the 2009 2010 eruption of gaua volcano vanuatu archipelago eruptive dynamics and unsuspected strong halogens source gaua a little known volcano in the northern part of vanuatu archipelago went through a long term eruptive activity between september 2009 and july 2010 the eruption started by a phreatic to phreatomagmatic activity which progressively shifted into a magmatic discharge the first eruptive phase involved the hydrothermal system in place the latter was likely influenced by seawater seepage leading to the formation of anhydrite magma involved hereafter this opening phase is of basaltic andesite and basaltic trachyandesite composition high k calc alkaline series typical of the northern part of the vanuatu archipelago the 2009 2010 activity discharged at least 184 kt of so2 and a significant amount of halogens 72 kt cl and 217 kt f such halogen releases indicate that gaua is a strong source of halogens into the atmosphere high and sustained amount of f discharges are known to induce health issues and should not be ignored on gaua island during this eruption the quiescent and voluminous lake letas was slightly affected by the eruption nevertheless the hydrothermal discharge point into the lake situated on the southeastern part of mt garet appeared to be relatively active at this particular location rock forming elements leached out from volcanic rock by acid fluids released by the new intrusion of magma were discharged along with anions into lake letas this release has triggered localized chemistry changes in the lake we speculate that this discharge has also disturbed the bottom water in a limited perimeter remobilizing reduced fe to the surface and subsequently triggering the change in the water color by fe oxidation

magmatic anhydrite in plutonic rocks at the el teniente cu mo deposit chile and the role of sulfur and copper rich magmas in its formation anhydrite occurs along with biotite feldspars quartz fe oxides and sulfides in fine grained igneous rocks that form the small porphyry a stock at el teniente these minerals crystallized together in the space generated by the intrusion of this stock and they do not replace preexisting phases planar crystal boundaries between anhydrite and other phases as well as the fact that plagioclase and biotite are fresh and unaltered also suggest that anhydrite is an igneous phase and not the product of secondary hydrothermal alteration plagioclase is unusually na rich ranging from oligoclase in mafic varieties of these rocks with 20 percent biotite to albite in more felsic samples with 20 percent these unusual anhydrite bearing plutonic rocks which contain up to 3 wt percent s and 0 5 wt percent cu are isotopically similar to all other igneous rocks related to the deposit these rocks formed during a late miocene period of regional compressive deformation with no coeval volcanic activity in the area of the deposit which prevented devolitalization of the oxidized parent magma in the large productive magma chamber inferred to have underlain el teniente at 4 km below the paleosurface this allowed igneous fractionation involving the recharge of mantle derived mafic magmas into the base of the chamber as well as volatile transfer and concentration near its roof to produce the cu and s rich magmas that formed the anhydrite bearing intrusive rocks

high temperature hydrothermal activities around suboceanic moho an example from diopsidite and anorthosite in wadi fizh oman ophiolite abstract reaction products between hydrothermal fluids and uppermost mantle harzburgite lowermost crustal gabbro have been reported along wadi fizh northern oman ophiolite they are named mantle diopsidite md or crustal diopsidite cd depending on the stratigraphic level they construct network like dikes crosscutting structures of the surrounding harzburgite or gabbro the md is mainly composed of diopsidic clinopyroxene whereas the cd is of diopsidic clinopyroxene and anorthitic plagioclase here we report a new reaction product crustal anorthosite ca from the lowermost crustal section the ca is always placed in the center of the cd network and mainly consists of anorthitic plagioclase with minor titanite and chromian minerals such as chromite and uvarovite aqueous fluid inclusions forming negative crystals are evenly distributed in minerals of the ca the fluid inclusions contain angular shaped or rounded daughter minerals as calcite or calcite anhydrite composite which were identified by raman spectroscopic analysis we estimated their captured temperature at 530 c at least by conducting microthermometric analysis of the fluid inclusions furthermore we examined their chemical characteristics by direct laser shot sampling conducted by laser ablation inductively coupled plasma mass spectrometer la icp ms the results indicate that the trapped aqueous fluids contain an appreciable amount of na but no k and cr hydrothermal fluids involved in the ca formation transported cr which was probably taken up from chromite seams in the uppermost mantle section cr got soluble by forming complexes with anions as so 4 2 co 3 2 and cl in addition these hydrothermal fluids transported fe mg and trace elements ti sr y zr and rare earth elements governing whole rock chemical compositions of the mds cds and cas our estimation for the condition of ca formation yielded rather low temperatures 530 600 c which indicates a later stage production of the ca than the md and cd 800 c a series of high temperature hydrothermal events had been significantly contributed to the chemical flux occurring around the moho boundary between the mantle and crustal sections

redox effects on calcite portlandite fluid equilibria at forearc conditions carbon mobility methanogenesis and reduction melting of calcite 2014 by walter de gruyter berlin boston oxygen fugacity fo2 is a fundamental parameter that controls carbon mobility in aqueous fluids in geological environments such as subduction zones where reduced serpentinite fluids have the potential to infiltrate oxidized carbonate bearing lithologies using experiments and calculations we describe how mineral fluid equilibria evolve as fo2decreases in the model ca c o h system at forearc conditions 300 700 c and 2 10 kbar experimental calcite solubility was constant at fo2values from quartz fayalite magnetite qfm to hematite magnetite hm at lower fo2values of iron magnetite im or wustite magnetite wm calcite reacted with h2to form methane plus portlandite or melt these results were consistent with thermodynamic calculations and indicate that carbon mobility as parameterized by total aqueous carbon ctot is strongly dependent on fo2 at constant pressure and temperature carbon mobility is minimized at oxidizing conditions where ctot is controlled by calcite solubility carbon mobility is maximized at the most reducing conditions because all the carbon in the system is present as ch4 an intermediate region of carbon mobility exists in which calcite is stable with a ch4 bearing fluid as pressure increases from 2 to 10 kbar the fo2range over which calcite is stable with a methane rich fluid shifts to more reducing conditions the variety of geological conditions with the potential for redox enhancement of carbon mobility becomes more restricted with depth reduction melting was observed at 700 c and 6 kbar and at 650 c and 10 kbar due to the partial reaction of calcite to portlandite at conditions above the hydrous melting curve of calcite portlandite although likely metastable in the present experiments reduction melting may occur in nature whenever h2partially reduces carbonate minerals at pressures and temperatures above the hydrous melting curve of calcite portlandite whether it causes melting or not calcite reduction is likely an important mechanism for abiotic methanogenesis in natural systems such as subduction zone forearcs or similar environments with the potential for interaction of reduced fluids with carbonate minerals because calcite solubility at oxidized conditions is already known to increase substantially with pressure the additional increase in carbon mobility provided by calcite reduction implies that subduction zones may host some of the most carbon rich aqueous fluids on earth

peak last glacial weathering intensity on the north american continent recorded by the authigenic hf isotope composition of north atlantic deep sea sediments we have retrieved radiogenic hafnium hf isotope compositions hf from authigenic fe mn oxyhydroxides of deep northwest atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from ne america during the last deglaciation the extraction of seawater derived hf isotopic compositions from fe mn oxyhydroxides is not a standard procedure comparisons between the al hf ratios and hf isotopic compositions of the chemically extracted authigenic phase on the one hand and those of the corresponding detrital fractions on the other provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures this is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper blake ridge for which consistent replicates were produced throughout the hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central north atlantic seawater comparison with previously published seawater nd and pb isotope compositions obtained on the same cores shows that both hf and pb were released incongruently during incipient chemical weathering but responded differently to the deglacial retreat of the laurentide ice sheet hafnium was released more congruently during peak glacial conditions of the last glacial maximum lgm and changed to typical incongruent interglacial hf signatures either during or shortly after the lgm this indicates that some zircon derived hf was released to seawater during the lgm conversely there is no clear evidence for an increase in the influence of weathering of lu rich mineral phases during deglaciation possibly since relatively unradiogenic hf contributions from feldspar weathering were superimposed while the authigenic pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental north america during the transition to the holocene a similar incongruent excursion is notably absent in the hf isotope record the early change towards more radiogenic hf in relation to the lgm may provide direct evidence for the transition from a cold based to a warm based laurentide ice sheet on the atlantic sector of north america

radiogenic nd isotope labeling of the northern ne atlantic during mis 2 paleoceanographic reconstructions rely on chemical proxies which are controlled by physical chemical and biological marine parameters the accurate interpretation of proxy records relies on the integrity of proxy environmental relationships through time and under changing conditions in this study we closely examine paleo controls on authigenic nd isotope records from five cores in the northern ne atlantic approximating a depth transect allowing spatial and temporal relationships to be reconstructed we compare our nd isotope records with other paleocirculation proxies and consider the sedimentalogical controls on nd isotope signals by comparing ice rafted detritus lithology and counts detrital sediment chemistry and redox sensitive element concentrations measured on foraminifera authigenic coatings with this suite of geochemical and sedimentalogical data we show that nd isotope records in the northern ne atlantic were labeled by radiogenic sediments however this modification did not occur in the pore waters of each core but instead likely reflects changes in the nd isotopic composition of deep waters caused by the input of ice rafted sediment during heinrich events and the last glacial maximum this study has implications for understanding how localized changes in the nd isotope signal can set a watermass end member composition decoupling chemical proxy circulation relationships locally but providing a signal which can be potentially traced along the deep water flowpath such scenarios must be considered in future interpretations of glacial nd isotope records taken from within the ice rafted detritus belt and downstream along watermass flowpaths

compositions of biotite amphibole apatite and silicate melt inclusions from the tongchang mine dexing porphyry deposit se china implications for the behavior of halogens in mineralized porphyry systems abstract the dexing deposit located in the circum pacific ore belt is the largest porphyry copper deposit in eastern china it is composed of 3 separate plutons which host three mines tongchang fujiawu and zhushahong mines the porphyritic granodiorite samples studied in this investigation were collected from the tongchang ore forming pluton of this giant deposit this paper presents electron microprobe analyses of biotite apatite amphibole plagioclase potassium feldspar and rehomogenized glassy melt inclusions from the tongchang porphyritic granodiorites petrographic observations of the samples are consistent with portions of the granodioritic magma represented by our samples being overprinted by potassic hydrothermal fluid which variably altered these minerals all of the studied micas are mg rich biotites the biotites are separated into altered magmatic and secondary types based on their petrographic and geochemical characteristics the phlogopite components of the secondary biotites are typically higher than those of the altered magmatic biotites and the x mg values of all biotites correlate negatively with cl contents consistent with the mg cl avoidance principle the x mg values also correlate negatively with k 2 o na 2 o bao feo and tio 2 for both generations of biotites the calculated log f h 2 o f hcl values for 690 k of the coexisting potassic fluids which are determined from the altered magmatic biotite compositions range from 4 43 to 4 67 and are very similar to those of other major porphyry deposits however the log f h 2 o f hf and log f hf f hcl values for the same batch of hydrothermal fluids are significant higher and lower than those of these other porphyry deposits respectively the cl concentrations of amphiboles and melt inclusions range from 0 18 to 0 32 wt and 0 15 to 0 44 wt respectively most apatites trapped in biotite and plagioclase phenocrysts display a bimodal cl distribution 0 19 to 1 35 wt and 1 48 to 3 73 wt similarly the s contents of the apatite also show a distinct bimodal distribution reflecting the effects of variable anhydrite saturation during evolution of the tongchang melt and variable dissolution of anhydrite by saline aqueous fluids the cl contents of the apatites from the tongchang system are typically higher than those of other studied porphyry deposits furthermore the cl contents of the melt inclusions are at or very near the cl saturation levels 0 36 to 0 46 wt at 850 c and 50 mpa and 0 42 to 0 54 wt at 850 c and 200 mpa for these melt compositions at shallow crustal pressures these findings suggest that the area of the granodioritic magma represented by our samples and perhaps the bulk of the tongchang granodioritic magma was rich in cl the melt inclusion compositions are consistent with a high salinity hydrosaline liquid being exsolved directly from the granodioritic melt directly this high salinity hydrosaline liquid was likely very efficient at dissolving transporting and precipitating ore metals in the mineralizing magmatic hydrothermal system

oxide and sulphide minerals in highly oxidized rb depleted archaean granulites of the shevaroy hills massif south india oxidation states and the role of metamorphic fluids the shevaroy hills of northern tamil nadu southern india expose the highest grade granulites of a prograde amphibolite facies to granulite facies deep crustal section of late archaean age these highly oxidized quartzofeldspathic garnet charnockites generally show minor high tio2 biotite and amphibole as the only hydrous minerals and are greatly depleted in the incompatible elements rb and th peak metamorphic temperatures garnet orthopyroxene and pressures garnet orthopyroxene plagioclase quartz are near 750 degrees c and 8 kbar respectively pervasive veinlets of k feldspar exist throughout dominant plagioclase in each sample and show clean contact with orthopyroxene they are suggested to have been produced by a low h2o activity migrating fluid phase under granulite facies conditions most likely a concentrated chloride carbonate brine with high alkali mobility accompanied by an immiscible co2 rich fluid silicate oxide and sulphide mineral assemblages record high oxygen fugacity pyroxenes in the felsic rocks have high mg mg fe 0 5 0 7 the major oxide mineral is ilmenite with up to 60 mole per cent exsolved hematite utilizing three independent oxygen barometers ferrosilite magnetite quartz ferrosilite hematite quartz and magnetite hematite in conjunction with garnet orthopyroxene exchange temperatures samples with x hm ilm 0 1 yield a consistent oxygen fugacity about two log units above fayalite stability less oxidized samples x hm ilm 0 4 pyrite is the dominant sulphide and pyrrhotite is absent pyrite grains in these samples have marginal alteration to magnetite along the rims signifying a high temperature oxidation event moderately oxidized samples 0 1 x hm ilm 0 4 have abundant co existing pyrrhotite pyrite and magnetite the most reduced granulite samples have pyrrhotite as the dominant sulphide with little or no pyrite and no coexisting magnetite chalcopyrite is a common accessory mineral of pyrite and pyrrhotite in all the samples textures in some samples suggest that it formed as an exsolution product from pyrrhotite extensive vein networks of magnetite and pyrite associated principally with the pyroxene and amphibole give evidence for a pervasive highly oxidizing fluid phase thermodynamic analysis of the assemblage pyrrhotite pyrite and magnetite yields consistent high oxidation states at 700 800 degrees c and 8 kbar the oxygen fugacity in our most oxidized pyrrhotite bearing sample is 10 12 65 bar at 770 degrees c there are strong indications that the shevaroy hills granulites recrystallized in the presence of an alkali rich low h2o activity fluid probably a concentrated brine it cannot be demonstrated at present whether the high oxidation states were set by initially oxidized protoliths or effected by the postulated fluids the high correspondence of maximally rb depleted samples with the highest recorded oxidation states suggests that the rb depletion event coincided with the oxidation event probably during breakdown of biotite to orthopyroxene k feldspar we speculate that these alterations were effected by exhalations from deep seated alkali basalts which provided both heat and high oxygen fugacity low a h2o fluids it will be of interest to determine whether greatly rb depleted granulites in other precambrian terranes show similar highly oxidizing signatures

isotopic and geochemical evidence for crust mantle interaction during late archaean crustal growth abstract the charnockites and enderbites of the north marginal zone of the limpopo belt in southern zimbabwe represent a suite of dry magmas of tonalite trondhjemite granodiorite ttg affinity which crystallised directly in the lower crust they were emplaced between 2 6 and 2 7 ga and were derived from a source which showed remarkable lead isotope homogeneity unlike many other lower crustal rocks they have low k rb and low k u ratios and have not experienced depletion of their heat producing elements th u k and rb and thus represent an unusual suite of granulites in this study we have combined the constraints of trace element and isotope geochemistry to characterise the nature of the protolith to the nmz enderbites and charnockites we use a combination of high values calculated lead and strontium isotope initial ratios and old nd model ages to show that the enderbites and chamockites were derived from a protolith which was in part formed more than 500 ma before magma genesis we argue from the very high values that this protolith constituted two separate components an old high low sm nd crustal component and a younger low high sm nd mantle derived component both of which were homogenised by extensive mixing prior to 2 7 ga the presence of an older crustal component contrasts with other archaean ttg suites worldwide which show little evidence for a crustal prehistory the process of mantle crust interaction during late archaean crustal growth in southern zimbabwe invites comparison with modern convergent margins such as the andes

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

south pacific dissolved nd isotope compositions and rare earth element distributions water mass mixing versus biogeochemical cycling despite its enormous extent and importance for global climate the south pacific has been poorly investigated in comparison to other regions with respect to chemical oceanography here we present the first detailed analysis of dissolved radiogenic nd isotopes end and rare earth elements rees in intermediate and deep waters of the mid latitude 40 s south pacific along a meridional transect between south america and new zealand the goal of our study is to gain better insight into the distribution and mixing of water masses in the south pacific and to evaluate the validity of nd isotopes as a water mass tracer in this remote region of the ocean the results demonstrate that biogeochemical cycling scavenging processes in the eastern equatorial pacific and release of lrees from the sediment clearly influence the distribution of the dissolved ree concentrations at certain locations nevertheless the nd isotope signatures clearly trace water masses including aaiw antarctic intermediate water average end 8 2 0 3 lcdw lower circumpolar deep water average end 8 3 0 3 npdw north pacific deep water average end 5 9 0 3 and the remnants of nadw north atlantic deep water average end 9 7 0 3 filtered water samples taken from the sediment water interface under the deep western boundary current off new zealand suggest that boundary exchange processes are limited at this location and highlight the spatial and temporal variability of this process these data will serve as a basis for the paleoceanographic application of nd isotopes in the south pacific

sedimentary fe mn oxyhydroxides as paleoceanographic archives and the role of aeolian flux in regulating oceanic dissolved ree in the marine environment authigenic ferromanganese fe mn oxides precipitate from seawater incorporating many dissolved trace elements such as nd pb whose isotopic composition is a direct proxy for ambient seawater thus isotopic studies of the fe mn oxyhydroxide component leached from sedimentary records can provide information on changes in erosional input or ocean circulation changes such studies may be complicated however by the presence of detrital material containing a fe mn oxide component which may mask the true seawater signal in addition the formation of fe mn oxyhydroxides in the marine environment remains poorly understood in particular the phase carbonates detrital particles that controls the delivery of authigenic fe mn oxides to the sediments has not yet been determined in this study we have analysed the ree and nd isotopic compositions of fe mn oxyhydroxide fractions dispersed in marine sediment cores from the cape and angola basins in the se atlantic cruise images ii for the angola basin deep sea core located at 1000 km south of the congo river mouth both the ree and nd isotopic compositions nd measured in recent fe mn oxyhydroxide fractions are typical of congo river borne fe mn oxides this shows that preformed fe mn oxides associated with detrital fractions can locally contaminate the seawater signal recorded by authigenic oxyhydroxides by contrast examination of ree distributions nd isotope data and mass accumulation rates in cape basin sediments shows paradoxically that the flux of fe mn oxides to sediments is controlled by aeolian particles from the nearby namib desert even though their ree and nd compositions point clearly to an authigenic origin it is proposed that partial dissolution of aeolian dust occurs in the water column releasing into solution its easily leachable fe mn component the dissolved fe2 and mn2 would then fuel the reprecipitation of authigenic fe mn oxyhydroxides scavenging additional dissolved trace elements from the ocean most probably from deep water masses in this case calculations suggest that aeolian deposition acts as a net sink for dissolved nd in the cape basin rather than a source and allows us to estimate the rate of removal of dissolved nd associated with atmospheric deposition yielding a global oceanic residence time for nd nd of between 500 and 1400 years

the nature of orthomagmatic hydrothermal fluids in the oka carbonatite quebec canada evidence from fluid inclusions fluid inclusions in apatite monticellite and calcite from the oka carbonatite complex generally comprise either aqueous liquid vapour or aqueous liquid vapour halite some inclusions also contain a variety of trapped solids including calcite strontianite nahcolite and mirabilite microthermometry and raman spectroscopy indicate that co2 is not an important constituent of these fluids microthermometric data also indicate that the hydrothermal fluids liberated from the carbonatitic magma had a wide range of salinities 4 2 to 49 eq wt nacl and densities 0 77 to 1 26 g cm3 most of the fluids had relatively low concentrations of so42 and co32 6 wt however the nature of the trapped minerals and the phase behaviour of some inclusions indicate that some fluids may have had higher concentrations of so42 co32 and or hco3 textural relationships indicate that the crystallization sequence for the host minerals was monticellite apatite calcite which when combined with fluid inclusion data from the three minerals indicates that fluid salinity decreased and fluid density increased during progressive crystallization of the magma the density increase is thought to have been mainly caused by decreasing temperature isochoric projections indicate that the fluids were exsolved at minimum pressures of 4 to 8 kb these data provide a basis with which to assess the involvement of orthomagmatic aqueous fluids in the formation of hydrothermal rare element mineralization associated with carbonatites

oxide and sulphide isograds along a late archean deep crustal profile in tamil nadu south india oxide sulphide fe mg silicate and titanite ilmenite textures as well as their mineral compositions have been studied in felsic and intermediate orthogneisses across an amphibolite north to granulite facies south traverse of lower archean crust tamil nadu south india titanite is limited to the amphibolite facies terrane where it rims ilmenite or occurs as independent grains pyrite is widespread throughout the traverse increasing in abundance with increasing metamorphic grade pyrrhotite is confined to the high grade granulites ilmenite is widespread throughout the traverse increasing in abundance with increasing metamorphic grade and occurring primarily as hemo ilmenite in the high grade granulite facies rocks magnetite is widespread throughout the traverse and is commonly associated with ilmenite it decreases in abundance with increasing metamorphic grade in the granulite facies zone reaction rims of magnetite quartz occur along fe mg silicate grain boundaries magnetite also commonly rims or is associated with pyrite both types of reaction rims represent an oxidation effect resulting from the partial subsolidus reduction of the hematite component in ilmenite to magnetite this is confirmed by the presence of composite three oxide grains consisting of hematite magnetite and ilmenite magnetite and magnetite pyrite micro veins along silicate grain boundaries formed over a wide range of post peak metamorphic temperatures and pressures ranging from high grade so2 to low grade h2s dominated conditions oxygen fugacities estimated from the orthopyroxene magnetite quartz orthopyroxene hematite quartz and magnetite hematite buffers average 2 5 log units above qfm it is proposed that the trends in mineral assemblages textures and composition are the result of an external infiltrating concentrated brine containing an oxidizing component such as caso4 during high grade metamorphism later acted upon by prograde and retrograde mineral reactions that do not involve an externally derived fluid phase

neodymium associated with foraminiferal carbonate as a recorder of seawater isotopic signatures neodymium isotopic ratios in marine environments have been used as a tracer of water masses and exchange processes between dissolved and particulate phases the interest in this tracer has been growing with improvement of our knowledge on its chemical behaviour in the modern ocean and the identification of sedimentary phases that preserve past seawater epsilon nd values in the last few decades the nd isotopic composition measured on fe mn crusts sediment leachates bulk carbonate fraction corals and fish teeth have been increasingly interpreted in the context of understanding the role of the ocean in paleoclimate changes in particular calcareous foraminiferal tests shells have acquired increasing attention as an archive of seawater nd isotopic signatures because it allows continuous high resolution records to be measured and directly compared to other proxies including stable isotopes and trace metals the main challenge of interpreting the nd isotopic composition of foraminifera is determining the origin of the nd preserved within them in this review we present an overview of methodological progress including that of bulk foraminifera and microanalyses within foraminiferal tests as well as geochemical meaning of extracted nd concentrations and isotopic compositions the growing body of evidence suggests that nd isotopic signatures of sedimentary planktonic foraminifera correspond to bottom water values rather than surface water ones the nd rich phases associated with sedimentary foraminifera are adhesive nano scale particles of mn and fe oxides and hydroxides and mn rich carbonates formed within layers of foraminiferal calcite mechanical cleaning to remove clay minerals is likely to be sufficient in most cases to reconstruct past bottom water circulations unresolved issues include the potential influence of pore water nd on epsilon nd values extracted from sedimentary foraminiferal tests under different sedimentalogical and oceanographic conditions c 2013 elsevier ltd all rights reserved

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

microscale neodymium distribution in sedimentary planktonic foraminiferal tests and associated mineral phases neodymium isotopic ratios recorded in calcareous foraminiferal tests shells and associated authigenic minerals were used to trace past water masses although the origin of preserved nd signals is still a matter of debate we determined for the first time the microscale nd distribution in two planktonic foraminifera species globigerinoides ruber and neogloboquadrina dutertrei and coexisting authigenic minerals from two selected time slices 15 6 and 129 kyr of a marine sediment core in the panama basin elemental mapping of nd ca fe mn and si was performed using nanosims ion probe and electron probe microanalysis epma on uncleaned tests together with scanning electron microscopy sem imagery epma and sem images revealed the presence of fe rich framboidal minerals inside test pores and inner chambers particularly in the old samples the young sample presented fe and mn rich patches on the inner test wall the nd intensity in fe mn rich patches and in some framboids was much higher than in foraminiferal calcite where the nd distribution was randomly heterogeneous with no systematic features such as an ontogenic nd rich layer or species specific differences the relationship between nd fe and mn confirmed a significant role of fe mn oxides as a nd carrier the high nd enrichment in some framboids could be explained by nd adsorption onto oxidized surface of fe sulfides particles rather than direct incorporation since the authigenic precipitates are major nd carrier phases the nd isotopic signals in sedimentary foraminiferal tests likely reflect bottom pore water values rather than surface water ones

weathering versus circulation controlled changes in radiogenic isotope tracer composition of the labrador sea and north atlantic deep water geological reconstructions and general circulation models suggest that the onset of both northern hemisphere glaciation 2 7 myr ago and convection of labrador sea water lsw were caused by the closure of the panama gateway 4 5 myr ago time series data that have been obtained from studies of ferromanganese crusts from the northwestern atlantic suggest that radiogenic isotopes of intermediate ocean residence time pb and nd can serve as suitable tracers to reconstruct these events however it has been unclear until now as to whether the changes that have been observed in isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering in this paper we adopt a box model approach to demonstrate that the shifts in radiogenic isotope compositions are unlikely to be due to changes in convection in lsw but can be explained in terms of increases of erosion levels due to the glaciation of greenland and canada furthermore we provide experimental evidence for the incongruent release of a labile fraction of strongly radiogenic pb and nonradiogenic nd from continental detritus eroding into the labrador sea this can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in radiogenic pb should provide such a rich supply of radiogenic pb to the oceans an important general conclusion is that the compositions of radiogenic isotopes in seawater are not always a reflection of their continental sources perhaps more importantly the transition from chemical weathering to mechanical erosion is likely to result in significant variations in radiogenic tracers in seawater

trace element rich brines in eclogitic veins implications for fluid composition and transport during subduction primary and pseudosecondary fluid inclusions occur in oscillatory and sector zoned omphacite in eclogitic veins from the monviso ophiolitic complex in the western alps the inclusions contain aqueous brines and daughter crystals of halite sylvite calcite dolomite albite anhydrite and or gypsum barite baddeleyite rutile sphene fe oxides pyrite and monazite this daughter mineral suite indicates high solubilites of na k ca mg fe zr ti p ba ce la th and s species and provides direct evidence for transport of high fieldstrenght large ion lithophile and light rare earth elements as dissolved species during subduction fluid inclusion heterogeneities preserved within and between adjacent grains in the veins however suggest that the scale of fluid equilibration was small a crack seal geometry in some of the veins implies that fluid release in pulses rather than steady flow controlled mineral deposition and growth in the veins from these observations we develop a model of fluid release and entrapment in which pulses of fluid are associated in time with increments of shear and tensile failure the rate of fluid release and the reduction in porosity both depend on the rate of plastic flow vein fluids may initially be derived from decreptitation of early fluid inclusions in the host eclogites small scale fluid heterogeneities implied by the fluid inclusions in the veins are best interpreted in terms of limited fluid flow and hence limited metasomatism we conclude that element recycling into the mantle wedge during subduction will depend at least as strongly on fluid transport mechanisms as on element solubilities in the fluid phase at monviso despite evidence for high trace element solubilities in saline brines the elements were not removed from the downgoing slab prior to teaching depths of 40 km

rare earth element distribution in 400 c hot hydrothermal fluids from 5 s mar the role of anhydrite in controlling highly variable distribution patterns abstract two submarine hydrothermal vent fields at 5 s mid atlantic ridge mar turtle pits and comfortless cove emanate vapor phase fluids at conditions close to the critical point of seawater 407 c 298 bars in this study the concentration and distribution of rare earth element ree and yttrium y has been investigated independent of the major element composition the fluids display a strong temporal variability of their ree y concentrations and relative distributions at different time scales of minutes to years chondrite normalized distributions range from common fluid patterns with light ree enrichment relative to the heavy ree accompanied by positive eu anomalies type i to strongly ree y enriched patterns with a concave downward distribution with a maximum enrichment of sm and weakly positive or even negative eu anomalies type ii the larger the sum of ree the smaller cecn ybcn and eu eu we also observed a strong variability in fluid flow and changing fluid temperatures correlating with the compositional variability as evident by the positive correlation of total ree ca and sr concentrations in turtle pits and comfortless cove fluids precipitation dissolution of hydrothermal anhydrite controls the variability in ree concentrations and distributions in these fluids and the transformation of one fluid type to the other the variable distribution of ree can be explained by the accumulation of particulate anhydrite with concave downward ree distribution and negative eu anomaly into a fluid with common ree distribution type i followed by the modification of the ree fluid signature due to dissolution of incorporated anhydrite a second model in which the type ii fluids represent a primary ree reaction zone fluid pattern which is variably modified by precipitation of anhydrite can also explain the observed correlations of total ree fractionation of lree hree and size of eu anomaly as well as ca sr the emanation of such a fluid may be favored in a young hydrothermal system in its high activity phase with short migration paths and limited exchange with secondary minerals however this model is not as well constrained as the other and requires further investigations the strongly variable ree fluid signature is restricted to the very hot actively phase separating hydrothermal systems turtle pits and comfortless cove at 5 s and has not been observed at the neighboring red lion vent field which continuously emanates 350 c hot fluid and displays a stable ree distribution type i

testing the extraction of past seawater nd isotopic composition from north atlantic deep sea sediments and foraminifera neodymium isotopes provide a paleoceanographic proxy for past deep water circulation and local weathering changes and have been measured on various authigenic marine sediment components including fish teeth ferromanganese oxides extracted by acid reductive leaching cleaned foraminifera and foraminifera with fe mn oxide coatings here we compare nd isotopic measurements obtained from ferromanganese oxides leached from bulk sediments and planktonic foraminifera as well as from oxidatively reductively cleaned foraminiferal shells from sediment cores in the north atlantic sedimentary volcanic ash contributes a significant fraction of the nd when the ferro manganese fe mn oxide coatings are leached from bulk sediments reductive leachates of marine sediments from north atlantic core tops near iceland or directly downstream from iceland scotland overflow waters record nd values that are significantly higher than seawater indicating that volcanic material is easily leached by acid reductive methods the nd values from sites more distal to iceland are similar to modern seawater values showing little contamination from iceland derived volcanogenic material in all comparisons core top planktonic foraminifera nd values more closely approximate modern deep seawater than the bulk sediment reductive leached value suggesting that the foraminifera provide a route toward quantifying the nd isotopic signature of deep north atlantic water masses

a 750 kyr detrital layer stratigraphy for the north atlantic iodp sites u1302 u1303 orphan knoll labrador sea abstract integrated ocean drilling program iodp sites u1302 u1303 drilled on the se flank of orphan knoll labrador sea preserve a record of detrital layers and other proxies of hydrographic change that extend the record of ice sheet ocean interactions through most of the brunhes chron the age model is built by tandem matching of relative paleointensity rpi and oxygen isotope data 18o from neogloboquadrina pachyderma sin to reference records indicating a mean brunhes sedimentation rate of 14 cm kyr sedimentation back to marine isotope stage mis 18 is characterized by detrital layers that are detected by higher than background gamma ray attenuation gra density peaks in x ray fluorescence xrf indicators for detrital carbonate ca sr and detrital silicate si sr and an ice rafted debris ird proxy wt 106 m the age model enables correlation of site u1302 03 to iodp site u1308 in the heart of the central atlantic ird belt where an age model and a similar set of detrital layer proxies have already been derived ages of heinrich h layers h1 h2 h4 h5 and h6 are within 2 kyr at the two sites h0 h3 and h5a are not observed at site u1308 and agree with previous work at orphan knoll within 3 kyr at site u1308 brunhes detrital layers are restricted to peak glacials and glacial terminations back to marine isotope stage mis 16 and have near synchronous analogs at site u1302 03 detrital layers at site u1302 03 are distributed throughout the record in both glacial and most interglacial stages we distinguish heinrich like layers associated with ird from detrital layers marked by multiple detrital layer proxies including ca sr but usually not associated with ird that may be attributed to lofted sediment derived from drainage and debris flow events funneled down the nearby northwest atlantic mid ocean channel namoc the prominent detrital layers at sites u1302 03 and u1308 can be correlated to millennial scale features in the chinese speleothem monsoon record over the last 400 kyr implying a link between monsoon precipitation and laurentide ice sheet lis instability the detrital layer stratigraphy at site u1302 03 provides a long record of lis dynamics against which other terrestrial and marine records can be compared

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials

neodymium isotopes in planktonic foraminifera a record of the response of continental weathering and ocean circulation rates to climate change the neodymium nd isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka here we present the first nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative reductive techniques the data along with mn ca ratios suggest that cleaned foraminifera provide a reliable record of nd in seawater and hold out the prospect of using nd in foraminifera to examine changes in seawater that accompany glacial interglacial climatic cycles the principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic fe mn coatings these contain large amounts of nd and other trace elements but can be cleaned off using highly reducing reagents mn ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range 10 100 mol mol that has yielded success in studies of transition elements in forams mass balance modelling suggests that for residual mn ca ratios 100 mol mol nd added to the foram in the coating will never shift the measured nd isotope composition significantly away from the seawater value acquired by the foram test in the water column additionally nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids finally core top planktonic foraminifera for two sites have nd isotope compositions that are identical to local surface seawater the data we present here for labrador sea forams over the past 2 5 m y are interpreted in terms of changes in the seawater isotopic composition the data show a pronounced shift from end values of 12 to 19 in the period 2 5 1 5 ma this change is interpreted to result from the initiation of northern hemisphere glaciation and the increased derivation of labrador sea nd via ice rafting from archaean terranes in central canada in combination with stable isotope and foraminiferal relative species abundance data the new nd data are consistent with the surface hydrography of the labrador sea being dominated by a fluctuating balance between cold polar waters containing unradiogenic nd and warm subtropical waters containing more radiogenic nd the major change in labrador sea nd that is observed in the past 2 5 ma can on its own account for the change in the nd isotope composition of north atlantic deep water over the same time period

reversed determination of the reaction phlogopite quartz enstatite potassium feldspar h 2 o in the ranges 750 875 degrees c and 2 12 kbar at low h 2 o activity with concentrated kcl solutions the reaction of phlogopite plus quartz to enstatite potassium feldspar and aqueous fluid in the system kmash kcl was reversed at 2 12 kbar and 750 875 degrees c and at low h 2 o activities by reversal of the h 2 o content of concentrated kcl solutions equilibrated with product and reactant assemblages synthetic 1m phlogopite kmg 3 alsi 3 o 10 oh 2 and enstatite mgsio 3 maintained end member stoichiometry throughout and the potassium feldspar kalsi 3 o 8 was a high sanidine based on unit cell refinements the broad p t xh 2 o and narrow reversal ranges of this investigation were possible because of the low and well defined h 2 o activity yet powerful fluxing action of concentrated kcl solutions solubility experiments on quartz and potassium feldspar in our p t xh 2 o range showed that fluid phase solution of silicate constituents was too small to have affected the h 2 o activity in the experiments the new determinations are more definitive than previous work done at very low pressures with pure h 2 o or in co 2 h 2 o mixtures they establish the standard free energy of the reaction in the experimental range with an uncertainty of about 1 kj and indicate that the synthetic phlogopite has maximal al si disorder under our experimental conditions the standard enthalpy of reaction at 298 k is 106 54 or 2 0 kj 2sigma based on our reversals a value 6 kj less positive than that currently used by many workers in calculations of biotite stability and h 2 o activity in the petrogenesis of high grade metamorphic rocks the lower thermal stability that we find for phlogopite requires revision in estimates of h 2 o activity of granulite facies metamorphism typical values for the natural assemblage orthopyroxene biotite garnet potassium feldspar plagioclase quartz at deep crustal metamorphic conditions 750 850 degrees c 5 10 kbar are alpha h2o 0 4 0 6 compared with values of 0 15 0 30 which would have been estimated with previously available data on phlogopite stability an important consequence of the expanded h 2 o activity range of granulites is that alkali chloride solutions of only moderate concentration xh 2 o 0 5 0 7 which are the values observed in actual fluid inclusions in many kinds of igneous and metamorphic rocks are a feasible alternative to the vapor absent conditions considered necessary by many workers based on previous low estimates of h 2 o participation of concentrated brines in deep crust upper mantle metamorphic processes enables alkali metasomatism and other kinds of chemical transport in an aqueous fluid without large scale melting of the crust

fluid composition and evolution in coesite bearing rocks dora maira massif western alps implications for element recycling during subduction fluid inclusions and f cl concentration of hydrous minerals were analysed in the coesite pyrope quartzite the interlayered jadeite quartzite and their country rock gneiss from the dora maira massif using a combination of microthermometry raman spectrometry synchrotron x ray microfiuorescence and electron microprobe analysis three populations of fluid inclusions were recognized texturally and can be related to distinct metamorphic stages a low salinity aqueous fluid occurs in the retrogressed country gneiss and as late secondary inclusions in jadeite quartzite and chloritized pyrope an earlier secondary population is found in matrix quartz of the jadeite and pyro pe quartzites this population can be related to the early decompression and so to incipient breakdown of garnet into phlogopite bearing assemblages the inclusion fluid is highly saline up to 84 wt equivalent nacl and contains na ca fe cu and zn as major cations in pyrope quartzite additional k was found in these brines which locally coexist with co2 rich inclusions the oldest fluid inclusions are preserved in kyanite grains included in fresh pyrope and in pyrope itself in pyrope all inclusions have decrepitated and contain magnesite an mg phosphate sheet silicate s a chloride and an opaque phase with no fluid preser ved in contrast the kyanite inclusions in pyrope preserve primary h2o co2 low salinity fluid inclusions probably owing to the low compressibility of the kyanite inclusions and host garnet in spite of in situ re equilibration these inclusions can be interpreted as relics of the dehydration fluid that attended pyrope growth these correlations between textural and chemical fluid inclusion data and metamorphic stages are consistent with the fluid composition calculated from the halogen content of different generations of phlogopite and biotite the preservation of different fluid compositions both in time and space is evidence for local control and possibly origin of the fluids in agreement with isotopic data these results in particular the absence of co2 in the jadeite quartzite are best interpreted in terms of a fluid melt system evolution with increasing metamorphism partitioning of h2o na ca fe and heavy metals into melt jadeite quartzite and mg na k f co2 and p into a residual aqueous fluid can account for depletion in na ca and fe of the pyrope quartzite during the retrograde path a h 2 o rose as melt crystallized generating the two populations of hypersaline and water rich fluids that were highly reactive to pyrope the process of fluid melt interaction envisioned here coupled with models of melt extraction in subduction zones provides an attractive opportunity for the instantaneous 1 ma and selective transport of elements between a downgoing slab and the overlying mantle wedge

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

variability of surface water characteristics and heinrich like events in the pleistocene midlatitude north atlantic ocean biomarker and xrd records from iodp site u1313 mis 16 9 1 a reconstruction of milankovitch to millennial scale variability of sea surface temperature sst and sea surface productivity in the pleistocene midlatitude north atlantic ocean marine isotope stage mis 16 9 and its relationship to ice sheet instability was carried out on sediments from integrated ocean drilling program iodp site u1313 this reconstruction is based on alkenone and n alkane concentrations u37k index total organic carbon toc and carbonate contents x ray diffraction data magnetic susceptibility and accumulation rates increased input of ice rafted debris occurred during mis 16 12 and 10 characterized by high concentrations of dolomite quartz and feldspars and elevated accumulation rates of terrigenous matter minimum input values of terrigenous matter on the other hand were determined for mis 13 and 11 peak values of dolomite coinciding with quartz plagioclase and kalifeldspar peaks and maxima in long chain n alkanes indicative for land plants are interpreted as heinrich like events related to sudden instability of the laurentide ice sheet during early and late deglacial phases of the glacials the coincidence of increased toc values with elevated absolute concentrations of alkenones suggests increased glacial productivity probably due to a more southern position of the polar front alkenone based sst reached absolute maxima of about 19 c during mis 11 3 and absolute minima of 10 c during mis 12 and 10 within mis 11 prominent cooling events mis 11 22 and 11 24 occurred the absolute sst minima recorded directly before and after the glacial maxima mis 10 2 and 12 2 are related to heinrich like event meltwater pulses as supported by the coincidence of sst minima and maxima in c37 4 alkenones and dolomite these sudden meltwater pulses especially during terminations iv and v probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations ice sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the northern high latitudes

contribution of mafic melt to porphyry copper mineralization evidence from mount pinatubo philippines and bingham canyon utah usa mount pinatubo in the philippines known for its cataclysmic eruption in 1991 hosts several porphyry copper deposits and active geothermal systems an underlying mafic melt supplied much of the sulphur for the dacitic magma and its injection into the dacitic magma chamber triggered the eruption the eruption caused purging of the sulphur rich fluid from the dacite to the atmosphere and extensive fracturing similar events took place at bingham canyon utah site of the largest copper and gold deposit in north america at 38 ma the bingham canyon mineralization took place beneath an active stratovolcano and pyroclastic flows contemporaneous with the mineralization show evidence for magma mingling ascent of mafic melt supplied sulphur and chalcophile elements to the felsic magma which consolidated to form the bingham stock and its underlying magma chamber injections of the mafic melt caused periodic eruptions of felsic magma to form the stratovolcano and deposition of sulphide minerals in highly fractured rocks in and around the stock

magmatic co 2 and saline melts from the sybille monzosyenite laramie anorthosite complex wyoming there are three populations of fluid inclusions in quartz from the sybille monzosyenite early co2 secondary co2 and rare secondary brines the oldest consist of low density co2 0 70 inclusions that appear to be co magmatic the densities of these inclusions are consistent with the inferred crystallization conditions of the sybille monzosyenite namely 3 kilobars and 950 1000 c the other types of inclusions are secondary they contain co2 0 50 and secondary brine inclusions that form trains radiating out from a decrepitated inclusion the sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate rather than fluid inclusions feldspar contain abundant solid inclusions these consist of magmatic minerals hedenbergite hornblende ilmenite apatite and graphite intimately associated with k na chlorides we interpret these relations as follows the sybille monzosyenite formed from a magma that contained immiscible droplets of a halide rich melt along with a co2 vapor phase the salt was trapped along with the other obvious magmatic minerals during growth of the feldspars co2 may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved both the saline melt and the co2 vapor were trapped in the quartz the melt inclusions in the quartz later decrepitated perhaps due to progressive exsolution of fluids to produce the secondary h2o and co2 inclusions these observations indicate that the sybille monzosyenite which is a markedly anhydrous rock was actually vapor saturated rather than being h2o however the vapor was co2 rich and possibly related to an immiscible chloride rich melt

experimental constraints on sulphur behaviour in subduction zones implications for ttg and adakite production and the global sulphur cycle since the archean we performed crystallization experiments at 2 3 gpa at 700 9508c on basaltic and pelitic lithologies with added water and sulphur to constrain the factors controlling sulphur behaviour in subduction zones and how it may have varied through geological time the resulting hydrous silicic melts have up to 20 times more dissolved sulphur up to 1wt than at 0 2 0 4 gpa when moderately oxidized conditions prevail such high solubilities appear to result from the combined effects of enhanced solubility of water in high pressure silicate melts 10 20 wt h2o which acts to decrease silica activity and oxidizing conditions the results confirm previous findings that high sulphur contents in silicate melts do not necessarily require iron rich compositions suggesting instead that sulphur water complexes play a fundamental role in sulphur dissolution mechanisms in iron poor silicic melts in agreement with recent spectroscopic data the experimental melts reproduce phanerozoic slab derived magmas in particular their distinct ca and mg rich composition the results also show that sulphur increases the degree of melting of basalt lithologies hence we suggest that subducted slabs will preferentially melt where sulphur is present in abundance and that the variability in arc magma sulphur output reflects in part the vagaries of sulphur distribution in the slab source in contrast comparison with the composition of archean felsic rocks suggests that in the early earth much less sulphur was present in subducted slabs in agreement with a number of independent lines of evidence showing that the archean ocean hence the hydrothermally altered subducted archean oceanic crust was considerably poorer in sulphur than at present volcanic degassing of sulphur was thus probably much weaker during the archean than in proterozoic phanerozoic times

acquisition of the neodymium isotopic composition of the north atlantic deep water the north atlantic deep water nadw neodymium isotopic composition nd ic is increasingly used in oceanography and paleoceanography to trace large scale circulation and weathering processes notably to investigate past variations of the global thermohaline circulation although the present day nadw nd ic is well characterized at nd 13 5 the acquisition of this isotopic signature in other words the causes of this value has so far been very sparsely documented such an understanding is however fundamental to the interpretation of paleo records nd ic and rare earth element concentrations were measured at 9 stations within the north atlantic subpolar gyre signature cruise summer 1999 the comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the nadw the labrador sea water lsw nd 13 9 0 4 north east atlantic deep water neadw nd 13 2 0 4 and north west atlantic bottom water nwabw nd 14 5 0 4 acquire their nd ic through distinct water mass mixings and lithogenic inputs these different mechanisms acting upon water masses from very diverse sources seem to bring the nd ic of the three nadw layers to values close together and similar to that of the nadw it is suggested that sediment seawater interactions significantly lower the neadw and nwabw nd ic along the south east greenland margin since these interactions do not significantly modify the nd content of these water masses sediment remobilizations leading to the nd ic variations are probably associated with nd removal fluxes from the water mass toward the sediment a process called boundary exchange on the other hand lsw seems to acquire its nd ic from the subpolar mode waters from which it is formed by deep convection and no other mechanism needs to be invoked its unradiogenic signature could ultimately be linked to fresh water runoff from the canadian shield these conclusions should allow more precise interpretations of paleoceanographic nd ic records taking into account the distinct histories of the three nadw layers including distinct water mass mixings and distinct lithogenic inputs

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

water contents temperatures and diversity of the magmas of the catastrophic eruption of nevado del ruiz colombia november 13 1985 abstract the petrology of the highly phyric two pyroxene andesitic to dacitic pyroclastic rocks of the november 13 1985 eruption of nevado del ruiz colombia reveals evidence of 1 increasingly fractionated bulk compositions with time 2 tapping of a small magma chamber marginally zoned in regard to h 2 o contents 1 to 4 temperature 960 1090 c and amount of residual melt 35 to 65 3 partial melting and assimilation of degassed zones in the hotter less dense interior of the magma chamber 4 probable heating thermal disruption and mineralogic and compositional contamination of the magma body by basaltic magma underplating and 5 crustal contamination of the magmas during ascent and within the magma chamber near crater fall back or spill over emitted in the middle of the eruptive sequence produced a small pyroclastic flow that became welded in its central and basal portions because of ponding and thus heat conservation on the flat glaciated summit near the arenas crater the heterogeneity of ruiz magmas may be related to the comparatively small volume 0 03 km 3 of the eruption nearly ten times less than the 0 2 km 3 of the plinian phase of mount st helens and probable steep thermal and p h 2 o gradients of a small source magma chamber estimated at 300 m long and 100 m wide for an assumed ellipsoidal shape

nd ca ratios in plankton towed and core top foraminifera confirmation of the water column acquisition of nd planktic foraminifera have been used as recorders of the neodymium nd isotopic composition of seawater although there is still controversy over the precise provenance of the nd signal we present an extensive multispecific plankton tow nd ca data set from several geographic locations se atlantic ne atlantic norwegian sea and western mediterranean together with core top samples from the mediterranean region the range of nd ca ratios in plankton towed foraminifera cleaned only of organic material from all regions 0 01 0 7 mol mol is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps with distribution coefficients kd ranging between 4 and 302 for the mediterranean where core top and plankton tow data are both available the range for plankton tows 0 05 0 7 mol mol is essentially identical to that for the core tops 0 1 0 5 mol mol readsorption of nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process we find a relationship between manganese mn and nd in plankton tow samples that is mirrored by a similar correlation in core top samples this relationship suggests that fe mn coatings are of negligible importance to the nd budgets of foraminifera as the nd mn ratio it implies is over an order of magnitude greater than that seen in other fe mn oxide phases rather since both plankton tows and core tops present a similar behavior the nd mn relationship must originate in the upper water column the data are consistent with the acquisition of nd and mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes collectively the results help to explain two abiding puzzles about nd in sedimentary planktic foraminifera their high ree contents and the fact that they record a surface water nd isotopic signal regardless of the cleaning procedure used

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

high grade k feldspar veining in granulites from the ivrea verbano zone northern italy fluid flow in the lower crust and implications for granulite facies genesis we present observations of extensive networks of k feldspar microveins associated with quartz and plagioclase in granulite facies rocks from the ivrea verbano zone northern italy back scattered electron images of the granulite facies samples show a continuous system of k feldspar veins along quartz plagioclase and plagioclase plagioclase grain boundaries that can be traced across the entire length of a thin section quartz grain rims in contact with these veins show evidence of extensive corrosion in contrast contact between the veins and the orthopyroxene and garnet grains is very clean with no signs of secondary alteration k feldspar quartz plagioclase of the same compositions as the veins are commonly found as near rim inclusions within garnet microprobe traverses from the interiors of the k feldspar veins to their rims show increasing ba indicating a metasomatic origin some veins display a boudinaged texture possibly related to the d2 deformation event in the ivrea verbano zone and the

variations of north atlantic inflow to the central arctic ocean over the last 14 million years inferred from hafnium and neodymium isotopes the warm and saline north atlantic inflow to the arctic ocean is a major component of high northern latitude circulation and the main mechanism of deep water renewal in the arctic ocean knowledge of its past variability is critical for understanding the high latitude feedback mechanisms of the climate system here we present the first combined seawater hf and nd isotope compositions of past arctic intermediate water extracted from the authigenic fe mn oxyhydroxide fraction of two sediment cores recovered near the north pole to reconstruct changes in contributions from glacial brines of the eurasian shelf and past inflow of atlantic waters the hf and nd isotopic compositions obtained from leachates of the authigenic fraction show closely coupled and environmentally controlled variations over the past 14 million years an observed offset of these data from seawater ehf and end compositions from other ocean basins seawater array is interpreted as the result of continuously prevailing glacial weathering conditions on the high latitude eurasian continent in the late quaternary large amplitude hf and nd isotopic variations of arctic intermediate water aiw was characterized by more radiogenic isotope signatures generally prevailing under glacial conditions and less radiogenic values during interglacial periods on the basis of the close coupling between nd and hf isotopes we suggest that the evolution of hf isotope compositions of central arctic aiw has primarily been controlled by changes in ocean circulation and provenance of weathering inputs rather than changes in weathering regime

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

the solubility of apatite in h 2 o kcl h 2 o nacl h 2 o at 800 c and 1 0 gpa implications for ree mobility in high grade saline brines abstract apatite is an important host for lree f and cl and thus can be used to monitor elemental mass transfer in high p t settings in this investigation the solubilities of synthetic fluor and chlorapatite and natural durango fluorapatite were measured in h2o kcl h2o and nacl h2o fluids at 800 c and 1 0 gpa using the piston cylinder apparatus the solubility of apatite is reported in parts million by weight ppm and is calculated via the formula map map h2o kcl or nacl map 106 where map map in map out the experimental results indicate a strong increase in apatite solubility in aqueous fluids with moderate kcl and nacl mole fractions xkcl and xnacl under all conditions synthetic fluorapatite and synthetic chlorapatite dissolve congruently the solubility of synthetic fluorapatite increases from 19 ppm in pure h2o to 2123 ppm at xkcl 0 52 the solubility of synthetic chlorapatite rises from 37 ppm in pure h2o to 2590 ppm at xkcl 0 50 at xkcl 0 5 the solubility of synthetic fluorapatite decreases to 1691 xkcl 0 72 and the solubility of synthetic chlorapatite decreases to 2284 ppm xkcl 0 65 in contrast natural durango fluorapatite dissolves incongruently at xkcl 0 2 the solubility of natural durango fluorapatite increases from 70 ppm in pure h2o to 2073 ppm at xkcl 0 50 respectively in contrast to the kcl h2o system apatite solubilities are considerably higher in the nacl h2o system the solubility of synthetic fluorapatite increases to 4909 ppm at xnacl 0 51 and the solubility of synthetic chlorapatite rises to 5144 ppm at xnacl 0 50 compared to fluorite calcite and anhydrite apatite solubility is significantly lower in h2o nacl h2o and kcl h2o after completion of each experiment the ph was measured and a comprehensive step by step procedure limiting reactant concept was used to model the observed quench ph in the system apatite kcl h2o

neodymium budget in the modern ocean and paleo oceanographic implications the oceanic nd budget is calculated using a steady state 10 box model and a compilation of field data this is the first attempt to propose consistent estimates of the nd fluxes entering the ocean as well as indicating possible nd sources and the proportion of nd fluxes exchanged between dissolved and particulate fractions with presently available nd data the best estimates give a total nd influx of 9 x 10 9 g yr which leads to an oceanic nd residence time of 500 years from modeling tests we suggest that the authigenic nd scavenged by particulates is 100 remineralized in the deep ocean the total exchanged nd flux may be as high as 2 x 10 10 g yr the epsilon nd 0 values of the influxes are 22 11 1 and 4 for the north atlantic surface atlantic north pacific and surface indo pacific regions respectively atmospheric and riverine nd fluxes are insufficient to explain the magnitude and regional variability of calculated nd influxes and epsilon nd 0 we propose continental margins as an additional source supplying nd to the ocean using the model calibrated for nd we examine the sensitivity of deep water epsilon nd 0 to variations of nd inputs to the ocean deep water nd concentrations and epsilon nd 0 vary with the changes in nd influxes and their epsilon nd 0 as nd sources to the ocean may change during glacial interglacial periods the epsilon nd 0 shifts recorded in ferromanganese nodules and crusts do not necessarily reflect changes in paleoceanic circulation the effects of continental erosion should be considered in reconstructing patterns of ocean circulation using nd isotopes

generation of porphyry copper deposits by gas brine reaction in volcanic arcs we acknowledge research funding from bhp billiton a benjamin meaker visiting professorship to j m and a royal society wolfson research merit award and erc advanced grant critmag to j b

continental weathering fluxes during the last glacial interglacial cycle insights from the marine sedimentary pb isotope record at orphan knoll nw atlantic abstract regional weathering intensity must have changed dramatically at high latitudes during the quaternary as a consequence of repeated continental glaciation investigation of these glacial interglacial changes at high temporal resolution is possible with the recent development of pb isotopes in femn oxyhydroxide phases as a proxy for region specific weathering intensity where increases in the radiogenic component are thought to correspond to increased continental weathering fluxes here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from iodp sites u1302 3 on orphan knoll 3500 mbsl nw atlantic spanning the last 37 ka located at the eastern edge of the laurentide ice sheet lis site u1302 3 is well placed to monitor changes in weathering intensity associated with lis glacial history overall the data show a close correspondence to local surface water 18o with least radiogenic values during times of heavy 18o glacial maximum and most radiogenic values during times of light 18o holocene this supports the prediction that weathering intensity in glaciated regions of the north atlantic correlates with the exposure age of glacial debris superimposed on these background trends are extreme radiogenic excursions e g variation in 206pb 204pb from 19 2 21 0 contemporaneous with heinrich events and the younger dryas these data are substantially more radiogenic than existing records from the nw atlantic and most likely represent episodes of exceptionally high inputs of pre formed femn oxyhydroxides during drainage of the lis due to its extreme isotope composition at least in the nw atlantic region pb would appear to be a good proxy for the fluxes of weathered continental material and perhaps by inference nutrients to the surface ocean

solubility of anhydrite caso4 in nacl h2o solutions at high pressures and temperatures applications to fluid rock interaction anhydrite solubility in h2o nacl solutions was measured at 6 14 kbar 600 800 c and nacl mole fractions xnacl of 0 0 3 in piston cylinder apparatus solubilities were determined by weight changes of natural anhydrite in perforated pt envelopes confined with fluid in larger pt capsules in initially pure h2o at 10 kbar and 800 c caso4 concentration is low 0 03molal though much larger than at the same temperature and 1 kbar hematite buffered experiments showed slightly lower solubilities than unbuffered runs caso4 solubility increases enormously with nacl activity at 800 c and 10 kbar and xnacl of 0 3 caso4 molality is 200 times higher than with pure h2o whereas caso4 solubility in pure h2o decreases with rising t at low t and p the high p results show that anhydrite solubility increases with t at constant p at all xnacl investigated the effects of salinity and temperature are so great at 10 kbar that critical mixing between sulfate rich hydrosaline melts and aqueous salt solutions is probable at 900 c at xnacl 0 3 recent experimental evidence that volatile laden magmas crystallizing in the deep crust may evolve concentrated salt solutions could in light of the present work have important implications regarding such diverse processes as mount pinatubo type s rich volcanism high fo2 regional metamorphism and emplacement of porphyry cu mo ore bodies where anhydrite hematite alteration and fluid inclusions reveal the action of very oxidized saline solutions rich in sulfur

temporal stability of the neodymium isotope signature of the holocene to glacial north atlantic the neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial timescales unlike nutrient proxies such as 13 c or cd ca nd isotopes are not thought to be altered in any significant way by biological processes and thus they can serve as a quasi conservative water mass tracer however the application of nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the north atlantic end member through time here we present the first results of nd isotopes measured in u th dated deep sea corals from the new england seamounts in the northwest atlantic ocean our data are consistent with the conclusion that the nd isotopic composition of north atlantic deep and intermediate water has remained nearly constant through the last glacial cycle the results address long standing concerns that there may have been significant changes in the nd isotopic composition of the north atlantic end member during this interval and substantiate the applicability of this novel tracer on millennial timescales for paleoceanography research

the use of foraminifera as a record of the past neodymium isotope composition of seawater 1 we present new isotopic data for sedimentary planktonic foraminifera as well as for potential water column and sedimentary sources of neodymium nd which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary nd the faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater nd is difficult to explain given their variable and high nd ca ratios ratios that are often sedimentary foraminifera ratios that are often much higher than is plausible for direct incorporation within the calcite structure we present further data that demonstrate a similarly large range in nd ca ratios in plankton tow foraminifera a range that may be controlled by redox conditions in the water column cleaning experiments reveal in common with earlier work that large amounts of nd are released by cleaning with both hydrazine and diethylene triamine penta acetic acid but that the nd released at each step is of surface origin while further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal nd isotope systematics these new data place the use of planktonic foraminifera as recorders of surface water nd isotope ratios and thus of variations in the past supply of nd to the oceans from the continents via weathering and erosion on a reasonably sure footing

sapphirine bearing paragneiss from the northern grenville province in labrador canada protolith composition and metamorphic p t conditions sapphirine has recently been found to be abundant throughout proterozoic 1 7 1 6 ga granulite facies quartzofeldspathic paragneiss in central labrador the pressure temperature p t trajectory of metamorphism culminated at 900 c and 9 kbar and was succeeded by nearly isobaric cooling the paragneiss has 18 o enrichment and chemical compositions which suggest that the protolith was probably highly oxidized shale chemical constraints render the involvement of partial melting during the formation of the paragneiss unlikely

reconstructing deglacial north and south atlantic deep water sourcing using foraminiferal nd isotopes during the last few decades neodymium isotopes have been increasingly used as a paleoceanographic and paleoclimate proxy on million year through millennial time scales the widespread use of the nd isotope proxy depends on whether the nd isotopic composition of past seawater can be reliably extracted from authigenic sediment phases here we show evidence that planktonic foraminifera with authigenic coatings preserve a deep water nd isotopic signature and thus can be used to reconstruct past deep water nd isotopes applying this method downcore on south atlantic deep cape basin core tno57 21 41 1 s 7 9 e 4981 m the nd isotopic composition of the planktonic foraminiferal fe mn oxide coatings is identical with and confirms that of the reductively leached bulk sediment fraction piotrowski et al 2004 2005 2008 as reflecting changes in bottom water sourcing in the case of northeastern north atlantic core bofs 8k 52 5 n 22 1 w 4045 m the planktonic foraminiferal fe mn oxide coatings have different nd isotopes from reductive sediment leaches clearly acid reductive leaching must be tested in more detail we observe that the nd isotopic composition of the deep northeastern atlantic core shifted during the deglaciation from glacial values similar to the south atlantic cape basin towards holocene values similar to the bermuda rise roberts et al 2010 taken as a whole the nd isotope record from foraminiferal authigenic coatings suggests large scale changes in the proportion of northern and southern deep water sources occurred throughout the atlantic ocean with substantial chemical gradients at times during the last deglaciation

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

comparative oxygen barometry in granulites bamble sector se norway oxygen fugacities have been estimated for the high grade portion of the bamble granulite facies terrane se norway using both titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers the two oxygen barometers show good agreement for samples indicating high titaniferous magnetite ilmenite temperatures whereas agreement is poor for low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably lower than those estimated from orthopyroxene titaniferous magnetite quartz this discrepancy increases with a decrease in temperature which appears to reflect preferential resetting of the hematite content in the ilmenite grains without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains the mean temperature for the non reset samples 795 60 c 1 agrees well with temperatures obtained from garnet orthopyroxene k d exchange thermometry in the same region 785 60 c 1 most non reset o

extracting foraminiferal seawater nd isotope signatures from bulk deep sea sediment by chemical leaching the seawater radiogenic neodymium 143nd 144nd isotope signature is an invaluable tool for the reconstruction of past deep water provenance sedimentary foraminifera or fish teeth are among the most reliable archives known for nd isotope based reconstructions of past seawater as the distribution and preservation of these archives are limited the extraction of hydrogenetic ferromanganese oxyhydroxides from bulk sediments provide an easily applicable alternative this method however implies the risk of generating artefacts due to the possible release of non seawater derived nd during the extraction procedure here we revisit and further investigate the reliability of the extraction of seawater derived nd isotope signatures via leaching of bulk deep sea sediments with two commonly used buffered acetic acid and acid reductive mix solutions repeated application of such stepwise leaching procedures to different non decarbonated sediments from distinct settings across the deep atlantic ocean shows pronounced elemental and nd isotope trends during the leaching process in the laboratory our results show that seawater nd isotope compositions are extracted together with carbonates and manganese oxides only at the beginning of the leaching series during chemical extraction the carbonates effectively work as a buffer preventing acid induced mobilisation of fe oxides and volcanogenic material once this buffer is consumed potentially present volcanogenic phases are considerably attacked leading to shifts in the extracted nd isotope signal of up to 12 epsilon units such volcanogenic phases are a significant source of contaminant nd reflected by markedly elevated al nd signatures we consequently propose a revised weak leaching protocol for carbonate bearing deep sea sediments which is simple to use provides excellent agreement with data obtained from uncleaned foraminifera and can be easily screened for contamination

whole rock phosphate and silicate compositional trends across an amphibolite to granulite facies transition tamil nadu india chemical trends from north amphibolite facies to south granulite facies along a 95 km traverse in tamil nadu southern india include whole rock depletion of rb cs th and u enrichment in ti and f and depletion in fe and mn in biotite and amphibole increases in al and decreases in mn in orthopyroxene enrichment of fluorapatite in f k feldspar blebs are widespread along quartz plagioclase grain boundaries and could indicate either partial melting or metasomatism in the northernmost portion of the traverse the principal rare earth element ree bearing minerals are allanite and titanite south of a clinopyroxene isograd monazite grains independent of fluorapatite are the major ree and th bearing phase further south independent monazite is rare but th free monazite inclusions are common in fluorapatite during prograde metamorphism independent monazite was replaced by ree rich fluorapatite in which the monazite inclusions later formed the loss of independent monazite was accompanied by a loss of whole rock th and possibly a small depletion in light ree most mineralogical features along the traverse can be accounted for by progressive dehydration and oxidation reactions trace element depletion is best explained by the action of an externally derived low h2o activity brine migrating from a source at greater depth possibly preceded or accompanied by partial melting

significance of high temperature fluids and melts in the grasberg porphyry copper gold deposit abstract a study of quartz sulfide veins from the grasberg cu au deposit has shown that the quartz crystals initially grew from the walls of the veins into open fractures cathodoluminescence cl imaging shows concentric growth zones in the larger crystals and changes in the orientation of the growth zones with occasional truncation of the zoning towards the centre of veins the crystals become smaller and irregularly shaped but exhibit cl banding parallel to vein walls which is normally associated with crack seal processes the vein quartz contains silicate and sulfide rich melt inclusions virtually water free salt melt inclusions and coexisting hypersaline and vapour rich inclusions late stage secondary aqueous inclusions are also present in some veins most fluid inclusions homogenised at temperatures below 620 c however hypersaline b2 inclusions had a very complex behaviour and exhibited partial homogenisation to salt melt and clear immiscible fluid at temperatures ranging from 820 c to 1300 c these inclusions contain the highest cu concentrations up to 6 3 wt suggesting they play a role in metal transport the contemporaneous trapping of the k feldspar rich melt inclusions hypersaline and vapour rich inclusions suggests a common source for these fluids and a process involving heterogeneous entrapment of immiscible silicate melt hypersaline fluid and vapour as previously proposed for other porphyry copper deposits furthermore the grasberg deposit is estimated to have formed at pressures below 400 bar which may explain the presence of salt melt inclusions as the vapour halite field of the h2o nacl system is dominant below 800 c at these pressures the unrealistically high temperatures reported herein may have resulted from entrapment of either immiscible silicate melt hypersaline fluid and vapour or cumulates of an evolving silicate melt saturated in k spar brine and vapour although these temperatures may not be directly useful these inclusions give important clues to metal enrichment processes these melt and fluid inclusions record cycles of transitory high temperature 700 c hydrofracturing melt and fluid release and vein formation in a cooler 500 600 c background host rock thermal regime high sulfur and cu contents of sulfide melt and hypersaline b2 inclusions are interpreted to be the fluid composition before the main sulfide precipitation event and therefore may be used as tracers of the magmatic body from which they exsolved at depth

the solubility of cepo4 monazite and ypo4 xenotime in kcl h2o fluids at 800 c and 1 0 gpa implications for ree transport in high grade crustal fluids

pressure temperature time paths and a tectonic model for the evolution of granulites petrologic studies and application of well calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains 1 peak metamorphic pressure and temperature conditions cluster around values of 7 5 pm 1 kbar and 800 pm 50 c implying average geothermal gradients of 30 35 c km 2 in comparison with upper amphibolite facies rocks especially in paired amphibolite granulite terrains it is evident that granulites are distinguished from amphibolites by the former s higher metamorphic temperatures but not higher pressure 3 initial cooling of granulite terrains from peak conditions is nearly isobaric for garnet closure temperatures of 600 pm 50 c the dp dt retrograde paths inferred from compositionally zoned garnet rims are 2 8 b c in most granulites 4 primary coarse sillimanite is found in most granulites and retrograde kyanite is known in a few these data suggest that granulites form as a result of anomalous thermal gradients

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

the solubility of fluorite in h2o and h2o nacl at high pressure and temperature abstract the solubility of fluorite in h2o and h2o nacl has been measured at 600 1000 c 0 5 2 0 gpa in a piston cylinder apparatus fluorite dissolves congruently at all conditions investigated the data indicate that the concentration of fluorite dissolved in h2o is low at 600 c and 0 5 gpa 0 0014 mol kg h2o but increases strongly with temperature t and pressure p to 0 247 mol kg h2o at 1000 c 2 gpa the data were fit with the equation log mcaf2 6 587 2 774p1 2 2 266 10 3 4 699 10 4p t where mcaf2 is molality of caf2 t is in kelvin and p is in gpa fluorite solubility was also measured in h2o nacl fluids at 800 c and 1 0 gpa results indicate a strong increase in dissolved fluorite concentration with increasing nacl content from 0 028 mol kg h2o at xnacl 0 to 1 673 mol kg h2o at xnacl 0 486 where xnacl is the mole fraction of nacl in the fluid the data were fit to mcaf2 0 01035 1 141xnacl 4 694xnacl2 the results indicate that f mobility will be further enhanced by saline brines in high p t igneous and metamorphic environments high f solubility in h2o and h2o nacl in the deep crust and upper mantle can promote mobilization of high field strength elements rare earth elements u and th through transport as f bearing complexes

silicate oxide and sulphide trends in neo archean rocks from the nilgiri block southern india the role of fluids during high grade metamorphism the nilgiri block southern india represents an exhumed section of lower late archean 2500 ma crust the northern highlands of the nilgiri block are characterized by metagabbros with pyroxenite inlayers a two pyroxene granulite zone acts as a transition between the metagabbros and charnockites which are exposed in the central and southern part of the nilgiri highlands thermobarometry results indicate a sw ne regional trend both in temperature similar to 650 800 degrees c and in pressure 700 1100 mpa over the nilgiri highlands in the charnockites composite rutile ilmenite grains are the dominant oxide assemblage in the two pyroxene granulites hemo ilmenite magnetite is dominant with coexisting rutile ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites in the metagabbros hemo ilmenite magnetite is the dominant oxide assemblage the principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite chalcopyrite exsolution lamellae or blebs in the two pyroxene granulites and the metagabbros the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite pyrrhotite chalcocopyrite associations from these observations a specific oxidation trend is seen the northern granulite facies metagabbros and two pyroxene granulites of the nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions this higher oxidation state is proposed to be the result of highly oxidizing agents probably as so3 in low h2o activity grain boundary nacl saline fluids with a dissolved caso4 component present during granulite facies metamorphism of the metagabbros and two pyroxene granulites eventually these agents became more reducing owing to the inherent buffering of the original tonalite granodiorite granitoids at the graphite co2 buffer such that s took the form of h2s during the granulite facies metamorphism of the charnockites at the same time these saline fluids were also responsible the solid state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro two pyroxene granulite and charnockite

anhydrite pyrrhotite and sulfur rich apatite tracing the sulfur evolution of an oligocene andesite eagle mountain co usa abstract the oldest known occurrence of magmatic anhydrite in a shallow sub volcanic rock is at the oligocene andesitic eagle mountain volcanic center huerto formation san juan volcanic field which immediately postdates the pyrrhotite bearing fish canyon tuff estimates of intensive parameters derived from the compositions of coexisting minerals hornblende plagioclase anhydrite pyrrhotite s rich apatite augite hypersthene feti oxides indicate that the eagle mountain magma was wet oxidized and s rich it was much like k rich andesitic and dacitic anhydrite bearing magmas recently erupted from the subduction related volcanoes el chichon mt pinatubo and lascar although the oligocene geodynamic setting of the san juan volcanic field is poorly constrained and its enormous volume is not easily reconciled with an arc setting the eagle mountain occurrence emphasizes how closely some of its magmas resemble those from active continental margin arcs s rich magmas similar to the eagle mountain andesite also may have contributed to the formation of some hydrothermal ore deposits of the san juan volcanic field

solubility of cepo4 monazite and ypo4 xenotime in h2o and h2o nacl at 800 c and 1 gpa implications for ree and y transport during high grade metamorphism abstract monazite and xenotime are important accessory minerals in metasediments because they host ree and are useful for geochronology and geothermometry it is therefore essential to understand their behavior during metasomatic processes that attend metamorphism and subduction in order to constrain the solubility of monazite and ypo 4 xenotime at high pressure and temperature we carried out weight loss experiments on synthetic single crystals of cepo 4 monazite and ypo 4 xenotime using hydrothermal piston cylinder methods at 800 c and 1 gpa in h 2 o and h 2 o nacl fluids results indicate that cepo 4 and ypo 4 dissolved congruently and that their solubilities in pure h 2 o are very low 0 04 0 04 and 0 25 millimolal respectively the solubility of cepo 4 rises to an increasing extent with added nacl to 7 94 0 07 millimolal at 50 mol nacl in contrast the solubility of ypo 4 rises to a decreasing degree with increasing nacl to 4 36 0 08 millimolal at 50 mol nacl best fit equations for the solubilities of the two phases are m cepo 4 3 56 10 5 5 82 10 3 x nacl 1 97 10 2 x 2 nacl and m ypo 4 2 48 10 4 1 26 10 2 x nacl 8 89 10 3 x 2 nacl the solubility of ypo 4 is greater than that of cepo 4 at nacl mole fractions x nacl of 0 00 0 27 the solubility enhancement behavior implies that ce dissolves as anhydrous chloride complexes whereas y forms mixed cl oh solutes the results provide a simple mechanism for redistributing ree and y in deep crustal and upper mantle environments the h 2 o ce ratio inferred for subduction zone melts and silicate rich fluids can also be produced by a cepo 4 saturated fluid with x nacl 0 1 in addition neutral ph h 2 o nacl fluids can transport substantial ree and y obviating the need to invoke highly acid solutions in environments where they are unlikely

oceanographic and climatic evolution of the miocene mediterranean deduced from nd sr c and o isotope compositions of marine fossils and sediments isotopic compositions of marine sediments and fossils have been investigated from northern basins of the mediterranean to help constrain local oceanographic and climatic changes adjacent to the uplifting alps stable c and o isotope compositions of benthic and planktonic foraminifera from the umbria marche region umc have an offset characteristic for their habitats and the changes in composition mimic global changes suggesting that the regional conditions of climate and the carbon cycle were controlled by global changes the radiogenic isotope composition of these fossil assemblages allows recognition of three distinct periods in the first period from 25 to 19 ma high nd values and low 87sr 86sr of sediments and fossils support intense tectonism and volcanism related to the opening of the western mediterranean in the second period from 19 to 13 ma the 87sr 86sr ratio of mediterranean umc deviate from the global ocean which is compatible with rapid uplift of the hinterland and intense influx of sr from mesozoic carbonates of the western apennines this local control on the seawater was driven by a humid and warm climate and indicates restricted exchange of water with the global ocean generally the nd values of the fossils are very similar to those of indian ocean water with brief periods of a decrease in the nd values coinciding with volcanic events and maybe sea level variation at 15 2 ma in the third period from 13 to 10 ma the fossils have 87sr 86sr similar to those of miocene seawater while their nd values change considerably with time this indicates fluctuating influence of the atlantic versus the paratethys and or locally evolved seawater in the mediterranean driven by global sea level changes other investigated localities near the alps and from the odp 900 site are compatible with this oceanographic interpretation however in the late early miocene enhanced local control reflecting erosion of old crustal silicate rocks near the alps results in higher 87sr 86sr

sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith uniformly sulfur rich cores abruptly zoned to sulfur poor rims 1 to 0 2 wt so3 in apatite from the yerington batholith nevada indicate that early magma that is crystal poor oxidizing and sulfate rich evolved to sulfate poor magma via crystallization of anhydrite a mineral observed in magmas from pinatubo and el chichon we predict that the characteristic zonation to sulfur poor rims of apatite in the yerington batholith is common in other oxidized hydrous calc alkaline magmas and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution sulfate rich arc magmas such as yerington magmas may crystallize to produce hydrothermal fluids rich in chlorine copper and sulfur and porphyry copper ores

evolution of the norwegian current and the scandinavian ice sheets during the past 2 6 m y evidence from odp leg 104 biogenic carbonate and terrigenous records abstract records of biogenic and terrigenous components have been obtained from the interval corresponding to the last 2 6 m y of odp sites 643 and 644 in order to reconstruct surface and deep water regimes in the norwegian sea surface water regimes record long lasting moderate glacial conditions during the interval 2 6 1 0 ma small intrusions of atlantic water episodically penetrated into the norwegian sea forming a narrow tongue along the eastern margin which is documented at site 644 the polar front was most probably situated between the site 644 and 643 locations on the outer voring plateau during these time intervals deep water regimes reflect long term persistent corrosive bottom waters most probably due to a weakly undersaturated water column and a low rate of carbonate shell production in surface waters deep water production in the norwegian greenland sea may have operated in a different way e g brine formation during winter sea ice growth bottom waters were oxygenated throughout the entire period and deep water was exchanged persistently with the north atlantic increased glacial interglacial environmental contrasts are documented reflecting a strengthening of the norwegian current and intensified glaciations on the surrounding land masses during the interval 1 0 0 6 ma during this time a major shift in the mode of deep water production occurred the onset of large amplitudes in glacial interglacial environmental conditions with maximum contrasts in surface water regimes different modes of deep water production and intensified exchange with the north atlantic marks the last 0 6 ma a broad development of the norwegian current is observed during peak interglacials while during glacials seasonally variable sea ice cover and iceberg drift dominate surface water conditions

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

neodymium isotopic composition of the oceans a compilation of seawater data a global compilation of the neodymium isotopic composition of seawater is presented with 880 data points it confirms the gradual end increase for intermediate deep water masses from the northwest north atlantic via the austral and indian oceans to the pacific this confirms the usefulness of this tracer for studying large scale oceanic circulation the compilation stresses the need for documenting the oceans south of 30 s from which less than 4 of the data are derived the associated neodymium concentrations display heterogeneous vertical gradients among major oceanic basins in addition to particle remineralization along the global thermohaline circulation the database suggests that basin size differences also contribute to that heterogeneity

anhydrite stability and the effect of ca on the behavior of sulfur in felsic magmas the distribution of sulfur in the system na2o k2o cao al2o3 sio2 h2o s was investigated at 2 kbar 750 950 c and oxygen fugacities ranging from the co coo to the re reo2 buffer anhydrite caso4 crystallized in all the experiments conducted at oxidizing conditions ni nio 0 5 to 1 and above under otherwise equal conditions an inverse relationship between sulfur and cao concentration was observed in melts coexisting with anhydrite with the solubility product k cao so3 being constant where cao and so3 are the molar fraction of cao and so3 in the quenched glasses this suggests that anhydrite dissociates upon dissolution in the melt according to caso4 anhydrite ca2 melt so42 melt the solubility product strongly depends on temperature with lnk 28 573 917 t 11 26 0 80 this corresponds to an enthalpy of dissolution of h r 237 5 7 6 kj mol under reducing conditions co coo and ni nio buffer cao has no effect on the fluid melt partition coefficient of sulfur d sfluid melt at 850 c 2 kbar partition coefficients were 519 30 at the ni nio buffer and 516 11 at the co coo buffer for cao contents in the melt up to 1 wt these data are virtually identical to those measured in the cao free haplogranite system under reducing conditions however under more oxidizing conditions the fluid melt partition coefficient of sulfur appeared to have increased somewhat in the presence of cao this increase may however also be related to the fact that the final melt compositions in these runs were distinctly peraluminous our data show that calcium has no effect on the degassing of sulfur at reducing conditions but it greatly reduces the amount of sulfur available for rapid degassing under oxidizing conditions by stabilizing anhydrite

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

authigenic pb isotopes from the laurentian fan changes in chemical weathering and patterns of north american freshwater runoff during the last deglaciation climate dependent chemical weathering trends have a strong impact on the dissolved pb isotopic composition of continental runoff during glacial terminations so that this tracer can be used to reconstruct the impact of the north american deglaciation on aspects of freshwater runoff and ocean chemistry here we present authigenic fe mn oxyhydroxide derived pb isotope records from lower laurentian fan sediments that trace the local deglacial continental runoff signal through the gulf of st lawrence we use these records to investigate changes in the pb isotopic composition of the north american runoff and their relationship to deglacial processes the new pb isotope records are very similar to those from the subtropical deep nw atlantic locations though the new data are at higher resolution and exhibit much greater amplitudes of change due to their laurentide ice sheet proximal setting unradiogenic compositions 206pb 204pb as low as 18 8 at 18 5 ka during the latest glacial change towards highly radiogenic compositions during the early holocene 206pb 204pb 20 1 at 11 2 ka late holocene 206pb 204pb values return to intermediate values around 206pb 204pb 19 6 these new data support previous inferences that the pb isotopic composition of the deep atlantic is controlled during deglaciation by changes in the pattern and intensity of continental chemical weathering in more detail the most significant change in the entire pb isotope record starts at 12 5 ka and lasts until about 11 ka this observation of strong pb isotopic changes across a climatically cold period in the north atlantic region suggests that at this location pb isotopic compositions recorded in deep marine authigenic fe mn oxyhydroxides not only trace deglacial changes in chemical weathering intensity but also highly depend on major freshwater runoff routes in interior north america our data suggest a gradual opening of the eastward freshwater runoff route in the course of the younger dryas

modelling nd isotopes with a coarse resolution ocean circulation model sensitivities to model parameters and source sink distributions the neodymium nd isotopic composition nd of seawater is a quasi conservative tracer of water mass mixing and is assumed to hold great potential for paleoceanographic studies here we present a comprehensive approach for the simulation of the two neodymium isotopes 143nd and 144nd using the bern3d model a low resolution ocean model the high computational efficiency of the bern3d model in conjunction with our comprehensive approach allows us to systematically and extensively explore the sensitivity of nd concentrations and nd to the parametrisation of sources and sinks previous studies have been restricted in doing so either by the chosen approach or by computational costs our study thus presents the most comprehensive survey of the marine nd cycle to date our model simulates both nd concentrations as well as nd in good agreement with observations nd covaries with salinity thus underlining its potential as a water mass proxy results confirm that the continental margins are required as a nd source to simulate nd concentrations and nd consistent with observations we estimate this source to be slightly smaller than reported in previous studies and find that above a certain magnitude its magnitude affects nd only to a small extent on the other hand the parametrisation of the reversible scavenging considerably affects the ability of the model to simulate both nd concentrations and nd furthermore despite their small contribution we find dust and rivers to be important components of the nd cycle in additional experiments we systematically varied the diapycnal diffusivity as well as the atlantic to pacific freshwater flux to explore the sensitivity of nd concentrations and its isotopic signature to the strength and geometry of the overturning circulation these experiments reveal that nd concentrations and nd are comparatively little affected by variations in diapycnal diffusivity and the atlantic to pacific freshwater flux in contrast an adequate representation of nd sources and sinks is crucial to simulate nd concentrations and nd consistent with observations the good agreement of our results with observations paves the way for the evaluation of the paleoceanographic potential of nd in further model studies

evidence for magmatic vapor deposition of anhydrite prior to the 1991 climactic eruption of mount pinatubo philippines anhydrite caso4 phenocrysts from mount pinatubo pumices show evidence of having responded dynamically to changing conditions prior to the june 15 1991 climactic eruption micrometer sized and smaller pyramidal surface growth features and lesser numbers of etch pits on anhydrite surfaces are documented by scanning electron microscopy chemical analyses indicate that the pyramids are a caso4 polymorph and electron backscatter diffraction patterns show conclusively that the pyramids are indeed orthorhombic anhydrite and not another ca sulfate phase unit cell measurements of volcanic anhydrite are identical with evaporitic anhydrite as determined from single crystal x ray diffraction patterns the computer program solvgas was used to identify conditions under which the pyramids may have precipitated thermodynamic modeling of a cooling magmatic gas h2o co2 so2 at 500 bars maximum model pressure and nno 1 7 was performed assuming that the gas contained 10 9 mol ca and 4 mol so2 the program indicates that anhydrite will precipitate homogeneously at approximately 780 c whereas an isothermal drop in pressure would likely lead to dissolution pyramids located between a phenocryst and adjacent glass provide physical evidence that at least a portion of the pyramids nucleated and grew before the melt quenched we propose a mechanism to account for these previously unrecognized surface growths which is that the anhydrite pyramids precipitated from a fluid or vapor phase that had separated from the magma at depth at least a portion of the pinatubo anhydrite phenocrysts provided substrates for nucleation and epitaxial growth of anhydrite because the anhydrite pyramids resemble products of chemical vapor deposition of metals and ceramics we propose that this previously unrecognized process be termed magmatic vapor deposition evidence of high temperature magmatic vapor deposition of anhydrite could be used as an indicator that a pre eruptive gas phase was accumulating or stored at depth especially at arc volcanoes where excess amounts of sulfur are vented into the atmosphere

sulfur isotopic compositions of deep arc cumulates abstract heavy sulfur isotopic compositions of arc lavas suggest a seawater component in the sulfur budget of arc lavas but whether the seawater signature derives from the subducting slab or from magma interactions with lithologies in the upper plate is unclear to see through the effects of degassing or crustal processing a study was conducted on the s isotopic composition of deep arc cumulates from 45 90 km beneath the sierra nevada batholith in california a cretaceous continental arc these cumulates represent the crystal line of descent from magmatic differentiation of hydrous arc basalts the deepest up to 60 90 km and most primitive cumulates are low in fe and have high molar mg mg fe whereas the shallow and more evolved cumulates are high in fe and have low mg mg fe bulk rock 34 s correlates with fe and negatively with mg mg fe the most primitive cumulates are isotopically similar to the earth s mantle whereas the more evolved cumulates are heavier by 6 in the direction of seawater sulfate the mantle like s isotopic signatures of the primitive cumulates indicate that the contribution of slab derived sulfate to arc lavas may not be as large as widely thought heavy s isotopic signatures are seen only in the evolved arc cumulates which suggests that the seawater signature of arc lavas may not all derive directly from the slab but perhaps during magma interaction with pre arc crust in continental arcs pre arc crust is dominated by accreted marine metasediments and metabasalts and in island arcs by seawater altered oceanic crust in the upper plate the limited contribution of slab sulfate to the mantle source of sierran arc magmas if generalizable suggests that sulfate in the subducting slab is efficiently released well before the arc magmatic front such a scenario would be consistent with the higher solubility of sulfate in aqueous fluids compared to that of sulfide in summary it is suggested here that the upper plate in the form of seawater altered crust and sediments may be as or more important for the sulfur budget in arc magmas than the subducting slab early loss of sulfate from the slab during subduction suggests that the dominant s species transported to the deep mantle is in the reduced form sulfide