the deep subterranean biosphere abstract the main purpose with this review is to summarise present research on the microbiology of deep subterranean environments deeper than 50 100 m included are mainly studies where drilling excavation core sampling and ground water sampling have been made for research studies done in environments penetrated for commercial purposes such as water wells mining oil recovery etc have been dismissed because of the obvious risk for contamination during the penetration different measures that can be applied to reduce the risk of microbial contamination of sampled specimens by the access operations are discussed the requirement for reliable estimations of the present microbial biomass its activity and diversity in subterranean ecosystems is fundamental an array of different methods to achieve this goal are presented the depth limit for subterranean life is suggested to be set by temperature provided there is energy available for microbial life if so it should be possible to enrich thermophilic bacteria from deep hot ground waters which also has been done there are only a few sites where the subterranean microbiology has been studied in multidisiplinary programs including chemistry and geology the two most extensively published sites are the sediments of the atlantic coastal plain of south carolina usa studied in a subsurface program initiated and sponsored by the u s department of energy and crystalline bed rock in sweden studied in a program concerning the safety of future underground repositories for nuclear waste this review presents an array of independent reports suggesting that microbial life is widespread at depth in the crust of earth the deep subterranean biosphere the obvious consequences is that microbes may be involved in many subterranean geochemical processes such as diagenesis weathering precipitation and in oxidation or reduction reactions of metals carbon nitrogen and sulfur just as they are in most terranean environments

petroleum formation by fischer tropsch synthesis in plate tectonics a somewhat speculative hypothesis of petroleum genesis in the upper lithosphere is proposed based on fischer tropsch synthesis this hypothesis is distinct from both the organic biogenic model and the inorganic model of hydrocarbon degassing from the earth s interior fischer tropsch synthesis is a well known industrial process whereby millions of tons of hydrocarbon oil resembling petroleum are produced annually from carbon monoxide or carbon dioxide and hydrogen gases reacting on a metallic iron or iron oxide catalyst like natural petroleum this synthetic oil consists of gas gasoline diesel oil and wax fractions all rich in saturated aliphatic hydrocarbons and enriched in the light 12c isotope the hypothesis presented in this paper proposes that petroleum liquids form by fischer tropsch synthesis on magnetite and hematite catalysts when carbon dioxide derived by massive metamorphic or igneous decarbonation of subducted sedimentary carbonates reacts with hydrogen generated by the serpentinization in the absence of air of shallow mantle lithosphere and ophiolite thrust sheets oblique plate movements may favor hydrocarbon formation by creating deep faults that aid fluid flow and serpentinization the world s richest oil provinces including those of the middle east may be tentatively interpreted to have formed by this mechanism

abyssal serpentinites as gigantic factories of marine salts and oil abstract serpentinites occur worldwide in various geological settings such as in magma starved oceanic basins abyssal serpentinites are long term storage for chlorine and carbon the latter forming dominantly reduced and subordinately oxidized compounds hence serpentinites salts and reduced carbon phases coexist in an abyssal association although huge reservoirs of salts and reduced carbonaceous matter in abyssal serpentinites are thought to be lacking this may be more a reflection of intrinsic limits in research methods than an indication of their absence on the other hand shallow seated hydrocarbon rich mud volcanoes and diapirs consisting of salts hydrocarbons oils and gases and clayey muds including mudded serpentines can provide evidence for such an oceanic association here we search for scientific data in support of the oceanic association and hence we propose a reappraisal of exploitable worldwide salt hydrocarbon reservoirs even gigantic in size abyssal serpentinites are well known source rocks of abiotic gaseous hydrocarbons via fischer tropsch type reaction ftt whereas macromolecular carbonaceous matter mostly bitumen found in serpentinites is postulated to be biogenic this inference is based mainly on three assumptions i ftt in nature does not yield oils ii hydrocarbons derive essentially from the thermal alteration of microbial molecules iii the presence of biomarkers traditionally considered evidence of the biological origin of oils nevertheless some lines of strong evidence disprove these accepted conventions i lab experiments demonstrated that ftt can synthesize significant quantities of liquid hydrocarbons oils under conditions compatible with the deeper and more reduced level of serpentinite hosted hydrothermal systems ii macromolecules generally thought to derive from microbial activity can be abiotically generated as documented in extraterrestrial bodies iii biomarkers are evidence for the proliferation of microbial communities which subsist on serpentinization and ftt products thus they are biological pollutants moreover seawater driven serpentinization consumes water producing huge amounts 11 kg halite m 3 of peridotite of salts that can be stored in the deeper zone of abyssal type hydrothermal systems thus the origin of shallow sited salt deposits even gigantic in size can be related to either the advective upwelling of hot hydrothermal brines due to the dehydration of abyssal serpentinites or to the passive upwelling of buoyant saline geobodies piercement structures are indeed seismically imaged in several localities such as south atlantic the gulf of mexico the serpentinite belt extending from cuba to hispaniola the north sea trench and the zagros orogenic belt similar lines of evidence at the microscopic scale have been found in some hyblean serpentinite xenoliths south eastern sicily being representative of the unmetamorfosed in situ relic of the palaeo tethys ocean upon which sicily and its off shore areas lie in spite of the accepted stereotype of hydrocarbons as fossil fuels and hence finite resources reduced carbon compounds abiotically produced in abyssal serpentinites may be copious protracted over time and thus renewable

the provenance formation and implications of reduced carbon phases in martian meteorites this review is intended to summarize the current observations of reduced carbon in martian meteorites differentiating between terrestrial contamination and carbon that is indigenous to mars indeed the identification of martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade including the mars science laboratory and mars 2020 organic carbon compounds are essential building blocks of terrestrial life so the occurrence and origin biotic or abiotic of organic compounds on mars is of great significance however not all forms of reduced carbon are conducive to biological systems this paper discusses the significance of reduced organic carbon including methane in martian geological and astrobiological systems specifically it summarizes current thinking on the nature sources and sinks of martian organic carbon a key component to martian habitability based on this compilation reduced organic carbon on mars including detections of methane in the martian atmosphere is best described through a combination of abiotic organic synthesis on mars and infall of extraterrestrial carbonaceous material although conclusive signs of martian life have yet to be revealed we have developed a strategy for life detection on mars that can be utilized in future life detection studies

plate flexure and volcanism late cenozoic tectonics of the tabar lihir tanga feni alkalic province new ireland basin papua new guinea abstract late cenozoic tabar lihir tanga feni tltf alkaline volcanism new ireland basin png is associated with extensional cracks along the crests of flexed ridges developed on the new ireland microplate new name the tectonic alignment of the tltf volcanic arc is essentially perpendicular to the flexed ridges suggesting that fractures parallel to the direction of maximum horizontal compression facilitated the rapid ascent of alkaline magmas from the mantle region perhaps 60 70 km depth the mainly pliocene to pleistocene volcanoes were localized at the intersection of ridge parallel kabang structures and arc parallel niffin structures suggesting that the kabang niffin structural intersections underlying each of the tltf island groups provided a well developed clustered network of open conduits which tapped the mantle source region periodic post miocene locking and unlocking along the strike slip kilinailau fault new name are thought to have functioned as a valve turning on pliocene and then turning off pleistocene volcanic activity respectively partial locking of the kilinailau fault during the pliocene resulted in the accumulation of intraplate stresses within the new ireland microplate and caused plate flexure and ridge development plate cracking along ridge crests and the development of arc parallel regional fractures parallel to the direction of maximum compression unlocking of the kilinailau fault in the pleistocene resulted in the release of intraplate stresses in the new ireland microplate and a cessation of volcanic activity across most of the tltf arc the style and scale of plate flexure and cracking accompanied by within plate alkaline volcanism from equally spaced ridge top eruptive centers confined to a narrow linear volcanic arc are unknown from any other tectonic province

initial indications of abiotic formation of hydrocarbons in the rainbow ultramafic hydrothermal system mid atlantic ridge in the presence of water olivine of ultramafic rock is oxidized during the process referred to as serpentinization water in contact with the olivine is reduced to molecular hydrogen h2 with the concomitant oxidation of fe ii the molecular hydrogen formed may be used as an energy source by lithotrophic bacteria but may at high temperature also be combined with co2 for the abiotic formation of organic compounds such as hydrocarbons and fatty acids through fischer tropsch type ftt synthesis our analyses of fluids from the peridotite hosted rainbow hydrothermal field on the mid atlantic ridge indicate de novo synthesis of linear saturated hydrocarbons the chain length of the hydrocarbons is between 16 and 29 carbon atoms the discovery of ftt reactions in ultramafic hydrothermal systems on earth provides an alternative pathway for the formation of early membranes and the origin of life

intense ch4 plumes generated by serpentinization of ultramafic rocks at the intersection of the 15 20 n fracture zone and the mid atlantic ridge abstract as part of the fara french us program designed to study the mid atlantic ridge mar between 15 n and the azores twenty three dives with the submersible nautile were conducted during the french us faranaut 15n cruise on the eastern and western parts of the 15 20 n fracture zone ridge axis intersection south of the eastern ridge transform fault intersection nine nautile dives were made within the rift valley and along the western rift valley wall ch4 concentrations in the bottom waters reach 53 2 nmol kg along faulted zones on top and on the east flank of the ultramafic inner corner high 15 05 n 44 59 w where serpentinized rocks outcrop no 3he anomaly is associated with methane ruling out any primary mantle component fourteen dives were also made in the rift valley to the north close to the western intersection of the 15 20 n transform high ch4 anomalies up to 22 nmol kg are also present in the bottom waters of the rift valley northern segment on both the western and eastern valley walls and on the inner high adjacent to the eastern wall where ultramafic rocks outcrop seven vertical hydrocasts carried out in the axial valley 4500 m deep show an intense ch4 anomaly with a maximum 35 8 nmol kg at 3200 m depth this ch4 concentration is among the highest found along the mid atlantic ridge charlou and donval 1993 charlou et al 1997 ch4 concentrations of 9 9 14 9 nmol kg are also present on the western wall along the 3200 m isobath the high ch4 concentrations correspond to only weak 3he anomalies this ch4 rich plume is also associated with active fault zones that expose peridotite rocks ch4 output from ultramafic outcrops on the western and eastern intersections of the 15 20 n fracture zone with the mar is believed to reflect ongoing serpentinization these results associated with many other ch4 anomalies measured in the water column above ultramafic outcrops found between 12 n and the azores most likely reflect serpentinization processes extending along the whole slow spreading mid atlantic ridge

μxanes study of iron redox state in serpentine during oceanic serpentinization serpentinization of ultramafic rocks at mid ocean ridges generates significant amounts of h2 ch4 and supports specific biological communities the abiotic h2 production is attributed to the reduction of h2o during serpentinization which balances oxidation of ferrous iron contained in primary minerals mainly olivines and pyroxenes to ferric iron contained in secondary minerals mainly serpentines and magnetite magnetite has thus far been considered as the sole fe3 carrier for estimating bulk h2 production notably because the valence of iron in serpentine minerals and its relationship with both magnetite abundance and serpentinization degree are usually not determined we show that the serpentine contribution to the fe and fe3 budget has a significant effect on h2 production we performed xanes analysis at the fe k edge on thin sections of peridotites with various degrees of serpentinization from odp leg 153 mark region 23 n fe3 fetot in oceanic serpentines is highly variable from 0 2 to 1 at the thin section scale and it is related non linearly to the local degree of serpentinization a typical value of 0 7 is observed above 60 serpentinization the highest values of fe3 fetot observed within or close to late veins suggest that the fe3 fetot in serpentine record the local water rock w r ratio as previously proposed from thermodynamic modeling we estimate that the w r ratio increased from 0 6 to 25 during serpentinization at mark and locally reached 100 in veins mass balance calculations combining all mineral and bulk rock analyses provide the distribution of fe and fe3 as serpentinization progresses serpentine dominates the fe3 budget of the rock over magnetite during the first 75 of serpentinization contributing up to 80 of the total fe3 at later stages serpentine contribution to the fe3 budget decreases down to 20 while magnetite formation exponentially increases iron transfer from serpentine to magnetite balances the bulk fe3 content of the rock that increases almost linearly with the advance of the reaction formation of serpentine accounts for the majority of fe3 and h2 production at early stages of serpentinization at a depth 2 km at mark where the concentration of h2 can reach more than 100 mm according to the low w r h2 production values and depths can vary from one site to another depending on the evolution of the temperature w r ratio inlet fluid composition and favored formation of serpentine vs magnetite at mark fe3 in serpentine represents 15 27 of the total fe contained in a rock serpentinized to more than 80 and accounts for 25 of the total h2 production that is estimated at 325 335 mmol kg of rock the absence of magnetite does not necessarily mean a negligible h2 production even at low t conditions 150 200 c under which the fe and fe3 richest serpentines have been observed serpentine minerals are important fe3 carrier in the altered ocean lithosphere and may affect mantle redox state while dehydrating at depth in subduction zones

incipient hydration of mantle lithosphere at ridges a reactive percolation experiment a reactive percolation experiment was conducted by injecting seawater into a permeable olivine aggregate at 190 c and 19 mpa to explore the relationships between hydration reactions and hydrodynamic properties during the onset of serpentinization in the ultramafic lithosphere exposed at mid ocean ridges the experiment was stopped after 23 days when the sample became impermeable the initial flow rate was 0 2 ml h and then was decreased down to 0 06 ml h after 8 days permeability decreased continuously throughout the experiment the analyses of fluid chemistry time series and of the mineralogy and structure of the reacted sample showed olivine dissolution and precipitation of proto serpentine brucite and fe oxides these reactions are controlled by coupled hydrodynamic and chemical processes interacting at different time and spatial scales their first characteristic is the production of silica rich outlet fluids in disequilibrium with the observed reacted mineral assemblages these compositions are interpreted as resulting from a suite of coupled dissolution precipitation reactions controlled at the pore scale by surface kinetic processes that rapidly reaches steady state constant fluid composition independent of fluid flux hence the effective rate of serpentinization was controlled to the first order by the transport of reactants during the experiment mass balance calculations show that the rate of olivine conversion was fast 0 2 0 5 wt day yet only 8 wt of the olivine sample reacted because the permeability drop limited fluid circulation porosity varied little during the experiment compared to permeability changes the decrease of permeability was explained by the structure of the newly formed serpentine favouring the clogging of fluid paths the rate at which permeability decreased was the fastest at low flux conditions this suggests that permeability changes were not controlled simply by the kinetics of the serpentinization reactions but mainly reflected the development of low peclet pore scale zones forming micro environments that control the serpentinization reaction paths these results outline the need to take into account the coupling of hydrodynamic and chemical processes when modelling the effects of reactive transport within the hydrating oceanic lithosphere

carbon geochemistry of serpentinites in the lost city hydrothermal system 30 n mar abstract the carbon geochemistry of serpentinized peridotites and gabbroic rocks recovered at the lost city hydrothermal field lchf and drilled at iodp hole 1309d at the central dome of the atlantis massif mid atlantic ridge 30 n was examined to characterize carbon sources and speciation in oceanic basement rocks affected by long lived hydrothermal alteration our study presents new data on the geochemistry of organic carbon in the oceanic lithosphere and provides constraints on the fate of dissolved organic carbon in seawater during serpentinization the basement rocks of the atlantis massif are characterized by total carbon tc contents of 59 ppm to 1 6 wt and 13ctc values ranging from 28 7 to 2 3 in contrast total organic carbon toc concentrations and isotopic compositions are relatively constant 13ctoc 28 9 to 21 5 and variations in 13ctc reflect mixing of organic carbon with carbonates of marine origin saturated hydrocarbons extracted from serpentinites beneath the lchf consist of n alkanes ranging from c15 to c30 longer chain hydrocarbons up to c40 are observed in olivine rich samples from the central dome iodp hole 1309d occurrences of isoprenoids pristane phytane and squalane polycyclic compounds hopanes and steranes and higher relative abundances of n c16 to n c20 alkanes in the serpentinites of the southern wall suggest a marine organic input the vent fluids are characterized by high concentrations of methane and hydrogen with a putative abiotic origin of hydrocarbons however evidence for an inorganic source of n alkanes in the basement rocks remains equivocal we propose that high seawater fluxes in the southern part of the atlantis massif likely favor the transport and incorporation of marine dissolved organic carbon and overprints possible abiotic geochemical signatures the presence of pristane phytane and squalane biomarkers in olivine rich samples associated with local faults at the central dome implies fracture controlled seawater circulation deep into the gabbroic core of the massif thus our study indicates that hydrocarbons account for an important proportion of the total carbon stored in the atlantis massif basement and suggests that serpentinites may represent an important as yet unidentified reservoir for dissolved organic carbon doc from seawater

low silica activity for hydrogen generation during serpentinization an example of natural serpentinites in the mineoka ophiolite complex central japan the textural evolution in the serpentinite of the mineoka ophiolite complex has been investigated to constrain the natural environment for hydrogen production in the serpentinite hosted hydrothermal vent systems textural relations of the serpentinites from the mineoka ophiolite indicate at least two stages in the process of serpentinization with the replacement of olivine by a mesh texture of serpentine and brucite followed by the development of magnetite bearing or free serpentine veins the generation of hydrogen during serpentinization which accompanies the formation of magnetite involves a silica depletion reaction as evidenced by the low abundance of serpentine in the magnetite bearing veins and the absence of magnetite in pseudomorphs of orthopyroxene direct evidence for the production of hydrogen and strongly reducing conditions is provided by ch4 and h2 bearing inclusions in relic olivine crystals the production of methane and hydrogen may have provided a suitable environment for microbial activity in hydrothermal vent systems along the seafloor our results indicate that low silica activity plays a key role in the generation of hydrogen during serpentinization and that low silica activity environments are possible in olivine rich rocks such as dunite or during local disequilibrium in other silica poor rocks in the mantle lithosphere

micrometer scale carbon isotopic study of bitumen associated with athabasca uranium deposits constraints on the genetic relationship with petroleum source rocks and the abiogenic origin hypothesis abstract in situ analytical techniques fourier transform infrared microspectroscopy ftir and ion microprobe have been used to unravel the origin of solid bitumen associated with the uranium deposits of athabasca saskatchewan canada both aliphaticity and carbon isotopic compositions within the samples are heterogeneous but spatially organized in concentric zonations at the micrometer scale finally the 13 c values are positively correlated to the aliphatic contents over an extremely large isotopic range from 49 to 31 we infer that this positive correlation may be related to the carbon isotopic fractionations associated with the synthesis of bitumen through the catalytic hydrogenation of co 2 rather than the result of pre existing petroleum product precipitation and or alteration such as radiolysis this explanation is consistent with i published results of abiogenic synthesis experiments in which the differences in 13 c values between saturated and unsaturated hydrocarbons range from 2 and 19 in contrast to the differences systematically observed in conventional bitumen and petroleum ranging from 0 to 4 ii the absence of a similar positive correlation between aliphatic contents and 13 c values in the other bitumen analyzed in the present study for which a biogenic origin has been unequivocally established samples from oklo gabon and lodeve france uranium deposits iii the presence of co 2 and h 2 in the gas phase of fluid inclusions in the athabasca uranium deposits h 2 resulting from water radiolysis the present results suggest that the 13 c vs aliphaticity correlation could be used as a criterion to discriminate between abiogenic vs biogenic origin of macromolecular organic matter

comparative multi scale analysis of filamentous microfossils from the c 850 ma bitter springs group and filaments from the c 3460 ma apex chert filamentous microfossils belonging to cephalophytarion from the 850 ma bitter springs group have previously been used as key analogues in support of a biological interpretation for filamentous objects from the 3460 ma apex chert here we provide a new perspective on this interpretation by combining raman data with correlative electron microscopy data from both cephalophytarion and apex specimens we show that when analysed at high spatial resolution the apex filaments bear no morphological resemblance to the younger bitter springs microfossils cephalophytarion filaments are shown to be cylindrical comprising chains of box like cells of approximately constant dimensions with lateral kerogenous walls and transverse kerogenous septa they exhibit taphonomic shrinkage and folding possess fine cylindrical sheaths and are permineralized by sub micrometric quartz grains they fulfil all established biogenicity criteria for trichomic microfossils in contrast apex filaments do not possess lateral cell walls are not cylindrical in nature and vary considerably in diameter along their length their kerogenous carbon does not have a cell like distribution and their chemistry is consistent with an origin as exfoliated phyllosilicate grains this work demonstrates the importance of high resolution data when interpreting the microstructure and origins of putative precambrian microfossils

the problem of deep carbon an archean paradox black carbon rich chert dikes are common features of early archean terranes and are especially prominent on the pilbara craton of western australia the dikes cut across the local stratigraphy before truncating abruptly at specific stratigraphic horizons where they can be seen to interfinger with the stratigraphic succession these uniquely archean dike complexes are enigmatic and raise significant questions about the source of the carbon they contain is it biogenic and therefore indicative of the early biosphere or abiotic and perhaps indicative of prebiotic conditions that led to the appearance of the first life on earth the strelley pool chert which is exposed on the pilbara craton of western australia forms part of the warrawoona group and rests unconformably on older ultramafic volcanics the formation which is generally less than 30 m thick consists of a relatively consistent lithologic succession found over a wide area locally a basal transgressive sandstone is overlain by a sequence of carbonate barite black and white laminated chert and grey green chert which is locally stained blue green by weathered fuchsite the formation is intersected by normal faults about which the depositional successions thickens and thins the mineralogy and geochemistry including stable isotope data of the underlying dike complex closely parallels that of the lithologies preserved in the strelley pool chert similarly the depositional sequence of minerals in voids within the dike complex parallels that of the depositional sequence above this new data from the strelley pool chert and its associated dike complex show that the black chert dikes are an integral part of a hydrothermal mineralogical complex the complex accumulated around vents fed by growth fault controlled dikes that extended to a depth of more than 2 km below the archean paleo seafloor the mineralogy of the sedimentary succession reflects deposition during the declining temperature regime of an evolving hydrothermal system driven by an intruding granitoid complex below the fault system and associated hydrothermal complex evolved in the tensional environment developed during doming above the intermittently intruding granitoid complex that forms the framework of the pilbara protocontinent carbonaceous compounds contained within the black chert dikes could have been generated abiotically by a process similar to fischer tropsch synthesis at elevated temperatures 200 300 c and pressures 500 bar at a paleo depth of 2 km within the hydrothermal system the primordial medium in which life first evolved may thus have been a silica rich slurry with a low ph and a high co 2 content which contained basic abiotic organic building blocks fundamental to the origins of life the abiotic organic output from these hydrothermal systems may overwhelm any early biospheric geochemical signal and may therefore be the most difficult environment in which to recognise the early biospheric record 2005 elsevier b v all rights reserved

asphaltene bearing mantle xenoliths from hyblean diatremes sicily abstract microscopic blebs of sulfur bearing organic matter om commonly occur between the secondary calcite grains and fibrous phyllosilicates in extensively serpentinized and carbonated mantle derived ultramafic xenoliths from hyblean nephelinite diatremes sicily italy rarely coarse bituminous patches give the rock a blackish color micro fourier transform infrared spectra ftir point to asphaltene like structures in the om due to partially condensed aromatic rings with aliphatic tails consisting of a few c atoms x ray photoelectron spectroscopy xps analysis indicates the occurrence of minor s o either sulphonyl or sulphoxide functional groups in the om solubility tests in toluene thermo gravimetric tga and differential thermal dta analyses confirm the presence of asphaltene structures it is proposed that asphaltenes derive from the in situ aromatization with decrease in h c ratio of previous light aliphatic hydrocarbons field evidence excludes that hydrocarbon from an external source percolated through the xenolith bearing tuff breccia the discriminating presence of hydrocarbon in a particular type of xenolith only and the lack of hydrocarbon in the host breccia matrix are also inconsistent with an interaction between the ascending eruptive system and a supposed deep seated oil reservoir assuming that the hyblean unexposed basement consists of mantle ultramafics and mafic intrusive rocks having hosted an early abyssal type hydrothermal system one can put forward the hypothesis that the hydrocarbon production was related to hydrothermal activity in a serpentinite system although a bacteriogenesis or thermogenesis cannot be ruled out the coexisting serpentine ni fe ores and hydrocarbon strongly suggest a fischer tropsch type ftt synthesis subsequent variations in the chemical and physical conditions of the system for example an increase in the water rock ratio gave rise to partial oxidation and late carbonation of the serpentinite hosted hydrocarbon admitting an authigenic origin for most of the modal calcite 30 50 by volume in these rocks one can conclude as a general rule that un carbonated serpentinites tectonically emplaced at shallow crustal levels are potential reservoir rocks as well putative source rocks for exploitable petroleum reserves

early archean serpentine mud volcanoes at isua greenland as a niche for early life the isua supracrustal belt greenland of early archean age 3 81 3 70 ga represents the oldest crustal segment on earth its complex lithology comprises an ophiolite like unit and volcanic rocks reminiscent of boninites which tie isua supracrustals to an island arc environment we here present zinc zn isotope compositions measured on serpentinites and other rocks from the isua supracrustal sequence and on serpentinites from modern ophiolites midocean ridges and the mariana forearc in stark contrast to modern midocean ridge and ophiolite serpentinites zn in isua and mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average based on recent results of zn isotope fractionation between coexisting species in solution the isua serpentinites were permeated by carbonate rich high ph hydrothermal solutions at medium temperature 100 300 c zinc isotopes therefore stand out as a ph meter for fossil hydrothermal solutions the geochemical features of the isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the mariana forearc the reduced character and the high ph inferred for these fluids make archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids

vent fluid chemistry of the rainbow hydrothermal system 36 n mar phase equilibria and in situ ph controls on subseafloor alteration processes abstract the rainbow hydrothermal field is located at 36 13 8 n 33 54 15 w at 2300 m depth on the western flank of a non volcanic ridge between the south amar and amar segments of the mid atlantic ridge the hydrothermal field consists of 10 15 active chimneys that emit high temperature 365 c fluid in july 2008 vent fluids were sampled during cruise knox18rr providing a rich dataset that extends in time information on subseafloor chemical and physical processes controlling vent fluid chemistry at rainbow data suggest that the mg concentration of the hydrothermal end member is not zero but rather 1 5 2 mmol kg this surprising result may be caused by a combination of factors including moderately low dissolved silica low ph and elevated chloride of the hydrothermal fluid combining end member mg data with analogous data for dissolved fe si al ca and h2 permits calculation of mineral saturation states for minerals thought appropriate for ultramafic hosted hydrothermal systems at temperatures and pressures in keeping with constraints imposed by field observations these data indicate that chlorite solid solution talc and magnetite achieve saturation in rainbow vent fluid at a similar ph t p 400 c 500 bar of approximately 4 95 while higher ph values are indicated for serpentine suggesting that serpentine may not coexist with the former assemblage at depth at rainbow the high fe mg ratio of the rainbow vent fluid notwithstanding the mole fraction of clinochlore and chamosite components of chlorite solid solution at depth are predicted to be 0 78 and 0 22 respectively in situ ph measurements made at rainbow vents are in good agreement with ph t p values estimated from mineral solubility calculations when the in situ ph data are adjusted for temperature and pressure calculations further indicate that ph t p and dissolved h2 are extremely sensitive to changes in dissolved silica owing to constraints imposed by chlorite solid solution fluid equilibria indeed the predicted correlation between dissolved silica and h2 defines a trend that is in good agreement with vent fluid data from rainbow and other high temperature ultramafic hosted hydrothermal systems we speculate that the moderate concentrations of dissolved silica in vent fluids from these systems result from hydrothermal alteration of plagioclase and olivine in the form of subsurface gabbroic intrusions which in turn are variably replaced by chlorite magnetite talc tremolite with important implications for ph lowering dissolved sulfide concentrations and metal mobility

low temperature hydrothermal oil and associated biological precursors in serpentinites from mid ocean ridge abstract the origin of light hydrocarbons discovered at serpentinite hosted mid ocean hydrothermal fields is generally attributed to the abiogenic reduction of carbon di oxide by molecular hydrogen released during the progressive hydration of mantle derived peridotites these serpentinization by products represent a valuable source of carbon and energy and are known to support deep microbial ecosystems unrelated to photosynthesis in addition the pool of subsurface organic compounds could also include materials derived from the thermal degradation of biological material we re investigate the recently described relics of deep microbial ecosystems hosted in serpentinites of the mid atlantic ridge 4 6 n in order to study the ageing and hydro thermal degradation of the preserved biomass an integrated set of high resolution micro imaging techniques scanning electron microscopy high resolution transmission electron microscopy raman and fourier transform infra red microspectroscopy confocal laser scanning microscopy and scanning transmission x ray microscopy at the carbon k edge has been applied to map the distribution of the different organic components at the micrometer scale and to characterize their speciation and structure we show that biologically derived material containing aliphatic groups along with carbonyl and amide functional groups has experienced hydrothermal degradation and slight aromatization in addition aliphatic compounds up to c 6 c 10 with associated carboxylic functional groups wet the host bastite and the late serpentine veins crosscutting the rock these compounds represent a light soluble organic fraction expelled after biomass degradation through oxidation and thermal cracking the detected complex organic matter distribution recalls a typical petroleum system where fossil organic matter of biological origin maturates expelling the soluble fraction which then migrates from the source to the reservoir ecosystem hosting serpentinites can thus be seen as source rocks generating a net transfer of hydrocarbons and or fatty acids issued from oxidative processes and primary cracking reactions then migrating upward through the serpentine vein network this finally suggests that deep thermogenic organic compounds of biological origin can be a significant contributor to the organic carbon balance at and far below peridotite hosted hydrothermal fields

a serpentinite hosted ecosystem in the southern mariana forearc several varieties of seafloor hydrothermal vents with widely varying fluid compositions and temperatures and vent communities occur in different tectonic settings the discovery of the lost city hydrothermal field in the mid atlantic ridge has stimulated interest in the role of serpentinization of peridotite in generating h2 and ch4 rich fluids and associated carbonate chimneys as well as in the biological communities supported in highly reduced alkaline environments abundant vesicomyid clam communities associated with a serpentinite hosted hydrothermal vent system in the southern mariana forearc were discovered during a dsv shinkai 6500 dive in september 2010 we named this system the shinkai seep field ssf the ssf appears to be a serpentinite hosted ecosystem within a forearc convergent margin setting that is supported by fault controlled fluid pathways connected to the decollement of the subducting slab the discovery of the ssf supports the prediction that serpentinite hosted vents may be widespread on the ocean floor the discovery further indicates that these serpentinite hosted low temperature fluid vents can sustain high biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life

hydrothermal activity on the southern mid atlantic ridge tectonically and volcanically controlled venting at 4 5 s we report results from an investigation of the geologic processes controlling hydrothermal activity along the previously unstudied southern mid atlantic ridge 3 7 s our study employed the noc uk deep tow sidescan sonar instrument tobi in concert with the whoi usa autonomous underwater vehicle abe to collect information concerning hydrothermal plume distributions in the water column co registered with geologic investigations of the underlying seafloor two areas of high temperature hydrothermal venting were identified the first was situated in a non transform discontinuity ntd between two adjacent second order ridge segments near 4 02 s distant from any neovolcanic activity this geologic setting is very similar to that of the ultramafic hosted and tectonically controlled rainbow vent site on the northern mid atlantic ridge the second site was located at 4 48 s at the axial summit centre of a second order ridge segment there high temperature venting is hosted in an 18 km2 area of young lava flows which in some cases are observed to have flowed over and engulfed pre existing chemosynthetic vent fauna in both appearance and extent these lava flows are directly reminiscent of those emplaced in winter 2005 06 at the east pacific rise 9 50 n and reference to global seismic catalogues reveals that a swarm of large m 4 6 5 6 seismic events was centred on the 5 s segment over a 24 h period in late june 2002 perhaps indicating the precise timing of this volcanic eruptive episode temperature measurements at one of the vents found directly adjacent to the fresh lava flows at 5 s mar turtle pits have subsequently revealed vent fluids that are actively phase separating under conditions very close to the critical point for seawater at 3000 m depth and 407 c the hottest vent fluids yet reported from anywhere along the global ridge crest

methane rich fluids in the oceanic crust analyses of fluid inclusions in plutonic rocks recovered from the slow spreading southwest indian ridge swir record ch4 concentrations of 15 40 times those of hydrothermal vent fluids and of basalt hosted volcanic gases and provide the first direct sampling of co2 ch4 h2o h2 c bearing fluids in the oceanic crust compositional thermal and spatial analyses of these fluids are used to model the evolution of volatiles during the crystallization and cooling of mid ocean ridge magma chambers and to assess the potential importance of carbon bearing fluids in geochemical processes in the lower crustal component of hydrothermal systems results from these analyses show that the earliest fluids to be exsolved from the melts are dominated by co2 rich vapors which with progressive fractionation evolved to more h2o rich compositions these later fluids were most likely exsolved under immiscible conditions and involved the development of co2 h2o rich vapors and co2 h2o nacl brines that were trapped during mineral growth as well as during later high temperature fracturing events co2 ch4 h2o rich fluids in olivine and plagioclase minerals that contain up to 30 50 mol co2 and 33 mol ch4 may reflect respeciation of magmatic co2 during cooling and attendant graphite precipitation phase equilibria suggest that these fluids reequilibrated at 500 600 c and at fo2 s 3 log units below to close to qfm conditions alternatively the inclusions may record respeciation of magmatic fluids attendant with the inward diffusion of h2 into the inclusions and reduction of entrapped co2 during degassing and cooling of the gabbros throughout the subsolidus regime subsequent seawater reaction at minimum temperatures of 400 c with mafic rich layers within the gabbroic rocks or with ultramafic material that underlies the plutonic sequence resulted in the formation of ch4 h2o fluids that contain up to 40 mol ch4 molecular h2 and graphite daughter minerals these data provide strong evidence that the ch4 h2o rich fluids produced during serpentinization reactions were trapped under equilibrium conditions in the presence of graphite at very near to qfm conditions the ubiquitous occurrence of ch4 rich fluids in oceanic crustal layer 3 rocks from the swir indicates that these fluids may be a significant and previously unrecognized source for these volatile species in some hydrothermal systems venting on the seafloor and that the deep seated fluids most likely play an important role in the transfer of carbon from the lithosphere to the hydrosphere

carbon isotopes and petrography of kerogens in 3 5 ga hydrothermal silica dikes in the north pole area western australia more than 600 specimens of 3 5 ga old hydrothermal silica dikes from the north pole area pilbara craton western australia have been studied petrographically the kerogens in 44 samples have been analyzed isotopically c and n and chemically c n and h the silica dikes are composed mainly of fine grained silica modal abundance 97 and are classified into two types by minor mineral assemblages b black type and g gray type the b type silica dikes contain kerogen 0 37 to 6 72 mgc g average 2 44 mgc g n 21 and disseminated sulfides dominantly pyrite and fe poor sphalerite in some cases carbonate and apatite are also present their silica dominated and sulfide poor mineral assemblages suggest precipitation from low temperature reducing hydrothermal fluid likely 100 200 c on the other hand the g type silica dikes are sulfide free and concentrations of kerogen are relatively low 0 05 to 0 41 mgc g average 0 17 mgc g n 13 they typically contain fe oxide mainly hematite which commonly replaces cubic pyrite and rhombic carbonate some g types occur along secondary quartz veins these textures indicate that the g type silica dikes were formed by postdepositional metasomatism oxidation of the b types and that the b types probably possess premetasomatic signatures the 13c values of kerogen in the b types are 38 1 to 33 1 average 35 9 n 21 which are 4 lower than those of the g types 34 5 to 30 0 average 32 2 n 19 and 6 lower than bedded chert 31 2 to 29 4 average 30 5 n 4 this indicates the preferential loss of 12c during the metasomatism estimated fractionation factor 0 9985 considering the metasomatic effect on carbon isotopes with probably minor diagenetic and metamorphic overprints we conclude that the original 13c values of the kerogen in the silica dikes would have been heterogeneous 5 and at least some material had initial 13c values of 38 the inferred 13c depletions of organic carbon could have been produced by anaerobic chemoautotrophs such as methanogen but not by aerobic photoautotrophs this is consistent with the estimated physical and chemical condition of the hydrothermal fluid which was probably habitable for anaerobic and thermophilic hyperthermophilic chemoautotrophs alternatively the organic matter may have been possibly produced by abiological reaction such as fischer tropsch type ftt synthesis under the hydrothermal condition however the estimated condition is inconsistent with the presence of the effective catalysts for the ftt reaction i e fe ni alloy magnetite and hematite these lines of evidence suggest the possible existence of biosphere in the 3 5 ga sub seafloor hydrothermal system

a search for minerals associated with serpentinization across mars using crism spectral data sites associated with serpentinization processes both on earth and throughout the solar system are becoming increasingly compelling for the study of habitability and astrobiology the co occurrence of serpentine mg carbonate and talc saponite on mars is most like terrestrial sites where this mineral suite is produced in low temperature serpentinizing environments and where on earth these reactions support biological activity this study aims to understand the global distribution of minerals associated with serpentinization we performed a comprehensive analysis of the compact reconnaissance imaging spectrometer for mars crism spectral dataset using factor analysis and target transformation methods to efficiently parse through the large quantity of data these methods allow for the rapid analysis of thousands of images and provide a quantitative means to determine the significant spectral constituents of an image these methods were used to produce a global distribution map of crism images with a significant likelihood of containing the spectral types of interest previous detections of serpentine using traditional crism analysis techniques were typically corroborated and additional detections were identified in isolated locations across the martian southern highlands most serpentine across mars is associated with another fe mg phyllosilicate phase like talc and or saponite except for in the nili fossae region serpentine shows no clear relationship with ultramafic bedrock or with the other mineral phases investigated mg carbonate and talc saponite most serpentine detections were found in isolated exposures associated with crater ejecta knobby terrain or as part of discontinuous layers in crater or valley walls nili fossae shows more pervasive and extensive detections of a serpentine phyllosilicate endmember than previously recognized particularly in the eastern portion of nili fossae where the highest concentration of olivine rich basalts is located these findings imply that large regional scale near surface serpentinizing systems were likely rare on mars however low concentration serpentine detections across the southern highlands do suggest more pervasive serpentinization early in mars history when the planet was more geologically active

the high pco2 caprese reservoir northern apennines italy relationships between present and paleo fluid geochemistry and structural setting abstract the chemical and isotopic compositions of i co2 rich fluids exploited from the 5 000 m deep pieve santo stefano 1 pss1 borehole located in the upper tiber basin northern apennines italy and ii natural gas seeps located in its surroundings mainly in the mt fungaia ophiolitic bearing complex ligurian unit are presented and discussed deep seismic profiles have allowed to identify a thrust related antiform caprese antiform a regional geological structure trapping the pressurized deep fluids fluids from the caprese reservoir cr consist of a co2 n2 rich gas phase sourced by both mantle degassing and thermal degradation of carbonate rocks and organic rich sediments of the umbro tuscan sedimentary series and a na cl saline up to 82 g l of tds brine gases naturally discharging in the study area are related to those present in the cr these gases during their uprising toward the surface mix with shallow aquifers addition of i h2 and h2s derived by the interaction with ophiolite bearing ligurian units and ii thermogenic hydrocarbons originated from the degradation of organic matter contained in the turbiditic sandstone rich formations cervarola falterona unit was also evidenced fluid inclusions trapped in calcite and quartz crystals from the pss1 drill core at the depth of 3864 to 3867 m contain co2 n2 and h2o nacl phases the different paleo co2 n2 contents and densities found with respect to the fluids currently exploited from the cr have been related to the evolution of the reservoir throughout the time compositional data of fluids exploited from pss1 borehole provide a unique opportunity to better characterize chemical physical processes and source regions of past and present deep fluids circulating in northern apennines

high precision pb isotope measurements reveal magma recharge as a mechanism for ore deposit formation examples from lihir island and conical seamount papua new guinea abstract lihir island part of the tabar lihir tanga feni island chain in the sw pacific hosts the giant ladolam gold deposit polymetallic gold mineralization also was discovered offshore at conical seamount in 1998 during rv sonne cruise so 133 the seamount and the island are composed mainly of trachybasalts and basaltic trachyandesites although some monzonites are found on lihir sr isotopic analyses of mineralized samples from the island and the seamount suggest that most of the sr is derived from the local alkaline lavas elevated 87sr 86sr ratios in some of the samples suggest that during the waning stages of the hydrothermal system part of the sr was contributed either from seawater or the thick sequence of marine sediments underlying the island high precision pb isotopic analyses conducted with mc icp ms show that the ores and volcanic rocks share similar pb isotopic compositions suggesting that the pb in the mineralized zones was ultimately derived from local magmatic sources the pb isotopic data however reveal small but significant differences between the mineralized zones and the associated host lavas mineralized samples from lihir have slightly less radiogenic lead isotopic ratios than their host lavas these lead isotopic compositions are similar however to some of the fresh lavas recovered from conical seamount and to a monzonite intrusion underlying the ladolam deposit lead isotopic ratios in mineralized samples from conical seamount are slightly more radiogenic than their host lavas and similar to those of fresh lavas recovered from nearby tubaf and edison seamounts petrographic observations and microprobe elemental analyses reveal a complex magmatic history for the magma chamber inferred beneath conical seamount based on zoning patterns in the conical seamount clinopyroxenes it appears that a sub seamount magma chamber was recharged with a mafic magma similar to the most primitive volatile rich and xenolith bearing lavas recovered from tubaf and edison seamounts rapid cooling of this mafic magma accompanied by exsolution of metal bearing fluids in the relatively shallow magma chamber is proposed as the mechanism that ultimately led to the formation of the gold mineralization similarity of the lead isotopic ratios between the ores and the mafic magmas in the area indicate that the ore metals were primarily derived from the recharging magma not by hydrothermal leaching of the host lavas suggesting that ore deposit genesis can be related to a single volatile rich magmatic pulse within otherwise barren polyphased volcano magmatic complex

evidence from fluid seeps atop serpentine seamounts in the mariana forearc clues for emplacement of the seamounts and their relationship to forearc tectonics abstract the mariana forearc is a non accretionary forearc with numerous seamounts dredge hauls from these seamounts are composed primarily of serpentinite indicating a non volcanic origin in addition dredged carbonate samples reveal 1 the presence of aragonite in water depths greater than the aragonite compensation depth 2 unusual porosity and cement types 3 light carbon and heavy oxygen isotopic compositions and 4 an unusual trace element geochemistry of aragonite and calcite these mineralogic petrologic and geochemical characteristics formed the basis of a prediction that methane bearing fluids are venting from these seamounts subsequent to this prediction submersible dives on a mariana forearc seamount found and sampled chimneys seeping cool water that contains dissolved methane the serpentine substrate beneath the chimneys appears to form from cold gravitational flows of serpentine material fluid inclusion contents of chimney samples also show an earlier history of methane as well as longer chain hydrocarbons aromatics and acetate ions drilling into the flank and the summit of this seamount by the ocean drilling program during leg 125 confirmed the presence of methane other light alkanes and organic acids in the present day interstitial pore fluid of the cores the presence of aromatic compounds and organic acids if derived from the maturation of organic compounds indicates a thermogenic origin for these volatiles strontium isotopic ratios of the aragonitic chimney samples and of the present day interstitial waters range from present day seawater values to significantly lower values the strontium isotopic ratios of the pore waters within the seamount trend toward a relatively less radiogenic composition with increasing depth below the seafloor this strontium isotopic signature is probably not the consequence of near surface processes but more likely a contribution from an igneous source deeper in the lithosphere the lack of a large accretionary prism in the mariana forearc removes the complication of fluid contribution from dewatering of the prism by compression during convergence as in the oregon washington or barbados margins the organic compounds in the fluid inclusions and interstitial pore fluids as well as the isotopic and the geochemical composition of the carbonates and the dissolved constituents suggest that fluids are derived from dewatering compression and dehydration of subducted sediments and the subducting plate furthermore the composition of the fluid is influenced by thermal maturation of organics in subducted sediments as well as by a contribution from a deep igneous source

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

discovery of ancient and active hydrothermal systems along the ultra slow spreading southwest indian ridge 10 16 e 1 we report the discovery of active and fossil hydrothermal systems during r v knorr cruise 162 legs vii and ix along a 400 km long segment of the ultra slow southwest indian ridge swir between 10 and 16 e where the effective spreading rate for mantle upwelling is the slowest of any ocean ridge explored to date 8 4 mm yr 1 full rate eight of forty one optical temperature profiles contain hydrothermal plume characteristics that indicate firm evidence for two active vent sites and tentative evidence for as many as three others fossil hydrothermal material was recovered in 6 of the 38 dredge hauls and includes an occurrence of partially oxidized sulfide breccias four deposits ofsepiolite and silica as well as mn oxide and nontronite cemented breccias the massive sulfide deposit likely developed during mixing of upwelling hot fluids with cold seawater within a shallow permeable fault breccia along a deep seated normal fault bounding the southern rift valley wall silica and sepiolite deposits were found mostly on the rift valley walls and likely formed during low to moderate temperature ultramafic hosted hydrothermal activity the abundance of hydrothermal material and the frequency of localized hydrothermal activity is remarkable because the mantle upwelling and magma supply rates and hence the magmatic heat input along this section of the swir are lower than on any other explored segment of the global mid ocean ridge system this observation suggests that high mantle upwelling and magma supply rates are not required to drive mid ocean ridge hydrothermal systems and that a close relationship between magmatic heat input and hydrothermal activity may not be established at the ultra slow end of the ridge spreading spectrum the frequency and distribution of hydrothermal activity in the study area may reflect a largely tectonic control on fluid circulation with hydrothermal vent sites being preferentially associated with long lived faults that provide fluid pathways our results suggest the contribution of magma starved ridge segments to the global ocean lithosphere geochemical budget is potentially much larger than previously thought

the spatial and temporal distribution of pipe formation offshore namibia a group of nearly 400 pipe structures from the continental slope of northern namibia are analysed for their spatial and temporal distribution the pipes most likely formed as a result of highly focused fluid venting and understanding the factors controlling their distribution in space and time is key to their genesis we analysed their spatio temporal distribution using an arbitrary chronostratigraphic timescale from which it is concluded that the pipes did not form at the same time pipe formation is shown to be intermittent and persistent with 2 29 pipes forming in each of the 20 arbitrary time intervals that are considered to span the neogene period the spatial distribution of these pipes is clustered to dispersed spatial statistics conducted on the distribution of pipe formation timings have shown that two statistically significant groups of pipes exist within the population 1 in the north and west and 2 in the south with the former occurring prior to the latter locally pipe formation is sporadic with clusters and outliers occurring during the same time period a conceptual model is proposed whereby pipe formation in specific locations is the result of localised breaching of the seals for isolated pressure cells which are locally independent yet broadly controlled an inferred basinal fluid source is thought to determine the broader patterns of pipe formation and the focus of this fluid source shifts from north to south with time at a local scale multiple local factors interact producing a sporadic pipe formation distribution through a prolonged period of highly focused fluid migration once formed the pipes continued to focus fluids intermittently leading in some cases to later pockmark formation

geochemistry of hydrothermal fluids from the ultramafic hosted logatchev hydrothermal field 15 n on the mid atlantic ridge temporal and spatial investigation abstract mantle derived ultramafic rocks commonly occur on the seafloor at slow spreading axes and are tectonically emplaced along shear zones since the early 1990s a growing number of hydrothermal systems have been detected in ultramafic settings but chemical data for fluid compositions in active systems are still limited besides the logatchev field at 15 n on the mid atlantic ridge mar the only other active high temperature 300 c hydrothermal field known to be strongly influenced by ultramafics is the rainbow field at 36 n on the mar the field at logatchev consists of six active vent sites at about 3000 m water depth situated along a nw se trending line with distances of 50 200 m between the individual sites the vent sites were mapped in detail and re sampled during two cruises in 2004 and 2005 using a rov the geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen up to 3 5 mm and 19 mm respectively related to serpentinization processes in the reaction zone together with moderate si concentrations of 9 mm a depletion in b compared to seawater and li concentrations lower than in basaltic systems this fluid composition has been identified as characteristic signature of high temperature hydrothermal fluids reacting with ultramafic rocks however additional alteration of gabbroic intrusions is likely the fluid composition is very similar at all vent sites indicating a common source in the reaction zone and little variation during upflow spatial differences in fluid composition were observed between smoking craters and the complex chimney system irina ii but are restricted to elements with strong temperature controlled solubility as cu and co these differences can be related to different exit temperatures up to 350 c and as it is known that more ultramafic hosted hydrothermal systems exist along slow spreading ridges this type of hydrothermal systems might have a significant influence on the elemental budget of the oceans detailed information about the fluid geochemistry and its spatial and temporal variations is an important prerequisite for an estimation of elemental fluxes in ultramafic hosted systems and their relative importance compared to basaltic hosted systems

critical testing of potential cellular structures within microtubes in 145 ma volcanic glass from the argo abyssal plain abstract microtubes within 145 ma volcanic glass from the argo abyssal plain possess intriguing internal microtextures that under light microscopy resemble biological septa and ovoid microbial cells these microtextures have previously been used as part of a suite of evidence to support the biogenicity of such microtubes and similar textures are beginning to be used in attempts to taxonomically classify microtubes from both the modern and ancient oceanic crust within an ichnofossil trace fossil hierarchy here we use high spatial resolution correlative microscopy to characterize the morphology and chemistry of the argo microtubes in order to critically assess the origin of these microtextures and increase our understanding of the potential formation mechanisms of microtubes in volcanic glass electron microscopy shows that the microtubes contain abundant elongated void spaces and when these are reconstructed in three dimensions they closely replicate the morphology and distribution of the previously described septa no organic material is associated with the void spaces and so we reinterpret the septa as cracks within the clay mineral phase that infills the microtubes probably formed during sample collection and or preparation one ovoid body also appears to correlate with void space but further data are required to substantiate such an origin we caution that the study of micro textures within volcanic glass hosted microtubes by optical microscopy alone may be misleading hence each individual occurrence should be subject to detailed micro to nano scale in situ morphological and chemical investigation before being used as a potential biosignature several microtubes do contain elevated levels of carbon typically found within amorphous carbonate minerals that along with nontronite clay have precipitated within the microtubes one microtube contains organic carbon this is heterogeneously distributed occurs away from void spaces and is spatially associated with elevated levels of titanium this organic carbon could originate from in situ biological activity but it could also have been introduced by circulating seawater titanium adsorbed onto this organic material may provide a titanium source for the commonly observed titanite mineralization found in ancient volcanic glass hosted microtubes within greenstone belts and ophiolites that have experienced low grade metamorphism elemental enrichments and depletions in three chemically distinct regions glass alteration rim and tube interior provide further insights into microtube formation mechanisms alteration rims have sharply defined edges are about 0 1 m wide independent of microtube diameter and are primarily composed of si al o ti the tube interiors are depleted in si and al and most other elements ca mg na mn relative to fresh glass but k and fe may be enriched there is no evidence for depletion of elements in the glass immediately exterior to the alteration rim this favours a mechanism whereby microtubes grow by increasing in length rather than increasing in diameter in this model protons are the major agent of glass alteration and the supply of protons and the kinetics of the formation of the si al alteration rim control the diameter of the microtubes

sulfur in peridotites and gabbros at lost city 30 n mar implications for hydrothermal alteration and microbial activity during serpentinization variations in sulfur mineralogy and chemistry of serpentinized peridotites and gabbros beneath the lost city hydrothermal field at the southern face of the atlantis massif mid atlantic ridge 30n were examined to better understand serpentinization and alteration processes and to study fluid fluxes redox conditions and the influence of microbial activity in this active peridotite hosted hydrothermal system the serpentinized peridotites are characterized by low total sulfur contents and high bulk d 34 s values close to seawater composition low concentrations of 34 s enriched sulfide phases and the predominance of sulfate with seawater like d 34 s values indicate oxidation loss of sulfide minerals and incorporation of seawater sulfate into the serpentinites the predominance of pyrite in both serpentinites and gabbros indicates relatively high fo2 conditions during progressive serpentinization and alteration which likely result from high fluid fluxes during hydrothermal circulation and evolution of the lost city system from temperatures of 250 to 150 c sulfate and sulfide minerals in samples from near the base of hydrothermal carbonate towers at lost city show d 34 s values that reflect the influence of microbial activity our study highlights the variations in sulfur chemistry of serpentinized peridotites in different marine environments and the influence of long lived moderate temperature peridotite hosted hydrothermal system and high seawater fluxes on the global sulfur cycle

influence of pyroxene and spinel on the kinetics of peridotite serpentinization hydrothermal experiments were performed at 311 degrees c and 3 0 kbar on natural olivine and peridotite to investigate the kinetics of serpentinization the results show that the rates of reaction strongly depend on grain sizes of solid reactants with smaller grain sizes resulting in faster kinetics after 27 days of reaction the reaction extent was 99 for peridotite with grain sizes of 30 mu m and the reaction extent was 28 for grain sizes of 100 177 mu m compared to peridotite olivine is serpentinized at much slower rates e g 5 3 of reaction extent was achieved for olivine with grain sizes of 100 177 mu m after 27 days approximately five times lower than that reached during peridotite serpentinization such contrasting results are due to the presence of pyroxene and spinel an interpretation which is supported by a marked increase in reaction extents for experiments with the addition of pyroxene and spinel the reaction extent achieved in experiments with 3 wt spinel greatly increased to 98 after 27 days much higher than that achieved during olivine serpentinization these results appear to be related to pyroxene and spinel releasing al and cr during serpentinization as indicated by compositions of serpentine orthopyroxene lost similar to 60 of al at a reaction extent of 59 influence of al and cr is suggested by a dramatic increase in reaction extents with the addition of al2o3 and cr2o3 powders olivine in natural geological settings is commonly associated with pyroxene and spinel consequently serpentinization kinetics may be much faster than previously thought

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

metasomatic origin of quartz pyroxene rock akilia greenland and implications for earth s earliest life a quartz pyroxene rock interpreted as a banded iron formation bif from the island of akilia southwest greenland contains 13 c depleted graphite that has been claimed as evidence for the oldest 3850 million years ago life on earth field relationships on akilia document multiple intense deformation events that have resulted in parallel transposition of early archean rocks and significant boudinage the tails of which commonly form the banding in the quartz pyroxene rock geochemical data possess distinct characteristics consistent with an ultramafic igneous not bif protolith for this lithology and the adjacent schists later metasomatic silica and iron introduction have merely resulted in a rock that superficially resembles a bif an ultramafic igneous origin invalidates claims that the carbon isotopic composition of graphite inclusions represents evidence for life at the time of crystallization

constraints on fluid origins and migration velocities along the marmara main fault sea of marmara turkey using helium isotopes abstract fluids venting from the submarine portion of the marmara main fault part of the north anatolian fault system turkey were sampled in ti bottles deployed by submersible the fluids consist of mixtures of fault derived gases fault related cold seep fluids and ambient seawater these components can readily be distinguished using the isotopes of he and the he ne ratios 3he 4he ratios range between 0 03 0 1 and 4 9 0 4 ra indicating that both crustal and mantle derived sources of helium are sampled by the fault the dominant gas in all the samples analyzed is methane with the abundance of co2 below detection 2 in the mantle rich high 3he 4he fluids this is in contrast to nearly all mantle derived fluids where the c species are dominated by co2 while high ch4 co2 ratios may reflect organic or inorganic reactions within the crust which reduce mantle derived co2 to methane this is not a priori necessary we show that simple dilution of mantle fluids with methane produced within local sediments could result in the high 3he 4he methane rich gases currently emanating from the fault this observation is supported by an anticorrelation between 3he 4he and c 3he which is consistent with addition of c and 4he simultaneously to the fluids the highest 3he 4he ratios were found in the tekirdag basin at the foot of the escarpment bordering the western sea of marmara where seismic data are consistent with the presence of a fault network at depth which could provide conduits permitting deep seated fluids to rise to the surface the lack of recent volcanism or any evidence of underlying magmatism in the area along with low temperature fluids strongly suggests that the 3he rich helium in these fluids was derived from the mantle itself with the marmara main fault providing a high permeability conduit from the mantle to the surface assuming that the mantle source to the fluids originally had a 3he 4he ratio of 6 ra the minimum fluid velocities considering only vertical transport and no mixing with parentless 4he implied by the high 3he 4he ratios are of the order of 1 100 mm yr 1

fluid geochemistry and geothermometry in the western sector of the sabatini volcanic district and the tolfa mountains central italy abstract a geochemical survey of 197 fluid discharges cold and thermal waters and bubbling pools and 15 gas emissions from the western sector of the sabatini volcanic district and the tolfa mountains latium central italy was carried out in 2007 2008 the chemical and isotopic compositions of the fluid discharges indicate the occurrence of two main sources 1 relatively shallow aquifers with ca na k hco 3 and ca mg hco 3 compositions when trapped in volcanic and sedimentary formations respectively and 2 a deep reservoir which is hosted in the mesozoic carbonate sequence rich in co 2 and having a ca so 4 hco 3 composition dissolution of a co 2 rich gas phase into the shallow aquifers produces high tds and high pco 2 cold waters while oxidation of deep derived h 2 s to so 4 2 generates low ph the 13 c co 2 values for gas emissions from 2 8 to 2 7 vs vpdb suggest that the origin of co 2 associated with the deep fluids is mainly related to thermo metamorphic reactions within the carbonate reservoir although significant mantle contribution may also occur however r r a values 0 37 0 62 indicate that he is mainly produced by a crustal source with a minor component from a crust contaminated mantle on the basis of the 13 c ch 4 and d ch 4 values from 25 7 to 19 5 vs vpdb and from 152 to 93 4 vs vsmow respectively ch 4 production is associated with thermogenic processes possibly related to abiogenic co 2 reduction within the carbonate reservoir the 34 s h 2 s values from 9 3 to 10 4 vs vcdt are consistent with the hypothesis of a sedimentary source of sulfur from thermogenic reduction of triassic sulfates geothermometric evaluations based on chemical equilibria co 2 ch 4 and separately h 2 s suggest that the reservoir equilibrium temperature is up to 300 c the d and 18 o data indicate that water recharging both the shallow and deep aquifers has a meteoric origin fluid geochemistry coupled with gravimetric data and tectonic lineaments supports the idea that significant contributions from a deep seated geothermal brine are present in the stigliano thermal fluid discharges exploration surveys investigated this area during 70 s 90 s for geothermal purposes nevertheless presently the area is still under exploited the presence of thermal waters and anomalous heat flow together with the demographic growth of the last years makes this site a suitable location for direct applications of the geothermal resource

a starving majority deep beneath the seafloor the rocks and sediments beneath the seafloor may harbor most of earth s microorganisms molecular approaches are beginning to provide clues regarding the energy sources fueling their metabolic activity

diverse microstructures from archaean chert from the mount goldsworthy mount grant area pilbara craton western australia microfossils dubiofossils or pseudofossils abstract a diverse assemblage of indigenous carbonaceous microstructures classified here as highly probable microfossils to pseudomicrofossils is present in the ca 2 97 ga farrel quartzite gorge creek group at mount grant and mount goldsworthy pilbara craton western australia the microstructures are an integral part of the primary sedimentary fabrics preserved in black chert beds the interbedding of chert with layers of large silicified crystal pseudomorphs and fine to coarse grained volcaniclastic clastic beds indicate deposition in a partially evaporitic basin with terrigenous clastic and volcaniclastic input similar associations of microstructures are present at the same stratigraphic level in outcrops more than 2 km apart four major microstructural types are present thread like film like spheroidal and lenticular to spindle like each of which can be further subdivided into several sub types most of the microstructures were deposited as part of an assemblage of chemical and clastic sediments although there are some thread like microstructures present for which a synsedimentary origin cannot be confirmed many specimens appear to have originally had flexible but breakable walls and some occur in colony like aggregations size distributions for the four major types are generally narrow a feature typical of biogenic structures the microstructures are composed of disordered carbon as revealed by raman spectroscopy and the bulk isotopic composition of the carbon is 13 c the combined morphological and geological evidence suggests that the film like structures small spheres associated with films large spheroids and spindle like structures are probable to highly probable fossil remains of microorganisms the morphological variety among the microstructures suggests that a diverse microbial ecosystem flourished in the pilbara region during the archaean

seismic imaging of magma sills beneath an ultramafic hosted hydrothermal system hydrothermal circulation at mid ocean ridge volcanic segments extracts heat from crustal magma bodies however the heat source driving hydrothermal circulation in ultramafic outcrops where mantle rocks are exhumed in low magma supply environments has remained enigmatic here we use a three dimensional p wave velocity model derived from active source wide angle refraction reflection ocean bottom seismometer data and pre stack depth migrated images derived from multichannel seismic reflection data to investigate the internal structure of the rainbow ultramafic massif which is located in a non transform discontinuity of the mid atlantic ridge seismic imaging reveals that the ultramafic rocks composing the rainbow massif have been intruded by a large number of magmatic sills distributed throughout the massif at depths of 2 10 km these sills which appear to be at varying stages of crystallization can supply the heat needed to drive high temperature hydrothermal circulation and thus provide an explanation for the hydrothermal discharge observed in this ultramafic setting our results demonstrate that high temperature hydrothermal systems can be driven by heat from deep sourced magma even in exhumed ultramafic lithosphere with very low magma supply

organic acid metastability in sedimentary basins thermodynamic calculations indicate that co sub 2 in sedimentary basins may be in stable redox equilibrium with organic acids found in basinal brines but that ch sub 4 is not these calculations also show that the high concentrations of carboxylic acids are from equilibrium with decarboxylation reactions a compilation of recent analyses of carboxylic acids from aqueous solutions associated with petroleum reservoirs shows that there is no trend in acid concentrations with temperature however inspection of these data at approximately 100 c indicates that acetic and propanoic acids are in homogeneous metastable equilibrium oxygen fugacities indicated by this metastable assemblage are consistently lower than those set by iron oxide assemblages this is not surprising because both hematite and magnetite are unstable relative to siderite in the presence of detectable concentrations of acetic acid

critical testing of earth s oldest putative fossil assemblage from the 3 5ga apex chert chinaman creek western australia abstract structures resembling cyanobacterial microfossils from the ca 3465 ma old apex chert of the warrawoona group in western australia have until recently been accepted as providing the oldest morphological evidence for life on earth and have been taken to support an early beginning for oxygen releasing photosynthesis eleven species of filamentous prokaryote principally distinguished by shape and geometry have been put forward as meeting the criteria required of authentic archaean microfossils they were contrasted with other microfossils that were dismissed as either unreliable or irreproducible the aim of this paper is to provide a detailed account of research recently reported by us on the type and recollected material involving optical and electron microscopy digital image analysis and other techniques all previously figured holotype materials are illustrated here and the context for all the published materials is re evaluated the apex chert microfossils occur near the top of a 1 5 km long chert dyke complex associated with major synsedimentary growth faults highly localised glassy felsic tuffs erupted explosively from this and other fissures during the early stages of volcanism and were followed by the deposition of essentially hydrothermal black and white baso4 rich cherts that infiltrated the feeder dykes underplating and dilating adjacent stratiform cherts before the start of the next volcanic cycle the apex chert microfossils occur within multiple generations of these metalliferous hydrothermal vein cherts some 100 m down the dyke system comparable structures occur in associated volcanic vent glass and in hydrothermal cherts at least 1 km deep we find no supporting evidence for a primary biological origin we reinterpret the purported microfossil like structures as pseudofossils that formed from the reorganization of carbonaceous matter mainly during recrystallization from amorphous to spherulitic silica

controls on magmatism in an island arc environment study of lavas and sub arc xenoliths from the tabar lihir tanga feni island chain papua new guinea the tabar lihir tanga feni tltf islands of papua new guinea mainly comprise high k calc alkaline and silica undersaturated alkaline rocks that have geochemical features typical for subduction related magmatism numerous sedimentary mafic and ultramafic xenoliths recovered from tubaf seamount located on the flank of lihir island provide a unique opportunity to study the elemental and isotopic composition of the crust and mantle wedge beneath the arc and to evaluate their relationships to the arc magmatism in the region the sedimentary and mafic xenoliths show that the crust under the islands is composed of sedimentary sequences and oceanic crust with pacific affinity a majority of the ultramafic xenoliths contain features indicating wide spread metasomatism in the mantle wedge under the tltf arc leaching experiments reveal that the metasomatized ultramafic xenoliths contain discrete labile phases that can account for up to 50 or more of elements such as cu zn rb u pb and light ree rare earth elements most likely introduced in the xenoliths via hydrous fluids released from a subducted slab the leaching experiments demonstrated that the light ree enrichment pattern can be more or less removed from the metasomatized xenoliths and the residual phases exhibit ree patterns that range from flat to light ree depleted sr nd isotopic data for the ultramafic residues show a coupled behavior of increasing 87sr 86sr with decreasing 143nd 144nd ratios the labile phases in the ultramafic xenoliths represented by the leachates show decoupling between sr and nd with distinctly more radiogenic 87sr 86sr than the residues both leachates and residues exhibit very wide range in their pb isotopic compositions indicating the involvement of three components in the mantle wedge under the tltf islands two of the components can be identified as pacific oceanic mantle and pacific sediments some of the ultramafic samples and clinopyroxene separates however exhibit relatively low 206pb 204pb at elevated 207pb 204pb suggesting that the third component is either indian ocean type mantle or australian subcontinental lithospheric mantle geochemical data from the ultramafic xenoliths indicate that although the mantle wedge in the area was extensively metasomatized it did not significantly contribute to the isotopic and incompatible trace element compositions of tltf lavas compared to the mantle samples the tltf lavas have very restricted pb isotopic compositions that lie within the pacific morb range indicating that magma compositions were dominated by melts released from a stalled subducted slab with pacific morb affinity interaction of slab melts with depleted peridotitic component in the mantle wedge followed by crystal fractionation most likely generated the geochemical characteristics of the lavas in the area

hydrothermal activity on the ultra slow spreading southern knipovich ridge we report first evidence for hydrothermal activity from the southern knipovich ridge an ultra slow spreading ridge segment in the norwegian greenland sea evidence comes from optical backscatter anomalies collected during a systematic side scan sonar survey of the ridge axis augmented by the identification of biogeochemical tracers in the overlying water column that are diagnostic of hydrothermal plume discharge mn ch4 atp analysis of coregistered geologic and oceanographic data reveals that the signals we have identified are consistent with a single high temperature hydrothermal source located distant from any of the axial volcanic centers that define second order segmentation along this oblique ridge system rather our data indicate a hydrothermal source associated with highly tectonized seafloor that may be indicative of serpentinizing ultramafic outcrops consistent with this hypothesis the hydrothermal plume signals we have detected exhibit a high methane to manganese ratio of 2 3 1 this is higher than that typical of volcanically hosted vent sites and provides further evidence that the source of the plume signals reported here is most probably a high temperature hydrothermal field that experiences some ultramafic influence compare to rainbow and logachev sites mid atlantic ridge while such sites have previously been invoked to be common on the sw indian ridge this may be the first such site to be located along the arctic ultra slow spreading ridge system

sources of ree in sediment cores from the rainbow vent site 36 14 n mar a geochemical investigation was carried out on two sediment cores collected at 2 and 5 km from the rainbow hydrothermal vent site bulk sediment compositions indicate that these cores record clear enrichments in fe cu mn v p and as from hydrothermal plume fallout cave et al 2002 cave r r german c r thomson j nesbitt r w 2002 fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge geochim cosmochim acta 66 11 1905 1923 sequential dissolution of the bulk sediments has been used to discriminate between a leach biogenic and oxy hydroxide component and a residual phase detrital and sulphide sulphate fractions major element data al fe ti mn mg ca si and index reveal that the hydrothermal input as recorded in the leach phase is much stronger than apparent from bulk sediment analyses alone ree patterns for the leach phase record contributions from both biogenic carbonate mimicking seawater ree patterns and hydrothermal oxy hydroxides with the latter exhibiting positive eu anomalies hydrothermal derived and negative ce anomalies seawater derived based on major element and ree data the residue contains contributions from aeolian dust input local morb material and a hydrothermal component ternary ree mixing calculations indicate that most of the ree within the residual fraction 80 is derived from hydrothermal material while detrital contributions to the ree budget as deep sea clay and volcanic debris are

some perspectives on isotope biosignatures for early life abstract the idea of using stable isotope compositions of light elements particularly of carbon as a sign of biological activities biosignatures both present and past dates back to the dawn of stable isotope geochemistry in the 1940s in the wake of the discovery of large variations in 13 c 12 c ratios among various carbon bearing materials including plants and fossil fuels the contentious debate ensued between kalervo rankama and harmon craig in the early 1950s whether the origin of graphitic carbon in ancient rocks biogenic vs abiogenic can be uniquely identified by its isotopic compositions during the last half century great progress has been made in understanding biogeochemical processes in modern and ancient terrestrial environments rapid developments in the last decade of novel analytical techniques and the birth of new geoscience fields such as geomicrobiology and astrobiology has prompted resurgence in the application not only of conventional light stable isotopes but also of those of metal and other intermediate elements however recent debates on the origin of graphitic carbons from early archean rocks from australia and greenland are very much reminiscent of the rankama craig debate half a century ago here an attempt is made to review briefly the history of isotope biosignatures and to critically assess current criteria for early life a number of possible abiotic pathways exist that lead to the synthesis of various organic and reduced carbon compounds alkanes pah amino acids lipids graphitic carbon etc depleted in 13 c due to large kinetic isotope effects up to ca 60 it also seems very likely that the mantle contains indigenous carbons graphite diamond dissolved carbons carbide with low 13 c values 20 to 30 which have previously been considered recycled sedimentary organic carbons or surface contamination this analysis prompts us to reassess our current and future strategies for identifying early and extraterrestrial life using isotope biosignatures

formation of h2 ch4 and n species during low temperature experimental alteration of ultramafic rocks abstract hydrogen methane and ammonium are important chemical species for chemolithotrophic microorganisms that sustain subsurface endolithic communities it is well known that production of h 2 through serpentinization of the primary fe ii containing minerals olivine and pyroxene in ultramafic rocks and reduction of co 2 to ch 4 are processes that occur at higher temperatures knowledge is however limited about these reactions under low temperature conditions and how they are affected by fe ii containing secondary minerals such as brucite and serpentine which are commonly found in these environments in this experimental study we explored the formation of h 2 ch 4 and nh 4 during low temperature 25 c reactions between deionised water and 1 unaltered 2 medium altered and 3 highly altered dunites over a period of 99 days hydrogen was detected in all three experiments and the concentration increased over time the o 2 concentration decreased over time but o 2 was still present at significant levels when h 2 started to form this suggests that the h 2 was formed locally at the surface of mineral grains rather than in the hypoxic solution the highly altered dunite gave the highest and the unaltered dunite the lowest h 2 concentrations and while the o 2 concentration decreased fast with the medium altered dunite significant amounts of o 2 still remained with the unaltered dunite at the end of the experiments both the medium and highly altered dunite gave o 2 concentrations close to or below the detection limit during the last part of the experiment factors that likely affected the h 2 production are fe content mineralogy dissolution rates and surface areas of the minerals as well as the presence of catalytic minerals such as chromite and magnetite methane was also detected and increased with time in all experiments the results indicate that ch 4 formation also occurred locally on the surface of minerals detection of both nh 4 and no 3 in the aqueous solutions indicates that previously absorbed n species were leached out during the experiment increasing nh 4 and decreasing no 3 concentrations over time suggest no 3 reduction likely catalysed by mineral surfaces the results imply that low temperature water rock reactions in moderately to highly altered ultramafic rocks provide reduced chemical species that can be utilized as electron donors in energy yielding metabolic processes by subsurface microorganisms such reactions could play an important role in sustaining subsurface microbial communities particularly in ophiolites and near seafloor parts of the ultramafic oceanic lithosphere at slow spreading mid ocean ridges and possibly also in other rocks and sediments the results suggest that brucite and possibly also serpentine may be more important sources of fe ii and thus h 2 formation than olivine in low temperature ultramafic systems formation of h 2 in reducing microenvironments on mineral surfaces surrounded by oxic conditions increases the extent of h 2 formation and the subsurface habitat for aerobic h 2 oxidizing microorganisms

microbial utilization of abiogenic carbon and hydrogen in a serpentinite hosted system abstract mantle rocks exposed on the seafloor constitute a highly reactive chemical and thermal system in which interaction with seawater to produce serpentinite has major consequences for lithospheric cooling global geochemical cycles and microbial activity serpentinite hosted hydrothermal activity is exemplified by the lost city hydrothermal field 30 n mid atlantic ridge where fluid rock reactions in the underlying ultramafic rocks result in high concentrations of abiotic hydrogen methane c 2 alkanes and formate such systems have been proposed as possible analogs to the early earth environments that gave rise to the first biochemical pathways thus characterizing the local microbial communities and their potential link with abiogenic compounds is of particular significance here we demonstrate that in active carbonate chimneys where microbial sulfate reduction is important up to 50 of the microbial biomass is synthesized from mantle carbon conversely mantle carbon contributes only 10 of the biomass in areas with minimal sulfate reduction we attribute this difference to greater incorporation of formate or methane by the dominant microbial species the lost city methanosarcinales in locations where sulfate reducers are able to facilitate this assimilation the ability of autotrophic communities at lost city to capitalize on the steady stream of chemical products resulting from serpentinization reactions and to utilize abiogenic mantle carbon lend credence to the hypothesis that early biosynthetic pathways could have developed in similar environments

climatic basis for sluggish macroevolution during the late paleozoic ice age rates of origination and extinction for marine invertebrates fell at the onset of the late paleozoic ice age in late mississippian time and remained low until glaciation ended in middle permian time through the use of a database of stratigraphic and geographic occurrences of brachiopod genera these macroevolutionary changes are traced to the loss of genera with narrow latitudinal ranges which had intrinsically high turnover rates at the onset of glaciation in late visean time when glaciation waned in late sakmarian time narrowly distributed genera rebounded abruptly and restored the global fauna to its pre ice age configuration because narrowly distributed brachiopod genera had dominated tropical diversity the major biotic effects of the late paleozoic ice age were felt at low latitudes the climatic regime of this ice age thus altered the marine ecosystem to one characterized by broadly adapted long lived genera

tectonic controls on atmospheric climatic and biological evolution 3 5 2 4ga abstract this paper presents a speculative scenario for the evolution of the earth s surface environment and biological community 3 5 2 4 ga based on the geologic record and its interpretation available geologic evidence suggests that the earth s climate before 3 2 ga was hot probably 60 73 c as a result of a co 2 and ch 4 greenhouse the early biological community was probably dominated by anoxygenic photosynthetic thermophiles cyanobacteria if they evolved before 3 1 ga would have struggled to survive at such high temperatures as a result the atmosphere contained extremely low levels of o 2 and 33 s shows wide departures from 0 indicating mass independent fractionation of s isotopes in the upper atmosphere this hot early climate collapsed 3 1 3 0 ga due to growth of large new blocks of continental crust cratons the weathering of which resulted in the depletion of atmospheric co 2 and eventual drawdown of ch 4 due to formation and rainout of methane aerosols cooling may have culminated in glaciation about 3 0 2 9 ga this climatic catastrophe and attendant changes in atmospheric composition drove a major biological revolution 3 0 2 7 ga characterized by the emergence of new low temperature taxa including cyanobacteria and their spread throughout surface environments at the expense of extreme thermophiles including methanogens during a period of general tectonic stability 3 0 2 7 ga the earth s surface was characterized by overall clement conditions with temperatures 2 after 2 75 ga and by 2 7 ga surface temperatures had returned to 60 c cyanobacteria were again suppressed o 2 production waned and atmospheric mass independent fractionation is again indicated by extreme variations in 33 s these conditions persisted perhaps intermittently until about 2 5 2 4 ga when weathering and erosion of vast new blocks of continental crust formed about 2 65 2 6 ga caused the second and probably last collapse of a 60 c surface climate broad tectonic climatic and biological events 3 5 2 9 ga are remarkably parallel to those of the late archean and paleoproterozoic 2 75 2 2 ga and neoproterozoic 1 0 0 50 ga these 500 myr long cycles of greenstone volcanism and crustal generation climatic and atmospheric instability and biological innovation reflect the long term interaction of the tectonic atmospheric climatic and biological components of the earth s surface system they suggest that the evolution of the earth s interior expressed through its control on the formation of large blocks of continental crust has influenced atmospheric composition and climate which in turn have provided a fundamental control on the timing and directions of biological evolution throughout earth history

microbial remains in some earliest earth rocks comparison with a potential modern analogue abstract carbonaceous matter cm from ca 3 5 ga hydrothermal black cherts of the pilbara craton of western australia and the barberton greenstone belt of south africa yielded transmission electron microscopy tem images that are suggestive of microbial remains and possible remnants of microbial cell walls these are compared to a potential modern analogue the hyperthermophilic methanocaldococcus jannaschii derived from an active seafloor hydrothermal environment and cultured under similar conditions a striking resemblance to the early archaean forms was evident in wall structure and thermal degradation mode cell disintegration of the cultures occurred at 100 c marking the limits of life complete disintegration deformation and shrinkage occurred at 132 c a multidisciplinary approach to the characterisation of the cm was undertaken using organic petrology tem coupled with electron dispersive spectral analysis eds high resolution tem hrtem to determine molecular ordering and elemental and carbon isotope geochemistry reflectance measurements of the cm to determine thermal stress yielded a range of values corresponding to several populations and pointing to different sources and processes the 13c values of dresser formation cm 36 5 to 32 1 are negatively correlated with toc 0 13 0 75 and positively correlated with c n ratio 134 569 which is interpreted to reflect the relative abundance of high ro oxidised recycled cm and preferential loss of 12c and n during thermal maturation tem observations inferred carbon isotopic heterogeneity and isotope fractionations of 27 to 32 are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the cm

dynamic control on serpentine crystallization in veins constraints on hydration processes in oceanic peridotites deformation and hydration processes are intimately linked in the oceanic lithosphere but the feedbacks between them are still poorly understood especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and or mass transfer serpentinization is accompanied by abundant veining marked by different generations of vein filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation we use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow spreading ridges we have selected a representative set of veins from ocean floor serpentinites of the mid atlantic ridge near kane transform fault 23 n and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy sem tem with electron microprobe analyses four main veining episodes v1 to v4 accompany the serpentinization the first episode identified as vein generation v1 is interpreted as the tectonically controlled penetration of early seawater dominated fluid within peridotites enhancing thermal cracking and mesh texture initiation at 3 4 km up to 8 km depth and at t 300 350 c the two following vein stages v2 and v3 formed in a closed diffusive system and accommodate volume expansion required to reach almost 50 serpentinization of the protolith the cracks exploited by these veins were caused by the progressive unroofing at depths of 4 to 2 km along a detachment fault degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization and this capacity is in turn linked to the exhumation rate and local tectonics during this period water consumed by hydration may prevent the establishment of convective hydrothermal cells the onset of an open hydrothermal system in the shallow lithosphere 2 km where brittle fracturing and advective transfer dominate and enable the completion of serpentinization is marked by the last vein generation v4 these results show a complete history of alteration with the crystallization of different types of serpentine recording different tectonic events chemical conditions and modes of hydrothermal alteration of the lithosphere

hydrogen generation from mantle source rocks in oman hydrogen gas associated with ca2 oh rich alkaline groundwaters ph 10 12 is at present emanating from ultramafic rocks of the oman ophiolite isotopic and chemical evidence indicates that hydrogen is formed by low temperature redox reactions in a closed groundwater environment this is normally a cryptic process in the hydrosphere but is fortuitously revealed by the unusual hydrogeological conditions in oman where atmospheric oxygen is totally assimilated it is suggested that hydrogen generation in mantle source rocks at depth and in the early archaean surface environment may be more widespread than has hitherto been realised

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

multiple origins of methane at the lost city hydrothermal field abstract the high concentrations of methane in the vent fluids of the lost city hydrothermal field represent the sum of abiotic and biological sources and sinks stable isotopes of carbon are of limited value in discriminating between the various sources of methane because the isotope effects associated with the multiple processes forming and consuming methane are each poorly constrained and the products of these processes are pooled furthermore reservoir effects complicate interpretation the near quantitative reduction of inorganic carbon to methane under highly reducing conditions limits the isotope effects associated with methanogenesis however the carbon isotope compositions of lipids derived from anaerobic methanotrophs suggest that more than one isotopically distinct pool of methane exists at lost city in this analysis we integrate multiple lines of evidence to constrain the relative contribution of various processes at lost city the processes that we consider here include i fischer tropsch type ftt abiotic synthesis of methane and other hydrocarbons ii the sabatier process for the abiotic synthesis of methane alone iii biological methane production by methanosarcinales and iv biological methane consumption by anaerobic and aerobic methanotrophs this analysis suggests that abiotic processes particularly the sabatier reaction are likely to be the dominant source of methane at lost city biological methane is present in the vent fluids but does not compose a high fraction of the total methane pool these observations imply that ultramafic systems could have supplied abundant reduced carbon to the early earth even without biological catalysis

origin of methane in serpentinite hosted hydrothermal systems the ch4 h2 h2o hydrogen isotope systematics of the hakuba happo hot spring abstract serpentinite hosted hydrothermal systems have attracted considerable attention as sites of abiotic organic synthesis and as habitats for the earliest microbial communities here we report a systematic isotopic study of a new serpentinite hosted system the hakuba happo hot spring in the shiroumadake area japan 36 42 n 137 48 e we collected water directly from the hot spring from two drilling wells more than 500 m deep all water samples were strongly alkaline ph 10 and rich in h2 201 664 mol l and ch4 124 201 mol l despite the relatively low temperatures 50 60 c thermodynamic calculations suggest that the h2 was likely derived from serpentinization reactions hydrogen isotope compositions for happo 1 happo 3 were found to be as follows d h 2 700 710 d ch 4 210 300 and d h 2 o 85 84 the carbon isotope compositions of methane from happo 1 and 3 were found to be c 13 34 5 and 33 9 respectively the ch4 h2 h2o hydrogen isotope systematics indicate that at least two different mechanisms were responsible for methane formation happo 1 has a similar hydrogen isotope compositions to other serpentinite hosted systems reported previously the elevated d ch 4 with respect to the equilibrium relationship suggests that the hydrogen of the happo 1 methane was not sourced from molecular hydrogen but was derived directly from water this implies that the methane may not have been produced via the fischer tropsch type ftt synthesis but possibly by the hydration of olivine conversely the depleted d ch 4 with respect to the equilibrium relationship in happo 3 suggests the incorporation of biological methane based on a comparison of the hydrogen isotope systematics of our results with those of other serpentinite hosted hydrothermal systems we suggest that abiotic ch4 production directly from h2o without mediation by h2 may be more common in serpentinite hosted systems hydration of olivine may play a more significant role in abiotic methane production than previously thought

fossil evidence for serpentinization fluids fueling chemosynthetic assemblages among the deep sea hydrothermal vent sites discovered in the past 30 years lost city on the mid atlantic ridge mar is remarkable both for its alkaline fluids derived from mantle rock serpentinization and the spectacular seafloor carbonate chimneys precipitated from these fluids despite high concentrations of reduced chemicals in the fluids this unique example of a serpentinite hosted hydrothermal system currently lacks chemosynthetic assemblages dominated by large animals typical of high temperature vent sites here we report abundant specimens of chemosymbiotic mussels associated with gastropods and chemosymbiotic clams in approximately 100 kyr old lost city like carbonates from the mar close to the rainbow site 36 n our finding shows that serpentinization related fluids unaffected by high temperature hydrothermal circulation can occur on axis and are able to sustain high biomass communities the widespread occurrence of seafloor ultramafic rocks linked to likely long range dispersion of vent species therefore offers considerably more ecospace for chemosynthetic fauna in the oceans than previously supposed

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

mineral catalyzed organic synthesis in hydrothermal systems an experimental study using time of flight secondary ion mass spectrometry 1 hydrothermal fluids enriched in hydrocarbons of apparent abiotic origin vent from fe ni sulfide bearing chimney structures on the seafloor at slow spreading mid ocean ridges here we show results from a hydrothermal experiment using carbon isotope labeling techniques and mineral analytical data that indicate that pentlandite fe2ni7 s8 enhances formation of c2 and c3 alkanes while also contributing to the formation of other more complex hydrocarbons such as alcohols and carboxylic acids tof sims data reveal the existence of isotopically anomalous carbon on the pentlandite surface and thus for the first time provide unambiguous evidence that mineral catalyzed surface reactions play a role in carbon reduction schemes under hydrothermal conditions we hypothesize that hydroxymethylene choh serves as intermediary facilitating formation of more complex organic compounds the experimental results provide an explanation for organic synthesis in ultramafic hosted hydrothermal systems on earth and on other water enriched planetary bodies as well

thermodynamics of organic transformations in hydrothermal fluids hydrothermal fluids obtain organic compounds through diverse pathways in submarine systems organic compounds are already dissolved in seawater that is heated and transformed into hydrothermal fluids through water rock reactions microbes inhabiting hydrothermal systems produce metabolites that enter the fluids and cells can be carried into the reaction zones by circulating fluids and pyrolyzed analogous sources of organic compounds can be anticipated in continental systems with the possible addition of novel plant and soil derived organic compounds from the surface in addition hydrothermal systems possess large potentials for abiotic organic synthesis that may add a novel suite of compounds when sedimentary rocks are present ancient biogenic organic matter can be mobilized or transformed by hot fluids these transformations accompany the generation of petroleum coal and other fossil fuels suggesting that expectations for hydrothermal transformations can be built on those that occur in sedimentary basins likewise some types of ore deposition are accompanied by transformations of organic compounds and metal organic complexes may be involved in enhancing the transport of metals in ore forming and other crustal fluids with these thoughts in mind this review starts with an inventory of the types of organic compounds found in hydrothermal systems and some ways that hydrothermal organic compounds are transformed methane can be generated biotically and abiotically from organic or inorganic reactants and since it lacks a carbon carbon bond some researchers would not consider it to be an organic compound nevertheless more data exist for methane in hydrothermal fluids than for any organic compound that fits the definition methane has been quantified in continental and submarine hydrothermal fluids fumarolic gases associated with hydrothermal systems oil field brines deep fluids in sedimentary basins and igneous basement rocks fluids associated with active serpentinization and fluid inclusions in minerals from ore deposits sedimentary basins and deep crustal settings recent examples include

thermodynamic constraints on the formation of condensed carbon from serpentinization fluids abstract recent studies have identified carbonaceous material in serpentinite bodies but whether these deposits have a biologic or abiotic origin remains uncertain in this work thermodynamic calculations were performed to examine the potential for abiotic condensed carbonaceous material to be produced from serpentinization derived fluids under hydrothermal conditions calculation of reaction pathways during serpentinization of olivine showed that fluid compositions should equilibrate with condensed carbonaceous material which controls the h 2 and co 2 activities fluids from laboratory serpentinization experiments and from the lost city and the rainbow hydrothermal field are shown to be consistent with this model the predictions indicate that carbonaceous material should be the dominant carbon product of co 2 reduction in these hydrothermal settings which would have significant implications for a number of processes including the deep earth carbon cycle by creating a pool of relatively immobile reduced carbon the extent of h 2 production in ultrabasic environments and mechanisms leading to abiotic reduced carbon compounds

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

aliphatic hydrocarbons in metasomatized gabbroic xenoliths from hyblean diatremes sicily genesis in a serpentinite hydrothermal system abstract many tholeiite gabbro xenoliths from the hyblean tuff breccia deposits sicily southern italy present mineralogical and geochemical evidence for hydrothermal alteration at different temperatures and water rock ratios in some cases the primary mineral assemblage has been entirely replaced by na rich alkali feldspar chlorite smectite interlayers zeolites aegirine augite titanite zircon etc hence the chemical composition of such metasomatic rocks displays larger amounts of volatiles alkalis zr hf u th and lower ca mg fe with respect to the original gabbro five hydrothermally altered gabbroic xenoliths were selected for thermal decrepitation and bulk gas analyses by quadrupole mass spectrometry all the samples analyzed display the same electron impact direct pyrolysis mass spectra ei dpms these show a series of peaks differing by 14 mass units due to loss of methylene groups ch 2 by a fragmentation process typical of saturated aliphatic and aliphatic aromatic hydrocarbons in addition fourier transform infrared ft ir spectra of the samples present several bands typical of vibration frequencies of aliphatic hydrocarbons the high molecular weight hydrocarbons observed probably originated from fischer tropsch type ft t synthesis in the high temperature section of a serpentinite hosted hydrothermal system this suggestion may lend support to the recent hypothesis regarding the original oceanic nature of the hyblean lithospheric basement

mapping clay content for subsurface drainage in the nile delta abstract drain envelope requirements for large scale subsurface drainage projects are often estimated based on the surface area with clay percentages less than a given threshold value contouring clay percentage data can be done by computer using spatial interpolation methods cross validation was used to evaluate the precision of estimation for clay percentage using five interpolation techniques closest neighbor moving average weighted moving average kriging and cokriging for a study area of 33 500 ha in the nile delta the clay content was measured at 485 sites cokriging used the correlation between clay percentage and saturated hydraulic conductivity which had been measured at 3488 sites the lowest mean absolute difference mad between observed and interpolated clay percentage values was obtained for cokriging 12 01 mad values were very close to that of cokriging in the case of moving average 12 13 weighted moving average 12 23 and kriging 12 21 whereas for the closest neighbor method a mad value of 16 44 was obtained surface areas under 30 and 40 percent clay were over estimated for the closest neighbor method and under estimated for the moving average method surface areas and contour maps based on weighted moving average kriging and cokriging were very similar use of moving average resulted in a loss of precision due to the smoothing effect

expanding frontiers in deep subsurface microbiology abstract the subsurface biosphere on earth appears to be far more expansive and physiologically and phylogenetically complex than previously thought here several aspects of subsurface microbiology are discussed molecular and biogeochemical data as well as characteristics from new isolates suggest that ecosystems below deep sea hydrothermal vents are inhabited primarily by thermophilic archaea and bacteria the void spaces and conduits in basalt at mid ocean ridges and even more so at sediment covered hydrothermal vent sites represent promising hunting grounds for novel chemosynthetic archaea and bacteria as examples we highlight the subsurface microbial communities within the basalt flanks of the juan de fuca ridge off british columbia and the hydrothermal sediments at the guaymas basin in the gulf of california and at middle valley on the juan de fuca ridge in the deep continental subsurface microbial studies have primarily targeted aquifers in basaltic and granitic rock with an almost exclusive emphasis on h2 driven chemolithoautotrophy for example in the subsurface water from lidy hot springs idaho usa h2 consuming methanogenic archaea represent the most populous organisms comprising 95 of all cells besides h2 other potential sources of chemical energy reducing power are considered including abiotically synthesized organic matter and reduced sulfur compounds in addition the well established sequences of redox couples in microbial metabolism are investigated at elevated temperatures using a thermodynamic approach values of peo for 11 common reduction half reactions are tabulated at 25 50 100 and 150 c although many modes of metabolism may be employed by subsurface biota sulfate reduction appears to be one of the more ubiquitous strategies recent studies of sulfate reducing archaea and bacteria in marine and continental systems are reviewed

origin of the natural gas seep of cirali chimera turkey site of the first olympic fire abstract the olympos mountain located to the west of the city of antalya sw turkey in the cirali chimera area is well known since 2500 years ago for the occurrence of gas seeps from ophiolites the area comprises a large allochthonous slab known as the tekirova ophiolite and is represented by intensely serpentinized ultramafic rocks the chimera gas escapes through fracture zones in the ophiolite the ophiolitic slab is structurally bounded by a carbonate platform termed the beydaglari autochthon emplacement of the ophiolite nappes onto the carbonate platform took place in the tertiary eocene this study is aimed at determining the origin and possible source rocks of this gas several samples of both gas and the ophiolite were collected at different sites to determine the molecular and isotopic composition of the gases and mineralogical composition of the ophiolites the seep gases contain hydrocarbons up to c 5 carbon dioxide 91 the stable carbon isotope ratios of methane ethane and propane are defined with a 13 c 1 of 12 5 to 11 6 13 c 2 of 23 5 to 22 0 and 13 c 3 of 23 7 to 21 0 respectively the d 1 values of methane range from 129 to 96 xrd measurements on the ophiolite revealed the presence of brucite hydromagnesite aragonite calcite and lizardite chrysotile mineral assemblage two possible sources are determined for the chimera gas the first is an abiogenic process of serpentinization within the tekirova ophiolite which would result in heavy methane formation the second are the upper paleozoic to lower mesozoic organic rich shales in which methane to pentane hydrocarbons were thermally generated

characterization of hydrothermally generated oil from the uzon caldera kamchatka abstract this paper reports the analyses of unusual oils that accumulate in the uzon caldera situated in the central volcanic region of kamchatka russia gas chromatography mass spectrometry gc ms was used to determine the primary constituents and the 13 c and 14 c compositions provided information about the potential source and age of the oils the 14 c ages determined are 1030 40 a bp measured or 940 40 a bp conventional the 13 c value is 30 6 versus the pdb standard a value consistent with a biological origin the nearly contemporary age of the c content indicates a geologically recent origin from biogenic detritus and not by synthesis from mantle c the biogenic origin is supported by the presence of sterane and hopane biomarkers and the 13 c value of the bulk oil the overall compositions of the oils indicate that they are derived from rapid hydrothermal alteration of algal bacterial mat detritus buried by volcanic ashfall deposits of the uzon caldera the oils represent the youngest hydrothermal petroleum reported to date

origins of methane discharging from volcanic hydrothermal geothermal and cold emissions in italy abstract we have addressed the origins of methane in fumarolic thermal and cold emissions discharging from a diversity of geological settings spread all over the italian peninsula and at panarea and pantelleria islands fluid discharges from the main geothermal systems of the peri tyrrhenian area including mt amiata larderello latera and manziana show 13c ch4 and d ch4 values 28 v pdb and 160 v smow respectively and c1 c2 concentration ratios 1000 these patterns suggest that ch4 discharged from these systems is primarily generated by abiogenic reduction of co2 and or co methane seems to have at least partially a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or alternatively to methane polymerization fumaroles from the volcanic systems of solfatara vesuvio panarea and pantelleria have c1 c2 concentration ratios in a wide range from 17 to 4300 but 13c ch4 and d ch4 values 21 v pdb and 120 v smow respectively such isotopic values are very similar to those reported for ch4 discharging from ultramafic hydrothermal systems in agreement with recent evidence provided for solfatara and pantelleria we therefore infer that the ch4 in the volcanic fumaroles is mainly abiogenic too the 13c ch4 from 21 6 to 36 9 v pdb and d ch4 from 113 to 164 v smow values as well as the c1 c2 concentration ratios from 19 to 2240 in the co2 rich fluid discharges located between the geothermal volcanic systems and the apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish suggesting that the ch4 production is mainly related to thermogenic processes according to this general trend the ch4 dominated fluids from mud volcanoes located eastwards of the co2 rich emissions are fed by an almost pure thermogenic source the easternmost fluid discharges from the po valley and the adriatic coast where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient record the lowest 13c ch4 and d ch4 values i e as low as 69 v pdb and