nominally hydrous magmatism on the moon for the past 40 years the moon has been described as nearly devoid of indigenous water however evidence for water both on the lunar surface and within the lunar interior have recently emerged calling into question this long standing lunar dogma in the present study hydroxyl as well as fluoride and chloride was analyzed by secondary ion mass spectrometry in apatite ca5 po4 3 f cl oh from three different lunar samples in order to obtain quantitative constraints on the abundance of water in the lunar interior this work confirms that hundreds to thousands of ppm water of the structural form hydroxyl is present in apatite from the moon moreover two of the studied samples likely had water preserved from magmatic processes which would qualify the water as being indigenous to the moon the presence of hydroxyl in apatite from a number of different types of lunar rocks indicates that water may be ubiquitous within the lunar interior potentially as early as the time of lunar formation the water contents analyzed for the lunar apatite indicate minimum water contents of their lunar source region to range from 64 ppb to 5 ppm h2o this lower limit range of water contents is at least two orders of magnitude greater than the previously reported value for the bulk moon and the actual source region water contents could be significantly higher

crustal partial melting on vesta evidence from highly metamorphosed eucrites we have performed a mineralogical and geochemical study of eight metamorphosed basaltic eucrites these are classified into granulitic eucrites and type 4 7 eucrites on the basis of their textures and pyroxene mineralogy and display mineralogical evidence for high temperature metamorphism including partial melting in particular rare earth element ree patterns of a number of the eucrites studied show varying degrees of light ree depletion due to partial melting with subsequent melt extraction a simple correlation between metamorphic grade as deduced from pyroxene mineralogy and the degree of light ree depletion was not detected this can be explained by the fact that homogenization exsolution and inversion of pigeonite would have required prolonged heating at moderate temperatures not vert similar800 1000 c whereas partial melting would have taken place over a short time interval where temperatures exceeded that of the solidus the eucrites studied therefore record a two stage thermal regime consisting of short high temperature reheating events superimposed on long duration global crustal metamorphism the short reheating events may have been caused by impact events and or intrusions of hot magmas the results of this study demonstrate that the thermal history of eucritic crust was more complex than can be explained by a simple burial model alone in particular the origin of stannern trend eucrites requires contamination of main group magmas by partial melts extracted from residual eucrites

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

hydrous melting of the martian mantle produced both depleted and enriched shergottites the search for water in our solar system is one of the primary driving forces for planetary science and exploration because water plays an important role in many geologic processes and is required for biologic processes as we currently understand them excluding earth mars is the most promising destination in the inner solar system to find water as it is undoubtedly responsible for shaping many geomorphologic features observed on the present day martian surface however the water content of the martian interior is currently unresolved much of our information about the martian interior comes from studies of the basaltic martian meteorites shergottites in this study we examined the water contents of magmatic apatites from a geochemically enriched shergottite the shergotty meteorite and a geochemically depleted shergottite the queen alexandria range 94201 meteorite from these data we determined that there was little difference in water contents between the geochemically depleted and enriched shergottite magmas the water contents of the apatite imply that shergottite parent magmas contained 730 2870 ppm h 2 o prior to degassing furthermore the martian mantle contains 73 290 ppm h 2 o and underwent hydrous melting as recently as 327 ma in the absence of plate tectonics the presence of water in the interior of mars requires planetary differentiation under hydrous conditions this is the first evidence of significant hydrogen storage in a planetary interior at the time of core formation and this process could support elevated h abundances in the interiors of other terrestrial bodies like the moon mercury venus large differentiated asteroids and earth

hydrogen isotope evidence for loss of water from mars through time 1 the high d h of the martian atmosphere 5 6 terrestrial is considered strong evidence for the loss of martian water to space the timing and magnitude of the loss of water from mars can be constrained by measurements of d h in martian meteorites previous studies of martian meteorites have shown a large range in d h from terrestrial values to as high as the current martian atmosphere here we show that the ancient 4 ga mars meteorite alh84001 has a d h 4 terrestrial and that the young 0 17 ga shergotty meteorite has a d h 5 6 terrestrial we also find that the young los angeles shergottite has zoning in d h that can be correlated to igneous growth zoning strongly suggesting assimilation of d enriched water during igneous crystallization near the martian surface in contrast to previous studies we find higher and less variable d h ratios in these three meteorites our results suggest a two stage evolution for martian water a significant early loss of water to space prior to 3 9 ga followed by only modest loss to space in the last 4 billion years the current martian atmospheric d h has remained essentially unchanged for the last 165 ma

timing of crystallization of the lunar magma ocean constrained by the oldest zircon the primitive moon was covered with a thick layer of melt known as the lunar magma ocean whose crystallization resulted in the moon s surface as it is observed today dating of the oldest zircon so far in lunar rocks indicates that much of the magma was probably crystallized within 100 million years of the moon s formation

mineralogical records of early planetary processes on the howardite eucrite diogenite parent body with reference to vesta abstract mineralogical information recovered from the howardite eucrite diogenite hed meteorites was employed to reconstruct the history of the parent body and relate it to 4 vesta these interpreted crustal evolution processes were then compared to the expected geological features on the surface of a likely proto planet 4 vesta the original crustal materials of the hed parent body were preserved as mineral grains and lithic clasts but in many eucrites fe mg ratios in pyroxenes were homogenized by diffusion after crystallization the crystallization trend of the protocrust has been deciphered by 1 examining monomict and crystalline samples and using their mineralogical and chemical information to formulate a sequence of crystallization and cooling trends and by 2 reconstructing the original crust prior to cratering events from lithic clasts and mineral fragments in polymict breccias such as howardites and polymict eucrites mineral components are identical both in the individual hed and in polymict breccias and no remnants of primitive materials were preserved in the polymict breccias a layered crust model reconstructed from such breccias consists of an upper crust with extrusive lava like eucrites that have been brecciated and metamorphosed diogenite mantle and cumulate eucrites of varying thickness between them this model can be used to explain the surface geological features of vesta observed from the hubble space telescope a large crater with diogenitic orthopyroxene at the crater floor is consistent with the deepest diogenitic layer of the layered crust model and an underlying olivine layer is expected from early crystallized olivine in the crystal fractionation model the old terrain of eucritic surface materials of vesta can be howardites polymict eucrites or regolith like eucrites produced from eucrites extruded and impacted on the surface partial melting models of eucrites seem to be favored by the rare earth element ree chemistry and experimental studies unfortunately partial melting models have not demonstrated how the hed parent body is converted to a layered crust without producing any metamorphosed primitive material in the layered crust the origin of cumulate eucrites with systematic variation of textures and chemistries of pyroxene can be explained by the layered crust model with excavation and mixing of trapped liquid discovery of basaltic materials with na rich plagioclase and augite in iron meteorites which are the products of partial melting suggests that eucrites may be unique to a body that underwent large scale differentiation and metamorphism

lunar apatite with terrestrial volatile abundances the moon is thought to be depleted relative to the earth in volatile elements such as h cl and the alkalis nevertheless evidence for lunar explosive volcanism has been used to infer that some lunar magmas exsolved a co rich and co 2 rich vapour phase before or during eruption although there is also evidence for other volatile species on glass spherules until recently there had been no unambiguous reports of indigenous h in lunar rocks here we report quantitative ion microprobe measurements of late stage apatite from lunar basalt 14053 that document concentrations of h cl and s that are indistinguishable from apatites in common terrestrial igneous rocks these volatile contents could reflect post magmatic metamorphic volatile addition or growth from a late stage interstitial sulphide saturated melt that contained 1 600 parts per million h 2o and 3 500 parts per million cl both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable terrestrial materials one possible implication is that portions of the lunar mantle or crust are more volatile rich than previously thought

low mg rock debris in howardites evidence for kreepy lithologies on vesta the northwest africa nwa 1664 and 1769 howardites contain fragments of low mg lithologies these clasts consist of plagioclase fe rich pyroxenes high ca pyroxene and an fe rich pigeonite or pyroxferroite partially to totally converted to a silica fayalite hedenbergite symplectite k ba feldspars hyalophane silica troilite phosphates merrillite and apatite ilmenite baddeleyite and zircon textural considerations and phase compositions show that these clasts cannot be unrepre sentative debris of mesostasis rich areas from eucrites but are instead remnants of evolved rocks the occurrence of hyalo phane and the modal abundances of phosphates in the largest of them suggest that their source rocks were much more k and p rich than regular heds moreover the rare earth element abundances of the pyroxenes indicate that their parental melts were rich in incompatible trace elements possibly at the level of 100 ci or much higher for heavy rees with variable negative eu anomalies although their petrogenesis is uncertain they demonstrate that magmatic activity on vesta has been able to generate a diversity of rocks greater than generally thought and local lithologies with possible kreep affinities

radiometric ages of basaltic achondrites and their relation to the early history of the solar system pbpb mineral isochrons were determined for three cumulate eucrites moama moore county and serra de mage and three noncumulate eucrites nuevo laredo bouvante and stannern two noncumulate eucrites bereba and cachari show disturbed pb isotope patterns the mineral isochron ages of cumulate eucrites range from 4 40 ga to 4 48 ga the latter is the age of moore county 4 484 0 019 ga which was also dated by the smnd method at 4 456 0 025 ga nuevo laredo and bouvante give the same pb pb age 4 514 0 015 ga and 4 510 0 004 ga respectively the pb isochron of stannern corresponds to 4 128 0 016 ga which is a reequilibration age both cachari and bereba show evidence of isotope resetting at about 4 ga a pb pb multicotrelation approach is introduced and applied to the data the younger ages of the cumulate eucrites preclude their formation by fractional crystallization from the melts that produced the noncumulate eucrites the 1 of the source of the cumulate eucrites is 14 whereas that of the source of the noncumulate eucrites is 150 this large difference in 1 values suggests that eucrites were derived from separate planetesimals or from a single heterogeneous layered parent body

investigations of the stillwater complex part v apatites as indicators of evolving fluid composition variations in the f cl and oh contents of apatite are not constrained by crystal chemical factors in contrast to micas and amphiboles and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks microprobe analysis of intercumulus apatites from the stillwater complex reveal that cl rich apatites typically containing 6 0 wt cl occur throughout the lower 1 3 of the complex excluding the basal series a change from cl rich to more f rich apatite occurs within olivine bearing zone i ob i of the banded series the host zone of the platiniferous j m reef although apatite compositions are somewhat variable above the j m reef more f rich apatites predominante and typically contain 1 2 wt f and 3 0 wt cl the most f rich apatites occur in the uppermost exposed cumulates pristine apatites from coeval sills and dikes from below the complex and from the basal series are similarly f rich in all apatites the cl and f contents are lower in rocks affected by later metamorphic fluids rare earth element ree concentrations in chlorapatites show a marked peak in the olivine rich rocks of the j m reef and contain up to 2 wt ce2o3 la2o3 the trend of first increasing then decreasing cl f ratios with stratigraphic height is modeled by a vapor driven zone refining process occurring within the cumulate pile causing cl enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of cl from the magma as crystallization proceeded the abrupt change from cl rich to more f rich apatites within ob i is interpreted as the result of a breakdown of the cl rich zone refining front and mixing with cl poor supernatant melt any high temperature fluids that exsolved and circulated through the lower 1 3 of the complex must have been enriched in cl and could have transported ree and trace metals

the late accretion and erosion of vesta s crust recorded by eucrites and diogenites as an astrochemical window into the formation of jupiter and the early evolution of the solar system abstract the circumsolar disc was the birthplace of both planetesimals and giant planets yet the details of their formation histories are as elusive as they are important to understand the origins of the solar system for decades the limited thickness of vesta s basaltic crust revealed by the link between the asteroid and the howardite eucrite diogenite family of meteorites and its survival to collisional erosion offered an important constraint for the study of these processes some results of the dawn mission however cast doubts on our understanding of vesta s interior composition and of the characteristics of its basaltic crust weakening this classical constraint in this work we investigate the late accretion and erosion experienced by vesta s crust after its differentiation and recorded in the composition of eucrites and diogenites and show that it offers an astrochemical window into the earliest evolution of the solar system in our proof of concept case study focusing on the late accretion and erosion of vesta s crust during the growth and migration of jupiter the water enrichment of eucrites appears to be a sensitive function of jupiter s migration while the enrichment in highly siderophile elements of diogenites appears to be particularly sensitive to the size frequency distribution of the planetesimals the picture depicted by the enrichments created by late accretion in eucrites and diogenites is not qualitatively affected by the uncertainty on the primordial mass of vesta crustal erosion instead is more significantly affected by said uncertainty and vesta s crust survival appears to be mainly useful to study violent collisional scenarios where highly energetic impacts can strip significant amounts of vestan material while limitedly contributing to vesta s late accretion while our proof of concept case study is based on a simplified physical model and explores only a limited set of scenarios our results suggest that the astrochemical record of the late accretion and erosion of vesta s crust provided by eucrites and diogenites can be used as a tool to investigate any process or scenario associated to the evolution of primordial vesta and of the early solar system

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

formation of unequilibrated r chondrite chondrules and opaque phases abstract sulfide assemblages are commonly found in chondritic meteorites as small inclusions in the matrix or in association with chondrules these assemblages are widely hypothesized to form through pre accretionary corrosion of metal by h2s gas or through parent body processes we report here on two unequilibrated r chondrite samples that contain large chondrule sized sulfide nodules in the matrix both samples are from mount prestrud pre 95404 chemical maps and spot and broad beam electron microprobe analyses empa were used to assess the distribution stoichiometry and bulk composition of sulfide nodules and silicate chondrules in the clasts oxygen isotope data were collected via secondary ion mass spectrometry sims to assess the relationship of chondrules to other chondrite groups scanning electron microscopy sem focused ion beam fib and transmission electron microscopy tem analyses were used to assess fine scale features and identify crystal structures in sulfide assemblages thermodynamic models were used to assess the temperature sulfur fugacity fs2 total pressure dust to gas ratio and oxygen fugacity fo2 conditions during sulfide nodule and chondrule formation the unequilibrated clasts include a mixture of type i and type ii chondrules as well as non porphyritic chondrules chondrule oxygen isotopes overlap with ordinary chondrite chondrules sulfide nodules average 200 m in diameter have rounded shapes and are primarily composed of pyrrhotite pentlandite and magnetite some are deformed around chondrules in a petrologic relationship similar in appearance to compound chondrules both nodules and sulfides in chondrules include phosphate inclusions and cu rich lamellae which suggests a genetic relationship between sulfides in chondrules and in the matrix ni co ratios for matrix and chondrule sulfides are solar while fe and ni are non solar and inversely related we hypothesize that sulfide nodules formed via pre accretionary melt processes during chondrule formation precursors composed of a mixture of silicate and sulfide material were heated to form immiscible melt droplets which separated and cooled to form si rich chondrules and s rich nodules sulfide melt was stabilized by a high total pressure 1 atm in a dust or ice enriched environment heating of this material contributed to a high fs2 2 10 3 atm at 1138 c and high fo2 iw 1 to iw 4 in an environment with peak temperatures between 1539 c and 1750 c oxygen isotopic compositions in this region were similar to those recorded by the ll chondrite chondrules

a combined sm nd rb sr and u pb isotopic study of mg suite norite 78238 further evidence for early differentiation of the moon abstract lunar mg suite norite 78238 was dated using the sm nd rb sr and u pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of mg suite magmatism as well as to provide a direct comparison between the three isotopic systems the sm nd isotopic system yields a crystallization age for 78238 of 4334 37 ma and an initial e nd 143 value of 0 27 0 74 the age initial e nd 143 t i systematics of a variety of kreep rich samples including 78238 and other mg suite rocks kreep basalts and olivine cumulate nwa 773 suggest that lunar differentiation was completed by 4492 61 ma assuming a chondritic uniform reservoir bulk composition for the moon the rb sr isotopic systematics of 78238 were disturbed by post crystallization processes nevertheless selected data points yield two rb sr isochrons one is concordant with the sm nd crystallization age 4366 53 ma the other is 4003 95 ma and is concordant with an ar ar age for 78236 the 207pb 206pb age of 4333 59 ma is concordant with the sm nd age the u pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the pb pb system and may reflect fractionation of u and pb during sample handling despite the disturbed nature of the u pb systems a time averaged 238u 204pb value of the source can be estimated at 27 30 from the pb pb isotopic systematics because kreep rich samples are likely to be derived from source regions with the highest u pb ratios the relatively low value calculated for the 78238 source suggests the bulk moon does not have an exceedingly high value

secondary volatiles linked metallic iron in eucrites the dual origin metals of camel donga the unique occurrence of abundant 1 vol near pure fe metal in the camel donga eucrite is more complicated than previously believed in addition to that component of groundmass metal scattered within the meteorite are discrete nodules of much higher kamacite abundance we have studied the petrology and composition of two of these nodules in the form of samples we call cd2 and cd3 the nodules are ovoids 11 cd2 to 15 cd3 mm across with metal or inferred preweathering metal abundances of 12 17 vol cd2 is unfortunately quite weathered the cd3 nodule also includes at its center a 5 mm ovoid clumping 6 vol of f apatite both nodules are fine grained so the high fe metal and apatite contents are clearly not flukes of inadequate sampling the metals within the nodules are distinctly ni rich 0 3 0 6 wt compared to the pure fe ni generally 0 01 wt groundmass metals bulk analyses of three pieces of the cd2 nodule show that trace siderophile elements ir os and co are commensurately enriched au is enriched to a lesser degree the siderophile evidence shows the nodules did not form by in situ reduction of pyroxene feo moreover the nodules do not show features such as silica phase enrichment or pyroxene with reduced feo as constrained by feo mgo and especially feo mno predicted by the in situ reduction model the oxide minerals even in groundmass samples well away from the nodules also show little evidence of reduction although the nodule boundaries are generally sharp groundmass metal ni content is anti correlated with distance from the cd3 nodule we infer that the nodules represent materials that originated within impactors into the camel donga portion of the eucrite crust but probably were profoundly altered during later metamorphism metasomatism origin of the pure fe groundmass metal remains enigmatic in situ reduction probably played an important role and association in the same meteorite of the fe nodules is probably significant but the fluid during alteration was probably not as previously modeled purely s and o of simple heat driven internal derivation we conjecture a two stage metasomatism as fluids passed through camel donga after impact heating of volatile rich chondritic masses survivors of gentle accretionary impacts within the nearby crust first reduction to form troilite may have been triggered by fluids rich in s2 and co derived from the protonodules and then in a distinct later stage fluids were comparatively h2o rich and thus reacted with troilite to form pure fe metal along with h2s and so2 the early eucrite crust was in places a dynamic fluid bearing environment that hosted complex chemical processes including some that engendered significant diversity among metal sulfide alterations

possible fluid rock interactions on differentiated asteroids recorded in eucritic meteorites the eucritic meteorites are basaltic rocks that originate from the upper part of the crust of some small bodies as exemplified possibly by asteroid 4 vesta a few eucrites appear to have been modified by different degrees of a late stage alteration process that caused significant variations in mineralogy three distinct alteration stages are identified 1 fe enrichment along the cracks that cross cut the pyroxene crystals fe metasomatism secondary olivine and minute amounts of troilite are found only occasionally in cracks at this stage 2 deposits of fe rich olivine fa64 86 and minor amounts of troilite are frequent inside the cracks sporadic secondary ca rich plagioclase an97 98 is associated with the fayalitic olivine 3 at this stage the fe enrichment of the pyroxene is accompanied by a marked al depletion moreover secondary ca rich plagioclase is more frequent and partly fills some cracks or rims of the primary plagioclase crystals the composition of the secondary phases on one hand the lack of incompatible trace element enrichment in the metasomatized pyroxenes on the other hand rule out a silicate melt as the metasomatic agent although no hydrous phase has been yet identified in the studied samples aqueous fluids are plausible candidates for explaining the deposits of ferroan olivine and anorthitic plagioclase inside the fractures of the studied unequilibrated eucrites

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

petrology of the unbrecciated eucrites abstract twenty nine unbrecciated eucrites have been thoroughly characterized in terms of the petrologic factors that affect their spectra such as mineral chemistry modal adundances grain sizes and textures we have conducted a combined petrologic and spectral study designed to provide insight into the petrogenesis of the basaltic crust of vesta and the variety of rock types that exist within it as well as aid in the petrologic interpretation of spectra to be collected by the dawn orbiting spacecraft this paper details the petrology part of the study unbrecciated eucrite samples were selected to avoid the complications of lithologic mixing in the accompanying spectral study a wide variety of textural types are seen within the basaltic eucrites encompassing quenched coarse grained and granoblastic samples zoned pyroxenes in eucrites and those that preserve a history of initial rapid cooling are rare nearly all eucrite samples have been thermally metamorphosed and would commonly be classified as equilibrated however this term reflects only the quadrilateral mg fe and ca compositions of pyroxenes and considerable variations are seen within the minor elements al ti and cr in pyroxenes as well as plagioclase compositions determination of both pyroxene and plagioclase compositions together with pyroxene geothermometry provides a better estimate for the relative degree of thermal metamorphism a eucrite has experienced the petrologic differences observed here might allow different eucrites to be distinguished spectrally this is especially true for the varying pyroxene compositions as the spectra of eucrites are dominated by absorption features attributed to pyroxene

fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration rocks from the lower oceanic crust show both petrologic and isotopic evidence for extensive alteration by circulating hydrothermal fluids derived from seawater deeply circulating fluids may have a substantial but as yet largely undetermined impact on the thermal regime of spreading centers magmatic processes at mid ocean ridges and elemental fluxes at ridge hydrothermal systems in the present study the consequences of water rock interactions during the penetration of seawater into hot lower oceanic crust were investigated using thermodynamic reaction path models alteration assemblages predicted for reaction of an evolving seawater with olivine gabbro gabbronorite and troctolite during heating from 300 to 900 c closely resemble alteration assemblages observed in rock samples from the lower oceanic crust these assemblages include sodic plagioclase actinolite diopsidic clinopyroxene epidote chlorite prehnite analcime quartz at lower temperatures 300 500 c and plagioclase hornblende diopside chlorite trace magnetite at intermediate temperatures 500 700 c the relative abundances of these alteration products show much greater variation with temperature than with water rock w r ratio indicating that variations in the amounts of hydrated minerals such as amphiboles may not be an accurate indication of the w r ratio experienced by rocks in the lower crust since the same amount of fluid may produce widely differing amounts of amphibole at slightly different temperatures depending on the temperature of interaction some rocks in the lower oceanic crust may have experienced much higher w r ratios than has previously been proposed based on the amount of amphibole present at higher temperatures 750 900 c the models predict that very little alteration occurs before the fluid equilibrates with the rock producing only trace amounts of amphibole as an alteration phase with the remainder of the rock retaining its igneous mineral composition essentially unchanged this result suggests that extensive penetration of rocks by aqueous fluids may occur in the lower ocean crust at temperatures 700 c and leave very little conspicuous petrologic evidence for their presence such cryptic alteration is consistent with isotopic evidence for hydrothermal alteration of oxygen and sr isotopes by seawater in lower ocean crust rock samples which otherwise retain their igneous compositions and textures taken together the model results allow for much more extensive circulation of fluids in the lower oceanic crust and at much higher temperatures than has been proposed by previous studies based on petrologic interpretations

the abundance and isotopic composition of water in eucrites volatile elements play a key role in the dynamics of planetary evolution extensive work has been carried out to determine the abundance distribution and source s of volatiles in planetary bodies such as the earth moon and mars a recent study showed that the water in apatite from eucrites has similar hydrogen isotopic compositions compared to water in terrestrial rocks and carbonaceous chondrites suggesting that water accreted very early in the inner solar system given the ancient crystallization ages 4 5 ga of eucrites here the measurements of water reported as equivalent h2o abundances and the hydrogen isotopic composition d of apatite from five basaltic eucrites and one cumulate eucrite are reported apatite h2o abundances range from 30 to 3500 ppm and are associated with a weighted average d value of 34 67 no systematic variations or correlations are observed in h2o abundance or d value with eucrite geochemical trend or metamorphic grade these results extend the range of previously published hydrogen isotope data for eucrites and confirm the striking homogeneity in the h isotopic composition of water in eucrites which is consistent with a common source for water in the inner solar system

post crystallization reheating and partial melting of eucrite eet90020 by impact into the hot crust of asteroid 4vesta 4 50 ga ago we performed petrologic radiometric ar ar sm nd and mn cr ages and ion microprobe studies of the basaltic eucrite eet90020 this is one of the few rare basaltic eucrites whose 39ar 40ar age has not been reset during impact bombardment on the hed parent body 4 ga ago and thus should provide a unique opportunity to study the nature of the early thermal events on its parent body presumably asteroid 4vesta hand specimen inspection shows that the rock consists of a fine grained and a coarse grained lithology microscopy indicates that the fine grained lithology has a granulitic texture with a coarser grained area and a large opaque assemblage embedded in the granulitic matrix the coarse grained lithology has an igneous subophitic texture the rock has pyroxenes similar to those in type 5 eucrites type 5 pyroxene and experienced prolonged thermal metamorphism after rapid crystallization from a near surface melt however minor mineral assemblages are unusual and suggest a complex thermal history tridymite occurs as large laths irregular crystals 1 5 gpa after the reheating event eet90020 seems to have experienced the following thermal history 1 crystallization during rapid cooling near the surface 2 some brecciation by impact 3 thermal metamorphism that produced type 5 pyroxene and 4 short reheating that caused partial melting and rapid cooling 39ar 40ar measurements show a relatively flat pattern and an age of 4 49 0 01 ga which is consistent with rapid cooling from high temperature event 4 resetting of the sm nd ages at 4 51 0 04 ga appears to be closely related to the remelting of ca phosphates rb sr data suggest rb loss from tridymite during partial melting the resetting of the mn cr age may have been related to the formation of cr ulvospinels event 4 we suggest that all these ages were reset by partial melting event 4 we further suggest that the partial melting event event 4 that reset the ages 4 50 ga ago was caused by an impact into eet90020 which was part of the hot crust of 4vesta and resulted in an increase in the temperature from the ambient temperature of 870 c to above the subsolidus temperature of eucrites of 1060 c

compositional variability of terrestrial mantle apatites thermodynamic modeling of apatite volatile contents and the halogen and water budgets of planetary mantles abstract apatites in ultramafic xenoliths from hawaii kamchatka nunivak island lunar crater volcanic field and the navajo volcanic field have variable volatile f cl oh compositions that correlate with their petrogenesis apatites in metasomatized lherzolite harzburgite xenoliths are relatively cl rich whereas apatites in igneous pyroxenite and amphibolite xenoliths are relatively f rich our results support the generalization of o reilly and griffin 2000 that metasomatic apatites tend to be cl rich and magmatic apatites tend to be f rich mantle metasomatism may largely be the consequence of devolatilization of cl rich fluids from subducted lithosphere however the occurrence of metasomatic xenoliths far removed from subduction zones e g bullenmerri as well as the geochemistry of cl in some plume basalts and diamonds indicates that not all metasomatism is subduction triggered thermodynamic modeling of the influence on apatite compositions of variable f cl h2o and p abundances as well as temperature is consistent with the idea that terrestrial mantle fluids are h2o rich and that halogen enrichment in terrestrial apatites need not represent large absolute halogen abundances in the fluids the models indicate that the occurrence of volatile poor calcium phosphate merrillite whitlockite in the martian and terrestrial mantles is facilitated by halogen and phosphorus rich and water poor environments the rarity of this assemblage in the terrestrial mantle compared to mars is consistent with the relatively wet and halogen and phosphorus poor nature of the terrestrial mantle compared to that of mars

39ar 40ar ages of eucrites and thermal history of asteroid 4 vesta eucrite meteorites are igneous rocks that derived from a large asteroid probably 4 vesta past studies have shown that after most eucrites formed they underwent metamorphism in temperatures up to 800 c much later many were brecciated and heated by large impacts into the parent body surface the less common basaltic unbrecciated eucrites also formed near the surface but presumably escaped later brecciation while the cumulate eucrites formed at depths where metamorphism may havepersisted for a considerable period to further understand the complex hed parent body thermal history we determined new 39ar 40ar ages for 9 eucrites classified as basaltic but unbrecciated 6 eucrites classified as cumulate and several basaltic brecciated eucrites precise ar ar ages of 2 cumulate eucrites moama and eet 87520 and 4 unbrecciated eucrites give a tight cluster at 4 48 0 02 gyr not including any uncertainties in the flux monitor age ar ar ages of 6 additional unbrecciated eucrites are consistent with this age within theirrelatively larger age uncertainties by contrast available literature data on pb pb isochron ages of 4 cumulate eucrites and 1 unbrecciated eucrite vary over 4 4 4 515 gyr and 147sm 143nd isochron ages of 4 cumulate and 3 unbrecciated eucrites vary over 4 41 4 55 gyr similar ar ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites as was previously proposed we suggest that these cumulate and unbrecciated eucrites resided at a depth where parent body temperatures were sufficiently high to cause the k ar and some other chronometers to remain as open diffusion systems from the strong clustering of ar ar ages at 4 48 gyr we propose that these meteorites were excavated from depth in a single large impact event 4 48 gyr ago which quickly cooled the samples and started the k ar chronometer a large 460 km crater postulated to exist on vesta may be the source of these eucrites and of many smaller asteroids thought to be spectrally or physically associated with vesta some pb pb and sm nd ages of cumulate and unbrecciated eucrites are consistent with the ar ar age of 4 48 gyr and the few older pb pb and sm nd ages may reflect an isotopic closure before the large cratering event one cumulate eucrite gives an ar ar age of 4 25 gyr 3 additional cumulate eucrites give ar ar ages of 3 4 3 7 gyr and 2 unbrecciated eucrites give ar ar ages of 3 55 gyr we attribute these younger ages to a later impact heating furthermore the ar ar impact reset ages of several brecciated eucrites and eucritic clasts in howardites fall within the range of 3 5 4 1 gyr among these piplia kalan the first eucrite to show evidence for extinct 26al was strongly impact heated 3 5 gyr ago when these data are combined with eucrite ar ar ages in the literature they confirm that several large impact heating events occurred on vesta between 4 1 3 4 gyr ago the onset of major impact heating may have occurred at similar times for both vesta and the moon but impact heating appears to have persisted for a somewhat later time on vesta

pre 4 2 ae mare basalt volcanism in the lunar highlands abstract the concept that the plutonism of the lunar highlands and the mare type volcanism are two separate problems in both time 4 4 ae versus apollo 14 breccia 14305 contains a clast 122 which is an olivine gabbronorite that is texturally and mineralogically similar to several apollo 12 basalts e g 12005 12035 12040 it consists of cumulus olivine 40 modal fo 62 70 and ti chromite 2 5 modal post cumulus phases include low ca pyroxene 29 modal wo 7 13 en 68 75 augite 10 modal wo 31 40 en 47 50 plagioclase 15 modal an 82 93 and ilmenite 4 modal 5 7 mgo the tio2 content of this rock 4 3 cao al2o3 1 0 cao 5 1 mgo feo 1 0 mgo 21 9 the ree pattern normalized to chondritic abundances is approximately 30 ch and hump shaped with a pronounced eu depletion and a non kreepy signature a four point rb sr isochron reveals an age of 4 23 0 05 ae the sample has a low initial 87sr 86sr 0 69911 3 the data presented here show that non kreepy mare type volcanism commenced at least as early as 4 2 ae in the fra mauro region and probably across much of the lunar surface massive bombardment during the terminal cataclysm and the subsequent veneer of younger mare basalts has obliturated most of the evidence for these ancient volcanic events these old mare type volcanics may be related to basin forming events such as made procellarum i e impact triggered igneous activity

chemical zoning and homogenization of pasamonte type pyroxene and their bearing on thermal metamorphism of a howardite parent body we studied thermal metamorphism in the surface layer of a eucrite parent body by examining pyroxene zoning ca mg fe zoning of pyroxenes in the pasamonte eucrite can be classified into three types type 1 with a core composition of ca5mg62fe32 and rim of ca41mg20fe4o type 2 with core of ca5mg62fe32 and rim of ca25mg34fe41 and type 3 with core of ca5mg66fe29 and rim of ca7mg32fe61 type 1 typically occurs adjacent to a mesostasis type 2 typically occurs adjacent to a surrounding plagioclase and type 3 is common in pyroxenes in the matrix pasamonte is less metamorphosed than previously believed because of the wide range of composition of zoned pyroxenes on the basis of ca mg fe variation data we have calculated the degree of homogenization of zoned pyroxenes by numerically solving the diffusion equation a pasamonte type pyroxene may yield a juvinas type pyroxene by thermal metamorphism the homogenization of juvinas pyroxene could not have taken place during initial cooling and may be related to reheating events although our calculation rests upon some assumptions

apatite in felsic rocks a model for the estimation of initial halogen concentrations in the bishop tuff long valley and tuolumne intrusive suite sierra nevada batholith magmas

vesta as the howardite eucrite and diogenite parent body implications for the size of a core and for large scale differentiation if vesta is the parent body of the howardite eucrite and diogenite hed meteorites then geo chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of vesta to 1 determine the size of a possible metal core in vesta and 2 model the igneous differentiation and internal structure of vesta the density of vesta and petrologic models for hed meteorites together suggest that the amount of metal in the parent body is 25 mass with a best estimate of 5 assuming no porosity for a porosity of up to 5 in the silicate fraction of the asteroid the permissible metal content is 30 these results suggest that any metal core in the hed parent body and vesta is not unusually large a variety of geochemical and other data for hed meteorites are consistent with the idea that they originated in a magma ocean it appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites excepting such eucrites as bouvante and statinem formed by subsequent crystallization of the residual melts modelling results suggest that the hed parent body is enriched in rare earth elements by a factor of 2 5 3 5 relative to ci chondrites and that it has approximately chondritic mg si and al sc ratios stokes settling calculations for a vesta wide nonturbulent magma ocean suggest that early crystallizing magnesian olivine orthopyroxene and pigeonite would have settled relatively quickly permitting fractional crystallization to occur but that later crystallizing phases would have settled or floated an order of magnitude more slowly allowing instead a closer approach to equilibrium crystallization for the more evolved eucritic melts this would have inhibited the formation of a plagioclase flotation crust on vesta plausible models for the interior of vesta which are consistent with the data for hed meteorites and vesta include a metal core 130 km radius an olivine rich mantle 65 220 km thick a lower crustal unit 12 43 km thick composed of pyroxenite from which diogenites were derived and an upper crustal unit 23 42 km thick from which eucrites originated the present shape of vesta with 60 km difference in the maximum and minimum radius suggests that all of the crustal materials and possibly some of the underlying olivine from the mantle could have been locally excavated or exposed by impact cratering

the volatile content of vesta clues from apatite in eucrites apatite was analyzed by electron microprobe in 3 cumulate and 10 basaltic eucrites eucritic apatite is fluorine rich with minor chlorine and hydroxyl calculated by difference we confirmed the hydroxyl content by measuring hydroxyl directly in apatites from three representative eucrites using secondary ionization mass spectroscopy overall most eucritic apatites resemble fluorine rich lunar mare apatites but intriguing oh and cl rich apatites suggest a role for water and or hydrothermal fluids in the vestan interior or on other related differentiated asteroids most late stage apatite found in mesostasis has little hydroxyl or chlorine and is thought to have crystallized from a degassed magma however several apatites exhibit atypical compositions and or textural characteristics for example the isotopically anomalous basaltic eucrite pasamonte has apatite in the mesostasis with significant oh apatites in juvinas also have significant oh and occur as veinlets crosscutting silicates euhedral apatites in the moore county cumulate eucrite occur as inclusions in pyroxene and are also hydroxyl rich 0 62 wt oh the oh was confirmed by sims analysis and this apatite clearly points to the presence of water at least locally in the vestan interior portions of elephant moraine eet 90020 have large and abundant apatites which may be the product of apatite accumulation in a zone of melt rock reaction relatively chlorine rich apatites occur in basaltic eucrite graves nunataks gra 98098 approximately 1 wt cl particularly striking is the compositional similarity between apatite in gra 98098 and apatites in lunar kreep which may indicate the presence of residual magmas from an asteroid wide magma ocean on vesta

widespread magma oceans on asteroidal bodies in the early solar system our solar system formed about 4 6 billion years ago and within 4 million years small planetary bodies had formed some melting to form volcanic and related rocks two families of meteorites the heds and angrites are thought to have originated from asteroids that melted at this time new oxygen isotope measurements confirm that these meteorites are from two distinct asteroids that underwent large scale melting in the early solar system these new results show that early global scale melting was a feature of all the differentiated planets earth moon and mars and asteroids so far sampled immediately following the formation of the solar system small planetary bodies accreted1 some of which melted to produce igneous rocks2 3 over a longer timescale 15 33 myr the inner planets grew by incorporation of these smaller objects4 5 through collisions processes operating on such asteroids strongly influenced the final composition of these planets4 including earth5 currently there is little agreement about the nature of asteroidal igneous activity proposals range from small scale melting to near total fusion and the formation of deep magma oceans2 here we report a study of oxygen isotopes in two basaltic meteorite suites the heds howardites eucrites and diogenites which are thought to sample the asteroid 4 vesta6 and the angrites from an unidentified asteroidal source our results demonstrate that these meteorite suites formed during early global scale melting 50 per cent events we show that magma oceans were present on all the differentiated solar system bodies so far sampled magma oceans produced compositionally layered planetesimals the modification of such bodies before incorporation into larger objects can explain some anomalous planetary features such as earth s high mg si ratio

detection of structurally bound hydroxyl in fluorapatite from apollo mare basalt 15058 128 using tof sims fluorapatite grains from apollo 15 mare basalt 15058 128 were analyzed by raman spectroscopy raman spectral imaging time of flight secondary ion mass spectrometry tof sims field emission scanning electron microscopy fe sem and electron probe microanalysis epma in an attempt to detect structurally bound oh in the fluorapatite although oh could not be definitively detected by raman spectroscopy because of ree induced photoluminescence hydroxyl was detected in the fluorapatite by tof sims the tof sims technique is qualitative but capable of detecting the presence of hydroxyl even at trace levels electron microprobe data indicate that on average f and cl f cl fill the monovalent anion site in these fluorapatite grains within the uncertainties of the analyses about 0 07 0 01 atoms per formula unit however some individual spot analyses have f cl deficiencies greater than analytical uncertainties that could represent structural oh on the basis of epma data the fluorapatite grain with the largest f cl deficiency constrains the upper limit of the oh content to be no more than 4600 2000 ppm by weight the equivalent of 2400 1100 ppm water the tof sims detection of oh in fluorapatite from apollo sample 15058 128 represents the first direct confirmation of structurally bound hydroxyl in a lunar magmatic mineral this result provides justification for attributing at least some of the missing structural component in the monovalent anion site of other lunar fluorapatite grains to the presence of oh moreover this finding supports the presence of dissolved water in lunar magmas and the presence of at least some water within the lunar interior

u pb and 207pb 206pb ages of zircons from basaltic eucrites implications for early basaltic volcanism on the eucrite parent body we have undertaken petrologic and shrimp u th pb isotopic studies on zircons from basaltic eucrites yamato y 75011 y 792510 asuka a 881388 a 881467 and padvarninkai with different thermal and shock histories eucritic zircons are associated with ilmenite in most cases and have subhedral shapes in unmetamorphosed and metamorphosed eucrites some zircons in highly metamorphosed eucrites with granulitic texture occur alone in pyroxene and typically have rounded to subrounded shapes due to recrystallization superchondritic zr hf ratios of eucritic zircons indicate that they crystallized from incompatible element rich melts after crystallization of ilmenite concentrations of uranium and thorium in zircons in the unmetamorphosed eucrite y 75011 are higher than those in metamorphosed eucrites the u pb systems of eucritic zircons are almost concordant but some zircon grains show reverse discordance radiogenic lead loss up to 48 from zircons is observed in the shock melted eucrite padvarninkai the 207pb 206pb ages of zircon in y 75011 4550 9 ma n 5 are nearly identical within analytical uncertainty to the ages of zircons from the metamorphosed eucrite y 792510 4545 15 ma n 13 the highly metamorphosed eucrites a 881388 4555 54 ma n 5 and a 881467 4558 13 ma n 8 and the shock melted eucrite padvarninkai 4555 13 ma n 18 the averaged 207pb 206pb age of zircon from five eucrites analyzed in this study is 4554 7 ma 95 confidence limits n 49 indistinguishable from the averaged u pb age 4552 9 ma of the same samples because of the high closure temperature of lead in zircon tclosure 1050 c with a cooling rate of 0 2 c yr the 207pb 206pb ages of eucritic zircon do not represent metamorphic ages but crystallization ages of extrusive lavas this fact strongly suggests that volcanism of the eucrite parent body occurred at a very early stage of the solar system history 7 20 ma after cai formation 4567 2 0 6 ma thus basaltic eucrites crystallized from parental magmas within a short interval following the differentiation of their parent body the u pb ages of eucritic zircons are older than the u pb sm nd and rb sr ages of some basaltic eucrites which is consistent with differences in closure temperatures of each isotopic system and suggests that thermal and shock metamorphism affected the isotopic systems of pyroxene plagioclase and phosphates

experimental investigation of f cl and oh partitioning between apatite and fe rich basaltic melt at 1 0 1 2 gpa and 950 1000 c apatite melt partitioning experiments were conducted in a piston cylinder press at 1 0 1 2 gpa and 950 1000 c using an fe rich basaltic starting composition and an oxygen fugacity within the range of iw 1 to iw 2 each experiment had a unique f cl oh ratio to assess the partitioning as a function of the volatile content of apatite and melt the quenched melt and apatite were analyzed by electron probe microanalysis and secondary ion mass spectrometry techniques the mineral melt partition coefficients d values determined in this study are as follows d fap melt 4 4 19 d clap melt 1 1 5 d ohap melt 0 07 0 24 this large range in values indicates that a linear relationship does not exist between the concentrations of f cl or oh in apatite and f cl or oh in melt respectively this non nernstian behavior is a direct consequence of f cl and oh being essential structural constituents in apatite and minor to trace components in the melt therefore mineral melt d values for f cl and oh in apatite should not be used to directly determine the volatile abundances of coexisting silicate melts however the apatite melt d values for f cl and oh are necessarily interdependent given that f cl and oh all mix on the same crystallographic site in apatite consequently we examined the ratio of d values exchange coefficients for each volatile pair oh f cl f and oh cl and observed that they display much less variability k dcl fap melt 0 21 0 03 k doh fap melt 0 014 0 002 and k doh clap melt 0 06 0 02 however variations with apatite composition specifically when mole fractions of f in the apatite x site were low x f 0 18 were observed and warrant additional study to implement the exchange coefficient to determine the h2o content of a silicate melt at the time of apatite crystallization apatite based melt hygrometry the h2o abundance of the apatite an apatite melt exchange k d that includes oh either oh f or oh cl and the abundance of f or cl in the apatite and f or cl in the melt at the time of apatite crystallization are needed f if using the oh f k d and cl if using the oh cl k d to determine the h2o content of the parental melt the f or cl abundance of the parental melt is needed in place of the f or cl abundance of the melt at the time of apatite crystallization importantly however exchange coefficients may vary as a function of temperature pressure melt composition apatite composition and or oxygen fugacity so the combined effects of these parameters must be investigated further before exchange coefficients are applied broadly to determine volatile abundances of coexisting melt from apatite volatile abundances

plastic deformation of olivine rich diogenites and implications for mantle processes on the diogenite parent body numerous petrologic and geochemical studies so far on the howardite eucrite and diogenite hed meteorites have produced various crystallization scenarios for their parent body believed to be the differentiated asteroid 4 vesta structural analyses of diogenites can reveal important insights into postcrystallization deformation on the parent body recently published results tkalcec et al 2013 of structural analysis on the olivine rich diogenite nwa 5480 reveal that it underwent solid state plastic deformation although not at the base of a magma chamber dynamic mantle downwelling has been proposed as a plausible deformation mechanism tkalcec et al 2013 the purpose of this study is to investigate whether the plastic deformation found in nwa 5480 is an isolated case we expand the structural analysis on nwa 5480 and extend it to nwa 5784 and mil 07001 6 two other samples of rare olivine rich diogenites using electron backscattered diffraction ebsd techniques our ebsd results show that the diogenites analyzed in this study underwent solid state plastic deformation confirming that the observed deformation of nwa 5480 was not an isolated case on the diogenite parent body the lattice preferred orientations lpos of olivine in nwa 5784 and nwa 5480 are clearly distinct from that typical for cumulate rocks at the base of magma chambers indicating a different stress environment and a different deformation mechanism the lpo of olivine in mil 07001 is less conclusive the structural results of this study suggest that plastic deformation occurred on the diogenite parent body at high temperatures 1273 t 1573 k in the solid state i e after crystallization of the diogenites themselves in a dynamic environment with active stress fields

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

oman diopsidites a new lithology diagnostic of very high temperature hydrothermal circulation in mantle peridotite below oceanic spreading centres abstract mafic ultramafic dykes scattered in the mantle section of ophiolites are generally crystallisation products from common silicate melts in the frame of a global survey of these melt migration relics in the oman mantle harzburgites we discovered a peculiar lithology made essentially of pure diopside 0 95 m g m g f e total 1 whose characteristics do not match a magmatic or mantle origin arguments against a magmatic or mantle origin for these diopsidites combine compositional and textural evidence in spite of their refractory composition they are strongly depleted in cr cr2o3 0 2 wt by the same way other minor elements al ti na and rare earth elements have peculiarly low abundances and plot away from magmatic differentiation trends in a few samples the paragenetic association includes pure anorthite an up to 0 99 minor amounts of forsterite fo 0 95 or traces of andradite when not deformed the diopsides are automorphic and their texture points to metamorphic growth in a matrix composed of antigorite and or carbonate diopsidites have textures reminiscent to that of skarns developing in contact metamorphic halos or that of rodingite frequently present in the serpentine bodies of the ophiolitic crust they frequently appear as dykes former cracks with a few mm to few tens of cm wide transitional zones which contain high amounts of hydrous minerals between the diopsidite facies and its host rock the diopsidites are not randomly distributed in the oman ophiolite being more abundant near former asthenospheric diapirs emplaced at shallow depth in the lithosphere we interpret the diopsidites as the footprint of very high temperature circulation of seawater and carbonated fluids 800 c which may have leached plagioclase rich lithologies before penetrating the mantle as shown by a well developed positive eu anomaly our data confirm the prediction of mccollom and shock t m mccollom e l shock fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration j geophys res 103 b1 1998 547 575 who proposed that common anhydrous minerals like pyroxene plagioclase and olivine may crystallise from high temperature fluids intermediate between silicate melts and supercritical water this confirms that there is no clear cut thermal and chemical boundary between the fields of magmatic and hydrothermal crystallisations

glasses in howardites impact melts or pyroclasts we have analyzed glasses in eight howardites with the aim of distinguishing their origins as impact melts or pyroclasts although theoretical calculations predict that pyroclastic eruptions could have taken place on vesta the occurrence of pyroclastic glasses in hed meteorites has not been documented this study involved petrographic examination of textures electron microprobe analysis of major and minor elements and la icp ms analysis for selected trace elements previously documented textural and compositional differences between lunar impact melt and pyroclastic glasses partly guided this study this work yielded no positive identification of pyroclastic glasses the most likely explanation is that pyroclastic glasses never formed either because vesta contains insufficient volatiles to have powered explosive eruptions or because eruptive conditions produced optically dense fire fountains that allowed melt drops to collect as lava ponds the impact melt glasses were grouped low alkali ca rich and k rich based on compositions we suggest that these glasses are the result of impacts onto known hed lithologies the low alkali glasses are impact melts of bulk hed lithologies we hypothesize that the ca rich and k rich glasses result from oversampling of plagioclase and of mesostasis that experienced liquid immiscibility respectively during micrometeorite impacts into eucrite targets

survey and evaluation of eucrite bulk compositions the purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting fractional crystallization and magma ocean theories for the eucrite parent body in order to evaluate bulk elemental abundances for the eucrites 296 peer reviewed articles monographs theses or books and 143 abstracts dating from 1938 to 1997 were surveyed of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature 20 were selected for in depth examination the selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist the mean bulk elemental abundance 1 standard deviation and the percent deviation were calculated for each element in a given eucrite in order to evaluate the quality of the mean abundances the elements were then grouped according to availability of data and percent deviations possible reasons for the different deviations in the different groups are briefly discussed from the major element abundances the normative cipw composition the molar compositions of pyroxene olivine and plagioclase and the bulk densities were calculated and compared to petrographic observations the calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not possible reasons for this are discussed unfortunately analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty therefore future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites especially those of key elements used for planetary modeling

ancient water on asteroid 4 vesta evidence from a quartz veinlet in the serra de mage eucrite meteorite abstract the meteorite serra de mage a eucrite inferred to be from the asteroid 4 vesta contains quartz veinlets they are identical to antitaxial or crack seal quartz veinlets in terrestrial rocks and are extraterrestrial and ancient because they pre date a 4 40 ga metamorphism the quartz was likely deposited from liquid water solutions as are terrestrial veins other potential solvents or transport mechanisms are inadequate or unlikely because there is no indication of internal magmatic water in the eucrite meteorites and thus in vesta the water from which the veinlet was deposited probably came from outside vesta by analogy with water ice deposits on the moon and mercury vesta and similar asteroids may have had or now have polar ice deposits possibly derived from comet impacts

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

partitioning of fluorine and chlorine between apatite and aqueous fluids at high pressure and temperature implications for the f and cl content of highp t fluids abstract experiments in a piston cylinder apparatus equilibrated natural fluorapatite with aqueous hcl nacl naoh na 2 co 3 and co 2 h 2 o mixtures at 1 2 0 gpa and 950 1050 c post experiment apatite compositions were determined by electron microprobe and fluid compositions were calculated from mass balance this enabled calibration of the fluorine and chlorine contents of apatite coexisting with a variety of fluids at high p and t and provides better constraints on the halogen composition of aqueous fluids which may exist in the deep crust and upper mantle results obtained at 2 0 gpa and 1050 c indicate that the ratio x clap x ohap in apatite x fap x clap and x ohap are the mole fractions of fluor chlor and hydroxyapatite is proportional to the chlorine content of the fluid up to 1 h 2 o co 2 5 h 2 o hcl and 15 h 2 o nacl wt cl in contrast the ratio x fap x ohap was found to vary in proportion to the fluorine content of the fluid only at concentrations of 0 15 h 2 o hcl and 0 4 h 2 o nacl wt f arising from changes in the activities of aqueous hcl and hf the results of this study demonstrate that fluid composition in addition to the absolute abundances of f and cl in the fluid will determine the amounts of these elements incorporated into coexisting apatite specifically relatively low cl and f concentrations in acidic h 2 o hcl fluids are required to obtain high ratios of x clap x ohap and x fap x ohap in apatite whereas much higher abundances of cl and f in basic fluids i e na bearing are required to achieve the same result in addition resulting from dilution of the aqueous phase with co 2 and the subsequent reduction in the activity of h 2 o apatites with high ratios of x clap x ohap and x fap x ohap may be produced by co 2 h 2 o fluids with relatively low levels of cl or f application of these results to apatites from a suite of ultramafic xenoliths from southeastern australia indicates chlorine abundances of 500 3500 ppm in the fluid phase and points to chlorine as a potentially important component of some mantle fluids

magnesium oxide iron oxide mass balance constraints and a more detailed model for the relationship between eucrites and diogenites according to a currently popular model for petrogenesis on the howardite eucrite and diogenite hed parent asteroid the diogenites are not comagmatic with most eucrites but instead formed in separate orthopyroxenite dominated plutons this model can be tested for consistency with mass balance for mgo and feo assuming the overall diogenite diogenite eucrite ratio d of the parent asteroid is at least comparable to the average d for the eucrite diogenite dominated howardite regolith breccias average mg mgo mgo feo is much lower for eucrites especially noncumulate eucrites than for diogenites unless the diogenite parent magmas eventually produced a large proportion of low mg residual basalt and gabbro rbg the implied initial magma s mg is vastly higher than that of any noncumulate eucrite starting from a source previously depleted by putative primary eucrite genesis melt mg can be estimated as a function of the exchange reaction kd and degree of melting using several very conservative assumptions e g assuming that the total mgo feo concentration is nearly the same in the nascent melt as in the residual solids the degree of melting required to yield a melt with mg high enough to satisfy mass balance without implying an rbg component that accounts for 50 of all eucrites is an implausibly high 60 80 wt the separate orthopyroxenitic plutons sop model also seems inconsistent with the uniform density of melts across the diogenite eucrite compositional spectrum 2 77 2 82 g cm3 which implies that diogenitic magmas should have been as capable as eucrites of extruding to form lavas this difficulty cannot be reduced by simply assuming that later formed magmas were systematically both more plutonic and more mgo rich than earlier ones because the plutonic cumulate eucrites equilibrated with melts systematically lower in mg than noncumulate eucrites conceivably the bulk mg of the asteroid s silicate system was increased between primary melt eucrite genesis and sop diogenite genesis by graphite fueled reduction of feo however the graphite oxidation process generates a huge proportion of gas which would have enhanced the buoyancy of the nascent diogenite parent magmas thus exacerbating the difficulty of achieving the implied high degrees of partial melting to avoid these difficulties but still form most eucrites as rapidly cooled extrusives i propose the nerd noncumulate eucrites as extruded residua of diogenites model in this model the diogenites form as early cumulates from a large magma system probably a global magma ocean that yields a large proportion of eucritic melt as residuum this residual melt zone undergoes relatively little crystallization during a period when it is episodically tapped to produce extrusions dikes and sills of rapidly cooled noncumulate eucrites slight 5 10 porosity in the nascent eucritic crust keeps it marginally buoyant over the residual melt zone the common thermal metamorphism of noncumulate eucrites results from baking by superjacent flows during the episodic venting of the melt zone the nerd model s greatest advantage is that it does not require implausibly high degrees of localized melting in the mature stages of igneous evolution of the hed asteroid

partitioning behavior of chlorine and fluorine in the system apatite silicate melt fluid the partitioning behavior of cl among apatite mafic silicate melt and aqueous fluid and of f between apatite and melt have been determined in experiments conducted at 1066 to 1150 c and 199 205 mpa the value of dclapatite melt wt fraction of cl in apatite cl in melt 0 8 for silicate melt containing less than 3 8 wt cl at higher melt cl contents small increases in melt cl concentration are accompanied by large increases in apatite cl concentration forcing dclapatite melt to increase as well melt containing less than 3 8 cl coexists with water rich vapor that containing more cl coexists with saline fluid the salinity of which increases rapidly with small increases in melt cl content analogous to the dependency of apatite composition on melt cl content this behavior is due to the fact that the solubility of cl in silicate melt depends strongly on the composition of the melt particularly its mg ca fe and si contents once the melt becomes saturated in cl additional cl must be accommodated by coexisting fluid apatite or other phases rather than the melt itself because cl solubility depends on composition the cl concentration at which dclapatite melt and dclfluid melt begin to increase also depends on composition the experiments reveal that dfapatite melt 3 4 in contrast to cl the concentration of f in silicate melt is only weakly dependent on composition mainly on melt ca contents so dfapatite melt is constant for a wide range of composition the experimental data demonstrate that the fluids present in the waning stages of the solidification of the stillwater and bushveld complexes were highly saline the cl rich apatite in these bodies crystallized from interstitial melt with high cl f oh ratio the latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated

oxygen isotopic constraints on the origin and parent bodies of eucrites diogenites and howardites abstract a few eucrites have anomalous oxygen isotopic compositions to help understand their origin and identify additional samples we have analyzed the oxygen isotopic compositions of 18 eucrites and four diogenites except for five eucrites these meteorites have 17o values that lie within 2 of their mean value viz 0 242 0 016 consistent with igneous isotopic homogenization of vesta the five exceptional eucrites nwa 1240 pasamonte both clast and matrix samples pca 91007 a 881394 and ibitira have 17o values that lie respectively 4 5 5 15 and 21 away from this mean value nwa 1240 has a 18o value that is 5 below the mean eucrite value four of the five outliers are unbrecciated and unshocked basaltic eucrites like nwa 011 the first eucrite found to have an anomalous oxygen isotopic composition the fifth outlier pasamonte is composed almost entirely of unequilibrated basaltic clasts published chemical data for the six eucrites with anomalous oxygen isotopic compositions including nwa 011 exclude contamination by chondritic projectiles as a source of the oxygen anomalies only nwa 011 has an anomalous fe mn ratio but several anomalous eucrites have exceptional na ti or cr concentrations we infer that the six anomalous eucrites are probably derived from five distinct vesta like parent bodies pasamonte and pca 91007 could come from one body these anomalous eucrites like the isotopically normal unbrecciated eucrites with 4 48 gyr ar ar ages are probably deficient in brecciation and shock effects because they were sequestered in small asteroids 10 km diameter during the late heavy bombardment following ejection from vesta like bodies the preservation of vesta s crust and the lack of deeply buried samples from the hypothesized vesta like bodies are consistent with the removal of these bodies from the asteroid belt by gravitational perturbations from planets and protoplanets rather than by collisional grinding

understanding the origin and evolution of water in the moon through lunar sample studies a paradigm shift has recently occurred in our knowledge and understanding of water in the lunar interior this has transpired principally through continued analysis of returned lunar samples using modern analytical instrumentation while these recent studies have undoubtedly measured indigenous water in lunar samples they have also highlighted our current limitations and some future challenges that need to be overcome in order to fully understand the origin distribution and evolution of water in the lunar interior another exciting recent development in the field of lunar science has been the unambiguous detection of water or water ice on the surface of the moon through instruments flown on a number of orbiting spacecraft missions considered together sample based studies and those from orbit strongly suggest that the moon is not an anhydrous planetary body as previously believed new observations and measurements support the possibility of a wet lunar interior and the presence of distinct reservoirs of water on the lunar surface furthermore an approach combining measurements of water abundance in lunar samples and its hydrogen isotopic composition has proved to be of vital importance to fingerprint and elucidate processes and source s involved in giving rise to the lunar water inventory a number of sources are likely to have contributed to the water inventory of the moon ranging from primordial water to meteorite derived water ice through to the water formed during the reaction of solar wind hydrogen with the lunar soil perhaps two of the most striking findings from these recent studies are the revelation that at least some portions of the lunar interior are as water rich as some mid ocean ridge basalt source regions on earth and that the water in the earth and the moon probably share a common origin

in situ pb pb dating of silica rich northwest africa nwa 6594 basaltic eucrite and its constraint on thermal history of the vestan crust

trace element inventory of meteoritic ca phosphates most extraterrestrial samples feature the two accessory ca phosphates apatite group minerals and merrillite which are important carrier phases of the rare earth elements ree the trace element concentrations ree sc ti v cr mn co as rb sr y zr nb ba hf ta pb th and u of selected grains were analyzed by la icp ms and or sims ree only this systematic investigation includes 99 apatite and 149 merrillite analyses from meteorites deriving from various asteroidal bodies including 1 carbonaceous chondrite 8 ordinary chondrites 3 acapulcoites 1 winonaite 2 eucrites 5 shergottites 1 ureilitic trachyandesite 2 mesosiderites and 1 silicate bearing iab iron meteorite although ca phosphates predominantly form in metamorphic and or metasomatic reactions some are of igneous origin as late stage phases that often incorporate the vast majority of their host s bulk ree budget the investigated ca phosphates have ree enrichments of up to two orders of magnitude compared to the host rock s bulk concentrations within a single sample each phosphate species displays a uniform ree pattern and variations are mainly restricted to their enrichment therefore indicating similar formation conditions exceptions are brecciated samples i e the adzhi bogdo ll3 6 ordinary chondrite despite this uniformity within single samples distinct meteorite groups do not necessarily have unique ree patterns four basic shapes dominate the ree patterns of meteoritic ca phosphates 1 flat patterns smoothly decreasing from la lu with prominent negative eu anomalies acapulcoites eucrites apatite from the winonaite and the ureilitic trachyandesite merrillite from ordinary chondrites 2 unfractionated patterns with only minor or no anomalies mesosiderites enriched shergottites iab iron meteorite 3 lree enriched patterns with either positive or slightly negative eu anomalies chondritic apatite and 4 strongly lree depleted patterns with negative eu anomalies depleted shergottites the patterns do not correlate with the grade of metamorphism petrologic type specific adjacent mineral assemblages or with ca phosphate grain size neither the proportions of different ree nor particular ree patterns themselves are universally correlated to a specific formation mechanism yet eu i e magnitude of the eu anomaly is a sensitive indicator to evaluate the timing of plagioclase and phosphate crystallization based on our data u and th abundances in apatite increase almost linearly with the grade of metamorphism as well as with the differentiation of their host rock

hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the moon water has been found in many lunar rock samples but its sources are unknown isotopic analyses of apollo samples of lunar mare basalts and highlands rocks suggest that a significant volume of water was delivered to the moon by comets shortly after its formation by giant impact

heterogeneous distribution of h2o in the martian interior implications for the abundance of h2o in depleted and enriched mantle sources we conducted a petrologic study of apatite within 12 martian meteorites including 11 shergottites and one basaltic regolith breccia these data were combined with previously published data to gain a better understanding of the abundance and distribution of volatiles in the martian interior apatites in individual martian meteorites span a wide range of compositions indicating they did not form by equilibrium crystallization in fact the intrasample variation in apatite is best described by either fractional crystallization or crustal contamination with a cl rich crustal component we determined that most martian meteorites investigated here have been affected by crustal contamination and hence cannot be used to estimate volatile abundances of the martian mantle using the subset of samples that did not exhibit crustal contamination we determined that the enriched shergottite source has 36 73 ppm h2o and the depleted source has 14 23 ppm h2o this result is consistent with other observed geochemical differences between enriched and depleted shergottites and supports the idea that there are at least two geochemically distinct reservoirs in the martian mantle we also estimated the h2o cl and f content of the martian crust using known crust mantle distributions for incompatible lithophile elements we determined that the bulk martian crust has 1410 ppm h2o 450 ppm cl and 106 ppm f and cl and h2o are preferentially distributed toward the martian surface the estimate of crustal h2o results in a global equivalent surface layer gel of 229 m which can account for at least some of the surface features on mars attributed to flowing water and may be sufficient to support the past presence of a shallow sea on mars surface

apatite as a probe of halogen and water fugacities in the terrestrial planets abstract apatite preserves a record of the halogen and water fugacities that existed during the waning stages of crystallization of planetary magmas when they became saturated in phosphates we develop a thermodynamic formalism based on apatite merrillite equilibria that makes it possible to compare the relative values of halogen and water fugacities in martian lunar and terrestrial basalts accounting for possible differences in pressure temperature and oxygen fugacities among the planets we show that each of these planetary bodies has distinctive ratios among volatile fugacities at apatite saturation and that these fugacities are in some cases related in a consistent way to volatile fugacities in the mantle magma sources our analysis shows that the martian mantle parental to basaltic snc meteorites was dry and poor in both fluorine and chlorine compared to the terrestrial mantle the limited data available from mars show no secular variation in mantle halogen and water fugacities from 4 ga to 180 ma the water and halogens found in present day martian surface rocks have thus resided in the planet s surficial systems since at least 4 ga and may have been degassed from the planet s interior during a primordial crust forming event in comparison to the earth and mars the moon and possibly the eucrite parent body too appear to be strongly depleted not only in h 2 o but also in cl 2 relative to h 2 o chlorine depletion is strongest in mare basalts perhaps reflecting an eruptive process characteristic of large scale lunar magmatism

ibitira a basaltic achondrite from a distinct parent asteroid and implications for the dawn mission i have done a detailed petrologic study of ibitira a meteorite that has been classified as a basaltic eucrite since 1957 the mean fe mn ratio of pyroxenes in ibitira with 10 mole wollastonite component is 36 4 0 4 this value is well resolved from those of similar pyroxenes in five basaltic eucrites studied for comparison which range from 31 2 to 32 2 data for the latter five eucrites completely overlap ibitira pyroxenes have lower fe mg than the basaltic eucrite pyroxenes thus the higher fe mn ratio does not reflect a simple difference in oxidation state ibitira also has an oxygen isotopic composition alkali element contents and a ti hf ratio that distinguish it from basaltic eucrites these differences support derivation from a distinct parent asteroid thus ibitira is the first recognized representative of the fifth known asteroidal basaltic crust the others being the hed mesosiderite angrite and nwa 011 parent asteroids 4 vesta is generally assumed to be the hed parent asteroid the dawn mission will orbit 4 vesta and will perform detailed mapping and mineralogical compositional and geophysical studies of the asteroid ibitira is only subtly different from eucritic basalts a challenge for the dawn mission will be to distinguish different basalt types on the surface and to attempt to determine whether 4 vesta is indeed the hed parent asteroid