nebular thermal evolution and the properties of primitive planetary materials models of the solar nebula are constructed to investigate the hypothesis that surviving planetary objects began to form as the nebula cooled from an early hot epoch the imprint of such an epoch might be retained in the spatial distribution of planetary material the systematic deviations of its elemental composition from that of the sun chemical indicators of primordial oxidation state and variations in oxygen and other isotopic compositions our method of investigation is to calculate the time dependent two dimensional temperature distributions within model nebulas of prescribed dynamical evolution and to deduce the consequences of the calculated thermal histories for coagulated solid material the models are defined by parameters which characterize nebular initial states mass and angular momentum mass accretion histories and coagulation rates and efficiencies it is demonstrated that coagulation during the cooling of the nebula from a hot state is expected to produce systematic heterogeneities which affect the chemical and isotopic compositions of planetary material the radial thermal gradient at the midplane results in delayed coagulation of the more volatile elements vertical thermal gradients isolate the most refractory material and concentrate evaporated heavy elements in the gas phase it is concluded that these effects could be responsible for the distribution of terrestrial planetary masses the systematic depletion patterns of the moderately volatile elements in chondritic meteorites and the earth the range of oxygen isotopic compositions exhibited by calcium aluminum rich inclusions cais and other refractory inclusions and some geochemical evidence for a moderately enhanced oxidation state however nebular fractionations on a global scale are unlikely to account for the more oxidizing conditions inferred for some cais and chondritic silicates which require dust enhancements greater than a few hundred this conclusion along with the well established evidence from studies of chondrules and cais for thermal excursions of short duration make it likely that local environments unrelated to nebular thermal evolution were also important

bulk chondrite variability in mass independent magnesium isotope compositions implications for initial solar system 26al 27al and the timing of terrestrial accretion abstract we have determined 26 mgdsm 3 the mass independent variations in 26mg 24mg of primitive bulk meteorites to precisions better than 3 ppm 2se our measurements of samples from 10 different chondrite groups show 26 mgdsm 3 that vary from 5 to 22 ppm our data define an array with a positive slope in a plot of 26 mgdsm 3 against 27al 24mg which can be used to determine 26al 27al 0 i e initial 26al 27al and 26 mgdsm 3 0 i e initial 26 mgdsm 3 on such an isochron plot the best fit of our new measurements combined with literature data implies 26al 27al 0 of 4 67 0 78 10 5 and 26 mgdsm 3 0 of 31 6 5 7 ppm 2se for ordinary and carbonaceous chondrites other than cr chondrites which have anomalously low 26 mgdsm 3 these parameters are within uncertainty of those defined by previous measurements of bulk calcium aluminium rich inclusions cais that set canonical 26al 27al 0 5 10 5 the most straightforward interpretation of all these observations is that differences in the al mg of bulk ordinary and carbonaceous chondrites are dominantly controlled by variable contributions of early formed refractory and major silicate components derived from a common canonical reservoir the 26 mgdsm 3 of enstatite chondrites are slightly more radiogenic 3 ppm at similar al mg to the ordinary chondrites we speculate that this is related to the timing of removal of a refractory component from the source reservoirs of these different meteorite groups the higher 26 mgdsm 3 of the enstatite chondrites suggests later 0 5 ma post cais condensation and loss of this refractory component despite inferred consistency of 26al 27al 0 and 26 mgdsm 3 0 across most chondrite groups some nebular heterogeneity is required to account for the compositions of cr chondrites our preferred interpretation is that the cr source region has lower 26 mgdsm 3 0 as the most appropriate isotopic reference for the earth our new mean enstatite chondrite composition allows us to assess possible ingrowth of 26mg from live 26al during accretion of the earth the earth has 26 mgdsm 3 within uncertainty of enstatite chondrites despite its higher al mg this requires that the terrestrial increase in al mg which we attribute to vapour loss during accretion must have happened 1 5 ma post cai formation in an instantaneous fractionation model

in situ benthic fluxes from an intermittently active mud volcano at the costa rica convergent margin along the erosive convergent margin off costa rica a large number of mound shaped structures exist built by mud diapirism or mud volcanism one of these mound 12 an intermittently active mud volcano currently emits large amounts of aqueous dissolved species and water chemosynthetic vent communities authigenic carbonates and methane plumes in the water column are manifestations of that activity benthic flux measurements were obtained by a video guided benthic chamber lander bcl deployed at a vent site located in the most active part of mound 12 the lander was equipped with 4 independent chambers covering adjacent areas of the seafloor benthic fluxes were recorded by repeated sampling of the enclosed bottom waters while the underlying surface sediments were recovered with the lander after a deployment time of one day one of the chambers was placed directly in the centre of an active vent marked by the occurrence of a bacterial mat while the other chambers were located at the fringe of the same vent system at a lateral distance of only 40 cm a transport reaction model was developed and applied to describe the concentration profiles in the pore water of the recovered surface sediments and the temporal evolution of the enclosed bottom water repeated model runs revealed that the best fit to the pore water and benthic chamber data is obtained with a flow velocity of 10 cm yr 1 at the centre of the vent the flux rates to the bottom water are strongly modified by the benthic turnover benthic filter the methane flux from below at the bacterial mat site is as high as 1032 mol cm 2 yr 1 out of which 588 mol cm 2 yr 1 is oxidised in the surface sediments by microbial consortia using sulphate as terminal electron acceptor and 440 mol cm 2 yr 1 are seeping into the overlaying bottom water sulphide is transported to the surface by ascending fluids 238 mol cm 2 yr 1 and is formed within the surface sediment by the anaerobic oxidation of methane aom 588 mol cm 2 yr 1 however sulphide is not released into the bottom water but completely oxidized by oxygen and nitrate at the sediment water interface the oxygen and nitrate fluxes into the sediment are high 781 and 700 mol cm 2 yr 1 respectively and are mainly driven by the microbial oxidation of sulphide benthic fluxes were much lower in the other chambers placed in the fringe of the vent system thus methane and oxygen fluxes of only 28 and 89 mol cm 2 yr 1 respectively were recorded in one of these chambers our study shows that the aerobic oxidation of methane is much less efficient than the anaerobic oxidation of methane so that methane which is not oxidized within the sediment by aom is almost completely released into the bottom water hence anaerobic rather than aerobic methane oxidation plays the major role in the regulation of benthic methane fluxes moreover we demonstrate that methane and oxygen fluxes at cold vent sites may vary up to 3 orders of magnitude over a lateral distance of only 40 cm indicating an extreme focussing of fluid flow and methane release at the seafloor

sediment transport over an accretional intertidal flat with influences of reclamation jiangsu coast china this paper focuses on the hydrodynamic and suspended sediment transport processes in response to sequential reclamations over the intertidal flat jiangsu coast which used to be one of the widest intertidal flats in china investigations into the sediment transport patterns reveal that net suspended sediment fluxes increased from 102 kg m 1 on the upper intertidal flat to 103 4 kg m 1 on the lower intertidal flat per tidal cycle this variation was caused mainly by the phases of the current velocity suspended sediment concentration ssc local bed geomorphology inundation patterns and extreme weather conditions the longshore component of tidal currents intensifies seaward over the intertidal flat extreme weather conditions e g storms and strong winds were important factors affecting the current velocity structures the intensity of residual currents and the sscs the sscs were characterized by several peaks throughout the tidal cycle these peaks were associated with strong currents combined wave current interactions and intense turbulences due to the initial flood surge furthermore the suspended sediment was finer and contained more clay materials during the flood phase of the tidal cycle than during the ebb fine particles were transported within the upper water column by landward residual currents but coarse particles were transported within the lower water column by seaward residual currents overall residual currents were apt to transport fine grained sediment landward and coarse grained sediment seaward this pattern indicates that the suspended sediment fluxes are highly variable in the water column even for very shallow tidal environments the cross shore component accounted only for a small percentage of the total sediment flux however this part of sediment supply dominated accretion over the intertidal flat the intertidal flat has become narrower and steeper following sequential reclamations a negative feedback process existed to maintain the convex profile shape although the human activities i e reclamation could have modified the natural process the surficial sediment tended to become finer on the mid upper intertidal flat but coarser on the lower intertidal flat following reclamations in response to a reduction in the tidal currents over the intertidal zone and enhancement of wave action over the lower intertidal flat accretion with high rates was maintained by landward transport of sediment in such an accretional system with influences of reclamation the width or slope of the intertidal flat is adjusted continuously before the cease of reclamation the intertidal flat is unable to achieve an equilibrium shape

er yb and hf isotopic compositions of refractory inclusions an integrated isotopic fingerprint of the solar system s earliest reservoir abstract the oldest dated solids in our solar system calcium aluminum rich inclusions cais contain isotopic anomalies in a whole suite of elements relative to later formed solar system materials previous work has reported differences in the proportions of nucleosynthetic components between cais and terrestrial rocks as a function of mass however the nucleosynthetic fingerprint of the cai forming region is still lacking significant data in the heavier mass range a 154 therefore we present the first erbium er and ytterbium yb isotopic data along with hafnium hf isotopic compositions in a wide variety of cais derived from a variety of cv and ck chondrites this work presents new methods for er and yb isotopic investigation that were explored using both thermal ionization mass spectrometry tims and multicollector inductively coupled plasma mass spectrometry mc icpms relative to terrestrial rock standards cais regardless of host rock petrologic or chemical classification have uniform and resolvable er yb and hf isotopic compositions the cai isotopic patterns correspond to r process deficits or s process excesses relative to terrestrial values of 9 ppm for er 18 ppm for yb and 17 ppm for hf this new er yb and hf data help complete the nucleosynthetic fingerprint of the cai forming region further highlighting the systematic difference between the cais and later formed bulk planetary bodies such a systematic difference between cais and terrestrial rocks cannot be caused by different amounts of any known single presolar phase but is likely the result of a well mixed reservoir made of diverse stellar sources

extreme early solar system chemical fractionation recorded by alkali rich clasts contained in ordinary chondrite breccias abstract new k ca and rb sr isotopic analyses have been performed on alkali rich igneous rock fragments in the yamato y 74442 and bhola ll chondritic breccias to better understand the extent and timing of alkali enrichments in the early solar system the y 74442 fragments yield a k ca age of 4 41 0 28 ga for 40k 0 5543 ga 1 with an initial 40ca 44ca ratio of 47 1618 0 0032 studying the same fragments with the rb sr isotope system yields an age of 4 420 0 031 ga for 87rb 0 01402 ga 1 with an initial ratio of 87sr 86sr 0 7203 0 0044 an igneous rock fragment contained in bhola shows a similar alkali fractionation pattern to those of y 74442 fragments but does not plot on the k ca or rb sr isochron of the y 74442 fragments calcium isotopic compositions of whole rock samples of angrite and chondrites are primordial indistinguishable from mantle derived terrestrial rocks and here considered to represent the initial composition of bulk silicate earth the initial e40ca value determined for the source of the alkali clasts in y 74442 that is 0 5 e units higher than the solar system value implies an early alkali enrichment multi isotopic studies on these alkali rich fragments reveal that the source material of y 74442 fragments had elemental ratios of k ca 0 43 0 18 rb sr 3 45 0 66 and k rb 170 that may have formed from mixtures of an alkali rich component possibly an alkali enriched gaseous reservoir produced by fractionation of early nebular condensates and chondritic components that were flash heated during an impact event on the ll chondrite parent body 4 42 ga ago further enrichments of potassium and rubidium relative to calcium and strontium as well as a mutual alkali fractionation k rb 50 and heavier alkali enrichment would have likely occurred during subsequent cooling and differentiation of this melt alkali fragments in bhola might have undergone similar solid vapor fractionation processes to those of y 74442 fragments but appear to have formed via a distinct impact melting event

volatile degassing of basaltic achondrite parent bodies evidence from alkali elements and phosphorus abstract the volatile alkali element na k rb cs and p abundances in eucrites diogenites and basaltic clasts from polymict eucrites howardites and mesosiderites were compared with an average of highly incompatible refractory ahir elements ba la ce nd sm hf th u normalized to cosmic abundances ratios of e g rb ahir remain constant during normal magmatic differentiation because the very low and approximately equal mineral melt partition coefficients for these elements are inefficient in causing fractionation in the melt the na ahir ratio in eucrites is essentially constant at 0 050 cosmic basaltic eucrites and basaltic clasts show a positive correlation between k rb and cs and alkali element ahir ratios the averages for basaltic eucrites are k ahir 0 043 rb ahir 0 0088 cs ahir 0 0040 cosmic the positive correlations between alkali elements and alkali ahir are due to progressive volatile loss of the alkali elements from the basalts and not to source region heterogeneities this process probably had a minor effect on the parent body inventory of volatile elements in diogenites the alkali ahir ratios are systematically greater than in basaltic eucrites and are more variable the lower values are 1 4 2 the means for basaltic eucrites while the higher values are similar to those of cv and co chondrites for k rb and cs the highest alkali ahir ratios were obtained on the most incompatible poor of the diogenites and indicate minimum ratios for the parent body of na ahir 0 24 k ahir 0 49 rb ahir 0 55 and cs ahir 0 14 cosmic there are well defined negative correlations between k rb cs and alkali ahir ratio in the diogenites the data are consistent with progressive alkali loss through volatile outgassing during crystallization of one or more parent magmas this process resulted in 90 loss of the volatile element inventory from the parent body phosphorus also shows evidence for volatile loss from the basaltic eucrites and elevated p ahir ratios in diogenites the low p ahir ratio in eucrites is largely controlled by volatile loss rather than through equilibration with a metallic liquid as previously suggested the parent body of the basaltic achondrites appears to have initially contained alkali element and presumably other volatile element abundances comparable to those in co and cv chondrites and perhaps higher

rubidium isotopic composition of the earth meteorites and the moon evidence for the origin of volatile loss during planetary accretion abstract understanding the origin of volatile element variations in the inner solar system has long been a goal of cosmochemistry but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations an improved method for the chemical purification of rb for high precision isotope ratio measurements by multi collector inductively coupled plasma mass spectrometry this method has been used to measure the rb isotopic composition for a suite of planetary materials including carbonaceous ordinary and enstatite chondrites as well as achondrites eucrite angrite terrestrial igneous rocks basalt andesite granite and apollo lunar samples mare basalts alkali suite volatile depleted bodies e g hed parent body thermally metamorphosed meteorites are enriched in the heavy isotope of rb by up to several per mil compared to chondrites suggesting volatile loss by evaporation at the surface of planetesimals in addition the moon is isotopically distinct from the moon in rb the variations in rb isotope compositions in the volatile poor samples are attributed to volatile loss from planetesimals during accretion this suggests that either the rb and other volatile elements were lost during or following the giant impact or by evaporation earlier during the accretion history of theia

on the iron isotope composition of mars and volatile depletion in the terrestrial planets iron is the most abundant multivalent element in planetary reservoirs meaning its isotope composition expressed as 57fe may record signatures of processes that occurred during the formation and subsequent differentiation of the terrestrial planets chondritic meteorites putative constituents of the planets and remnants of undifferentiated inner solar system bodies have fe57 0 an isotopic signature shared with the martian shergottite nakhlite chassignite snc suite of meteorites the silicate earth and moon as represented by basaltic rocks are distinctly heavier fe57 0 1 however some authors have recently argued on the basis of iron isotope measurements of abyssal peridotites that the composition of the earth s mantle is fe57 0 04 0 04 indistinguishable from the mean martian value to provide a more robust estimate for mars we present new high precision iron isotope data on 17 snc meteorites and 5 mineral separates we find that the iron isotope compositions of martian meteorites reflect igneous processes with nakhlites and evolved shergottites displaying heavier fe57 0 05 0 03 whereas mgo rich rocks are lighter fe57 0 01 0 02 these systematics are controlled by the fractionation of olivine and pyroxene attested to by the lighter isotope composition of pyroxene compared to whole rock nakhlites extrapolation of the fe57 snc liquid line of descent to a putative martian mantle yields a 57fe value lighter than its terrestrial counterpart but indistinguishable from chondrites iron isotopes in planetary basalts of the inner solar system correlate positively with fe mn and silicon isotopes while mars and iv vesta are undepleted in iron and accordingly have chondritic 57fe the earth experienced volatile depletion at low 1300 k temperatures likely at an early stage in the solar nebula whereas additional post nebular fe loss is possible for the moon and angrites

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

chemical and structural characteristics of gas hydrates from the haima cold seeps in the qiongdongnan basin of the south china sea abstract crystalline structure cage occupancy and gas composition are important gas hydrate characteristics which can be used to calculate the gas hydrate s stability and to estimate the energy potential in may and october of 2015 a guangzhou marine geological survey team investigated two sites in the haima cold seeps in the qiongdongnan basin northern south china sea they recovered massive gas hydrate samples by conventional gravity coring after the shenhu sea area and dongsha sea area the qiongdongnan basin became a new area on the northern slope of the south china sea where gas hydrates have been found in order to reveal the structural and geochemical characteristics of the natural gas hydrates samples were analyzed by micro raman spectroscopy and x ray diffraction under ambient pressure and low temperature conditions the results indicate that the gas hydrate samples from the haima cold seeps are typical structure i hydrates with a hydration number of 6 12 6 19 in addition trace amounts of h2s trapped in the hydrate were identified based on its characteristic vibrational signature the gas composition and 13c ch4 of the hydrate bound gas samples were analyzed for gas source correlation all of the gas samples are dominated by methane with small amounts of ethane and propane and had relatively light 13c ch4 indicating that all of the hydrate bound gases are mixtures of biogenic and thermogenic gas the thermogenic gas is inferred to be mainly derived from the coal layers of the late miocene pliocene yacheng formation in the northern lingshui sag

gas hydrate distributions in sediments of pockmarks from the nigerian margin results and interpretation from shallow drilling a joint research expedition between the french ifremer and the german marum was conducted in 2011 using the r v pourquoi pas to study gas hydrate distributions in a pockmark field 1141 1199 meters below sea surface at the continental margin of nigeria the sea floor drill rig mebo of marum was used to recover sediments as deep as 56 74 meters below seafloor the presence of gas hydrates in specific core sections was deduced from temperature anomalies recorded during continuous records of infrared thermal scanning and anomalies in pore water chloride concentrations in situ sediment temperature measurements showed elevated geothermal gradients of up to 258 c km in the center of the so called pockmark a which is up to 4 6 times higher than that in the background sediment 72 c km the gas hydrate distribution and thermal regime in the pockmark are largely controlled by the intensity periodicity and direction of fluid flow the joint interaction between fluid flow gas hydrate formation and dissolution and the thermal regime governs pockmark formation and evolution on the nigerian continental margin

26al 26mg dating of asteroidal magmatism in the young solar system abstract we present high precision mg isotope data for most classes of basaltic meteorites including eucrites mesosiderite silicate clasts angrites and the ungrouped northwest africa nwa 2976 measured by pseudo high resolution multiple collector inductively coupled plasma mass spectrometry and utilising improved techniques for chemical purification of mg with the exception of the angrites angra dos reis lewis cliff lew 86010 nwa 1296 and nwa 2999 and the diogenite bilanga which have either been shown to have young ages by other dating techniques or have low al mg ratios all bulk samples of basaltic meteorites have 26mg excesses 26 mg 0 0135 to 0 0392 the 26mg excesses cannot be explained by analytical artefacts cosmogenic effects or heterogeneity of initial 26al 27al al mg ratios or mg isotopes in asteroidal parent bodies as compared to earth or chondrites the 26mg excesses record asteroidal melting and formation of basaltic magmas with super chondritic al mg and confirm that radioactive decay of short lived 26al was the primary heat source that melted planetesimals model 26al 26mg ages for magmatism on the eucrite mesosiderite angrite and nwa 2976 parent bodies are 2 6 3 2 3 9 4 1 and 3 5 myr respectively after formation of calcium aluminium rich inclusions cais however the validity of these model ages depends on whether the elevated al mg ratios of basaltic meteorites result from magma ocean evolution on asteroids through fractional crystallisation or directly during partial melting mineral isochrons for the angrites sahara sah 99555 and d orbigny and nwa 2976 yield ages of 5 06 0 05 0 06 myr and 4 86 0 09 0 10 myr respectively after cai formation both isochrons have elevated initial 26 mg values given the brecciated and equilibrated texture of nwa 2976 it is probable that its isochron age and elevated initial 26 mg 0 0175 0 0034 reflects thermal resetting during an impact event and slow cooling on its parent body however in the case of the angrites the marginally elevated initial 26 mg 0 0068 0 0058 may reflect either 26 mg ingrowth in a magma ocean prior to eruption and crystallisation or in an older igneous protolith with super chondritic al mg prior to impact melting and crystallisation of these angrites or partial internal re equilibration of mg isotopes after crystallisation 26al 26mg model ages and an olivine pyroxene whole rock isochron for the angrites sah 99555 and d orbigny are in good agreement with age constraints from 53mn 53cr and 182hf 182w short lived chronometers suggesting that the 26al 26mg feldspar controlled isochron ages for these angrites may be compromised by the partial resetting of feldspar mg isotope systematics even when age constraints from the 26al 26mg angrite model ages or the mafic mineral whole rock isochron are considered the relative time difference between sah 99555 d orbigny crystallisation and cai formation cannot be reconciled with pb pb ages for sah 99555 d orbigny and cais which are ca 1 0 myr too old angrites or too young cais for reasons that are not clear this discrepancy might indicate that 26al was markedly lower ca 40 in the planetesimal and planet forming regions of the proto planetary disc as compared to cais or that cai pb pb ages may not accurately date cai formation which might be better dated by the 182hf 182w and 26al 26mg chronometers as 4568 3 0 7 burkhardt et al 2008 and 4568 5 0 3 ma herein respectively when mapped onto an absolute timescale using pb pb ages for angrites

147 146sm 143 142nd 176lu 176hf and 87rb 87sr systematics in the angrites implications for chronology and processes on the angrite parent body abstract angrites are a group of basaltic achondrites with distinctive mineralogic and geochemical characteristics that have the potential to provide insights into processes occurring on planetesimals in the early solar system these achondrites have been used as anchors linking the relative age information obtained from short lived extinct chronometers e g al mg hf w and mn cr with absolute chronometers e g u pb angrites provide excellent examples of early differentiation processes such as core formation and silicate differentiation on protoplanetary bodies the significant increase in the number of known angrite samples in recent years has offered the opportunity to compare several short and long lived isotopic systems in samples with different petrogenetic histories that formed on the same parent body to this end the 147sm 143nd 146sm 142nd 176lu 176hf and 87rb 87sr isotope systematics have been investigated in a suite of plutonic coarse grained nwa 4590 nwa 4801 and nwa 2999 and quenched fine grained d orbigny angrites the coupled 147 146sm 143 142nd systematics indicate possible isotopic disturbances in two angrites d orbigny and nwa 2999 resulting from post crystallization processes the internal 146sm 142nd isochrons of two coarse grained angrites nwa 4590 and nwa 4801 provide an updated best estimate of the initial solar system 146sm 144sm ratio i e at 4568 ma of 0 0084 0 0003 the 176lu 176hf isotope systematics in these angrites do not provide evidence of a previously proposed intense irradiation event in the early solar system the internal 176lu 176hf isochrons for the nwa 4590 and d orbigny angrites provide an estimate for the solar system initial 176hf 177hf ratio of 0 279775 0 000031 2 that agrees within uncertainty with the value of average chondrites reported by bouvier et al 2008 finally the calculated initial 87sr 86sr ratios based on the measured sr isotopic composition of plagioclase in these angrites yield an estimated initial 87sr 86sr ratio of 0 698980 0 000011 for the angrite parent body this is indistinguishable from a recently determined value for the solar system initial 87sr 86sr based on values measured in calcium aluminum rich inclusions cais after correcting for nucleosynthetic effects in the cais the low initial 87sr 86sr of the angrite parent body implies that it acquired its volatile element depleted characteristic within 1 8 ma of solar system formation likely because it accreted from volatile depleted planetesimals that formed in the hot inner nebula these integrated isotopic systematics suggest a complex history for the angrite parent body not previously inferred from short lived chronometers and provide new estimates for the initial isotopic composition of the early solar system

chronology of the angrite parent body and implications for core formation in protoplanets abstract angrites formed by some of the earliest igneous activity in the solar system and provide insights into the early stages of planetary melting and differentiation moreover they are pivotal reference points for early solar system chronology in order to study the processes and timescales of metal segregation in early protoplanets and to assess the distribution of short lived radionuclides in the early solar system the 182 hf 182 w system was applied to a comprehensive suite of angrites 182 hf 182 w isochron ages for angrites are in excellent agreement with previously reported 207 pb 206 pb and 53 mn 53 cr results but are 1 myr older than ages obtained from 26 al 26 mg chronometry these inconsistencies probably reflect a disturbance of the al mg system in the angrite feldspars but could alternatively be explained by a heterogeneous distribution of 26 al in the early solar system based on the hf w results four texturally and temporally resolved groups of angrites can be identified that were derived from at least two distinct mantle sources these mantle sources are the result of separate events of core formation both of which took place within 2 myr of cai formation thus core formation in the angrite parent body did not occur as a single event of metal segregation from a global magma ocean but rather took place under varying conditions by several more local events the disparate hf w systematics of the two distinct angrite source regions indicate that convection in the magma ocean was inefficient in homogenizing the composition of the mantle possibly as a result of a continuous bombardment with small planetesimals during ongoing core formation such impacts could have constantly removed primordial and earlier formed crust facilitating rapid cooling of the magma ocean which solidified as early as 3 6 0 7 myr after cai formation

the geologic history of vesta inferred from combined 207pb 206pb and 40ar 39ar chronology of basaltic eucrites abstract eucrites represent samples of mafic crust of the parent body likely vesta and record a complex geologic history involving magmatism metamorphism impact processing and metasomatism for better understanding of the geologic history we present combined 207pb 206pb and 40ar 39ar chronology of four basaltic eucrites showing distinct petrologic features agoult an equilibrated eucrite with granulitic textures camel donga a brecciated equilibrated eucrite enriched in metallic iron dag 380 a partially equilibrated monomict eucrite and nwa 049 a metasomatized polymict eucrite comprising mostly unequilibrated clasts the 207pb 206pb dating in combination with the acid washing technique was applied to pyroxene rich and plagioclase rich fractions while the 40ar 39ar dating was performed mainly on plagioclase grains using the laser incremental heating method the pb isotopic data for acid leaching residues are more radiogenic than those for acid washes reflecting efficient removal of non radiogenic pb components by the acid washing among the residues however only those of the agoult and camel donga plagioclase rich fractions yielded isochrons rather than errorchrons with 207pb 206pb ages of 4532 39 0 87 ma and 4515 43 0 42 ma respectively the trace element systematics further suggest that these residues essentially represent contaminant oxide minerals such as ilmenite and chromite rather than plagioclase on the other hand the ar isotopic data for agoult and camel donga yielded plateau ages with weighted means of 4494 9 ma and 3749 25 ma in contrast to those for dag 380 and nwa 049 that did not return any plateau the 207pb 206pb and 40ar 39ar ages of agoult are interpreted to reflect the time of the u pb and k ar system closure during a prolonged thermal metamorphism by combining the ages reported here and in the literature with the calculated closure temperatures the cooling rate of agoult is determined to be 11 2 c ma this cooling rate corresponds to a burial depth of 10 20 km indicating that granulitic eucrites were originally crystallized near the surface and were subsequently buried and metamorphosed the 20 ma younger 207pb 206pb ages of camel donga than agoult are considered to reflect delayed burial metamorphism in the source region whereas the plateau 40ar 39ar age would record the time of an impact causing brecciation and efficient ar degassing of the buried crust furthermore the model 207pb 206pb dates calculated for acid washed pyroxenes imply that the burial metamorphism of agoult and dag 380 were broadly contemporaneous and also that nwa 049 was metasomatized by fluids within the uppermost crust later than 4 4 ga

samarium neodymium chronology and rubidium strontium systematics of an allende calcium aluminum rich inclusion with implications for 146sm half life abstract calcium aluminum rich inclusions cais are primitive objects that formed within the protoplanetary disk surrounding the young sun recent pb pb chronologic studies have demonstrated that cais are the oldest solar system solids crystallizing 4567 ma ago amelin et al 2002 connelly et al 2012 the isotope systematics of cais therefore provide critical insight into the earliest history of the solar system although sm nd and rb sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early solar system previous studies of cais have revealed evidence for isotopically disturbed systems here we report new age data for allende cai al3s4 derived from both the long lived 147sm 143nd and short lived 146sm 142nd isotopic systems the 147sm 143nd chronometer yields an age of 4560 34 ma that is concordant with 207pb 206pb ages for cais and indicates that the sm nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes the slope of the 146sm 142nd isochron defines the solar system initial 146sm 144sm of 0 00828 0 00044 this value is significantly different from the value of 0 0094 determined by kinoshita et al 2012 ages recalculated from all published 146sm 142nd isochron data using the traditional 103 ma half life and the initial 146sm 144sm value determined here closely match pb pb and 147sm 143nd ages determined on the same samples in contrast ages recalculated using the 68 ma half life determined by kinoshita et al 2012 and either of the initial 146sm 144sm values are often anomalously old this is particularly true for the youngest samples with 146sm 142nd isochron ages that are most sensitive to the choice of 146sm half life used in the age calculation in contrast to the sm nd isotope system the rb sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 110 ma although the rb sr system in cais appears to be disturbed the initial 87sr 86sr value determined from the isochron is 0 698942 0 000008 and closely approximates estimates of the initial solar system value although this isochron may be a mixing line it might also record alteration on the allende parent body in which rb was added to the al3s4 cai that was initially largely devoid of rb

gas hydrate of lake baikal discovery and varieties abstract this paper summarizes the results of recent gas hydrate studies in lake baikal the only fresh water lake in the world containing gas hydrates in its sedimentary infill we provide a historical overview of the different investigations and discoveries and highlight some recent breakthroughs in our understanding of the baikal hydrate system so far 21 sites of gas hydrate occurrence have been discovered gas hydrates are of structures i and ii which are of thermogenic microbial and mixed origin at the 15 sites gas hydrates were found in mud volcanoes and the rest six near gas discharges additionally depending on type of discharge and gas hydrate structure they were visually different investigations using mir submersibles allowed finding of gas hydrates at the bottom surface of lake baikal at the three sites

chronologic implications for slow cooling of troctolite 76535 and temporal relationships between the mg suite and the ferroan anorthosite suite abstract ages have been obtained using the 87 rb 87 sr 147 sm 143 nd and 146 sm 142 nd isotopic systems for one of the most slowly cooled lunar rocks apollo 17 mg suite troctolite 76535 the 147 sm 143 nd 146 sm 142 nd and rb sr ages derived from plagioclase olivine and pyroxene mineral isochrons yield concordant ages of 4307 11 ma 4299 29 35 ma and 4279 52 ma respectively these ages are slightly younger than the age determined on ferroan anorthosite suite fas rock 60025 and are therefore consistent with the traditional magma ocean model of lunar differentiation in which the mg suite is intruded into the anorthositic crust however the sm nd ages record when the rock passed below the closing temperature of the sm nd system in this rock at 825 c whereas the rb sr age likely records the closure temperature of 650 c a cooling rate of 3 9 c ma is determined using the ages reported here and in the literature and calculated closure temperatures for the ar ar pb pb rb sr and sm nd systems this cooling rate is in good agreement with cooling rates estimated from petrographic observations slow cooling can lower apparent sm nd crystallization ages by up to 80 ma in the slowest cooled rocks like 76535 and likely accounts for some of the variation of ages reported for lunar crustal rocks nevertheless slow cooling cannot account for the overlap in fas and mg suite rock ages instead this overlap appears to reflect the concordance of mg suite and fas magmatism in the lunar crust as indicated by ages calculated for the solidus temperature of 76535 and 60025 of 4384 24 ma and 4383 17 respectively not only are the solidus ages of 76535 and 60025 nearly concordant but the sm nd isotopic systematics suggest they are derived from reservoirs that were minimally differentiated prior to 4 38 ga although the sr isotopic composition of 60025 indicates its source was minimally differentiated the sr isotopic composition of 76535 indicates it underwent fractionation just prior to solidification of the 76535 these observations are consistent with both a magma ocean or a serial magmatism model of lunar differentiation in either model differentiation of lunar source regions must occur near the solidification age of thee samples perhaps the best estimate for the formation age of lunar source regions is the rb sr model age of the 76535 source region age of 4401 32 ma this is in good agreement with sm nd model ages for the formation of ur kreep and suggests that differentiation of a least part of the moon could not have occurred prior to 4 43 ga

a deep crust mantle boundary in the asteroid 4 vesta the asteroid 4 vesta was recently found to have two large impact craters near its south pole exposing subsurface material modelling suggested that surface material in the northern hemisphere of vesta came from a depth of about 20 kilometres whereas the exposed southern material comes from a depth of 60 to 100 kilometres large amounts of olivine from the mantle were not seen suggesting that the outer 100 kilometres or so is mainly igneous crust here we analyse the data on vesta and conclude that the crust mantle boundary or moho is deeper than 80 kilometres

high temperature strontium stable isotope behaviour in the early solar system and planetary bodies abstract this study presents comprehensive strontium stable isotope 88sr 86sr data measured by multiple collector inductively coupled plasma mass spectrometry mc icp ms for a suite of carbonaceous chondrites differentiated meteorites lunar martian and terrestrial samples carbonaceous chondrites comprise a mixture of refractory inclusions and chondrules that have light 88sr values between 0 35 to 0 05 and matrix material that possesses a heavy 88sr composition of 0 65 confirming the results of earlier studies consequently bulk carbonaceous chondrites are relatively heterogeneous in composition ranging from 0 12 to 0 35 most likely reflecting clast matrix variability the light 88sr compositions of the refractory inclusions are consistent with mass dependent fractionation of other refractory elements ca and eu and are most likely produced by non equilibrium fractionation undercooling in the nebula gas during condensation of hibonite from the solar nebula simon and depaolo 2010 stable calcium isotopic composition of meteorites and rocky planets earth planet sci lett 289 457 466 carbonaceous chondrites angrites and martian meteorites have indistinguishable compositions at the level of analytical uncertainty of this study however statistical analysis indicates that melts derived from the earth s mantle have heavier 88sr values than bulk carbonaceous chondrites and martian meteorites but compositions indistinguishable from eucrites 88sr 0 26 0 12 moreover terrestrial basalts and andesites have restricted 88sr values 0 30 0 07 suggesting that mantle melting delivers rather homogenous melts to the earth s surface with respect to 88sr in contrast glasses from evolved terrestrial rocks and lunar basalts extend to very light 88sr values 0 20 the sr stable isotope composition covaries with europium anomaly eu eu as an index of plagioclase fractionation and 88sr can be successfully modelled by the heavy isotopes of sr being preferentially partitioned into plagioclase with a fractionation factor of 1 0007 for 88sr 86sr our results demonstrate that sr stable isotopes may be significantly fractionated at high temperatures and their measurement can provide insights into planetary evolution and magmatic processes

correlated study of initial sr 87 sr 86 and al mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the allende meteorite we have studied a suite of six coarse grained ca al rich inclusions cais from the allende meteorite applying in concert detailed petrographic and chemical characterization ion probe mass spectrometric analyses of the al mg isotopic system to determine the abundance and distribution of 26a1 and thermal emission mass spectrometric analyses of the rb sr system to determine initial 87sr86sr ratios the simplest inclusion is a type bl usnm 3529 z that shows evidence of minor alteration and recrystallization since solidification from a melt droplet e g some of the coarse grained anorthite in the inclusion especially near the inclusion rim apparently formed by recrystallization or melting of fine grained secondary anorthite that had replaced melilite four other type bs contain evidence of more widespread recrystallization in addition to evidence of local replacement of melilite by coarse anorthite e g melilite zoning is complex and not igneous in origin and in one inclusion usnm 3529 21 melilite and pyroxene crystals enclose relicts of an earlier generation of the same phases the sixth inclusion usnm 3898 is a type a whose properties appear to be largely metamorphic in origin all six inclusions show variations in mg isotopic compositions indicating that they incorporated 26a1 in 3529 z the relative abundance of 26a1 26al27al 4 0 0 1 10 5 is close to the canonical value 26al27al 5 10 5 for cais but both anorthite and melilite show minor departures from a strict isochron relationship between mg and al in particular the coarse anorthite near the inclusion rim has initial 26al27al ratios of 1 2 10 5 implying formation at least 1 5 million years after the first generation anorthite the other four type bs exhibit larger disturbances of the al mg system that can be understood in terms of local recrystallization and isotopic exchange primarily between anorthite and melilite only 3898 is consistent with a strict al mg isochron relationship but this cai lacks primary anorthite and the small range of al mg among the phases analyzed may preclude resolution of any small isotopic disturbances the rb sr isotopic system also typically indicates some level of disturbance some of which must have been relatively recent nevertheless phases characterized by very low rb sr permit precise identification of initial 87sr86sr our al mg and sr data are largely consistent with a simple chronological interpretation of both systems i e the 26al results suggest that all the initial 87sr86sr ratios should have the same value and with one exception our initial 87sr86sr ratios are consistent with a single value this value is somewhat higher than the primitive value all reported by gray et al 1973 however also with one exception the very low rb sr cai data reported by gray et al 1973 are consistent with the same value the exception is the same inclusion in both studies our analysis of usnm 3898 yields an initial 87sr86srhigher than that of the other cais while gray et al 1973 obtained an initial 87sr86srlower than that of the other cais for the same inclusion labeled as d7 on which all is based neither result can be readily explained as a chronological aberration since 3898 has nearly canonical 26al27al the present data are the first which establish a firm association between primitive 26al27al and primitive 87sr86sr by analysis of both isotopic systems in the same inclusions the comparison of both isotopic systems interpreted as simple nebular chronometers does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of 26al

high precision strontium isotope analysis of geological samples by thermal ionisation mass spectrometry abstract we present a method for the efficient separation of sr from geological materials followed by high precision measurement of sr isotopes by thermal ionisation mass spectrometry tims these analyses focus on high precision measurements of the low abundance isotope 84sr 0 56 which is of high interest for cosmochemical applications the robust dataset obtained through the analysis of a range of basalts and anorthosites sheds light on a number of issues regarding sr isotopic analyses specifically concerns that analytical artefacts may produce a spurious signal on 84sr have been investigated the external reproducibility based on replicate measurements of the basalt standard bcr 2 for e84sr is 0 36 2sd and is 0 51 2sd for repeated analyses of nist srm 987 in contrast with the static measurements of previous work andreasen and sharma 2007 moynier et al 2012 paton et al 2013 brennecka et al 2013 our dynamic data reveal no 84sr variations in terrestrial rocks or standard material the dataset indicates that by the analytical procedure employed 84sr variations in extra terrestrial material larger than 0 5e are resolvable

rb sr chronology of volatile depletion in differentiated protoplanets babi ador and all revisited abstract a strong depletion in moderately volatile elements is a characteristic feature of many planetary bodies in the inner solar system and either reflects the rapid accretion of planetesimals from an incompletely condensed solar nebula or is the result of energetic collisions during planetary accretion to better constrain the origin and timescales of this volatile depletion we have precisely measured sr isotope compositions in angrites eucrites and ca al rich inclusions cai angrites have an initial 87sr 86sr ador 0 698978 0 000004 which is indistinguishable from 87sr 86sr babi 0 698970 0 000028 obtained for eucrites in agreement with earlier studies we find that angrites and eucrites have higher initial 87sr 86sr ratios than cai at face value corresponding to model timescales for volatile loss of several millions of years however all the investigated cai are characterized by elevated 84sr 86sr ratios compared to angrites and eucrites which we interpret to reflect an excess of r process sr in the cai if this is correct then the nucleosynthetic sr isotope anomalies in the cai require an upward correction of their measured 87sr 86sr after this correction cai have an initial 87sr 86sr cai 0 698975 0 000008 which is indistinguishable from ador and babi this implies volatile loss from the angrite and eucrite parent bodies within less than 1 ma after formation of cai the volatile depleted nature of these differentiated protoplanets thus most likely reflects their rapid accretion from volatile poor dust in an incompletely condensed solar nebula

cosmochemical and spectroscopic properties of northwest africa 7325 a consortium study this work is part of a project to build an infrared database in order to link ir data of planetary materials and therefore possible mercury material with remote sensing observations of mercury which will probably be obtained by the mertis instrument on the forthcoming bepicolombo mission the unique achondrite northwest africa nwa 7325 which has previously been suggested to represent the first sample from mercury was investigated by optical and electron microscopy and infrared and raman spectroscopy in addition the oxygen strontium xenon and argon isotopes were measured and the abundance of selected trace elements determined the meteorite is a cumulate rock with subchondritic abundances of hfse and ree and elevated sr contents which underwent a second heating and partial remelting process oxygen isotope measurements show that nwa 7325 plots in the ureilite field close to the alm a trachyandesitic fragment found in the unique almahata sitta meteorite breccia on the other hand mineralogical investigations of the pyroxenes in nwa 7325 provide evidence for similarities to the lodranites and acapulcoites furthermore the rock is weakly shocked and argon isotope data record ancient 4 5 ga plateau ages that have not been reset the sample records a cosmogenic exposure age of 19 ma systematics of rb sr indicate an extreme early volatile depletion of the precursor material similar to many other achondrite groups however despite its compositional similarities to other meteorite groups our results suggest that this meteorite is unique and unrelated to any other known achondrite group an origin for nwa 7325 as a sample from the planet mercury is not supported by the results of our investigation in particular the evidence from infrared spectroscopy indicates that a direct relationship between nwa 7325 and the planet mercury can be ruled out no acceptable spectral match between laboratory analyses and remote sensing observations from mercury has been obtained however we demonstrate that infrared spectroscopy is a rapid and nondestructive method to characterize mineral phases and thus an excellent tool for planetary surface characterization in space missions

global crustal metamorphism of the eucrite parent body abstract we conducted a petrologic study of 18 equilibrated eucrites with the goal of understanding the formation and evolution of the crust of asteroid 4 vesta the likely source of eucrite meteorites their textures indicate that eucrites were basaltic igneous rocks but modified by postcrystallization brecciation recrystallization and impact melting recrystallized rocks are the most common among clasts in the eucrites impact melt breccias are rare equilibration temperatures of the metamorphic clasts range from 700 to 1000 c with most in the 800 900 c range complex exsolution and recrystallization textures in pyroxenes suggest that eucrites cooled very slowly from high peak temperatures after reheating this extended period of thermal metamorphism requires a high interior temperature in a vesta sized body this metamorphism could have taken place during and shortly after crust formation we suggest the crust of vesta evolved through the eruption rapid cooling and subsequent burial and reheating of lava flows as the crust grew in thickness the depth of burial increased causing temperatures to rise and leading to global metamorphism this resulted in only a small percentage of unequilibrated eucrites only the last few percent of basalts erupted would not be metamorphosed and a wide range of metamorphic temperatures and durations for the equilibrated eucrites

nucleosynthetic strontium isotope anomalies in carbonaceous chondrites abstract precise sr isotopic compositions in samples from sequential acid leaching experiments have been determined for three carbonaceous chondrites allende murchison and tagish lake together with those in the bulk aliquots of these meteorites the chondritic acid leachates and residues were characterized by sr isotope anomalies with variable 84sr values 106 relative deviation from a standard material ranging from 120 to 4700 ppm documenting multiple nucleosynthetic sources within a single meteorite in addition the 84sr patterns across leaching samples for individual chondrites differed from one another the highest 84sr values were observed for leaching step 3 hcl h2o 75 c for allende and murchison likely because of the incorporation of calcium and aluminum rich inclusions cais in contrast extremely low 84sr values were observed in the later fractions steps 6 and 7 for murchison and tagish lake suggesting the existence of s process enriched presolar sic grains derived from agb stars a 84sr 54cr diagram was prepared with the cais and bulk aliquots of carbonaceous chondrites and other meteorites noncarbonaceous that were plotted separately however they still formed a global positive correlation cais presented the highest 84sr and 54cr values whereas carbonaceous chondrites and noncarbonaceous meteorites had intermediate and the lowest 84sr and 54cr values respectively the positive trend was interpreted as resulting from global thermal processing in which sublimation of high 84sr and 54cr carriers generated the excess 84sr and 54cr signatures in cais while noncarbonaceous planetesimals accreted from materials that underwent significant thermal processing and thus had relatively low 84sr and 54cr values apart from the global trend the carbonaceous chondrites and noncarbonaceous meteorites both exhibited intrinsic variations that highlight an isotopic dichotomy similar to that observed in other isotope combinations e g 54cr 50ti 54cr 17o a plausible scenario for creation of the intrinsic variations involves local thermal processing e g flash heating for chondrule formation caused by additional selective destruction of presolar grains differently than that caused by global thermal processing the existence of such a global positive trend and local variations for two meteorite groups suggests a complicated dynamic history for the dust grains with respect to thermal processing material transportation and mixing in the protoplanetary disk prior to planetesimal formation

u pb rb sr and ar ar systematics of the ungrouped achondrites northwest africa 6704 and northwest africa 6693 abstract we report u pb 87rb 87sr 40ar 39ar and 238u 235u isotopic data for paired ungrouped achondrites nwa 6704 and nwa 6693 that were derived from a highly oxidised parent body with broadly chondritic composition warren et al 2013 hibiya et al 2019 pb isotopic ages derived from isochrons for multiple acid leached pyroxene fractions are 4562 76 0 22 0 30 ma for nwa 6704 and 4562 63 0 29 0 21 ma for nwa 6693 calculated using 238u 235u ratio of 137 7784 0 0097 measured in nwa 6704 the rb sr mineral isochron age of 4543 46 ma initial 87sr 86sr 0 699013 0 000055 is consistent with the pb isotopic age together with 187re 187os isochron age of 4576 250 ma for nwa 6704 hibiya et al 2019 and 26al 26mg and 53mn 53cr ages calculated using the rapidly crystallized angrite d orbigny as a time anchor are also consistent with the pb isotopic age sanborn et al 2019 these data indicate that the parent rocks of nwa 6693 and nwa 6704 remained closed to migration of both lithophile and siderophile elements since crystallisation and initial cooling the whole rock 40ar 39ar age of 4199 32 ma suggests a complete resetting of the k ar system approximately 360 ma after crystallisation a later event at 2 12 ga partially reset the k ar system as shown by the low temperature heating steps both meteorites have high 87rb 86sr ratios up to 7 0 in nwa 6693 pyroxene and very radiogenic 87sr 86sr up to 1 15 together with the absence of secondary disturbance in the rb sr and u pb systems this makes them suitable for cross calibration of the isotopic chronometers these meteorites are also promising candidates to serve as age reference samples for the early solar system chronology as an alternative or complement to angrites of the early generation d orbigny sahara 99555 that are currently used for this purpose plagioclase in nwa 6704 has a sufficiently low rb sr ratio to define precise initial 87sr 86sr of 0 698997 0 000027 which corresponds to the time of separation of the parent body precursor material from the solar nebula of 1 5 2 1 ma this value suggests that the parent asteroid accreted within 3 6 ma after cai formation or before 4563 7 ma using the cai age of 4567 3 ma connelly et al 2012

impact of anaerobic oxidation of methane on the geochemical cycle of redox sensitive elements at cold seep sites of the northern south china sea abstract cold hydrocarbon seepage is a frequently observed phenomenon along continental margins worldwide however little is known about the impact of seeping fluids on the geochemical cycle of redox sensitive elements pore waters from four gravity cores d 8 d 5 d 7 and d f collected from cold seep sites of the northern south china sea were analyzed for so42 mg2 ca2 sr2 dissolved inorganic carbon dic 13cdic dissolved fe mn and trace elements e g mo u the sulfate concentration depth profiles 13cdic values and dic ca2 mg2 so42 ratios suggest that organoclastic sulfate reduction osr is the dominant process in d 8 core besides osr anaerobic oxidation of methane aom is partially responsible for depletion of sulfate at d 5 and d 7 cores the sulfate consumption at d f core is predominantly caused by aom the depth of sulfate methane interface smi and methane diffusive flux of d f core are calculated to be 7 m and 0 035 mol m 2 yr 1 respectively the relatively shallow smi and high methane flux at d f core suggest the activity of gas seepage in this region the concentrations of dissolved uranium u were inferred to decrease significantly within the iron reduction zone it seems that aom has limited influence on the u geochemical cycling in contrast a good correlation between the consumption of sulfate and the removal of molybdenum mo suggests that aom has a significantly influence on the geochemical cycle of mo at cold seeps accordingly cold seep environments may serve as an important potential sink in the marine geochemical cycle of mo

permian strontium isotope stratigraphy cvu acknowledges funding from the leopoldina german national academy of sciences grant no lpds 2014 08

high precision al mg isotopic systematics in usnm 3898 the benchmark all for initial 87sr 86sr in the earliest solar system abstract the allende cai usnm 3898 is the basis for all the lowest measured initial 87sr 86sr value in any solar system material including other cais gray et al 1973 if the value all is correct debated then usnm 3898 must be 1 2 million years older than other cais podosek et al 1991 this would require in turn that it have a much higher initial 26al 27al value than other cais on the order of 4 10 4 podosek et al 1991 showed that this is not the case with initial 26al 27al 4 5 0 7 10 5 but their mg isotopic data had large error bars and there was clear isotopic disturbance in the data having the highest 27al 24mg without the latter data the slope of their isochron is higher 5 10 1 19 10 5 and within large error of being supracanonical we used high precision sims to re determine the initial 26al 27al in this cai and obtained a value of 5 013 0 099 10 5 with an intercept 26 mg 0 008 0 048 and mswd 1 3 this value is indistinguishable from that measured in many other cais and conclusively shows that usnm 3898 is not uniquely ancient we also confirmed evidence of later isotopic disturbance similar to what podosek et al found indicating a re melting and evaporation event some 200 000 years after initial cai solidification

evaluation of the 87rb decay constant by age comparison against the u pb system abstract the rb sr decay system is one of the most widely used geochronometers for obtaining ages and cooling rates of terrestrial magmatic metamorphic and hydrothermal events it has also been extensively applied to date extraterrestrial early solar system events the accuracy of rb sr ages however strongly depends on the accuracy of the 87 rb decay constant 87 rb we determined 87 rb relative to the decay constants of 235 u and 238 u by comparing rb sr ages of minerals with u pb ages obtained from the same intrusion comparison of u pb emplacement ages with high precision rb sr mineral ages from three rapidly cooled igneous rocks covering an age range of ca 2 5 ga yields an unweighted mean 87 rb of 1 393 0 004 10 11 yr 1 i e 0 3 corresponding to a half life of 49 76 10 9 years because this decay constant is 2 lower than the presently recommended one many previously published ages are 2 too young and the resulting geologic interpretations may need revision

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

excess 180w in iiab iron meteorites identification of cosmogenic radiogenic and nucleosynthetic components abstract the origin of 180 w excesses in iron meteorites has been a recently debated topic here a suite of iiab iron meteorites was studied in order to accurately determine the contribution from galactic cosmic rays gcr and from potential decay of 184 os to measured excesses in the minor isotope 180 w in addition to w isotopes trace element concentrations re os ir pt w were determined on the same samples as well as their cosmic ray exposure ages using 36 cl 36 ar systematics these data were used in combination with an improved model of gcr effects on w isotopes to correct effects resulting from neutron capture and spallation reactions after these corrections the residual 180 w excesses correlate with os w ratios and indicate a clear contribution from 184 os decay a newly derived decay constant is equivalent to a half life for 184 os of 3 38 2 13 10 13 a furthermore when the data are plotted on an os w isochron diagram the intercept e 180 w i 0 63 0 35 reveals that the iiab parent body was characterized by a small initial nucleosynthetic excess in 180 w upon which radiogenic and gcr effects were superimposed this is the first cogent evidence for p process variability in w isotopes in early solar system material

numerical models of the thermomechanical evolution of planetesimals application to the acapulcoite lodranite parent body the acapulcoite lodranite meteorites are members of the primitive achondrite class the observation of partial melting and resulting partial removal of fe fes indicates that this meteorite group could be an important link between achondrite and iron meteorites on the one hand and chondrite meteorites on the other thus a better understanding of the thermomechanical evolution of the parent body of this meteorite group can help improve our understanding of the evolution of early planetesimals here we use 2 d and 3 d finite difference numerical models to determine the formation time initial radius of the parent body of the acapulcoite lodranite meteorites and their formation depth inside the body by applying available geochronological thermal and textural constraints to our numerical data our results indicate that the best fit to the data can be obtained for a parent body with 25 65 km radius which formed around 1 3 ma after calcium aluminum rich inclusions the 2 d and 3 d results considering various initial temperatures and the effect of porosity indicate possible formation depths of the acapulcoite lodranite meteorites of 9 19 and 14 25 km respectively our data also suggest that other meteorite classes could form at different depths inside the same parent body supporting recently proposed models elkins tanton et al 2011 weiss and elkins tanton 2013