light hydrocarbon gases in guaymas basin hydrothermal fluids thermogenic versus abiogenic origin light hydrocarbon gases methane through pentane in high temperature hydrothermal fluids of the guaymas basin gulf of california are predominantly derived from thermocatalysis of organic carbon in sediments intruded by mid ocean ridge volcanic rocks the spectrum of c1 c5 gases in guaymas basin hydrothermal fluids is characterized by a preponderance of alkanes with essentially no alkenes present comparison with high temperature fluids from 21 n on the east pacific rise where geochemical evidence indicates a distinct lack of thermogenic gas and where methane is derived abiogenically from the basalts shows that the 21 n hydrocarbon gases are characterized by a prominent ethylene signature stable isotope compositions of guaymas basin m thane differ from 21 n gas guaymas basin has dgr13c values of 43 to 51 pmil vs pdb compared to 21 n where values as high as 15 pmil have been measured these differences reflect the different origins of light hydrocarbon gases in the two systems with guaymas methane being overwhelmingly of an organic thermogenic derivation and showing no evidence of the abiogenic basalt derived gas that characterizes the 21 n environment carbon isotope analyses of dissolved inorganic carbon in guaymas basin hydrothermal fluids indicate that high temperature hydrocarbon oxidation may be an important process acting in conjunction with high temperature thermocatalytic hydrocarbon generation

cyanobacteria are confined to dewless habitats within a dew desert implications for past and future climate change for lithic microorganisms although covering almost all rock outcrops around the world little is known regarding the factors that govern the spatial distribution of lithic cyanobacteria and lichens this is also the case in the negev desert where cyanobacteria predominate on the rock outcrops of the south facing slopes and lichens on the rock outcrops of the north facing slopes hypothesizing that abiotic conditions determine their distribution radiation temperature rain dew and fog were monitored over a two year period 2008 2010 at cyanobacteria and lichen dwelling habitats within a first order drainage basin in the negev highlands while non significant differences characterized the rain amounts substantial differences in substrate temperatures were recorded which resulted in turn in fundamental differences in the non rainfall water regime while dew condensed at the rock outcrops of the lichen habitat no condensation took place at the cyanobacteria habitat contrary to the common belief cyanobacteria were found to inhabit dewless habitats as a result cyanobacteria solely rely on rain precipitation for growth and can therefore serve as bioindicators for dewless habitats within the dewy negev desert the findings may have important implications regarding earth colonization soil forming processes and geochemical processes following climate warming they may explain lichen expansion and subsequent o2 increase during the mid neoproterozoic providing indirect support for substantial photosynthetic activity and high weathering rates during this era

high archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3 5 ga swaziland supergroup south africa new and compiled oxygen isotope data combined with the results of geological and sedimentological studies demonstrate that enclaves of synsedimentary to very early diagenetic cherts are widely preserved in the 3 5 3 2 ga swaziland supergroup barberton greenstone belt south africa the low 1 8 o values of these cherts indicate extremely high ocean temperatures of 55 85 c previously the large depletion in 1 8 o shown by all barberton cherts relative to their phanerozoic counterparts has been attributed to low 1 8 o in archean oceans chert formation during late diagenesis wholesale loss of 1 8 o during alteration and or regional silicification of sediments around hot springs these alternative explanations are not compatible with the new results cherts in the onverwacht group display an isotopic stratigraphy that is inversely repeated in conglomerates in the overlying fig tree and moodies groups demonstrating that the chert 8 0 o values were fixed prior to archean uplift and erosion which started at 3 26 ga the maximum 1 8 o value in barberton cherts 22 is lower than the minimum values 23 in phanerozoic bedded cherts precluding late diagenesis as the explanation of the overall low 1 8 o values regional metamorphic hydrothermal or long term resetting of original 1 8 o values is also precluded by preservation of 1 8 o values across different metamorphic grades and by systematic 1 8 o differences among interbedded chert types stratigraphic units and conglomerate clasts the 7 1 8 o variation of these archean cherts is similar to that of phanerozoic deep sea cherts formed when opal converted to microquartz during burial but the actual archean values are 10 lower marine opal was apparently converted to microquartz during burial to depths of 1 km cherts with 1 8 o 15 reflect conversion during deepest burial or in local areas of enhanced geothermal gradient and or hydrothermal activity cherts with higher 1 8 o values formed during early diagenesis and indicate an extremely hot archean ocean and surface environment

the meteoritical bulletin no 85 2001 september meteoritical bulletin no 85 lists information for 1376 newly classified meteorites comprising 658 from antarctica 409 from africa 265 from asia 262 of which are from oman 31 from north america 7 from south america 3 from australia and 3 from europe information is provided for 11 falls dergaon dunbogan gujba independence itqiy moravka oued el hadjar sayama sologne valera and worden noteworthy non antarctic specimens include 5 martian meteorites dar al gani 876 northwest africa 480 and 817 and sayh al uhaymir 051 and 094 6 lunar meteorites dhofar 081 280 and 287 and northwest africa 479 482 and 773 an ungrouped enstatite rich meteorite itqiy a bencubbin like meteorite gujba 9 iron meteorites and a wide variety of other interesting stony meteorites including ch ck cm co cr cv r enstatite and unequilibrated ordinary chondrites primitive achondrites hed achondrites and ureilites

new constraints on methane fluxes and rates of anaerobic methane oxidation in a gulf of mexico brine pool via in situ mass spectrometry abstract deep sea biogeochemical cycles are in general poorly understood owing to the difficulties of making measurements in situ recovering samples with minimal perturbation and in many cases coping with high spatial and temporal heterogeneity in particular biogeochemical fluxes of volatiles such as methane remain largely unconstrained because of the difficulties with accurate quantification in situ and the patchiness of point sources such as seeps and brine pools to better constrain biogeochemical fluxes and cycling we have developed a deep sea in situ mass spectrometer isms to enable high resolution quantification of volatiles in situ here we report direct measurements of methane concentrations made in a gulf of mexico brine pool located at a depth of over 2300 m concentrations of up to 33 mm methane were observed within the brine pool whereas concentrations in the water directly above were three orders of magnitude lower these direct measurements enabled us to make the first accurate estimates of the diffusive flux from a brine pool calculated to be 1 1 0 2 mol m 2 yr 1 integrated rate measurements of aerobic methane oxidation in the water column overlying the brine pool were 320 mol m 2 yr 1 accounting at most for just 0 03 of the diffusive methane flux from the brine pool calculated rates of anaerobic methane oxidation were 600 1200 m yr 1 one to two orders of magnitude higher than previously published values of aom in anoxic fluids these findings suggest that brine pools are enormous point sources of methane in the deep sea and may in aggregate have a pronounced impact on the global marine methane cycle

hydrothermal venting and mineralization in the crater of kick em jenny submarine volcano grenada lesser antilles kick em jenny is a frequently erupting shallow submarine volcano located 7 5 km off the northern coast of grenada in the lesser antilles subduction zone focused and diffuse hydrothermal venting is taking place mainly within a small 70 110 m depression within the 300 m diameter crater of the volcano at depths of about 265 m much of the crater is blanketed with a layer of fine grained tephra that has undergone hydrothermal alteration clear fluids and gas are being discharged near the center of the depression from mound like vents at a maximum temperature of 180 c the gas consists of 93 96 co2 with trace amounts of methane and hydrogen gas flux measurements of individual bubble streams range from 10 to 100 kg of co2 per day diffuse venting with temperatures 5 35 c above ambient occurs throughout the depression and over large areas of the main crater these zones are colonized by reddish yellow bacteria with the production of fe oxyhydroxides as surface coatings fragile spires up to several meters in height and elongated mounds up to tens of centimeters thick a high resolution photomosaic of the inner crater depression shows fluid flow patterns descending the sides of the depression toward the crater floor we suggest that the negatively buoyant fluid flow is the result of phase separation of hydrothermal fluids at kick em jenny generating a dense saline component that does not rise despite its elevated temperature

venting of a separate co2 rich gas phase from submarine arc volcanoes examples from the mariana and tonga kermadec arcs submersible dives on 22 active submarine volcanoes on the mariana and tonga kermadec arcs have discovered systems on six of these volcanoes that in addition to discharging hot vent fluid are also venting a separate co2 rich phase either in the form of gas bubbles or liquid co2 droplets one of the most impressive is the champagne vent site on nw eifuku in the northern mariana arc which is discharging cold droplets of liquid co2 at an estimated rate of 23 mol co2 s about 0 1 of the global mid ocean ridge mor carbon flux three other mariana arc submarine volcanoes nw rota 1 nikko and daikoku and two volcanoes on the tonga kermadec arc giggenbach and volcano 1 also have vent fields discharging co2 rich gas bubbles the vent fluids at these volcanoes have very high co2 concentrations and elevated c 3he and 13c co2 ratios compared to mor systems indicating a contribution to the carbon flux from subducted marine carbonates and organic material analysis of the co2 concentrations shows that most of the fluids are undersaturated with co2 this deviation from equilibrium would not be expected for pressure release degassing of an ascending fluid saturated with co2 mechanisms to produce a separate co2 rich gas phase at the seafloor require direct injection of magmatic co2 rich gas the ascending co2 rich gas could then partially dissolve into seawater circulating within the volcano edifice without reaching equilibrium alternatively an ascending high temperature co2 rich aqueous fluid could boil to produce a co2 rich gas phase and a co2 depleted liquid these findings indicate that carbon fluxes from submarine arcs may be higher than previously estimated and that experiments to estimate carbon fluxes at submarine arc volcanoes are merited hydrothermal sites such as these with a separate gas phase are valuable natural laboratories for studying the effects of high co2 concentrations on marine ecosystems

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

hydrothermal fluid emanations from the submarine kick em jenny volcano lesser antilles island arc abstract little is known about the role of island arcs as hydrothermal sources to the ocean when compared to the extensive research that has been carried out on hydrothermal systems at spreading ridges although increasingly more work is being done on intraoceanic arcs here we present fluid geochemistry data from the kick em jenny kej submarine volcano of the lesser antilles island arc discharge of diffuse hydrothermal fluid was discovered on the southwestern flanks of the volcano hydrothermal input into the water column was recognized from ch4 and trace metal anomalies in water column profiles in a depth range of 500 700 m samples collected directly on the seafloor also showed evidence for hydrothermal emissions where mg and cl were depleted in the fluids compared to ambient seawater while ch4 and several trace metals were enriched the chemical composition of these samples including o and h isotope data suggests that the fluids are a mixture between a condensed vapor phase derived from a phase separated hydrothermal fluid which was conductively cooled in the sub surface and seawater increased dissolved organic carbon doc concentrations of the fluids also indicate interaction with the sediment layer through which the fluids percolated although the volcanic crater could not be sampled directly due to safety concerns 3he and some trace metal values in seawater samples indicate fluid input containing a mantle component probably from a hot focused flow source in the crater region around 200 300 m depth

cambrian explosion triggered by geosphere biosphere feedbacks 1 a new hypothesis for the cause of the cambrian explosion is presented for that the evolution of the planet earth is described by the co evolution of the geospherebiosphere system here we specify our previously published earth system model for the long term carbon cycle by introducing three different types of biosphere procaryotes eucaryotes and complex multicellular life they are characterized by different global temperature tolerance windows the biotic enhancement of silicate weathering by complex multicellular life adds an additional feedback to the system and triggers the cambrian explosion the cambrian explosion is characterized by a sudden increase of biomass and a rapid cooling which amplified the spread of complex multicellular life cooling events in the neoproterozoic however could force a premature appearance of complex multicellular life index terms 0330 atmospheric composition and structure geochemical cycles 8125 tectonophysics evolution of the earth 9699 information related to geologic time general or miscellaneous 3220 mathematical geophysics nonlinear dynamics 0315 atmospheric composition and structure biosphere atmosphere interactions citation von bloh w c bounama and s franck cambrian explosion triggered by geosphere biosphere feedbacks geophys res lett 30 18 1963 doi 10 1029 2003gl017928 2003

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

26al survey of antarctic meteorites abstract an 26 al survey by non destructive gamma ray spectrometry was conducted as part of the preliminary examination effort for antarctic meteorites a total of 220 samples were studied the majority of the samples were from the allan hills area however samples from several other sites including the yamato mountains were studied compared to worldwide falls and finds the antarctic group shows a clear trend toward lower 26 al levels at leasr 10 of the samples studied were clearly undersaturated in 26 al the frequency of undersaturated samples suggests that terrestrial ages of several hundred thousand years are common among the antarctic meteorite collection the absence of samples with extremely low 26 al implies that the upper limit for terrestrial ages in the antarctic is on the order of 1 million years

variations in the chemical and stable isotope composition of carbon and sulfur species during organic rich sediment alteration an experimental and theoretical study of hydrothermal activity at guaymas basin gulf of california organic rich diatomaceous ooze was reacted with seawater and a na ca k cl fluid of seawater chlorinity at 325 400 c 400 500 bars and fluid sediment mass ratios of 1 56 2 35 to constrain factors regulating the abundance and stable isotope composition of c and s species during hydrothermal alteration of sediment from guaymas basin gulf of california alteration of inorganic and organic sedimentary components resulted in extensive exchange reactions the release of abundant h2s co2 ch4 and corganic to solution and recrystallization of the sediment to an assemblage containing albitic plagioclase quartz pyrrhotite and calcite the 34scdt values of dissolved h2s varied from 10 9 to 4 3 during seawater sediment interaction at 325 and 400 c and from 16 5 to 9 0 during na ca k cl fluid sediment interaction at 325 and 375 c in the absence of seawater so4 h2s is derived from both the transformation of pyrite to pyrrhotite and s released during the degradation of organic matter in the presence of seawater so4 reduction of so4 contributes directly to h2s production sedimentary organic matter acts as the reducing agent during pyrite and so4 reduction requisite acidity for the reduction of so4 is provided by mg fixation during early stage sediment alteration and by albite and calcite formation in mg free solutions organically derived ch4 was characterized by 13cpdb values ranging between 20 8 and 23 1 whereas 13cpdb values for dissolved corganic ranged between 14 8 and 17 7 mass balance calculations indicate that 13c values for organically derived co2 were 14 8 residual solid sedimentary organic c showed small 0 7 depletions in 13c relative to the starting sediment the experimental results are consistent with the isotopic and chemical composition of natural hydrothermal fluids and minerals at guaymas basin and permit us to better constrain sources and sinks for c and s species in subseafloor hydrothermal systems at sediment covered spreading centers our data show that the sulfur isotope composition of hydrothermal sulfide minerals in guaymas basin can be explained by derivation of s from diagenetic sulfide and seawater sulfate basaltic s may also contribute to hydrothermal sulfide precipitates but is not required to explain their isotopic composition estimates of seawater sediment mass ratios based on sulfur isotopic composition of sulfide minerals and the abundance of dissolved nh3 in vent fluids range from 3 29 during hydrothermal circulation sources of c in guaymas basin hydrothermal fluids include thermal degradation of organic matter bacteriogenic methane production and dissolution of diagenetic carbonate

in situ carbon isotopic exploration of an active submarine volcano abstract the geologic and biogeochemical cycling of carbon in deep ocean environments has important implications for our understanding of the functioning of earth systems across a wide range of spatial and temporal scales to improve our ability to study the cycling and fluxes of carbon in the deep ocean new technologies are emerging for making in situ measurements of carbon compounds over a range of environmental contexts within many of these deep sea environments fluxes of carbon compounds often occur as either venting fluids or rising gas bubbles key compounds of interest include methane ch4 dissolved inorganic carbon dic and carbon dioxide co2 a component of dic in particular measurement of the carbon isotopic composition 13c of these pools can offer a better understanding of the nature of sources fluxes and cycling processes involving these compounds here we present the advancement of an in situ laser spectrometer initially developed for measurement of 13cch4 only into a sensor that can measure 13c of both ch4 and co2 in both deep sea bubble plumes as well as geologic fluids we present results of a 2014 telepresence enabled investigation of a back arc submarine volcano kick em jenny in the caribbean sea in situ isotopic analysis of both bubbles and fluids suggest a primarily thermogenic origin for ch4 and a magmatic origin for co2 yet highlight the occurrence of some heterogeneities indicating locally elevated contribution of organic matter to dic fluxes

water and geodynamics hydrogen is the most abundant element fig 1 in the galaxy and our solar system lodders 2003 therefore it is not astonishing that hydrogen is a key player in the geodynamic evolution of planets its fate in the early earth after condensation of the solar nebula the accretion of our planet and hydrogen reprocessing through early asteroidal and cometary bombardment dauphas et al 2000 and segregation of a proto earth into iron core and silicate mantle is described elsewhere in this volume marty and yokochi 2006 figure 1 abundance of elements in the solar system in numbers of atoms per 106 atoms of silicon lodders 2003 this chapter concerns itself with the geodynamics of the modern earth where nowadays hydrogen occupies only a very small mass fraction less than 0 1 wt although its abundance is thus drastically diminished it is still believed to have a profound influence on the geodynamics of the present planet the reason why hydrogen can have a profound influence on geodynamics even when it is diluted to ppm levels relies on its fundamental influence on both rock mechanics kohlstedt 2006 and the melting relationships kohn 2006 however both the micromechanical mechanism and the large scale implications are not yet fully understood in this review geodynamic processes which may be triggered by a rock mechanical hydrogen threshold value are reviewed in addition to resulting styles of planetary convection controlled by melt and rock mechanics this review will conclude with a more speculative discussion of the possible implications for planetary evolution from an early earth to the present day and highlight areas of future work following current practice in the literature the term water will be used interchangeably for hydrogen recent breakthroughs in computational geodynamics are throwing a new light on the possible evolution of planetary tectonics simulations

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

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

the fall of the st robert meteorite the st robert quebec canada meteorite shower occurred on 1994 june 15 at 0h02m ut accompanied by detonations audible for 200 km from the fireball endpoint the fireball was recorded by visual observers in vermont new york state new hampshire quebec and ontario as well as by optical and infrared sensors in earth orbit penetration to an altitude of 36 km occurred 60 km to the northeast of montreal where the bolide experienced several episodes of fragmentation a total of 20 fragments of this h5 chondrite comprising a total mass of 25 4 kg were recovered in an ellipse measuring 8 3 5 km one fragment of the shower partially penetrated the aluminum roof of a shed interpretation of the visual and satellite data suggests that the fireball traveled from south southwest to north northeast with a slope from the horizontal of 55 61 a statistical evaluation of the likely heliocentric orbits for the body prior to collision with the earth coupled with theoretical modeling of the entry suggests an entry velocity in the range of 12 7 13 3 km s the meteoroid had moved in a low inclination orbit with orbital perihelion located extremely close to the earth s orbit from satellite optical data it is found that the photometric mass consumed during the largest detonation is 1200 kg estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0 5 kt tnt equivalent energy which corresponds to a mass of order 10 metric tonnes this measure is uncertain to approximately one order of magnitude theoretical modeling of the entry of the object suggests a mass near 1600 kg cosmogenic radionuclide activities constrain the lower initial mass to be 700 kg with an upper limit near 4000 kg seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground the total mass estimated to have reached the ground is 100 kg in material comprising 55 g fragments while the preatmospheric mass is found to be most probably in the range of 1200 2000 kg

influence of subsurface biosphere on geochemical fluxes from diffuse hydrothermal fluids hydrothermal vents along mid ocean systems host unique highly productive biological communities based on microbial chemoautotrophy that thrive on the sulphur metals nitrogen and carbon emitted from the vents into the deep ocean geochemical studies of vents have centred on analyses of high temperature focused hydrothermal vents which exhibit very high flow rates and are generally considered too hot for microbial life geochemical fluxes and metabolic activity associated with habitable lower temperature diffuse fluids remain poorly constrained as a result little is known about the extent to which microbial communities particularly in the subsurface influence geochemical flux from more diffuse flows here we estimate the net flux of methane carbon dioxide and hydrogen from diffuse and focused hydrothermal vents along the juan de fuca ridge using an in situ mass spectrometer and flowmeter we show that geochemical flux from diffuse vents can equal or exceed that emanating from hot focused vents notably hydrogen concentrations in fluids emerging from diffuse vents are 50 to 80 lower than predicted we attribute the loss of hydrogen in diffuse vent fluids to microbial consumption in the subsurface and suggest that subsurface microbial communities can significantly influence hydrothermal geochemical fluxes to the deep ocean

methane sources and production in the northern cascadia margin gas hydrate system abstract the oceanographic and tectonic conditions of accretionary margins are well suited for several potential processes governing methane generation storage and release to identify the relevant methane evolution pathways in the northern cascadia accretionary margin a four site transect was drilled during integrated ocean drilling program expedition 311 the 13c values of methane range from a minimum value of 82 2 on an uplifted ridge of accreted sediment near the deformation front site u1326 1829 mbsl meters below sea level to a maximum value of 39 5 at the most landward location within an area of steep canyons near the shelf edge site u1329 946 mbsl an interpretation based solely on methane isotope values might conclude the 13c enrichment of methane indicates a transition from microbially to thermogenically sourced methane however the co existing co2 exhibits a similar trend of 13c enrichment along the transect with values ranging from 22 5 to 25 7 the magnitude of the carbon isotope separation between methane and co2 ec 63 8 5 8 is consistent with isotope fractionation during microbially mediated carbonate reduction these results in conjunction with a transect wide gaseous hydrocarbon content composed of 99 8 by volume methane and uniform dch4 values 172 8 that are distinct from thermogenic methane at a seep located 60 km from the expedition 311 transect suggest microbial co2 reduction is the predominant methane source at all investigated sites the magnitude of the intra site downhole 13c enrichment of co2 within the accreted ridge site u1326 and a slope basin nearest the deformation front site u1325 2195 mbsl is 5 at the mid slope site site u1327 1304 mbsl the downhole 13c enrichment of the co2 is 25 and increases to 40 at the near shelf edge site u1329 this isotope fractionation pattern is indicative of more extensive diagenetic alteration at sites with greater 13c enrichment the magnitude of the 13c enrichment of co2 correlates with decreasing sedimentation rates and a diminishing occurrence of stratigraphic gas hydrate we suggest the decreasing sedimentation rates increase the exposure time of sedimentary organic matter to aerobic and anaerobic degradation during burial thereby reducing the availability of metabolizable organic matter available for methane production this process is reflected in the occurrence and distribution of gas hydrate within the northern cascadia margin accretionary prism our observations are relevant for evaluating methane production and the occurrence of stratigraphic gas hydrate within other convergent margins

the worden meteorite a new ordinary chondrite fall from michigan usa an ordinary chondrite fall in southeast michigan usa near the crossroads hamlet of worden in northeast washtenaw county penetrated the garage roof of a private home on 1997 september 1 the worden chondrite comprises silicate matrix mineral fragments chondrules chondrule fragments and opaque primary phases electron microprobe analyses olivine fa23 9 orthopyroxene fs20 1 en78 8 w01 indicate diagnostic l chondrite silicate mineral compositions recognizable chondrules and chondrule fragments constitute up to 42 vol chondrule boundaries are readily discernable especially where chondrules have rims of opaque material but not sharp and discrete plagioclase crystals are visible in the devitrified mesostasis of barred olivine chondrules together these characteristics suggest petrologic type s the spatially averaged ensemble of shockrelated features optical extinction of olivine grains minor localized shock melt suggests assignment of a shock stage of s3 the 26 al and 22na activities are typical for an l chondrite worden fell near the most recent solar minimum in 1997 and the 22na production rate should have been at a level approaching the maximum levels due to solar modulation of the galactic cosmic ray flux the low value for the worden 22na activity relative to those observed in chondrite falls associated with the 1969 solar maximum and 1976 solar minimum suggests a relatively small preatmospheric size the 60co activity confirms the indication of a small body the 56co activity was essentially zero indicating that none of the recovered meteorite contained material exposed to solar cosmic rays the worden chondrite is the fourth documented fall in michigan and the fourth stony meteorite recovered in michigan all other michigan meteorites are finds not observed falls and are iron meteorites all michigan falls to date are ordinary chondrites the three falls prior to worden were allegan hs fell 1899 rose city hs brecciated black dark matrix fell 1921 and coleman l6 veined shocked osborn et ai 1997 fell 1994 worden has a much lighter matrix than rose city and is less extensively thermally and shock metamorphosed than either rose city stoffler et ai 1991 or coleman

peculiar features of suiyo seamount hydrothermal fluids izu bonin arc differences from subaerial volcanism abstract this is the first report of the dissolved gas composition of a deep sea venting hydrothermal system originating from arc volcanism the origin of dissolved gases in hydrothermal fluids from the suiyo seamount in the southern izu bonin ogasawara arc is discussed on the basis of chemical and isotopic compositions twelve high temperature up to 310 c fluid samples were collected from three vents of the hydrothermal system using the submersible shinkai 2000 the average 3 he 4 he ratio of the dissolved he is 8 1 r r atm which is within the range of values reported for n morb the co 2 3 he ratio is 12 109 which is within the range of arc volcanic gas values the 13c values of co2 and ch4 are 1 and 8 5 respectively which is quite high compared with other subaerial arc volcanic gases and those from mid ocean ridges these results which do not accord with those from subaerial volcanism are unlikely to result from fractionation or addition of carbon sources during the fluid circulation but are regarded as characteristic of the magma source of suiyo seamount a simple mixing of 97 morb mantle with 3 subducting slab explains well the composition of the helium and carbon in the parent magma

igneous rims on low feo and high feo chondrules in ordinary chondrites abstract many ordinary chondrite oc chondrules are surrounded by rims that show evidence of appreciable melting and can be called igneous these rims formed after the melting and solidification of the host chondrule we studied thirteen igneous rims on low feo chondrules fa or fs 10 mol in ordinary chondrites of petrographic type 3 5 by electron microprobe analysis and scanning electron microscopy in both sets olivine and pyroxene compositions of the rims are similar to or moderately higher in feo than those in the host igneous rims around low feo chondrules show evidence of large degree 80 melting including 1 resorbed chondrule surfaces 2 rounded metal troilite nodules and feldspathic mesostasis 3 euhedral and subhedral morphology of olivine and pyroxene and limited ranges in grain sizes and 4 a rarity of relict grains most low feo chondrules have olivine as their major phase but pyroxene is commonly the predominant phase in their rims rims on high feo chondrules generally have smaller grain sizes and exhibit lower degrees of melting than rims around low feo chondrules mg rich relict grains are observed in high feo rims most low feo chondrules have matrix like rims around the igneous rims but matrix like rims are rare around rims on high feo chondrules there is a continuum between igneous rims and enveloping secondaries of compound chondrules the existence of both sets of objects supports the view that in the oc region most mm size grain assemblages experienced more than one melting event the precursors melted to produce the igneous rims on low feo chondrules differ from those that comprise the rims on high feo chondrules a sizeable fraction of the precursors of low feo rims are from the host chondrule most high feo rims appear to consist largely of melted matrix like materials if the rim precursors are mainly independent the similar fa and fs contents in mafic minerals of rims and host chondrules indicate that 1 oc nebular subregions bounded in space and or in time were dominated by well mixed solids 2 many chondrules experienced multiple heating events during a short period and were then withdrawn from the chondrule forming region and 3 chondrules formed at different times were mixed before agglomeration to form chondrites if the host chondrules were the main source of the low feo rim materials the fact that pyroxene is generally more abundant than in the host suggests that sio 2 normative matrix was also an important ingredient and or that kinetics favored pyroxene crystallization in the rim rims around high feo chondrules were heated to lower temperatures than rims around low feo chondrules the rarity of matrix like rims around high feo igneous rims may indicate that the dust chondrule ratio was lower where they formed

fall recovery and description of the coleman chondrite a 0 5 kg stony meteorite associated with a bright bolide seen over southeastern michigan on 1994 october 20 has been recovered the circumstances of the fall and recovery of this chondrite named coleman are presented the most likely trajectory from the observations of the event implies preatmospheric orbital parameters typical of meteorites gamma ray spectrometry of the cosmogenic radionuclides showed that the recovered mass was an interior fragment of a larger body and revealed abnormally high 22na and 26al activity electron microprobe analysis yielded compositions of fa24 1 and fs20 3 which are consistent with an l chondrite classification petrographically the presence of chondrules the observed mineralogy and the degree of chondrule matrix integration suggests assignment to petrologic type 6