and nonmodified mantle wedge domains high or low 7li in lavas from anomalous arcs e g panama tomascak et al 2000 may indicate that the volumes of mantle sampled in these magmatic events are smaller and thus more likely to reflect the signatures of hydrated plums e g allegre and turcotte 1986 phipps morgan and morgan 1999 with extremely high or low 7li

trace element partitioning between vapor brine and halite under extreme phase separation conditions abstract experiments were conducted to investigate the partitioning of li br rb cs and b between vapor brine and halite during subcritical and supercritical phase separation in the nacl h2o system 388 550 c 250 350 bars results indicate that li and br partition preferentially into the low salinity vapor fluids while rb and cs become more enriched in the coexisting brines under more extreme conditions of pressure and temperature in the two phase region especially near the vapor brine halite boundary strong salting out effects imposed on neutral aqueous species enhance significantly partitioning of all trace elements into the low salinity fluid dissolved boron is strongly affected by this and a particularly strong enrichment into vapors is observed a trend that can be effectively correlated with changes in reduced density exclusion of li br rb cs and b from halite when precipitated further increases the solubility of these species in the coexisting cl poor fluid in general the lack of distortion in the partitioning behavior of trace elements between vapor brine and or halite with the transition from subcritical to supercritical conditions in the nacl h2o system precludes the need for special reference to the critical point of seawater when interpreting phase relations in submarine hydrothermal systems the combination of experimentally determined trace element partitioning data with constraints imposed by mineral solubility provides a means to better understand the origin and evolution of hot spring vent fluids for example in brandon hydrothermal system 21 s epr supercritical phase separation and subseafloor mixing appear to be the main heat and mass transport mechanisms fueled by a shallow magmatic intrusion with boron systematics ruling out major contributions from magmatic degassing processes accompanying the near seafloor volcanism

structural evolution of the bayanhongor region west central mongolia abstract most of previous models suggest that the central asia orogenic belt grew southward in the phanerozoic however in the bayanhongor region in west central mongolia volcanic arc accretionary prism ophiolite and passive margin complexes accreted northeastward away from the baydrag micro continent and hence the region constitutes the southwestern part of a crustal scale syntaxis close to the west the syntaxis should be original because presumably reorientation due to strike slip faulting can be ignored it is reconfirmed that the baydrag eventually collided with another micro continent the hangai to the northeast a thick sedimentary basin developed along the southern passive margin of the hangai micro continent this region is also characterized by an exhumed metamorphosed accretionary complex and a passive margin complex which are both bounded by detachment faults as well as basal reverse faults which formed simultaneously as extrusion wedges this part of the central asia orogenic belt lacks exhumed crystalline rocks as observed in the himalayas and other major collisional orogenic belts in addition we identified two phases of deformation which occurred at each phase of zonal accretion as d1 through cambrian and devonian and a synchronous phase of final micro continental collision of devonian as d2 the pre collisional ocean was wide enough to be characterized by a mid ocean ridge and ocean islands two different structural trends of d1 and d2 are observed in accretionary complexes formed to the southwest of the late cambrian mid ocean ridge that is the relative plate motions on both sides of the mid ocean ridge were different accretionary complexes and passive margin sediments to the northeast of the mid ocean ridge also experienced two periods of deformation but show the same structural trend unmetamorphosed cover sediments on the accretionary prism and on the hangai micro continent experienced only the d2 event due to micro continental collision these unmetamorphosed sediments form the hanging walls of the detachment faults moreover they were at least partly derived from an active volcanic arc formed at the margin of the baydrag micro continent

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

the southern oscillation part v the anomalies in the lower stratosphere of the northern hemisphere in winter and a comparison with the quasi biennial oscillation abstract the mean anomalies of 50 mb height in the northern winter for seven warm events in the southern oscillation show a weak polar vortex and an enhanced aleutian high in the mean for six cold events the polar vortex is unusually strong and the aleutian high is weakened and displaced far to the southwest these anomalies are consistent with the corresponding anomalies in sea level pressure pattern the warm events of 1963 and 1982 did not fit this pattern as in both years the polar vortex was cold and intense these events happened in years when volcanoes injected large amounts of gases and aerosols into the stratosphere and the temperature of the tropical stratosphere became unusually high in other warm events the temperature of the tropical stratosphere was abnormally low the mean anomalies of the quasi biennial oscillation for the winter as a whole west minus east phase computed from years with no cold or warm events are zonally symmetrical and shaped as four concentric regions with alternatin

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

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

reactivation of a collisional suture by miocene transpressional domes associated with the red river and song chay detachment faults northern vietnam abstract elongate miocene gneissose and granitic domes in northern vietnam formed in a dextral transpressional ductile shear regime possibly associated with large scale restraining step overs along dextral faults initial anticlinal d1 doming involved folding of both basement and hanging wall rocks with d1 secondary folds that verge toward the anticlinal axes such folds reflect dome scale flexural slip folding with continued shortening d2 detachment faults developed on the flanks of the anticlines along the hanging wall basement interface so that the basement was extruded vertically into the overlying hanging wall rocks the detachment faults were associated with d2 drag folds that verge away from the anticlinal axes the hanging wall assemblage lacks a well ordered stratigraphy displaying primarily block in matrix fabric we identified bedded cherts associated with umbers and alkalic basaltic intrusions within these hanging wall rocks a first report of such rocks from vietnam the association of cherts umbers and basaltic intrusions and extrusions with block in matrix units with clastic rocks strongly suggest that the hanging wall rocks comprise part of a subduction complex because the base of a subduction complex is a former subduction megathrust horizon the hanging wall basement interface represents a reactivated collisional suture such a suture was probably associated with the indosinian orogeny and the basement should be the indochina continental block this structure may have influenced the position of miocene dextral faulting in addition to controlling the position of the dome detachments the well known red river fault marks the boundary of one of the domes but in this region it appears to be a detachment normal fault rather than a dextral strike slip fault however the association with the dome evolution with large scale restraining step overs suggests that dextral faulting associated with dome development may lie further away from the dome axes than the detachment

formation of the yakuno ophiolite accretionary subduction under medium pressure type metamorphic conditions abstract the notion that the yakuno ophiolite and overlying maizuru group represents an accretionary prism formed during the permian evolution of japan on the yakuno eruptive sequence association of hemipelagic mudstone with silicic tuff exotic fossiliferous limestones derived from previously accreted sea mounts upward coarsening of sequences terrigenous sandstone and conglomerate and mildly deformed permian and triassic forearc basin formations the most important indicator however is the seaward imbrication and repetition observed in both the maizuru group and the ophiolite itself d1 deformation structures include axial planar foliations pressure solution cleavage for the maizuru group and granulite amphibolite metamorphic layering in the ophiolite flattening type strain symmetric pressure shadows and fringes and isoclinal folds showing axial planar foliations and thrust faulting at their overturned limb the exceptional asymmetry observed indicates seaward directed shearing near the thrust while d1 structures in the maizuru zone are explained by off scraping above the basal decollement the later jurassic d2 kink fold structure includes a first order asymmetric kink with a brittle thrust at its overturned limb more or less coeval with m2 retrograde metamorphism medium pressure m1 prograde metamorphism in the yakuno ophiolite produced layering of granulite and amphibolite and in the maizuru group formation of illite along pressure solution cleavage of mudstones the metamorphic grade is controlled by the stratigraphic relationships and appears typical of that in ocean floor regions however there was only one episode of m1 prograde metamorphism which occurred contemporaneously with d1 off scraping given that subduction zones are normally characterized by high p t metamorphic regimes the observed p t history appears to reflect relatively unusual conditions such high thermal gradients may plausibly reflect the approach of a young hot oceanic plate which continued subducting beneath the japanese arc accordingly the yakuno ophiolite was probably formed at the trench trench ridge triple junction

lithium isotope evidence for light element decoupling in the panama subarc mantle the systematics of fluid mobile trace elements in arc lavas from panama relative to their li isotopic compositions provide unique evidence for the fertilization and subsequent differential extraction of mobile species from the subarc mantle calc alkaline lavas that crystallized between 20 and 5 ma old group that possess 7 li as high as 11 2 have low b be otherwise identical and similarly old calcalkaline lavas with high b be to 23 have mid ocean ridge basalt morb like 7 li 4 7 to 5 6 adakite lavas 3 ma young group possess 7 li from 1 4 to 4 2 and have consistently lower b be than old group lavas consistent with derivation from melting of a devolatilized morb slab if li and b had comparable fluid mobility in the subarc mantle then slab fluids would carry both high b concentrations and elevated 7 li signatures into arc sources and samples with the highest 7 li would also have the highest b be our data suggest that although both li and b are initially derived from the slab older 7 li signatures may be preserved in the mantle beneath arcs as a result regions of the lithospheric mantle will develop li isotope signatures that are heavier than typical morb mantle

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

deep water circulation at the northern pyrenean thrust implication of high temperature water rock interaction process on the mineralization of major spring water in an overthrust area abstract in an overthrust context of the northern pyrenean area groundwater is affected by high mineralization sources a multi isotopic approach was used to track the origin of mineralization in a complex multilayer aquifer system through the study of a major regional spring the oeillal spring water osw which shows a not yet investigated geochemical singularity the aims of this study are to understand the hydrogeochemical evolution and the mineralization mechanisms of groundwater in a large scale aquifer extending over the northern pyrenean overthrust oriental corbieres based on an adequate set of geochemical and isotopic tracers including cosmogenic stable and radiogenic isotopes we have revealed complex hydrogeochemical processes that cannot be tracked with traditional hydrochemical and isotopic tracers the high 87 sr 86 sr ratios of the osw associated with relatively high concentrations in trace elements cs rb sr b li suggest the influence of brine from the triassic deposits containing saliferous clay orsaline fluids from the fractured basement the basement hypothesis may be considered regarding the hydro geochemical fingerprint of the paleozoic basement as demonstrated in previous study and further data would be required to validate the contribution of basement fluids contrasting with marine primary brine and current seawater the relatively high 37 cl 0 22 and 0 39 of osw attests the non marine origin of the chloride ion 36 cl cl shows that the osw is issued from a mixing process between recently recharged water lightly mineralized and significantly marked in 36 cl by the thermonuclear bomb pulse and a saline deep end member at secular equilibrium this indicates that cl in these springs is primarily derived from subsurface non meteoric sources the osw s low br cl molar ratio suggests the influence of simple dissolution of halite and or the contribution of more complex secondary brine the deep saline water may results from meteoric infiltration into the lower jurassic aquifer in contact with triassic deposits or deeper high temperature promotes water rock interaction enhancing leaching of mg k rich saliferous clay this is supported by environmental scanning electron microscopy esem analyses showing that i cl is found in accessory minerals from the kcl mgcl 2 h 2 o system of the triassic deposits and ii cs rb molar ratio is similar to that of osw ranging between 0 13 and 0 7 and from 0 13 to 0 4 respectively laboratory experiments carried out on triassic material show that high temperature water rock interaction is suitable to explain the relatively high 87 sr 86 sr observed in groundwater such process can be investigated to confirm the deep origin of the osw and to explain the signature of deep brines in contact with the triassic deposits under high temperature conditions basement fluid contribution may also be considered regarding the hydro geochemical fingerprint of the paleozoic basement as shown in previous studies further data would be required to validate this hypothesis

on the structure and teleconnections of north atlantic decadal variability abstractdecadal variability in the north atlantic has been associated in the literature with a tripolar pattern of sea surface temperature sst anomalies that show one sign in the western midlatitudinal north atlantic and the opposite in the subpolar and tropical north atlantic the present analysis of observed sst from 1870 to 2009 leads to the dissection of the sst tripole into two components each with a different time scale in the decadal band and different teleconnections in the atlantic basin while the subpolar and tropical poles present quasi decadal variations with a period of about 9 years essentially uncorrelated with other parts of the basin the center of action in the western midlatitudes is characterized by a longer time scale of about 14 years and significant correlations with the tropical south atlantic and the norwegian and north sea s the 9 yr period variations are associated with an atmospheric configuration resembling the east atlantic pattern whereas the 14 yr period fluctuation

block in matrix fabrics that lack shearing but possess composite cleavage planes a sedimentary melange origin for the yuwan accretionary complex in the ryukyu island arc japan while melanges have been taken to be a significant component of accretionary complexes the use of this term has been mostly descriptive given the lack of consensus concerning their genesis however many workers have interpreted asymmetric shear fabrics in melanges as evidence of a tectonic origin i e giving rise to tectonic melanges in contrast to olistostromes which are considered to be purely sedimentary in origin due at least in part to the lack of such shear fabrics it is still uncertain whether accretionary processes include those that involve the intense shearing of oceanic lithologies along with for example the incorporation and entrapment of exotic blocks by muddy matrices during sediment deposition and deformation in axial deep sea trench settings here we argue that the so called block in matrix fabrics that characterize accretionary complexes are primarily sedimentary in origin and are distinct from shear fabrics represented by tectonic melanges we also propose that following their accretion subsequent recycling of such oceanic materials is a common feature within evolving accretionary prisms lastly we draw attention to the observation that d1 pressure solution cleavage planes notably widespread in the lower cretaceous yuwan complex amami oshima island in the ryukyu arc sw japan are absent from the minor asymmetric shear structures that often characterize tectonic melanges in contrast we suggest that the yuwan complex represents the effects of broadly symmetric flattening this scenario is supported by our observation that the number of sedimentary and deformation events differs significantly compared to the single phase of shearing expected in tectonic melanges d minus 1 d 1 pressure solution and axial planar cleavages are only observed in exotic blocks and exhibit older accretionary deformation events within a preexisting accretionary prism of the existing structural associations sd1 is the oldest predating the d 1 sedimentary episode and it represents an oceanic sedimentary phase associated with the formation of a distinct type of block in matrix fabric produced by the accumulation of debris flows at seamount margins sd2 represents a succeeding sedimentary episode characterized by trench axis debris flow including oceanic inclusions derived from collapsed material from an older accretionary prism the resulting sd2 block in matrix fabric is one of the main lithologic components of the amami oshima yuwan complex here the sd2 episode typically includes an igneous fabric consisting of nonexotic intrusive and extrusive basalts within a terrigenous matrix suggesting that the yuwan prism may have also been associated with a trench trench ridge triple junction d1 coaxial deformation is observed to overprint all of the episodes represented although it has not destroyed or significantly sheared their respective fabrics especially in regard to the main sd2 block in matrix structures which are therefore considered to represent original sedimentary structures

using a large ensemble of simulations to assess the northern hemisphere stratospheric dynamical response to tropical volcanic eruptions and its uncertainty the observed strengthening of the northern hemisphere nh polar vortex after tropical volcanic eruptions appears to be underestimated by coupled climate models however there is only a limited number of observed eruptions which makes the attribution of volcanic signals difficult because the polar vortex is also influenced by other external forcing factors as well as internal variability we show with a 100 member ensemble of historical 1850 2005 simulations with the mpi esm lr that an ensemble larger than what is provided by the coupled model intercomparison project phase 5 cmip5 models is needed to detect a statistically significant nh polar vortex strengthening the most robust signal can be found when only the two strongest eruptions krakatau and pinatubo are considered in contrast to including smaller eruptions to increase the sample size for these two strongest eruptions also the mean of 15 cmip5 models shows a statistically significant strengthening of the nh polar vortex

archean oceanic flake tectonics assuming that the archean mantle was hotter and the oceanic crust thicker than at present we estimate that the archean oceanic lithosphere had a sandwich rheology with the lower crust behaving as a soft ductile layer accordingly the archean oceanic lithosphere had a rheological structure similar to present day continental lithosphere but unlike present day oceanic lithosphere the thickness of the ductile layer is a decreasing function of age while its strength is an increasing function of age the buoyancy problem in archean subduction could be overcome by delamination of oceanic upper crust but mass balance calculation indicates that most archean oceanic crust must have been recycled where the right dynamic conditions existed for delamination oceanic flake tectonics may have been an important process leading to the preservation of oceanic upper crust in greenstone belts that are characteristic of archean terrains

volcanic eruptions large scale modes in the northern hemisphere and the el nino southern oscillation abstract the author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large scale variability modes of sea level pressure in the northern hemisphere winter the paper focuses on the arctic oscillation ao and the north atlantic oscillation nao to address the question about the physical nature of these modes the hypothesis that the phase of the el nino southern oscillation enso may control the geographical extent of the dominant mode in the northern hemisphere is also investigated as well as the related possibility that the impact of the eruptions may be different according to the phase of enso the author finds that both the ao and the nao are excited in the first winter after the eruptions with statistical significance at the 95 level both the signal and the significance are larger for the nao than for the ao the excitation of the ao and the nao is connected with the excitation of a secondary mode which resembles an augmented pacific north ame

effect of el nino southern oscillation on the dynamical thermal and chemical structure of the middle atmosphere 1 a simulation of the middle atmosphere is presented using a general circulation model gcm forced with observed sea surface temperature for the period 1950 2000 the gcm extends to the lower thermosphere and reproduces realistic dynamical and temperature distributions the period contains several el nino and la nina events which are identified using the nino3 index composite anomalies of relevant meteorological fields are obtained by stratifying the northern winter season according to the nino3 index these anomalies have the structure of vertically propagating planetary waves extending from the troposphere to the mesosphere circulation anomalies in the middle atmosphere are accompanied by large temperature anomalies that are of opposite sign in the stratosphere and mesosphere the former being warmer and the latter colder during el nino events near the summer mesopause changes in momentum deposition by parameterized gravity waves results in warming during el nino detailed statistical analysis is used to determine the significance of these anomalies a chemical transport simulation is carried out using output from the gcm it shows that when the lower stratosphere is colder as during la nina events some ozone depletion takes place conversely when the lower stratosphere is warmer and more disturbed as is the case during el nino events heterogeneous chemical processes are inhibited

high paleogeothermal gradient with ridge subduction beneath the cretaceous shimanto accretionary prism southwest japan paleotemperature in the jurassic chichibu and the cretaceous shimanto accretionary complexes southwest japan increases southward generally without regard to the early phase geologic structure there is an exceptional peak in the okitsu melange and the thermal structure probably formed after accretion of the complex the estimated geothermal gradient is more than 90 c km in the okitsu melange and more than 50 c km elsewhere in the complex the ophiolitic okitsu melange formed concurrently with eocene subduction of the kula pacific ridge under the cretaceous accretionary prism the previous thermal structure was overprinted by this event

north atlantic oscillation induced changes of the upper layer circulation in the northern north atlantic ocean 1 hydrographic data of the 1990s along world ocean circulation experiment sections a1e greenland ireland and a2 newfoundland france indicate a redistribution of cold low saline subarctic waters and warm saline subtropical waters in the upper layer of the northern north atlantic within about 2 years after the north atlantic oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997 in the latter period subarctic waters spread preferably southward along the continental slope east of newfoundland rather than eastward with the north atlantic current nac into the irminger iceland and west european basins as a consequence the subarctic front and the associated nac shifted eastward in the newfoundland basin where subarctic waters accumulate and westward in the iceland basin where a large warm and saline anomaly was found in 1996 and 1997 indicating a contraction of the subpolar gyre in the irminger basin the anomaly occurred in 1998 and 1999 whereas the cyclonic circulation in the irminger and iceland basins weakened it intensified in the newfoundland basin where a strengthened labrador current retroflection joined the nac this and the increased anticyclonic recirculation of subtropical waters in the newfoundland and west european basins caused a considerable reduction of the northward heat transport across 47 n in the upper layer in 1997 the anticyclonic circulation occurring in the west european basin suggested a northward expansion of the subtropical gyre

lithium isotopic systematics of granites and pegmatites from the black hills south dakota to study li isotopic fractionation during granite differentiation and late stage pegmatite evolution li isotopic compositions and concentrations have been measured for the s type harney peak granite the spatially associated tin mountain pegmatite and possible metasedimentary source rocks in the black hills south dakota the harney peak granite is isotopically heterogeneous with 7 li varying from 3 1 to 6 6 the 7 li values of proterozoic metasedimentary rocks that are possible sources of the harney peak granite range from 3 1 to 2 5 and overlap with post archean shales and the harney peak granite for the granite suite there is no correlation between 7 li and elements indicative of degrees of granite differentiation sio2 li rb etc the li isotopic composition of the harney peak granite therefore appears to res ect the source composition minerals from the zoned tin mountain pegmatite have extremely high li contents and heavier li isotopic compositions than the granite or surrounding black hills metasedimentary rocks the heavier compositions may res ect li isotopic fractionation resulting from extensive crystal melt fractionation lithium concentrations decrease in the order spodumene 3 7 wt muscovite 0 2 to 2 0 wt plagioclase 100 1100 ppm quartz 30 140 ppm plagioclase muscovite and spodumene in all zones display a relatively narrow range in 7 li of 7 9 to 11 4 in contrast quartz is isotopically heavier and more variable 14 7 to 21 3 with 7 li showing an inverse correlation with li concentration this correlation res ects the mixing of isotopically heavy li in quartz and lighter li in s uid inclusions as documented by s uid inclusion compositions

the forced response of the el nino southern oscillation indian monsoon teleconnection in ensembles of earth system models abstractwe study the teleconnection between el nino southern oscillation enso and the indian summer monsoon im in large ensemble simulations the max planck institute earth system model mpi es

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

influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the northern hemisphere winter it has been suggested that the zonal mean stratospheric zonal wind anomalies can propagate downward into the troposphere producing considerable changes on the other hand volcanic aerosols are thought to produce a stronger polar vortex in the winter stratosphere if these suggestions are correct the influence of volcanic eruptions can be expected to produce changes in the northern hemisphere winter troposphere through stratospheric process in the present study this idea is examined by analyzing changes in the january circulation after three recent volcanic eruptions regional features of observed changes in tropospheric temperatures due to volcanic eruptions can be explained by the changes in the propagation of stationary waves associated with dipole type anomalies in the zonal mean zonal winds which are similar to those observed in a previous work on the influence of polar night jet

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

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

spatial variations in vent chemistry at the lucky strike hydrothermal field mid atlantic ridge 37 n updates for subseafloor flow geometry from the newly discovered capelinhos vent

off scraping accretionary process under the subduction of young oceanic crust the shimanto belt of okinawa island ryukyu arc the eocene kayo formation exposed at the southwestern end of the shimanto belt in the ryukyu arc records the progressive development of off scraping accretion accompanied by increase in lithification and burial as well as synaccretionary thermal imprint the formation consists almost wholly of coherent trench turbidites supplied by axial currents detailed structural analysis has revealed that two successive deformation stages are recognized in the formation the early deformation stage 1 occurred by horizontal shortening related to the initial stage of off scraping accretion in this stage sands were water rich and nearly unlithified and the competence contrast between sandstone and shale was low the late deformation stage 2 is marked by the formation of seaward verging imbricate fold and thrust system within the accretionary wedge compared with stage 1 sands in stage 2 were more dewatered and lithified and the competence contrast between sandstone and shale increased in accordance with this deformation history structures caused by high pore fluid pressure indicate increased cohesion of sands during off scraping accretion studies of the vitrinite reflectance and the illite crystallinity clearly suggest that the formation became buried and suffered thermal imprint pressure solution cleavage developed as an axial planar to the stage 2 folds thermal imprint on the formation is characterized by high paleotemperatures at approximately 250 c 300 c in a region of the prehnite pumpellyite facies metamorphism this thermal event took place during and slightly after the stage 2 probably associated with subduction of a young and hot oceanic plate

boron lithium and nitrogen isotope geochemistry of nh4 illite clays in the fossil hydrothermal system of harghita bai east carpathians romania abstract coarse 2 0 0 2 m and fine boron in nh4 i s clays ranges from 513 to 1457 ppm and reached 1000 ppm in the k i nh4 k i the 11b measured in nh4 i s ranges from 12 6 to 22 4 0 3 and in k i nh4 k i is consistently 5 5 to 5 1 0 3 boron isotopes systematically become lighter in the nh4 i s series as temperature increased from 90 to 270 c low li content 1 to 8 ppm was found in illitic clay fractions the 7li shows negative values ranging from 8 6 to 12 3 0 8 for the coarser 2 0 0 2 m nh4 i s clays and from 4 3 to 14 1 1 for the finer the 11b of k i nh4 k i clays reflect a magmatic source whereas the nh4 i s series is consistent with the influx of isotopically light b waters derived from hydrothermal leaching of continental evaporites and or organic rich sediments the 7li signature measured on k i nh4 k i clays also support a magmatic fluid enriched in heavy li followed by precipitation of coarser nh4 i s from more recent sedimentary contributions of isotopically light li this interpretation is also supported by the 15n which reflect an influx of waters from an organic sediment origin the 15n of 14 6 0 6 measured on nh4 i s could be attributed to the presence of meteoric waters mixed with hydrothermal fluids the isotopic data obtained trace the mobility of magmatic and organic sedimentary components in the upper continental crust

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

geochemical mass balance for lithium boron and strontium in the gulf of papua papua new guinea project tropics a mass balance has been calculated for the elements li b and sr in the gulf of papua from sampling undertaken during 1993 to 1999 parameters measured included fly kikori and purari river inputs of dissolved and particulate phases removal flux to sediment traps at the base of the continental shelf slope and century scale accumulation rates in shelf and slope sediments derived from excess 210pb profiles in sediment cores about 91 of river input li was in particulate form and there was conservative behavior of dissolved li in the salinity gradient of the estuaries li accumulation rate in inner shelf sediments was slightly less than river inputs suggesting that more than 90 of li river inputs were trapped in rapid aluminosilicate mud accumulation zones of the inner shelf 50 m depth li removal rate to sediment traps at the base of the slope at 1000 m water depth was an order of magnitude smaller than the inner shelf sedimentation export of li to deep water coral sea was estimated to be 1 2 108 mol yr 1 and this amount is equivalent to the riverine dissolved li annual supply rate about 66 of river input of b was in the particulate phase and low dissolved b concentrations in freshwater were conservatively mixed with higher concentrations of b in seawater across the salinity gradient removal of b to inner shelf sediments was about 83 of the total river input indicating a small export of b 1 2 108 mol yr 1 to the coral sea about half of the dissolved b input from rivers is sorbed to particles and trapped in inner shelf sediments only 24 of river input of sr was in particulate form and low freshwater concentrations of dissolved sr were conservatively mixed with higher concentrations of sr in seawater across the salinity gradient only 20 of total river inputs of sr were buried in shelf sediments and there was a large export 7 3 108 mol yr 1 of sr off the shelf to the coral sea a sediment core from a rapidly accumulating mud deposition zone of the inner shelf shows twofold sympathetic variations in li b and sr ca supply rates over 200 to 1000 yr time intervals

enso response to high latitude volcanic eruptions in the northern hemisphere the role of the initial conditions a large ensemble of earth system model simulations is analyzed to show that high latitude northern hemisphere eruptions give rise to el nino like anomalies in the winter following the eruption the

response of the north atlantic subpolar gyre to persistent north atlantic oscillation like forcing the response of the north atlantic subpolar gyre spg to a persistent positive or negative phase of the north atlantic oscillation nao is investigated using an ocean general circulation model forced with idealized atmospheric reanalysis fields the integrations are analyzed with reference to a base line integration for which the model is forced with idealized fields representing a neutral state of the nao in the positive nao case the results suggest that the well known cooling and strengthening of the spg are after about 10 years replaced by a warming and subsequent weakening of the spg the latter changes are caused by the advection of warm water from the subtropical gyre stg region driven by a spin up of the atlantic meridional overturning circulation amoc and the effect of an anomalous wind stress curl in the northeastern north atlantic which counteracts the local buoyancy forcing of the spg in the negative nao case however the spg response does not involve a sign reversal but rather shows a gradual weakening throughout the integration the asymmetric spg response to the sign of persistent nao like forcing and the different time scales involved demonstrate strong non linearity in the north atlantic ocean circulation response to atmospheric forcing the latter finding indicates that analysis based on the arithmetic difference between the two nao states e g nao minus nao may hide important aspects of the ocean response to atmospheric forcing

bi decadal variability excited in the coupled ocean atmosphere system by strong tropical volcanic eruptions decadal and bi decadal climate responses to tropical strong volcanic eruptions sves are inspected in an ensemble simulation covering the last millennium based on the max planck institute earth system model an unprecedentedly large collection of pre industrial sves up to 45 producing a peak annual average top of atmosphere radiative perturbation larger than 1 5 wm 2 is investigated by composite analysis post eruption oceanic and atmospheric anomalies coherently describe a fluctuation in the coupled ocean atmosphere system with an average length of 20 25 years the study provides a new physically consistent theoretical framework to interpret decadal northern hemisphere nh regional winter climates variability during the last millennium the fluctuation particularly involves interactions between the atlantic meridional overturning circulation and the north atlantic gyre circulation closely linked to the state of the winter north atlantic oscillation it is characterized by major distinctive details among them the most prominent are a a strong signal amplification in the arctic region which allows for a sustained strengthened teleconnection between the north pacific and the north atlantic during the first post eruption decade and which entails important implications from oceanic heat transport and from post eruption sea ice dynamics and b an anomalous surface winter warming emerging over the scandinavian western russian region around 10 12 years after a major eruption the simulated long term climate response to sves depends to some extent on background conditions consequently ensemble simulations spanning different phases of background multidecadal and longer climate variability are necessary to constrain the range of possible post eruption decadal evolution of nh regional winter climates