tracing the migration of mantle co2 in gas fields and mineral water springs in south east australia using noble gas and stable isotopes abstract geochemical monitoring of co2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of co2 during injection storage and any subsequent migration here we analyse a natural analogue of co2 storage migration and leakage to the atmosphere using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the co2 we present the most comprehensive evidence to date for mantle sourced co2 in south east australia including well gas and co2 rich mineral spring samples from the otway basin and central victorian highlands cvh 3he 4he ratios in well gases and co2 springs range from 1 21 to 3 07 ra and 1 23 3 65 rc ra respectively we present chemical fractionation models to explain the observed range of 3he 4he ratios he ne ar kr xe concentrations and 13c co2 values in the springs and the well gases the variability of 3he 4he in the well gases is controlled by the gas residence time in the reservoir and associated radiogenic 4he accumulation 3he 4he in co2 springs decrease away from the main mantle fluid supply conduit we identify one main pathway for co2 supply to the surface in the cvh located near a major fault zone solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and 13c co2 values measured in the mineral spring samples this process is also responsible for low 3he concentrations and associated high co2 3he which are commonly interpreted as evidence for mixing with crustal co2 the elevated co2 3he can be explained solely by solubility fractionation without the need to invoke other co2 sources the noble gases in the springs and well gases can be traced back to a single end member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing this work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected co2 to the shallow subsurface

transformation textures mechanisms of formation of high pressure minerals in shock melt veins of l6 chondrites and pressure temperature conditions of the shock events the high pressure polymorphs of olivine pyroxene and plagioclase in or adjacent to shock melt veins smvs in two l6 chondrites sahara 98222 and yamato 74445 were investigated to clarify the related transformation mechanisms and to estimate the pressure temperature conditions of the shock events wadsleyite and jadeite were identified in sahara 98222 wadsleyite ringwoodite majorite akimotoite jadeite and lingunite naalsi3o8 hollandite were identified in yamato 74445 wadsleyite nucleated along the grain boundaries and fractures of original olivine the nucleation and growth of ringwoodite occurred along the grain boundaries of original olivine and as intracrystalline ringwoodite lamellae within original olivine the nucleation and growth of majorite took place along the grain boundaries or fractures in original enstatite jadeite containing assemblages have complicated textures containing particle like stringer like and polycrystalline like phases coexistence of lingunite and jadeite containing assemblages shows a vein like texture we discuss these transformation mechanisms based on our textural observations and chemical composition analyses the shock pressure and temperature conditions in the smvs of these meteorites were also estimated based on the mineral assemblages in the smvs and in comparison with static high pressure experimental results as follows 13 16 gpa 1900 c for sahara 98222 and 17 24 gpa 2100 c for yamato 74445

noble gases in formation fluids from deep sedimentary basins a review abstract atmospheric ne ar kr and xe are observed in fluids occurring in deep basins modifications of their abundance patterns reveal modes of recharge and brine formation phase separations during boiling and association of natural gas with water or oil radiogenic 4 he and 40 ar serve as age indicators of entrapped fluids effective over a significant portion of the geological time scale simultaneous application of 13 c atmospheric noble gases and radiogenic 4 he and 40 ar is recommended to identify a recent bacterial natural gas formation not accompanied by oil and b natural gas formed along with oil in a mature source rock

widespread distribution of ascending fluids transporting mantle helium in the fore arc region and their upwelling processes noble gas and major element composition of deep groundwater in the kii peninsula southwest japan abstract chemical and isotopic studies including analyses of noble gases were comprehensively conducted on the groundwater of the entire kii peninsula which is located in the fore arc region of southwest japan groundwater of na cl hco3 na hco3 cl and na cl types was shown to be distributed across the whole area groundwater in the inland central part of the peninsula shows relatively low salinity whereas groundwater from the area along the ene trending median tectonic line mtl on the north side of the peninsula shows high salinity up to 18 800 mg l of cl and the presence of unusual heavy oxygen isotopes this trend is similar to that documented in saline waters from the arima region the so called arima type thermal water high 3he 4he ratios relative to the atmospheric value up to 6 7 ra were recorded throughout the kii peninsula covering a wider area than documented previously the saline groundwater is also strongly depleted in 20ne and heavy noble gases from the wide distribution of high 3he 4he values and the associated 20ne and cl concentrations we infer that aqueous fluids derived from dehydration of the subducting slab are present at depth beneath almost the entire kii peninsula these aqueous fluids may ascend along the major north dipping boundary faults the isotopic composition of groundwater from the southern part of the peninsula suggests that the contribution from these dehydration derived fluids is relatively small in this region however volatile components e g noble gases and co2 in the groundwater of this area may originate from the dehydration derived fluids upwelling of arima type thermal water of the na cl hco3 type is expected to undergo a phase separation of volatile species due to decompression as the fluid ascends the variety of water types documented may be due to this water gas separation and the subsequent incorporation of gaseous species into shallow meteoric groundwater the observed high 3he 4he ratios in the absence of a mantle wedge below the southern part of the kii peninsula may reflect the oblique ascent of these fluids along north dipping boundary faults

noble gases in crude oils from the paris basin france implications for the origin of fluids and constraints on oil water gas interactions in order to investigate the potential of noble gases to trace the dynamics of oil reservoirs we have analysed the abundance and isotopic composition of all noble gases he ne ar kr and xe in crude oils from the paris basin france using a new extraction and purification procedure the main oil reservoirs are presently located in the jurassic dogger limestone and in the triassic keuper sandstone but hydrocarbons originated from a common source rock formation located in the interbedded liassic sequence despite this common origin the abundance and isotopic ratios of the noble gases differ between the dogger and the keuper the isotopic compositions of kr and xe are indistinguishable from that of air 3he 4he ratios higher than those predicted from radiogenic production in the sediments or in the crust are attributed to the occurrence of mantle derived 3he in the basin each sedimentary sequence is characterised by well defined and homogeneous 21ne 22ne and 40ar 36ar ratios which average 0 0306 0 0008 and 312 10 for the dogger and 0 0367 0 0012 and 664 30 for the keuper respectively the main source of radiogenic noble gases appears to be the continental crust underlying the basin with possible regional contributions of noble gas isotopes produced in the sediments the helium and argon isotopic ratios of the dogger oils are very similar to those observed in geothermal waters flowing in the dogger aquifer throughout the basin demonstrating that noble gases in oils derive from associated groundwaters oil reservoirs in the paris basin therefore accumulate noble gases from wide regions of the continental crust through cross formational flow of groundwaters and subsequent partitioning into oil this observation implies that noble gases cannot be directly used to date oils but can provide time constraints if 1 water oil interactions are quantified and 2 the residence time as well as the noble gas characteristics of associated groundwaters are known oil water gas partitioning processes are well recorded in the fractionation of noble gas elemental abundance two distinct processes have been identified 1 accumulation of atmosphere derived ang and radiogenic noble gases both initially dissolved in groundwaters resulting in a positive correlation between absolute amount of ang and the extent of heavy noble gas fractionation and 2 subsequent fractional degassing resulting in a negative correlation between ang abundance and heavy noble gas fractionation degassing is particularly evident for the keuper oils and might have occurred in the reservoirs following hydrodynamic gas stripping the ang abundance in the dogger reservoirs requires that about one order of magnitude more water than presently observed has interacted with the oil given current estimates of the residence time for groundwaters in the dogger aquifer the duration of oil water interaction is in qualitative agreement with a palaeocene oligocene age for the major episode of secondary oil migration in the paris basin high xenon contents in keuper reservoirs suggest that they have experienced hydrodynamic interactions between flowing waters and oils for long time and that the trias might have reached hydrostatic condition only recently

high pressure minerals in shocked meteorites heavily shocked meteorites contain various types of high pressure polymorphs of major minerals olivine pyroxene feldspar and quartz and accessory minerals chromite and ca phosphate these high pressure minerals are micron to submicron sized and occur within and in the vicinity of shock induced melt veins and melt pockets in chondrites and lunar howardite eucrite diogenite hed and martian meteorites their occurrence suggests two types of formation mechanisms 1 solid state high pressure transformation of the host rock minerals into monomineralic polycrystalline aggregates and 2 crystallization of chondritic or monomineralic melts under high pressure based on experimentally determined phase relations their formation pressures are limited to the pressure range up to 25 gpa textural crystallographic and chemical characteristics of high pressure minerals provide clues about the impact events of meteorite parent bodies including their size and mutual collision velocities and about the mineralogy of deep planetary interiors the aim of this article is to review and summarize the findings on natural high pressure minerals in shocked meteorites that have been reported over the past 50 years

dating ultra deep mine waters with noble gases and 36cl witwatersrand basin south africa abstract concentrations and isotopic ratios of dissolved noble gases 36cl d and 18o in water samples from the ultra deep gold mines 0 718 to 3 3 km below the surface in the witwatersrand basin south africa were investigated to quantify the dynamics of these ultra deep crustal fluids the mining activity has a significant impact on the concentrations of dissolved gases as the associated pressure release causes the degassing of the fissure water the observed under saturation of the atmospheric noble gases in the fissure water samples 70 98 normalized to asw at 20 c and 1013 mbar is reproduced by a model that considers diffusive degassing and solubility equilibration with a gas phase at sampling temperature corrections for degassing result in 4he concentrations as high as 1 55 10 1cm3stp4he g 1 40ar 36ar ranging between 806 and 10331 and 134xe 132xe and 136xe 132xe ratios above 0 46 and 0 44 respectively corrected 134 136 xe 132xe and 134 136 xe 4he ratios are consistent with their production ratios whereas the nucleogenic 4he 40ar and 134 136 xe 40ar ratios generally indicate that these gases are produced in an environment with an average u th k content 2 3 times above that of crustal average in two scenarios one considering only accumulation of in situ produced noble gases the other additionally crustal flux components the model ages for 14 individual water samples range from 13 to 168 ma and from 1 to 23 ma respectively the low 36cl ratios of 4 37 10 15 and comparatively high 36cl concentrations of 8 350 10 15 atoms 36cl l 1 reflect subsurface production in secular equilibrium indicating an age in excess of 1 5 ma or 5 times the half life of 36cl in combination the results suggest residence times of the fluids in fissures in this region up to 3 3 km depth are of the order of 1 100 ma we cannot exclude the possibility of mixing and that small quantities of younger water have been mixed with the very old bulk

fingerprinting coal derived gases from the uk abstract the large scale extraction of unconventional hydrocarbons in the united states has led to fears of methane contamination of shallow groundwaters differentiating between the deep gas released during extraction shale gas coal bed methane and underground coal gasification and natural shallow sourced methane is imperative for the monitoring and managing of environmental risks related to the extraction process here for the first time we present measurements of the major gas and stable and noble gas isotope composition of coal bed methane cbm from central scotland and coal mine methane cmm from central england uk the molecular c1 c2 c3 21 to 121 and stable isotope compositions 13cch4 39 5 to 51 1 dch4 163 to 238 indicate a thermogenic origin for the methane they are distinct from the majority of shallow sourced gases in uk both sample suites exhibit high he concentrations 338 to 2980 ppmv that are considerably above atmospheric and groundwater levels simple modelling shows that these high 4he concentrations cannot be solely derived from in situ production since coal deposition and hence the majority is derived from the surrounding crust the scottish cbm contains a resolvable mantle he ne and ar contribution that may originate from melts in the deep crust demonstrating the uk coals have acted as a store for deep volatiles for 10s of millions of years the high 4he in the coal derived gases has the potential to be used as a novel diagnostic fingerprint to track fugitive release of deep methane from future unconventional gas extraction operations in the uk

multiple atmospheric noble gas components in hydrocarbon reservoirs a study of the northwest shelf delaware basin se new mexico the northwest shelf of the delaware basin se new mexico is the site of several large and productive oil and gas fields the most productive reservoirs are located in the late pennsylvanian morrow and early permian abo formations production from the latter more important play is predominately from fluvial abo red beds of the pecos slope field the oxidizing conditions implied by the reddish color of the formation require an external hydrocarbon source to test the existing migration model for the region and constrain the location of potential hydrocarbon sources we measured the elemental and isotopic composition of noble gases produced along with the hydrocarbons we found the hydrocarbons to be highly enriched in radiogenic 4he 40 ar and nucleogenic 21 ne f 4he 44 000 250 000 40ar 36ar 400 3145 21ne 22ne 0 044 0 071 the greatest enrichments occur in the pecos slope gas fields the hydrocarbons also contain three independent nonradiogenic noble gas components each with an atmospheric isotopic composition one component is most likely air saturated water asw the second component is enriched in the heavy noble gases f 130xe 8 5 and is derived from the hydrocarbon sources the third component is enriched in ne f 20ne 0 8 that we believe is degassed from sources within the reservoirs this component is correlated with but decoupled from the dominant source of radiogenic 4he and 40 ar very high concentrations of 4he up to 1 by volume in the pecos slope reservoirs require a source external to the reservoirs such as the underlying precambrian basement granites and sedimentary equivalents structural buckles cutting through the pecos field may act as high flux vertical pathways for the radiogenic 4he if the hydrocarbons in the pecos slope fields have migrated northward from the deeper delaware basin as suggested by compositional trends then perhaps the buckles also play an important role in the distribution and filling of the pecos slope reservoirs

formation of high pressure minerals in shocked l6 chondrite yamato 791384 constraints on shock conditions and parent body size we have studied the high pressure phases observed in yamato 791384 l6 chondrite host meteorite mainly consists of olivine pyroxenes and plagioclase glass mineral fragments observed in the veins and the vein margin region of the host meteorite were partially or totally transformed into high pressure phases ringwoodite majorite akimotoite naalsi3o8 hollandite and jadeite matrix of the shock vein contains majorite pyrope solid solution the spatial distribution indicates that high pressure phases are present in the shock veins and host rocks adjacent to the shock veins investigation of the high pressure phases revealed that in y791384 fragments and adjacent matrix were subjected to pressures around of 18 23 gpa and the vein experienced temperatures around 2300 c during the shock event ringwoodite lamellae were observed in the host olivine adjacent to the vein kinetic investigation for ringwoodite lamellar growth in olivine indicates that the shocked meteorite experienced the pressure for at least 4 s such long duration of the pressure pulse indicates that the size of the parent body was greater than 10 km

evidence for bacterially generated hydrocarbon gas in canadian shield and fennoscandian shield rocks hydrocarbon rich gases found in crystalline rocks on the canadian and fennoscandian shields are isotopically and compositionally similar suggesting that such gases are a characteristic feature of precambrian shield rocks gases occure in association with saline groundwaters and brines in pressurized pockets formed by sealed fracture systems within the host rocks when released by drilling activities gas pressures as high as 5000 kpa have been recorded typical gas flow rates for individual boreholes range from 0 25 l min to 4 l min the highest concentrations of ch4 are found in the deepest levels of the boreholes associated with ca na cl and na ca cl brines n2 is the second major component of the gases and with ch4 accounts for up to 80 to 90 vol higher hydrocarbon c2 concentrations range from 1 to 10 vol with c1 c2 c3 ratios from 10 1000 isotopically the gases show a wide range of values overall 13c 57 5 to 41 1 d 245 to 470 but a relatively tight cluster of values within each sampling locality the enonkoski mine methanes are unique with 13c values between 65 4 and 67 3 and d values between 297 and 347 the shield gases are not readily reconcilable with conventional theories of methanogenesis the range of c1 c2 c3 ratios for the shield gases is too low to be consistent with an entirely bacterial origin in addition dch4 values are in general too depleted in the heavy isotope to be produced by thermogenic methanogenesis or by secondary alteration processes such as bacterial oxidation or migration however isotopic and compositional evidence indicates that bacterially derived gas can account for a significant component of the gas at all shield sites conventional bacterial gas accounts for 75 94 vol of the occurrences at enonkoski mine in finland at each of the other shield sites bacterial gas can account for up to 30 50 vol of the total gas accumulation this study and other recent evidence of active bacterial communities in deep hydrogeological environments emphasize the need for more comprehensive investigation of the role of microorganisms in the deep subsurface

pressure induced amorphization of albitic plagioclase in an externally heated diamond anvil cell 1 high pressure and high temperature experiments of albitic plagioclase up to 41 gpa and 270 c were carried out using an externally heated diamond anvil cell raman spectroscopy and transmission electron microscopy of the recovered samples revealed that the amorphization of albite was complete at 37 gpa and room temperature the amorphization pressure at 170 c was nearly the same as that at room temperature in contrast the pressure largely decreased to 31 gpa at 270 c in comparison with the amorphization pressure of albite in laboratory shock experiments that in the present static compression experiments is significantly lower 10 gpa even at room temperature this suggests that shorter pressure duration results in a lower degree of amorphization of plagioclase the formation of maskelynite in shocked meteorites does not necessarily require the very high shock pressure 30 90 gpa that was previously estimated on the basis of shock recovery experiments

regional groundwater focusing of nitrogen and noble gases into the hugoton panhandle giant gas field usa the hugoton panhandle giant gas field located across sw kansas and the texas and oklahoma panhandles in the usa is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations we collected 31 samples from producing wells in a north south traverse of the 350 km long field the samples reflect the previously observed north south change in 4he n2 with values changing from 0 020 to 0 049 respectively 3he 4he 21ne 22ne and 40ar 36ar vary between 0 14 0 25 ra 0 0373 0 0508 and 818 1156 respectively and are caused by quantifiable contributions from mantle crustal and atmosphere derived sources the atmosphere derived 20ne 36ar ratios are indistinguishable from groundwater values the crustal 4he 21ne and 4he 40ar ratios show a 60 excess of 4he compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust the mantle 3he n2 and groundwater recharge 36ar n2 ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field n2 which is dominantly crustal in origin correlated 20ne n2 and 4he n2 shows mixing between two distinct crustal n2 components one n2 component n2 is associated with the crustal 4he and groundwater derived 20ne and the other with no resolvable noble gas contribution measured 15nn2 values vary from 2 7 to 9 4 the n2 and non he associated n2 endmembers are inferred to have 15nn2 3 and 13 and contribute from between 25 60 and 75 40 of the nitrogen respectively the non he associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column the 15nn2 value is not compatible with a crystalline or high grade metamorphic source and similar to the 4he is inferred to be from a shallow or low metamorphic grade source rock 4he mass balance requires a regional crustal source its association with significant magmatic 3he pointing to a tectonically active source to the west of the hugoton system the volume of groundwater required to source the 20ne in the gas field demonstrates the viability of the groundwater system in providing the collection transport and focusing mechanism for the 4he and n2 the n2 20ne ratio shows that the n2 transport must be in the aqueous phase and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase

natural gas association with water and oil as depicted by atmospheric noble gases case studies from the southeastern mediterranean coastal plain a model for the equilibrium distribution of atmospheric noble gases ang between natural gas and water phases was extended to include the gas oil relationship the basic assumption is that the ang are introduced into hydrocarbon systems via recharge or seawater theoretical ang patterns of natural gas at equilibrium with water fall between the air pattern and that of air saturated water theoretical ang patterns of natural gas degassed from oil which had previously equilibrated with a water phase cover a wide range including the range calculated for gas water equilibration ang patterns in natural gas which fall outside the overlapping range may thus indicate association of the gas with oil the model was tested in the case of hydrocarbon systems of the southeastern mediterranean coastal plain other geochemical evidence indicates that the ashdod sadot shallow gas wells are not related to oil the relative ang abundances in gas samples from these wells lie within the range predicted for gas water association the relative ang abundances in samples degassed from oils of the helez kokhav oilfield are similar to specific patterns predicted for the degassing of oil which was previously associated with water published and new analyses of methane dominated natural gas samples from california japan and northern israel also reveal ang patterns of the type predicted by the model the results of the case studies support our hypothesis that water is responsible for transport of atmospheric noble gases into subsurface hydrocarbon systems this forms the basis for identification of oil associated natural gases via ang study

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

jadeite formation in shocked ordinary chondrites abstract albitic feldspar in shocked ordinary chondrites yamato 791384 l6 and yamato 75100 h6 and albite recovered from static high pressure and high temperature synthetic experiments kubo et al 2010 were investigated with a transmission electron microscope tem subsequent to a conventional micro raman spectroscopy analysis to clarify albite dissociation reaction under high pressure and high temperature condition when jadeite forms from albite sio 2 phase as a residual phase of albite dissociation reaction should accompany jadeite from the stoichiometry however albitic feldspar in and adjacent to shock melt veins of the shocked chondrites dissociates into jadeite residual amorphous or poorly crystallized material having varied chemical compositions between jadeite and sio 2 phase tem observations of albitic feldspar in the shocked chondrites and albite recovered from the static high pressure and high temperature synthetic experiments show that jadeite crystallization is initiated by grain refinement of albite or albitic feldspar nucleation occurs along grain boundaries or at triple junctions of the fine grained albite crystal assemblage jadeite crystal starts to grow from the nucleus through grain boundary diffusion considering pressure condition recorded in the shock melt veins of the shocked chondrites stishovite is the most likely as a residual sio 2 phase accompanying jadeite high pressure and high temperature condition induced by a dynamic event is very short stishovite would be hardy formed through a dynamic event due to sluggish nucleation rate of stishovite compared with that of jadeite thus leading to induce heterogeneous and incomplete albite dissociation reaction albite dissociates into jadeite residual amorphous material

dating the cooling of exhumed central uplifts of impact structures by the u th he method a case study at manicouagan abstract forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the manicouagan impact structure were dated by the u th he technique a u th he central age of 207 1 6 4 ma 2 standard error se n 40 has been determined with 4 outlier ages removed the central age is refined to 208 9 5 1 ma 2 se both of these ages are within error of the previously determined u pb zircon age of 214 1 ma 2 derived from the impact melt manicouagan s central uplift formed due to rapid elevation from 7 10 km depth as part of the modification stage of the impact process which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the u th he system in titanite correlation with the previous u pb zircon 214 1 ma impact melt crystallization age indicates that the u th he titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets or other melt products the youngest ca 195 ma u th he dates preserved in some titanite fragments are synchronous with early jurassic rift induced lithospheric thinning and associated igneous activity that defines the central atlantic magmatic province camp the u th he titanite data from manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of camp activity

coupled use of carbon isotopes and noble gas isotopes in the potiguar basin brazil fluids migration and mantle influence abstract we used the carbon isotope ratios of hydrocarbons and co 2 and the proportions of noble gas isotopes of associated gases from several geological provinces of the potiguar basin brazil for gas source rock correlation and to determine maturity post genetic processes migration leakage biodegradation and to assess the possible interactions between hydrocarbons and surrounding waters barriers of permeability at the basin scale the amount of water interacting with the accumulated hydrocarbons proportion of meteoric water and contamination of the fluids by the mantle were quantified for the distinct petroleum systems defined in this basin four hydrocarbon provinces have been defined in the potiguar basin the first is located in the southern part of the basin and the other three are in the northern part with offshore pods of generation migration occurred along ne sw horst and grabben structures all gases are mainly thermogenic 13 c of methane between 49 and 34 except for biodegraded gases with isotopically lighter methane generated in the oil window and only two fields from one of the trends seem to have been significantly biodegraded 13 c of propane up to 5 8 per mil the source rocks were lacustrine for the gases from the southwest of the basin and mixed marine lacustrine for two trends the third trend as well as an offshore field appears to have a lacustrine source rock and the hydrocarbon generation and accumulation are older than for the other fields each of the three trends is generally isolated in terms of fluid migration except in one location where noble gas isotopes indicate that the guamare trend is invaded by fluids of the macau trend an important contamination by mantle fluids has been confirmed for all the hydrocarbon fields close to the shore 3 he 4 he ratios up to 1 6 times the atmospheric ratio the mantle contribution as high as 20 of total helium decreases inland the mantle contribution provides some chronological constraints for the hydrocarbon accumulations and may have had an influence in hydrocarbon generation due to an igneous activity associated influence in the hydrocarbon generation pod

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

rare gas isotopic compositions in natural gases of japan isotopic and elemental compositions of rare gases in various types of gas samples collected in the japanese islands were investigated excess3he was found in most samples many samples showed a regionally uniform high3he 4he ratio of about 7 times the atmospheric ratio the he concentrations varied from 0 6 to 1800 ppm and they were low in co2 rich gases and high in n2 rich gases ne isotopic deviations from the atmospheric ne were detected in most volcanic gases the deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements ar was a mixture of mass fractionated ar atmospheric ar and radiogenic ar and the contribution of radiogenic40ar was small in all samples except for he elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere several samples were highly enriched in kr and xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water the component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust

shock metamorphism and petrography of the shergotty achondrite the shergotty subsamples 1 and 12 consist of augite and pigeonite 67 5 maskelynite 24 ilmenite and titanomagnetite 2 pyrrhotite 0 4 whitlockite 1 8 apatite 0 1 quartz 0 5 baddeleyite trace fayalite 0 4 mesostasis 3 and shock induced local polymineralic melt products 0 6 the overall modal composition is similar to other shergotty samples except for the rather high whitlockite content the shock effects observed in the mineral constituents include mosaicism deformation bands planar fractures and mechanical twin lamellae in clinopyroxene isotropization of plagioclase with very rare remnants of birefringence planar deformation structures mosaicism and strongly reduced birefringence in quartz mechanical twinning of ilmenite localized in situ melting of neighbouring minerals at the contact of low and high density phases based on the refractive index of maskelynite average 1 5467 with average an content of 49 and the degree of isotropization of the plagioclase an equilibrium shock pressure of 29 1 gpa is derived the inferred post shock temperature is 200 20 c no heating event could have exceeded 400 c duke 1968 local stress and temperature concentrations reach 60 80 gpa and 1600 2000 c the observed shock effects can be explained by a single shock event a second weaker shock event as found by others appears to be highly improbable equilibrium shock pressures and post shock temperatures for the other known shergottites are 31 2 gpa and 220 50 c zagami 43 2 gpa and 400 800 c alha 77005 the pressure estimate for eeta 79001 by lambert 1985 is confirmed 34 1 gpa the post shock temperature is 250 50 c the abundance and textural setting of localized melt products in these meteorites confirm increasing shock pressures in the sequence shergotty zagami eeta 79001 alha 77005 undoubtedly the melts could have been formed by the same single shock which produced the equilibrium shock effects e g maskelynitization in these meteorites the shock induced particle velocities inferred from hugoniot data of basalts are in the 1 5 2 0 km s range for the parental rocks of the shergottites ejection velocities are therefore in the order of 3 4 km s special ejection mechanisms are required in order to exceed the escape velocity of a planet like mars without producing higher degrees of shock e g melting than those observed in the shergottites

fossil brines preserved in the st lawrence lowlands quebec canada as revealed by their chemistry and noble gas isotopes abstract brines in cambrian sandstones and ordovician dolostones of the st lawrence lowlands at becancour quebec canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path in addition to quantifying their residence time major ion chemistry indicates that the brines are of na ca cl type possibly derived from halite dissolution 87 sr 86 sr ratios and ca excess indicate prolonged interactions with silicate rocks of the proterozoic grenville basement or the cambrian potsdam sandstone the brines constrain a 2 3 contribution of mantle 3 he and large amounts of nucleogenic 21 ne and 38 ar and radiogenic 4 he and 40 ar 4 he 40 ar and 21 ne 40 ar ratios corrected for mass fractionation during incomplete brine degassing are identical to their production ratios in rocks the source of salinity halite dissolution plus the occurrence of large amounts of 40 ar in brines constrain the residence time of becancour brines as being older than the cretaceous evaporites in the st lawrence lowlands likely existed only during devonian silurian time brines might result from infiltration of devonian water leaching halite penetrating into or below the deeper cambrian ordovician aquifers during the devonian the basin reached temperatures higher than 250 c allowing for thermal maturation of local gas prone source rocks utica shales and possibly facilitating the release of radiogenic 40 ar into the brines the last thermal event that could have facilitated the liberation of 40 ar into fluids and contributed to mantle 3 he is the cretaceous monteregian hills magmatic episode for residence times younger than the cretaceous it is difficult to find an appropriate source of salinity and of nucleogenic radiogenic gases to the becancour brines

estimating shock pressures based on high pressure minerals in shock induced melt veins of l chondrites here we report the transmission electron microscopy tem observations of the mineral assemblages and textures in shock induced melt veins from seven l chondrites of shock stages ranging from s3 to s6 the mineral assemblages combined with phase equilibrium data are used to constrain the crystallization pressures which can be used to constrain shock pressure in some cases thick melt veins in the tenhaml6 chondrite contain majorite and magnesiowstite in the center and ringwoodite akimotoite vitrified silicate perovskite and majorite in the edge of the vein indicating crystallization pressure of 25 gpa however very thin melt veins 5 30 m wide in tenham contain glass olivine clinopyroxene and ringwoodite suggesting crystallization during transient low pressure excursions as the shock pressure equilibrated to a continuum level melt veins of umbarger include ringwoodite akimotoite and clinopyroxene in the vein matrix and fe2sio4 spinel and stishovite in sio2 feo rich melt indicating a crystallization pressure of 18 gpa the silicate melt veins in roy contain majorite plus ringwoodite indicating pressure of 20 gpa melt veins of ramsdorf and nakhon pathon contain olivine and clinoenstatite indicating pressure of less than 15 gpa melt veins of kunashak and la lande include albite and olivine indicating crystallization at less than 2 5 gpa based upon the assemblages observed crystallization of shock veins can occur before during or after pressure release when the assemblage consists of high pressure minerals and that assemblage is constant across a larger melt vein or pocket the crystallization pressure represents the equilibrium shock pressure

release of gas bubbles from lake sediment traced by noble gas isotopes in the sediment pore water abstract the release of gas bubbles from lacustrine or oceanic sediments into the overlying water ebullition is a major mechanism for the discharge of biogenic or geogenic gases into the water body ebullition of methane or carbon dioxide for instance contributes considerably to the release of these potent greenhouse gases through the sediment water interface depending on the rate of ebullition the pore water will show a depletion in dissolved atmospheric noble gases because the poorly soluble noble gases escape from the pore water into the gas bubbles in this study the depletion of dissolved noble gases in sediment pore water was analyzed for the first time to study bubble formation and ebullition in sediments the noble gases in the pore water of the sediments of soppensee switzerland show a distinct depletion due to ebullition of biologically produced methane this depletion is lowest in the deep sediment and increases towards the sediment surface the noble gas isotope ratios in the pore water indicate that vertical diffusion barely affects the observed noble gas profiles the isotope ratios further show that the methane bubbles remain long enough in the sediment to attain noble gas solubility equilibrium before escaping into the overlying water the volume of gas released from the sediment by ebullition can therefore be reconstructed from the extent of the noble gas depletion in the pore water using a simple gas equilibration model the noble gas profiles in the sediment indicate that ebullition increased in soppensee during the holocene and that ebullition contributed strongly to the release of methane from the sediment our case study thus illustrates that noble gases are sensitive proxies for the release of gas from lacustrine and marine sediments or similar aquatic environments

carbon helium neon and argon isotopes in a po basin northern italy natural gas field the abundance and isotopic composition of he ne and ar have been determined in 19 gas samples taken from the dosso degli angeli hydrocarbon gas field between 3000 and 3750 m depth in the po basin carbon isotope ratios in these samples vary between 13c ch4 67 5 and 73 4 indicating a predominantly biogenic source for the methane c2 c2h6 c3h8 concentrations increase systematically from 0 04 to 0 17 by volume with depth suggesting that there is a small additional thermogenic or diagenetic hydrocarbon contribution to these gases ch4 36ar ratios in the dosso degli angeli gases are in the range predicted for a groundwater which has derived its rare gas by equilibration with the atmosphere and is ch4 saturated under reservoir conditions there is also up to 10 excess of ch4 which is not associated with the groundwater these results are consistent with 90 of the ch4 in the dosso degli angeli reservoir originating from ch4 saturated groundwater measured 20ne 36ar ratios depart from the predicted ratio in air equilibrated groundwater this fractionation is consistent with water gas phase equilibration under reservoir conditions and is similar to that observed in gas reservoirs in the vienna and pannonian basins austria and hungary respectively the he in the dosso degli angeli gases is almost entirely radiogenic and derived from the crust the concentration of 4he in the reservoir gases requires that he is mostly sourced from outside the reservoir volume radiogenic 4he 40ar ratios input into the reservoir gas must be much higher than averaged crustal production ratios as no shift from the atmospheric 40ar 36ar ratio is observed preferential release of 4he over 40ar from the sites of their production is the preferred explanation this observation contrasts with previous studies from active extensional basins in which radiogenic 4he and 40ar appear to have been stored released and transported at near production ratio on a regional scale the most obvious difference between these studies is the comparatively low thermal gradient of the po basin

air xe enrichments in elk hills oil field gases role of water in migration and storage hydrocarbons from the elk hills naval petroleum reserve npr 1 bakersfield ca are enriched in heavy noble gases the 132xe 36ar ratios are as high as 576 times the ratio in air and represent the largest relative xe enrichments ever observed in terrestrial fluids the xe isotopic composition is indistinguishable from air we show that these samples cannot be explained by equilibration of oil with air saturated water and secondary enrichment via a rayleigh distillation gas stripping process based on laboratory studies of others with potential petroleum source rocks we believe the source of this enriched heavy noble gas component was adsorbed air initially trapped in on the source rocks that was expelled and mixed with the hydrocarbons during expulsion and primary migration kr and xe enrichments decrease with increasing 36ar concentration we propose a model in which an initial kr xe enriched hydrocarbon becomes diluted with noble gases extracted from air saturated groundwater during expulsion migration and storage the model generates an integrated water hydrocarbon ratio for the production fluid which indicates a minimal role for water in hydrocarbon expulsion and migration the results are interpreted to provide time geometrical constraints on the mechanisms by which hydrocarbons can migrate as a separate phase

shock events in the solar system the message from minerals in terrestrial planets and asteroids impacts are central to the origin and evolution of planets of the solar system the shapes of craters which can reach up to 1 000 km in diameter on the moon provide critical information on the large scale dynamics of the impact and related shock minerals formed at high pressure and temperature found in shocked terrestrial rocks and meteorites give additional and complementary insights on the shock process at a smaller scale typically from a few micrometers to a few millimeters local flaws in rocks such as voids and mineral interfaces are the preferential sites for the formation of high pressure melts and minerals calculations based on the physics of shocks and the thermodynamics and kinetics of mineral transformations provide orders of magnitude for the duration transient pressure and prevailing temperature conditions of shock events case studies on shocked terrestrial and extraterrestrial materials illustrate the links between these parameters and impact duration many of the high pressure min

basin scale natural gas source migration and trapping traced by noble gases and major elements the pakistan indus basin he ne and ar concentrations he and ar isotopic ratios carbon isotopic ratios and chemical compositions of hydrocarbon gases were measured in natural gas samples from gas producing wells in the indus basin pakistan where no oil has ever been found 3he 4he ratios are in the range 0 01 0 06 ra ra is the atmospheric value of 1 38 10 6 indicating the absence of mantle derived helium despite the trias extension 40ar 36ar ratios range from 296 to 800 consistent with variable additions of radiogenic argon to atmospheric groundwater derived argon rare gas concentrations show large variations from 6 10 5 to 1 10 3 mol mol for 4he and from 3 10 7 to 3 10 5 mol mol for 36ar in general 36ar concentrations are high compared to literature data for natural gas co2 and n2 concentrations are variable ranging up to 70 and 20 respectively mantle derived he is not observed therefore co2 and n2 are not mantle derived either hydrocarbon gas maturity is high but accumulation efficiency is small suggesting that early produced hydrocarbons including oil were lost as well as mantle helium this is consistent with the generally late pliocene trap formation and explains the high n2 concentrations since n2 is the final species generated at the end of organic matter maturation based on 13c data co2 originates from carbonate decomposition very elevated 20ne 36ar ratios are found reaching a maximum of 1 3 compared to 0 1 0 2 for air saturated water and 0 5 for air and these high values are related to the lowest rare gas concentrations we suggest that this highly fractionated signature is the trace of the past presence of oil in the basin and appeared in groundwater we propose a model where oil water contact is followed by gas water contact both with rayleigh distillation for rare gas abundance ratios thereby generating the fractionated 20ne 36ar signature in groundwater first and transferring it to gas later assuming the gas water contact occurred shallower than present reservoir depths this model explains the generally high 36ar concentrations and low ch4 36ar ratios compared to other studies on younger basins it thus provides a historical perspective on fluid transfer in a sedimentary basin where a gas accumulation may have been buried to greater depth since formation rare gas and major element data point to mixing between two gas pulses produced successively the very co2 n2 rich gases are terminal products of organic matter maturation which have been trapped after important migration this gas was followed by a more typical thermogenic gas which mixed with it

combined geophysical and analytical methods to estimate offshore freshwater extent abstract offshore fresh groundwater is increasingly suggested as a potential water resource for onshore human demands in many cases onshore pumping already draws significant fresh groundwater from offshore however offshore aquifers and the extent of offshore freshwater are usually poorly characterised due to data scarcity this study combines geophysical data hydraulic information and a first order mathematical analysis to investigate offshore freshwater extent in the gambier embayment australia a large seismic data set combined with onshore and offshore bore log geological profiles are used to explore the regional offshore hydro stratigraphy aquifer hydraulic parameters and onshore heads are obtained from onshore investigations a novel application of archie s law geophysical data and onshore hydrochemical data provide useful insights into the salinity profiles within four offshore wells these are compared to steady state sharp interface estimates of the freshwater extent obtained from a recently developed analytical solution albeit using simplified conceptual models salinities derived from resistivity measurements indicate that in the south of the study area pore water with total dissolved solids tds of 2 2 g l 1 is found up to 13 2 km offshore offshore pore water salinities are more saline in the northern areas most likely due to thinning of the offshore confining unit the analytical solution produced freshwater saltwater interface locations that were approximately consistent with the freshwater saltwater stratification in two of the offshore wells although analytical uncertainty is high this investigation provides a leading example of offshore freshwater evaluation applying multiple techniques demonstrating both the benefit and uncertainty of geophysical interpretation and analytical solutions of freshwater extent

host rock solid state transformation in a shock induced melt vein of tenham l6 chondrite abstract the host rock fragments entrained in a 580 m wide melt vein of the tenham l6 chondrite were investigated using field emission scanning electron microscopy fesem and transmission electron microscopy tem to better understand the solid state transformation mechanisms and the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide that crystallized from immiscible melts and sub rounded host rock fragments that have been entrained in the melt and transformed to polycrystalline high pressure silicates by solid state transformation mechanisms these high pressure phases include ringwoodite low ca majorite clinoenstatite hollandite structured plagioclase and ca rich majorite the ca rich majorite occurs as a symplectitic intergrowth with a ca poor amorphous silicate phase in a 200 m diameter chondrule in the vein this intergrowth seems to be the result of a disproportionate breakdown of a ca rich clinopyroxene precursor into ca rich majorite and femg sio 3 perovskite which subsequently vitrified upon pressure release the tem observations suggest that most solid state transformations in the tenham are reconstructive the transformation of olivine to polycrystalline ringwoodite appears to involve incoherent intracrystalline nucleation and interface controlled growth lamellae in partially transformed olivine are not continuous coherent lamellae but rather lamellae of polycrystalline ringwoodite which is inconsistent with a coherent lamellar transformation mechanism growth rate calculations based on published kinetic data suggest that the time required to grow 1 m ringwoodite crystal is 100 ms at 1600 k suggesting that the minimum shock pulse of approximately 100 ms

a magnus opus helium neon and argon isotopes in a north sea oilfield this study of the magnus oilfield located in the east shetland basin northern north sea represents the most detailed investigation of noble gas isotope systematics in a liquid hydrocarbon reservoir yet undertaken samples from nine producing wells across this middle jurassic field were taken and the helium neon and argon isotopic ratios and abundances in the oil were determined both the helium and the neon isotope systematics require a contribution from a mantle source if the mantle endmember is modeled using mid ocean ridge mor values 2 3 4 5 of the 4he and 4 3 6 2 of the 21ne is mantle derived the remainder of the 4he and 9 0 12 0 of the 21ne is crustal radiogenic and the remaining 21ne is atmosphere derived the resolved mantle derived he ne ratio is quite distinct from upper mantle values estimated from mor samples but indistinguishable from values resolved in other regions of continental extension this result provides strong evidence that the subcontinental lithospheric mantle not only has a different noble gas inventory to the convecting mantle under mors but also has a near uniform composition the quantity of radiogenic noble gas associated with the magnus oil groundwater system can only be accounted for by production predominantly from outside the volume of the magnus sandstone aquifer reservoir drainage area and the associated kimmeridge clay source rock formation and together with the mantle derived noble gases provides strong evidence for cross formational communication with deeper regions of the crust the 20ne and 36ar must have been input into the oil phase by interaction with an air equilibrated groundwater noble gas partitioning between a seawater derived groundwater and the oil phase at the average magnus sandstone aquifer temperature requires a subsurface seawater oil volume ratio of 110 40 to account for both the 20ne and 36ar concentrations in the central and southern magnus samples the volume of groundwater which has equilibrated with the magnus oil is indistinguishable from the static volume of water estimated to be in the down dip magnus aquifer reservoir drainage volume this suggests that the magnus oil has obtained complete equilibrium with the groundwater in the reservoir drainage volume probably during secondary migration and further suggests that concurrent cementation of the magnus sandstone aquifer has occurred with little or no large scale movement of air equilibrated groundwater through the aquifer system higher concentrations of 20ne and 36ar in the n magnus oil cannot be accounted for by equilibration with a seawater derived groundwater this is qualitatively consistent with the earlier and more mature oil in this section equilibrating with freshwater which is known to have been trapped in the crest of the reservoir structure

the microstructural response of quartz and feldspar under shock loading at variable temperatures shock recovery experiments were carried out on westerly granite and hospital hill quartzite targets in the peak pressure range 8 to 25 gpa preshock temperatures of 25 450 and 750 c and pulse durations of 2 to 7 s using internally heated momentum traps and explosive plane wave generators optical and transmission electron microscopy analyses of quartz and feldspar shocked at 25 c revealed the previously documented progression with increasing pressure 1 fracturing 2 planar fractures and shock mosaicism 3 shock mosaicism and planar deformation features pdfs and 4 isotropization this same sequence is observed for experiments at elevated preshock temperature but with specific microstructures occurring at lower pressures than those in previous experiments at room temperature at 750 c strong shock mosaicism partially thermally recovered is characteristic of feldspar shocked to 8 gpa whereas 15 gpa is required for its development in quartz and for the generation of pdfs in both minerals the results suggest that threshold pressures for formation of the various microstructures and phases are expected to vary systematically as a function of the preshock temperature of the target material we suggest that pdfs are generated in the shock transition by progressive heterogeneous phase transformation of the crystal structure to form dense glass or high pressure polymorphs the onset pressures for pdfs in specific crystallographic orientations is not influenced strongly by temperature but the character of the pdfs does change as preshock temperature is increased at the same peak shock stress the change from multiple sets of thin pdfs at low temperature to thicker single sets of pdfs at moderate temperature and finally to complete isotropization at high temperatures reflects a change in the phase transformation mechanism as a function of temperature in contrast development of shock mosaicism in quartz and feldspar occurs throughout the duration of shock loading and is better developed at elevated temperatures where the kinetics are enhanced by the additional thermal energy in the target

shock experiments on pre heated α and β quartz ii x ray and tem investigations quartz single crystals pre heated to different temperatures 20 275 540 and 630 c were experimentally shocked to pressures ranging from 20 to 40 gpa with the shock front propagating parallel to 1010 or 0001 shocked quartz pre heated to 630 c is nearly x ray amorphous at 26 gpa while quartz shocked at room temperature still displays several x ray diffraction lines up to 30 gpa all samples that were still crystalline when shocked above 25 gpa exhibit lattice expansion internal strain and reduced crystallite sizes lattice expansion was up to 1 for the constants a o and co and up to 3 for the cell volume v o quartz shocked parallel to 1010 always shows larger lattice constants and is more strained than quartz shocked parallel to 0001 indicating that shock effects are controlled by the structural anisotropy internal strain is anisotropic with minimum strain in the planes belonging to 1012 the dominant shock defect revealed by tem are sets of parallel lamellae consisting of pure sio 2 glass so called planar deformation features pdfs below 25 gpa pdfs are extremely rare and thin 30 nm at pressures above 25 gpa however pdfs occur frequently and are about ten times thicker this qualitative observation of increasing pdf frequency and thickness with increasing pressure is quantified by calculations of the amount of glass using x ray and density data the results of this study substantiate the crucial role of pdfs for the lattice expansion of quartz and the formation of diaplectic glass and lechatelierite lattice expansion is ascribed to the enormous expansion of pdfs during decompression leading to elastic stretching in adjacent crystalline areas the observation that pdfs occur predominantly parallel to 1012 where minimum strain is present supports this hypothesis the increasing amount of pdfs above 25 gpa is interpreted as the cause for the formation of diaplectic glass shock temperature calculations support the assumption that these pdfs consist under compression of superheated melt the heat is possibly sufficient to melt crystalline areas adjacent to the superheated pdfs at enhanced pressures such molten bands coalesce to a total melt which is quenched upon decompression thus diaplectic glass represents a quenched high pressure melt while lechatelierite sio 2 glass with a fluidal texture is interpreted as quenched low pressure melt

halogens and noble gases in sedimentary formation waters and zn pb deposits a case study from the lennard shelf australia abstract halogen ratios br cl and i cl and concentrations provide important information about how sedimentary formation waters acquire their salinity but the possible influence of organic br derived from sedimentary wall rocks is rarely quantified here it is demonstrated that br cl versus i cl mixing diagrams can be used to deconvolve organic br contributions that organic matter has a limited range of br i ratios and that organic br is a more significant component in zn pb deposit ore fluids than previously recognised the significance of these findings is illustrated for the lennard shelf zn pb deposits of western australia fluid inclusions related to lennard shelf zn pb mineralisation have variable salinity and hydrocarbon contents the halogen data from these fluid inclusions require mixing of three fluid end members 1 an evaporated seawater bittern brine 30 wt nacl equiv with greater than seawater br cl ratio 2 a lower salinity pore fluid 5 wt nacl equiv with moderately elevated br cl and i cl and 3 fluids with br cl ratios of 5 times seawater and extremely elevated i cl ratios of 11 500 times seawater the first two fluids have 40 ar 36 ar of 300 400 and greater than air saturated water 36 ar concentrations that are typical of fluid inclusions related to zn pb mineralisation the third organic rich fluid has the highest 40 ar 36 ar ratio of up to 1500 and a depleted 36 ar concentration mineralisation is interpreted to have resulted from mixing of zn rich evaporitic brines and h 2 s present in hydrocarbons it is suggested that aqueous fluids acquired organic br and i from hydrocarbons and that hydrocarbons exsolving from the aqueous fluid removed noble gases from solution interaction of variably saline brines and hydrocarbons could account for the variable br cl and i cl composition and 36 ar concentrations recorded by lennard shelf fluid inclusions the distinct 40 ar 36 ar signature of the fluid with the highest i cl ratio suggests the hydrocarbons and brines were sourced independently from different parts of the sedimentary basin these data indicate the complementary nature of halogen and noble gas analysis and provide new constraints on important mixing processes during sediment hosted zn pb mineralisation

the nature of maskelynite in shocked meteorites not diaplectic glass but a glass quenched from shock induced dense melt at high pressures abstract maskelynite an important constituent of shocked meteorites once thought to be diaplectic plagioclase glass formed by shock induced solid state transformation our systematic investigation of shocked l chondrites and snc meteorites indicates that maskelynite does not contain inherited fractures or cleavage and shock induced fractures we found no evidence for models calling for melting that initiated in pdfs and affected the whole crystals maskelynite grains are smooth and display radiating cracks emerging from their surfaces into neighboring pyroxene this is indicative of shock induced melting and quenching of the dense melt at high pressure thus erasing the inherited and shock induced fractures this was followed by relaxation of the dense plagioclase glass which induced the expansion cracks in pyroxene and olivine enrichment in potassium deviation from stoichiometry degradation of igneous zoning the presence of offshoots of maskelynite in pyroxene the lack of vesiculation in the melt pockets melt veins and molten mesostasis are clear evidence for melting and quenching under high pressure our investigations present unequivocal evidence that maskelynite in meteorites is not diaplectic plagioclase glass formed by solid state transformation but a dense quenched glass the duration of the shock pulse in natural events can be several orders of magnitude longer than in shock experiments since kinetic effects are crucial factors in promoting phase transitions vitrification and melting experimentally induced solid state vitrification of plagioclase produced in dynamic experiments is inadequate for calibration of peak shock pressures in maskelynite bearing natural samples

thermal constraints on crustal rare gas release and migration evidence from alpine fluid inclusions the palfris marl of the helvetic alpine nappes contains four distinct vein fill generations ch4 rich gas is found in abundant fluid inclusions within these carbonate veins while free ch4 gas has also been produced from exploratory boreholes through this formation the stable isotope and helium neon and argon isotopic composition of these fluids has been determined a constant radiogenic 40ar concentration of 1 25 0 13 1 ppm in these differently sited fluids requires an intimate association between the 40arrad source and the hydrocarbon phase this can only be reasonably explained if the 40arrad was input into the hydrocarbon phase during hydrocarbon generation migration or storage prior to entrapment in the fluid inclusions stable isotope results constrain the maturity of hydrocarbon production while fluid inclusion formation pressures and temperatures record values of up to 2 5 kbars and 250 c these values place limits on the range of thermal conditions in which the hydrocarbon 40arrad relationship was established all fluids within inclusions also contain radiogenic 4he40ar values at predicted crustal production ratios these observations provide the first evidence that both 4herad and 40arrad can be quantitatively released on a regional scale bounded by the thermal conditions required to produce the hydrocarbon phase and the conditions under which the fluid inclusions were formed t 190 250 c these results require that negligible quantities of excess 40arrad decoupled from 4herad have been released into this system given the wide array of mechanisms which can potentially cause decoupling of these two species this result provides an important constraint on the role of these processes within the sedimentary fluid regime in contrast the free borehole gas contains excess radiogenic 4he and 21ne relative to 40arrad in proportions which can be accounted for by local production and subsequent diffusion from the surrounding marl the latter pattern is consistent with rare gas migration in lower temperature environments a conceptual model which considers both diffusional and metamorphic release of helium and argon and the ability of the surrounding fluid regime to transport the rare gases from their respective mineral production sites is consistent with both these results and data from regional rare gas studies

plagioclase breakdown as an indicator for shock conditions of meteorites the collision history of asteroids in the early solar system is difficult to reconstruct a study of plagioclase breakdown using x ray diffraction measurements under increasing pressures and temperatures suggests that peak pressures in collisions that formed shocked meteorites have been overestimated shocked meteorites that were formed when their parent body underwent shock metamorphism often contain the mineral plagioclase either in an amorphous form or in its high pressure phase the peak pressures in shock metamorphism can be constrained by shock recovery experiments that determine the amorphization pressures of plagioclase1 2 3 however in these experiments temperatures have been unrealistically low and timescales much shorter than those in natural events here we present in situ x ray diffraction measurements of two kinds of plagioclase feldspar in conditions of increasing pressures and temperatures we find that the amorphization pressure of plagioclase decreases with increasing temperature suggesting that previous studies overestimated this parameter1 2 3 we also found that the mineral jadeite forms first from amorphous plagioclase whereas the nucleation of other minerals such as stishovite or garnet is significantly delayed the occurrence of jadeite in shocked meteorites that do not contain stishovite4 5 6 7 8 can therefore be explained as a result of the crystallization kinetics we conclude that the study of plagioclase breakdown can constrain the pressure temperature time history of shock events and thus help to reconstruct the collisional history of asteroids in the early solar system

the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters noble gases inert elements having isotopes produced by the decay of long half life radionuclides offer a powerful approach for tracing fluid circulation and dating groundwaters the u th 4he water ages calculated from the accumulation rate in water of radiogenic 4he produced by decay of u and th contained in the aquifer rocks is frequently higher than the hydrological ages this discrepancy is generally interpreted by two contrasting models i heterogeneities of the aquifers which allow water stagnation and accumulation of large amounts of radiogenic 4he or ii addition of 4he produced in deeper regions of the continental crust in this contribution we propose that the apparent contrast between u th 4he ages and hydrological ages in the paris basin reflects the mixing of different types of water having different residence times we show using the helium isotopic signatures of waters that this mixing occurs between three aquifers the middle jurassic the triassic and the palaeozoic basement which have contrasting helium contents and heterogeneous chemical compositions and permeabilities the difference of radiogenic 4he 4 ratios between the aquifers of triassic and middle jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks this implies residence times for groundwaters circulating in the middle jurassic carbonate aquifer much longer than those obtained from hydrological studies independent fluid age estimates based on the ground palaeotemperatures recorded in the same groundwaters by the atmospherederived noble gases seem to confirm the presence of very old groundwaters in the paris basin the estimation of the residence time of ancient groundwaters is the most challenging problem in basin hydrology e g chapman 1987 typical water residence times of 104 108 years outreach the range of half lives of most of the geochronometers available in hydrology e g 3h 14c and prolonged water rock interactions alter the chemical and isotopic signature of water preventing the identification of the fluid sources on the other hand hydrological modelling faces serious problems of estimating space and time variations of critical parameters such as the permeability due to the petro physical heterogeneities of the aquifers and fluid velocity estimates can be valid only on a local scale e g alexander et al 1987 because noble gases are inert and have isotopes produced by natural decay of long halflife radionuclides these elements have received increasing attention as tracers of groundwater movements in deep aquifers e g marine 1979 andrews et al 1982 1985 bottomley et at 1984 1990 torgersen clarke 1985 zaikowski et al 1987 ballentine et al 1991 stute et al 1992 marty et al 1993 o nions ballentine 1993 groundwaters contain noble gases derived from the atmosphere the crust and the mantle fig 1 studies on water dating are focused mainly on the crustal derived radiogenic noble gas component for obvious reasons although the mantle derived component has the capacity of tracing fluid sources oxburgh et al 1986 and the atmosphere derived component can provide independent estimates on the water residence times pinti et al 1997 in continental environments mantle derived noble gases are generally observed in regions of active volcanism or extensional tectonics ballentine et al 1991 the source is probably sub continental magma intrusion and underplating with successive episodic and tectonically controlled advective transport in the crust torgersen 1993 mantle derived helium can be easily identified from its isotopic signature indeed the mantle is enriched in primordial 3he as indicated by 3he 4he ratios greater than 10 5 whereas the atmospheric ratio is l a x 10 6 and crustalderived radiogenic helium has 3he 4he ratios in the range of 10 8 consequently the geographical distribution of the 3he 4he ratios in sedimentary fluids can be used to identify the fluids pinti d l marty b 1998 the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters in parnell j ed 1998 dating and duration of fluid flow and fluid rock interaction geological society london special publications 144 53 68 by guest on january 5 2014 http sp lyellcollection org downloaded from

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

sampling of volcanic gases the role of noble gas measurements a case study of vulcano south italy abstract collection of volcanic gases during a workshop at vulcano south italy revealed that the atmospheric noble gases are sensitive monitors to air contamination whereas indigenous deep seated compounds such as he co 2 hcl and h 2 s are insensitive to such contaminations fumaroles at the vulcano crater contained high concentrations of he 1 3 10 3 cm 3 stp g h 2 o and he ne equaled 1000 in the least contaminated sample compared to 0 2 in air saturated water 40 ar 36 ar was up to 692 radiogenic 40 ar was 11 10 4 cm 3 stp g h 2 o and radiogenic 4 he 40 ar equaled 1 2 these characteristics resemble those of steam separated from boiling geothermal fluids occurrences of vigorous bubbling drowned fumaroles were studied at the vulcano beach and at the adjacent hippopotamus pond he ne was 20 40 indicating the presence of some radiogenic he accompanied by no significant radiogenic ar the ratio of atmospheric noble gases to dry gas was 10 times higher in the drowned fumaroles at the beach than in the crater fumaroles the water of the hippopotamus pond contained 9690 mg 1 1 cl 11 800 mg 1 1 so 2 4 the ph measured in the laboratory was 1 2 these characteristics indicate that the fumaroles loose reactive gases co 2 h 2 s hcl while passing shallow water

determining fluid migration and isolation times in multiphase crustal domains using noble gases geochemical characteristics in subsurface fluid systems provide a wealth of information about fluid sources migration and storage conditions determining the extent of fluid interaction aquifer hydrocarbon connectivity is important for oil and gas production and waste storage applications but is not tractable using traditional seismic methods furthermore the residence time of fluids is critical in such systems and can vary from tens of thousands to billions of years our understanding of the transport length scales in multiphase systems while equally important is more limited noble gas data from the rotliegend natural gas field northern germany are used here to determine the length scale and isolation age of the combined water gas system we show that geologically bound volume estimates i e gas to water volume ratios match closed system noble gas model predictions suggesting that the rotliegend system has remained isolated as a closed system since hydrocarbon formation radiogenic helium data show that fluid isolation occurred 63 129 m y after rock and or groundwater deposition ca 300 ma which is consistent with known hydrocarbon generation from 250 to 140 ma thus corroborating long term geologic isolation it is critical that we have the ability to distinguish between fluid systems that despite phase separation have remained closed to fluid loss from those that have lost oil or gas phases these findings are the first to demonstrate that such systems remain isolated and fully gas retentive on time scales 100 m y over 10 km length scales and have broad implications for saline aquifer co2 disposal site viability and hydrocarbon resource prediction which both require an understanding of the length and time scales of crustal fluid transport pathways

noble gases solubility models of hydrocarbon charge mechanism in the sleipner vest gas field abstract noble gases are chemically inert and variably soluble in crustal fluids they are primarily introduced into hydrocarbon reservoirs through exchange with formation waters and can be used to assess migration pathways and mechanisms as well as reservoir storage conditions of particular interest is the role groundwater plays in hydrocarbon transport which is reflected in hydrocarbon water volume ratios here we present compositional stable isotope and noble gas isotope and abundance data from the sleipner vest field in the norwegian north sea sleipner vest gases are generated from primary cracking of kerogen and the thermal cracking of oil gas was emplaced into the sleipner vest from the south and subsequently migrated to the east filling and spilling into the sleipner ost fields gases principally consist of hydrocarbons 83 93 co2 5 4 15 3 and n2 0 6 0 9 as well as trace concentrations of noble gases helium isotopes 3he 4he are predominantly radiogenic and range from 0 065 to 0 116 ra reported relative to air ra 1 4 10 6 clarke et al 1976 sano et al 1988 showing predominantly 98 crustal contributions consistent with ne 20ne 22ne from 9 70 to 9 91 21ne 22ne from 0 0290 to 0 0344 and ar isotopes 40ar 36ar from 315 to 489 air derived noble gas isotopes 20ne 36ar 84kr 132xe are introduced into the hydrocarbon system by direct exchange with air saturated water asw the distribution of air derived noble gas species are controlled by phase partitioning processes in that they preferentially partition into the gas i e methane phase due to their low solubilities in fluids therefore the extent of exchange between hydrocarbon phases and formation waters that have previously equilibrated with the atmosphere can be determined by investigating air derived noble gas species we utilize both elemental ratios to address process i e open vs closed system and concentrations to quantify the extent of hydrocarbon water exchange i e volumetric gas water ratios these data are discussed within the framework of several conceptual models i total gas stripping model which assumes all noble gases have been stripped from the water phase thus defining the minimum volume of water to have interacted with the hydrocarbon phase ii equilibrium model which assumes equilibration between groundwater and hydrocarbon phase at reservoir p t and salinity and iii open and closed system gas stripping models using concentrations and elemental ratios by applying these models to ne ar data from sleipner we estimate volumetric gas water ratios v g v w between 0 02 and 0 07 which are lower than standard geologic gas water estimates of 0 24 estimated by combining gas in place estimates with groundwater porosity estimates sleipner vest data can be best approximated by an open system model which predicts more than an order of magnitude more groundwater interaction during migration than geologic estimates indicating a dynamic aquifer system and or a hydrous migration pathway in an open system the extent of gas loss can be estimated to be between 8 and 10 reservoir volumes which have passed through the system and been lost i e filled and spilled

the noble gas isotope record of hydrocarbon field formation time scales abstract noble gases may be considered as the most prominent tracers of natural fluids including hydrocarbons the atmosphere is the only source of 20ne 36ar 84kr 130xe in subsurface environments and their concentrations in pore waters after recharge are known from the solubility data this allows modelling of noble gas partitioning between coexisting gas oil and water phases in the course of hydrocarbon formation migration and storage radiogenic isotopes 4he 21ne 40ar 136xe after being released from source rocks are mixed with air derived noble gases already present in the pore space concentrations of radiogenic species in the pore space of typical hydrocarbon fields are generally so high that they can hardly be accumulated in situ and thus indicate noble gas transfer from ground waters the time bearing ratios 4he 20ne 21ne 20ne 4he 40arair 40ar 40arair in hydrocarbon fields are thus proportional to the time interval between the ground water recharge and noble gases partitioning into the hydrocarbon phase s the recharge partition interval the largest available data set allows the recharge partition intervals to be constrained for a large number of hydrocarbon fields situated in different tectonic settings ancient plates young plates mobile belts these intervals increase systematically with the ages of hydrocarbon source and trap lithologies and are comparable with these ages this important feature valid in general for different hydrocarbon fields implies i local sources of radiogenic noble gas isotopes in ground waters ii relatively recent formation of hydrocarbon fields and iii their short formation time scales in some cases the duration of formation of a hydrocarbon field can be constrained for example nearly constant 21ne 20ne 40ar 40arair ratios measured in samples from the magnus oil field north sea give an accumulation time scale 10 ma it should be emphasized that the above noble gas isotope ratios give the time estimates which are independent of geological reconstructions sometimes the noble gas inventory in a hydrocarbon field and ground waters allows characterization of the source rock volume involved in formation of the field generally this volume exceeds that of the hydrocarbon field rocks by orders of magnitude

the noble gas geochemistry of natural co2 gas reservoirs from the colorado plateau and rocky mountain provinces usa identification of the source of co2 in natural reservoirs and development of physical models to account for the migration and interaction of this co2 with the groundwater is essential for developing a quantitative understanding of the long term storage potential of co2 in the subsurface we present the results of 57 noble gas determinations in co2 rich fields 82 from three natural reservoirs to the east of the colorado plateau uplift province usa bravo dome nm sheep mountain co and mccallum dome co and from two reservoirs from within the uplift area st john s dome az and mcelmo dome co we demonstrate that all fields have co2 3he ratios consistent with a dominantly magmatic source the most recent volcanics in the province date from 8 to 10 ka and are associated with the bravo dome field the oldest magmatic activity dates from 42 to 70 ma and is associated with the mcelmo dome field located in the tectonically stable centre of the colorado plateau co2 can be stored within the subsurface on a millennia timescale the manner and extent of contact of the co2 phase with the groundwater system is a critical parameter in using these systems as natural analogues for geological storage of anthropogenic co2 we show that coherent fractionation of groundwater 20ne 36ar with crustal radiogenic noble gases 4he 21ne 40ar is explained by a two stage re dissolution model stage 1 magmatic co2 injection into the groundwater system strips dissolved air derived noble gases asw and accumulated crustal radiogenic noble gas by co2 water phase partitioning the co2 containing the groundwater stripped gases provides the first reservoir fluid charge subsequent charges of co2 provide no more asw or crustal noble gases and serve only to dilute the original asw and crustal noble gas rich co2 reservoir scale preservation of concentration gradients in asw derived noble gases thus provide co2 filling direction this is seen in the bravo dome and st john s dome fields stage 2 the noble gases re dissolve into any available gas stripped groundwater this is modeled as a rayleigh distillation process and enables us to quantify for each sample 1 the volume of groundwater originally stripped on reservoir filling and 2 the volume of groundwater involved in subsequent interaction the original water volume that is gas stripped varies from as low as 0 0005 cm3 groundwater cm3 gas stp in one bravo dome sample to 2 56 cm3 groundwater cm3 gas stp in a st john s dome sample subsequent gas groundwater equilibration varies within all fields each showing a similar range from zero to 100 cm3 water cm3 gas at reservoir pressure and temperature