magnetism on the angrite parent body and the early differentiation of planetesimals angrites are among the oldest known pristine basaltic meteorites and record the earliest stages of planet formation and differentiation our paleomagnetic analysis of three angrites found that they record a past magnetic field of 10 microteslas on the angrite parent body extending from 4564 to at least 4558 million years ago because the angrite paleomagnetic record extends beyond the expected lifetime of the early circumstellar disk these paleofields were probably generated internally on the angrite parent body possibly by an early dynamo in a rapidly formed metallic core

seismic detection of the lunar core despite recent insight regarding the history and current state of the moon from satellite sensing and analyses of limited apollo era seismic data deficiencies remain in our understanding of the deep lunar interior we reanalyzed apollo lunar seismograms using array processing methods to search for the presence of reflected and converted seismic energy from the core our results suggest the presence of a solid inner and fluid outer core overlain by a partially molten boundary layer the relative sizes of the inner and outer core suggest that the core is 60 liquid by volume based on phase diagrams of iron alloys and the presence of partial melt the core probably contains less than 6 weight of lighter alloying components which is consistent with a volatile depleted interior

interior of the moon the presence of garnet in the primitive deep lunar mantle new trace element data have been generated by inductively coupled plasma mass spectrometry icp ms for 65 high and low ti mare basalts from the apollo 11 12 14 15 and 17 landing sites these data demonstrate that ratios of the high field strength elements and yttrium are generally chondritic in the mare source regions for the low ti basalts but nonchondritic in the high ti basalts and potassium rare earth elements and phosphorus kreep such differences can be explained by addition and subtraction respectively of ilmenite this interpretation is consistent with derivation of the basalts from lunar magma ocean lmo cumulates through which late stage ilmenite has sunk and mixed with earlier magma ocean products compositional differences between the mare basalts and volcanic glass beads suggest that at least some of the latter were derived from a garnet bearing source region siderophile and chalcophile element data suggest that the garnet bearing source escaped the lmo melting event and thus represents primitive moon material the remaining glasses are generally very low ti vlt and appear to have been derived from early lmo cumulates i e olivine and orthopyroxene similar to the vlt basalts the remaining glasses were derived from below the lmo cumulates and as the magmas rose they underwent sequential assimilation to varying degrees initially of an ilmenite rich cumulate followed by a kreep component this study presents geochemical evidence for the existence of garnet in a mare source and demonstrates the likelihood that the lmo was not whole moon thus preserving primitive lunar material which has acted as the source region for at least some of the volcanic glasses

isotopic fractionation of germanium in iron meteorites significance for nebular condensation core formation and impact processes abstract the siderophile and volatile nature of germanium allow ge isotopes to be used to investigate the early history of planetesimals by tracing processes of core formation and impact through the study of magmatic and non magmatic iron meteorites germanium isotopic compositions were measured using a hexapole collision cell mc icpms with an external reproducibility of 0 06 amu iron meteorites display heavy ge isotopic compositions 74ge 74ge 70ge 0 27 to 1 92 with respect to a jmc ge standard which contrast with the light isotopic compositions of the studied terrestrial materials aldrich ge standard 74ge 1 68 1 72 0 22 sphalerite 74ge 0 69 all the data fall on the theoretical mass fractionation line indicating no isotopic anomalies the samples from magmatic irons iia iib iiiab iic have relatively homogeneous ge isotopic compositions of 74ge 1 77 0 22 2 for a large range of ge contents 36 189 ppm in contrast the samples of the non magmatic groups iab iie have lower and more variable ge isotopic compositions with 74ge 1 15 0 20 for iab group ge 254 493 ppm 74ge 0 27 to 0 43 for iie old group ge 63 69 ppm and 74ge 1 40 0 22 for the watson sample ge 50 ppm from the iie young group except for iie samples no within group correlation of 74ge with ir or ge contents is observed demonstrating that fractional crystallization or crystal segregation do not fractionate ge isotopes the lack of inter group correlation between the ge isotopic composition of magmatic irons and ni content an indicator of redox processes suggests that if ge isotopes are fractionated by redox induced diffusion during metal silicate segregation isotopic equilibration towards the initial composition must also occur during isotopic exchange at high temperature thus the average 74ge value of 1 77 0 22 should be representative of their parent body precursors the lack of correlation between the ge isotopic composition and ge ni ratios and the high ge ni ratio of iia samples ge ni in ci chondrites may reflect the high proportion of metal condensates present in the parent body before metal silicate differentiation these metal phases would carry the ge isotopic signature of a ge enriched gas phase of the solar nebula for the iab non magmatic group the light and homogeneous ge isotopic composition may result from condensation from a 70ge enriched vapour subsequent to partial melting within a porous parent body the origin of the heating event 26al decay or impact on the surface of the chondritic body cannot be distinguished in contrast it can be demonstrated that impact events are involved in the formation of iie irons the negative 74ge ge correlation with increasing 74ge values from the old group to the watson sample of the young group would result from non rayleigh evaporation of 70ge during impact with gas melt back reaction the high 74ge of the watson sample young group is consistent with successive impacts on the surface of the iie parent body the very light ge isotopic composition of the old less impacted iie irons compared to other studied iron meteorites suggests a light ge isotopic composition for the iie parent body

temporal variability of ultraviolet cloud features in the venus stratosphere abstract statistics on the temporal variability of uv cloud features on venus during 66 days of nominal mission imaging by the pioneer venus orbiter cloud photopolarimeter reveal at least five types of systematic variability on large scales 1 a low latitude global scale wave of period 3 94 0 1 days corresponding to longitudinal motion of the dark equatorial band and propagating westward relative to the mean flow 2 a midlatitude wave of period 5 20 0 2 days corresponding to wavenumber 1 oscillations of the latitude of the bright polar bands and propagating eastward relative to the mean flow 3 2 to 3 week fluctuations in the slope of longitudinal cloud brightness power spectra at intermediate wavenumbers manifested by variations in the intensity of large bow shaped features 4 2 month variations in polar region brightness consistent with polar brightening episodes observed from earth and 5 a monotonic decrease in the disk integrated brightness of venus during the nominal mission which may be either a true time variation or a solar locked longitudinal dependence of brightness small scale features appear to correlate with large scale albedo patterns specifically cellular features exist primarily where large scale dark material is present while the orientation of streak features with respect to latitude circles oscillates with the same 4 day period as the large scale features at low latitudes the wide range of time scales present in the data suggests the complexity of venus stratospheric dynamics extended observations over many years may be becessary to define the general circulation

variations of the isotopic composition of sulfur in enstatite and ordinary chondrites abstract high precision sulfur isotopic analyses 33s 34s and 36s of bulk ordinary and enstatite chondrites demonstrate that systematic variations exist the average 34s values are 0 26 0 07 0 02 0 06 and 0 49 0 16 for enstatite and ordinary and carbonaceous chondrites respectively isotopic variations of different sample specimens of primitive meteorites e g qingzhen and abee have been observed which may be attributed to heterogeneity in the early solar nebula sulfur isotopic fractionations in both bulk samples and mineral separates are mass dependent and no nuclear isotopic anomalies have been detected the sulfur isotopic compositions of both mineral and density separates have been measured the sulfur isotopic compositions of separated chondrules from chainpur and bjurbole are reported significant isotopic difference for the chondrules from the bulk meteorite are noted for both meteorites

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

origin of isotopic heterogeneity in the solar nebula by thermal processing and mixing of nebular dust we have investigated mo and w isotope compositions in acid leachates and an insoluble residue from the murchison carbonaceous chondrite the new data reveal variable enrichments of s and r process isotopes and demonstrate that several isotopically diverse presolar components are present in murchison the insoluble residue is enriched in s process mo and w evidently due to the enrichment of presolar sic grains in contrast mo and w released by leaching with weak acids are depleted in s process isotopes most likely reflecting the isotope composition of the homogenized portion of the protosolar nebula the mo and w isotope compositions of the different leach steps are broadly correlated as expected from s process nucleosynthesis theory indicating that mo and w are presumably hosted in the same carriers however at the bulk meteorite scale no nucleosynthetic w isotope anomalies have been identified except for ivb iron meteorites in spite of large mo isotope heterogeneities among the same samples this decoupling of mo and w isotopes in bulk meteorites may reflect physical mixing of varying proportions of isotopically diverse presolar components with a normal solar nebula component due to the high w mo ratio and near terrestrial w isotope composition of the latter such mixing has no measurable effect on w isotopes but results in large mo isotope variations alternatively thermal processes within the solar nebula imparted mo isotope heterogeneity on an initially homogeneous mixture of presolar dust while w was not affected removal of volatile mo oxides during the thermal destruction of fragile presolar components would have created isotopically heterogeneous reservoirs of nebular dust accretion of meteorite parent bodies from such variably processed dust would thus result in mo isotope heterogeneities at the bulk meteorite scale other elements such as os and w were not or only slightly affected because they were more refractory during thermal processing and therefore remained isotopically homogeneous thermal processing of presolar dust within the solar nebula can thus account for both isotope heterogeneities observed for some elements and the lack of such isotopic heterogeneity for other elements

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

densities and temperatures in the venus mesosphere and lower thermosphere retrieved from soir on board venus express retrieval technique the soir instrument flying on board venus express operates in the infrared spectral domain and uses the solar occultation technique to determine the vertical profiles of several key constituents of the venus atmosphere the retrieval algorithm is based on the optimal estimation method and solves the problem simultaneously on all spectra belonging to one occultation sequence vertical profiles of h2o co hcl and hf as well as some of their isotopologues are routinely obtained for altitudes ranging typically from 70 to 120 km depending on the species and the spectral region recorded in the case of co2 a vertical profile from 70 up to 150 km can be obtained by combining different spectral intervals rotational temperature is also retrieved directly from the co2 signature in the spectra the present paper describes the method used to derive the above mentioned atmospheric quantities and temperature profiles the method is applied on some retrieval cases illustrating the capabilities of the technique more examples of results will be presented and discussed in a following companion paper which will focus on the co2 vertical profiles of the whole data set

the cosmic molybdenum ruthenium isotope correlation dauphas et al astrophys j 565 2002 640 644 reported molybdenum isotopic anomalies in differentiated and bulk primitive meteorites it is shown here that these isotopic anomalies correlate with one another in exactly the way expected from nucleosynthesis theory if different regions of the nebula received different contributions of s process matter synthesized in lowmass agb stars furthermore when bulk measurements are grouped by meteorite class the molybdenum isotopic anomalies correlate with the ruthenium isotopic anomalies recently reported by chen et al lunar planet sci xxxiv 2003 1789 again indicating a heterogeneous distribution of s process matter as molybdenum is only moderately siderophile most of the molybdenum presently in the mantle was delivered before the completion of core formation in contrast because ruthenium is highly siderophile nearly all of the mantle ruthenium was delivered by a late veneer after the end of core formation thus the fact the silicate earth lies on the mo ru cosmic correlation supports the idea that the earth accreted homogeneously stated otherwise the feeding zone of the earth did not change drastically with time as both the bulk of the earth and the late veneer accreted from material from the same mo ru isotopic reservoir d 2004 elsevier b v all rights reserved

extensive crustal extraction in earth s early history inferred from molybdenum isotopes estimates of the volume of the earliest crust based on zircon ages and radiogenic isotopes remain equivocal stable isotope systems such as molybdenum have the potential to provide further constraints but remain underused due to the lack of complementarity between mantle and crustal reservoirs here we present molybdenum isotope data for archaean komatiites and phanerozoic komatiites and picrites and demonstrate that their mantle sources all possess subchondritic signatures complementary to the superchondritic continental crust these results confirm that the present day degree of mantle depletion was achieved by 3 5 billion years ago and that earth has been in a steady state with respect to molybdenum recycling mass balance modelling shows that this early mantle depletion requires the extraction of a far greater volume of mafic dominated protocrust than previously thought more than twice the volume of the continental crust today implying rapid crustal growth and destruction in the first billion years of earth s history

sunlight refraction in the mesosphere of venus during the transit on june 8th 2004 abstract many observers in the past gave detailed descriptions of the telescopic aspect of venus during its extremely rare transits across the solar disk in particular at the ingress and egress the portion of the planet s disk outside the solar photosphere has been repeatedly perceived as outlined by a thin bright arc aureole those historical visual observations allowed inferring the existence of venus atmosphere the bright arc being correctly ascribed to the refraction of light by the outer layers of a dense atmosphere on june 8th 2004 fast photometry based on electronic imaging devices allowed the first quantitative analysis of the phenomenon several observers used a variety of acquisition systems to image the event ranging from amateur sized to professional telescopes and cameras thus collecting for the first time a large amount of quantitative information on this atmospheric phenomenon in this paper after reviewing some elements brought by the historical records we give a detailed report of the ground based observations of the 2004 transit besides confirming the historical descriptions we perform the first photometric analysis of the aureole using various acquisition systems the spatially resolved data provide measurements of the aureole flux as a function of the planetocentric latitude along the limb a new differential refraction model of solar disk through the upper atmosphere allows us to relate the variable photometry to the latitudinal dependency of scale height with temperature in the south polar region as well as the latitudinal variation of the cloud top layer altitude we compare our measurements to recent analysis of the venus express virtis m vmc and spicav soir thermal field and aerosol distribution our results can be used a starting point for new more optimized experiments during the 2012 transit event

molybdenum in eucrites evidence for a metal core in the eucrite parent body molybdenum concentrations from 15 to 70 ppb in eucrites have been determined with a new method of neutron activation these values are very low compared to chondrites and are in agreement with the large depletions of other siderophile elements in eucrites the eucrites have a mean mo la ratio of 0 0066 which is a factor of 570 lower than the ci chondritic ratio 3 75 the depletions of siderophiles in eucrites were presumably caused by segregation of metal molybdenum however is fractionated as an incompatible element similar to la among the individual eucrites the variable concentrations but roughly constant ratio of mo to la indicate that metal was absent during the fractionation that produced the eucrites and imply that core formation occurred before the fractionation the need for a relatively large degree of partial melting to completely segregate metal argues for a fractional crystallization model for the production of the eucrite magmas the amount of metal in the eucrite parent body epb required to obtain the observed depletion of the mo la ratio depends on the degree of partial melting during metal silicate equilibrium the depletion of co has a dependence on the degree of partial melting different from mo and w and using co together with mo and w the metal content and degree of partial melting can be estimated a metal content of 30 to 50 and metal segregation at approximately 50 partial melting of the silicates is consistent with the data if the epb had a ratio of co to refractory lithophile elements less than ci chondrites a metal content as low as 20 with metal segregation at 20 partial melting is possible a large metal core in the epb vesta may therefore be detectable from a spacecraft

high altitude venus haze from pioneer venus limb scans abstract high vertical resolution scans of the venus limb made by the pioneer venus orbiter cloud photopolarimeter at 365 nm and 690 nm wavelengths are used to investigate the level of the haze top and haze particle properties and scale height haze particle vertical optical depth 0 01 occurs at altitude 80 to 85 km based on knowledge of instrument pointing the lowest haze tops were observed close to subsolar longitudes but the data set supports a longitude dependence no more than a temporal variation single scattering computations for a spherical shell atmosphere show good agreement with observed intensities for particles smaller than 0 3 m radius and refractive index less than 1 7 consistent with but not limited to concentrated sulfuric acid particle scale height in the 0 5 to 2 mbar pressure regions varies between 1 and 3 km over the season 12 of 92 days latitude 15 45 n and local time 0900 1800 ranges of the observations detached layers of haze are sometimes present an average particle scale height of 2 2 km at 84 km altitude yields an eddy diffusion coefficient of 1 3 10 5 cm 2 sec 1

evidence for mo isotope fractionation in the solar nebula and during planetary differentiation abstract mass dependent mo isotope fractionation has been investigated for a wide range of meteorites including chondrites enstatite ordinary and carbonaceous chondrites iron meteorites and achondrites eucrites angrites and martian meteorites as well as for lunar and terrestrial samples magmatic iron meteorites together with enstatite ordinary and most carbonaceous chondrites define a common 98 95 mo value of 0 16 0 02 relative to the nist srm 3134 mo standard which is interpreted to reflect the mo isotope composition of bulk planetary bodies in the inner solar system heavy mo isotope compositions for iab iron meteorites most likely reflect impact induced evaporative losses of mo from these meteorites carbonaceous chondrites define an inverse correlation between 98 95 mo and metal content and a positive correlation between 98 95 mo and matrix abundance these correlations are mainly defined by cm and ck chondrites and may reflect the heterogeneous distribution of an isotopically light metal and or an isotopically heavy matrix component in the formation region of carbonaceous chondrites alternatively the elevated 98 95 mo of the cm and ck chondrites could result from the loss of volatile isotopically light mo oxides that formed under oxidized conditions typical for the formation of these chondrites the mo isotope compositions of samples derived from the silicate portion of differentiated planetary bodies are heavy compared to the mean composition of chondrites and iron meteorites this difference is qualitatively consistent with experimental evidence for mo isotope fractionation between metal and silicate the common 98 95 mo values of 0 05 0 03 of lunar samples derived from different geochemical reservoirs indicate the absence of significant mo isotope fractionation by silicate differentiation or impact metamorphism volatilization on the moon the most straightforward interpretation of the mo isotope composition of the lunar mantle corresponds to the formation of a lunar core at a metal silicate equilibration temperature of 1800 200 c the investigated martian meteorites angrites and eucrites exhibit more variable mo isotope compositions which for several samples extend to values above the maximum 98 95 mo 0 14 that can be associated with core formation for these samples post core formation processes such as partial melting metamorphism and in the case of meteorite finds terrestrial weathering must have resulted in mo isotope fractionation estimates of the metal silicate equilibration temperatures for mars 2490 770 c and the angrite parent body 1790 230 c are thus more uncertain than that derived for the moon although the mo isotope composition of the bulk silicate earth has not been determined as part of this study a value of 0 16 98 95 mo 0 can be predicted based on the chondrite and iron meteorite data and by assuming a reasonable temperature range for core formation in the earth this estimate is in agreement with four analyzed basalt standards 0 10 0 10 improved application of mass dependent mo isotope fractionation to investigate core formation most of all requires an improved understanding of potential mo isotope fractionation during processes not related to metal silicate differentiation

a petrologic study of the iab iron meteorites constraints on the formation of the iab winonaite parent body abstract we have studied iab iron meteorites and their silicate bearing inclusions to elucidate the origin of their parent body we have divided iab irons into five categories which best describe the inclusions and other properties of the irons these are 1 sulfide rich irons such as mundrabilla that contain a significant volume fraction of troilite with or without associated silicates 2 irons with non chondritic silicate inclusions such as basaltic inclusions in caddo county 3 irons with rounded troilite and or graphite inclusions sometimes containing embedded angular silicate inclusions 4 irons with angular silicate inclusions similar to those of the winonaites where silicates may comprise up to 40 vol of the rock and 5 irons with phosphate bearing inclusions such as the brianite bearing iab san cristobal similarities in mineralogy mineral and oxygen isotopic compositions suggest that iab irons and winonaites are almost certainly from a common parent body iiicd irons may also have originated on this parent body although evidence supporting this suggestion is less convincing previous models for the origin of iab irons propose that they are either products of selective impact melting in the megaregoliths of a chondritic asteroid or products of partial melting and fractional crystallization during formation of a sulfur rich core the former model suffers from the fact that impact is incapable of causing preferential melting of metal and sulfide on a large scale and pooling of these selective melts into sizable bodies the latter model does not readily explain the occurrence of often fragmentary angular silicate clasts in a metallic fe ni host we propose a new model for the origin of iab irons that incorporates aspects of both previous models we suggest that a chondritic possibly heterogeneous parent body was heated by a non collisional heat source which caused partial but not complete melting of the body after peak temperatures were reached and cooling and crystallization had begun a major impact catastrophically fragmented this body and the debris gravitationally reassembled scrambling the parent body lithologies we suggest that the impact caused extensive mixing of molten metallic fe ni and solid silicate material resulting in the formation of iab irons with silicate inclusions whereas winonaites represent metamorphosed rocks and partial melt residues of the precursor silicate lithologies high temperatures of some of the reassembled debris and deep burial resulted in continued fractionation and formation of the 2

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

sr stable isotope composition of earth the moon mars vesta and meteorites abstract high precision stable sr isotopic variations 88 sr 86 sr are reported in a variety of terrestrial samples martian and lunar meteorites hed undifferentiated primitive meteorites chondrules and refractory inclusions almost all the whole rock samples are isotopically indistinguishable at a 50 parts per million ppm level the exceptions are cv and co chondrites which are isotopically light and for which we believe that their isotopic composition is controlled by the proportion of refractory material five separated chondrules and one refractory inclusion from allende are isotopically light with 88 86 sr fractionations up to 1 73 whereas the matrix is enriched in the heavy isotopes 88 86 sr 0 66 the depletion in heavy isotopes observed in chondrules and refractory inclusions could be attributed to the condensation of a material already depleted in sr however in that case more than 60 of the original material would be unaccounted we propose instead that isotopic fractionation by electromagnetic sorting of ionized heavy sr from neutral sr in the early solar system for the origin of the fractionation observed in refractory inclusions and redistribution of sr by aqueous alteration for the origin of the fractionation observed in chondrules and matrix we conclude that cv and co chondrites are not the primary building blocks for earth and mars

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

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

scale heights and detached haze layers in the mesosphere of venus from spicav ir data abstract spicav ir one channel of spicav soir instrument suite onboard venus express performed solar occultation measurements of the atmosphere at terminators in 0 65 1 7 m spectral range we analyze the properties of the upper part of the venus aerosol layer upper haze 70 95 km altitude from 798 observations performed from may 2006 through november 2014 vertical profiles of slant optical depth extinction coefficient effective radius and number density of haze particles from 222 orbits were analyzed in a previous publication luginin et al 2016 their diurnal latitudinal and interannual variabilities were investigated the present paper is devoted to analysis of scale heights and properties of detached haze layers from 147 orbits at mid to high northern latitudes where the best spatial resolution was obtained scale heights retrieved from 43 orbits were equal to 4 5 5 km at the north pole 82 n 90 n decreasing to 2 4 km at 60 n 80 n latitudes as an explanation of such latitudinal variations we propose a mechanism based on vertical transport driven by winds that are directed upward at the north pole and downward at 60 n 80 n latitudes detached layers were detected in 93 occultations at 58 n 90 n the detached layers are presumably formed through condensation of water vapor on droplets of sulfuric acid water solution they were mostly seen at 80 88 km at the morning terminator and at 84 90 km at the evening one this difference in altitude of the detached layers can be explained by diurnal variations in thermal structure of venusian mesosphere the vertical optical depth of detached layers varies broadly around the mean dl 0 8 3 10 3 no difference between the morning and the evening terminators was observed the effective radius and number density of aerosol particles in the detached layers group around a very wide maximum at the morning terminator 0 65 0 25 m and 0 6 0 4 cm 3 and two maxima at the evening terminator 0 4 0 1 m and 0 85 0 15 m 0 3 0 2 cm 3 and 4 5 2 5 cm 3 this could be explained by differences in initial altitudes at which condensation of particles occurs

forming a moon with an earth like composition via a giant impact in the giant impact theory the moon formed from debris ejected into an earth orbiting disk by the collision of a large planet with the early earth prior impact simulations predict that much of the disk material originates from the colliding planet however earth and the moon have essentially identical oxygen isotope compositions this has been a challenge for the impact theory because the impactor s composition would have likely differed from that of earth we simulated impacts involving larger impactors than previously considered we show that these can produce a disk with the same composition as the planet s mantle consistent with earth moon compositional similarities such impacts require subsequent removal of angular momentum from the earth moon system through a resonance with the sun as recently proposed

experimental determination of the si isotope fractionation factor between liquid metal and liquid silicate abstract the conditions of core formation and the abundances of the light elements in earth s core remain debated silicon isotope fractionation provides a tool contributing to this subject we present experimentally determined si isotope fractionation factors between liquid metal and liquid silicate at 1450 c and 1750 c which allow calibrating the temperature dependence of si isotope fractionation experiments were performed in a centrifuging piston cylinder at 1 gpa employing both graphite and mgo capsules tin was used to lower the melting temperature of the metal alloys for experiments performed at 1450 c tests reveal that neither sn nor c significantly affects si isotope fractionation an alkaline fusion technique was employed to dissolve silicate as well as metal phases prior to ion exchange chemistry and mass spectrometric analysis the results show that metal is consistently enriched in light isotopes relative to the silicate yielding average metal silicate fractionation factors of 1 48 0 08 and 1 11 0 14 at 1450 c and 1750 c respectively the temperature dependence of equilibrium si isotope fractionation between metal and silicate can thus be described as 30 si metal silicate 4 42 0 05 10 6 t 2 the si isotope equilibrium fractionation is thus about 1 7 times smaller than previously proposed on the basis of experiments a consequence of this smaller fractionation is that the calculated difference between the si isotope composition of the bulk earth and that of the bulk silicate earth generated by core formation is smaller than previously thought it is therefore increasingly difficult to match the si isotope composition of the bulk silicate earth with that of chondrites for metal silicate equilibration temperatures above 2500 k this suggests that si isotopes were more sensitive to the early stages of core formation when low oxygen fugacities allowed significant incorporation of si into metal

tungsten stable isotope compositions of terrestrial samples and meteorites determined by double spike mc icpms abstract tungsten stable isotopes hold great potential to examine a variety of physical and chemical processes operating during the accretion and differentiation of asteroids and terrestrial planets such as core formation and mantle crust differentiation to assess the magnitude and origin of w isotope fractionations we determined the w stable isotopic compositions of six usgs geological reference materials a nist steel and 24 iron meteorites and chondrites the w isotope data were obtained using multi collector inductively coupled plasma mass spectrometry mc icpms and using a 180 w 183 w double spike chondrites and iron meteorites exhibit a very narrow range in w stable isotope compositions resulting in a mean 184 183 w 0 027 0 007 95 conf relative to the nist 3163 w standard this value represents a good estimate for the w stable isotope composition of bulk planetary bodies from the inner solar system the 184 183 w of some iron meteorites slightly deviates from this value most likely due to w isotope fractionations induced during crystallization of the metal cores of iron meteorite parent bodies the investigated terrestrial silicate rocks exhibit a narrow range in 184 183 w which for most samples is indistinguishable from the mean value of chondrites and iron meteorites however felsic samples tend to be isotopically lighter than mafic samples indicating that magmatic processes on earth induced w isotope fractionations these fractionations are possibly related to the fluid mobility of w in subduction zones but more data are needed to test this hypothesis given that most terrestrial igneous rocks are isotopically indistinguishable from chondrites and iron meteorites core formation on earth does not seem to have induced a measurable isotopic fractionation for w however more data are needed to firmly arrive at this conclusion

isotopic composition of zinc copper and iron in lunar samples abstract we determined by icp ms the concentrations and isotopic ratios of fe cu and zn in the ti rich lunar basalt 74275 in the lunar orange glass 74220 and in up to 10 lunar soils namely 14163 15231 64501 66041 68841 69941 70011 72501 75081 and 76501 two analyses of zinc in lunar basalt 74275 give 66 zn 0 17 and 0 75 values within the range of those measured in terrestrial basalts copper in lunar basalt 74275 has 65 cu 1 4 which is isotopically heavier than values observed in terrestrial basalts in the orange glass we measured 56 fe 0 24 65 cu 0 42 and 66 zn 3 6 these values of are more negative than those obtained for 74275 and for typical lunar basalts but for cu comparable to those observed in terrestrial sulfides and meteorites in lunar soils we found 0 11 56 fe 0 51 2 6 65 cu 4 5 and 2 2 66 zn 6 4 insofar as we can generalize from a small sample set s fe cu zn and cd show similar trends in isotopic fractionation on the moon lunar basalts have nearly terrestrial isotopic ratios relative to the lunar basalt 74275 the pyroclastic glass 74220 is enriched in the lighter isotopes of fe cu and zn and the soils are enriched in the heavier isotopes of fe cu and zn the patterns in the basalts are likely inherited from the source material the light isotope enrichments seen in the orange glass originated during lava fountaining or less probably during partial condensation of vapor and the heavy isotope enrichments in the lunar soils were likely created by a combination of processes that included micrometeorite vaporization and sputtering in the orange glass the light isotope enrichments relative to lunar basalts of zn are larger than those of cu if these enrichments reflect accurately the isotopic composition of the gas they suggest that cu is more volatile than zn in the liquid from which the gas derived a simple model built on the known flux of micrometeorites to the lunar surface and a published estimate that micrometeorites generate 10 times their own mass of vapor predicts heavy isotope enrichments comparable to those observed in soils but only if the regolith gardening rate is set at about one twentieth of the generally accepted value of 1 cm my this discrepancy may reflect the difference in the time constants for micrometeorite milling and decimeter scale gardening or the importance of sputtering

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

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

determination of molybdenum isotope fractionation by double spike multicollector inductively coupled plasma mass spectrometry 1 molybdenum isotopic compositions are precisely determined by mc icp ms measurements using a mo double spike the double spike is added prior to chemical purification so that laboratory and instrumental mass fractionations are separated from natural mass dependent fractionation fractionation is determined on four mo mass ratios providing an internal consistency check the external standard reproducibility is at 0 06 per mil on the 98mo 95mo ratio 2 standard deviation using a normal microconcentric nebuliser with a cyclonic spray chamber the minimum quantity of mo is 1 g for high precision results a hydrothermal molybdenite shows fractionation of 0 3 per mil on the 98mo 95mo ratio relative to our standard johnson matthey 1000 g ml 0 3 icp standard solution lot 602332b fine grained sediments show fractionation of 0 1 and 0 3 per mil on the 98mo 95mo ratio the observed mo isotope fractionation is small but resolvable with the presented high resolution technique

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

the double spike toolbox the double spike technique is a well established method for correcting for instrumental mass fractionation in mass spectrometry the precision of the technique is controlled by the choices of double spike composition and the proportions in which the double spike and sample are mixed to make these choices easier we provide software the double spike toolbox for calculating optimal double spikes which are chosen purely on the basis of minimising error propagation in addition we provide cocktail lists of optimal double spikes for all 33 elements that have 4 or more naturally occurring isotopes using some sensible default parameters as examples we discuss the application of the software to fe pb and ca isotopes

precise determination of the isotopic composition of potassium application to terrestrial rocks and lunar soils we detail a method for the precise and accurate determination of isotopic variations in the 41k39k ratio with a precision of 0 5 2 m purified potassium is chemically extracted from rocks soils minerals or solutions by ion exchange chromatography complete chemical yields 99 8 are achieved in order to avoid laboratory induced isotopic fractionations the purified potassium is converted to a glass by melting with barium borate flux and the resultant bead is mounted for ion probe analysis the sims method utilized by the ion probe produces extremely stable k ion beams with no measurable temporal variability in the isotope ratio the instrumental fractionation is steady at about 4 and is corrected for by measurement of a standard the measurement of gravimetrically prepared isotopic standards indicates that the method is accurate at the stated level of precision and free of egregious errors analysis of terrestrial samples including peridotite basalts granites carbonatite biotite schists and seawater indicate the complete absence of isotopic variations in 41 1k among terrestrial materials at the 0 5 o level application to lunar soils and a regolith breccia confirms previously observed large isotopic fractionation effects garner et al 1975a church et al 1976 some lunar soils e g 14163 are shown to have large sample heterogeneity 7 o while others e g soils and a regolith breccia at several apollo 15 sites station 79 are homogeneous at the level of analytical precision the presence of potassium isotopic effects in bulk soils up to 12 7 in this study with magnitudes comparable to the rayleigh fractionation factor 25 indicates that volatility during micrometeorite impact melting played a large role in lunar regolith formation as much as 15 of the regolith potassium has been lost from the moon through the tenuous lunar atmosphere

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

the isotopic signature of the global riverine molybdenum flux and anoxia in the ancient oceans despite important biological and biogeochemical consequences of extensive ocean anoxic events their identification is controversial the marine isotope geochemistry of molybdenum can help quantify the past oxygenation state of the ocean if the riverine input of mo isotopes is known analysis of a set of rivers that account for 28 of global river runoff suggests more variable mo isotopic ratios in rivers that are also isotopically enriched in the heavy isotopes suggesting near total anoxia in the proterozoic ocean and during mesozoic ocean anoxic events despite its important biological and biogeochemical consequences1 2 3 the identification of extensive oceanic anoxia in the geological record is controversial in particular global anoxia is difficult to distinguish from spatially restricted anoxia in the deep ocean or in tectonically isolated basins such as the modern black sea the marine isotope geochemistry of molybdenum mo can help quantify the past oxygenation state of the ocean4 5 6 7 8 9 10 11 12 13 14 because to first approximation under oxic conditions lighter isotopes of mo are preferentially removed to sediments whereas in euxinic conditions quantitative removal leads to no fractionation however the isotopic composition of the mo input from rivers the main contributor of mo to the oceans is poorly constrained and had been assumed to be isotopically comparable to the narrow range found in a small dataset of continental rocks4 5 6 7 8 9 10 11 12 13 14 here we present an isotopic analysis of mo in a set of rivers that together account for 22 of the global riverine water discharge we find a broad range of variability in the mo isotopic composition of these rivers with almost all samples enriched in the heavy isotopes compared with continental rocks our data remove key uncertainties associated with the marine mo isotope budget14 and strongly suggest near total anoxia in the mid proterozoic ocean8 as well as during mesozoic ocean anoxic events13

cooperation among tectonic and surface processes in the st elias range earth s highest coastal mountains investigations of tectonic and surface processes have shown a clear relationship between climate influenced erosion and long term exhumation of rocks numerical models suggest that most orogens are in a transient state but observational evidence of a spatial shift in mountain building processes due to tectonic climate interaction is missing new thermochronology data synthesized with geophysical and surface process data elucidate the evolving interplay of erosion and tectonics of the colliding yakutat microplate with north america focused deformation and rock exhumation occurred in the apex of the colliding plate corner from 4 to 2 ma and shifted southward after the 2 6 ma climate change the present exhumation maximum coincides with the largest modern shortening rates highest concentration of seismicity and the greatest erosive potential we infer that the high sedimentation caused rheological modification and the emergence of the southern st elias intercepting orographic precipitation and shifting focused erosion and exhumation to the south

the molybdenum isotopic compositions of i s and a type granitic suites this study reports mo isotopic compositions for fifty two palaeozoic granitic rocks with contrasting source affinities a i and s type from the lachlan fold belt lfb and the new england batholith neb both in se australia and three compositionally zoned plutons loch doon criffell and fleet located in the southern uplands of scotland the results show relatively large variations in 98mo for igneous rocks ranging from 1 73 to 0 59 with significant overlaps between different types no relationships between 98mo and 18o or asi alumina saturation index are observed indicating that mo isotopes do not clearly distinguish igneous vs sedimentary source types instead effects of igneous processes source mixing regional geology as well as hydrothermal activity control the mo isotope compositions in these granites it is found that mo is mainly accommodated in biotite and to a lesser extent in hornblende hornblende and fe3 rich minerals may preferentially incorporate light isotopes as reflected by negative correlations between 98mo and k rb and fe2o3 there is a positive correlation between initial 87sr 86sr and 98mo in i type granitic rocks reflecting the admixing of material from isotopically distinct sources granitic rocks from scotland and australia display strikingly similar curvilinear trends in 98mo vs initial 87sr 86sr despite the differing regional geology localized hydrothermal effects can result in low 98mo in granite as seen in three samples from loch doon and criffell which have anomalously light 98mo of 1 based on this study an estimate of 98mo 0 14 0 07 95 s e for the phanerozoic upper crust is proposed this is slightly heavier than basalts indicating an isotopically light lower crust and or a systematic change to the crust resulting from subduction of isotopically light dehydrated slab and or pelagic sediment over time

the formation of eucrites constraints from metal silicate partition coefficients this study explores the controls of oxygen fugacity and temperature on the solubilities of fe ni co mo and w in natural eucritic liquids to better constrain the formation of eucritic melts the solubilities of all five elements in molten silicate in equilibrium with fenico femo and fewalloys increase with increasingly oxidizing conditions and decrease with decreasing temperatures in applying these data to formation scenarios of the eucrite parent body we find that the siderophile element abundances in eucrites meteoritic basalts cannot be explained by a single step partialmelting process from a chondritic metal containing source the ni content of the partial melt is too high and the w and mo contents are too low compared to the abundances in eucritic meteorites but fe ni and co concentrations in eucrites can be modeled by metal silicate equilibrium during more or less complete melting of the eucrite parent body with subsequent fractional crystallization of olivine and orthopyroxene however the computed values of mo are still too low and those of w too high when compared with mo and w abundances in eucritic meteorites one possibility is that the mo and w partition coefficients strongly depend on pressure although the howardite eucrite diogenite hed parent body only had a minimal pressure gradient maximum interior pressure 0 1 gpa alternatively sulfides may have played some role in establishing mo abundances

accretion and core formation on mars molybdenum contents of melt inclusion glasses in three snc meteorites abstract molybdenum cerium barium yttrium and rubidium contents of glasses in melt inclusions in three snc meteorites lew 88516 governador valadares and chassigny have been measured by ion microprobe ratios of mo ba and mo ce have been used to estimate the mo content of the primitive martian mantle 120 60 ppb abundances of five moderately siderophile elements ni co mo w and p and re in the martian mantle are consistent with metal silicate equilibrium between s bearing metallic liquid in a core 22 wt of the planet and peridotite melt at 75 kb 1620 c and oxygen fugacity 1 4 logfo2 units below the iw buffer this homogeneous accretion scenario is different than many heterogeneous accretion models for the earth but similar to recent studies suggesting homogeneous accretion in the presence of a deep terrestrial magma ocean

silicon isotope evidence against an enstatite chondrite earth the compositions of earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems although this suggests that earth largely accreted from enstatite chondrites definitive proof of this model has been lacking by comparing the silicon si isotope signatures of several extraterrestrial materials with terrestrial samples we show that they cannot be explained by core formation scenarios involving a bulk earth of enstatite chondrite composition si isotope similarities between the bulk silicate earth and the moon preclude the existence of a hidden reservoir in the lower mantle a necessary condition of the enstatite chondrite model and require an equilibrium process after the moon forming impact a three end member chondritic mixing model for earth reconciles the si isotope similarities between enstatite chondrites and earth

melting temperatures of the allende meteorite implications for a hadean magma ocean abstract melting temperatures of the silicate fraction of the allende cv3 meteorite at upper mantle pressures are several hundred degrees lower than that of fertile peridotite xenoliths or pyrolite if the earth accreted from material similar to chondrites then deep mantle melting could have occurred with a relatively modest heat budget it is concluded that initial chemical composition is an important variable in realistic magma ocean models

vertical structure of the venus cloud top from the vera and virtis observations onboard venus express abstract we investigate the venus cloud top structure by joint analysis of the data from visual and thermal infrared imaging spectrometer virtis and the atmospheric temperature sounding by the radio science experiment vera onboard venus express the cloud top altitude and aerosol scale height are derived by fitting virtis spectra at 4 5 m with temperature profiles taken from the vera radio occultation our study shows gradual descent of the cloud top from 67 2 1 9 km in low latitudes to 62 8 4 1 km at the pole and decrease of the aerosol scale height from 3 8 1 6 km to 1 7 2 4 km these changes correlate with the mesospheric temperature field in the cold collar and high latitudes the cloud top position remarkably coincides with the sharp minima in temperature inversions suggesting importance of radiative cooling in their maintenance this behaviour is consistent with the earlier observations spectral trend of the cloud top altitude derived from a comparison with the earlier observations in 1 6 27 m wavelength range is qualitatively consistent with sulphuric acid composition of the upper cloud and suggests that particle size increases from equator to pole

the evolution of partially differentiated planetesimals evidence from iron meteorite groups iab and iiicd group iab irons probably come from a parent body that partially differentiated into a sulfur rich molten core and a primitive silicate outer layer in which only minor or localized melting occurred although the complexity of meteorites from this parent body or bodies irons with and without massive silicate inclusions stony meteorites like winona sulfide rich meteorites like mundrabilla etc implies a complicated history the partial differentiation model is consistent with most properties of these meteorites the behavior of five model parent bodies of different composition during heating to 1400 k the temperature recorded in many i ab silicates shows that meteorites like iab irons can form by this process sulfide rich parent bodies differentiate into a liquid s rich core and a primitive metal bearing mantle around 1230 k but in parent bodies lower in sulfide abundance this process may be delayed until minor melting of silicates occurs 1370 30 k in most cases any silicate melt that may have formed resolidified in situ the sulfide melt fractionally crystallized along the fe ni fes cotectic some melt was injected into silicates to form copiapo type breccias considerations of graphite metal silicate equilibrium and the retention of noble gases suggest that brecciated iabs formed at depth inside a moderately large a few tens to a hundred kilometers parent body the correlation of i xe ages with ni content is interpreted as the result of an excess 129xe component associated with the s rich melt which increases with melt evolution

silicon isotopes in lunar rocks implications for the moon s formation and the early history of the earth silicon isotopic data from a range of lunar samples are presented to assess the degree of heterogeneity of the lunar mantle and its similarity to bulk silicate earth bse multi collector inductively coupled plasma mass spectrometry mc icpms was used to analyse 24 samples including both high and low ti basalts as well as highland anorthosites and picritic glasses covering all the apollo sample return missions no systematic 30si differences are found between any of the bulk sample lithologies 2 sd 30silow ti basalt 0 29 0 06 30sihigh ti basalt 0 32 0 09 30silunar glass 0 29 0 05 and 30sihighland rocks 0 27 0 10 the average of the lunar samples is 30si 0 29 0 08 2 sd which is identical to the composition of bse 30si 0 29 0 08 2 sd from savage et al 2010 the bse si isotope composition is thought to be the result of si partitioning between metal and silicate and consequent isotopic fractionation during core formation the moon forming impactor would not be expected to share that composition because it is thought to have been relatively small 0 1 earth masses like mars and formed under relatively low temperatures and pressures that are insufficient for si to partition into the core therefore the identical lunar and bse si isotope data show that si isotopes like those of oxygen must have homogenised in the aftermath of the moon forming impact if smooth particle hydrodynamic simulations of the giant impact are correct in showing that most lunar material should have originated from the impactor rather than the earth the data presented here are in agreement with other isotope systems and experimental studies that indicate that the majority of core formation happened early and before the giant impact it has been predicted pahlevan et al 2011 that the moon and the bse should show a 0 14 offset in 30si for the moon to have an fe fe mg ratio twice that of bse the current resolution and sample population size of the si data for the moon and earth would allow such an offset to be detected the fact that is it not observed can put constraints on the element ratios and lunar budgets as modelled by pahlevan et al 2011 in particular it constrains the fe fe mg ratio of the moon to be only 1 1 3 bse

evidence for oxidizing conditions in the solar nebula from mo and w depletions in refractory inclusions in carbonaceous chondrites abstract depletions of mo and w relative to other refractory metals of similar volatility re os ir ru pt are common in a suite of 16 ca al rich inclusions cais from 5 carbonaceous chondrites twelve of the 16 cais from allende grosnaja leoville and ornans show mo depletions six of these 12 inclusions also show w depletions the one cai analyzed from the essebi chondrite shows no depletions the mo and w depletions have a very characteristic pattern with mo always more depleted than w the same mo and w depletion pattern occurs in calculated refractory metal alloy compositions formed at oxygen fugacities 10 3 to 10 4 times greater than the canonical solar nebula oxygen fugacity we conclude that mo and w depletions are common in cais from carbonaceous chondrites and that the depletions result from high temperature oxidation the oxidation may have occurred during the evaporation of primitive dust into cais but is also consistent with condensation at high oxygen fugacities no potential alternative processes appear to be capable of producing the observed mo and w depletion patterns

a hit and run giant impact scenario abstract the formation of the moon from the debris of a slow and grazing giant impact of a mars sized impactor on the proto earth cameron and ward 1976 lunar planet sci conf canup and asphaug 2001 nature 412 708 is widely accepted today we present an alternative scenario with a hit and run collision asphaug 2010 chem erde 70 199 with a fractionally increased impact velocity and a steeper impact angle

a planetary perspective on the deep earth earth s composition evolution and structure are in part a legacy of provenance where it happened to form and chance the stochastics of that formation