feldspathic clasts in yamato 86032 remnants of the lunar crust with implications for its formation and impact history abstract low concentrations of th and fe in the yamato y 86032 bulk meteorite support earlier suggestions that y 86032 comes from a region of the moon far distant from the procellarum kreep terrain pkt probably from the lunar farside 39 ar 40 ar rb sr sm nd and sm isotopic studies characterize the chronology of y 86032 and its precursors in the mega regolith one of the rock types present in a light gray breccia lithology is an anorthosite characterized by plagioclase with an 93 i e more sodic than lunar fans but with very low 87 rb 86 sr and 87 sr 86 sr similar to those of fans fan stands for ferroan anorthosite this an93 anorthosite has nd isotopic systematics similar to those of nearside norites a fan like an97 anorthosite is present in a second light colored feldspathic breccia clast and has a more negative e nd value consistent with residence in a lree enriched environment as would be provided by an early plagioclase flotation crust on the lunar magma ocean lmo this result contrasts with generally positive values of e nd for apollo 16 fans suggesting the possibility of assymetric development of the lmo other possible explanations for the dichotomy in e nd values are advanced in the text the y 86032 protolith formed at least 4 43 0 03 ga ago as determined from a sm nd isochron for mineral fragments from the breccia clast composed predominantly of an93 anorthosite and a second clast of more varied composition we interpret the mineral fragments as being predominatly from a cogenetic rock suite an 39 ar 40 ar age of 4 36 4 41 0 035 ga for a third clast composed predominantly of an97 anorthosite supports an old age for the protolith initial 143 nd 144 nd in that clast was 0 64 0 13 e units below 143 nd 144 nd in reservoirs having chondritic sm nd ratios consistent with prior fractionation of mafic cumulates from the lmo a maximum in the 39 ar 40 ar age spectrum of 4 23 0 03 ga for a second sample of the same feldspathic breccia clast probably reflects some diffusive 40 ar loss lack of solar wind and lunar atmosphere implanted ar in the light gray breccia clast allows determination of an 39 ar 40 ar age of 4 10 0 02 ga which is interpreted as the time of initial brecciation of this litholgy after correction for implanted lunar atmosphere 40 ar impact melt and dark regolith clasts give ar ages of 3 8 0 1 ga implying melt formation and final breccia assembly 3 8 ga ago some breccia lithologies were exposed to thermal neutron fluences of 2 10 15 n cm 2 only about 1 of the fluence experienced by some other lunar highlands meteorites other lithologies experienced neutron fluences of 1 10 15 n cm 2 thus y 86032 spent most of the time following final brecciation deeply buried in the megaregolith the neutron fluence data are consistent with cosmogenic 38 ar cos cosmic ray exposure ages of 10 ma variations among differing lithologies in the amount of several regolith exposure indicators including cosmogenic noble gas abundances neutron capture induced variations in sm isotopic abundances and ir contents are consistent with a period of early 3 8 ga ago lunar regolith exposure subsequent deep burial at 5 m depth and ejection from the moon 7 10 ma ago

permeability anisotropy of natural clays as a function of strain seven series of tests have been performed on specimens from five natural soft clay sites to determine the variation of the vertical and horizontal permeabilities when the soil is unidimensionally compressed the results show that the permeability anisotropy does not increase significantly with compression up to strains of 25 for marine clays in varved clays mostly because the clay laminae are more compressible than the silty laminae the anisotropy increases with vertical compression key words permeability clay anisotropy laboratory compression

low temperature hydrothermal maturation of organic matter in sediments from the atlantis ii deep red sea abstract hydrocarbons and bulk organic matter of two sediment cores no 84 and 126 chain 61 cruise located within the atlantis ii deep have been analyzed although the brines overlying the coring areas were reported to be sterile microbial inputs and minor terrestrial sources represent the major sedimentary organic material this input is derived from the upper water column above the brines both steroid and triterpenoid hydrocarbons show that extensive acid catalyzed reactions are occurring in the sediments in comparison with other hydrothermal guaymas basin or intrusive systems cape verde rise the atlantis ii deep exhibits a lower degree of thermal maturation this is easily deduced from the elemental composition of the kerogens and the absence of polynuclear aromatic hydrocarbons of a pyrolytic origin in the bitumen the lack of carbon number preference among the n alkanes suggests especially in the case of the long chain homologs that the organic matter of atlantis ii deep sediments has undergone some degree of catagenesis however the yields of hydrocarbons are much lower than those observed in other hydrothermal areas the effect of lower temperature and poor source rock characteristics appear to be responsible for the differences

carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from middle valley northeastern pacific ocean abstract individual aliphatic hydrocarbons in samples of bulk hydrothermal petroleum from middle valley odp site 858 were submitted to compound specific isotope analysis to trace their origins the c isotope compositions of the n alkanes and isoprenoid hydrocarbons means n alkanes 30 1 1 01 858a 28 3 1 7 858c and 24 8 1 4 858d isoprenoids 26 0 2 7 858c and 27 9 0 4 858d respectively reflect mixed marine and terrestrial organic matter sources biphytane from thermophiles has a 13 c value of 21 0

hydrothermal effects on organic matter high vs low temperature components abstract hydrothermal activity and sea bed mounds have been explored in guaymas basin central gulf of california by the deep sea drilling project piston coring dredging and diving with the d s r v alvin the deep seated magmatic heat flow causes extensive thermal alteration of both organic and mineral matter especially in the case of the south rift of guaymas basin this results in hydrothermal circulation with concomitant migration of organic pyrolysate to the seabed the bitumen at depth of dsdp sites 477 and 481 contained thermogenic components such as primary olefins thermodynamically stabilized molecular markers 17 h hopanes and elemental sulfur with traces of polynuclear aromatic hydrocarbons pah the major components were n alkanes with no carbon number predominance and unresolvable complex branched and cyclic hydrocarbons hump which are typical of mature petroleum and were generated by the heat from the intrusives and magma dredge samples recovered from a mound in guaymas basin contained petroleum of a thermogenic origin as confirmed by the presence of gasoline range hydrocarbons a broad distribution of n alkanes c13 c33 no carbon number predominance hump pristane and phytane olefins and pah and large amounts of aromatic naphthenic and asphaltic material similar petroleums subsequently recovered from other active mounds in the southern rift by the d s r v alvin had analogous compositions ranging from volatile to heavy oils in pyrrhotite chimneys the extractable organic matter consisted of mainly higher molecular weight pah these petroleums are derived from the immature primarily marine organic matter at depth by thermal alteration rapid quenching by hydrothermal removal and migration followed by condensation at the sea bed results in the manifestations of oil as part of the sulfide formations exterior exposed oil samples are degraded and leached whereas interior samples are essentially unaltered the pah are high temperature resynthesis aromatization products that condense in the hottest parts of the vent systems

hydrothermal petroleum from lacustrine sedimentary organic matter in the east african rift cape kalamba oil seeps occur at the south end of the ubwari peninsula at the intersection of faults controlling the morphology of the northern basin of the tanganyika rift east africa oil samples collected at the surface of the lake 3 4 km offshore from cape kalamba have been studied the aliphatic hydrocarbon and biomarker compositions with the absence of the typical suite of polynuclear aromatic hydrocarbons indicate an origin from hydrothermal alteration of immature microbial biomass in the sediments these data show a similarity between a tar sample from the beach and the petroleum from the oil seeps and confirm that the source of these oils is from organic matter consisting mainly of bacterial and degraded algal biomass altered by hydrothermal activity the compositions also demonstrate a 200 degrees c temperature for formation generation of this hydrothermal petroleum similar to the fluid temperature identified for the pemba hydrothermal site located 150 km north of cape kalamba the 14c age of 25 6 ka b p obtained for the tar ball suggests that pleistocene lake sediments could be the source rock hydrothermal generation may have occurred slightly before 25 ka b p during a dry climatic environment when the lake level was lower than today these results also suggest that the cape kalamba hydrothermal activity did not occur in connection with an increased flux of meteoric water higher water tables and lake levels as demonstrated in the kenya rift and for the pemba site hydrothermal petroleum formation is a facile process also in continental rift systems and should be considered in exploration for energy resources in such locales

multi scale aquifer characterization and groundwater flow model parameterization using direct push technologies direct push dp technologies are typically used for cost effective geotechnical characterization of unconsolidated soils and sediments in more recent developments dp technologies have been used for efficient hydraulic conductivity k characterization along vertical profiles with sampling resolutions of up to a few centimetres until date however only a limited number of studies document high resolution in situ dp data for three dimensional conceptual hydrogeological model development and groundwater flow model parameterization this study demonstrates how dp technologies improve building of a conceptual hydrogeological model we further evaluate the degree to which the dp derived hydrogeological parameter k measured across different spatial scales improves performance of a regional groundwater flow model the study area covers an area of 60 km2 with two overlying mainly unconsolidated sand aquifers separated by a 5 7 m thick highly heterogeneous clay layer in north eastern belgium the hydrostratigraphy was obtained from an analysis of cored boreholes and about 265 cone penetration tests cpts the hydrogeological parameter k was derived from a combined analysis of core and cpt data and also from hydraulic direct push tests a total of 50 three dimensional realizations of k were generated using a non stationary multivariate geostatistical approach to preserve the measured k values in the stochastic realizations the groundwater model k realizations were conditioned on the borehole and direct push data optimization was performed to select the best performing model parameterization out of the 50 realizations this model outperformed a previously developed reference model with homogeneous k fields for all hydrogeological layers comparison of particle tracking simulations based either on the optimal heterogeneous or reference homogeneous groundwater model flow fields demonstrate the impact dp derived subsurface heterogeneity in k can have on groundwater flow and solute transport we demonstrated that dp technologies especially when calibrated with site specific data provide high resolution 3d subsurface data for building more reliable conceptual models and increasing groundwater flow model performance

ultramafic exposures and the gravity signature of the lithosphere near the fifteen twenty fracture zone mid atlantic ridge 14 16 5 n abstract we analyze geological and geophysical data near the fifteen twenty fracture zone to constrain the processes of magmatic accretion and tectonic extension in the area characterized by extensive outcrops of ultramafic rocks at the seafloor close to the fracture zone 60 km the crust is thicker associated with circular or elongated gravity lows bull s eyes axis parallel faults and abyssal hills and no peridotite outcrops consistent with a more homogeneous and magmatic crust simple melting models predict magmatic crustal thicknesses that differ substantially from the gravity estimates and the outcrop of peridotites seems inconsistent with the high degrees of partial melting in the area inferred from basalt and peridotite geochemistry we explain these discrepancies primarily a by the entrapment of melt in the lithosphere at deep levels particularly near the transform b by along axis melt migration away from the transform and c by variations in the degree and depth of serpentinization of a heterogeneous crust composed of gabbro and peridotite the along axis variations in melt supply lithospheric thickness and alteration of the lithosphere can result in a change of rheological structure and therefore in fault pattern as observed along the ridge axis identified detachment faults in the area provide a mechanism for the uplift of ultramafic rocks to the seafloor these detachments are not systematically associated with or formed at the inside corner of discontinuities as described elsewhere the origin and evolution of these structures is yet unconstrained but we suggest that they can be initiated at mechanical heterogeneities in the deep lithosphere and that once formed they localize strain due to the presence of weak serpentinites along the fault planes

bromide chloride fractionation in seafloor hydrothermal fluids from 9 10 n east pacific rise hydrothermal fluids collected from 9 10 n epr during 5 cruises between 1991 and 1994 were analyzed for br and cl the chlorinity of these fluids ranges between 32 6 and 860 mmol kg in comparison to local seawater values of 540 mmol kg these very low chlorinity fluids some with temperatures high enough to be within the vapor stability field were collected following a volcanic eruption in 1991 1 although fluids with chlorinities less than 250 mmol kg had been sampled once previously at axial volcano 2 the vent fluid chlorinities at 9 10 n epr were much lower than at axial volcano fluids with cl 250 mmol kg hadbr cl ratios identical to seawater in agreement with previous studies in contrast fluids with cl 250 mmol kg collected from this area hadbr cl ratios as much as 40 less than the seawater value bromide depletions observed in the low chlorinity fluids from 9 10 n epr were probably the result of fractionation of br from cl during subcritical phase separation this fractionation process appeared to be limited to fluids with cl 250 mmol kg and to require open system phase separation to produce vapors with cl 250 mmol kg at pressure and temperature conditions appropriate for 9 10 n epr requires conditions that are close to the critical point where the properties of the vapor and liquid phases are quite similar resulting in lack of fractionation in thebr cl ratio between the two phases

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

a modified method for estimating permeability of clayey soils based on piezocone sounding results a modified method for estimating permeability of clayey deposits in the horizontal direction kh based on piezocone sounding ucpt results is proposed most of the currently available methods rel

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

composition and origin of hydrothermal petroleum and associated lipids in the sulfide deposits of the rainbow field mid atlantic ridge at 36 n the lipid components in hydrothermal sulfide deposits from the rainbow vent field mid atlantic ridge at 36 n were studied by gas chromatography mass spectrometry the rainbow vent field is one of two known active hydrothermal systems related to abyssal circulation where high temperature fluids are formed during serpentinization of ultrabasic crustal rocks the major amount of the extractable organic matter from the sulfides consists of normal and branched alkanes ucm pahs terpenoids and fatty acids the branched alkanes are comprised of unique gem diethylalkane series possibly from sulfide oxidizing bacteria and biphytanes from archaea the characteristic lipid and biomarker compounds found in the hydrothermal samples support a predominantly biological origin of the bitumens from the thermal transformation of the biomass of microorganisms bacteria and archea and minor macrofauna of this vent field a search for molecular evidence for abiogenic thermocatalytic synthesis of organic compounds was negative however methane in the hydrothermal fluids and possibly a minor amount of the alkanes in the sulfides may be of an abiogenic origin in the rainbow vent field

solving the martian meteorite age conundrum using micro baddeleyite and launch generated zircon the age of the representative martian meteorite nwa 5298 is determined using spatially correlated electron beam nanostructural and uranium lead isotopic measurements of microminerals resolving a paradox of different age interpretations for the evolution of martian crust a few of the many meteorites that fall to earth are of martian origin the true age of these rare samples of the martian surface has been the subject of a decades long debate with interpreted ages differing by up to 4 billion years desmond moser and colleagues resolve this problem using a new approach to dating meteorite launch events through nanoscale investigation of crystal growth zoning and structures their analysis of the resistant micromineral baddeleyite and host igneous minerals in the highly shocked martian meteorite northwest africa 5298 reveals it as a crystallization product of martian volcanism of the past 400 million years previous estimates of a 4 billion year age of formation have actually dated a remnant signature of the ancient mantle melting event from which the magma was derived these findings confirm the presence of an ancient non convecting mantle beneath a relatively young volcanic martian crust invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites1 however the interpreted ages of the ejected igneous crust of mars differ by up to four billion years1 2 3 4 5 6 a conundrum7 due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and the ages of the impact events that launched debris towards earth here we solve the conundrum by combining in situ electron beam nanostructural analyses and u pb uranium lead isotopic measurements of the resistant micromineral baddeleyite zro2 and host igneous minerals in the highly shock metamorphosed shergottite northwest africa 5298 ref 8 which is a basaltic martian meteorite we establish that the micro baddeleyite grains pre date the launch event because they are shocked cogenetic with host igneous minerals and preserve primary igneous growth zoning the grains least affected by shock disturbance and which are rich in radiogenic pb date the basalt crystallization near the martian surface to 187 33 million years before present primitive non radiogenic pb isotope compositions of the host minerals common to most shergottites1 2 3 4 do not help us to date the meteorite instead indicating a magma source region that was fractionated more than four billion years ago9 10 11 12 to form a persistent reservoir so far unique to mars1 9 local impact melting during ejection from mars less than 22 2 million years ago caused the growth of unshocked launch generated zircon and the partial disturbance of baddeleyite dates we can thus confirm the presence of ancient non convecting mantle beneath young volcanic mars place an upper bound on the interplanetary travel time of the ejected martian crust and validate a new approach to the geochronology of the inner solar system

discordant k ar and young exposure dates for the windjana sandstone kimberley gale crater mars k ar and noble gas surface exposure age measurements were carried out on the windjana sandstone kimberley region gale crater mars by using the sample analysis at mars instrument on the curiosity rover the sandstone is unusually rich in sanidine as determined by chemin x ray diffraction contributing to the high k 2o concentration of 3 09 0 20 wt measured by alpha particle x ray spectrometer analysis a sandstone aliquot heated to 915 c yielded a k ar age of 627 50 ma reheating this aliquot yielded no additional ar a second aliquot heated in the same way yielded a much higher k ar age of 1710 110 ma these data suggest incomplete ar extraction from a rock with a k ar age older than 1710 ma incomplete extraction at 900 c is not surprising for a rock with a large fraction of k carried by ar retentive k feldspar likely variability in the exact temperature achieved by the sample from run to run uncertainties in sample mass estimation and possible mineral fractionation during transport and storage prior to analysis may contribute to these discrepant data cosmic ray exposure ages from 3he and 21 ne in the two aliquots are minimum values given the possibility of incomplete extraction however the general similarity between the 3he 57 49 and 18 32 ma mean 30 ma and 21 ne 2 32 and 83 24 ma mean 54 ma exposure ages provides no evidence for underextraction the implied erosion rate at the kimberley location is similar to that reported at the nearby yellowknife bay outcrop

hydrothermal petroleum genesis migration and deposition in guaymas basin gulf of california hydrothermal activity and seabed mounds have been explored in guaymas basin by the deep sea drilling project dsdp piston coring dredging and diving with the deep submersible research vessel dsrv alvin sedimentary organic matter derived primarily from immature degraded microbial detritus is easily converted to petroleum under the hydrothermal regime these petroleums are mature and migrate in the fluids and by diffusion to the seabed the fluid migration is aided by near critical aqueous solution and supercritical carbon dioxide and hydrocarbons petroleum compositions vary from condensates to naphthenic to waxy all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons pah the heavy ends condense at the seabed depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds the pah are high temperature resynthesis aromatiza

geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges abstract rare earth element data are reported for vent fluids collected from eight deep sea hydrothermal areas including samples from sediment hosted and bare rock hydrothermal systems the morb normalized ree patterns from these diverse settings are remarkably similar to each other but distinctly different than seawater or basalt being lree enriched and possessing a strikingly positive eu anomaly the ree concentrations making up these patterns vary widely however both on a spatial and temporal basis when plotted against ionic radii these fluid trends are remarkably linear and show the same fractionation patterns exhibited by plagioclase during magma segregation this analysis suggests that the partitioning of the ree between fluid and rock during high temperature hydrothermal alteration of morb is dominated by crystochemical exchange during dissolution and recrystallization reactions at the exposed surfaces of plagioclase phenocrysts a comparison of ree ionic radii in eight coordination indicate that the partitioning of 3ree and 2eu are dominated by chemical substitution for ca 2 and sr 2 respectively these considerations predict that the total 3ree content of vent fluid varies in a systematic way during the transition from an rich morb plagioclase to ab rich hydrothermal plagioclase and that these parameters can be used as indicators of the average extent of alteration inside active hydrothermal systems

the significance of the strain path analysis in the interpretation of piezocone dissipation data when a piezocone is driven into the ground pore water pressures are set up as a result of the stress changes the dissipation of these pore pressures occurs in the subsequent con solidation process in a manner dependent on the initial stress distribution as well as on the coefficient of consolidation the process of analysis therefore has two distinct components the first is to identify the appropriate total stress distribution caused by driving the piezocone which acts as the initial condition for the consolidation the second is to solve the consolidation problem itself this approach has been followed by levadoux baligh 1986 j geotech engng asce 112 no 7 707 726 baligh levadoux 1986 j geotech engng asce 112 no 7 727 745 and by houlsby teh 1988 penetration testing 1988 ed j de ruiter balkema amsterdam vol 2 pp 777 783 each of the two sets of authors uses the same consolidation theory for the second stage of the analysis and a strain path method to identify the

fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge abstract a geochemical investigation has been conducted of a suite of four sediment cores collected from directly beneath the hydrothermal plume at distances of 2 to 25 km from the rainbow hydrothermal field as well as a large biogenic component 80 caco3 these sediments record clear enrichments of the elements fe cu mn v p and as from hydrothermal plume fallout but only minor detrital background material systematic variations in the abundances of hydrothermal elements are observed at increasing distance from the vent site consistent with chemical evolution of the dispersing plume further pronounced ni and cr enrichments at specific levels within each of the two cores collected from closest to the vent site are indicative of discrete episodes of additional input of ultrabasic material at these two near field locations radiocarbon dating reveals mean holocene accumulation rates for all four cores of 2 7 to 3 7 cm kyr 1 with surface mixed layers 7 to 10 cm thick from which a history of deposition from the rainbow hydrothermal plume can be deduced deposition from the plume supplies elements to the underlying sediments that are either directly hydrothermally sourced e g fe mn cu or scavenged from seawater via the hydrothermal plume e g v p as holocene fluxes into to the cores surface mixed layers are presented which typically are an order of magnitude greater than background authigenic fluxes from the open north atlantic one core collected closest to the vent site indicates that both the concentration and flux of hydrothermally derived material increased significantly at some point between 8 and 12 14c kyr ago the preferred explanation is that this variation reflects the initiation intensification of hydrothermal venting at the rainbow hydrothermal field at this time perhaps linked to some specific tectonic event in this fault controlled hydrothermal setting

chemical characteristics of newly discovered black smoker fluids and associated hydrothermal plumes at the rodriguez triple junction central indian ridge abstract the chemical characteristics of hydrothermal fluids in the indian ocean have been revealed for the first time a hydrothermal field called the kairei field including active black smoker chimneys was discovered by rov kaiko dives at 25 19 17 s 70 02 40 e 2450 m depth on the southwestern flank of an off axis knoll located 15 miles north of the rodriguez triple junction central indian ridge after detailed tow yo surveys of the hydrothermal plume distribution the temperature of the fluid expelled from the most active chimney was almost stable 359 360 c throughout three successive days of fluid sampling the endmember fluid has a chemical composition similar to the hydrothermal fluids sampled from sediment starved mid ocean ridges in the pacific and the atlantic oceans suggesting typical interactions between hot fluid and mid ocean ridge basalts in the subseafloor reaction zone

a two step k ar experiment on mars dating the diagenetic formation of jarosite from amazonian groundwaters following k ar dating of a mudstone and a sandstone a third sample has been dated by the curiosity rover exploring gale crater the mojave 2 mudstone which contains relatively abundant jarosite yielded a young k ar bulk age of 2 57 0 39 ga 1 precision a two step heating experiment was implemented in an effort to resolve the k ar ages of primary and secondary mineralogical components within the sample this technique involves measurement of 40 ar released in low temperature 500 c and high temperature 930 c steps and a model of the potassium distribution within the mineralogical components of the sample using this method the high temperature step yields a k ar model age of 4 07 0 63 ga associated with detrital plagioclase compatible with the age obtained on the cumberland mudstone by curiosity the low temperature step associated with jarosite mixed with k bearing evaporites and or phyllosilicates gave a youthful k ar model age of 2 12 0 36 ga the interpretation of this result is complicated by the potential for argon loss after mineral formation comparison with the results on cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials correcting for plausible extents of argon loss is still less than 3 ga suggesting post 3 ga aqueous processes occurred in the sediments in gale crater such a result is inconsistent with k bearing mineral formation in gale lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on mars is thought to have largely ceased

crustal evolution of the mid atlantic ridge near the fifteen twenty fracture zone in the last 5 ma author posting american geophysical union 2003 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geochemistry geophysics geosystems 4 2003 1024 doi 10 1029 2002gc000364

the current martian cratering rate abstract the discovery of 248 dated impact sites known to have formed within the last few decades allows us to refine the current cratering rate and slope of the production function at mars we use a subset of 44 of these new craters that were imaged before and after impact by mars reconnaissance orbiter s context camera a thoroughly searched data set that minimizes biases from variable image resolutions we find the current impact rate is 1 65 10 6 craters with an effective diameter 3 9 m km2 yr with a differential slope power law exponent of 2 45 0 36 this results in model ages that are factors of three to five below the hartmann hartmann w k 2005 icarus 174 294 320 and neukum et al neukum g ivanov b a hartmann w k 2001 space sci rev 96 55 86 ivanov ivanov b a 2001 space sci rev 96 87 104 model production functions where they overlap in diameter the best fit production function we measure has a shallower slope than model functions at these sizes but model function slopes are within the statistical errors more than half of the impacts in this size range form clusters which is another reason to use caution when estimating surface ages using craters smaller than 50 m in diameter

geochemistry of north cleft segment vent fluids temporal changes in chlorinity and their possible relation to recent volcanism hydrothermal vent fluids from the north cleft segment of the juan de fuca ridge between 44 54 and 45 00 n were sampled in 1988 1990 1991 and 1992 in 1988 chloride depleted relative to seawater diffuse fluids with low dissolved metal concentrations relative to other mid ocean ridge mor fluids were sampled over a distance of 10 km along axis in 1990 and 1991 both high temperature 200 c and diffuse vents were consistently metal and chloride enriched the end member compositions of high temperature vents and nearby diffuse vents were very similar there were small but significant correlated changes in diffuse and high temperature composition from 1990 to 1991 the large scale but temporary venting of low chlorinity fluids over the entire north cleft segment provides a resolution to the apparent mass imbalance implied by observations of continuous venting of chloride enriched fluids it is possible that a volcanic event along the north cleft segment prior to 1987 for which there is firm geologic evidence initially caused a boiling event which resulted in the preferential venting of vapor enriched fluids through 1988 followed by a transition to brine enriched fluids by 1990 high iron low sodium and low sr ca ratios in the high chlorinity fluids suggest that the brine phase has continued to react and approach reequilibration with an alteration mineral assemblage after the phase separation event the absence of chloride depleted fluids from 1990 onward and the systematics of lithium boron and manganese with chloride in the high temperature fluids from north cleft suggest that the evolution toward lower chlorinity at monolith vent from 1990 to 1992 is caused by progressive dilution of a brine with hydrothermal seawater

an approach to evaluation of field cptu dissipation data in overconsolidated fine grained soils dissipation of excess pore pressures during piezocone testing in firm to stiff overconsolidated fine grained soils provides data curves that cannot be interpreted using published theoretical soluti

the early martian evolution constraints from basin formation ages impact basin formation ages give insight into the early evolution of a planet the martian basins hellas isidis and argyre provide an important time marker for the cessation of the magnetic dynamo and the crustal thickness distribution both established before 4 ga ago no martian surfaces are older than 4 15 ga based on crater count statistics and all are younger than the oldest lunar ones i show that the heavy bombardment period on the moon and mars evolved similarly but endogenic processes have removed the oldest martian basin record the basin forming projectile population appears to be different from the impactor population observed today in the inner solar system it is yet uncertain whether the heavy bombardment period is cataclysmic or characterized by the decaying flux of planetary formation

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

fault rotation and core complex formation significant processes in seafloor formation at slow spreading mid ocean ridges mid atlantic ridge 13 15 n 1 the region of the mid atlantic ridge mar between the fifteen twenty and marathon fracture zones displays the topographic characteristics of prevalent and vigorous tectonic extension normal faults show large amounts of rotation dome shaped corrugated detachment surfaces core complexes intersect the seafloor at the edge of the inner valley floor and extinct core complexes cover the seafloor off axis we have identified 45 potential core complexes in this region whose locations are scattered everywhere along two segments 13 and 15 n segments steep outward facing slopes suggest that the footwalls of many of the normal faults in these two segments have rotated by more than 30 the rotation occurs very close to the ridge axis as much as 20 within 5 km of the volcanic axis and is complete by 1 my producing distinctive linear ridges with roughly symmetrical slopes this morphology is very different from linear abyssal hill faults formed at the 14 n magmatic segment which display a smaller amount of rotation typically 15 we suggest that the severe rotation of faults is diagnostic of a region undergoing large amounts of tectonic extension on single faults if faults are long lived a dome shaped corrugated surface develops in front of the ridges and lower crustal and upper mantle rocks are exposed to form a core complex a single ridge segment can have several active core complexes some less than 25 km apart that are separated by swales we present two models for multiple core complex formation a continuous model in which a single detachment surface extends along axis to include all of the core complexes and swales and a discontinuous model in which local detachment faults form the core complexes and magmatic spreading forms the intervening swales either model can explain the observed morphology

monotonic and dilatory pore pressure decay during piezocone tests in clay during a pause in cone penetration in fine grained soils pore water pressure dissipation tests are performed to evaluate the coefficient of consolidation for standard piezocones with shoulder fil

geochemistry and morphology of metalliferous sediments and oxyhydroxides from the endeavour segment juan de fuca ridge abstract we present first data on the geochemistry mineralogy and morphology of near vent sediments 35 and 200 m from active vent and ridge flank sediments approximately 3 km from the vent field as well as oxyhydroxide deposits from the endeavour segment juan de fuca ridge the purpose of the study was to understand better the origin and characteristic features of metalliferous sediments associated with base and precious metal massive sulfides in volcanic terrains hydrothermal components in sediments are fe si s rich and mn fe si rich phases sulfides and barite which were exclusively derived from plume fallout sulfides are only a minor constituent of near vent sediments 2 4 wt and were not detected in ridge flank sediments the study suggests that the distribution of hydrothermal phases and associated elements in near vent and ridge flank sediments is affected mainly by processes of agglomeration dissolution absorption and settling that take place within a plume and to a lesser extent post depositional processes rapid deposition of sulfides in the vicinity of the vents is reflected in a sharp drop of the cu concentrations in sediments with increasing distance from the vents besides sulfides important carriers of pb cu zn and co in near vent sediments are fe mn oxyhydroxides that occur together with silica as aggregates of gel like material and flaky particles and as coatings on filaments away from the vents trace metals are mostly in fe mn oxyhydroxides and authigenic fe rich montmorillonite oxyhydroxides at the main endeavour field are interpreted to have originated from oxidation of mound sulfides accompanied by precipitation of primary fe oxyhydroxide silica from low temperature fluids at the mothra field seafloor deposits and chimney crusts composed of fe oxyhydroxide mn silica are considered to be direct precipitates from hydrothermal fluids that have been less diluted with seawater oxyhydroxide deposits exhibit unique microtextures that resemble mineralized microorganisms and may indicate existence of diverse microbial communities

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

the distribution of helium 3 in the deep western and southern indian ocean almost a decade after the geochemical ocean sections study indian expedition the new deep 3he data from the indigo program give a further insight into the distribution of this tracer in the indian ocean this distribution exhibits some major features related on one hand to a hydrothermal 3he input in the gulf of aden and on the mid indian ocean ridge and on the other to the origin of the water masses and to the characteristics of the deep circulation the main pattern is a significant north south 3he gradient with deep waters of the southern ocean showing 3he values around 8 9 due to the influence of the atlantic deep waters poor in 3he and relatively high values in the northern and central regions 15 to 18 between 2000 m and 3000 m depth originating from the hydrothermal activity in the easternmost part of the basin the 3he values exhibit a significant increase at shallower depths around 1000 m probably due to the pacific water flow through the indonesian sills whereas the data in the indian sector of the antarctic ocean show a maximum of the order of 10 south of the polar front interpreted as showing the presence of the pacific deep waters in the antarctic circumpolar current these different aspects are summarized by mapping the horizontal distribution of the 3he maxima all over the indian basin this map points out some characteristics of the deep circulation but also stresses the need for further measurements in order to clarify the description of this tracer in several key areas

geochemical controls on hydrothermal fluids from the kairei and edmond vent fields 23 25 s central indian ridge prior to 2000 no mid ocean ridge hydrothermal systems were identified and sampled in the indian ocean the kairei field central indian ridge was discovered and sampled in 2000 gamo et al 2001 hashimoto et al 2001 this paper reports the chemical composition of hydrothermal fluids collected in 2001 from both the kairei and newly discovered edmond hydrothermal systems data are used to infer subsurface processes and conditions at the two sites as well as to place them within the global context of known hydrothermal sites on the mid ocean ridge system while both sites are located on the intermediate spreading central indian ridge their hydrologic systems have affinities with those observed on slow spreading ridges although the compositions of fluids from the four individual vents sampled at edmond and the three individual vents sampled at kairei vary respectively our interpretation is that a single source fluid at each site is subsequently modified by processes including phase separation subsurface mixing with seawater and deposition and or remobilization of metal sulfide deposits to generate the observed range of compositions both fields are located 6 km from the neovolcanic zone on steps on the east wall of the axial valley with the edmond field 160 km north of kairei and almost 1000 m deeper 3300 versus 2450 m the edmond fluids are extremely hot with maximum measured temperatures of 382 c compared to 365 c for kairei all of the fluids sampled have chlorinities greater than local ambient seawater due to phase separation of seawater at supercritical conditions visual observations suggest both sites have been active for a substantial period of time again similar to observations of slow spreading ridges our chemical data suggest that the substrate underlying kairei is highly altered while that at edmond is not significant albitization appears to be occurring below the edmond field but not at kairei the edmond fluids are by far the hottest brines yet observed venting from a mid ocean ridge hydrothermal site resulting in unusually high concentrations of several transition metals

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

hydrothermal activity along the southwest indian ridge twenty years after the discovery of sea floor hot springs vast stretches of the global mid ocean ridge system remain unexplored for hydrothermal venting the southwest indian ridge is a particularly intriguing region as it is both the slowest spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the atlantic and pacific oceans2 a recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest spreading ridge sections thus impeding migration and enhancing faunal diversity2 here however we report evidence of hydrothermal plumes at six locations within two 200 km long sections of the southwest indian ridge indicating a higher frequency of venting than expected these results suggest that fluxes of heat and chemicals from slow spreading ridges may be greater than previously thought and that faunal migration along the southwest indian ridge may serve as an important corridor for gene flow between pacific and atlantic hydrothermal fields

characteristics and source of inorganic and organic compounds in the sediments from two hydrothermal fields of the central indian and mid atlantic ridges a combined inorganic and organic geochemical study was carried out on sediments collected from the kairei hydrothermal field on the central indian ridge cir and the logatchev hydrothermal field on the mid atlantic ridge mar analysis of the major and trace elements as well as the minerals shows that the kairei hydrothermal sediments are formed by the mixing of silica rich hydrothermal fluids with mg rich seawaters but the logatchev sediments are associated with pelagic carbonate oozes containing some precipitates derived from hydrothermal plume fall out the rare earth element ree patterns of kairei sediments show a character of light ree lree enrichment and positive eu anomaly whereas two of the three logatchev sediment samples lack positive eu anomaly and have negative ce anomaly patterns of aliphatic hydrocarbon fractions in the sediments from both hydrothermal fields exhibit high relative concentrations of volatile resolved components smooth n alkane distributions and high concentrations of the isoprenoids pristane and phytane the composition of organic matter and c isotope composition of individual n alkanes indicate that they come from marine photosynthetic autotrophs and hydrothermal organisms as well as terrestrial inputs in the kairei and the logatchev hydrothermal fields several parameters of organic geochemistry used for assessing the maturity of bitumen are well correlated with one another in general these parameters indicate that the kairei sediments are more mature than the logatchev sediments the relationship between the inorganic parameters ree fe and eu eu and the organic parameter bitumen maturity might reflect changes of the hydrothermal influence on the sediments the results of this study provide an insight into the variation of inorganic and organic geochemistry in deep sea hydrothermal systems

moon mars mercury basin formation ages and implications for the maximum surface age and the migration of gaseous planets abstract basin formation ages for moon mars and mercury are determined by cratering statistics compared and evaluated with respect to their maximum surface ages and available isotope ages and two possible solar system evolution models both mars and mercury appear to have undergone significant resurfacing so that at least the first 200 400 million years are not recorded on their surfaces basin frequency and crater frequencies below 150 km indicate that the moon has the oldest surface mercury has an intermediate age and mars has the youngest preserved terrain an offset between the basin size frequency distribution the smaller crater size frequency distribution and the main belt asteroid size frequency distribution is observed in all three cases suggesting an age difference of about 150 ma between basin and smaller crater distribution based ages i interpreted this in terms of lack of understanding of the basin formation process and suggest that one possible explanation for the apparently under representative basin frequency could be a different lower average impact velocity compatible with the nice flux model the basin formation pattern derived with the standard monotonically decaying or the sawtooth like nice model flux does not reveal a coherent picture according to the late heavy bombardment idea this is here attributed to an incomplete understanding of the cratering rate ratios between the planetary bodies considered here because of the moon s unique formation history i also suggest that it is questionable whether the moon is a suitable analogue for the formation evolution and cratering record of the other terrestrial bodies

chemistry of vent fluids and its implications for subsurface conditions at sea cliff hydrothermal field gorda ridge we report here the first compositional data for fluids from the sea cliff hydrothermal field northern gorda ridge collected in 2000 2002 and 2004 an unusual aspect of this site is its location 2 6 km east of the axis of spreading leading to speculation since its discovery in 1988 that this may be an older hydrothermal field as it occurs on crust that the spreading rate would predict to be 100 000 years old our results suggest this hydrothermal system is being driven by subsurface magma as evidenced by 1 elevated 3he heat ratios 2 relatively high concentrations of he and 3 chloride contents less than seawater in the hydrothermal fluids the measured fluid temperatures were 308 c but we infer they were 400 c at depth in spite of these elevated temperatures the fluids exiting from these vents are clear a consequence of extremely low transition metal concentrations we attribute the low transition metal contents to loss of these metals below the seafloor most likely as a result of the slightly elevated ph of the fluids neither the fluid compositions nor the setting provides evidence that buried sediments and or organic matter are responsible for raising the fluid ph our favored explanation for the elevated ph is that calcite deposited as a vein filling mineral at this site perhaps when it was closer to the axis and a hydrothermal downflow zone is currently being dissolved by the hydrothermal fluids this hypothesis is supported by our geochemical modeling results that suggest the fluids are close to saturation with calcite at in situ conditions elevated fluid ph is observed at a number of hydrothermal sites on the global mid ocean ridge system and the reason for this has not been well understood dissolution of previously deposited calcite may be a heretofore unrecognized mechanism that can explain these observations finally our data suggest the compositions of these fluids are unchanged from 2002 to 2004 and are consistent with water column observations first made at this site in 1985 we therefore interpret the sea cliff site to be another hydrothermal area marked by long term stability in fluid compositions and temperatures

limits in determining permeability from on the fly ucpt sounding limits are defined for the transition from partially drained to undrained penetration during ucpt testing these limits prescribe the range of cone metrics for which coefficient of permeability mag

intracellular and extracellular mineralization of a microbial community in the edmond deep sea vent field environment abstract microbial biomineralization in submarine hydrothermal environments provides an insight into the formation of vent microfossils and the interactions between microbes elements and minerals throughout the geological record here we investigate microbial biomineralization of a deep sea vent community in the edmond vent field and provide ultrastructural evidence for the formation of microfossils and biogenic iron rich minerals related to archaea and bacteria environmental scanning electron microscopy esem analysis shows that filamentous and spiral microbes are encrusted by a non crystalline silica matrix and minor amounts of iron oxides examination by transmission electron microscopy tem reveals acicular iron rich particles and aggregates that occur either intracellularly or extracellularly a culture independent molecular phylogenetic analysis demonstrates a diverse range of bacteria and archaea the majority of which are related to sulfur metabolism in the microbial mats both archaea and bacteria have undergone silicification in a similar manner to microorganisms in some terrestrial hot springs and indicating that silicification may be driven by silica supersaturation and polymerization formation mechanisms of intracellular and extracellular iron oxides associated with microbes are discussed these results enhance our understanding of microbial mineralization in extreme environments which may be widespread in the earth s modern and ancient hydrothermal vent fields

geochemistry of fluid phases and sediments relevance to hydrothermal circulation in middle valley odp legs 139 and 169 geochemical and isotopic studies of pore fluids and solid phases recovered from the dead dog and bent hill hydrothermal sites in middle valley ocean drilling program leg 169 have been compared with similar data obtained previously from these sites during ocean drilling program leg 139 although generally the hydrothermal systems reflect non steady state conditions the data allow an assessment of the history of the hydrothermal processes sediment k al ratios as well as the distribution of anhydrite in the sediments suggest that the dead dog hydrothermal field has been and still is active in contrast similar data in the bent hill hydrothermal field indicate a waning of hydrothermal activity pore fluid and hydrothermal vent data in the dead dog hydrothermal field are similar in nature to the data collected during odp leg 139 in the area of the bent hill sulfide deposit however the pore water data indicate that recent wholesale flushing of the sediment column with relatively unaltered seawater has obliterated a previous record of hydrothermal activity in the pore fluids data from the deepest part of hole 1035a in the bent hill locality show the presence of hydrothermal fluids at greater depths in this area this suggests the origin of the hydrothermal fluids found to be emanating from hole 1035f which constitutes one of the first man made hydrothermal vents in the middle valley hydrothermal system similarly corked hole 858g because of seal failures has acted as a hydrothermal vent with sulfide deposits forming inside the cork

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

an archaean heavy bombardment from a destabilized extension of the asteroid belt the late heavy bombardment lasted much longer than previously thought up to 1 7 billion years ago on earth with impacts on the moon and earth coming mostly from the e belt survivor hungaria asteroids the late heavy bombardment was a period of time generally put at about 4 1 billion to 3 8 billion years ago when the inner planets of the solar system were subjected to a high frequency barrage of asteroids this left its mark on the moon but on earth the craters quickly disappeared owing to tectonic processes and erosion in the first of two papers on the bombardment brandon johnson and jay melosh determine the properties of the asteroids by looking at spherule beds layers of debris ejected during the impacts the thickness of spherule layers is expected to vary according to the size of the impactor and the speed at which it hit earth this historical record of impacts indicates that the number of projectiles colliding with earth was substantially higher 3 5 billion years ago than it is today with a gradual decline in the number of strikes after the late heavy bombardment bottke et al modelled the evolution of an asteroid belt that extended farther towards mars than the present one they find that most of the impactors traced by the spherule beds probably originated in this e belt which was disrupted during migrations of some of the giant planets the barrage of comets and asteroids that produced many young lunar basins craters over 300 kilometres in diameter has frequently been called the late heavy bombardment1 lhb many assume the lhb ended about 3 7 to 3 8 billion years gyr ago with the formation of orientale basin2 3 evidence for lhb sized blasts on earth however extend into the archaean and early proterozoic eons in the form of impact spherule beds globally distributed ejecta layers created by chicxulub sized or larger cratering events4 at least seven spherule beds have been found that formed between 3 23 and 3 47 gyr ago four between 2 49 and 2 63 gyr ago and one between 1 7 and 2 1 gyr ago5 6 7 8 9 here we report that the lhb lasted much longer than previously thought with most late impactors coming from the e belt an extended and now largely extinct portion of the asteroid belt between 1 7 and 2 1 astronomical units from earth this region was destabilized by late giant planet migration10 11 12 13 e belt survivors now make up the high inclination hungaria asteroids14 15 scaling from the observed hungaria asteroids we find that e belt projectiles made about ten lunar basins between 3 7 and 4 1 gyr ago they also produced about 15 terrestrial basins between 2 5 and 3 7 gyr ago as well as around 70 and four chicxulub sized or larger craters on the earth and moon respectively between 1 7 and 3 7 gyr ago these rates reproduce impact spherule bed and lunar crater constraints

continuation of the hydrothermal fluid chemistry time series at tag and the effects of odp drilling new data are presented for major dissolved species in vent fluids from the tag hydrothermal mound on the mid atlantic ridge sampled in 1993 1994 and 1995 the latter two cruises bracket the drilling of the mound by the ocean drilling program in september november 1994 changes in venting patterns have been observed over this time period both before and after drilling however the major ion chemistry of venting fluids appears to be stable indicating that the drilling did not penetrate the primary plumbing system of the mound

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

hydrothermal pyrolysis of organic matter in guaymas basin i comparison of hydrocarbon distributions in subsurface sediments and seabed petroleums abstract the bitumens of a selection of subsurface sediments from guaymas basin gulf of california have been analyzed in order to assess the hydrothermal effects on the organic matter and to better delineate the processes influencing the generation deposition and alteration of the hydrothermal petroleums at the seabed although the thermally generated subsurface bitumens are generally rich in polar asphaltic materials as are the seabed oils the hydrocarbon transformations parallel the extent of hydrothermal alteration as reflected in the downcore mineralogy at dsdp sites 477 and 478 at site 477 a progressive change from n alkane to aromatic hydrocarbon dominated patterns in the high resolution gas chromatography resolvable fractions of the bitumens accompanies decreases in organic carbon and bitumen yields with depth these transformations are indicative of sequential hydrothermal alteration of the sediments with depth due to increasing temperature and or progressive passage of hydrothermal fluid through the sedimentary column the polycyclic aromatic hydrocarbon pah distributions undergo extensive transformations e g dealkylation consistent with hydrothermal alterations are dominant at depth and have the broadest range as thermal maturation indices the aliphatic and aromatic components of the seabed oils can be transported to the seabed independently as a result of their generation under different temperature or depth regimes and sequentially over time during pyrolysis the concentrations of the parent pah in the thermally altered subsurface bitumens are comparable to those in the seabed oils the differential dissolution of the more soluble aromatics and selective solidification condensation of the higher molecular weight pah out of the high temperature fluids exiting at the seabed chimneys result in aromatic distributions of the oils significantly skewed towards the larger components e g benzo ghi perylene relative to the subsurface bitumens comparison of the downcore hydrocarbon distributions with those in the seabed petroleums support the contention that the hydrothermal oils are mixtures of pyrolysates from different depths or thermal regimes and are significantly altered by differential solubilization during transport and at the seabed

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

interpretation of piezoball dissipation testing in clay full flow penetrometers such as the cylindrical t bar and spherical ball are now being used widely in soft seabed sediments due to their advantages of larger projected area and minimal correction for overburden pressure a ball penetrometer fitted with one or more pore pressure transducers piezoball is of special interest as it can provide information on the soil consolidation properties by means of dissipation tests although analytical and numerical solutions have been developed to evaluate the undrained resistance factor for the ball the absence of a similar theoretical basis has limited the use of piezoball dissipation testing this paper provides the results of numerical analyses undertaken to model the excess pore pressure field generated during penetration of a piezoball including its shaft and the decay of pore pressure during a subsequent dissipation test the analyses used a coupled large deformation finite element ldfe method incorporating the modified cam clay model the robustness and

geochemistry of shallow sediments in guaymas basin gulf of california hydrothermal gas and oil migration and effects of mineralogy offset of prograde hydrothermal alterations by retrograde reactions is evident in sediments from a piston core pc6 8 m long from the guaymas basin gulf of california geochemical and mineralogical analyses of sediments and pore fluids show superimposed geochemical signals that indicate currently active reactions are modifying previously formed secondary solids hydrothermal barite was formed in a previously active flow channel between 150 and 250 cm depth hydrothermal gypsum is presently dissolving at depths 780 cm below which hydrothermal fluid flow is channeled by a secondary dolomite layer thermal stress of organic matter generates hydrothermal gas and petroleum having wide ranges of compositions and maturities a significant amount of hydrothermally generated oil has been transported laterally through a porous debris flow approx 240 cm subbottom overwhelming the indigenous bituminous matter water soluble petroleum constituents have disseminated throughout the cored sediments from 400 to 700 cm depth the immature organic matter continues to experience thermally enhanced diagenesis and an even higher thermal stress has occurred at the bottom of the core enhanced bacterial degradation of organic matter has led to depletion of pore water sulfate and enrichment of ammonium nh4 in both pore fluid and sediment resulting in formation of nh4 bearing secondary clay minerals at depths below 780 cm

redefinition of the crater density and absolute age boundaries for the chronostratigraphic system of mars abstract for the boundaries of each chronostratigraphic epoch on mars we present systematically derived crater size frequencies based on crater counts of geologic referent surfaces and three proposed standard crater size frequency production distributions as defined by a a simple 2 power law b neukum and ivanov c hartmann in turn these crater count values are converted to model absolute ages based on the inferred cratering rate histories we present a new boundary definition for the late hesperian early amazonian transition our fitting of crater size frequency distributions to the chronostratigraphic record of mars permits the assignment of cumulative counts of craters down to 100 m 1 km 2 km 5 km and 16 km diameters to martian epochs due to differences in the standard crater size frequency production distributions a generalized crater density based definition to the chronostratigraphic system cannot be provided for the diameter range used for the boundary definitions the resulting model absolute age fits vary within 1 5 for a given set of production function and chronology model ages crater distributions translated to absolute ages utilizing different curve descriptions can result in absolute age differences exceeding 10

ketones in hydrothermal petroleums and sediment extracts from guaymas basin gulf of california the polar compound nso fractions of seabed petroleums and sediment extracts from the guaymas basin hydrothermal system have been analyzed by gas chromatography and gas chromatography mass spectrometry the oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolysates that have migrated to the seafloor by hydrothermal fluid circulation the downcore samples are representative of both thermally unaltered and thermally altered sediments the survey has revealed the presence of oxygenated compounds correlated with samples exhibiting a high degree of thermal maturity several homologous series of related ketone isomers are enriched in the interiors of the hydrothermal vent samples or in hydrothermally altered sequences of the downcore sediments dsdp holes 477 and 481a the n alkanones range in carbon number from c11 to c33 with a cmax from 14 to 23 distributions that are similar to those of the n alkanes the alkan 2 ones are usually in highest concentrations with lower amounts of 3 4 5 6 7 and higher alkanones and they exhibit no carbon number preference there is an odd carbon number preference of alkanones observed for downcore samples the alkanones are enriched in the interiors of the hydrothermal vent spires or in downcore hydrothermally altered sediments indicating an origin at depth or in the hydrothermal fluids and not from an external biogenic deposition minor amounts of c13 and c18 isoprenoid ketones are also present simulation of the natural hydrothermal alternation process by laboratory hydrous pyrolysis techniques provided information regarding the mode of alkanone formation hydrous pyrolysis of n c32h66 at 350 c for 72 h with water only or water with inorganic additives has been studied using a stainless steel reaction vessel in each experiment oxygenated hydrocarbons including alkanones were formed from the n alkane the product distributions indicate a reaction pathway consisting of n alkanes and olefins as primary cracking products with internal olefins and alkanones as secondary reaction products hydrous pyrolyses of messel shale spiked with molecular probes have been performed under similar time and temperature constraints to produce alkanone distributions like those found in the hydrothermal vent petroleums

hydrothermal petroleum at the seafloor and organic matter alteration in sediments of middle valley northern juan de fuca ridge abstract sediments from high heat flow areas of middle valley northern juan de fuca ridge contain traces of bitumens with insignificant amounts of thermogenic components and mainly lipid material which has experienced accelerated diagenesis these sediments have been exposed to mild hydrothermal conditions 50 120 c based on their bitumen compositions the hydrothermal bitumen in a barite alteration products the aliphatic fraction represents the mildly transformed and immature matter and the major polynuclear aromatic hydrocarbons are the high temperature constituents 300 c the 14c age of this bitumen is about 29 000 abp reflecting rapid organic carbon cycling

hydrothermal petroleum generation in red sea sediments from the kebrit and shaban deeps abstract petroleum impregnated sediments and massive sulfides have been found in two deeps of the northerns red sea biological marker distributions in extracts and polar fraction degradation products were analyzed in order to elucidate the source of the petroliferous material two organic phases could be distinguished according to their source and maturity the amounts of n alkanes show a marked decrease with depth whereas the concentrations of various branched and cyclic hydrocarbons increase resulting in a humpof unresolvable compounds in a depth as shallow as 300 cm changes in concentrations and distributions of hopanoids in the kebrit deep sediments indicate a rapid increase of maturity with depth the deepest core section 300 cm and the masive sulfide reveal comparable maturation indices typical for mature oils by chemical degradation of the polar fractions a series of c 40 isoprenoids was obtained which reveals a considerable contribution from methanogenic and thermophilic archapbacteria to the immature organic matter the data suggest that petroliferous material ofthermogenic origin migrates through the younger sequences superimposes the autochthonous organic substances in the sediments and furthermore forms asphaltic impregnations in the massive sulfides

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

a sawtooth like timeline for the first billion years of lunar bombardment abstract we revisit the early evolution of the moon s bombardment our work combines modeling based on plausible projectile sources and their dynamical decay rates with constraints from the lunar crater record radiometric ages of the youngest lunar basins and the abundance of highly siderophile elements in the lunar crust and mantle we deduce that the evolution of the impact flux did not decline exponentially over the first billion years of lunar history but also there was no prominent and narrow impact spike 3 9 gy ago unlike that typically envisioned in the lunar cataclysm scenario instead we show the timeline of the lunar bombardment has a sawtooth like profile with an uptick in the impact flux near 4 1 gy ago the impact flux at the beginning of this weaker cataclysm was 5 10 times higher than the immediately preceding period the nectaris basin should have been one of the first basins formed at the sawtooth we predict the bombardment rate since 4 1 gy ago declined slowly and adhered relatively close to classic crater chronology models neukum and ivanov 1994 overall we expect that the sawtooth event accounted for about one fourth of the total bombardment suffered by the moon since its formation consequently considering that 12 14 basins formed during the sawtooth event we expect that the net number of basins formed on the moon was 45 50 from our expected bombardment timeline we derived a new and improved lunar chronology suitable for use on pre nectarian surface units according to this chronology a significant portion of the oldest lunar cratered terrains has an age of 4 38 4 42 gyr moreover the largest lunar basin south pole aitken is older than 4 3 gy and therefore was not produced during the lunar cataclysm

confidence intervals for motion and deformation of the juan de fuca plate finite rotation parameters for 17 isochrons from anomalies 1 4a for the juan de fuca pacific plate pair are reported comparison of confidence intervals for plate rotations derived by different techniques indicates that a single plate misfit criterion significantly underestimates the confidence region defining the confidence interval by a threshold level of misfit determined by an f statistic gives similar results to the technique of bootstrap resampling for internally consistent data bootstrap resampling offers far greater robustness in the case of inconsistent data precision of about 1 km in the direction normal to isochrons is available for the younger anomalies this precision allows confident recognition of 2 5 km of eastward deformation of the pacific plate 50 100 km south of the active sovanco transform slight deformation of the northern juan de fuca plate adjacent to the nootka fault zone is also apparent east of the northern gorda ridge younger 3 ma anomalies do not show measurable deformation near the blanco fracture zone but older anomalies are up to 30 km east of their position predicted by rigid behavior of the juan de fuca plate reconstruction of the overlap geometry of past propagators shows no evidence that the extent of overlap has ever exceeded 70 km even with offset of 75 km in one case and 140 km in another new techniques for testing for intervals of constant plate motion require at least two changes in instantaneous motion at 99 confidence a clockwise change in motion direction at about 5 ma and an increase in the gradient of spreading rate since 2 ma two other changes in gradient since 5 ma are required at 95 confidence

the age of snc meteorites and the antiquity of the martian surface we report new sm nd lu hf and pb pb mineral and whole rock isotope data for the basaltic shergottite zagami as well as pb pb whole rock isotope data for the basaltic shergottite los angeles the lherzolitic shergottite dar al gani 476 dag 476 and the clinopyroxenite nakhla in agreement with previous findings our new sm nd and lu hf mineral ages on the martian meteorite zagami are young 155 and 185 ma respectively the 207pb 206pb 204pb 206pb compositions of the insoluble fractions of shergottites zagami los angeles and literature data for shergotty and eeta79001 form an excellent alignment indicative of a 4 0 ga crystallization age the range of pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial pb and argues against mixing relationships the age of 4 048 0 017 ga mswd 1 5 provided by the pb isotope compositions of the zagami whole rock and residues is therefore taken to date the crystallization of this rock which so far was believed to be only not vert similar 180 ma old based on this result we argue that the lithosphere of mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the martian surface this interpretation is consistent with photographic interpretations of erosional features on mars it also relieves the constraint imposed by the presence of anomalies of 142nd and 182w both products of extinct radioactive nuclides that the martian mantle should have preserved primordial isotopic heterogeneities thus allowing for the planet interior to be actively convecting

hydrothermal petroleum in the sediments of the andaman backarc basin indian ocean abstract recent sediments of the andaman backarc basin indian ocean between the andaman nicobar islands and the malay peninsula have been analyzed for biomarker lipids three cores were selected one each from the fault zone in a deep basin a graben between two fault systems another from a location adjacent to the fault and the third from the topographic high in the rift valley the molecular composition of the lipid classes n alkanes isoprenoids alkylbenzenes alkylcyclohexanes hopanoids polycyclic aromatic hydrocarbons steranes alcohols sterols and fatty acids was examined by gas chromatography gc and gc mass spectrometry to understand the nature and source of the hydrocarbons present and the processes of maturation of organic matter the data show that the hydrocarbons are of hydrothermal origin derived from thermal alteration of sedimentary organic matter consisting of a mixture predominantly of marine derived components with some terrestrial inputs normal alcohols and fatty acids also corroborate the distribution of n alkanes the distribution profiles and various parameters computed from the concentration of the target compounds suggest that oxidative reactions and microbial degradation in this environment are insignificant triterpane and pah compositions indicate that the thermal maturity of the bitumen in the samples is comparable to or lower than that found at other hydrothermal regions such as the northern juan de fuca ridge guaymas basin and escanaba trough

global resurfacing of mercury 4 0 4 1 billion years ago by heavy bombardment and volcanism analysis of craters on mercury s oldest most heavily cratered terrains shows that they were formed 4 0 4 1 billion years ago and that the planet s previous geological history was erased most probably by voluminous volcanism which may have been triggered by heavy asteroidal bombardment at that time the most heavily cratered terrains on mercury exhibit a lower density of craters smaller than about 100 km in diameter than on the moon a deficit that has been attributed to resurfacing by formation of ancient intercrater plains simone marchi et al used a crater areal density map based on data from the messenger spacecraft the colour coded foreground on cover with a global surface mosaic in the background to locate the oldest surfaces on mercury and interpret the crater populations in the framework of a recent lunar crater chronology they conclude that the oldest surfaces were emplaced just after the start of the late heavy bombardment 4 0 to 4 1 billion years ago the large impact basins not previously dated yield a similar surface age this agreement implies that resurfacing was global and due to volcanism perhaps aided by heavy bombardment as previously suggested the most heavily cratered terrains on mercury have been estimated to be about 4 billion years gyr old1 2 3 4 but this was based on images of only about 45 per cent of the surface even older regions could have existed in the unobserved portion these terrains have a lower density of craters less than 100 km in diameter than does the moon1 3 5 an observation attributed to preferential resurfacing on mercury here we report global crater statistics of mercury s most heavily cratered terrains on the entire surface applying a recent model for early lunar crater chronology6and an updated dynamical extrapolation to mercury7 we find that the oldest surfaces were emplaced just after the start of the late heavy bombardment lhb about 4 0 4 1 gyr ago mercury s global record of large impact basins8 which has hitherto not been dated yields a similar surface age this agreement implies that resurfacing was global and was due to volcanism as previously suggested1 5 this activity ended during the tail of the lhb within about 300 400 million years after the emplacement of the oldest terrains on mercury these findings suggest that persistent volcanism could have been aided by the surge of basin scale impacts during this bombardment

hydrothermal petroleum of lake chapala citala rift western mexico bitumen compositions from source sediments and application of hydrous pyrolysis hydrothermal simulation experiments were performed with contemporary sediments from lake chapala to assess the source of the lake tars the precursor product relationships of the organic compounds were determined for the source sediments and their hydrous pyrolysis products the pyrolysis products contained major unresolved complex mixtures of branched and cyclic hydrocarbons low amounts of n alkanes dinosterane gammacerane and immature and mature hopane biomarkers derived from lacustrine biomass sources the results support the proposal that the tar manifestations in the lake are not biodegraded petroleum but were hydrothermally generated from lacustrine organic matter at temperatures not exceeding about 250 c over brief geological times

ultramafic and gabbroic exposures at the mid atlantic ridge geological mapping in the 15 n region abstract the outcrops of mantle derived ultramafic rocks in the 15 n region are the most extensive yet reported for the mid atlantic ridge north of the fifteen twenty fracture zone these outcrops form a belt at least 20 km long along the west wall of the axial valley and also crop out on the east axial valley wall ultramafic rocks also crop out extensively south of the fifteen twenty fracture zone based on dredging and on a morphological analysis of the bathymetric map we propose that ultramafic outcrops may be common in the crust formed between 14 30 n and 15 50 n during at least the past 2 4 m y moderately dipping fault planes and large expanses of tectonic breccia have been observed during dives on the ultramafic outcrops diving observations also show that the ultramafic rocks are capped in stratigraphic contact by a thin layer of basalt this suggests that these rocks were tectonically emplaced at the axial seafloor or very close to it then uplifted in the footwall of the faults that bound the axial valley the occurrence of ultramafic rocks on both walls of the axial valley may be due to frequent changes of faulting polarity in the axial region instead of one master shear zone there would be a complex array of cross cutting conjugate faults and shear zones that could jump inward in the axial domain as spreading proceeds

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

estimating hydraulic conductivity from piezocone soundings a method for estimating the hydraulic conductivity of soils from piezocone penetration tests is suggested in this paper by invoking darcy s law over the finite time required for an increment of cone penetration it is argued that there will be some water movement through the soil around the cone albeit very small if the soil is very fine grained based on this argument and noting the comprehensive test data collected previously by elsworth lee a bi linear relation between the dimensionless piezocone sounding metric bqqt and the dimensionless hydraulic conductivity index kd plotted on double logarithmic scales has been proposed for soils ranging from sands to clays it is demonstrated that these revised relationships can be used to evaluate plausible values of hydraulic conductivity from piezocone sounding records taken at two different clay soil sites in saga and yokohama japan the major significance of this work is in extending the range of application of the method first proposed by elsworth l

hydrothermally derived petroleum examples from guaymas basin gulf of california and escanaba trough northeast pacific ocean petroleum is associated with sulfide rich sediment at two active oceanic spreading axes in the northeast pacific ocean in the guaymas basin a spreading axis in the gulf of california petroleum having a wide range of compositions forms by hydrothermal alteration of organic matter in quaternary sediment composed mainly of marine diatomaceous ooze and muddy turbidites in escanaba trough at the southern end of the gorda ridge spreading axis offshore northern california petroleum is formed by hydrothermal processes acting on mainly terrigenous organic material in quaternary turbiditic river derived sediment comparisons of the distributions of hydrocarbons n alkanes isoprenoids terpanes steranes and aromatics show that chemical differences among four petroleum samp es are such that two samples from guaymas basin can be distinguished from two samples from escanaba trough distinguishing characteristics resulting from differences in sources include n alkane distributions and certain sterane ratios distinguishing characteristics resulting from differences in thermal histories of the organic matter include hopane and sterane epimer ratios and various distributions of polycyclic aromatic hydrocarbons these oils differ from conventionally derived petroleum in that they are admixtures of products generated over a wide range of thermal regimes and their generation expulsion and migration occurred simultaneously over an instantaneous geological time period the potential economic significance of hydrothermally derived petroleum is uncertain but the act that petroleum can form at active oceanic spreading axes adds a new facet to understanding the processes of petroleum generation expulsion and migration

the timeline of the lunar bombardment revisited abstract the timeline of the lunar bombardment in the first gy of solar system history remains unclear basin forming impacts e g imbrium orientale occurred 3 9 3 7 gy ago i e 600 800 my after the formation of the moon itself many other basins formed before imbrium but their exact ages are not precisely known there is an intense debate between two possible interpretations of the data in the cataclysm scenario there was a surge in the impact rate approximately at the time of imbrium formation while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail end here we revisit the work of morbidelli et al 2012 that examined which scenario could be compatible with both the lunar crater record in the 3 4 gy period and the abundance of highly siderophile elements hse in the lunar mantle we use updated numerical simulations of the fluxes of asteroids comets and planetesimals leftover from the planet formation process under the traditional assumption that the hses track the total amount of material accreted by the moon since its formation we conclude that only the cataclysm scenario can explain the data the cataclysm should have started 3 95 gy ago however we also consider the possibility that hses are sequestered from the mantle of a planet during magma ocean crystallization due to iron sulfide exsolution o neil 1991 rubie et al 2016 we show that this is likely true also for the moon if mantle overturn is taken into account based on the hypothesis that the lunar magma ocean crystallized about 100 150 my after moon formation elkins tanton et al 2011 and therefore that hses accumulated in the lunar mantle only after this timespan we show that the bombardment in the 3 4 gy period can be explained in the accretion tail scenario this hypothesis would also explain why the moon appears so depleted in hses relative to the earth we also extend our analysis of the cataclysm and accretion tail scenarios to the case of mars the accretion tail scenario requires a global resurfacing event on mars 4 4 gy ago possibly associated with the formation of the borealis basin and it is consistent with the hse budget of the planet moreover it implies that the noachian and pre noachian terrains are 200 my older than usually considered

a pb isotopic resolution to the martian meteorite age paradox abstract determining the chronology and quantifying various geochemical reservoirs on planetary bodies is fundamental to understanding planetary accretion differentiation and global mass transfer the pb isotope compositions of individual minerals in the martian meteorite chassigny have been measured by secondary ion mass spectrometry sims these measurements indicate that chassigny has mixed with a martian reservoir that evolved with a long term 238u 204pb value two times higher than those inferred from studies of all other martian meteorites except 4 428 ga clasts in nwa7533 any significant mixing between this and an unradiogenic reservoir produces ambiguous trends in pb isotope variation diagrams the trend defined by our new chassigny data can be used to calculate a crystallization age for chassigny of 4 526 0 027 ga 2 that is clearly in error as it conflicts with all other isotope systems which yield a widely accepted age of 1 39 ga similar trends have also been observed in the shergottites and have been used to calculate a 4 ga age or alternatively attributed to terrestrial contamination our new chassigny data however argue that the radiogenic component is martian mixing occurred on the surface of mars and is therefore likely present in virtually every martian meteorite the presence of this radiogenic reservoir on mars resolves the paradox between pb isotope data and all other radiogenic isotope systems in martian meteorites importantly chassigny and the shergottites are likely derived from the northern hemisphere of mars while nwa 7533 originated from the southern hemisphere implying that the u rich reservoir which most likely represents some form of crust must be widespread the significant age difference between snc meteorites and nwa 7533 is also consistent with an absence of tectonic recycling throughout martian history

chemical and mineralogical influences on concentrations of trace metals in hydrothermal fluids abstract concentrations of trace metals in hydrothermal solutions from the southern juan de fuca ridge sjfr and the tag hydrothermal field on the mid atlantic ridge are influenced by the combined effects of source rock composition brine seawater mixing and complex interplay among various metals and minerals deposited and remineralized in vent mounds and chimneys copper mo and co show predicted sharp decreases in concentration for vent fluids as temperatures decrease below 350 c however concentrations of cu in 363 c fluids at the tag site are well above values determined from seawater basalt interactions due to subseafloor refining processes and remineralization of chalcopyrite concentrations of zn cd pb as and ga do not show any temperature dependence between 214 to 363 c however zn values do correlate well with cl on an area by area basis due to subseafloor mixing of brine with altered seawater zinc levels also correlate well with concentrations of cd pb and as for all vent fluid samples as well as with basalt and zn rich sulfides implying some continuity in behavior from source rock to vent fluid to sulfide minerals gallium values correlate with zn and cl levels for the sjfr but are high relative to zn at the tag site due to subseafloor refining processes concentrations of tl follow cl k and rb consistent with the behavior predicted for tl overall the cl and zn rich fluids from the sjfr are characteristic of a brine dominated system formed during recent volcanism in contrast high temperature fluids from the tag area are representative of a system that has evolved over the past 100 000 yr with high concentrations of cu co and ga that result from higher temperatures and complex refining processes within a large vent mound

petroleum associated with polymetallic sulfide in sediment from gorda ridge a sediment sample impregnated with asphaltic petroleum and polymetallic sulfide was dredged from the southern end of gorda ridge the escanaba trough off northern california within the offshore exclusive economic zone of the united states the molecular distributions of hydrocarbons in this petroleum show that it was probably derived from terrestrial organic matter in turbidite sediment filling the escanaba trough hydrothermal activity at the gorda ridge spreading center provided the heat for petroleum formation and was the source of fluids for sulfide mineralization

geochemistry of a hydrothermal sediment core from the obs vent field 21 n east pacific rise abstract we report a geochemical investigation of near vent hydrothermal sediment from the east pacific rise collected in a short 11 cm core by submersible from the obs vent site at 21 n the sediment has high concentrations of fe 23 25 cu 10 22 zn 4 13 and s 22 30 but low mn concentrations 108 279 ppm indicating a much fresher sulfidic input than in previously reported near vent sediments from the mid atlantic ridge further studies are required to fully characterise near field hydrothermal sediments but the data in this study allow the first comparisons with similar near vent material collected previously from the mid atlantic ridge as well as ridge flank data from the epr and juan de fuca ridge compared to ridge flank sediments the near field sediments exhibit high ratios of fe mn cu fe and zn fe unlike cu and zn pb is not so significantly enriched pb isotope compositions are indistinguishable from local morb indicating a dominant hydrothermal source for this element in these sediments this may not necessarily be the case for ridge flank sediments however where scavenging from seawater may also be important ree distributions throughout the core exhibit low concentrations and characteristics typical of vent fluids with lree enrichments and pronounced positive eu anomalies these patterns are similar to those of relatively fresh sulfides but there is also evidence for progressive oxidation downward into the core by ingressing seawater

hydrothermal alteration of organic matter in sediments of the northeastern pacific ocean part 1 middle valley juan de fuca ridge samples from the ocean drilling program leg 169 in middle valley ne pacific ocean were analyzed to study maturation by accelerated diagenesis and catagenesis of the sedimentary organic matter to hydrothermal petroleum some data from site 858 in middle valley leg 139 are also discussed for completeness sediments at sites 858 and 1036 in middle valley were altered either by the full variety of high temperature fluids which generated hydrothermal petroleum or by accelerated thermal diagenesis of the immature organic matter in situ without specific migration of those petroleum bitumen products the hydrothermal petroleums from the deeper sediments have migrated and accumulated in discrete intervals at shallower depths within a contemporary temperature window of 60 135 c at both of these sites maturation for the n alkanes proceeded from high cpi values immature to 1 0 mature i e strong even c number preference due to their low toc contents these sediments did not generate high amounts of hydrocarbons from the kerogen and thus revealed this unique even c number preference furthermore the significant content of terrestrial organic matter yielded petroleums low in gas and volatiles biomarkers were converted from the biological natural product precursors to the geological derivatives with maturities reflecting the thermal stress high temperature alteration also yielded polynuclear aromatic hydrocarbons

hydrothermal alteration of organic matter in sediments of the northeastern pacific ocean part 2 escanaba trough gorda ridge samples from the ocean drilling program leg 169 in escanaba trough gorda ridge ne pacific ocean were analyzed to study maturation by accelerated diagenesis and or by catagenesis of the sedimentary organic matter to hydrothermal petroleum at site 1038 the hydrothermal petroleums have migrated after generation to shallower horizons the n alkane maturation was indicated by the strong even c number preference i e cpi 1 0 as in the case of middle valley all samples contained admixed organic matter of terrigenous and marine components as indicated by the distributions of the biomarkers the biological precursors were catagenetically altered to their equivalent mature compounds the presence of high molecular weight pahs in some sediment sections at site 1038 reflected the high temperature alteration and reworking of organic matter into mature hydrothermal petroleum at site 1037 the reference hole in the escanaba trough the n alkanes with a strong predominance of odd c number homologs reflected immature non marine lipid components essentially throughout the hole maturation of organic matter was only observed below 450 mbsf with n alkanes showing a cpi 1 0 the strong even c number predominance in those intervals was attributed to initial maturation by high heat flow during the early rifting process

estimating coefficient of consolidation from piezocone tests data have been reviewed from sites in europe and north and south america as well as published data from south africa the review has concentrated on dissipation data from piezocone tests cptu to

chronology geochemistry and petrology of a ferroan noritic anorthosite clast from descartes breccia 67215 clues to the age origin structure and impact history of the lunar crust the petrology major and trace element geochemistry and nd ar sr isotopic compositions of a ferroan noritic anorthosite clast from lunar breccia 67215 have been studied in order to improve our understanding of the composition age structure and impact history of the lunar crust the clast designated 67215c has an unusually well preserved igneous texture mineral compositions are consistent with classification of 67215c as a member of the ferroan anorthositic suite of lunar highlands rocks but the texture and mineralogy show that it cooled more rapidly and at shallower depths than did more typical ferroan anorthosites fans incompatible trace element concentrations are enriched in 67215c relative to typical fans but diagnostic signatures such as ti sm sc sm plagiophile element ratios and the lack of zr hf and nb ta fractionation show that this cannot be due to the addition of kreep alternatively 67215c may contain a greater fraction of trapped liquid than is commonly present in lunar fans 147sm 143nd isotopic compositions of mineral separates from 67215c define an isochron age of 4 40 0 11 gyr with a near chondritic initial 143nd of 0 85 0 53 the 40ar 39ar composition of plagioclase from this clast records a post crystallization thermal event at 3 93 0 08 gyr with the greatest contribution to the uncertainty in this age deriving from a poorly constrained correction for lunar atmosphere 40ar rb sr isotopic compositions are disturbed probably by the same event recorded by the ar isotopic compositions trace element compositions of fans are consistent with crystallization from a moderately evolved magma ocean and do not support a highly depleted source composition such as that implied by the positive initial 143nd of the ferroan noritic anorthosite 62236 alternatively the nd isotopic systematics of lunar fans may have been subject to variable degrees of modification by impact metamorphism with the plagioclase fraction being more strongly affected than the mafic phases 147sm 143nd isotopic compositions of mafic fractions from the 4 ferroan noritic anorthosites for which isotopic data exist 60025 62236 67016c 67215c define an age of 4 46 0 04 gyr which may provide a robust estimate for the crystallization age of lunar ferroan anorthosites

mineralogy and geochemistry of hydrothermal sediments from the serpentinite hosted saldanha hydrothermal field 36 34 n 33 26 w at mar abstract the saldanha hydrothermal field is located at the top of a serpentinized massif mount saldanha ms at a non transform offset nto5 along the mid atlantic ridge mar south of the azores it is one of the rare known sites on a worldwide basis where direct evidence of low temperature 7 9 c hydrothermal activity has been provided by direct observation of hydrothermal fluid venting through small orifices in the ocean floor sedimentary cover this study focuses on the mineralogy and geochemistry of 14 sediment cores collected at ms for comparison four samples collected at the rainbow site nto6 were also studied mount saldanha hydrothermal sediments are highly diluted within a dominant foraminiferal nanofossiliferous ooze with small fragments of underlying rocks the mineral assemblage of the hydrothermal component is characterized by sulphides nontronite smectites poorly crystallized mn oxyhydroxides and amorphous material cu zn and fe sulphides mn mg oxy hydroxides and putative manganobrucite were also identified in one sample collected at an orifice vent in this sample micro chimneys conduits composed of isocubanite and sphalerite were also identified mount saldanha sediments show a clear enrichment in elements such as mn mg fe cu p and v derived from hydrothermal fluids and ni cr and co derived from ultramafic rocks the geochemical data together with the observed mineral assemblage suggest that the hydrothermal fluids are at a higher temperature than those measured at the escape orifices 7 9 c and a strong enrichment in mg mainly at the top of the mount agrees with extensive mixing of the hydrothermal fluid with unmodified seawater nevertheless the mineral assemblage of ms sediments is consistent with the precipitation from hydrothermal fluids at much lower temperatures than at rainbow the presence of serpentinized and steatitized talcshist ultramafic rocks and the occurrence of a strong methane anomaly within the overlying water column collectively suggest that the hydrothermal circulation at ms is driven by exothermic reactions closely associated with the serpentinization process rainbow sediments have a higher concentration in transition metals and consequently an enrichment in sulphides these differences are likely to be a consequence of the higher temperature of hydrothermal fluids reflected in the composition of hydrothermal solutions and of a stronger hydrothermal flux at the rainbow site

the rainbow vent fluids 36 14 n mar the influence of ultramafic rocks and phase separation on trace metal content in mid atlantic ridge hydrothermal fluids fluids were collected from the rainbow vent field 36 14 n on the mid atlantic ridge mar during the 1997 diving flores cruise this vent field in ultramafic rocks at a depth of 2300 m is composed of 10 black smokers emitting acidic ph 2 8 fluids at 365 c the low ph of the hot temperature rainbow fluids likely results from seawater ultramafic rock interaction that releases h ions into reducing hydrothermal fluids fluid chemistry is strongly influenced by phase separation generating cl rich brines clem 750 mm strongly enriched with mn fe co ni cu zn ag cd cs pb y and rare earth elements ree ree and transition metal abundance particularly fe and mn in the rainbow fluids is dramatically higher than in other mar fluids the abundance of trace element and ree enrichment is due to the greater solubility of these elements that is strongly favored by cl complexation at low ph and high temperature conditions chondrite normalized ree patterns show strong lree enrichment with evidence of the typical eu anomaly this ree partitioning suggests that either 1 ultramafic rocks represent only a part of rocks leached during hydrothermal alteration and or 2 that the unique rainbow fluid temperature ph and redox state issued from the ultramafic character of leached substratum can produce unique ree partitioning

source characteristics of marine oils as indicated by carbon isotopic ratios of volatile hydrocarbons carbon isotopic ratios of volatile hydrocarbon fractions of marine oils are diagnostic of organic facies and depositional environments of source rocks for carbonate oils low molecular weight volatile hydrocarbons c9 are isotopically lighter than high molecular weight volatile hydrocarbons c9 c17 in contrast for deltaic oils low molecular weight volatile hydrocarbons are isotopically heavier than high molecular weight volatile hydrocarbons marine shale oils show patterns intermediate between carbonate and deltaic oils this relative variation of carbon isotopic ratios among volatile hydrocarbons of oils is explained by earlier expulsion of marine oils derived from isotopically homogeneous algal bacterial kerogens in rich so rce rocks and secondary cracking of petroleum prior to expulsion for marine oils derived from isotopically heterogeneous terrestrial kerogens in lean source rocks in basins with multiple source rocks carbon isotopic ratios of volatile hydrocarbons are useful for determining oil oil correlation and for inferring oil source rock relationship