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

relationships between gas geochemistry and release rates and the geomechanical state of igneous rock massifs in contrast to sedimentary sequences the relationships between the stressed state of igneous rocks and the chemistry and physical properties of gases contained within them are not well known here we attempt to fill this gap by using as an example the apatite nepheline and rare metal ore deposits hosted within the khibiny and lovozero alkaline nepheline syenite complexes of the kola peninsula nw russia these massifs are characterized by unusually high for igneous rocks contents of multi component essentially hydrogen hydrocarbon gases and also by high hardness elasticity and unevenly distributed subhorizontal tectonic stresses relationships between the chemical and dynamic characteristics of the gases and the geomechanical properties of the host rocks have been examined using field observations and laboratory experiments patterns of gas release variations in time and space gas emissions from rock pillars during artificial loading variations of gas pressure in sealed shot holes and changes in liberation rates of gaseous components during experimental rock loading are suggested to result from changes in rock stress and deformation state gas compositions in sealed shot holes in stressed rocks change with time partly this is due to belated release of gases held in fluid inclusions and isolated voids and their subsequent mixing with gases held in interconnected fracture systems as the included gases are preferentially released as fluid inclusion arrays are opened during later stages of stress build up partly it may also be because released gases may react with new fracture surfaces to generate enhanced levels of reduced h2 gases

influence of oxygen fugacity on mineral compositions in peralkaline melts the katzenbuckel volcano southwest germany the igneous rocks of the katzenbuckel southwest germany represent a unique and unusual alkaline to peralkaline association within the european volcanic province the magmatic activity can be subdivided into two main phases phase i comprises the main rock bodies of phonolite and nepheline syenite which were later intruded by different peralkaline dyke rocks tinguaites and alkali feldspar syenite dykes of phase ii the dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late stage pneumatolytic activity causing autometasomatic alterations as is typical for alkaline to peralkaline igneous rocks early mafic minerals of phase i rocks comprise olivine augite and fe ti oxides which are substituted in the course of fractionation by na amphibole and na pyroxene for the early magmatic stage calculated temperatures range between 880 and 780 8c with low silica activities 0 4 to 0 6 but high relative oxygen fugacities between 0 5 and 1 9 log units above the fmq buffer even higher oxygen fugacities above the hm buffer are indicated for the autometasomatic alteration which occurred at temperatures between 585 and 780 8c and resulted in the formation of pseudobrookite and hematite the unusually high oxygen fugacities even during the early magmatic stage are recorded by the major element compositions of the mafic minerals forsterite content in olivine between 68 and 78 mol up to 6 2 wt zro2 and 8 5 wt tio2 in clinopyroxene the unusual mineral assemblages pseudobrookite freudenbergite and by the enrichment of fe 3 in the felsic

hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history abstract geochemical analysis of petroleum inclusions trapped in authigenic feldspar and quartz in the ula formation in the north sea ula oil field revealed a petroleum of markedly different composition than the oil presently in the reservoir using microthermometry and the burial history as a dating tools it is concluded that the petroleum in the k feldspar inclusions was present in the more porous and permeable parts of the ula formation as early as 45 75 my bp when the field was at a depth of about 1 0 1 5 km as compared with the current depth of 3 4 km this early petroleum which was trapped as inclusions in authigenic k feldspar shows a distinctly different distribution of tricyclic terpanes and pentacyclic triterpanes from that of the current petroleum charge in the ula formation which was derived from the mandal formation source rock in late neogene time molecular parameters show that the oil in the k feldspar inclusions is significantly less mature than the crude oil in the present reservoir the approximate 90 c temperature increase occurring after entrapment of the early petroleum in kfeldspar the field is currently at 143 c appears not to have reset the low maturity signature of the oil in the k feldspar inclusions this could suggest that the temperature in the inclusions is too low for isomerization selective thermal degradation to occur lack of catalysts or that there are other controls on the ratio of some of these parameters still parameters like the ratio of c21 to c28 triaromatic steroids and those based on dimethyl and trimethyl naphthalenes are comparatively similar in both the inclusions and in the reservoir crude the oil inclusions in authigenic quartz and albite formed from about 10 my bp burial depth 2 5 km until the present burial depth 3 4 km are interpreted as representing a palaeo petroleum charge having a composition intermediate between the oil found in k feldspar inclusions and the oil charge in the present reservoir our data suggest strongly that the petroleum trapped in the inclusions in quartz and plagioclase represents progressive dilution of the early reservoired oil now found only in k feldspar inclusions with oil from the mandal formation analysis of solution gas in these inclusions suggests that the first petroleum associated gas to arrive at the trap from the progressively maturing mandal formation had a much wetter composition than the current reservoir solution gas to explain the present comparatively drier and isotopically lighter reservoir solution gas composition the inference is made that there has been a recent during formation of k feldspar inclusions 45 75 my bp maturation of the upper jurassic mandal formation the main source rock in this region was limited possibly to the graben axis this suggests that the petroleum found in the k feldspar inclusions was most likely derived from a deeper post caledonian palaeozoic formation

the contribution of the precambrian continental lithosphere to global h 2 production the production of hydrogen gas from the precambrian continental lithosphere has been underestimated taking into account hydrogen from serpentinization and radiolysis may double estimates previously based on marine systems alone molecular hydrogen produced by interactions between water and rocks in the earth s subsurface and at deep ocean vents can sustain microbial ecosystems it was thought that global h2 production originates mainly from the marine lithosphere with a negligible contribution from precambrian rocks but here the authors present a global compilation of h2 concentration data that identifies the fracture waters in the precambrian continental subsurface as a domain of the terrestrial hydrosphere that produces h2 at a rate comparable to estimates from marine systems this finding revises our understanding of the production of reduced gases in the earth s subsurface and may aid in the exploration of life in deep habitat locations microbial ecosystems can be sustained by hydrogen gas h2 producing water rock interactions in the earth s subsurface and at deep ocean vents1 2 3 4 current estimates of global h2 production from the marine lithosphere by water rock reactions hydration are in the range of 1011 moles per year5 6 7 8 9 recent explorations of saline fracture waters in the precambrian continental subsurface have identified environments as rich in h2 as hydrothermal vents and seafloor spreading centres1 2 and have suggested a link between dissolved h2 and the radiolytic dissociation of water10 11 however extrapolation of a regional h2 flux based on the deep gold mines of the witwatersrand basin in south africa11 yields a contribution of the precambrian lithosphere to global h2 production that was thought to be negligible 0 009 1011 moles per year 6 here we present a global compilation of published and new h2 concentration data obtained from precambrian rocks and find that the h2 production potential of the precambrian continental lithosphere has been underestimated we suggest that this can be explained by a lack of consideration of additional h2 producing reactions such as serpentinization and the absence of appropriate scaling of h2 measurements from these environments to account for the fact that precambrian crust represents over 70 per cent of global continental crust surface area12 if h2 production via both radiolysis and hydration reactions is taken into account our estimate of h2 production rates from the precambrian continental lithosphere of 0 36 2 27 1011 moles per year is comparable to estimates from marine systems

bitumen biomarkers in the mid proterozoic ilimaussaq intrusion southwest greenland a challenge to the mantle gas theory abstract gc and gc ms ms analysis on rock extracts has shown that the bitumen in the peralkaline ilimaussaq intrusion previously assumed to be abiogenic is biotic in origin a biotic origin is in accordance with previously published stable carbon isotopic data on bituminous matter in the rocks the biomarker distribution in the bitumen including the less common bicadinanes resembles that of oil seeps on the central west greenland coast 2200 km farther north whose source rocks and migration history are relatively well established we use a recent re construction of the subsidence and later exhumation of the west greenland coastal region during the mesozoic cenozoic japsen et al 2006a b to anticipate that hydrocarbons migrated from deeper parts of the basin offshore west of greenland the rocks of ilimaussaq were probably more deeply invaded than the surrounding granites due to their higher proportion of corroded minerals which may explain why bitumen has not been observed elsewhere in the area hydrocarbon gases c1 c5 present in fluid inclusions were also analysed after having been released by treatment with hydrochloric acid that resulted in an almost complete disintegration of the ilimaussaq intrusion rocks the acid extraction method proved generally more efficient than the crushing procedure applied by others but gave similar results for the chemical composition of the gas ch4 88 97 and isotopic ratios 13 c ch 4 1 6 to 5 0 13 c c 2 h 6 9 2 to 12 5 with the exception of hydrocarbons hosted in quartz which showed significantly lower isotopic values for methane graser et al 2008 previous researchers have suggested an abiotic origin for these hydrocarbon gases but we suggest a biotic origin for the majority of them not just those in quartz assuming that the isotopic ratio of the constituents have changed due to loss of gas by diffusion the assumption of gas loss via diffusion is supported by published studies on micro fissures in minerals typical of the ilimaussaq and field investigations showing diffusive loss of gas from the peralkaline khibina and lovozero massifs on the kola peninsula russia which are in many respects of mineralogy and hydrocarbon content similar to the ilimaussaq intrusion both the hydrocarbon gases and bitumen in the khibina and lovozero massifs have been cited as prime examples of a deep mantle source although the carbon isotopic ratio of the bitumen clearly pointed to an organic origin the trends in carbon isotopic ratio of methane released with time from freshly exposed rocks also supports our hypothesis of 13c enrichment of the methane remaining within the rock thus there is good evidence that the hydrocarbons in the kola alkaline massifs are mostly biotic in origin in which case the probability of finding economic hydrocarbon accumulations from a deep mantle source seems exceedingly small

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

buffers barriers and blankets the dis connectivity of catchment scale sediment cascades abstract catchment configuration and the nature of connectivity within and between landscape compartments affect the operation of sediment cascades and geomorphic responses to disturbance events of differing magnitude and frequency this paper introduces the concept of landform impediments termed buffers barriers and blankets that impede sediment conveyance by limiting the connectivity between landscape compartments buffers restrict sediment delivery to channels barriers inhibit sediment movement along channels and blankets drape channel or floodplain surfaces affecting the accessibility of sediment to entrainment these features operate as a series of switches which turn on off processes of sediment delivery determining the effective catchment area at any given time using previously documented examples the role of these features in affecting the operation of sediment cascades in a low relief passive landscape setting such as the australian landmass is contrasted to examples from high relief uplifting settings in new zealand the australian examples are further explored by examining how changes to landscape connectivity brought about by human disturbance since european settlement have impacted upon landscape sensitivity and prospects for river recovery this approach to analysis of impediments to sediment conveyance is generic and can be applied in any environmental setting

volatiles in a peralkaline system abiogenic hydrocarbons and f cl br systematics in the naujaite of the ilimaussaq intrusion south greenland agpaitic rocks comprise most of the exposed part of the 1 16 ga old 8 17 km large and about 1700 m thick ilimaussaq intrusion in south greenland within these more than 600 m thick sequence of sodalite rich naujaites mainly sodalite arfvedsonite alkali feldspar nepheline eudialyte aenigmatite are interpreted as a sodalite flotation cumulate sodalites show two to three different zones in cathodoluminescence cl and at least two zones in thin sections the cl zones can be related to chemical differences detectable by electron microprobe whereas relations with optical zonations are less obvious compositional trends in sodalite reflect trends in the evolution of volatile contents in the melt the sodalite at ilimaussaq is almost free of ca and closely corresponds to the pure na cl sodalite endmember with about 7 wt of cl s contents reach up to 0 9 wt cl br ratios range from 500 to 1700 raman spectroscopy shows that s is present as so4 2 in sodalite although sphalerite zns is a stable phase in naujaites peralkalinity and fo2 conditions allow s2 and so4 2 to be present contemporaneously the whole naujaite sequence is divided into two parts an upper part with low homogeneous s contents and cl br ratios in the sodalite cores and a lower part with strongly variable and higher s contents and with cl br ratios which are decreasing downwards the details of the s content and the cl br ratio evolution show that sodalite strongly influences the halogen contents of the melt by scavenging cl and br the naujaites were formed from a highly reduced halogen rich magma in equilibrium with magmatic methane at about 800 c which upon ascent cooling and fractionation exsolved an aqueous fluid phase both fluids were trapped in separate inclusions indicating their immiscibility micrometer sized aegirine crystals and primary hydrocarbon bearing inclusions are abundant in the crystal cores the inclusions were trapped at pressures up to 4 kbar although the emplacement pressure of the intrusion is about 1 kbar this indicates growth of the sodalite during melt ascent and a very effective mechanism of trace element scavenging during sodalite growth sodalite rims are devoid of aegirine or primary hydrocarbon inclusions and probably reflect the emplacement stage

a review of the occurrence form and origin of c bearing species in the khibiny alkaline igneous complex kola peninsula nw russia abstract the khibiny complex hosts a wide variety of carbon bearing species that include both oxidized and reduced varieties oxidised varieties include carbonate minerals especially in the carbonatite complex at the eastern end of the pluton and na carbonate phases reduced varieties include abiogenic hydrocarbon gases particularly methane and ethane dispersed bitumens solid organic substances and graphite the majority of the carbon in the khibiny complex is hosted in either the carbonatite complex or within the so called central arch the central arch is a ring shaped structure which separates khibinites coarse grained eudialite bearing nepheline syenites in the outer part of the complex from lyavochorrites medium grained nepheline syenites and foyaites in the inner part the central arch is petrologically diverse and hosts the major ree enriched apatite nepheline deposits for which the complex is best known it also hosts zones with elevated hydrocarbon dominantly methane gas content and zones of hydrothermally deposited na carbonate mineralisation the hydrocarbon gases are most likely the product of a series of post magmatic abiogenic reactions it is likely that the concentration of apatite nepheline deposits hydrocarbon gases and na carbonate mineralisation is a function of long lived fluid percolation through the central arch fluid migration was facilitated by stress release during cooling and uplift of the khibiny complex as a result carbon with a mantle signature was concentrated into a narrow ring shaped zone

preliminary evaluation of trace hydrocarbon speciation and abundance as an exploration tool for footwall style sulfide ores associated with the sudbury igneous complex ontario canada deposits of cu ni platinum group elements pge rich sulfides occur along the north range footwall of the sudbury igneous complex ontario canada the deposits have been modified chemically mineralogically and texturally by multiple syn to postmagmatic hydrothermal events and are hosted mainly within sudbury breccia a contact metamorphosed and hydrothermally altered impact breccia the composition of c1 to c6 unsaturated and saturated hydrocarbons in bulk fluid inclusion volatiles in the matrix of the sudbury breccia was investigated using in line rock crushing gas chromatography gc in order to compare the hydrocarbon composition of this rock type in breccia zones containing economic footwall sulfide deposits at the morrison deposit levack mine north range sudbury ontario with barren breccia zones trace hydrocarbons possibly abiogenic in origin occur throughout the sudbury igneous complex footwall and country rocks investigated however there are differences in the composition and abundance of bulk hydrocarbons released from mineralized and barren sudbury breccia when fluid inclusions are opened volatiles released from samples of sudbury breccia from sulfide mineralized and sulfide barren environments showed the following 1 higher average abundances of light saturated hydrocarbons c1 c4 and an approximately 2 higher total abundance of hydrocarbons mol g of rock basis associated with samples from the mineralized study area and 2 comparable average unsaturated hydrocarbon abundances in both settings but a larger range in unsaturated hydrocarbon abundances in the mineralized study area differences in bulk hydrocarbon abundance and composition reflect differences in the abundance and hydrocarbon content of fluid inclusions trapped in the barren and mineralized sudbury breccia zones in addition the compositional modification of circulating fluids by processes and conditions unique to the mineralized sudbury breccia environment may have occurred prior to inclusion entrapment e g modification by mineral catalysts differences in temperature and oxygen fugacity preliminary spatial analysis of the hydrocarbon distribution within and surrounding the morrison deposit shows that the total hydrocarbon abundance in the sudbury breccia does not change with orebody proximity within a single host breccia zone however volatiles trapped in the sudbury breccia matrix near the top of the footwall deposit where it is physically connected to contact style ni cu pge ores have elevated unsaturated hydrocarbon abundances e g propene compared to other parts of the same breccia zone distal to this zone of physical connection samples of the pge enriched sudbury breccia and mineralized veins containing alteration assemblages characteristic of the footwall ore styles have higher unsaturated hydrocarbon abundances and unsaturated saturated ratios compared to sudbury breccia and vein samples that are pge poor localized enrichments in unsaturated hydrocarbons in sudbury breccia zones may be the result of specific ore minerals and metal complexes involving the pge and group viii metals that acted as catalytic agents modifying the composition of initially light saturated hydrocarbon species prior to entrapment in fluid inclusions to apply the analysis of hydrocarbon compositions in trapped fluid inclusions to discriminating mineralized from barren zones of sudbury breccia samples from targeted areas were compared to samples of barren sudbury breccia background although a large data set is presented here to establish these compositional fields analysis of smaller sample subsets from each environment yields a statistically significant separation between the two environments total hydrocarbon abundance c3 c1 ratios and unsaturated saturated hydrocarbon ratios are useful indicators of sulfide ore proximity and may help delineate regions enriched in pge

mineral forming and diagenetic processes related to tertiary hydrocarbon seepage at the bohemian massif outer western carpathians interface evidence from the hrabůvka quarry moravia czech republic v lomu hrab vka situovanem p i hranici ceskeho masivu reprezentovan m zvrasn n mi spodnokarbonsk mi siliciklastiky kulmske facie a terciernim sedimentarnim pokryvem zapadnich karpat tvo enem spodnobadensk mi siliciklastiky a vapnit mi jily byl v geologickem zaznamu zjist n fosilni v v r uhlovodik v clanku jsou prezentovany mineralogicke izotopove a geochemicke udaje a take data ze studia fluidnich inkluzi ktere umo nily vyhodnotit genezi dan ch hornin il a jejich fluid

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

transition metal catalysis in natural gas generation evidence from nonhydrous pyrolysis experiment abstract transition metal catalysis has been advocated as a critical mechanism for natural gas generation but its presence and significance in geological settings have long been debated due to conflicting results of laboratory experiments and the lack of reliable field indicator in this study a low rank coal sample from the shahezi formation of the songliao basin was subjected to nonhydrous pyrolysis with and without transition metal the chemical and isotopic compositions of gaseous products in experiments were analyzed to investigate the mechanism and potential indicator of transition metal catalysis in sedimentary basins the chemical and carbon isotopic compositions of hydrocarbon gases generated in pyrolysis experiments revealed that transition metal could catalyze both decomposition of organic matters and methane synthesis such as fischer tropsch type reactions during maturation of source rocks under experimental conditions resembling geological settings catalytic methane has uniform d values unrelated to source rock maturity which is helpful in identification of catalytic natural gases in sedimentary basins transition metal catalysis is probably not a common mechanism for natural gas generation in sedimentary basins due to the positive correlation between dch4 of natural gases and maturities of source rocks observed in most natural cases however transition metal catalysis could well interpret the restricted range of dch4 and carbon isotopic reversal phenomenon of natural gases in the yingcheng formation of the xujiaweizi fault depression whose origin has long been debated so we inferred that the transition metal catalysis may have occurred in deep strata of the xujiaweizi fault depression and played a significant role in natural gas generation our study revealed that restricted range of dch4 of natural gases with different maturities may serve as an effective indicator of transition metal catalysis in sedimentary basins it provides a new perspective to investigate the significance and universality of transition metal catalysis in different geological settings

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

the origin of ch4 rich fluids in reduced porphyry skarn cu mo au systems abstract although most of the methane on earth is of biogenic origin significant abiogenic methane has been identified in a variety of geological environments moreover the presence of methane has been reported recently in fluid inclusions from a number of reduced porphyry deposits the genesis of this methane however remains poorly understood here we present results of a study of magma exsolved ch4 rich aqueous fluid inclusions in the seleteguole reduced porphyry skarn cu mo au deposit nw china four types of fluid inclusions namely intermediate density two phase aqueous inclusions low density vapor inclusions brine inclusions and aqueous liquid inclusions have been distinguished on the basis of the phases present at room temperature the intermediate density inclusions were trapped as a single phase and contain 3 8 10 4 mol kg ch4 corresponding to an oxygen fugacity between fmq 1 and fmq 0 5 this attests to the remarkably reduced nature of the fluid the 13c value of the ch4 hosted fluid inclusions ranges from 29 4 to 19 1 pdb which distinguishes this methane from biogenic methane indeed the high homogenization temperature of the ch4 rich inclusions 400 c implies that the ch4 was exsolved directly from the magma given the environment in which the magma was likely generated i e at or immediately above a subducting plate we propose that the methane was produced by reactions involving organic matter bearing carbonate rocks in the subduction zone although cu mo and au in most porphyry systems are interpreted to have been transported under oxidizing conditions our results indicate that reduced aqueous liquids and vapors are also capable of transporting appreciable concentrations of these metals

geochemical characteristics and origin of natural gas in tarim basin china the tarim basin located in northwest china is one of the largest basins in the world that has not been well explored in recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields with an approximate 1 1 ratio of oil to gas resource this means that the natural gas resource is very important for the hydrocarbon resource in the tarim basin in this basin most of the discovered gases are condensate associated gas and oil associated gas research on chemical components and isotope composition of carbon and hydrogen of natural gases from the tarim basin shows that all discovered gases in this basin are thermogenic with respect to source organic matter there are two types of gases 1 oil type gas generated from sinian to lower paleozoic marine source rocks with the sapropelic organic matter with 44 5 to 33 8o oo of d13c1 42 0 to 28 1o oo of d13c2 35 4 to 28 4o oo of d13c3 and heavier than 200o oo of dd1 and 2 coal type gas generated from mesozoic terrestrial source rocks with the humic organic matter with 40 5 to 33 1o oo of d13c1 29 7 to 21 3o oo of d13c2 26 3 to 20 3o oo of d13c3 and lighter than 200o oo of dd1

combined raman microprobe spectrometry and microthermometry of fluid inclusions in minerals from igneous rocks of the gardar province south greenland abstract raman microprobe spectrometry has been applied to analysis of the gaseous phase in individual fluid inclusions in minerals from alkalic igneous rock types and associated hydrothermal veins from the gardar province south greenland quantitative analyses are given for co2 ch4 c2h6 h2 and h2s traces of co were observed in one co2 inclusion in conjunction with data from microthermometry the results permit calculation of the bulk chemical composition of entrapped fluids and evaluation of the possible pressure temperature oxygen fugacity and sulphur fugacity during entrapment of the individual fluid inclusions calculated oxygen fugacity values correspond to those of the nno and qfm buffer reactions at temperatures of 300 400 c and pressures of 0 5 1 0 kbar calculated sulphur fugacity values are within the range of normal ore forming solutions log fs2 6 to 10

a reassessment of models for hydrocarbon generation in the khibiny nepheline syenite complex kola peninsula russia although hydrocarbon bearing fluids have been known from the alkaline igneous rocks of the khibiny intrusion for many years their origin remains enigmatic a recently proposed model of post magmatic hc generation through fischer tropsch type reactions suggests a primary co2 fluid this hypothesis is based upon textural data gas bulk and isotopic composition and low entrapment temperature of fluid inclusions that indicate an abiogenic origin for the hc gases however new petrographic microthermometric laser raman bulk gas and isotope data are presented and discussed in the context of previously published work in order to reassess models of hc generation the gas phase is dominated by ch4 with only minor proportions of higher hydrocarbons no remnants of the proposed primary co2 rich fluid are found anywhere in the complex primary and secondary fluid inclusions show similar compositions and entrapment conditions the majority of the fluid inclusions are of secondary nature and trapped in healed microfractures this indicates a high fluid flux after magma crystallisation entrapment condtions for primary fluid inclusions are 450 550 c at 2 8 4 5 kbar these temperatures are too high for hc gas generation through the ft reaction chemical analyses of rims of fe rich phases suggest that they are not the result of alteration but instead represent changes in magma composition during crystallisation furthermore there is no clear relationship between the presence of fe rich minerals and fluid inclusion abundance as reported elsewhere fluid inclusion planes generally start and terminate at mineral boundaries 13c values for methane range from 22 4 to 5 4 confirming also an abiogenic origin for the gas these data support an abiogenic hc origin but are not consistent with a post magmatic ft type reaction the presence of primary ch4 dominated fluid and melt inclusions which contain a methane rich gas phase indicate that a magmatic origin is more likely an increase in methane content together with a decrease in 13c isotope values towards the intrusion margin suggest that magmatically derived abiogenic hydrocarbons may have mixed with biogenic hydrocarbons derived from the surrounding country rocks

the role of vegetation on gully erosion stabilization at a severely degraded landscape a case study from calhoun experimental critical zone observatory abstract gully erosion was evidence of land degradation in the southern piedmont site of the calhoun critical zone observatory cczo during the cotton farming era understanding of the underlying gully erosion processes is essential to develop gully erosion models that could be useful in assessing the effectiveness of remedial and soil erosion control measures such as gully backfilling revegetation and terracing development and validation of process based gully erosion models is difficult because observations of the formation and progression of gullies are limited in this study analytic formulations of the two dominant gullying processes namely plunge pool erosion and slab failure are utilized to simulate the gullying processes in the 4 km2 holcombe s branch watershed in order to calibrate parameters of the gully erosion model gully features e g depth and area extracted from a high resolution lidar map are used after the calibration the gully model is able to delineate the spatial extent of gullies whose statistics are in close agreement with the gullies extracted from the lidar dem several simulations with the calibrated model are explored to evaluate the effectiveness of various gully remedial measures such as backfilling and revegetation the results show that in the short term the reshaping of the topographical surface by backfilling and compacting gullies is effective in slowing down the growth of gullies e g backfilling decreased the spatial extent of gullies by 21 46 and decreased the average depth of gullies by up to 9 revegetation however is a more effective approach to stabilizing gullies that would otherwise expand if no gully remedial measures are implemented analyses of our simulations show that the gully stabilization effect of revegetation varies over a wide range i e leading to 23 69 reduction of the spatial extent of gullies and up to 45 reduction in the depth of gullies depending on the selection of plant species and management practices

free hydrogen hydrocarbon gases from the lovozero loparite deposit kola peninsula nw russia abstract the lovozero nepheline syenite massif in the north eastern fennoscandian shield well known to mineralogists and petrologists is also interesting with its high contents of hydrogen hydrocarbon gases in different forms of presence which is untypical of magmatic rocks the article systematizes and generalizes little known and unpublished data on the composition location character and scale intensity of the free gases fg emission within a major loparite deposit confined to the massif 4 and 2 are dominant in the fg composition the molecular weight distribution of hydrocarbon gas components corresponds to the classic anderson schulz flory distribution with a steep gradient carbon and hydrogen of the gases are characterized by rather heavy isotope compositions becoming lighter from the transition of methane to ethane the fg volume has been estimated as 0 2 1 6 m 3 of gas per 1 m 3 of undisturbed rock the gas recovery of walls in underground workings has been up to 0 2 ml min m 2 for 4 and 0 5 ml min m 2 for 2 in several years after their heading the discharge of some shot holes that characterizes the gas emission intensity 1 8 2 m deep and 40 mm in diameter is up to 300 ml min but its 1 2 orders lesser values dominate the discharge time in some sections varies from several days to 20 years the overpressure of gases towards the air mainly does not increase 100 hpa sometimes reaching 120 kpa it has been defined that fg distribute irregularly at the distance of centimeters to hundreds of meters and their composition and particularly emission intensity perform different temporal fluctuations the abiogenic origin of fg has been proposed with fg appearing as a mixture of gases in various proportions a gases remaining in microfissures at the massif s consolidation after the capture by fluid inclusions and those lost during degassing and b gases occurred in mechanic chemical reactions partial emission and concentration of occluded and diffusely scattered gases under the unstable stress strain mode of the rock mass combustible and explosive hydrogen hydrocarbon fg can accumulate in the air of underground workings and cause accidents disrupting the workflow the background for using characteristics of spatial temporal variations of the fg emission as precursors of dangerous geodynamic phenomena has been indicated

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

development of oil formation theories and their importance for peak oil this paper reviews the historical development of both biogenic and non biogenic petroleum formation it also examines the recent claim that the so called abiotic oil formation theory undermines t

volatiles associated with alkaline igneous rift activity fluid inclusions in the ilimaussaq intrusion and the gardar granitic complexes south greenland abstract fluid inclusions in minerals from si oversaturated and si undersaturated alkalic igneous complexes belonging to the precambrian gardar rift province in south greenland contain distinctly different carbon bearing gases granites and quartz syenites are characterized by co2 and only minor ch4 whereas agpaitic nepheline syenites are dominated by hydrocarbons essentially ch4 and contain only insignificant amounts of co2 and or co in the alkaline ilimaussaq intrusion the hydrocarbon rich gases may well reflect equilibration with graphite at magmatic temperatures and at oxygen fugacities approaching those defined by the synthetic mw buffer reaction in general formation of hydrocarbon gases in agpaitic nepheline syenites is considered to reflect the fulfillment of three basic conditions 1 low oxygen fugacities 2 a wide temperature range of crystallization and a low temperature solidus and 3 retention of volatiles during crystallization the characteristic carbon bearing vapour associated with continental alkaline igneous activity is however considered to be co2

carbon isotope composition of organic compounds produced by abiotic synthesis under hydrothermal conditions although it is widely believed that production of organic compounds by fischer tropsch synthesis and related processes occurs in many geologic environments unambiguous identification of compounds with an abiotic origin in natural samples has been hampered by a lack of means to discriminate between abiotic compounds and organic matter from biological sources while isotopic compositions might provide a means to discriminate between biologic and non biologic sources of organic matter there are few data presently available to constrain the isotopic composition of compounds produced by abiotic processes in geologic systems here we report results of laboratory experiments conducted to evaluate the isotopic composition of organic compounds synthesized abiotically under hydrothermal conditions we find the organic products are depleted in 13c to a degree typically ascribed to biological processes indicating that carbon isotopic composition may not be a particularly effective diagnostic means to differentiate between biologic and non biologic sources furthermore our results suggest that the isotopic compositions of reduced carbon compounds found in many ancient rocks that have heretofore been attributed to biological sources could be consistent with an abiotic origin in a hydrothermal setting

diagenetic source of fluids causing the hydrothermal alteration of teschenites in the silesian unit outer western carpathians czech republic petroleum bearing vein mineralization from the střibrnik site calcite pyrite veinlets containing a small amount of quartz chlorite sphalerite and marcasite occur in teschenite which is situated within the lower cretaceous flysch siliciclastics of the silesian unit fluid inclusion study demonstrated the presence of a heterogeneous mixture of a low salinity aqueous solution and mature methane rich petroleum during precipitation of calcite and quartz the 13c values of methane and dissolved carbonate 34s values of pyrite and 18o values of parent hydrothermal solutions are all consistent with the external source of the fluid phase derived from diagenetically modified flysch sediments the vein formation occurred during an increase in both temperature from 80 c to 220 c and pressure 100 700 bar the observed discrepancy between the maximum fluid temperature and the regional burial temperature together with fluctuations in petroleum density and significant variations in chemical and isotopic compositions of fluids are interpreted in terms of episodic tectonically induced generation of the fluid phase related to deeper burial the observed ree patterns of hydrothermal calcite and pyrite can be attributed to increased concentrations of organic ligands in the fluid phase and or involvement of sorption desorption processes

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

geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from mt etna and vulcano island sicily italy 1 in this paper fluid source s and processes controlling the chemical composition of volatile organic compounds vocs in gas discharges from mt etna and vulcano island sicily italy were investigated the main composition of the etnean and volcano gas emissions is produced by mixing to various degrees of magmatic and hydrothermal components vocs are dominated by alkanes alkenes and aromatics with minor though significant concentrations of o s and cl f substituted compounds the main mechanism for the production of alkanes is likely related to pyrolysis of organic matter bearing sediments that interact with the ascending magmatic fluids alkanes are then converted to alkene and aromatic compounds via catalytic reactions dehydrogenation and dehydroaromatization respectively nevertheless an abiogenic origin for the light hydrocarbons cannot be ruled out oxidative processes of hydrocarbons at relatively high temperatures and oxidizing conditions typical of these volcanic hydrothermal fluids may explain the production of alcohols esters aldehydes as well as o and s bearing heterocycles by comparing the concentrations of hydrochlorofluorocarbons hcfcs in the fumarolic discharges with respect to those of background air it is possible to highlight that they have a geogenic origin likely due to halogenation of both methane and alkenes finally chlorofluorocarbon cfc abundances appear to be consistent with background air although the strong air contamination that affects the mt etna fumaroles may mask a possible geogenic contribution for these compounds on the other hand no cfcs were detected in the vulcano gases which are characterized by low air contribution nevertheless a geogenic source for these compounds cannot be excluded on the basis of the present data

alteration hfse mineralisation and hydrocarbon formation in peralkaline igneous systems insights from the strange lake pluton canada abstract two characteristics of peralkaline igneous rocks that are poorly understood are the extreme enrichment in hfse notably zr nb y and ree and the occurrence of fluid inclusions dominated by methane and higher hydrocarbons although much of the hfse enrichment can be explained by magmatic processes the common intense alteration of the parts of the peralkaline intrusions most enriched in these elements suggests that hydrothermal processes also play an important role in hfse enrichment likewise although the origin of the higher order hydrocarbons that occur as inclusions in these rocks is still debated there is strong evidence that at least in some cases their formation involved hydrothermal processes the issues of hfse enrichment and hydrocarbon formation in peralkaline intrusions are examined using data from the strange lake pluton a small middle proterozoic intrusion of peralkaline granite in northeast canada this pluton contains some of the highest concentrations of zr ree and y ever reported in an igneous body and is characterised by abundant hydrocarbon dominated fluid inclusions in rocks that have been hydrothermally altered including those that form a potential hfse ore zone we show that hfse at strange lake were partly concentrated to near exploitable levels as a result of their transport in a high salinity magmatic aqueous liquid and that this fluid coexisted immiscibly with a carbonic phase which reacted with hydrogen and iron oxides generated during the associated hydrothermal alteration to produce hydrocarbons via a fischer tropsch synthesis as a result hydrocarbons and hfse mineralization are intimately associated we then go on to show that hydrothermal alteration hfse mineralisation and hydrocarbons are also spatially associated in other peralkaline complexes and present a model to explain this association which we believe may be applicable to any peralkaline intrusion where hfse enrichment was accompanied by calcium metasomatism hematisation and hydrothermal fluorite we also suggest that even where these criteria are not satisfied hydrothermally enriched hfse and hydrocarbons will be intimately associated simply because they are products of the same initial magmatic fluid finally we speculate that the association of hfse and hydrocarbons may in some cases actually be genetic if as seems possible unmixing or effervescence of a reduced carbonic fluid from the original magmatic fluid caused changes in temperature ph f o 2 or the activity of volatile ligands sufficient to induce the deposition of hfse minerals

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

sediment budget to assess the geomorphic effect of a cyclonic storm new zealand abstract a short term sediment budget was constructed to assess the erosion response of a soft rock hill country watershed to an intense rainstorm event the watershed is located in a landslide prone area on the east coast of the north island new zealand during march 1988 753 mm of rain was recorded over a four day period with 320 mm and 329 mm on successive days known as cyclone bola this was the largest rainstorm event in the tutira watershed in the 93 year rainfall record the budget quantifies the total sediment generated during the storm the relative contribution of erosion processes involved the amount of sediment held in storage and the amount discharged into two lakes within the watershed a landform map of the watershed was constructed and the contribution of each landform type to the total budget was calculated a total of 1 35 0 13 million m3 of sediment was generated during the storm at an average of 420 m3 ha this is equivalent to a denudation value of 42 mm for the total watershed 3208 ha and 83 mm for the landforms severely affected by landsliding 1427 ha of the sediment generated 21 remained on hillslopes 22 was deposited on valley floors 51 was deposited on the lakebeds and the remaining 6 was discharged from the watershed via the lake outlet most of the sediment generated during the storm was from primary source areas on hill slopes with sediment in secondary storage providing only a small contribution landslide erosion was the main process accounting for 89 of the sediment generated channel tunnel gully and sheet erosion were only minor contributors to the budget six hillslope landforms which occupy only 44 of the watershed generated 90 of the sediment the results of this sediment budget when put in context with the storm magnitude frequency history being analysed from lake cores contribute to the identification of sustainable land use and management of soft rock hill country

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

bicarbonate rich fluid inclusions and hydrogen diffusion in quartz from the libcice orogenic gold deposit bohemian massif abstract unusual paleofluid composition is reported for the libcice orogenic type gold deposit located in the central bohemian plutonic complex cbpc czech republic unexpected bicarbonate rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold bearing quartz vein a detailed microthermometry laser raman micro spectroscopy lrms and sem cathodoluminescence study was used to understand the complex chemistry and p t x history the results indicate the presence of h 2 o and h 2 o co 2 ch 4 n 2 h 2 s fluids the latter displaying variations of the co 2 ch 4 ratio in the gaseous phase from 6 8 to 0 06 variation of the ch 4 content across single grains and between different levels of the mine was recorded the presence of nahcolite h 2 up to 6 mol and ethane 0 0 2 mol in the fluids were also discovered by lrms potential models for the formation of different types of fluids present in the deposit are discussed including the genesis of hco 3 rich fluids as well as h 2 and c 2 h 6 presence in the primary fluid inclusions the potential influence of organic matter bearing sediments as well as the impact of the intrusion of cbpc re equilibration and or re speciation of fluid inclusions during the post entrapment history is considered to have the main impact on the complex paleofluid chemistry based on the thermodynamic modeling h 2 diffusion into the fluid inclusions was shown to be the main reason for the ch 4 variation on the scale of a single grain as well as across the whole vein although the exact processes of production formation of hco 3 and h 2 at the libcice deposit remain open to discussion reactions in the c o h system are considered to be a possible formation mechanism this work also contributes to our understanding of the importance of post entrapment modifications and reactions in the c o h system on interpretation deciphering the processes in orogenic type deposits

origin and stability of a permafrost methane hydrate occurrence in the canadian shield abstract relatively little attention has been given to the stability of methane hydrates formed during periods of past climate change currently in areas of continuous permafrost although a large portion of the canadian arctic is underlain by crystalline rocks the occurrence phase and origin of alkanes in crystalline rocks under thick permafrost conditions 500 m have not been reported for the first time composition and isotopic data for gases from a crystalline shield environment currently under permafrost conditions are presented gas and water samples were collected from exploration boreholes and seeps between 890 and 1130 m depths in the lupin gold mine nunavut canada gases were methane dominate 64 87 with nitrogen 10 37 the next largest component and smaller amounts of ethane propane and carbon dioxide pressure and temperature measurements indicated gas hydrates were stable at the site prior to mining operations a conclusion supported by noble gas and salinity determinations gas hydrate stability over the last 120 kyr glacial cycle was demonstrated by calculating transient subsurface pressure and temperature conditions utilizing the memorial university university of toronto glacial systems model mun uoft gsm and the hydrogeosphere groundwater flow model model results also indicated glacial loading increased subsurface pressures resulting in increased hydrate stability fields during glacial periods subglacial groundwater recharge would be limited by any significant formation of gas hydrates gas composition combined with carbon and hydrogen isotopic determinations on methane 56 to 42 vpdb and 349 to 181 vsmow carbon dioxide 55 to 15 vpdb ethane 37 to 27 vpdb and 330 to 228 vsmow and propane 34 to 27 vpdb and 196 to 172 vsmow indicated formation of natural gases by thermogenic processes mixed with bacteriogenic gas reasonable given site geologic history methane hydrate formation affected gas composition and gas 2 h values complicating the interpretation gas production is not a modern process at this location and the overall contribution to the global carbon budget is small glacial groundwater recharge models need to account for methane hydrate formation and dissipation due to changes in subsurface stability fields during glaciation and the effect of methane hydrate on hydraulic conductivity

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

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

geochemistry and accumulation of carbon dioxide gases in china we propose the following identification indicators for co2 of different origins based on data obtained from analyzing the molecular composition of 1198 gas samples the co2 carbon isotope values of 390 samples and the helium isotope composition of 256 samples collected from wells of 16 oil and gas bearing basins and gas seepages in china and reviewing literature on organic and inorganic co2 throughout the world co2 is of organic origin if co2 content 13cco22 is of inorganic origin if dgr13cco2 8 pmil or co2 60 and co2 is of either organic or inorganic origin or a mixtur of organic and inorganic origins if 10 pmil 13cco213cco2 values of organic co2 mainly range from 10 to 22 pmil in tectonically stable oil and gas bearing basins where deep faults and magmatism are undeveloped organic co2 occurs almost exclusively in tectonically active oil and gas bearing basins where active faults and magmatism are present or in areas of modern volcanic activity the dgr13cco2 values of inorganic co2 range from 2 to 8 pmil and are distributed along faults the inorganic co2 with a dgr13cco2 value of 0 3 pmil is of metamorphic origin and that with dgr13cco2 values of 6 2 pmil is mantle derived and of magmatic origin in china the dgr13cco2 values of inorganic co2 gas pools range from 3 41 to 8 44 pmil and the helium ratio r ra is 1 which indicates that these gases are typically derived from the mantle

application of the shetran basin scale landslide sediment yield model to the llobregat basin spanish pyrenees the first application of the shetran basin scale landslide erosion and sediment yield model is carried out for a major landsliding event in the upper 505 km2 of the llobregat basin in the eastern spanish pyrenees in november 1982 the model simulates the spatial distribution of shallow landslides and their sediment yield acknowledging uncertainty in the model parameter evaluation the aim of the application was not to reproduce the observed occurrence of landslides as accurately as possible with one simulation but to bracket the observed pattern with several simulations representing uncertainty in the key input conditions bounds on the landslide simulations were thus determined as a function of uncertainty in the vegetation root cohesion used in the model factor of safety calculations the resulting upper bound considerably overestimates the observed pattern 17 000 landslides compared with an observation of around 700 but it reproduces several of the principal clusters in the observed pattern the lower bound contains around 500 landslides the sediment yield estimates 2670 14 630 t km 2 are comparable to measurements elsewhere in the pyrenees for extreme events the results demonstrate an ability to simulate the basin scale landslide response to a rainfall event and the resulting sediment yield they also highlight the need for further research in setting the uncertainty bounds and in avoiding large overestimates of landslide occurrence arising in part from a current inability to model small scale controls for a basin of the given size copyright 2006 john wiley sons ltd

sublacustrine hydrothermal seeps and silicification of microbial bioherms in the ediacaran oued dar a caldera anti atlas morocco this paper presents a case study of the sublacustrine precipitation of hydrothermal silica tio2 in the ediacaran mancour group of the saghro inlier anti atlas morocco lacustrine carbonates containing stromatolitic mats and bioherms occur in ephemeral ponds developed within the oued da ra caldera its syn eruptive infill consists of pyroclastites ashflow tuffs and subsidiary lava flows and sills whereas inter eruptive deposition is mainly represented by slope related debris flow breccias and landslides alluvial fans and fluvial channels carbonate production took place in a mosaic of differentially subsiding fault bounded intra caldera blocks controlled by episodic collapse induced drowning pyroclastic blanketing and migration of alluvial fluvial environments after microbial carbonate production the carbonates recorded several early diagenetic processes punctuated by polyphase fissuring controlling secondary permeability locally linked to hydrothermal influx three generations of carbonate cements are recognisable i fibrous botryoidal and blocky drusy mosaics of calcite ii idiotopic mosaics of dolomite caused by flushing of hypersaline mg rich brines and iii euhedral to drusy calcite via dedolomitization the 13c and 18o values from carbonate cements broadly become successively isotopically lighter as a result of meteoric and hydrothermal influence and were probably overprinted by the panafrican 3 phase that affected the top of the mancour group two mechanisms of silicification are involved i early diagenetic occlusion of interparticle pores at the sediment water interface of pyroclastic substrates and reefal core and flanks and ii hydrothermal precipitation of silica tio2 lining fissures and vuggy porosity encased in the host rock silica conduits cross cutting lacustrine mats and bioherms exhibit high potential of preservation in collapsed volcanic calderas primary fluid inclusions of hydrothermal silica contain brine relics with nacl cacl2 ratios of 2 1 to 4 4 representing minimum entrapment temperatures of about 142 to 204 c and abiotic hydrocarbons heavy alkanes related to serpentinization of the volcanic and volcanosedimentary basement of the oued dar a caldera

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

baogutu an example of reduced porphyry cu deposit in western junggar abstract classic oxidized porphyry copper deposits opcd are characterized by high tonnage and elevated f o 2 and contain highly oxidized minerals including primary anhydrite and hematite in contrast the baogutu deposit contains abundant hypogene pyrrhotite and methane rich fluid inclusions characteristic of lower tonnage reduced porphyry copper deposits rpcd mineral paragenesis and mineral chemistry studies reveal two mineralization periods magmatic and hydrothermal with the hydrothermal period further subdivided into three paragenetic stages including ca na alteration potassic alteration and propylitization locally overlapped by phyllic alteration several independent geothermometers indicate that the temperatures of the magma potassic and propylitization alteration are estimated to be 600 900 c 200 400 c and 200 300 c respectively multiple indicators including mineral assemblages apatite so 3 content whole rock fe 2 o 3 feo ratios and fluid compositions indicate the f o 2 of the magma and hydrothermal fluid to be nno and nno nno 2 respectively hydrothermal fluids associated with primary biotite yield log f h 2 o f hcl fluids values of 4 8 6 2 for diorite and 4 1 4 5 for granodiorite porphyry the log f s2 of the magmatic and potassic alteration are estimated to be 0 7 to 3 0 and 5 5 to 11 0 respectively based on pyrrhotite and sulfide assemblages mineral assemblage and hessite composition suggest the log f te2 of the potassic alteration is 8 5 to 14 5 the low tonnage baogutu deposit displays significantly lower f o 2 than opcds nno 2 and on this basis could be classified as a rpcd other physicochemical conditions including t f s2 log f h2o f hcl fluid do not show obvious differences to those of opcds we deduce that the low f o 2 of baogutu metallogenic granitoids and aqueous fluids likely produced the unusual pyrrhotite arsenopyrite mineral assemblage and the nacl h 2 o ch 4 co 2 ore forming fluids and small tonnage typical of rpcds previous obtained fluid inclusion h o isotope data and sulfide s pb isotope data suggest the methane rich ore forming fluids were derived from deep mantle source with little contamination from sedimentary components however detailed studies are needed to clarify the origin of the ch 4

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

pressure temperature evolution of metapelitic granulites in a polymetamorphic terrane the rauer group east antarctica distinctive lithological associations and geological relationships and initial geochronological results indicate the presence of an areally extensive region of reworked archaean basement containing polymetamorphic granulites in the rauer group east antarctica structurally early metapelites from within this reworked region preserve complex and varied metamorphic histories which largely pre date and bear no relation to a late proterozoic metamorphism generally recognized in this part of east antarctica in particular magnesian metapelite rafts from long point record extreme peak p t conditions of 10 12 kbar and 100 1050 c and an initial decompression to 8 kbar at temperatures of greater than 900 c initial garnet orthopyroxene sillimanite assemblages contain the most magnesian and pyrope rich garnets xmg 0 71 yet found in granulite facies rocks a high temperature decompressional p t history is consistent with reaction textures in which the phase assemblages produced through garnet breakdown vary systematically with the initial garnet xmg composition reflecting the intersection of different divariant reactions in rocks of varied composition as pressures decreased this history is thought to relate to archaean events whereas a lower temperature c 750 800 c decompression to 5 kbar reflects late proterozoic reworking of these relict assemblages the major late proterozoic c 1000 ma granulite facies metamorphism is recorded in a suite of younger fe rich metapelites and associated paragneisses in which syn to post deformational decompression through 2 4 kbar from maximum recorded p t conditions of 7 9 kbar and 800 850 c is constrained by geothermobarometry and reaction textures this p t evolution is thought to reflect rapid tectonic collapse of crust previously thickened through collision

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

isotope major minor and trace element geochemistry of late magmatic fluids in the peralkaline ilimaussaq intrusion south greenland abstract the persodic 1 16 ga old ilimaussaq intrusion consists of alkali granites syenites and agpaitic nepheline syenites these rocks are cut by late magmatic veins and lenses consisting of albite aegirine ussingite na2alsi3o8 oh fluorite and occasionally quartz oxygen isotope compositions of quartz indicates both orthomagmatic 18oqtz 8 5 and country rock influenced 18oqtz 10 origin while albite and aegirine do not contain fluid inclusions suitable for investigations ussingite contains secondary hydrocarbon fluid inclusions fluorite contains brine inclusions of primary and secondary origin with up to 26 3 wt naclequiv and quartz contains predominantly secondary brine inclusions with up to 29 7 wt naclequiv or ch4 h2o nacl mixtures these fluids are interpreted to reflect fluids in equilibrium with late stage melts at ilimaussaq at 450 c the carbon and hydrogen isotope composition of ch4 in ussingite 13c 6 to 3 d 121 is indicative of a magmatic abiogenic origin however the isotopic composition of ch4 in fluid inclusions in quartz veins resembles the signature of thermogenic ch4 13c 43 to 23 d 176 to 121 but the higher hydrocarbons are mostly 13c depleted in relation to ch4 up to 7 3 which is typical of abiogenically derived hydrocarbons ion chromatography of fluid inclusion leachates from the late stage veins reveals cl br ratios of 100 as such values seem to be typical of peralkaline magmatic rocks at least in the gardar province of south greenland it is suggested that this ratio is typical of gardar magmatic fluids and may be characteristic of the cl br ratio of the lithospheric mantle from which these alkaline melts are derived

the kola alkaline province of the cis and finland precise rbsr ages define 380 360 ma age range for all magmatism abstract twenty one new rb sr mineral and biotite whole rock isochrons are presented for intrusive rock complexes of the palaeozoic kola alkaline province in the cis and finland samples from the ultrabasic alkaline and nepheline syenite complexes khibina lovozero afrikanda turiy mys ozernaya varaka sokli and iivaara all yield ages in the very narrow range from 361 7 to 377 3 ma i e late middle devonian to upper devonian these data represent crystallization rather than intrusion ages but are nevertheless argued as marking very closely the time of intrusion there is no indication of bimodal age distribution the emplacement of the alkaline magmas is related temporally to the subsidence of the kontozero graben of the central kola peninsula sr initial ratios of the agpaitic nepheline syenites of the giant khibina and lovozero intrusions scatter between 0 703 and 0 704 because of high rb sr ratios of the rocks these isotope ratios exclude long term pre enrichment of alkalis in the sources of the magmas prior to segregation and intrusion and thus episodic enrichment during earlier rifting events in the northern baltic shield the magma formation may be related to wrench movements in the surroundings of the major trollfjord komagelv fault which forms part of the late caledonian arctic north atlantic megashear system

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

water chemistry and abiogenic methane content of a hyperalkaline spring related to serpentinization in the argolida ophiolite ermioni greece abstract hyperalkaline mineral springs related to active continental serpentinization are a theme of growing interest since they may contain significant amounts of abiotic gas and have important implications for energy resource exploration subsurface microbiology and astrobiology we report the discovery of a new hyperalkaline ph 12 spring issuing in the agioi anargyroi monastery at ermioni greece connected to serpentinization of peridotites of the argolis ophiolite two water samples have been collected from separated springs and analysed for the chemical composition of major minor and trace elements and isotopic composition 2 h and 18 o of water by ic icp oes icp ms and irms and for the chemical h 2 o 2 n 2 ch 4 co 2 and c 2 h 6 and isotopic he 2 h ch 4 and 13 c ch 4 composition of dissolved gases the iliokastron melange unit comprising abundant serpentinized harzburgite represent the aquifer feeding the hyperalkaline springs the isotopic composition of water indicates a recent meteoric recharge probably through the close by and stratigraphically higher limestones of the faniskos unit the ca oh water composition resulted to be similar to other hyperalkaline waters of greece and worldwide although the concentrations of dissolved h 2 are very low tens of nmol l compared to other gases collected in similar manifestations the concentrations of ch 4 are considerable 38 314 mol l and display isotopic compositions indicating a substantial if not exclusive abiogenic origin methane oxidation is also hypothesized in one of the two springs

involvement of variably sourced fluids during the formation and later overprinting of paleoproterozoic au cu mineralization insights gained from a fluid inclusion assemblage approach abstract au cu mineralized quartz veins of the reef deposit wisconsin usa originally formed prior to or early in the paleoproterozoic penokean orogeny in central north america as either the root zone of a gold rich vms deposit or in an orogenic gold setting nearly 400 m y later magmatic hydrothermal fluids associated with a continental scale anorogenic magmatic event remobilized mineralization within the veins and still later during the paleozoic remobilization and perhaps upgrading of au and other metals occurred in response to circulation of fluids associated with mississippi valley type deposits found in overlying supracrustal rocks fluid constraints on the formation of the reef deposit and later overprinting over a 1 5 b y timeframe are examined using the fluid inclusion assemblage fia approach distinctive assemblages are examined on individual merit each offering individual stories to aid in our understanding of the protracted development of the reef deposit presumably primary fluid inclusions in au and cu bearing quartz sulfide veins that formed during the paleoproterozoic event show h2o co2 ch4 nacl compositions based on microthermometry and laser raman spectroscopy possibly primary h2o nacl and secondary h2o co2 ch4 nacl fia formed prior to regional deformation and are recognized as discrete relict and neonate clusters the intersection of isochores from the highest density neonate inclusions of either fluid composition indicates re equilibration at lower amphibolite conditions during regional deformation quartz hosted secondary fluid inclusion assemblages characterized by h2o ch4 and co2 ch4 compositions formed at high temperatures and have not been re equilibrated and are interpreted to post date regional metamorphism these fia occur along healed fractures with chalcopyrite mineralization these inclusions are likely associated with fluid circulation driven by emplacement of the adjacent wolf river batholith ca 1 45 ga that altered pyrite to pyrrhotite and remobilized or emplaced chalcopyrite at temperatures as high as 700 c this reduced fluid was in equilibrium with locally observed graphitic sediments secondary lower temperature

geomorphic change implied by regolith slope relationships on steepland hillslopes taranaki new zealand abstract slope angle and regolith depth were measured along profile lines covering a range of hillslopes in several small neighbouring drainage basins in taranaki hill country new zealand slope measurements show a cyclic variation along the length of broadly rectilinear profiles variation in slope on the lower portion of profiles adjacent to stream channels indicates that hillslopes have undergone phases of accelerated downcutting and hillslope rejuvenation a recent phase of increased erosion and hillslope rejuvenation is suggested for hillslopes steeper than 31 by the steep lowerslope and incised stream channel hillslope evolution occurs primarily by parallel retreat of steeper swale sites and slope decline during pauses in the rate of downcutting all slope profiles show a large range in regolith depth mean regolith depth of swale sites is highly correlated with mean profile slope angle mean regolith depth decreases and the frequency of landslides increase with increasing mean profile slope angle microtopographic variation in regolith depth is attributed mainly to vegetation effects recurrent landsliding and in part to bedrock curvature hillslope position and slope angle shallowing of regolith is caused by recurrent landsliding on steep swale sites fluvial erosion at the base of steep profiles and surface erosion on extremely convex spur sites the very shallow soil on the steep lowerslope portion of profiles suggests a phase of soil removal consistent with hillslope rejuvenation average depth of regolith is least at 97 cm and variability greatest on hillslopes with a profile mean exceeding 31 erosion rates are greater on these sites where soil is derived predominantly from underlying tertiary sandstone this is attributed to a greater frequency of landsliding compared to hillslopes with a profile slope less than 31 where a more regular and deeper average regolith of 153 cm infers a longer period of hillslope stability consistent with the high volcanic ash content of soils airfall andesitic volcanic ash deposited throughout the holocene has largely been removed from steeper sites the work demonstrates the need to interpret the frequency and distribution of landslides in context with natural geomorphic changes in order to assess the effect that landuse changes has on erosion rates

graphite ch4 h2o co2 equilibria at low grade metamorphic conditions equilibrium calculations and published phase equilibria are used to show that at temperatures below 400 c and pressures above 300 bar the fluids coexisting with graphite in the c o h system consist either of co2 h2o mixtures or ch4 h2o mixtures bulk fluid compositions consisting of ch4 h2o will unmix to methane rich fluid and h2o rich liquid at temperatures below about 325 c compositions on the co2 h2o join will unmix only at temperatures below about 275 c oxygen fugacity in the ch4 h2o graphite three phase region is fixed at constant p and t and approximately equal to that of the quartz magnetite fayalite assemblage in the co2 h2o graphite three phase region oxygen fugacity is about three orders of magnitude greater from the end stages of diagenesis to temperatures of 300 c and possibly 400 c in salt rich systems many metamorphic rocks may contain ch4 h2o fluids rather than co2 h2o mixtures thus metamorphic reactions involving carbonate minerals would involve ch4 graphite and h2o rather than co2 the immiscibility between ch4 and h2o could result in the common occurrence of methane natural gas in low grade metamorphic terrains

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

abiogenic fischer tropsch synthesis of hydrocarbons in alkaline igneous rocks fluid inclusion textural and isotopic evidence from the lovozero complex n w russia a detailed fluid inclusion study has been carried out on the hydrocarbon bearing fluids found in the peralkaline complex lovozero petrographic microthermometric laser raman and bulk gas data are presented and discussed in context with previously published data from lovozero and similar hydrocarbon bearing alkaline complexes in order to further understand the processes which have generated these hydrocarbons ch4 dominated inclusions have been identified in all lovozero samples they occur predominantly as secondary inclusions trapped along cleavage planes and healed fractures together with rare h2o dominant inclusions they are consistently observed in close association with either arfvedsonite crystals partially replaced by aegirine aegirine crystals or areas of zeolitization the majority of inclusions consist of a low density fluid with ch4 homogenisation temperatures between 25 and 120 c those in near surface hand specimens contain ch4 h2 up to 40 mol higher hydrocarbons however inclusions in borehole samples contain ch4 higher hydrocarbons h2 indicating that at depth higher hydrocarbons are more likely to form estimated entrapment temperatures and pressures for these inclusions are 350 c and 0 2 0 7 kbar a population of high density liquid ch4 dominant inclusions have also been recorded mainly in the borehole samples homogenising between 78 and 99 c these consist of pure ch4 trapped between 1 2 and 2 1 kbar and may represent an early ch4 bearing fluid overprinted by the low density population the microthermometric and laser raman data are in agreement with bulk gas data which have recorded significant concentrations of h2 and higher hydrocarbons up to c6h12 in these samples these data combined with published isotopic data for the gases ch4 c2h6 h2 he and ar indicate that these hydrocarbons have an abiogenic crustal origin and were generated during postmagmatic low temperature alteration reactions of the mineral assemblage this would suggest that these data favour a model for formation of hydrocarbons through fischer tropsch type reactions involving an early co2 rich fluid and h2 derived from alteration reactions this is in contrast to the late magmatic model suggested for the formation of hydrocarbons in the similar peralkaline intrusion ilimaussaq at temperatures between 400 and 500 c

fluid evolution in the nepheline syenites of the ditrău alkaline massif transylvania romania abstract the ditr u alkaline massif is an intrusion into the bucovina nappe system that is part of the mesozoic crystalline zone located in transylvania romania in the eastern carpathians nepheline syenites are the most abundant rocks in the central and eastern part of the massif and represent the last major intrusion of the complex fluid inclusions in nepheline aegirine and albite were trapped at magmatic conditions on or below the h 2 o saturated nepheline syenite solidus at about 400 600 c and 2 5 5 kbars early nepheline and to a lesser extent albite were altered by highly saline fluids to produce cancrinite sodalite and analcime during this process cancrinite also trapped fluid inclusions the fluids in most cases can be modeled by the h 2 o nacl system with varying salinity however inclusions with more complex fluid composition containing k ca co 3 etc in addition to nacl are common raman spectroscopic analyses of daughter minerals confirm the presence of alkali carbonate fluids in some of the earliest inclusions in nepheline aegirine and albite during crystallization the melts exsolved a high salinity carbonate rich magmatic fluid that evolved to lower salinity as crystallization progressed phases that occur early in the paragenesis contain high salinity inclusions while late phases contain low salinity inclusions the salinity trend is consistent with experimental data for the partitioning of chlorine between silicic melt and exsolved aqueous fluid at about 2 0 kbars the activity of water a h 2 o in the melt increases during crystallization resulting in the formation of hydrous phases during late stage crystallization of the nepheline syenites

resistance to shallow landslide failure through root derived cohesion in east coast hill country soils north island new zealand measured shear strength cohesion and friction of airfall derived east coast hill country regolith is insufficient for the maintenance of existing regolith depth slope angle relationships in the catchment of lake waikopiro in northern hawke s bay new zealand if these regoliths are attributed with an additional increment of cohesion derived mechanically from a turf mat membrane existing depth slope angle distributions are explicable sites where failure has occurred have been measured and back analysis used to derive a range of values for additional mechanical cohesion values are in the range 0 2 7 6 kpa consistent with earlier findings this range is narrowed further to 0 7 6 9 kpa with assumptions regarding soil moisture status at failure copyright 1999 john wiley sons ltd

hydrogen and carbon isotopic composition of methane as evidence for biogenic origin of natural gases from the green tuff basin japan abstract hydrogen and carbon isotopic analyses of methane were carried out to investigate the origin of natural gases commercially produced from volcanic rocks in the green tuff basin of northeast japan whose high 3he 4he ratios have been interpreted as an indication of their abiogenic origin methane isotopic signatures 13c 32 to 67 d 163 to 202 respectively suggest that these are thermogenic gases or mixtures of thermogenic gases with bacterial gases the correlations of methane d vs 13c for the gases from specific fields are consistent with a mixing model between bacterial and thermogenic end members which was previously proposed on the basis of 13c contents of c1 to c4 hydrocarbons sakata 1991 berner and faber 1996 the green tuff basin gases are isotopically distinct from well known abiogenic methanes e g geothermal methane from the east pacific rise a significant contribution of abiogenic methane would therefore be unlikely for these gases

the magmatic and fluid evolution of the motzfeldt intrusion in south greenland insights into the formation of agpaitic and miaskitic rocks the 1 275 ga motzfeldt intrusive complex in the gardar failed rift province in south greenland formed from six successively intruding melt batches sm1 sm6 interpreted to be derived from a common magma source at depth five units sm1 sm5 crystallized an alkaline to peralkaline miaskitic mineral assemblage of amphibole clinopyroxene feldspar nepheline fe ti oxides zircon apatite fluorite and rarely olivine the last magmatic batch sm6 is characterized by an agpaitic mineral assemblage of aegirine nepheline alkali feldspar eudialyte and rare fluorite or sodalite coexisting mafic minerals constrain the crystallization conditions of the miaskitic rocks to about 850 6008c whereas solidus temperatures below 5008c are indicated by coexisting alkali feldspars in the agpaitic rocks oxygen fugacities during the orthomagmatic stage are below the fmq fayalite magnetite quartz buffer fmq 0 5t o 2 0 whereas late hematite provides evidence of a higher relative oxygen fugacity during late stage alteration the nd and oxygen isotope compositions of amphiboles and pyroxenes are homogeneous throughout the complex and suggest a common mantle derived magma source for all six units which is comparable with other gardar intrusions the hydrogen isotopic composition of amphiboles dd 99 to 132 indicates lowtemperature fluid rock interaction with low fluid rock ratios fluid inclusion studies indicate that h2o nacl fluids present during the magmatic stages in the miaskitic units had salinities of510 wt nacl eq calcite crystals in fluid inclusions within these rocks suggest that co2 or hco3 was an important component of the original fluid phase in contrast the agpaitic unit is characterized by a ch4 h2o naclfluid the c o h isotope compositionsofthefluid inclusions in all units are consistent with mixing between a small volume of magmatic fluid and a large volume of meteoric water the chemical evolution of the motzfeldt complex is a type example of the connection of the transition from miaskitic to agpaitic mineral assemblages with redox dependent fluid solid equilibria thetransitionfromarelatively oxidized to a relatively reduced fluid is correlated with a change from a more reduced fe 2 bearing miaskitic taramite arfvedsonite zircon sm1 sm5 to a more oxidized fe 3 bearing agpaitic assemblage aegirine eudialyte sm6 we suggest that coupled fluid solid redox equilibria involving fe 2 f e 3 c o2 and ch4 in this case were simply driven by temperature decrease and an overall increase in na k in the melt this observation sheds light on the heavily debated miaskite agpaite transition the combined temperature and compositional effect stabilized fe 3 c h 4 and enhanced the solubility of zr possibly as na zr si o complexes in the latest stage melt sm6 resulting in the crystallization ofan agpaitic mineral assemblage in terms of redox conditions during crystallization the motzfeldt rocks represent an intermediate case in the gardar province between more oxidized co2dominated intrusions such as the syenite carbonatite complex of

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

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