geochemical evidence of secondary microbial methane from very slight biodegradation of undersaturated oils in a deep hot reservoir a rare finding of early mature undersaturated oils with low gas oil ratios enables us to document secondary microbial methane generation during very slight biodegradation in a deep hot reservoir in the ultradeep water of the gulf of mexico in three studied gas samples methane is enriched in 13 c 13 c is from 63 to 64 relative to pure thermogenic methane estimated 13 c is from 71 to 67 and pure primary microbial methane 13 c is 68 carbon dioxide in gases has 13 c values that negatively correlate with 13 c values of pure thermogenic methane methane is unusually enriched in heavy isotope 2 h relative to associated ethane some extracted oils are depleted in long chain alkyl aromatics these lines of geochemical evidence suggest anaerobic microbial degradation of oil and subsequent reduction of resulting carbon dioxide to methane although specific geobiological details of secondary microbial methane generation are unclear this process may be partially responsible for charging some of the largest gas and gas hydrate fields in the world

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

the origin of n2 h2 ch4 rich natural gas seepages in ophiolitic context a major and noble gases study of fluid seepages in new caledonia the study of natural gas seepages in new caledonia has shown the occurrence of two gas families one is n2 h2 ch4 rich the other is n2 rich the n2 h2 ch4 rich gases are bubbling in hyperalkaline springs oh rich known in the peridotite massif of the southern part of the island this family of gas shows contents of n2 between 50 and 62 h2 between 26 and 36 and ch4 between 11 and 16 13c values of methane are ranging from 39 to 32 we interpret the origin of h2 as a product of fluid rock interaction between basic ultrabasic rocks and water with oxidation of fe2 and reduction of underground water in the fracture system of the peridotites nappe methane is interpreted as the result of a reduction of dissolved inorganic and or organic carbon in subsurface aquifers the second family of gas emissions was found in thermal springs in the sedimentary units located structurally below the peridotites nappe the gas is composed mostly of n2 between 97 and 98 associated with relatively high concentration of he both gas families show notably high n2 vs fossil noble gas contents 36ar 20ne 84kr suggesting that n2 is not directly issued from gas dissolved in aquifers equilibrated with atmosphere but most likely finds its origin in a deep source probably within metamorphic sediments which are tectonically buried belowthe ophiolitic nappe weinterpret the n2 h2 ch4 rich family of gas as a result of a mixing between two end members 1 a h2 ch4 rich pole issued fromthe weathering of peridotite rocks and 2 a n2 rich pole which would be issued from the metamorphosed sediments buried below the ophiolitic units an unusual inverse correlation between the atmospheric noble gas isotopes 20ne and 36ar is interpreted as the result of a degassing of a relatively shallow confined aquifer related to a bubble flow from depth

methane flux and origin in the othrys ophiolite hyperalkaline springs greece abstract the occurrence and origin of methane ch4 generated by serpentinization of ultramafic rocks is of current timely interest in planetary geology astrobiology and energy resource exploration as it may contribute in particular to decipher the source of methane on mars the origin of life and the potential of abiotic hydrocarbon synthesis methane of dominant abiotic origin in serpentinized peridotites on continents ophiolites or igneous intrusions has been documented so far with complete carbon and hydrogen isotope composition in six countries in the philippines turkey oman new zealand japan and italy we report the discovery of two new sites in greece at archani and ekkara located in the othrys ophiolite massif portable sensors based on fourier transform infrared spectrometry ftir and tunable diode laser absorption spectroscopy tdlas allowed to realize that out of 21 ophiolitic springs methane is released only by four hyperalkaline ph from 10 7 to 11 3 and calcium hydroxide ca oh type waters all other 17 springs with ph

structure and geochemistry of tethyan ophiolites and their petrogenesis in subduction rollback systems suprasubduction zone ssz ophiolites in orogenic belts represent oceanic crust generation in subduction rollback cycles during the closing stages of basins prior to terminal continental collisions mantle flow and slab rollback result in one or more episodes of arc splitting and basin opening producing a collage of protoarc and forearc oceanic lithosphere in suprasubduction zone settings the jurassic cretaceous ssz tethyan ophiolites in the eastern mediterranean region i e mirdita pindos troodos kizildag oman generally have penrose type oceanic crust and contain well developed sheeted dike complexes indicative of magmatic extension beneath narrow rift zones during their seafloor spreading evolution igneous accretion of these ssz tethyan ophiolites involved upper plate extension and advanced melting of previously depleted asthenosphere in host basins showing a progressive evolution from morb like to iat island arc tholeiite to boninitic extremely refractory protoarc assemblages however there are some distinct differences in the geochemical evolution of these tethyan ophiolites that appear to have resulted from variations in their subduction zone geodynamics whereas a major part of the kizildag and troodos lavas shows island arc affinity similar to their counterparts in the pindos and mirdita ophiolites a significant component of the oman lavas indicates morb affinity and the majority of the kizildag and oman data plot within the mantle array between n morb and e morb on the nb yb th yb discriminant diagram furthermore the troodos and oman lavas do not show any particular th enrichment in their multi element patterns suggesting that fluid melt input from subducted sediments was not that significant in generation of their magmas although all ophiolites exhibit geochemical features indicating increased subduction influence during the melt evolution of their younger extrusive sequences and dike intrusions as evidenced by their negative nd values their overall characteristic trace element patterns seem to have been strongly affected by the maturity of the subduction systems in which they developed

evaluation of possible gas microseepage mechanisms petroleum microseepage anomalies over petroleum accumulations are commonly explained by rapid vertical migration of colloidal gas bubbles through fracture networks this article is a theoretical anal ysis of this mechanism and of continuous gas phase flow in frac tures the gas bubble ascent mechanism is much slower than re ported microseepage velocities so it cannot account for observed microseepage in contrast continuous gas phase flow through frac tures can equal or exceed reported microseepage velocity while maintaining total flux low enough so that petroleum accumulations can exist for geological lengths of time fracture entry pressure for bubbles is more than twice that of a continuous gas phase so con tinuous gas phase migration also requires a lower pressure threshold before initiating seepage vertical microseepage is therefore best explained by the same mechanism interpreted for macroseepage although this article provides a theoretically justified mecha nism for microseepage it also shows why interpretation of surface microseepage signals is problematic fracture geometry controls seepage velocity and flux so geochemical anomalies may indicate an increase in fracture aperture as well as possible subsurface ac cumulations larger fractures require very low gas capillary entry pressures so in some settings surface seepage could result from fractures over stratal migration pathways as well as over petroleum accumulations

the palaeozoic variscan oceans revisited abstract geological evidence supported by biogeographical data and in accord with palaeomagnetic constraints indicates that one ocean models for the variscides should be discarded and confirms instead the existence of three gondwana derived microcontinents which were involved in the variscan collision avalonia north armorica franconia and thuringia subdivided by a failed vesser rift and south armorica central iberia armorica bohemia all divided by small oceans in addition parts of south eastern europe including adria and apulia are combined here under the new name of palaeo adria which was also peri gondwanan in the early palaeozoic oceanic separations were formed by the break up of the northern gondwana margin from the late cambrian onwards most of the oceans or seaways remained narrow but much like the alpine cenozoic oceans gave birth to orogenic belts with hp uhp metamorphism and extensive allochthons the saxo thuringian ocean between north and south armorica and the galicia moldanubian ocean between south armorica and palaeo adria only the rheic ocean between avalonia and peri gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism and its north western arm closed before or during the emsian in europe ridge subduction under the northernmost part of armorica in the emsian created the narrow and short lived rheno hercynian ocean it is that ocean and not the rheic whose opening and closure controlled the evolution of the rheno hercynian foldbelt in south west iberia south west england germany and moravia czech republic devonian magmatism and sedimentation set within belts of early variscan deformation and metamorphism are probably strike slip related the first arrival of flysch on the forelands and or the age of deformation of foreland sequences constrains the sequential closure of the variscan seaways galicia moldanubian in the givetian saxo thuringian in the early famennian rheno hercynian in the tournaisian additional mid to late devonian and partly early carboniferous magmatism and extension in the rheno hercynian saxo thuringian and galicia moldanubian basins overlapped with variscan geodynamics as strictly defined the early carboniferous episode was the start of episodic anorogenic heating which lasted until the permian and probably relates to tethys rifting

abiogenic hydrocarbon isotopic signatures in granitic rocks identifying pathways of formation abstract the stability and isotopic composition of hydrocarbons formed in the mantle are controversial subjects knowing the range in isotopic compositions of abiogenically derived hydrocarbons is important for recognising biological signatures in ancient and extra terrestrial materials in an effort to enhance this database stable isotope results are reported here for hydrocarbon bearing fluid inclusions hosted in two peralkaline igneous complexes from lovozero russia and strange lake canada based on the distribution of isotopic compositions we propose three pathways for abiogenically generated hydrocarbons type 1 13cch4 13cco2 and 13cc2 represents mantle derived hydrocarbons generated in equilibrium with hyperagpaitic magmas in the upper mantle and suggests that mantle ch4 and c2h6 13c and 2h could have values of 5 3 and 112 and 10 8 and 162 respectively type 2 13cco2 13cch4 13cc2 represents fischer tropsch type hydrocarbon generation in quartz bearing peralkaline rocks with co2 as the initial magmatic gas phase for type 2 13cco2 values are 2 whereas 13cch4 and 2hch4 values range from 32 to 20 and 170 and 160 respectively the 13cc2h6 values are slightly lower than associated 13cch4 values type 3 13cco2 13cch4

some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins large volumes of carbon dioxide i e up to 90 v v have been encountered in sedimentary basins from various geological settings but their origins remain enigmatic evidence from carbon and noble gas isotope analyses indicate a variety of interpretations for the origins of the co2 including mantle degassing metamorphic reactions or magmatic processes the formation of large accumulations of large volumes of co2 in sedimentary basins is discussed with specific reference to published data from the pannonian basin hungary the cooper eromanga basin australia and the south viking graben north sea these basins have occurrences of large volumes i e over 15 v v of isotopically heavy carbon dioxide thought to be of inorganic origin and although they differ somewhat in terms of sedimentary fill all have major structural features close to the gas accumulations the available geochemical data are currently neither sufficient to confirm the specific origin s of the co2 e g mantle derived carbonate metamorphism nor unscramble co2 mixed from two or more sources ongoing studies especially those involving noble gas analyses should provide fuller answers

characterization of hyperalkaline fluids produced by low temperature serpentinization of mantle peridotites in the oman and ligurian ophiolites a regional survey of alkaline springs in oman and ligurian ophiolites shows that the alkaline water compositions significantly vary from one ophiolite to the other and within the same ophiolite the first order correlation between the na and k and cl concentrations points to fluid compositions only partly due to evaporation the scatter around the evaporation line implies that na and cl may not be conservative during the alteration of the ultramafic rocks mg is almost entirely depleted at ph 10 5 as a result of serpentine formation within the ultramafic body and of brucite and minor hydrotalcite precipitation at the springs ca accumulates in the high ph fluids and is consumed by ca carbonate formation at the springs by mixing with river waters or by the co2 supply from the atmosphere thermodynamic calculations show that brucite saturation is reached at ph values around 10 5 which triggers major changes in the water composition the waters evolve from a quartz saturated low ph continental environment to a brucite dominated high ph serpentinizing system at low temperature the highest water salinities are found in springs located along the basal thrust plane of the ophiolite the highest al concentrations are found in some springs located on the crustal side of the mantle crust boundary this poses the question of the hydrologic pathways and of the role of the mineralogical composition of the altered formations key points new temperature and composition of the alkaline waters brucite formation at ph 10 5 triggers major chemical and mineralogical changes relationship between the water compositions and the hydrologic pathways

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

experimental evidence for an ascending microflow of geogas in the ground a microflow of free ascending gas has been observed in 26 out of 30 tested boreholes at three different sites the flow rates vary between 60 10 4 and 4 cm3 min m2 horizontally projected borehole area sampling has been made in ground boreholes as well as in holes drilled downwards from the lowest levels in two mines the composition of the gas varies considerably the main components of the gas are nitrogen argon oxygen and methane traces of heavier hydrocarbons are observed at the site of the ground holes only traces of methane are observed in all sampled holes the existence of free oxygen is observed the nitrogen argon quotient is close to the atmospheric quotient in all sampled holes indicating a partly atmospheric origin of the gas the existence of methane and traces of heavier hydrocarbons indicates the existence of a second source

abiotic methane in continental ultramafic rock systems towards a genetic model abstract methane ch4 often in substantial quantities is reported for numerous surface manifestations seeps springs and aquifers in continental serpentinized ultramafic rocks in ophiolites peridotite massifs and intrusions frequently this gas is considered to have a dominant abiotic origin with variable though generally minor components of biotic gas thermogenic or microbial abiotic ch4 production through low temperature fischer tropsch type reactions ftt between a carbon c compound and h2 is endorsed by most of scholars but direct derivation from olivine hydration serpentinization magmatic sources and fluid inclusions have also been suggested here we review the application of ftt in geology discussing the appropriateness of several c compounds co2 co formic acid formate or elemental c as ch4 precursors and of aqueous versus gas phase reactions we examine published gas geochemical and flux data that provide clear constraints on the methane origins in the analysis we add new isotopic and gas seepage data acquired in surface gas manifestations at acquasanta in the voltri ophiolite genova italy multiple lines of evidence including a stable isotope compositions of ch4 co2 and helium b radiocarbon free ch4 c isotopic disequilibrium between ch4 and h2o d low temperatures of ch4 production based on clumped isotopes and heat flow data and e methane seepage forms and intensities suggest that ch4 is not formed directly in water or from magmatic sources or fluid inclusions rather all the lines of evidence taken together are compatible with the hypothesis of low temperature

geochemistry of reduced gas related to serpentinization of the zambales ophiolite philippines abstract methane hydrogen gas seeps with mantle like c and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the zambales ophiolite philippines new measurements of noble gas and 14c isotope abundances rock mixed volatile equilibrium calculations and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration the gas seeps are produced in rock dominated zones of serpentinization and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization

natural emissions of methane from geothermal and volcanic sources in europe it has recently been demonstrated that methane emission from lithosphere degassing is an important component of the natural greenhouse gas atmospheric budget globally the geological sources are mainly due to seepage from hydrocarbon prone sedimentary basins and subordinately from geothermal volcanic fluxes this work provides a first estimate of methane emission from the geothermal volcanic component at european level in europe 28 countries have geothermal systems and at least 10 countries host surface geothermal manifestations hot springs mofettes gas vents even if direct methane flux measurements are available only for a few small areas in italy a fair number of data on co2 ch4 and steam composition and flux from geothermal manifestations are today available for 6 countries czech republic germany greece iceland italy spain following the emission factor and area based approach the available data have been analyzed and have led to an early and conservative estimate of methane emission into the atmosphere around 10 000 ton yr 4000 16 000 ton yr basically from an area smaller than 4000 km2 with a speculative upper limit in the order of 105 ton yr only 4 18 of the conservative estimate about 720 ton yr is due to 12 european volcanoes where methane concentration in volcanic gases is generally in the order of a few tens of ppmv volcanoes are thus not a significant methane source while the largest emission is due to geothermal areas which may be situated next to volcanoes or independent here inorganic synthesis thermometamorphism and thermal breakdown of organic matter are substantial methane flux can reach hundreds of ton yr from small individual vents geothermal methane is mainly released in three countries located in the main high heat flow regions italy greece and iceland turkey is likely a fourth important contributor but the absolute lack of data prevents any emission estimate therefore the actual european geothermal volcanic methane emission could be easily projected to the 105 ton yr levels reaching the magnitude of some other natural sources such as forest fires or wild animals

methane in serpentinized ultramafic rocks in mainland portugal we report a new case of methane ch4 of apparent abiotic origin in continental serpentinized ultramafic rocks multiple analytical techniques on site and in the laboratory revealed methane and ethane degassing from hyperalkaline ph 11 ca2 oh mineral waters in boreholes drilled in the alter do chao igneous intrusion at cabeco de vide in mainland portugal the c and h isotopic composition of ch4 13c 20 2h 283 suggests a dominant abiotic origin although minor thermogenic contributions cannot be excluded similarly low methane to ethane ratios suggest a predominantly non microbial source consistent with previous microbiological data showing the lack of methanogenic archaea in these waters heavier hydrocarbons co2 and h2 are below detection limits this case study confirms that ch4 from serpentinized ultramafic rocks can be transported by hyperalkaline fluids linked to deep circulation of meteoric waters maximum depth of cabeco de vide serpentinized rocks is less than 1 km and present temperatures are likely lower than 50 c serpentinization and related gas formation may have occurred at any time during thermal evolution of the igneous intrusion so gas formation temperature cannot be easily determined this case is an opportunity to test thermometry provided by ch4 isotopologue analyses the existence of methane in continental serpentinized igneous rocks is more widespread than previously thought and petroleum systems with similar serpentinized ultramafics in reservoir rocks may have traces of the observed 13c enriched ch4

origins of high ph mineral waters from ultramafic rocks central portugal abstract this paper reviews the geochemical isotopic 2h 18o 13c 3h and 14c and numerical modelling approaches to evaluate possible geological sources of the high ph 11 5 na cl ca oh mineral waters from the cabeco de vide region central portugal water rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the cabeco de vide mineral waters which was corroborated by numerical modelling approaches the local shallow groundwaters belong to the mg hco3 type and are derived by interaction with the local serpentinized rocks at depth these type waters evolve into the high ph na cl ca oh mineral waters of cabeco de vide spas issuing from the intrusive contact between mafic ultramafic rocks and an older carbonate sequence the cabeco de vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization magnesium silicate phases brucite and serpentine seem to control mg concentrations in cabeco de vide mineral waters similar 2h and 18o suggest a common meteoric origin and that the mg hco3 type waters have evolved towards cabeco de vide mineral waters the reaction path simulations show that the progressive evolution of the ca hco3 to mg hco3 waters can be attributed to the interaction of meteoric waters with serpentinites the sequential dissolution at co2 g closed system conditions leads to the precipitation of calcite magnesite amorphous silica chrysotile and brucite indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks dunites present at depth the apparent age of cabeco de vide mineral waters was determined as 2790 40 a bp on the basis of 14c and 13c values which is in agreement with the 3h concentrations being below the detection limit

abiotic methane formation during experimental serpentinization of olivine fluids circulating through actively serpentinizing systems are often highly enriched in methane ch4 in many cases the ch4 in these fluids is thought to derive from abiotic reduction of inorganic carbon but the conditions under which this process can occur in natural systems remain unclear in recent years several studies have reported abiotic formation of ch4 during experimental serpentinization of olivine at temperatures at or below 200 c however these results seem to contradict studies conducted at higher temperatures 300 c to 400 c where substantial kinetic barriers to ch4 synthesis have been observed here the potential for abiotic formation of ch4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 c to 320 c a 13c labeled inorganic carbon source was used to unambiguously determine the origin of ch4 generated in the experiments consistent with previous high temperature studies the results indicate that abiotic formation of ch4 from reduction of dissolved inorganic carbon during the experiments is extremely limited with nearly all of the observed ch4 derived from background sources the results indicate that the potential for abiotic synthesis of ch4 in low temperature serpentinizing environments may be much more limited than some recent studies have suggested however more extensive production of ch4 was observed in one experiment performed under conditions that allowed an h2 rich vapor phase to form suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for abiotic synthesis of ch4

modern water rock reactions in oman hyperalkaline peridotite aquifers and implications for microbial habitability abstract the samail ophiolite in oman is undergoing modern hydration and carbonation of peridotite and may host a deep subsurface biosphere previous investigations of hyperalkaline fluids in oman have focused on fluids released at surface seeps which quickly lose their reducing character and precipitate carbonates upon contact with the o2 co2 rich atmosphere in this work geochemical analysis of rocks and fluids from the subsurface provides new insights into the operative reactions in serpentinizing aquifers serpentinite rock and hyperalkaline fluids ph 10 which exhibit millimolar concentrations of ca2 h2 and ch4 as well as variable sulfate and nitrate were accessed from wells situated in mantle peridotite near ibra and studied to investigate their aqueous geochemistry gas concentrations isotopic signatures mineralogy fe speciation and microbial community composition the bulk mineralogy of drill cuttings is dominated by olivine pyroxene brucite serpentine and magnetite at depth fe bearing brucite is commonly intermixed with serpentine whereas near the surface olivine and brucite are lost and increased magnetite and serpentine is detected micro raman spectroscopy reveals at least two distinct generations of serpentine present in drill cuttings recovered from several depths from two wells fe k edge x ray absorption near edge spectroscopy xanes analysis of the lizardite shows a strong tetrahedral fe coordination suggesting a mixture of both fe ii and fe iii in the serpentine magnetite veins are also closely associated with this second generation serpentine and 2 10 m magnetite grains overprint all minerals in the drill cuttings thus we propose that the dissolved h2 that accumulates in the subsurface hyperalkaline fluids was evolved through low temperature oxidation and hydration of relict olivine as well as destabilization of pre existing brucite present in the partially serpentinized dunites and harzburgites in particular we hypothesize that fe bearing brucite is currently reacting with dissolved silica in the aquifer fluids to generate late stage magnetite additional serpentine and dissolved h2 dissolved ch4 in the fluids exhibits the most isotopically heavy carbon in ch4 reported in the literature thus far the ch4 may have formed through abiotic reduction of dissolved co2 or through biogenic pathways under extreme carbon limitation the methane isotopic composition may have also been modified by significant methane oxidation 16s rrna sequencing of dna recovered from filtered hyperalkaline well fluids reveals an abundance of meiothermus thermodesulfovibrionaceae sulfate reducers and clostridia fermenters the fluids also contain candidate phyla op1 and od1 as well as methanobacterium methanogen and methylococcus sp methanotroph the composition of these microbial communities suggests that low temperature hydrogen and methane generation coupled with the presence of electron acceptors such as nitrate and sulfate sustains subsurface microbial life within the oman ophiolite

an unusual occurrence of light hydrocarbon gases in a well offshore northeast palawan island the philippines abstract sediments from a well offshore northeast palawan island the philippines appear to contain light hydrocarbons of possible abiogenic origin this observation is based on stable carbon isotope ratios organic petrography and chemical and geological considerations

origin of hydrogen nitrogen gas seeps oman six gas samples were collected from five thermal springs in the semail nappe ophiolite and the calcareous calcite and dolomite hajar formation northern oman the3he 4he 4he 20ne 40ar 36ar and38ar 36ar ratios chemical compositions h2 n2 co2 ch4 o2 ar and he and stable isotope compositions dh2 dh2o 13cco2 13cch4 and 15nn2 are reported samples from the ophiolite region are significantly anoxic with major constituents of h2 ch4 and n2 while those from calcite and dolomite regions are ordinary gas seeps consisting of n2 co2 and or o2 the former h2 rich gas is characterized by relatively high3he 4he ratio 0 4 0 8 ratm with low he content 300 ppm slight radiogenic40ar 36ar ratio high n2 ar ratio 77 97 and low 15nn2 value 0 observed dh2 value of 536 in h2 rich gas is distinguished from the literature value of 699 in the ophiolite region giving discrepant isotope formation temperatures

abiogenic methanogenesis in crystalline rocks isotopically anomalous ch4 rich gas deposits are found in mining sites on both the canadian and fennoscandian shields with 13cch4 values from 22 4 to 48 5 and dch4 values from 133 to 372 these methane deposits cannot be accounted for by conventional processes of bacterial or thermogenic methanogenesis compositionally the gases are similar to other ch4 rich gas occurrences found in canadian and fennoscandian shield rocks sherwood lollar et al 1993 however the isotopically anomalous gases of this study are characterized by unexpectedly high concentrations of h2 gas ranging from several volume percent up to 30 vol the h2 gases are consistently depleted in the heavy isotope with dh2 values of 619 to 659 3h 4he ratios in the range of 0 4 10 8 to 4 4 sx 10 8 indicate that there is no resolvable component of mantle derived he in these deposits based on these results a mantle derived source for the c bearing gases is unlikely several lines of evidence support an alternative abiogenic origin for the gases from sudbury canada and juuka and pori finland the d depleted h2 gas and calculated d ch4 h2 equilibration temperatures of 110 170 c at all three sites are in good agreement with results obtained for abiogenically produced ch4 and h2 in ophiolite sequences in oman and the philippines serpentinization and the hydration of ultramafic rocks are the proposed mechanisms for ch4 and h2 production in these ophiolite sequences the widespread occurrence of serpentinized and altered ultramafic rocks at juuka and at a number of other sites in both canada and finland implies that similar mechanisms may be involved in gas production at at least three sites on the shields the origin of the gases at the remaining shield sites is discussed alternative hypothesis include 1 production of the rest of the shield gases by mixing between abiogenic endmembers and bacterially generated hydrocarbon gas such as identified elsewhere on the canadian and fennoscandian shields sherwood lollar et al 1993 and 2 production of a series of isotopically distinct abiogenic ch4 endmembers at each site due to variability in the isotopic composition of available carbon sources we cannot conclusively distinguish between the alternative scenarios based on existing data however the evidence for an abiogenic ch4 endmember at at least three sites emphasizes the need for substantial revision of current theories of methanogenesis abiogenic processes of ch4 production may be considerably more widespread than previously anticipated

abiotic methane on earth 1 over the last 30 years geochemical research has demonstrated that abiotic methane ch4 formed by chemical reactions which do not directly involve organic matter occurs on earth in several specific geologic environments it can be produced by either high temperature magmatic processes in volcanic and geothermal areas or via low temperature 100 c gas water rock reactions in continental settings even at shallow depths the isotopic composition of c and h is a first step in distinguishing abiotic from biotic including either microbial or thermogenic ch4 herein we demonstrate that integrated geochemical diagnostic techniques based on molecular composition of associated gases noble gas isotopes mixing models and a detailed knowledge of the geologic and hydrogeologic context are necessary to confirm the occurrence of abiotic ch4 in natural gases which are frequently mixtures of multiple sources although it has been traditionally assumed that abiotic ch4 is mainly related to mantle derived or magmatic processes a new generation of data is showing that low temperature synthesis related to gas water rock reactions is more common than previously thought this paper reviews the major sources of abiotic ch4 and the primary approaches for differentiating abiotic from biotic ch4 including novel potential tools such as clumped isotope geochemistry a diagnostic approach for differentiation is proposed

abiotic methane flux from the chimaera seep and tekirova ophiolites turkey understanding gas exhalation from low temperature serpentinization and implications for mars abstract the emission of abiotic methane ch 4 into the atmosphere from low temperature serpentinization in ophiolitic rocks is documented to date only in four countries the philippines oman new zealand and turkey serpentinization produces large amounts of hydrogen h 2 which in theory may react with co 2 or co to form hydrocarbons fischer tropsch type synthesis ftt similar mechanisms have been invoked to explain the ch 4 detected on mars so that understanding flux and exhalation modality of ophiolitic gas on earth may contribute to decipher the potential degassing on mars this work reports the first direct measurements of gas ch 4 co 2 flux ever done on onshore ophiolites with present day serpentinization we investigated the tekirova ophiolites at cirali in turkey hosting the chimaera seep a system of gas vents issuing from fractures in a 5000 m 2 wide ophiolite outcrop at this site at least 150 190 t of ch 4 is annually released into the atmosphere the molecular and isotopic compositions of c 1 c 5 alkanes co 2 and n 2 combined with source rock maturity data and thermogenic gas formation modelling suggested a dominant abiotic component 80 90 mixed with thermogenic gas abiotic h 2 rich gas is likely formed at temperatures below 50 c suggested by the low deuterium hydrogen isotopic ratio of h 2 d h2 720 consistent with the low geothermal gradient of the area abiotic gas synthesis must be very fast and effective in continuously producing an amount of gas equivalent to the long lasting 2 millennia emission of 100 t ch 4 yr 1 otherwise pressurised gas accumulation must exist over the same ophiolitic formation 3 km away from chimaera we detected an invisible microseepage of abiotic ch 4 with fluxes from 0 07 to 1 g m 2 d 1 on mars similar fluxes could be able to sustain the ch 4 plume apparently recognised in the northern summer 2003 10 4 or 10 5 t yr 1 over the wide olivine bedrock and outcrops of hydrated silicates in the syrtis major and nili fossae just one seep like chimaera or more realistically a weak spatially sporadic microseepage would be sufficient to maintain the atmospheric ch 4 level on mars

low temperature alteration of serpentinized ultramafic rock and implications for microbial life abstract alteration serpentinization of ultramafic rocks is known to generate hydrogen through oxidation of ferrous iron in olivine or pyroxene and reduction of water hydrogen oxidation can act as a primary source for chemolithotrophic microbial communities and it is suggested that hydrogen availability is essential for the existence of a deep subsurface biosphere in this study we focus on ongoing low temperature water rock processes in partially serpentinized dunite from the leka ophiolite complex mid norway we aim to determine whether these reactions release reduced compounds and nutrients that can be utilized by the associated microbial communities the study is based on the chemical and physical alteration features of a 51 m deep rock core as well as the chemical composition of groundwater from the core s borehole the borehole intersects three main fracture zones observations during drilling indicated that water infiltration largely takes place along the deepest zone the rock in the fracture zones is nearly completely altered to serpentine brucite magnetite and minor calcite an increase in ph and decrease in mg si and alkalinity of the groundwater along the borehole from the deepest to the outermost fracture zone reflect ongoing water rock reactions where dissolution of brucite serpentine and calcite and precipitation of chrysotile hydromagnesite and iron hydroxide are most likely to occur detection of both h 2 and o 2 in the groundwater influenced by the outermost fracture zone suggests that the local development of highly reducing conditions in the narrow fractures is due to low water rock ratios and to dissolution of fe ii containing brucite and serpentine resulting in the formation and successive diffusion of h 2 into the oxic borehole oxidation of h 2 reduced fe and mn nh 4 and ch 4 are all potential energy yielding reactions that could be utilized by chemolithotrophic microorganisms using dissolved organic or inorganic carbon as possible carbon sources methane could result from microbial oxidation of h 2 and reduction of co 2 or from the degradation of organic matter the results demonstrate that low temperature water rock reactions in serpentinized ultramafic rock lead to production of reduced chemical species that could support primary producers in diverse microbial communities

organic synthesis during fluid mixing in hydrothermal systems hydrothermal circulation can lead to fluid mixing on any planet with liquid water and a source of heat aqueous fluids with differing compositions especially different oxidation states are likely to be far from thermodynamic equilibrium when they mix and provide a source of free energy that can drive organic synthesis from co 2 and h 2 and or supply a source of geochemical energy to chemolithoautotrophic organisms results are presented that quantify the potential for organic synthesis during unbuffered fluid mixing in present submarine hydrothermal svstems as well as hypothetical systems that may have existed on the early earth and mars dissolved hydrogen present in submarine hydrothermal fluids owing to the high temperature reduction of h 2 o as seawater reacts with oceanic crustal rocks provides the reduction potential and the thermodynamic drive for organic synthesis from co 2 or bicarbonate as hydrothermal fluids mix with seawater the potential for organic synthesis is a strong function of the h 2 content of the hydrothermal fluid which is in turn a function of the prevailing oxidation state controlled by the composition of the rock that hosts the hydrothermal system hydrothermal fluids with initial oxidation states at or below those set by the fayalite magnetite quartz mineral assemblage show the greatest potential for driving organic synthesis these calculations show that it is thermodynamically possible for 100 of the carbon in the mixed fluid to be reduced to a mixture of carboxylic acids alcohols and ketones in the range 250 50 c as cold seawater mixes with the hydrothermal fluid as the temperature drops larger organic molecules are favored which implies that fluid mixing could drive the geochemical equivalent of a metaholic system this enormous reduction potential probably drives a large portion of the primary productivity around present seafloor hydrothermal vents and would have been present in hydrothermal systems on the early earth or mars the single largest control on the potential for organic synthesis is the composition of the rock that hosts the hydrothermal system

low temperature volatile production at the lost city hydrothermal field evidence from a hydrogen stable isotope geothermometer although commonly utilized in continental geothermal work the water hydrogen and methane hydrogen isotope geothermometers have been neglected in hydrothermal studies here we report d ch4 and d h2 values from high temperature black smoker type hydrothermal vents and low temperature carbonate hosted samples from the recently discovered lost city hydrothermal field methane deuterium content is uniform across the dataset at 120 12 hydrogen d values vary from 420 to 330 at high temperature vents to 700 to 600 at lost city the application of several geothermometer equations to a suite of hydrothermal vent volatile samples reveals that predicted temperatures are similar to measured vent temperatures at high temperature vents and 20 60 c higher than those measured at the lost city vents we conclude that the overestimation of temperature at lost city reflects 1 that methane and hydrogen are produced by serpentinization at n110 c and 2 that isotopic equilibrium at temperatures b70 c is mediated by microbial sulfate reduction the successful application of hydrogen isotope geothermometers to low temperature lost city hydrothermal samples encourages its employment with lowtemperature diffuse hydrothermal fluids 2005 elsevier b v all rights reserved

boron lithium and methane isotope composition of hyperalkaline waters northern apennines italy terrestrial serpentinization or mixing with brine spring waters issuing from serpentinized ultramafic rocks of the taro ceno valleys northern apennine emilia romagna region italy were analyzed for major element trace element and dissolved gas concentrations and 11b 7li 18o h2o 2h h2o 13c ch4 and 2h ch4 isotope compositions similar to other springs worldwide that issue from serpentinites the chemical composition of the waters evolves with water rock interaction from ca hco3 through mg hco3 and ultimately to a hyperalkaline na ca oh composition most of the ca and mg hco3 springs have 11b ranging between 16 3 and 23 7 consistent with the range of low p t serpentinites very high 11b in two springs from mt prinzera pr10 39 pr01 43 can be related to isotopic fractionation during secondary phase precipitation as also inferred from 7li values in contrast to typical abiogenic isotope signatures of ch4 from serpentinized rocks dissolved ch4 from the taro ceno hyperalkaline springs has an apparent biotic thermogenic and or mixed thermogenic microbial signature with 13c ch4 ranging from 57 5 to 40 8 which is similar to that of hydrocarbons from production wells and natural seeps in adjacent hydrocarbon systems the data suggest that ch4 in the hyperalkaline springs investigated in this study may derive from organic matter of the sedimentary flysch and arenaceous formations underlying the ophiolite unit however small amounts of h2 were detected in one hyperalkaline spring pr10 but for two springs with very low ch4 concentrations pr01 and um15 the 2h value could not be measured so the occurrence of some abiotic ch4 cannot be excluded the occurrence of thermogenic ch4 in ophiolites may be a widespread phenomenon and thus the characterization of serpentinization related gases requires accurate evaluation of the regional context including a careful knowledge of the relationships with surrounding sedimentary rocks and their hydrocarbon potential

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

geochemistry and geobiology of a present day serpentinization site in california the cedars ultra basic ph 11 12 reducing 656 to 585 mv groundwater springs discharging from serpentinized peridotite of the cedars ca were investigated for their geochemistry and geobiology the spring waters investigated were of meteoric origin however geochemical modeling suggests that there were two sources of groundwater a shallow source with sufficient contact with the cedars peridotite body to be altered geochemically by serpentinization and a deeper groundwater source that not only flows through the peridotite body but was also in contact with the marine sediments of the franciscan subduction complex fsc below the peridotite body we propose that the groundwater discharging from lower elevations gps1 and cs1 reflect the geochemistry of the deeper groundwater in contact with fsc while groundwaters discharging from springs at higher elevations ns1 and bsc were a mixture of the shallow peridotite only groundwater and the deeper groundwater that has been in contact with the fsc cell densities of suspended microbes within these waters were extremely low in the ns1 and bsc spring fluids cell densities ranged from 10 2 to 10 3 cells ml while suspended cells at gps were lower than 10 cells ml however glass slides incubated in the bsc and gps1 springs for 2 3 weeks were colonized by cells with densities ranging from 10 6 to 10 7 cells cm 2 attached to their surfaces all of the springs were very low 1 m in several essential elements and electron acceptors e g nitrate ammonium sulfate and phosphate required for microbial growth which is not uncommon at sites of continental serpentinization gases rich in n 2 h 2 and ch 4 were exsolving from the springs the stable carbon isotope value 13 c ch4 68 0 6 and the ch 4 c 2 10 3 of methane and other gaseous hydrocarbons exsolving from ns1 were typical of microbially sourced methane whereas the isotope values and the ch 4 c 2 of bsc and cs1 springs were more enriched in 13 c and had ch 4 c 2 10 3 suggesting a mixture of microbial and non microbial methane the concentrations of aromatic compounds and ethane propane iso and n butane were well described by simple physical mixing between the aromatic and alkane poor shallow groundwater and the relatively aromatic and alkane rich groundwater that flows through both the peridotite and the fsc suggesting that these aromatic and alkane compounds originated in the deeper fsc groundwater and are not produced in the shallow peridotite only groundwater the aromatic compounds most probably originated from the diagenesis degradation of organic matter in the marine sediments below the peridotite body while the gaseous alkanes may have multiple sources including thermal degradation of the organic matter in the marine sediments below the peridotite body and possibly by abiogenic reactions occurring within the peridotite body this geochemical study demonstrates the complexity of the cedars and the possible sources of hydrocarbons at continental sites of serpentinization

have olivine will gas serpentinization and the abiogenic production of methane on mars 1 spatial variability of methane ch4 on mars suggests the presence of localized subsurface sources here we show that olivine hydration in the martian regolith and crust may be a major ch4 source which contributed significantly to the warming of early mars methane production is kinetically and thermodynamically favored during low t aqueous alteration of olivine rich rocks sustained release of ch4 on present day mars may come through the breakdown of ancient ch4 hydrates and from springs driven by geothermal heat

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

reaction kinetics of gas generation in selected source rocks of the west siberian basin implications for the mass balance of early thermogenic methane abstract about one third of the actual global recoverable natural gas reserves is accumulated in the west siberian basin in several super giant and mega giant as well as numerous smaller gas fields the elucidation of the nature of this gas its mechanisms of formation and accumulation are still a matter of discussion for instance it is still not yet clear whether the enormous dry gas accumulations in cenomanian reservoirs are of microbial early thermogenic or catagenetic metagenetic origin or if they represent a mixture of these possible formation mechanisms the present contribution provides new results on the thermal gas generation properties of selected source rocks of the cretaceous pokur formation in the west siberian basin eight selected source rock core samples of the pokur formation and a recent peat sample of the same area were submitted to open system programmed temperature pyrolysis in order to quantify the formation of individual gas compounds i e methane as well as c2 and c3 hydrocarbons the rock samples were selected according to geological age and maturity i e from the aptian albian and cenomanian with the most immature samples from the latter organic carbon contents comprise the whole range from 3 to more than 60 the elevated values representing typical lignites a reaction kinetic model system was applied to the generation curves of the gases resulting in activation energy distributions and the corresponding pre exponential arrhenius factors the kinetic data were combined with the temperature history of two selected wells of the urengoy area obtained from basin modelling in order to calculate the gas generation on the geological time scale it was found that even for the low temperatures occurring in the pokur formation early gas generation could have taken place to a certain yet small degree under the assumption of a respective catchment area and the accumulation of this gas in the reservoirs however methane quantities are in the order of magnitude of the urengoy gas accumulation thus early thermogenic methane could at least partially contribute to the gas accumulated in the reservoirs

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

geochemistry of high ph waters from serpentinites of the gruppo di voltri genova italy and reaction path modeling of co2 sequestration in serpentinite aquifers abstract the large number of geochemical data gathered on the gruppo di voltri springs confirm that progressive interaction of meteoric waters with ultramafic rocks variably affected by serpentinization leads initially to the formation of mg hco3 waters when the system is open to co2 and na hco3 and ca oh type water upon further interaction with the rock under highly reducing closed system conditions with respect to co2 as indicated by 3h data these high ph waters have had long residence times underground in deep aquifers hosted by serpentinitic rocks these waters are the only available evidence of the presence of such deep aquifers high pressure injection of co2 into these deep aquifers was simulated by reaction path modeling results indicate that this is a feasible methodology to reduce the inputs of anthropogenic co2 into the atmosphere serpentinitic rocks have a high capacity for co2 sequestration mainly through formation of carbonate minerals dissolution of serpentinitic rocks and precipitation of magnesite and silica minerals occurs naturally in areas of high terrestrial co2 fluxes such as in southern tuscany corroborating the feasibility of this methodology of co2 sequestration however this process causes a progressive decrease in the porosity of the aquifer at least under closed system conditions these side effects must be carefully evaluated by means of further laboratory tests and field activities

hydrogen isotope fractionation in land based serpentinization systems comment on origin of methane in serpentinite hosted hydrothermal systems the ch4 h2 h2o hydrogen isotope systematics of the hakuba happo hot spring by suda et al earth planet sci lett 386 2014 112 125

geochemical evidence for active tropical serpentinization in the santa elena ophiolite costa rica an analog of a humid early earth serpentinization is a planetary process that has important consequences on geochemical cycles supporting microbial activity through the formation of h2 and ch4 and having the potential to sequester atmospheric co2 we present geochemical evidence of active serpentinization in the santa elena ophiolite costa rica which is sustained by peridotites with a degree of serpentinization less than 50 with no evidence of an internal heat source average spring water temperatures are 29 1 c two hyperalkaline spring systems were discovered with a spring fluid ph up to 11 18 the fluids are characterized by low mg 1 0 5 9 mg l and k 1 0 5 5 mg l and relative high ca 29 167 mg l na 16 27 mg l cl 26 29 mg l hydroxide 41 63 mg l and carbonate 31 49 mg l active ch4 24 3 v v vents coupled with carbonate deposits 13cco2 27 to 14 18oco2 17 to 6 also provide evidence for active serpentinization and carbonation isotope ratios of the alkaline fluids 18o 7 9 2h 51 4 and groundwater 18o 7 6 2h 48 0 suggests that during base flow recession springs are fed by groundwater circulation methanogenic archaea which comprises a relatively high percentage of the 16s rrna gene tag sequences suggests that biological methanogenesis may play a significant role in the system santa elena s extreme varying weather results in a scenario that could be of significant importance for a improving the knowledge of conditions on a humid early earth or mars that had periodic changes in water supply b revealing new insights on serpentinizing solute transport and c modeling hydrogeochemical responses as a function of recharge

pge fractionation in seafloor hydrothermal systems examples from mafic and ultramafic hosted hydrothermal fields at the slow spreading mid atlantic ridge the distribution of platinum group elements pges in massive sulfides and hematite magnetite pyrite assemblages from the recently discovered basalt hosted turtle pits hydrothermal field and in massive sulfides from the ultramafic hosted logatchev vent field both on the mid atlantic ridge was studied and compared to that from selected ancient volcanic hosted massive sulfide vhms deposits cu rich samples from black smoker chimneys of both vent fields are enriched in pd and rh pd up to 227 ppb and rh up to 149 ppb when compared to hematite magnetite rich samples from turtle pits pd up to 10 ppb rh up to 1 9 ppb a significant positive correlation was established between cu and rh in sulfide samples from turtle pits pge chondrite normalized patterns with a positive rh anomaly and pd and au enrichment pd pt and pd au ratios close to global morb and high values of pd ir and pt ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at turtle pits similarly shaped pge chondrite normalized patterns and high values of pd pt and pd ir ratios in cu rich sulfides at logatchev likely reflect a similar mechanism of pge enrichment but with involvement of ultramafic source rocks

origin and interactions of fluids circulating over the amik basin hatay turkey and relationships with the hydrologic geologic and tectonic settings abstract we investigated the geochemical features of the fluids circulating over the amik basin se turkey syria border which is crossed by the northern extension of the dsf dead sea fault and represents the boundary area of three tectonic plates anatolian arabian and african plates we collected 34 water samples thermal and cold from natural springs and boreholes as well as 8 gas samples bubbling and gas seepage besides the gases dissolved in the sampled waters the results show that the dissolved gas phase is a mixture of shallow atmospheric and deep components either of mantle and crustal origin coherently the sampled waters are variable mixtures of shallow and deep ground waters the latter being characterised by higher salinity and longer residence times the deep groundwaters from boreholes deeper than 1000 m have a ch 4 dominated dissolved gas phase related to the presence of hydrocarbon reservoirs the very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the african plate as well as basalts located to the north and east on the arabic plate the diffuse presence of co 2 enriched gases although diluted by the huge groundwater circulation testifies a regional degassing activity fluids circulating over the ophiolitic block are marked by h 2 dominated gases with abiogenic methane and high ph waters the measured 3 he 4 he isotopic ratios display contributions from both crustal and mantle derived sources over both sides of the dsf although the serpentinization process is generally independent from mantle type contribution the recorded helium isotopic ratios highlight variable contents of mantle derived fluids due to the absence of recent volcanism over the western side of the basin african plate we argue that co 2 rich volatiles carrying mantle type helium and enriched in heavy carbon are degassed by deep rooted regional faults rather than from volcanic sources

platinum group element distribution in chromite ores from ophiolite complexes implications for their exploration abstract compilation of some new data on ophiolites for greece and yugoslavia and published data from previous studies indicate that platinum group element pge and gold concentrations in chromite ores are generally low ranging from less than 100 ppb to a few hundred ppb however samples from several ophiolite complexes exhibit an enrichment of a few ppm a only in os ir and ru b only in pt and or pd or c in all pge this enrichment up to 10s ppm is mainly related with chromitites hosted in supra moho dunites and dunites of the uppermost stratigraphic levels of the mantle sequence and it seems to be local independent of the chromitite major element composition and the chromite potential of the ophiolite complexes the contents of pge combined with less chalcophile elements ni co cu the ratios of incompatible compatible elements and pge patterns provide evidence for discrimination between chromitites derived from primitive magmas and those derived from partially fractionated magmas although they have a similar major element composition thus they can be used for a stratigraphic orientation in the mantle sequence and therefore for exploration targets moreover pge data offer valuable information for the evaluation of the chromite potential in ophiolite complexes the most promising ophiolites seem to be those which apart from the petrological and geochemical characteristics indicating extensive degree of partial melting in the mantle source contain only one chromite ore type the other type being only in small proportion of limited compositional variation in both major elements and pge low ratios of pd ir while pge enriched chromitites in the mantle sequence are only occasionally present in contrast ophiolites which contain both high cr and al chromitites and where their chalcophile element data implies relatively extensive fractionation trend are not good exploration targets for chromite ores although they are related with a ssz environment

large compositional differences in the gases released from the kizildag ophiolitic body turkey evidences of prevailingly abiogenic origin abstract we investigated the geochemical features of the gases released from the kizildag ophiolitic complex hatay turkey twenty three samples both dissolved in hyperalkaline waters and free gases bubbling gases and dry seeps were collected samples were analysed for their chemical he h 2 o 2 n 2 ch 4 and co 2 and isotopic he 13 c ch 4 2 h ch 4 2 h h 2 composition including the content and c isotopic composition of c 2 to c 5 alkanes in free gases analytical results evidence h 2 production through low temperature 4 production through fischer tropsch type reactions in some sample small additions of methane either of microbial or of thermogenic origin can be hypothesized at one of the sites kisecik a clear fractionation pattern due to microbial methane oxidation leading to strongly enriched isotopic values 13 c 15 and 2 h 68 and depletion in methane concentrations has been evidenced at the dry gas seep of kurtbagi methane flux measurements have been made and a preliminary output estimation of about 1000 kg per year has been obtained

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

fischer tropsch synthesis of hydrocarbons during sub solidus alteration of the strange lake peralkaline granite quebec labrador canada abstract the composition of the carbonic phase s of fluid inclusions in pegmatite quartz from the strange lake peralkaline complex has been analysed by gas chromatography using online extraction of inclusion contents and a poraplot q capillary column the measured gas species are in order of abundance ch 4 h 2 c 2 h 6 co 2 n 2 ca n c 4 h 10 n c 5 h 12 c 2 h 2 i c 4 h 10 and c 2 h 4 minor amounts of i c 5 h 12 n c 6 h 14 i c 6 h 14 and neo c 6 h 14 were also detected but not quantified in some samples a suite of quartz samples from ca metasomatised pegmatites contains fluid inclusions with a similar distribution of hydrocarbons but much higher proportions of c0 2 the carbonic fluid coexisted immiscibly with a brine salvi and williams jones 1992 which on the basis of field and petrographic evidence was interpreted to have originated from the magma however thermodynamic calculations indicate that the above gas species specifically the hydrocarbons could not have coexisted at equilibrium in the proportions measured at any geologically reasonable conditions either prior to or post entrapment we propose instead that the gas compositions measured in the strange lake inclusions and in inclusions from other alkalic complexes resulted from the production of h 2 during the alteration of arfvedsonite to aegirine and the subsequent reaction of this h 2 with orthomagmatic c0 2 and co to form hydrocarbons in a magnetite catalysed fischer tropsch synthesis locally influx of an oxidised calcic brine derived externally from the pluton altered the original composition of the fluid by converting hydrocarbons to c0 2

abiotic methane seepage in the ronda peridotite massif southern spain abstract abiotic methane in serpentinized peridotites msp has implications for energy resource exploration planetary geology subsurface microbiology and astrobiology once considered a rare occurrence on earth reports of msp are increasing for numerous localities worldwide in low temperature land based springs and seeps we report the discovery of six methane rich water springs and two ponds with active gas bubbling in the ronda peridotite massif in southern spain water is hyperalkaline with typical hydrochemical features of active serpentinization ph 10 7 to 11 7 t 17 1 to 21 5 c ca oh facies dissolved ch4 concentrations range from 0 1 to 3 2 mg l the methane stable c and h isotope ratios in the natural spring and bubbling sites 13cch4 12 3 to 37 vpdb 2hch4 280 to 333 vsmow indicate a predominant abiotic origin in contrast springs with manmade water systems i e pipes or fountains appear to have mixed biotic abiotic origin 13cch4 44 to 69 2hch4 180 to 319 radiocarbon 14c analyses show that methane c in a natural spring is older than ca 50 000 y bp whereas dissolved inorganic carbon dic analysed in all springs has an apparent 14c age ranging from modern to 2334 y bp therefore most if not all of the ch4 is allochthonous i e not generated from the carbon in the hyperalkaline water methane is also released as bubbles in natural ponds and as diffuse seepages 101 102 mg ch4 m 2d 1 from the ground up to several tens of metres from the seeps and springs albeit with no overt visual evidence these data suggest that the gas follows independent migration pathways potentially along faults or fracture systems physically isolated from the hyperalkaline springs methane does not seem to be genetically related to the hyperalkaline water which may only act as a carrier of the gas gas bearing springs vents and invisible microseepage in land based peridotites are more common than previously thought in addition to other geological sources msp is potentially a natural source of methane for the troposphere and requires more worldwide flux measurements

oblique collision at about 1 1 ga along the southern margin of the kaapvaal continent south east africa the 1 1 ga natal metamorphic province nmp lies at the heart of a world wide system of grenville age mobile belts which welded early continental fragments into the mesoproterozoic supercontinent of rodinia structural analysis of the three tectonostratigraphic terranes in natal reveals a kinematic history characterized by prolonged ne sw plate convergence manifested as early thrust tectonics and later pervasive sinistral transcurrent shearing consequently superimposed on the natal tectonostratigraphic terranes is a kinematic subdivision into tectonic domains which are characterized by shallow south west dipping foliations south west plunging stretching lineations and north east verging recumbent folds and by younger domains with subvertical shear fabrics subhorizontal to oblique lineations and folding about near vertical axes microtextural and petrographic analyses suggest that the later shearing took place under high temperature conditions of at least 500 c the recorded kinematic indicators suggest that early subhorizontal compressional tectonics gave rise to tectonic thickening of the crust progressively followed by oblique transcurrent shearing within a transpressional regime the shearing event in the southern arc related terranes was associated with the widespread emplacement of late kinematic rapakivi granite charnockite plutons with a type granite geochemical characteristics this orogenic event took place around 1100 ma during prolonged ne sw collisional convergence along the southern margin of the stable archean foreland which lay to the north