sulfidation of major rock types of the oceanic lithosphere an experimental study at 250 c and 400 bars abstract circulation of hydrothermal fluids within the oceanic crust is a major factor in mass and heat transfer between hydrosphere and lithosphere many occurrences of massive sulfide have been reported along the mid ocean ridges showing effective mass transfer of sulfur and metals in these systems besides precipitation of sulfide at the seafloor replacive sulfide formation in the sub seafloor has been documented however different lithologies are expected to have different affinities to sulfidization to investigate the role of rock composition on sulfidization efficiency we have conducted batch experiments at 250 c and 400 bars that placed an h2s rich hydrothermal fluid into contact with four different rock types dunite olivine separates troctolite basalt and serpentinite these rocks were exposed to fluids containing 20 mmol kg total dissolved sulfide for durations between 1 and 10 weeks in situ fluid sampling allowed us to determine the evolution of the concentrations of ionic solutes and dissolved gases solid products were analyzed after termination of the experiments using xrd sem tg and vsm geochemical modeling was employed to compare observed reaction with equilibrium thermodynamic predictions sulfide in the form of euhedral pyrite crystals could be observed only in the basalt experiment in all other runs prevailing h2s activities were too low for sulfide formation despite high total sulfide concentrations instead the troctolite and peridotite experiments showed serpentinization of olivine and magnetite formation plagioclase in troctolite experienced desilicification resulting in andradite formation the stability field of sulfide in the h2 h2s activity plane is diminished due to the prevalence of andradite in hydrothermally reacted troctolite and sulfidization in the troctolite experiment was hence inhibited the serpentinite experiment showed very little reaction and no sulfide formation our results show that olivine rich seafloor lithologies are not very prone to sulfidation basaltic crust appears to have a larger potential to form sulfide deposits in some experiments pyrrhotite did not form although h2 h2s activities plot in the pyrrhotite stability field of the fe o s phase diagram we suggest that the higher oxidation state in basalt allows for the precipitation of pyrite which is not stable under the more reducing conditions prevailing where water interacts with olivine rich lithologies

carbon dioxide reaction processes in a model brine aquifer at 200 c and 200 bars implications for geologic sequestration of carbon the reactive behavior of supercritical co2 under conditions relevant to geologic storage and sequestration of c is largely unknown experiments were conducted in a flexible cell hydrothermal apparatus to determine the extent of fluid rock reactions in addition to carbonate mineral precipitation that may occur in a brine aquifer aquitard system that simulates a saline aquifer storage scenario the system was held at 200 c and 200 bars for 59 days 1413 h to approach steady state then injected with co2 and allowed to react for another 80 days 1924 h in addition to magnesite precipitation silicate minerals quartz plagioclase microcline and biotite in the aquifer and the aquitard display textures etch pits mineralization indicating significant reaction changes in elemental abundances in the brine following addition of co2 include ph decrease and enrichment in cl partly due to supercritical co2 desiccation of the brine geologic sequestration systems have potential for geochemical reactions that extend beyond simple aqueous dissolution of co2 and precipitation of carbonate these reactions may produce geochemical and geotechnical consequences for sequestration and provide important characteristics for monitoring and evaluation of stored co2 a n understanding of multi phase equilibrium relationships between supercritical co2 and aquifer brine systems also raises new questions for a variety of geologic systems multi phase fluid equilibria may for example account for the large amounts and heterogeneous distributions of calcite cement in a wide variety of geologic systems particularly in sedimentary basin sandstones published by elsevier science ltd

origin of the lethal gas burst from lake monoun cameroun abstract on 15 august 1984 a lethal gas burst issued from a submerged 96 m deep crater in lake monoun in cameroun western africa killing 37 people the event was associated with a landslide from the eastern crater rim which slumped into deep water waters below 50 m are anoxic dominated by high fe 2 600 mg l and hco 3 1900 mg l anoxic and supersaturated with siderite which is a major component of the crater floor sediments the unusually high fe 2 levels are attributed to reduction of laterite derived ferric iron gradually brought into the lake as loess and in river input sulfur compounds are below detection limits in both water and gas gases effervescing from depressurized deep waters are dominantly co 2 with minor ch 4 having 13 c of 7 18 and 54 8 per mil respectively bacterial decomposition of organic matter may account for the methane but 14 c of lake water indicates that only 10 of the carbon is modern giving an apparent age of 18 000 years the dominant source of carbon is therefore attributed to long term emission of co 2 as volcanic exhalation from vents within the crater which led to gradual build up of hco 3 in the lake the density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 august which triggered overturn of the lake and caused nucleation of co 2 in the deep water the resultant ebullition of co 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high people travelling through the gas cloud were asphyxiated presumably from co 2 and suffered skin discoloration from unidentified components

geochemical constraints on chemolithoautotrophic metabolism by microorganisms in seafloor hydrothermal systems mixing of hydrothermal fluids and seawater at the ocean floor combined with slow reaction kinetics for oxidation reduction reactions provides a source of metabolic energy for chemolithotrophic microorganisms which are the primary biomass producers for an extensive submarine ecosystem that is essentially independent of photosynthesis thermodynamic models are used to explore geochemical constraints on the amount of metabolic energy potentially available from chemosynthetic reactions involving s c fe and mn compounds during mixing of hydrothermal fluids with seawater for the vent fluid used in the calculations epr 21 n obs the model indicates that mixing environments are favorable for oxidation of h2s ch4 fe2 and mn2 only below 38 c with methanogenesis and reduction of sulfate or s favored at higher temperatures suggesting that environments dominated by mixing provide habitats for mesophilic but not thermophilic aerobes and thermophilic but not mesophilic anaerobes a maximum of 760 cal per kilogram vent fluid is available from sulfide oxidation while between 8 and 35 cal kg vent fluid is available from methanotrophy methanogenesis oxidation of fe or mn or sulfate reduction the total potential for chemosynthetic primary production at deep sea hydrothermal vents globally is estimated to be about 1013 g biomass per year which represents 0 02 of the global primary production by photosynthesis in the oceans thermophilic methanogens and sulfate and s reducers are likely to be the predominant organisms in the walls of vent chimneys and in the diffuse mixing zones beneath warm vents where biological processes may contribute to the high methane concentrations of vent fluids and heavy 34s32s s ratios of vent sulfide minerals the metabolic processes taking place in these systems may be analogs of the first living systems to evolve on the earth

carbonatization of oceanic crust by the seafloor hydrothermal activity and its significance as a co2 sink in the early archean abstract early archean 3 46 ga hydrothermally altered basaltic rocks exposed near marble bar eastern pilbara craton have been studied in order to reveal geological and geochemical natures of seafloor hydrothermal carbonatization and to estimate the co2 flux sunk into the altered oceanic crust by the carbonatization the basaltic rocks are divided into basalt and dolerite and the basalt is further subdivided into type i having original igneous rock textures and type ii lacking these textures due to strong hydrothermal alteration primary clinopyroxene phenocrysts are preserved in some part of the dolerite samples and the alteration mineral assemblage of dolerite chlorite epidote albite quartz actinolite indicates that the alteration condition was typical greenschist facies in other samples all primary minerals were completely replaced by secondary minerals and the alteration mineral assemblage of the type i and type ii basalts chlorite k mica quartz carbonate minerals albite is characterized by the presence of k mica and carbonate minerals and the absence of ca al silicate minerals such as epidote and actinolite suggesting the alteration condition of high co2 fugacity the difference of the alteration mineral assemblages between basalt and dolerite is probably attributed to the difference of water rock ratio that in turn depends on their porosity carbonate minerals in the carbonatized basalt include calcite ankerite and siderite but calcite is quite dominant the 13c values of the carbonate minerals are 0 3 1 2 and mostly within the range of marine carbonate indicating that the carbonate minerals were formed by seafloor hydrothermal alteration and that carbonate carbon in the altered basalt was derived from seawater whole rock chemical composition of the basaltic rocks is essentially similar to that of modern mid ocean ridge basalt morb except for highly mobile elements such as k2o rb sr and ba compared to the least altered dolerite all altered basalt samples are enriched in k2o rb and ba and are depleted in na2o reflecting the presence of k mica replacing primary plagioclase in addition noticeable co2 enrichment is recognized in the basalt due to the ubiquitous presence of carbonate minerals but there was essentially neither gain nor loss of cao this suggests that the co2 in the hydrothermal fluid seawater was trapped by using ca originally contained in the basalt the cao co2 ratios of the basalt are generally the same as that of pure calcite indicating that ca in the basalt was almost completely converted to calcite during the carbonatization although mg and fe were mainly redistributed into noncarbonate minerals such as chlorite the carbon flux into the early archean oceanic crust by the seafloor hydrothermal carbonatization is estimated to be 3 8 1013 mol yr based on the average carbon content of altered oceanic crust of 1 4 10 3 mol g the alteration depth of 500 m and the spreading rate of 1 8 1011 cm2 yr this flux is equivalent to or greater than the present day total carbon flux it is most likely that the seafloor hydrothermal carbonatization played an important role as a sink of atmospheric and oceanic co2 in the early archean

a geochemical study of oil migration at source rock reservoir contacts stable isotopes abstract whereas organic geochemical analyses of oils and potential source rocks have enabled correlations to be drawn and have been utilized to suggest modes of migration only limited data has been published relating a known source rock in contact with an oil filled reservoir this paper presents initial results from the examination of an approximately 100 m continuous core through the kimmeridge shale of the north sea the variability in extractable source rock hydrocarbon contents kerogen toc asphaltene and their carbon isotopic contents are documented nitrogen isotopic content of kerogens and asphaltenes as well as kerogen and asphaltene ton are relatively constant carbon isotopic compositions of kerogen extractable hydrocarbons and asphaltenes covaried significantly as did nitrogen isotopic compositions of kerogen and asphaltenes average isotopic compositions of the asphaltene free extracts and asphaltenes were nearly identical to the oil in the primary reservoir small chemical differences are noted among extracts

highly alkaline high temperature hydrothermal fluids in the early archean ocean abstract based on the petrology of hydrothermally altered archean basaltic greenstones thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high temperature 350 c hydrothermal fluid in an archean subseafloor basalt hosted hydrothermal system the results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high co2 condition and predict a generation of sio2 rich fe poor hydrothermal fluids in the archean subseafloor hydrothermal system the chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic neutral seawater are characterized by inverse ph and chemical polarity to modern hydrothermal systems leading to extensive precipitation of silica and iron oxyhydroxides on under the seafloor such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike the mechanism of silicification and the ph controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the archean ocean such high temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life

balloon borne observations of stratospheric aerosol and condensation nuclei during the year following the mt st helens eruption thirty six balloon flights carrying various particle counters are used to study the stratospheric aerosol layer during the year following the mt st helens volcanic eruption which occurred on may 18 1980 aerosol enhancements were observed to altitudes as high as 26 km for the first time stratospheric condensation nuclei r 0 01 m were observed in conjunction with a volcanic eruption time variation of these small particles suggests their continuous nucleation for at least 1 months after the eruption particles formed in the stratosphere following this eruption were generally smaller than those observed following the eruption of fuego in 1974 this may be related to a relative excess in condensation sites at the time of the mt st helens eruption thus resulting in smaller particles due to increased competition for the available sulfurous vapors involved in the nucleation process the excess mass concentration of volatile material which remained in the stratosphere about 6 months after the eruption was of the order 10 7g cm 2 column and if assumed to be uniform over the northern hemisphere would amount to about 0 25 tg this is about 3 times the background level but only one half that injected by the eruption of fuego in 1974

a chronology of annual mean effective radii of stratospheric aerosols from volcanic eruptions during the twentieth century as derived from ground based spectral extinction measurements stratospheric extinction can be derived from ground based spectral photometric observations of the sun and other stars as well as from satellite and aircraft measurements available since 1979 and is found to increase after large volcanic eruptions this increased extinction shows a characteristic wavelength dependence that gives information about the chemical composition and the effective or area weighted mean radius of the particles responsible for it known to be tiny aerosols constituted of sulfuric acid in a water solution the stratospheric particles at midlatitudes exhibit a remarkable uniformity of their column averaged effective radii r sub eff in the first few months after the eruption considering the seven largest eruptions of the twentieth century r sub eff at this phase of peak aerosol abundance is approx 0 3 micrometers in all cases a year later r sub eff either has remained about the same size almost certainly in the case of the katmai eruption of 1912 or has increased to approx 0 5 micrometers definitely so for the pinatubo eruption of 1991 the reasons for this divergence in aerosol growth are unknown

decrease of seawater co2 concentration in the late archean an implication from 2 6 ga seafloor hydrothermal alteration abstract before continents attained a critical aerial dimension on the early earth hydrothermal carbonation of subseafloor crust is considered to have played the dominant role in fixing co 2 from the co 2 rich ocean however it is uncertain how and when the seawater co 2 level decreased and the strong carbonation of oceanic crust ceased here we report the depth profiles of the volume concentration and the carbon isotopes of calcites in the late archean paleoproterozoic volcanic rocks fortescue and hamersley groups exposed in the southwestern pilbara craton western australia the depth profiles indicate that 2 6 ga seafloor hydrothermal carbonation is well preserved in the study area and that the co 2 content of subseafloor crust per seafloor unit area is estimated to be clearly lower than those in the early and middle archean and similar to the phanerozoic equivalents this suggests that the co 2 concentration in seawater decreased from the middle archean to the late archean this period broadly corresponds to the time of the first appearance of supercontinent on earth the amalgamation of continents has the potential to decrease seawater co 2 concentration due to the removal of platform carbonate to continental interior subsequent fragmentation of supercontinent likely cause the carbonate deposition around newly created continental shelves it is therefore implied that seawater co 2 concentration in the early earth was lowered by not only the hydrothermal carbonation of subseafloor crust but also through the formation and breakup of supercontinent in the late archean

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

experimental evaluation of in situ co2 water rock reactions during co2 injection in basaltic rocks implications for geological co2 sequestration 1 deep aquifers are potential long term storage sites for anthropogenic co2 emissions the retention time and environmental safety of the injected co2 depend on geologic and physical factors and on the chemical reactions between the co2 the aquifer water and the host rocks the ph buffer capacity of the aquifer water and the acid neutralization potential of the host rocks are important factors for the permanent stabilization of the injected co2 mafic rocks such as basalt which primarily consists of ca mg silicate minerals have a high acid neutralization capacity by providing alkaline earth elements that form stable carbonate minerals the carbonate minerals formed thus sequester co2 in a chemically stable and environmentally benign form in this study we present results from a small scale co2 injection test in mafic and metasedimentary rocks the injection test was conducted using a single well push pull test strategy co2 saturated water ph 3 5 was injected into a hydraulically isolated and permeable aquifer interval to study the acid neutralization capacity of ca mg silicate rocks and to estimate in situ cation release rates release rates for ca mg and na were calculated by use of solute compositions of water samples retrieved after the co2 injection the incubation time of the injected solution within the aquifer and geometric estimates of the reactive surface area of the host rocks our results confirm rapid acid neutralization rates and water rock reactions sufficient for safe and permanent storage of co2 carbonic acid was neutralized within hours of injection into a permeable mafic aquifer by two processes mixing between the injected solution and the aquifer water and water rock reactions calculated cation release rates decrease with increasing ph that is confirmed by laboratory based experiments large differences between release rates obtained from the field and laboratory experiments may be mainly due to uncertainties in the estimation of the reactive surface area in the field experiment and in hydrological and geological factors our results underscore the importance of defining bulk rock dissolution rates under in situ conditions in order to evaluate target formations for permanent mineral sequestration of carbon dioxide

volcanic degassing hydrothermal circulation and the flourishing of early life on earth a review of the evidence from c 3490 3240 ma rocks of the pilbara supergroup pilbara craton western australia abstract new data gathered during mapping of c 3490 3240 ma rocks of the pilbara supergroup in the pilbara craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism for most cherts fossil hydrothermal fluid pathways are preserved as silica barite fe bearing veins that cut through the footwall and up to the level of individual bedded chert units but not above indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events silica barite fe bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units and occurred under alternating high sulphidation and low sulphidation conditions these veins provided pathways to the surface for elements leached from the footwall e g si ba fe and volcanogenic emissions from underlying felsic magma chambers e g co 2 h 2 s hs so 2 stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of warrawoona group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and or degassing of these magmas heat from these intrusions drove episodes of hydrothermal circulation listric normal faulting during caldera collapse produced basins with restricted circulation of seawater eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components thereby providing habitats suitable for early life forms fossil stromatolites from two distinct stratigraphic units in the north pole dome grew in shallow water conditions but in two very different geological settings with different morphologies stratiform and domical stromatolites in the stratigraphically lower c 3490 ma dresser formation of the warrawoona group are intimately associated with barite and chert precipitates from hydrothermal vents suggesting that component microbes may have been chemoautotrophic hyperthermophiles evidence of shallow water to periodically exposed conditions active growth faulting and soft sediment deformation indicates that the volcanogenic emissions were erupted into a shallow water tectonically active caldera and concentrated therein to produce an extreme habitat for early life widespread conical and pseudocolumnar stromatolites in the c 3400 ma strelley pool chert at the base of the unconformably overlying kelly group occur in shallow marine platform carbonates silicification was the result of later hydrothermal circulation driven by heat from the overlying newly erupted euro basalt the markedly different morphology and geological setting of these only slightly younger stromatolites compared with the dresser formation suggests a diversity of microbial life on early earth the biogenicity of putative microfossils from this and younger hydrothermal silica veins in the warrawoona group remains controversial and requires further detailed study

abiogenic methanogenesis during experimental komatiite serpentinization implications for the evolution of the early precambrian atmosphere abstract hydrothermal alteration of oceanic ultramafic rocks can produce significant abiotic methane as a byproduct however the abundance of peridotites is limited in the modern basaltic oceanic crust abiogenic methanogenesis was likely more productive in the early precambrian when komatiitic volcanism delivered a much larger proportion of ultramafic material to the crust it is therefore possible that hydrothermal alteration in the hadean and archean could have led to a higher methane flux to the atmosphere than today potentially influencing the average surface temperature of the early earth this hypothesis was tested in a series of experiments in which natural and synthetic komatiite powders were reacted with an aqueous solution containing isotopically labeled formic acid at 300 c and 350 bars over 2 months experiments containing the natural powder generated labeled methane 13 ch 4 at a rate 5 8 faster than concurrent experiments containing the synthetic komatiite a similar difference was also observed between the natural komatiite and previous experiments on olivine serpentinization at the same conditions faster rates of methanogenesis in the natural komatiite experiments could be due to catalysis by magnesiochromite which was present only in the natural komatiites however this was ruled out because parallel experiments containing additional magnesiochromite failed to increase methane yields the most likely catalysts of the remaining candidate minerals were deduced to be ni sulfides common accessory minerals in komatiites that have previously been shown to accelerate organic reactions because ni sulfides were particularly abundant in archean komatiites the experiments imply that methane yields during seafloor alteration were higher on the early earth than today this inference in combination with the assumptions of faster crustal production rates and greater volumetric proportions of ultramafic lithologies leads to the conclusion that methane flux from serpentinization of an archean komatiite bearing oceanic crust was likely higher than that from metamorphism of the modern oceanic crust incorporation of this result into existing geodynamic and atmospheric models suggests that alteration of the archean seafloor may have contributed to the regulation of temperature of the paleoatmosphere however additional sources of greenhouse gases are required to solve the faint young sun paradox for the early archean

hydrothermal alteration of a seamount complex on la palma canary islands implications for metamorphism in accreted terranes the hydrothermal metamorphism of a sequence of pliocene age seamount extrusive and volcaniclastic rocks on la palma canary islands is characterized by a relatively complete low pressure high temperature facies series encompassing the zeolite prehnite pumpellyite and greenschist facies the observed mineral zonations imply metamorphic gradients of 200 300 c km the metamorphism of the seamount at least in its core region is distinct from ocean floor metamorphism the former is characterized by a serially continuous facies series encompassing zeolite prehnite pumpellyite and greenschist assemblages and the latter by a discontinuous metamorphic gradient in which prehnite pumpellyite assemblages are absent these metamorphic features presumably reflecting fundamental thermal tectonic differences between extending oceanic crust at mid oceanic ridges vs the more static crust underlying seamount volcanoes should aid in the recognition of incoherent fragments of seamount metamorphic rocks within accreted terranes which typically have undergone subsequent higher pressure temperature regional metamorphism albeit to comparable grades

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

short term biomarker variability in the monterey formation santa maria basin abstract forty eight samples of a 370 ft miocene monterey formation core from the union leroy 51 18 well santa maria basin california are examined for source rock potential and molecular distributions total organic carbon content rock eval pyrolytic yield vitrinite reflectance and distribution of regular steranes tricyclic and pentacyclic terpanes and aromatic steroids are measured the present day temperature range through the sampled interval is estimated to be less than 5 c maturity differences among samples are negligible source rock potential and molecular distribution differences are considered to arise entirely from the effects of source input diagenesis including lithologic effects and migration the sampled section is comprised of siliceous and phosphatic carbonate lithofacies and covariances between geochemical parameters source potential and biomarker distribution and lithofacies are recognized several molecular parameters change systematically with depth lithology including ethylcholestane ratios and c 20 and c 22 sterane and hopane epimer ratios the siliceous lithofacies possesses higher moretane hopane tricyclic pentacyclic terpane and sterane terpane ratios and lower mono mono tri aromatic steroid ratios bisnorhopane hopane ratios are up to 40 times higher in the phosphatic carbonate lithofacies than in the siliceous lithofacies increased relative concentrations of aromatic steroids are attributed to sulfur sterol reactions during very early diagenesis whereas increased relative bisnorhopane amounts are considered to result from massive input of specific anaerobic biota although kerogen elemental ratios change abruptly at the lithofacies boundary molecular distributions within the extractable organic matter change gradually beginning about 30 ft 9m above this interface this gradual change is tentatively attributed to upward migration of hydrocarbons originating in the phosphatic carbonate lithofacies probably through fractures within the lower part of the siliceous lithofacies interval

the in situ ph of hydrothermal fluids at mid ocean ridges abstract here we report the first in situ ph of hydrothermal vent fluids at mid ocean ridges measurements were made during dives with dsv alvin to the main endeavour field juan de fuca ridge and the east pacific rise at 21 n and 9 10 n using solid state electrochemical sensors vent fluid temperature and pressure ranged from 180 to 384 c and 220 to 250 bar respectively ph in situ of the highest temperature vent fluid is only slightly acidic 5 1 5 4 although sharply lower values occur at the seawater vent fluid interface knowledge of ph in situ is essential for unravelling the complex geochemical and biogeochemical processes controlling the evolution of seafloor hydrothermal systems

decoupling photochemical fe ii oxidation from shallow water bif deposition abstract oxidized fe minerals in archean paleoproterozoic banded iron formations bifs are commonly taken to indicate the presence of biogenic o 2 or photosynthetic fe ii oxidizing bacteria in the oceans photic zone however at least one viable abiogenic oxidation mechanism has been proposed prior to the rise of atmospheric oxygen and the development of a protective ozone layer the earth s surface was subjected to high levels of ultraviolet radiation bulk ocean waters that were anoxic at this time could have supported high concentrations of dissolved fe ii under such conditions dissolved ferrous iron species such as fe 2 and fe oh would have absorbed radiation in the 200 400 nm range leading to the formation of dissolved ferric iron fe iii which in turn would have hydrolyzed to form ferric hydroxide fe oh 3 at circumneutral ph cairns smith a g 1978 precambrian solution photochemistry inverse segregation and banded iron formations nature 76 807 808 braterman p s cairns smith a g and sloper r w 1983 photo oxidation of hydrated fe 2 significance for banded iron formations nature 303 163 164 this process has been invoked to account for bif deposition without need for biology francois l m 1986 extensive deposition of banded iron formations was possible without photosynthesis nature 320 352 354 here we evaluate the potential importance of photochemical oxidation using a combination of experiments and thermodynamic models the experiments simulate the chemistry of ambient precambrian seawater mixing with fe ii rich hydrothermal fluids with and without uv irradiation we find that if fe ii was effused from relatively shallow seamount type vent systems directly into an anoxic photic zone the photochemical contribution to solid phase precipitation would have been negligible instead most of the fe ii would have precipitated rapidly as an amorphous precursor phase to the ferrous silicate mineral greenalite fe 3 si 2 o 5 oh 4 and or the ferrous carbonate siderite feco 3 depending on different simulated atmospheric pco 2 levels conversely in experiments where fe ii was exposed either to phototrophic fe ii oxidizing bacteria or to o 2 ferric hydroxide formed rapidly and the precipitation of ferrous iron phases was not observed if as suggested on mass balance grounds bif deposition requires that fe be sourced from shallow seamount type systems then we are driven to conclude that oxide facies bif are the product of a rapid non photochemical oxidative process the most likely candidates being direct or indirect biological oxidation and that a significant fraction of bif could have initially been deposited as ferrous minerals

free energy distribution and hydrothermal mineral precipitation in hadean submarine alkaline vent systems importance of iron redox reactions under anoxic conditions abstract thermodynamic calculations of mixing between hypothetical seawater and hydrothermal fluid in the hadean deep ocean were carried out to predict saturation states of mineral precipitates and redox reactions that could occur in hadean submarine alkaline hydrothermal systems associated with the serpentinization of ultramafic rocks in the calculations the seawater was assumed to be weakly acidic ph 5 5 and to include carbon dioxide ferrous iron and silica with or without nitrate while the hadean hydrothermal fluid was assumed to be highly alkaline ph 11 and to contain abundant molecular hydrogen methane and bisulfide based on the archean geologic record the modern low temperature alkaline hydrothermal vent fluid lost city field and experimental and theoretical considerations the modeling indicates that potential mineral precipitates in the mixing zone hydrothermal chimney structures could consist mainly of iron sulfides but also of ferrous serpentine and brucite siderite and ferric iron bearing minerals such as goethite hematite and or magnetite as minor phases the precipitation of ferric iron bearing minerals suggests that chemical iron oxidation would be made possible by ph shift even under anoxic condition in the mixing zone comprising an inorganic barrier precipitated at the interface of the two contrasting solutions various redox reactions release free energy with the potential to drive endergonic reactions assuming the involvement of coupling inorganic protoenzymes hydrogenotrophic methanogenesis and acetogenesis long considered the most ancient forms of biological energy metabolisms are able to achieve higher maximum energy yield 0 5 kj kg hydrothermal fluid than those in the modern serpentinization associated seafloor hydrothermal systems e g kairei field furthermore the recently proposed methanotrophic acetogenesis pathway was also thermodynamically investigated it is known that methanotrophic acetogenesis would require additional exergonic reactions to compensate its most endergonic methane to methanol conversion reaction at the oxidative entry to the metabolic pathway our calculations support the view that this thermodynamic barrier could be overcome by the reduction of nitrate in seawater at low temperature as previously suggested however the thermodynamic calculations also revealed that the reduction of ferric iron bearing minerals would occur at the outer margin and within the hydrothermal chimney wall the maximum available energy of iron reducing methanotrophic acetogenesis was calculated to be 0 25 0 35 kj kg hydrothermal fluid although this value is lower than theoretically available through nitrate reduction which approaches 0 45 1 25 kj kg hydrothermal fluid on the outer cool margins of a putative hadean alkaline chimney it is higher than that of sulfate reducing anaerobic oxidation of methane in the lost city field these results suggest that iron reduction had the potential to drive methanotrophy and that the hadean hydrothermal mixing zone was energetically more favorable to methanotrophy than previously thought we conclude that iron oxidation and reduction in oxyhydroxides probably played important roles in the early evolution of energy metabolisms in the hadean alkaline hydrothermal system

evolution of the stratospheric aerosol in the northern hemisphere following the june 1991 volcanic eruption of mount pinatubo role of tropospheric stratospheric exchange and transport since the eruption of mount pinatubo in june 1991 measurements of particle size and concentration have intermittently been carried out from an er 2 aircraft at altitudes of up to 21 km at midlatitudes and high latitudes in the northern hemisphere they show the evolution and purge of the volcanic aerosol to be due to an interaction of aerosol mechanics with tropospheric stratospheric exchange processes transport and mixing during the first 5 months after the eruption the volcanic plume spread to higher latitudes in laminae and filaments producing steep spatial gradients in the properties of the stratospheric aerosol at the same time the concentration of newly formed particles in the plume rapidly decreased toward background values as a result of coagulation while particle size and aerosol surface area continued to increase by december 1991 the particle number mixing ratios and aerosol surface area mixing ratios had become spatially uniform over a wide range of latitudes above 18 km the surface area mixing ratios peaked in this region of the stratosphere at 35 times their background values in the winter of 1992 the corresponding condensed mass mixing ratio enhancement was by a factor of 200 after the winter of 1992 a gradual removal of the volcanic mass began and initially was dominated by sedimentation above 18 km the aerosol surface area mixing ratio thus decreased by an order of magnitude over 2 5 years and the aerosol volume or condensed mass mixing ratio decayed by an order of magnitude over approximately 1 7 years below 18 km the purging of the pinatubo aerosol at mid latitudes appeared sporadic and disorderly and was strongly influenced by episodal rapid quasi isentropic transport and dilution by tropical air of tropospheric origin having high condensation nuclei mixing ratios but low mixing ratios of aerosol surface area or condensed mass compared to the volcanic aerosol

chemical plumes from low temperature hydrothermal venting on the eastern flank of the juan de fuca ridge we report evidence for chemical anomalies in the water column from low temperature ridge flank hydrothermal venting during cruises in 1992 and 1994 samples were taken from the water column for trace metals nutrients dissolved gases and particles near each of three basaltic outcrops overlying 3 5 m y old crust on the eastern flank of the juan de fuca ridge in cascadia basin the water column above one of these outcrops baby bare which rises about 70 m above a flat turbidite plain was the most thoroughly sampled thermal chemical mn fe 3he ch4 and o2 and particulate anomalies in the water column confirm the existence of 1 early diagenesis of organic matter in seafloor sediment which produces a flux of dissolved metals and nutrients to bottom seawater 2 hydrothermal emissions which are both focused spring like and diffuse and 3 resuspension of sediment by turbulent flow of tidal currents about a topographical high on the basis of data from the water column and thermal and chemical pore water data from 46 piston and gravity sediment cores near and on baby bare flankflux 90 and 92 we constrain the composition of seawater in basement and thus the composition of spring like water given this composition no measurable dissolved silica or phosphate hydrothermal anomalies are expected in the water column

geochemical controls on hydrothermal fluids from the kairei and edmond vent fields 23 25 s central indian ridge prior to 2000 no mid ocean ridge hydrothermal systems were identified and sampled in the indian ocean the kairei field central indian ridge was discovered and sampled in 2000 gamo et al 2001 hashimoto et al 2001 this paper reports the chemical composition of hydrothermal fluids collected in 2001 from both the kairei and newly discovered edmond hydrothermal systems data are used to infer subsurface processes and conditions at the two sites as well as to place them within the global context of known hydrothermal sites on the mid ocean ridge system while both sites are located on the intermediate spreading central indian ridge their hydrologic systems have affinities with those observed on slow spreading ridges although the compositions of fluids from the four individual vents sampled at edmond and the three individual vents sampled at kairei vary respectively our interpretation is that a single source fluid at each site is subsequently modified by processes including phase separation subsurface mixing with seawater and deposition and or remobilization of metal sulfide deposits to generate the observed range of compositions both fields are located 6 km from the neovolcanic zone on steps on the east wall of the axial valley with the edmond field 160 km north of kairei and almost 1000 m deeper 3300 versus 2450 m the edmond fluids are extremely hot with maximum measured temperatures of 382 c compared to 365 c for kairei all of the fluids sampled have chlorinities greater than local ambient seawater due to phase separation of seawater at supercritical conditions visual observations suggest both sites have been active for a substantial period of time again similar to observations of slow spreading ridges our chemical data suggest that the substrate underlying kairei is highly altered while that at edmond is not significant albitization appears to be occurring below the edmond field but not at kairei the edmond fluids are by far the hottest brines yet observed venting from a mid ocean ridge hydrothermal site resulting in unusually high concentrations of several transition metals

geologic evidence for archean atmospheric and climatic evolution fluctuating levels of co2 ch4 and o2 with an overriding tectonic control the 3 5 3 2 ga sedimentary record shows evidence of surface temperatures of 70 15 c nahcolite nahco 3 as a primary evaporitic mineral and an aggressive weathering regime even in the absence of land vegetation these features are best explained by a mixed ch 4 and co 2 atmospheric greenhouse in which ch 4 co 2 ratios were 1 and pco 2 was at least 100 1000 times the present value and perhaps as high as several bars the formation of large areas of continental crust at 3 2 3 0 ga including the kaapvaal and pilbara cratons resulted in the gradual depletion of atmospheric co 2 through weathering by 2 9 2 7 ga declining pco 2 was associated with climatic cooling and siderite free soils transitory ch 4 co 2 ratios of 1 may have resulted in the sporadic formation of organic haze from atmospheric ch 4 reflected in one or more isotopic excursions involving global deposition of abnormally 1 3 c depleted organic c surface temperatures of 60 c after 2 9 ga may have also increased the distribution and productivity of oxygenic photosynthetic microbes eventual lowering of new continental blocks by erosion reduced loss of atmospheric co 2 due to weathering and continued long term tectonic recycling of co 2 resulted in rising pco 2 and decreasing ch 4 co 2 ratios in the later archean and eventual reestablishment of a mainly co 2 greenhouse similar events may have been repeated in the latest archean and earliest proterozoic but gradually rising production of o 2 effectively kept ch 4 co 2 ratios to 1 at this time

unsynchronized evolution of salinity and ph of a permian alkaline lake influenced by hydrothermal fluids a multi proxy geochemical study abstract hyperalkaline waters display unusually high productivity which makes them prime targets in the search for life elsewhere in the solar system however the formation mechanisms of alkaline waters are not well understood because the response of biogeochemical proxies to these conditions is poorly constrained to address this issue we assessed the influence of hydrothermal fluids on the salinity and ph of alkaline lakes based on a case study of an early permian paleo alkaline lake 290 ma fengcheng formation in the mahu sag northwestern junggar basin china multiple proxies indicate that hydrothermal fluids in the central salt rock and marginal tuff mudstone areas of the fengcheng formation were affected by deep and shallow hydrothermal fluids respectively a small part of the transitional area was affected by hydrothermal fluids with a hybrid nature the hydrothermal fluid activity gradually weakened up section in all areas while salinity inferred from carbon and oxygen isotopes increased and ph inferred from nitrogen isotopes and mineralogy decreased from hyperalkaline 9 25 to moderately alkaline conditions these trends suggest that hyperalkalinity was largely driven by hydrothermal processes in contrast evaporation which dominated towards the end of the lake s lifetime maintained an elevated ph but did evidently not have a similarly strong effect as hydrothermal fluids our data suggest that hydrothermal activity and evaporation in closed lacustrine basins have the potential to create extreme conditions for the formation of alkaline lakes the evolution of salinity and ph may not necessarily be synchronized

evolution of the composition of seawater through geologic time and its influence on the evolution of life abstract the redox state of the surface environment of the early earth is still controversial and a detailed and quantitative estimate is still lacking we carried out in situ analyses of major trace and rare earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea deposits in order to eliminate secondary carbonate and contamination of detrital materials and to estimate the redox condition of seawater through time based on the ce content and anomalies of the carbonate minerals at given parameters of atmospheric co2 content pco2 and ca content of seawater we calculated the oxygen contents of shallow and deep seawater respectively the results show that the oxygen content of the deep sea was low and constant until at least 1 9 ga the oxygen content of shallow seawater increased after 2 7 ga but fluctuated it became quite high at 2 5 and 2 3 ga but eventually increased after the phanerozoic in addition the calculation of a high pco2 condition shows that seawater was more oxic even in the archean than at present suggesting a relatively low pco2 through geologic time our detailed calculations from compositions of carbonate minerals in three gorge area south china show a low oxygen content of seawater after the snowball earth until the late ediacaran an increase in the late ediacaran and a significant decrease around the precambrian cambrian and nemakit daldynian tommotian boundaries these variations were possibly caused by global regression and dissolution of methane hydrates

ongoing hydrothermal activities within enceladus analysis of silicon rich nanometre sized dust particles near saturn shows them to consist of silica which was initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring their properties indicate their ongoing formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus hsiang wen hsu et al have analysed the silicon rich nanometre sized dust stream particles in the saturnian system using the cosmic dust analyser cda onboard the cassini spacecraft with the help of experiments and modelling the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on enceladus and released by sputter erosion in saturn s e ring their properties indicate their formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus detection of sodium salt rich ice grains emitted from the plume of the saturnian moon enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is or has been in contact with rock1 2 gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3 these findings imply rock water interactions in regions surrounding the core of enceladus the resulting chemical footprints are expected to be preserved in the liquid and subsequently transported upwards to the near surface plume sources where they eventually would be ejected and could be measured by a spacecraft4 here we report an analysis of silicon rich nanometre sized dust particles5 6 7 8 so called stream particles that stand out from the water ice dominated objects characteristic of saturn we interpret these grains as nanometre sized sio2 silica particles initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring the composition and the limited size range 2 to 8 nanometres in radius of stream particles indicate ongoing high temperature 90 c hydrothermal reactions associated with global scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of enceladus

seafloor hydrothermal alteration at an archaean mid ocean ridge a hydrothermally metamorphosed altered greenstone complex capped by bedded cherts exposed in the north pole pilbara carton western australia is interpreted as an accretionary complex it is distinc tive in being characterised by both duplex structure and an oceanic crust stratigraphy this complex is shown to represent an archaean upper oceanic crust with a mid ocean ridge hydrothermal meta morphism that increases in grade stratigraphically downward three mineral zones have been defined zone a of the zeolite facies the prehnite pumpellyite facies or the lower greenschist facies at high xco2 condition zone b of the greenschist facies and zone c of the greenschist amphibolite transition facies in zone a metabasites ca al silicates including ca zeolites prehnite and pumpellyite are absent and epidote clinozoisite is extremely rare instead abundant carbonates are present with chlorite suggesting high xco2 composition in the fluid on the other hand in zones b and c metabasites where ca amphibole epidote clinozoisite chlorite ca na plagioclase are the dominant assemblages carbonate is not identified the metamorphic conditions boundary of zones b c were estimated to be about 350 uc at a pressure of 0 5 kbar fluid compositions coexisting with archaean greenstones at the transition between zones b and c were estimated by thermodynamic calculation in the cafmasch system t 350 370 uc p 150 1000 bar at xco2 of 0 012 0 140 such values are higher than present day vent fluids collected near mid ocean ridges with low xco2 values up to 0 005 the archaean seawater depth at the mid ocean ridge was estimated to be 1600 m at xco2 0 06 using a depth to boiling point curve for a fluid the carbonation due to high xco2 hydrothermal fluids occurred near the ridge axis before or was coincident with ridge metamorphism

the effect of temperature on metal mobility in subseafloor hydrothermal systems constraints from basalt alteration experiments abstract crystalline basalt was reacted with a na ca k cl fluid of seawater chlorinity at 400 350 and 300 c 400 bar and a fluid rock mass ratio of 1 to assess the effect of temperature on metal mobility in ridge crest hydrothermal systems basalt alteration at 400 c yielded a fluid chemistry characterized by high zn cu fe mn sio 2 h 2 s and h 2 concentrations lowering temperature to 350 and then to 300 c caused dissolved metal concentrations to decrease drastically black smoker vent fluids generally have measured temperatures 355 c the dissolved concentrations of zn cu fe and mn observed in these fluids however could only be achieved or exceeded during the 400 c phase of the experiment indicating that hot spring fluids have lost heat and possibly dissolved fe and base metals on ascent to the seafloor from a high temperature reaction zone the relative rates at which zn cu fe and mn achieve new steady state concentrations in response to temperature reduction during basalt alteration are cu fe zn mn thus dissolved zn and especially mn concentrations are more likely to record accurately temperatures characterizing subseafloor reaction zones while fe and cu which respond rapidly to changes in temperature are likely to precipitate along fluid flow paths especially in near seafloor locations this trend is confirmed by the relative abundance of dissolved metals in hot spring fluids variably influenced by heat loss processes calculations suggest that hot spring fluids may lose heat by conduction through sulfide mounds and chimney walls at flow rates observed for many vent systems since heat loss processes influence the chemistry especially dissolved metals as well as measured temperatures of axial hot springs fluids these effects must be taken into account to model accurately phase relations and fluid mineral equilibria in deeply seated subseafloor reaction zones

the 1982 eruptions of el chichon volcano mexico 2 observations and numerical modelling of tephra fall distribution tephra fallout from the a 1 march 29 0532 ut b april 4 0135 ut and c april 4 1122 ut 1982 explosive eruptions of el chichon produced three tephra fall deposits over southeastern mexico bidirectional spreading of eruption plumes as documented by satellite images was due to a combination of tropospheric and stratospheric transport with heaviest deposition of tephra from the ene tropospheric lobes maximum column heights for the eruptions of 27 32 and 29 km respectively have been determined by comparing maximum lithic clast dispersal in the deposits with predicted lithic isopleths based on a theoretical model of pyroclast fallout from eruption columns these column heights suggest peak mass eruption rates of 1 1 108 1 9 108 and 1 3 108 kg s maximum column heights and mass eruption rates occured early in each event based on the normal size grading of the fall deposits sequential satellite images of plume transport and the production of a large stratospheric aerosol plume indicate that the eruption columns were sustained at stratospheric altitudes for a significant portion of their duration new estimates of tephra fall volume based on integration of isopach area and thickness yield a total volume of 2 19 km3 1 09 km3 dre dense rock equivalent or roughly twice the amount of the deposit mapped on the ground up to one half of the erupted mass was therefore deposited elsewhere as highly dispersed tephra

origin and mechanisms of k si metasomatism of ca 3 4 3 3ga volcaniclastic deposits and implications for archean seawater evolution examples from cherts of kittys gap pilbara craton australia and msauli barberton greenstone belt south africa abstract the effects of k si metasomatism during the formation of early archean replacement cherts have been quantified in this study by the investigation of two well known stratigraphic sections the msauli chert mc barberton greenstone belt south africa and the kittys gap chert kgc pilbara craton western australia the kgcs have a dacitic precursor similar to duffer formation dacites pilbara craton while the mcs are derived from al depleted komatiites similar to those from the weltevreden formation barberton greenstone belt mass balance calculations reveal that the volcaniclastic deposits had initial porosities of up to 85 vol for the kgc and of 65 vol for the mc secondary porosities 27 vol mc 8 vol kgc produced during k metasomatism are proportional to the dissolution of fe ca mg rich glass and precursor minerals komatiites have a higher chemical exchange potential than dacites each gram releasing 1 2 mmol fe2 2 8 mmol mg2 1 4 mmol ca2 and 1 1 mmol na to seawater together with 4 4 mmol o2 k metasomatism of 1 g of komatiite further implies an uptake of 0 67 mmol of k and 2 7 mmol of h the highest silica uptake is achieved for the kgc 82 mmol g of precursor this silica enrichment most likely operated in the water column and at the sediment water interface by sorption mechanisms on the surface of detrital particles and particulate organic matter as a result of seawater silica saturation acidic conditions ph 5 5 6 5 and hot temperatures 70 c favored the formation of k rich phyllosilicates by interaction with seawater during the early diagenetic alteration of the volcaniclastic particles the widespread occurrence of k si metasomatism in volcanic and sedimentary rocks can be regarded as a general alteration process of the early archean seafloor with a major influence on seawater composition the highly k selective metasomatism confirms previous studies suggesting that the archean ocean was acidic and probably in equilibrium with a co2 rich atmosphere

grain scale iron isotopic distribution of pyrite from precambrian shallow marine carbonate revealed by a femtosecond laser ablation multicollector icp ms technique possible proxy for the redox state of ancient seawater abstract the redox state of precambrian shallow seas has been linked with material cycle and evolution of the photosynthesis based ecosystem iron is a redox sensitive element and exists as a soluble fe ii species or insoluble fe iii species on earth s surface previous studies have shown that the iron isotopic ratio of marine sedimentary minerals is useful for understanding the ocean redox state although the redox state of the archean shallow sea is poorly known this is partly because the conventional bulk isotope analytical technique has often been used wherein the iron isotopic record may be dampened by the presence of isotopically different iron bearing minerals within the same sample here we report a microscale iron isotopic ratio of individual pyrite grains in shallow marine stromatolitic carbonates over geological time using a newly developed near infrared femtosecond laser ablation multicollector icp ms technique nir fs la mc icp ms we have determined that the grain scale iron isotopic distribution of pyrite from coeval samples shows a bimodal 2 7 and 2 3 ga or unimodal pattern 2 9 2 6 and 0 7 ga in particular pyrite from the 2 7 ga fortescue group shows a unique bimodal distribution with highly positive 1 0 defined as type 1 and negative 56fe values 1 8 defined as type 2 type 1 and 2 pyrites occasionally occur within different siliceous layers in the same rock specimen layer scale iron isotopic heterogeneity indicates that the iron isotopic ratios of the two types of pyrite are not homogenized by diagenesis after deposition some cubic pyrites have a core with a positive 56fe value 1 and a rim with a crustal 56fe value 0 the observed isotopic zoning suggests that the positive 56fe value is a primary signature at the time of stromatolite formation while secondary pyrite precipitated during diagenesis the positive 56fe value of type 1 and the large iron isotopic difference between type 1 and 2 2 8 suggest partial fe ii oxidation in the 2 7 ga shallow sea i e pyritization of 56fe enriched ferric oxyhydroxide type 1 and 56fe depleted fe2 aq in seawater type 2 type 2 pyrite was probably not produced by microbial iron redox cycling during diagenesis because this scenario requires a higher abundance of pyrite with 56fe of 0 than of 1 8 consequently the degree of fe ii oxidation in the 2 7 ga shallow sea can be estimated by a fe2 aq steady state model the model calculation shows that half the fe2 aq influx was oxidized in the seawater this implies that o2 produced by photosynthesis would have been completely consumed by oxidation of the fe2 aq influx grain scale iron isotopic distribution of pyrite could be a useful index for reconstructing the redox state of the archean shallow sea

collection of microparticles at high balloon altitudes in the stratosphere we report the collection of stratospheric particles at 34 36 km using balloon borne collectors the concentration of particles on the collection surfaces and element concentrations were measured on the majority of the particles using scanning electron microscope sem and proton induced x ray emission pixe analysis respectively particle morphologies elemental composition and electron diffraction data were obtained on a small number of the collected particles using transmission electron microscope tem techniques the concentration of particles between 0 045 lower imaging limit and 1 m in radius is several orders of magnitude above the blank levels on the collection surfaces while the concentration of particles above 1 m is near blank levels more than 106 submicron particles were collected the concentration of submicron particles is between 10 and 50 times the concentration expected at the sampling altitude based on models using the measured flux of extraterrestrial particles to the atmosphere the higher concentration of submicron particles may be due to contributions from volcanic particles inaccuracies in the influx of particles of this size to the earth or breakup of larger particles analysis of the elemental composition using pixe showed cl s ti fe br ni zr zn sr and cu in decreasing order of concentration elements below s could not be detected in the analysis cl s and br are believed to be present due to reaction of the collection surfaces and particles with atmospheric gases while the other elements are present in the particles the elemental composition of the particles does not allow an unequivocal origin to be assigned because particles from several of the possible sources listed above contain the measured elements tem analysis of 23 of the submicron particles showed 16 to be non graphitic the particles ranged from al rich silicates to almost pure fe to one containing almost exclusively ba and s none were definitely chondritic in composition this collection of particles complements existing collections obtained by aircraft they were colleted at much higher altitude and are predominantly submicron in size collection and analysis of particles at high altitudes using balloons presents unique challenges and opportunities in understanding the particle population in the stratosphere

on the temporal variation of stratospheric aerosol size and mass during the first 18 months following the 1982 eruptions of el chichon baloon borne particle counters at laramie and in southern texas are used to investigate the size and mass distribution of the aerosol which formed in the stratosphere during the first 18 months following the volcanic eruption of el chichon the latter appears to have reached a peak at laramie in early 1983 and began a decline in may measurements of average aerosol radius versus time are used to estimate a sulfuric acid concentration of about 10 to the 7th per cu cm 40 days after the eruption and a net acid vapor lifetime of 25 50 days in the 18 25 km altitude region

silica alteration zones in the barberton greenstone belt a window into subseafloor processes 3 5 3 3 ga ago abstract silicification of volcanic rocks ranging from komatiitic to dacitic in composition is a common phenomenon of the 3 5 to 3 2 ga old volcano sedimentary succession of the barberton greenstone belt silica enrichment occurs in zones several tens of metres thick at the top of volcanic sequences that are capped by sedimentary chert horizons sio2 contents increase upsection from the original igneous value up to 92 silicification is associated with a depletion of most elements commonly mobile during water rock interaction while k2o rb and ba are enriched in these zones some transition metals sc v and cr were immobile whereas ni and co and some other metals cu zn were mobile and are depleted the 18o values of volcanic rocks show a positive linear relationship with silica content and range from 9 0 to 17 3 the element depletion enrichment patterns and oxygen isotope data indicate low temperature c 100 150 c hydrothermal processes for the origin of the alteration zones the loss of most elements coupled with the addition of sio2 as well as ree systematics indicate high water rock ratios and a fluid ree composition typical of archaean seawater that had a 18o value of 0 hydrothermal activity is attributed to heat derived from cooling of volcanic rocks and a high regional heat flow in an oceanic plateau like setting and resulted in the establishment of shallow subseafloor convection cells diffuse venting of hydrothermal fluids over broad areas of the ancient ocean floor provided an ideal environment for both seafloor and subsurface biota 3 5 ga ago

hydrothermal alteration of a 1 km section through the upper oceanic crust deep sea drilling project hole 504b mineralogy chemistry and evolution of seawater basalt interactions deep sea drilling project hole 504b penetrates 1076 m into oceanic layer 2 and is the first hole to pass through the transition from pillow basalts altered at low temperatures into hydrothermally metamorphosed sheeted dikes alteration of the crust at site 504 occurred in four stages related to the movement of the crust away from the spreading axis 1 dikes reacted with seawater 200 300 c in the upwelling zone of an axial convection cell at the spreading axis resulting in the formation of greenschist facies parageneses in veins and host rocks mixing of the upwelling hydrothermal fluids with seawater circulating in the overlying more permeable pillow section occurred in the upper part of the lithologic transition zone causing a steep temperature gradient at the base of the pillow section secondary minerals formed in the lower pillow section from the resultant reducing mixed fluids at temperatures of around 100 c at the same time the initial effects of seafloor weathering began in the upper 320 m of the pillow section at low temperatures 50 c and under conditions of open circulation of oxidizing seawater 2 following refracturing of the dikes a second stage of axial upwelling occurred hydrothermal fluids 200 380 c were probably similar to those presently sampled from spreading ridges on the seafloor mixing of these fluids with seawater in the lithologic transition zone caused deposition of quartz epidote and sulfides in veins and formation of a sulfide rich stockworklike zone within this transition zone alteration of the pillow section proceeded under the prior conditions with the effects of seafloor weathering extending progressively downward into the crust 3 seawater recharge penetrated to depths of at least 1075 5 m subbasement and deposited anhydrite locally in veins 4 off axis alteration of the dikes was characterized by formation of zeolites calcite and prehnite in veins and host rocks from more highly evolved and lower temperature 100 250 c fluids alteration in the upper pillow section evolved from seafloor weathering conditions to more reducing and rock dominated as cracks in the basalt were sealed with secondary minerals and the basement was covered with a layer of sediment zeolites and calcite were the last phases to form throughout the pillow section sealing of the crust to convective cooling also allowed conductive reheating of the crust from below calculations of seawater crustal chemical fluxes from whole rock data are complicated by the low recovery and heterogeneity of alteration effects but indicate that basalt seawater interactions are a sink for seawater mg and k and a source for si and ca

hydrothermal vent waters at 13 n on the east pacific rise isotopic composition and gas concentration abstract gas concentrations and isotopic compositions of water have been measured in hydrothermal waters from 13 n on the east pacific rise in the most mg depleted samples 5 10 3 moles kg the gas concentrations are 3 4 5 10 5 cm 3 stp kg helium 0 62 1 24 cm 3 stp kg ch 4 10 80 16 71 10 3 moles kg co 2 the samples contain large quantities 95 126 cm 3 kg of h 2 and some carbon monoxide 0 26 0 36 cm 3 kg which result from reaction with the titanium sampling bottles 13 c in methane and co 2 16 6 to 19 5 and 4 1 to 5 5 respectively indicate temperatures between 475 and 550 c whereas 13 c co is compatible with formation by reduction of co 2 on ti at 350 c close to the sampling temperature 3 he 4 he are very homogeneous at 7 5 0 1 r a 3 he 4 he 1 0 10 5 and very similar to already published data as well as ch 4 3 he ratios between 1 4 and 2 1 10 6 18 o and d in water show enrichments from 0 39 to 0 69 and from 0 62 to 1 49 respectively these values correspond to w r ratios of 0 4 7 the distinct 18 o enrichments indicate that the isotopic composition of the oceans is not completely buffered by the hydrothermal circulations the 3 he enthalpy relationship is discussed in terms of both hydrothermal heat flux and 3 he mantle flux

the 1980 eruptions of mount st helens physical and chemical processes in the stratospheric clouds we investigate the physical and chemical properties of the stratospheric clouds produced by the recent eruptions of the mount st helens volcano the large and diverse set of observational data collected in the high altitude plumes of the may 18 may 25 and june 13 1980 eruptions is organized and analyzed for evidence of the processes at work the data are used to guide and constrain detailed model simulations of the volcanic clouds for this purpose a comprehensive one dimensional model of stratospheric sulfate aerosols sulfur precursor gases and volcanic ash and dust is utilized the model accounts for gas phase and condensed phase heterogeneous chemistry in the clouds aerosol nucleation and growth and cloud expansion computational results are given for the time histories of the gaseous species concentrations aerosol size distributions and ash burdens of the eruption clouds the long term buildup of stratospheric aerosols in the northern hemisphere and the persistent effects of injected chlorine and water vapor on stratospheric ozone are also investigated we conclude that so2 water vapor and ash were probably the most important substances injected into the stratosphere by the mount st helens volcano both with respect to their widespread effects on composition and their impact on climate despite the seemingly large magnitude of the mt st helens eruption we also find that the volcano had little influence on the climate 0 05 k surface cooling in the northern hemisphere or on stratospheric ozone 0 2 maximum hemispherical depletion the remaining problems in the field of volcanic cloud physics and chemistry and the requirements for future experimental work are also discussed

depth variation of carbon and oxygen isotopes of calcites in archean altered upperoceanic crust implications for the co2 flux from ocean to oceanic crust in the archean abstract middle archean greenstones with mid ocean ridge basalt affinity and overlying bedded chert banded iron formation bif are exposed in the cleaverville area pilbara craton western australia on the basis of the hydrothermal carbonation of these cleaverville greenstones we estimated the potential co2 flux from ocean to oceanic crust and the physical chemical conditions of the subseafloor hydrothermal system for the middle archean the greenstones exhibit various extents of carbonation and the igneous minerals contained in the greenstones are partly or completely replaced by calcite and other secondary minerals the degreeof carbonation correlates with stratigraphy the volume concentration of calcite in greenstones decreaseswith increasing depth below the chert bif horizon our results clearly indicate that the hydrothermal carbonation occurred along the axial zones of a middle archean mid ocean ridge both 13c and 18o values of calcite also change with the depth below the chert bif horizon the 18o value of calcite decreases with increasing depth reflecting increasing temperature while the 13c value of calcite changes from positive to negative stratigraphically downward a model reconstructing the 13c of calcite suggests that the observed isotopic variation reflects the thermal structure and that the carbon source for calcite was derived from seawater these mineralogical geochemical and geological features of calcite provide the amount of co2 in the whole oceanic crust per seafloor unit area 1 2 107 mol m2 based on this value co2 flux from the ocean to the oceanic crust in the middle archean can be estimated to be 1 5 1014 mol yr when the spreading rate m2 yr of archean oceanic crust is assumed to have been three times higher than it is today the estimated co2 flux into the oceanic crust is two orders of magnitude higher than the modern value which points to the significance of sea floor hydrothermal carbonation in the archean carbon cycle

capacity and suitability assessment of deep saline aquifers for co2 sequestration in the bohai bay basin east china co2 sequestration in deep saline aquifers has proven to be one of the most promising options to reduce anthropogenic co2 emissions sedimentary basins are chosen as targets of co2 sequestration due to the existence of deep saline aquifers this paper presents the first systematic investigation on the occurrence and characteristics of potential reservoirs for co2 sequestration in deep saline aquifers in the bohai bay basin bbb and offers detailed estimates on the storage capacity within the depth range from 800 to 3500 m a preliminary suitability assessment for preferential sites is also presented geological analyses show that deep saline aquifers in guantao formation ng of neogene dongying ed and shahejie formations es1 es2 es3 es4 of paleogene are potential reservoirs deep saline aquifers in the bbb may accommodate about 3922 mt co2 with 50 confidence level according to a modified cslf carbon sequestration leadership forum method the co2 storage capacity of individual depression varies from 65 mt liaohe depression to 934 mt liaodongwan bozhong depression the guantao formation ng of neogene is a regionally distributed reservoir with low tds total dissolved solids and favorable depth and thickness the capacity of which accounts for 84 of the total and is therefore considered as the most promising reservoir preliminary suitability assessment is carried out in terms of sedimentology tectonic stability geothermal conditions saline water characteristics potentially conflicting resources development as well as co2 emission sources the liaodongwan bozhong jiyang changwei and huanghua depressions are chosen as the most suitable sites for co2 storage jizhong and liaohe depressions are less suitable while linqing depression is not suitable due to its lower tectonic stability geological information and co2 emission sources although uncertainties exist the estimate in this study is significant for future study and implementation of co2 sequestration in the basin

biomarker geochemistry of the miocene monterey formation west san joaquin basin california implications for petroleum generation abstract much of the miocene monterey formation of california is rich in biogenic sediment especially organic matter and silica because of the geologic structure the monterey in the subsurface near lost hills in the san joaquin basin forms a natural laboratory for the study of the diagenetic responses of these materials rocks of similar age and lithology are buried to depths ranging between 500 and 3500 m and are thus exposed to a temperature range of 45 130 c the diagenetic progression of silica from opal a to opal ct to microquartz is well documented in monterey burial history studies however diagenetic indicators need to be established below the depth of complete conversion of opal ct to quartz which may be very shallow 1500 m or less at lost hills conventional maturity indicators are problematic the scarcity of vitrinite in many monterey samples hampers reflectance measurements in addition values that are measured may be anomalously low maximum pyrolysis temperatures are depressed due in part to high heavy bitumen content biomarker geochemistry provides effective alternative maturity indicators of particular interest are the stereochemical variations observed in the assemblages of steranes and triterpanes extracted from oil well core samples for example the 20s 20r ratio of 5 h 14 h 17 h 24 ethylcholestane increases from 0 09 to 0 56 over the depth range cited samples from petroleum accumulation zones are distinguished by anomalously mature biomarker assemblages considering their depth of burial this indicates that these bitumens are as mature as the deepest non production zone sample 3430 m even though they are from much shallower depths 580 1572 m other maturity and or migration indicators confirm this such as the relative increases in amounts of 14 h 17 h steranes rearranged steranes and tricyclic terpanes thus it appears that any immature indigenous bitumen in production zone samples is overwhelmed by a mature component which presumably migrated updip from deeper warmer strata since much oil is produced from shallow organic rich fractured monterey shales early in situ generation has previously been hypothesized however while both source and reservoir rock are lithologically similar and lie within the same formation biomarker geochemistry indicates that substantial generation occurs only in deeply buried monterey shales

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

comparative lidar study of the optical geometrical and dynamical properties of stratospheric post volcanic aerosols following the eruptions of el chichon and mount pinatubo the spatiotemporal evolution of aerosols formed from precursors injected into the stratosphere by major volcanic eruptions such as those of el chichon in 1982 and mount pinatubo in 1991 has been studied using a ground based lidar system located at the observatoire de haute provence ohp in southern france 44 n 5 e from the inversion of the lidar signals the optical geometrical and dynamical properties of the particles have been determined as a function of time after the eruption in immediate post volcanic conditions when the optical thickness of particles in the stratosphere is largely enhanced an estimate of the aerosols backscatter phase function has been evaluated directly from the lidar measurements using a size distribution model adjusted to in situ balloon measurements the precision of this determination lies in the 15 range values of the mean radius of the particles of their integrated content surface areas and sedimentation velocities are then derived from the systematic lidar measurements performed at ohp these values are compared for the two major volcanic eruptions which have occurred over the last decade although the injection of sulphur dioxide was twice as large for the mount pinatubo eruption as compared to the el chichon case the diffusion of the cloud in the two hemispheres due to the interaction of the particular phase of the quasi biennal oscillation with several other dynamical processes at the time of the eruption led to the observation of similar values for the aerosol content over the observatoire de haute provence in the months just following the two events however the residence time of the particles in atmospheric layers below 20 km are 4 months longer after the mount pinatubo eruption caused by the observed difference in the initial vertical distribution of the aerosol cloud

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

diagenetic fe carbonates in paleoarchean felsic sedimentary rocks hooggenoeg formation barberton greenstone belt south africa implications for co2 sequestration and the chemical budget of seawater abstract in order to evaluate the potential of felsic sediments as a co2 sink in the archean we studied felsic volcaniclastic epiclastic sedimentary rocks of the 3 45 ga hooggenoeg formation barberton greenstone belt which were affected by metasomatic processes during seafloor alteration and diagenesis water rock interactions leading to k si and co2 metasomatism were quantified the precursor rock a k metasomatized dacite was leached of ca mg fe na sr and ba and enriched in k rb and si prior to erosion and deposition the formation of k mica and quartz and minor k feldspar in the dacites suggests low ph metasomatic conditions likely produced by hydrothermally induced circulation of hot acidic and reduced archean seawater in equilibrium with a high p c o 2 atmosphere erosion and transport of k metasomatized dacitic detritus away from the felsic volcanic centers resulted in the deposition of conglomerate sandstone and shale by mass flow processes early diagenetic silicification affected mainly the fine grained sediments with higher silica sorption capacity forming impermeable layers while sand rich sediments were partly silicified and remained permeable trapped fluids precipitated two generations of fe rich dolomites and finally calcite up to 30 vol of siliciclastic coarse grained sediment was replaced by carbonates in a shallow burial high heat flow diagenetic regime depth 750 m temperature 80 160 c and likely throughout deposition of overlying volcano sedimentary units the carbon isotopic composition of fe rich dolomites 13cpdb 1 9 to 2 4 and the strong fe ca mg leaching of the paleoarchean volcanic formations support the influence of seawater derived fluids throughout co2 metasomatism for each gram of eroded dacite the overall chemical exchange involved by k si co2 metasomatism was characterized by a mass transfer of fe 1 2 mmol g na 2 1 mmol g and o2 2 0 mmol g to seawater in contrast seawater was depleted in si 10 mmol g ca 0 51 mmol g mg 0 43 mmol g k 1 5 mmol g and h 0 93 mmol g during incorporation of these elements in the volcanic and sedimentary rocks the average co2 uptake by the sedimentary rocks studied here is estimated to be 1 8 mmol g in the same order of magnitude as previous estimates for the paleoarchean basaltic crust although mafic ultramafic rocks are the most abundant rocks in paleoarchean greenstones belts and represent the most important atmospheric co2 sink upon seafloor alteration in the paleoarchean coarse felsic sedimentary rocks provide a non negligible contribution to the build up of the continental co2 reservoir

length of the global plate boundary at 2 4 ga phanerozoic data show that during continental dispersal the total length of the global plate boundary is directly related to the size distribution and the surface area of continental fragments we use this observation to test theories about the length of ancient plate boundaries and how the increased mantle heat production in the precambrian was manifested by the crust using monte carlo simulations of plate boundaries on a sphere we calculate estimates of global plate boundary length for the present day continents and plates the mean plate boundary lengths are within 1 of each other 3 40 x 10 5 km and 3 43 x 10 5 km from the size distribution and normalized area of archean cratons estimates of the length of plate boundary at 2 4 ga range from 1 7 to 2 7 times the present length the preferred mean value is 2 2 times the present length this result favors a model of sea floor tectonics in which global plate velocities and sea floor spreading rates were about 16 slower than at present and in which the oceanic crust was more than 20 km thick

stratospheric aerosol clouds due to very large volcanic eruptions of the early twentieth century effective particle sizes and conversion from pyrheliometric to visual optical depth spectral and pyrheliometric measurements of atmospheric transmission were made by staff members of the astrophysical observatory of the smithsonian institution at washington d c and at mount wilson california during the years 1901 1920 these valuable data are analyzed here with the help of a new inversion method to derive the effective or area weighted radii of stratospheric aerosols formed after three very large volcanic eruptions in this period after the great eruptions of katmai 1912 and santa maria 1902 reff remained close to 0 3 m for at least two years this near constancy of reff has been duplicated in modern times by the aerosols from el chichon 1982 following ksudach s 1907 eruption reff grew from 0 2 0 3 m to 0 4 0 5 m in about 1 year pinatubo s 1991 aerosols grew similarly generally speaking the pyrheliometric optical depth perturbation as measured for the three early eruptions is not equal to the visual optical depth perturbation but in fact the latter is larger by a factor of about 1 6 at least for reff 0 25 0 45 m wider physical implications of the present results are discussed

evaluation of ocean crustal sites 1256 and 504 for long term co2 sequestration 1 geologic storage of co2 in ocean basalt reservoirs is a potentially long term solution to offset anthropogenic greenhouse gas emissions prior drilling at deep sea drilling project dsdp ocean drilling program odp integrated ocean drilling program iodp sites 1256 and 504 provides evidence that the extrusive ocean crust has sufficient porosity and permeability to enable storage of large volumes of co2 six intervals are identified as potential reservoirs in the shallow crust at sites 1256 and 504 with new and reprocessed estimates of porosity from electrical resistivity logs ranging from 6 to 14 and permeability from 10 14 to 10 15 m2 calculations using specific reservoir thickness and porosity estimates suggest that even the smallest reservoir could provide storage capacity for decades of global anthropogenic carbon emissions in situ hydrologic experiments and pilot injection studies are needed to confirm high permeability and porosity estimates at sites 1256 and 504 as well as the potential for co2 injection and retention in these basalt reservoirs

hydrothermal plumes and the delivery of iron to banded iron formation most of the iron in banded iron formation bif was deposited during the period 2 7 1 8 ga within this period fe deposition rates were at least as high as 10 12 gm y according to new age models for the largest bifs peak deposition occurred between 2 4 2 3 ga it is likely that such high deposition rates would not be met by a solely continental source of iron unless significant quantities were remobilized in marine sediment estimates of global heat loss for the late archean early proterozoic suggest a hydrothermal cycling rate approximately three times greater than at present so hydrothermal water rock exchanges were a more important source of fe to the oceans than today hydro thermal plumes depleted in o 2 and enriched in fe were generated at mid ocean ridge crests with substantially shallower depths than present assuming hydrothermal effluent dilution factors of 10 4 plumes transported iron which had a dominantly hydrothermal source into the upper water column and transferred it to

the smectite to chlorite transition in a fossil seamount hydrothermal system the basement complex of la palma canary islands the hydrothermal metamorphism of a sequence of pliocene aged seamount extrusive and volcanoclastic rocks on la palma includes a relatively complete low p t facies series encompassing the zeolite prehnite pumpellyite and greenschist facies the observed mineral zonations imply metamorphic gradients of 200 300 c km 1 the transition from smectite to chlorite in the la palma seamount series is characterized by discontinuous steps between discrete smectite corrensite and chlorite which occur ubiquitously as vesicles and to a much lesser extent vein in fillings trioctahedral smectites mg fe mg 0 4 0 75 occur with palagonite and na ca zeolites such as analcime and a thompsonite natrolite solid solution corrensite mg fe mg 0 5 0 65 first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite discrete chlorite mg fe mg 0 4 0 6 becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases although random interstratifications of these phases have not been observed although smectite occurs as both low and high charge forms the la palma corrensite is a compositionally restricted 1 1 mixture of low charge trioctahedral smectite and chlorite electron microprobe analyses of coarse grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations calcium average 0 20 cations formula unit is the dominant interlayer cation with lesser mg k and na the absence of randomly interlayered chlorite smectite in the la palma seamount series may reflect high time integrated fluid fluxes through the seamount sequence this is consistent with the ubiquity of high variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples

reactions between basalt and co2 rich seawater at 250 and 350 c 500bars implications for the co2 sequestration into the modern oceanic crust and the composition of hydrothermal vent fluid in the co2 rich early ocean abstract this study aims to understand how basaltic rocks absorb co 2 in high temperature alteration zones in the subseafloor and to reconstruct hydrothermal alteration processes such as carbonatization of archean greenstones to this end we conducted two laboratory experiments simulating hydrothermal reactions between basalt synthesized under quartz fayalite magnetite oxygen fugacity and co 2 rich nacl fluid ph 6 5 at 25 c at high temperature and pressure as the water rock reactions progressed at 250 c and 350 c 500 bars total carbonic acid concentration co 2 reduced from its initial 400 mmol kg to near 0 and 100 mmol kg respectively meanwhile calcite was formed in the basalt as an alteration mineral this indicates that calcite destabilizes as temperature increases in the h 2 o co 2 basalt system and that crustal basalts can absorb almost all co 2 in the fluid as calcite at least at temperatures and initial co 2 concentrations below 250 c and 400 mmol kg respectively although the second aim was realized in the experiments minerals such as sericite dolomite ankerite and siderite present in archean greenstones were not identified in the alteration products possibly because k mg and fe were lacking in the initial solutions steady state concentrations of sio 2 mg and k in the fluids during water rock reactions were similar to those of high temperature fluids 250 c in modern basalt hosted hydrothermal systems however the final experimental ph in situ was 6 6 and 7 2 at 250 c and 350 c respectively higher than that in modern hydrothermal fluids approximately 5 and higher than the neutral ph 5 5 5 6 at 250 350 c 500 bars the results suggest that the presence of abundant co 2 in the initial fluid induced carbonatization of basalt consequently ph was buffered by precipitation and dissolution of calcite because ph in situ was elevated the dissolved fe and mn concentrations in the fluid were two to three orders of magnitude lower than those of modern hydrothermal fluids in modern oceans high temperature hydrothermal vent fluids are the second largest iron source after riverine input however because alkaline metal poor hydrothermal fluids are generated in co 2 rich systems co 2 rich seafloor hydrothermal systems may have behaved as iron sinks in early oceans

the rainbow vent fluids 36 14 n mar the influence of ultramafic rocks and phase separation on trace metal content in mid atlantic ridge hydrothermal fluids fluids were collected from the rainbow vent field 36 14 n on the mid atlantic ridge mar during the 1997 diving flores cruise this vent field in ultramafic rocks at a depth of 2300 m is composed of 10 black smokers emitting acidic ph 2 8 fluids at 365 c the low ph of the hot temperature rainbow fluids likely results from seawater ultramafic rock interaction that releases h ions into reducing hydrothermal fluids fluid chemistry is strongly influenced by phase separation generating cl rich brines clem 750 mm strongly enriched with mn fe co ni cu zn ag cd cs pb y and rare earth elements ree ree and transition metal abundance particularly fe and mn in the rainbow fluids is dramatically higher than in other mar fluids the abundance of trace element and ree enrichment is due to the greater solubility of these elements that is strongly favored by cl complexation at low ph and high temperature conditions chondrite normalized ree patterns show strong lree enrichment with evidence of the typical eu anomaly this ree partitioning suggests that either 1 ultramafic rocks represent only a part of rocks leached during hydrothermal alteration and or 2 that the unique rainbow fluid temperature ph and redox state issued from the ultramafic character of leached substratum can produce unique ree partitioning

life in the hydrated suboceanic mantle in the roots of the ocean crust mantle derived rocks are progressively hydrated by hydrothermal circulation raman spectroscopic analyses of hydrated rocks sampled from the ocean floor reveal accumulations of organic matter which point to the hydration process as a possible energy source

the composition of earth s oldest iron formations the nuvvuagittuq supracrustal belt quebec canada abstract the composition of iron formations in the 3 75 ga yr old nuvvuagittuq supracrustal belt in northern quebec provides a proxy for seawater composition of the eoarchean and perhaps hadean oceans as well as constraints on the types of nutrients available to earth s earliest life forms integrated petrologic and geochemical relationships mapped between mineral phases in thin section and whole rock chemistry provide a framework for interpreting bulk and micro scale variations in these chemical sedimentary precipitates results show that there are two distinct chemical sedimentary units in the nuvvuagittuq belt i a banded iron formation bif consisting of alternating micro bands of magnetite ca mg fe silicates and quartz and ii a more silicate rich fe poor unit the banded silicate formation bsf of alternating micro bands of quartz and ca mg fe silicates precursor bif and bsf deposits were likely layered amorphous silica and ferric oxyhydroxides fine grained carbonate oozes and or ca mg fe rich silicate gels deposited in a marine setting low al2o3 tio2 and hfse concentrations show that they are relatively detritus free with distinctively seawater like ree y profiles and consistently positive eu anomalies these features suggest that the rocks preserved their seawater like compositions despite metamorphic overprinting the most significant trace elements in the sediments are ni and zn experimentally derived partitioning coefficients show that ni was enriched in eoarchean seawater as compared to today up to 300 nm while zn was fairly similar up to 20 nm compositional resemblances between the nuvvuagittuq sediments and those documented in the ca 3 8 ga isua supracrustals west greenland provide a plausible case that global ocean processes in terms of trace metal abundances had reached steady state by the eoarchean

submarine hot springs and the origin of life commentaire sur l article de miller s l et bada j l paru dans nature 1988 334 609 611

calcium and sodium exchange during hydrothermal alteration of calcic plagioclase at 400 c and 400 bars a series of experiments were conducted to measure the effect of plagioclase composition on the composition of coexisting cl dominated hydrothermal fluids assemblages containing quartz and natural plagioclase with a composition of either an60 or an82 were reacted with na ca cl fluids at 400 c and 400 bars using flexible cell hydrothermal facilities plagioclase remained homogeneous during these experiments despite the fact that homogeneous solid solutions with intermediate compositions are likely metastable with respect to mechanical mixtures at these conditions it was found that ca and na exchange between fluids and minerals appears to be reversible and highly dependent on plagioclase composition but mca m2na ratios remained constant with increasing cl for a given plagioclase composition in fact a solid solution model which approaches ideal behavior appears to account best for the chemistry of fluids coexisting with an60 and an82 plagioclase these data may have a direct bearing on hydrothermal alteration processes responsible for the chemistry of hot spring fluids at mid ocean ridges which appear to have equilibrated with metastable plagioclase solid solutions of composition an60 to an70

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

compared geochemical signatures and the evolution of menez gwen 37 50 n and lucky strike 37 17 n hydrothermal fluids south of the azores triple junction on the mid atlantic ridge during the diva 1 cruise in may 1994 a series of 19 dives was conducted using the french submersible nautile at the topographic highs of three volcanic segments centered at 37 17 n 37 50 n and 38 20 n respectively south of the azores triple junction atj on the mid atlantic ridge mar hydrothermal fluids were collected at the lucky strike ls hydrothermal field discovered at 37 17 n in 1993 and at a new hydrothermal site called menez gwen mgw discovered at 37 50 n during this cruise both systems are relatively shallow compared to other mar systems with seafloor depths of 1700 and 850 m respectively characteristics which make them unique among the already known sites on the mar the characteristics of the ls fluids are the same as in 1993 and include temperatures ranging from 170 c to 324 c variable chlorinities lower than seawater low hydrogen sulfide 3 0 mmol kg high ba concentrations up to 80 mol kg low metal concentrations and high gas contents and distinct chemical end members indicative of significant geographic control of the venting system in contrast the very clear mgw fluids at 37 50 n show a rather uniform exit temperature 285 c and chemical compositions with chlorinities 360 380 mmol kg lower than at ls and corresponding lower concentrations of cations h2s 1 8 mmol kg metals and silica 8 11 5 mmol kg due to the lower temperature t and pressure p of the system in the two systems fluid chemistry is strongly affected by phase separation at the low pressure conditions of these sites phase relations in the nacl h2o system dictate production of an extremely low salinity the higher salinities observed in fluids thus indicate that mixing of extremely low salinity vapor with single phase hydrothermal seawater is the dominant process controlling cl concentrations depletions and enrichments of elements in solutions are also explained by the involvement of fluid rock reactions the enrichment of ba k cs and rb in the fluids is linked to the enriched character of these elements in basalts relatively high ph and ca low li sr and metals are related to the highly altered basaltic substrate in the reaction zone low sr ca and high ca na ratios are explained by albitization within the crust the increase of degassing when approaching the azores may be related to the carbon enriched basaltic crust near the azores hot spot isotopic ratios show that co2 ch4 and helium gases have a magmatic signature compared to other deeper sites on the mar all fluids collected at ls and mgw are gas enriched except for h2s and helium whose both concentration and isotopic ratio compare well with other hydrothermal fluids the high ch4 concentration associated with unsaturated hydrocarbons and the high ch4 3he ratios also suggest a contribution of ch4 generated by serpentinization of ultramafic rocks by fischer tropsch catalysis of co2 reduction

archean ocean floor metamorphism in the north pole area pilbara craton western australia abstract archean greenstones ca 3 49 3 46 ga in the north pole dome pilbara craton western australia have undergone prograde metamorphism from prehnite pumpellyite facies to greenschist amphibolite facies observations of 3000 thin sections shows that a metamorphic aureole was restricted to within a few kilometers of the contact with the 3459 ma north pole monzogranite three types of alteration were observed carbonate silicic and chlorite types the distribution of the three types of alteration suggests that secondary chemical migration of elements occurred in the whole area but that some samples were unaffected by this alteration the southern north pole area is outside of the contact metamorphic aureole and is composed of five units from north unit i to south unit v dipping south about 30 70 metamorphism of the north pole greenstones corresponds to the low pressure type which is broadly comparable to that inferred for ocean floor metamorphism prehnite pumpellyite pp transitional tr and greenschist gs facies prograde metamorphic zones occur from structural top to bottom within each of units metamorphic grade increases downward through the units and metamorphic isograds never cut unit boundaries

molecular thermal maturity indicators in oil and gas source rocks many detailed chemical parameters have been proposed as indicators of thermal maturity in oil and gas source rocks certain classical maturity parameters involving carbon preference indices and compound class ratios such as hydrocarbons extract yield and extract yield total organic carbon are less commonly used today having been complemented with detailed molecular parameters among these parameters the molecular distributions of metalloporphyrins cyclic hydrocarbons low molecular weight hydrocarbons and gases are most commonly used recent instrumental advances have allowed the routine measurement of molecular ratios in geochemical organic matter stimulating the development and use of biological markers such as steranes hopanes and metallated tetrapyrroles as thermal maturity indicators increased chromatographic resolution of source rock hydrocarbons has also led to the use of low molecular weight hydrocarbons methylphenanthrenes and aromatized steranes as maturity indicators in this paper we discuss these developments emphasizing the applications and the pitfalls of using molecular maturity indicators