geochemistry of diogenites still more diversity in their parental melts we report on the major and trace element abundances of 18 diogenites and o isotopes for 3 of them our analyses extend significantly the diogenite compositional range both in respect of mg rich e g meteorite hills met 00425 mgo 31 5 wt and mg poor varieties e g dhofar 700 mgo 23 wt the wide ranges of siderophile and chalcophile element abundances are well explained by the presence of inhomogeneously distributed sulfide or metal grains within the analyzed chips the behavior of incompatible elements in diogenites is more complex as exemplified by the diversity of their ree patterns apart from a few diogenite samples that contain minute amounts of phosphate and whose incompatible element abundances are unlike the orthopyroxene ones the range of incompatible element abundances and particularly the range of dy yb ratios in diogenites is best explained by the diversity of their parental melts we estimate that the feo mgo ratios of the diogenite parental melts range from about 1 4 to 3 5 and therefore largely overlap the values obtained for non cumulate eucrites our results rule out the often accepted view that all the diogenites formed from parental melts more primitive than eucrites during the crystallization of a magma ocean instead they point to a more complex history and suggest that diogenites were derived from liquids produced by the remelting of cumulates formed from the magma ocean

evidence for excavation of deep crustal material of a vesta like body from ca compositional gradients in pyroxene abstract recent discovery of basaltic achondrite asteroids in the main belt has provided a link between basaltic achondrites howardite eucrite and diogenite and asteroid 4 vesta a spectral study suggests that these asteroids are fragments ejected from vesta and that vesta s eucritic crust is of substantial thickness we computed the cooling rate and burial depth of the moore county cumulate eucrite on the basis of ca compositional gradients and the width of augite lamella in pyroxene to obtain information on the early evolution of the parent body our calculations show that 1 moore county cooled initially at a rate of 0 00016 c yr which corresponds to a burial depth of about 8 km 2 after this cooling a sudden temperature rise occurred probably due to an impact and finally 3 moore county cooled down again at a rate of 0 35 c yr the latter events may correspond to the excavation of crustal material the burial depth of moore county is consistent with the result of a recent spectral study in which the largest observed eucritic fragment 10 km sets a lower limit on the thickness of the eucritic crust reheating and excavation of a deep crustal material imply impact events which are supported by spectral observations

crystallization recrystallization and impact metamorphic ages of eucrites y792510 and y791186 abstract monomict eucrites y792510 and y791186 of pyroxene metamorphic type 6 contain areas of recrystallized mesostasis and granoblastic pyroxene textural comparisons suggest that the mesostasis areas in these eucrites originally resembled analogous areas in the pristine basaltic eucrite clast y75011 84 39ar 40ar ages were determined for microbreccias y791186 87 and y792510 62 and crystalline clast y792510 65 the 39ar 40ar ages for y791186 87 and y792510 62 are identical within error limits at 3 46 0 18 ga and 3 40 0 16 ga 2 respectively both these samples were involved in an impact event in which ar was quantitatively degassed 3 43 0 10 ga ago y792510 65 has an apparently older 39ar 40ar age of 3 60 0 04 ga 2 suggesting that it was degassed in a separate event or to a lesser degree rb sr and sm nd ages were determined for both y792510 clasts the rb sr age of 3 26 0 24 ga 2 for y792510 65 was totally reset by the impact event s whereas the rb sr age of 4 26 0 62 ga 2 for y792510 62 either was partially reset by the same event s or by earlier recrystallization of mesostasis the 147sm 143nd age calculated for y792510 65 including all data is 4 67 0 22 ga 2 but is likely to have been affected by weathering in the antarctic it becomes 4 57 0 09 ga if only data for the major minerals plagioclase and pyroxene are included in the isochron the 147sm 143nd age of y792510 62 is 4 34 0 06 ga 2 for the same mineral phases but may be biased by the presence of weathered ca phosphates in the pyroxene separate the 146sm 142nd age of y792510 65 is 4 42 0 06 0 04 ga corresponding to initial 146sm 144sm 0 0030 0 0010 relative to 146sm 144sm lew 0 0076 0 0009 for the lew86010 angrite at 4 558 ga ago the y792510 65 ages from the two sm nd chronometers are concordant at 4 48 ga which may be the crystallization age of this eucritic basalt late crystallization alternatively these sm nd ages may have been affected by the event in which ca phosphate and augite in mesostasis were recrystallized and augite and chromite in granoblastic areas were derived from cloudy pyroxenes late recrystallization the subsolidus recrystallization may be a consequence of a thermal spike in the midst of an otherwise monotonically cooling environment resulting from impact cratering of the hot crust of the newly formed eucrite parent body pyroxene homogenization probably occurred prior to formation of granoblastic pyroxene and close to the time of initial crystallization mn cr data provide only a hint of live 53mn t1 2 3 7ma and imply either chromium isotopic equilibration after decay of 53mn or late crystallization impact brecciation and lithification probably accompanied thermal annealing 3 4 3 6 ga ago as given by the 39ar 40ar ages the rb sr age of y792510 65 is consistent with this interpretation the 39ar 40ar and rb sr systematics of minute k rich inclusions in plagioclase and pyroxene formed by previous impact and thermal annealing events probably were reset then these young impact metamorphic ages demonstrate that impact resetting of radiometric ages on the hed parent body asteroid 4 vesta occurred over an interval of at least 0 7 ga

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

39ar40ar age of the ibitira eucrite and constraints on the time of pyroxene equilibration abstract we determined a 39 ar 40 ar age of 4 495 0 015 ga for the unbrecciated ibitira eucrite this age ranks among the oldest 39 ar 40 ar ages for eucrites and suggests that ibitira escaped the widespread impact resetting of k ar ages 4 1 3 5 ga ago indicated by other hed meteorites ibitira exhibits a relatively high degree of chemical equilibration of its pyroxene caused by prolonged annealing this equilibration must have occurred subsequent to the reported 207 pb 206 pb formation age for ibitira of 4 556 4 560 ga but prior to its determined ar ar age if pyroxene equilibration occurred during burial at significant depths or in a large impact deposit then the ar ar age may date this event

comparisons of antarctic and non antarctic achondrites and possible origin of the differences abstract in order to discuss differences between antarctic and non antarctic achondrites we investigated pairing of mainly the yamato achondrites by mineralogical techniques in addition to five paired specimens of the y74159 type polymict eucrites three new groups distinct from the y74159 type have been recognized one group y791960 of howarditic polymict eucrites is similar to those of non antarctic origin some antarctic monomict eucrites differ in texture and chemistry from the non antarctic specimens more than 50 diogenite specimens recovered from the yamato bare ice field can be grouped into two falls of separate locations compared with 8 from the usa collection and 9 from the non antarctic groups thirty antarctic ureilites are separate falls 2 pairings and their individual masses are small these observations suggest that discussion of differences between the antarctic and non antarctic achondrites largely depends on detection of pairings of the antarctic specimens the pairings of the specimens from victoria land have not been as well characterized as those of the yamato mountains comparisons with non antarctic meteorites show that the antarctic heds and ureilites differ from non antarctic specimens by the following criteria 1 1 polymict eucrites excluding those with howarditic affinity have not been found in the non antarctic collections 2 2 magnesian ureilites and augite bearing ureilites were found only in antarctica the differences may not be attributed to just one factor the above evidence of two unique diogenite falls preserved on the restricted ice fields suggests that the yamato diogenites may represent falls on restricted areas in the distant past the discovery of many small unique eucrites and ureilites suggests that within the large number of small specimens on a bare ice field there is a higher chance of finding unique varieties

surface lithologic heterogeneity of asteroid 4 vesta abstract high precision spectrophotometry of 4 vesta the third largest asteroid was used to establish the surface composition of this body and to investigate mineralogical variations across its surface the average surface of vesta is analogous to howardite and or polymict eucrite assemblages regolith derived members of the hed meteorite suite which consist of a eucrite matrix containing differing amounts of a diogenite component color and or spectral changes which exhibit a consistent relationship to rotational phasing are evident in 16 of 18 studies of vesta dating back to 1929 including the present work after elimination of possible sources of spurious spectral or color changes it is concluded that these variations arise from hemispheric variations in surface materials and hence provide a means of spatially resolving subhemispheric compositional units on the surface of vesta the background surface of vesta is a relatively dark howardite or polymict eucrite pyroxene plagioclase assemblage with several compositionally distinct bright regions clustered in one hemisphere viewed around the maximum in vesta s lightcurve these include what appears to be an olivine bearing unit suggested name leslie formation located near vesta s equator which probably represents an impact basin and or its associated ejecta that penetrated through the basaltic crust other high albedo compositional units including an apparently low calcium eucrite region and several diogenite pyroxenite regions at least one located near the southern pole may be smaller shallower impact basins by analogy to the eucrite meteorites which represent surface flows or shallow intrusions and which constitute the major component of the regolith derived howardites and polymict eucrites we conclude that the howardite polymict eucrite units represent a regolith gardened original surface of vesta it is probable that the low albedo of the background surface on vesta is due to an age related darkening effect similar to that inferred from the galileo images of gaspra and ida this mechanism is consistent with the correlation of absorption feature intensity with the lightcurve vesta appears to have an old eucritic surface darkened with age and represented among the meteorites by the regolith derived howardites and polymict eucrites on which several impacts on one hemisphere have exposed fresher brighter diogenite and olivine bearing material based on qualitative analysis of the mineralogical variations as a function of rotation a generalized lithologic map of vesta was produced there is reasonable control on the longitude of lithologic features but little control on their latitudes except where specifically noted in producing this map discrete circular features were used on the plausible assumption that impacts have been the most important geologic process on this surface for most of the age of the solar system the shape of the features has thus been assumed rather than derived and is subject to future revision as data improve

mineralogy and39ar 40ar age of an old pristine basalt thermal history of the hed parent body previous investigations of mineral chemistry and rbsr and smnd ages indicated that clast 84 from eucrite yamato 75011 had preserved the pristine nature of its initial crystallization during an early stage of the hed parent body microscale mineralogy and39ar 40ar ages of this clast however revealed local disturbance of micrtextures and partially reset ages this evidence suggests that in addition to initial crystallization and rapid cooling the y75011 84 clast experienced shock deformation reheating of short duration at higher temperature and brecciation these characteristics suggest two or more impact events fe rich olivine filling fractures in pyroxene may have been introduced during the accompanying shock fracturing the inferred39ar 40ar degassing ages for y75011 matrix and clast 84 are3 94 0 04 ga and3 98 0 03 ga respectively the suggested degassing age for a clast from y790020 believed to be paired with y75011 is 4 03 ga but could be younger we consider it likely that all three samples experienced a common degassing event3 95 0 05 ga ago but we cannot rule out two or more events spaced over a 0 1 ga interval higher temperature extractions of the two clast samples show significantly older apparent ages up to 4 5 ga and suggest that the time temperature regime of this event was not sufficient to degas ar totally most likely the k ar ages were reset by thermal metamorphism associated with one or more impact events associated with shock fracturing formation of fe rich olivine veins and or meteorite brecciation the pyroxene annealing that commonly occurs in many eucrites is likely to be a much earlier process than the impact produced textural changes and reset k ar ages observed in these meteorites the existence of mineralogical and chronological evidence for metamorphism in an otherwise pristine eucrite suggests that the hed parent body experienced an extensive degree of early cratering

antarctic geomagnetic reference model updated to 2010 and provisionally to 2012 abstract the antarctic reference model arm has been here updated using recent geomagnetic data measured over the antarctic continent from both ground observatories and satellites this regional geomagnetic model is based on a spherical cap harmonic analysis scha of geomagnetic field measurements over a polar cap of 30 half angle centred at the geographic south pole fixing the maximum spatial expansion index k max 8 and the maximum temporal order of polynomials q max 4 the importance of updating arm model lies for instance in its usefulness for the reduction of magnetic surveys performed during the period of model validity over the antarctica or for geomagnetic anomaly field estimations moreover so far arm still remains the only regional reference magnetic model specifically constructed for the antarctic continent the present updated version can be considered valid from 1955 5 to 2010 0 with predictive coefficients up to 2012 0 the model includes the most recent available data but in contrast to previous versions not only does it take advantage of a stricter selection of satellite data in order to consider even quieter periods of external magnetic activity but it also includes ground observatory data previous to 1960 going back to 1955 8 like the previous versions the new updated model has been tested and compared with major global models to show its reliability over the region under investigation

zinc isotopes in heds clues to the formation of 4 vesta and the unique composition of pecora escarpment 82502 the 66zn permil deviation of the 66zn 64zn ratio from a terrestrial standard values for a suite of 20 non antarctic hed howardite eucrite diogenite meteorites and one mesosiderite and for 8 antarctic eucrites and diogenites were measured in order to determine the role of volatization in the formation of their presumed parent body the asteroid 4 vesta the 20 non antarctic heds had 66zn values that ranged from 2 0 to 1 67 with a mean value of 0 01 0 39 2se this range likely represents a small scale heterogeneity due to brecciation induced by multiple impacts the non antarctic eucrites 66zn 0 00 0 58 2se n 12 were isotopically the same as the diogenites 66zn 0 31 0 80 2se n 4 and the howardites 66zn 0 26 0 37 2se n 4 on average non antarctic eucrite falls were isotopically heavier 0 50 than non antarctic finds 1 00 the antarctic finds studied were all unbrecciated samples and they were significantly heavier than the non antarctic samples with a 66zn range of 1 63 to 6 22 for 4 eucrites mean 4 32 and 0 94 to 1 60 for 3 diogenites mean 1 23 excluding one anomalous sample while their zn concentration is significantly lower than the brecciated samples these data suggest that the unbrecciated eucrites probably represent the eucritic crust shortly after differentiation and cooling of the parent asteroid at which time volatization of lighter zinc isotopes led to an isotopically heavy crust early impact events caused the ejection of these unbrecciated meteorites which were subsequently spared from brecciation caused by multiple additional impacts on the much larger vesta the range of 66zn values and zn concentration for the brecciated heds in this study supports a major contribution to the vestan surface by chondritic impactors 1 30 66zn 0 76 for ordinary and carbonaceous chondrites the anomalous eucrite pca 82502 66zn 7 75 is significantly isotopically lighter than the other heds and is the natural sample with the lightest zn isotopic composition reported in the solar system to date this meteorite most likely originated from a distinct parent body

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

ion microprobe investigation of exsolved pyroxenes in cumulate encrites determination of selected trace element partition coefficients we have examined the partitioning of selected minor and trace elements in exsolved pyroxenes from cumulate eucrites by secondary ion mass spectrometry sims solid solid partition coefficients d s for al cr ti seven rees sr y and zr have been determined between low ca and high ca pyroxenes from moore county binda serra de mage and moama equilibrium temperatures of the co existing pyroxenes were calculated to constrain the relevant temperatures for the partition coefficients trace element abundance patterns are similar for pyroxenes from the four cumulate eucrites and thus indicate similar distribution behaviors of the trace elements during exsolution there is a significant hree enrichment over lrees in the low ca pyroxenes and abundances of the rees in augite are greater than those found in the low ca pyroxene hosts this ree behavior reflects the pyroxene crystal structures the calculated solid solid partition coefficients are found to vary systematically as expected from pyroxene crystal chemical arguments calculated subsolidus equilibration temperatures are within the expected range produced by pyroxene solvus temperature composition relations and consistent with petrographic observations of the cumulates the trace element patterns and abundances indicate that three of the four cumulates examined binda moama serra de mage were formed from the same melt or similar melts crystallizing under similar conditions in their parent body moore county has much higher trace element concentrations and this suggests that it either formed from a more evolved melt than the other three cumulates and crystallized later in the fractionation sequence or alternatively it was derived from a different melt system

old sm nd ages for cumulate eucrites and redetermination of the solar system initial 146sm 144sm ratio article i nfo sm 142 nd systematics short lived 146 sm 142 nd and long lived 147 sm 143 nd chronometers have been measured in three cumulate eucrites binda moore county and moama the two major mineral phases plagioclase and pyroxene present in these achondrites are characterized by a wide range of sm nd ratios that allows well resolved sm nd isochrons this group of meteorites thus is suitable to better constrain the initial 146 sm 144 sm ratio of the solar system binda and moore county give concordant ages of 4544 88 and 4542 85 ma respectively with initial 143 nd 144 nd ratios slightly higher to within error of chondritic these ages are in agreement with most of the radiometric ages determined on basaltic eucrites a best estimate for the solar system initial 146 sm 144 sm ratio is obtained using the five point regression line determined for binda the 146 sm 144

the polymict eucrites the polymict eucrites are a suite of about 14 polymict achondritic meteorites that contain at least 90 vol of eucritic material and are found both in antarctica and elsewhere they are part of a continuum of polymict breccias that includes howardites and polymict diogenites rare gas data suggest that some are gas rich regolith breccias the clasts contained in polymict eucrites sample a variety of lithologies from their parent body and include eucritic clasts alkali enriched eucrites pyroxene cumulate eucrites two pyroxene mafic rocks possibly feldspar cumulate eucrites diogenites fayalitic lithologies and a variety of other mineral clasts the eucritic clasts are probably samples of near surface lithologies on the parent body but the presence of two pyroxene mafic rocks is considered to be evidence of magmatic activity at pressures in excess of 1 kbar in the parent body partial melt models may explain some of the diversity among the clasts but cumulus processes are believed to have been important if pressures greater than 1 kbar are confirmed then the basaltic achondrite parent body bap must have a diameter in excess of 200 km the variety of lithologies suggests that not all basaltic achondrites are samples of igneous rocks formed by single stage melting of a chondritic asteroid but are instead samples of an evolved and diverse crust produced by serial magmatism

partial melting and melt migration in the acapulcoite lodranite parent body we review petrologic evidence that the acapulcoites and lodranites formed by 1 vol to probably 20 vol whole rock partial melting of a chondritic precursor material at low degrees of partial melting only fe ni fes cotectic melting occurred migration distances for partial melts were short resulting in the formation of acapulcoites with essentially chondritic troilite and plagioclase contents but achondritic textures at high degrees of partial melting both fe ni fes and basaltic plagioclase pyroxene partial melts formed and the melts may have migrated out of the source rock the partial melt residues which are more or less depleted in fe ni fes and plagioclase are the lodranites melt migration was complex most acapulcoites which experienced relatively low degrees of partial melting lost little if any of the partial melt one acapulcoite lew 86220 represents a unique case in which fe ni fes and basaltic partial melts appear to have migrated from a lodranite source region into a cooler acapulcoite region where they were trapped in cases of the relatively high degrees of partial melting experienced by lodranites melts may have been partly selectively or totally removed from the rocks and fe ni fes and or basaltic partial melts may have been removed to different degrees and may in fact have been trapped on occasion in greater than chondritic proportions we model vein and dike formation and melt migration by calculating the excess pressures and vein and dike sizes for varying degrees of partial melting our calculations are broadly consistent with observations indicating that melt migration is inefficient at low degrees of partial melting and extremely efficient at high degrees of partial melting although the size of the acapulcoite lodranite parent body and the volatile contents of the chondritic precursor rocks are poorly constrained the lack of basaltic rocks in the world s meteorite collections complementary to the lodranites suggests that basaltic partial melts may have been accelerated off the body by explosive volcanism of the type envisioned by wilson and keil 1991 and ejected into space the diversity of rocks from the acapulcoite lodranite parent body may provide a basis for better understanding the diverse range of spectral subtypes recognized among the s type asteroids

a model for the origin of basaltic achondrites based on the yamato 7308 howardite the y 7308 howardite comprises a variety of lithic clasts and mineral fragments the mg mg fe atomic ratios of the pyroxenes in diogenitic clasts eucritic clasts and fayalite hedenbergite tridymite plagioclase clasts vary continuously from 0 76 to less than 0 30 olivine fragments in the matrix have a wide range of mg mg fe ratios from 0 88 to 0 71 this continuum of chemical compositions for olivine and pyroxene is explained by the fractional crystallization of a primary magma the composition of a liquid produced by removing olivine and pyroxene from the primary magma is almost identical to that of eucrites and the solidification of this liquid on the surface of a magma ocean might have formed a eucrite crust on the parent body a source material of carbonaceous or ll chondrite like composition may produce the hed howardites eucrites diogenites magma by partial or batch melting the volatile components such as alkalis sulfur oxides etc may have been lost and reduction of feo and fe203 components to fe metals also may have taken place prior to and or during the formation and crystallization of the hed magma

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

the diogenite eucrite links and the crystallization history of a crust of their parent body aspects of the crystallization history of the primitive crust of the hed howardites eucrites diogenites achondrite parent body have been deciphered from the microtextures and chemical compositions of pyroxene and plagioclase in some antarctic hed achondrites intermediate to diogenite and eucrite five new specimens related to yamato 75032 and three eucritic clasts in y791186 and y791208 have been investigated by electron microprobe analytical transmission electron microscope and x ray diffraction techniques their pyroxene compositions cover the entire range from fe rich diogenite to eucrite the pyroxene textures of the y75032 type achondrites indicate that many of them crystallized as low ca pigeonite and some as orthopyroxene later shock events modified the original inversion and exsolution textures the chemical compositions and the interstitial occurrence of plagioclase crystals in pyroxene indicate crystallization from intercumulus trapped liquid the pyroxene crystallization and the relation between the anorthite content an of plagioclase and the mg mg fe number of the coexisting pyroxene in these specimens reveal two crystallization trends one trend is intermediate to that of the mg rich suites of the lunar highland crust and that of ferroan anorthosite and the other is a trend with a steep decrease in the an content while the mg mg fe of the pyroxene remains effectively constant a model involving crystal fractionation in a shallow magma ocean or intrusion in the parent body has been proposed

the composition of the mantle of the eucrite parent body and the origin of eucrites abstract previous estimates of the composition of the epb have tacitly assumed chondritic abundances of refractory lil elements a model is presented here which utilizes refractory element ratios instead consideration of these ratios and of known olivine liquid partition coefficients for sc mg and si imply that the epb mantle may be accurately modeled as a simple mixture of 25 eucrite 75 olivine the model also implies that eucrites such as juvinas and sioux county were derived by large degrees of partial melting 20 30 comparison of the model epb mantle to known meteorite classes indicates a similarity between the element abundances of the epb and c3 chondrites

the bholghati howardite petrography and mineral chemistry abstract a 10 g sample of the bholghati howardite was disaggregated in order to separate two eucrite clasts several small carbonaceous clasts fragments of diogenitic pyroxene and bulk matrix the eucrite clasts show evidence of moderately rapid cooling from a melt followed by prolonged subsolidus annealing the carbonaceous clasts mostly resemble cm2 carbonaceous chondrites with low iron silicates and fe ni sulphides in a fine grained dark matrix one clast however is mineralogically petrographically and compositionally similar to a ci 1 chondrite both carbonaceous and eucritic clasts have a complex history prior to incorporation into the howardite matrix with no evidence of significant metamorphism since assembly most clasts in the howardite breccia are monomineralic with pyroxene and plagioclase pre dominant pyroxenes range from diogenitic to eucritic with diogenitic compositions most abundant a significant number of intermediate compositions are present consistent with derivation from a series of rocks related by fractionation

antarctic polymict eucrite yamato 792769 and the cratering record on the hed parent body yamato y792769 is a polymict breccia containing pyroxenes of a limited range in chemical compositions compared to most other yamato polymict eucrites y792769 includes fewer and smaller eucritic clasts with homogenized pyroxenes its fine grained matrix is shock compacted and sintered the time of the last thermal event which produced this texture and formed the breccia is determined by the well defined 39ar 40ar age of 3 99 0 04ga the complete resetting of the 39ar 40ar age is consistent with the texture of y792769 as viewed in the transmission electron microscope tem which suggests shock compaction converted part of the matrix plagioclase to maskelynite sm nd data define an apparent isochron corresponding to an age of 4 23 0 12ga this apparent age probably reflects partial resetting of the sm nd system during breccia formation but similar ages recorded in the highest temperature argon releases and in the rb sr model age of relict plagioclases lend some support to its reality sm nd data for relict pyroxenes fall on a 4 56 ga sm nd reference isochron and on or above a 4 56 ga rb sr reference isochron suggesting slight loss of rubidium during breccia formation the pyroxene data are most suggestive of a conventional 4 56 ga age for the protolith rocks the 3 99 ga39ar 40ar age predates the accepted age of formation of the lunar imbrium and serenitatis basins but probably reflects a period of intense meteoroid bombardment that affected the entire inner solar system

the parent magmas of the cumulate eucrites a mass balance approach the cumulate eucrite meteorites are gabbros that are related to the eucrite basalt meteorites the eucrite basalts are relatively primitive nearly flat ree patterns with la approx 8 30 x ci but the parent magmas of the cumulate eucrites have been inferred as extremely evolved la to greater than 100 x ci this inference has been based on mineral magma partitioning and on mass balance considering the cumulate eucrites as adcumulates of plagioclase pigeonite only both approaches have been criticized as inappropriate here mass balance including magma equilibrium pigeonite equilibrium plagiociase is used to test a simple model for the cumulate eucrites that they formed from known eucritic magma types that they consisted only of magma crystals in chemical equilibrium with the magma and that they were closed to chemical exchange after the accumulation of crystals this model is tested for major and rare earth elements ree the cumulate eucrites serra de mage and moore county are consistent in both ree and major elements with formation by this simple model from a eucrite magma with a composition similar to the nuevo laredo meteorite serra de mage as 14 magma 47 5 pigeonite and 38 5 plagioclase moore county as 35 magma 37 5 pigeonite and 27 5 plagioclase these results are insensitive to the choice of mineral magma partition coefficients results for the moama cumulate eucrite are strongly dependent on choice of partition coefficients for one reasonable choice moama s composition can be modeled as 4 nuevo laredo magma 60 pigeonite and 36 plagioclase selection of parent magma composition relies heavily on major elements the ree cannot uniquely indicate a parent magma among the eucrite basalts the major element composition of y 791195 can be fit adequately as a simple cumulate from any basaltic eucrite composition however y 791195 has lree abundances and la lu too low to be accommodated within the model using any basaltic eucrite composition and any reasonable partition coefficients postcumulus loss of incompatible elements seems possible it is intriguing that serra de mage moore county and moama are consistent with the same parental magma could they be from the same igneous body on the eucrite parent asteroid 4 vesta

comparison of yamato and victoria land polymict eucrites a view from mineralogical and isotopic studies new interior samples of four yamato polymict eucrites y74159 y74450 y75011 and y75015 have been studied by electron microprobe transmission electron microscope and x ray diffraction techniques and compared with several samples of the victoria land polymict eucrites these same samples have been analysed using rb sr and nd sm isotopic systematics several grains of inverted pigeonite with blebby augite similar to those in binda and moama have been identified in all four yamato eucrites coarse grained mesostasis rich subophitic basalts which contain mg rich pigeonite with fe rich olivine veinlets zoned outward to a subcalcic ferroaugite rims have also been found these unique clasts were not found in alh76005 77302 78040 78158 and 78165 and eet eucrites the tight grouping of rb sr and sm nd ratios and similar modal compositions of the yamato group indicate that they are most likely to be pieces from a single fall and distinct from the alh and eet groups however the yamato allan hills and elephant moraine groups may sample a few distinct magmas or similar but different source regions on the same parent body

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

rb sr and sm nd internal isochron ages of a subophitic basalt clast and a matrix sample from the y75011 eucrite the yamato polymict eucrite y75011 contains several coarse grained mesostasis rich basaltic clasts with subophitic texture the preservation of extensive mg fe chemical zoning in pyroxenes and the presence of a dark mesostasis shows that these clasts are representative of pristine lava like basalts extruded on the surface of the howardite eucrite diogenite hed parent body rubidium strontium analyses of a large clast y75011 84b yielded a precise internal isochron age of 4 60 0 05 b y for 87rb 0 0139 b y 1 or 4 50 0 05 b y for 87rb 0 0142 b y 1 the rb sr systematics of a matrix sample are nearly identical to those of the pristine clast showing that the matrix is dominantly comminuted mesostasis rich basalt the rb sr internal isochron age of the matrix is 4 56 0 06 b y for 87rb 0 0139 b y 1 or 4 46 0 06 b y for 87rb 0 0142 b y 1 these ages are within error limits of the rb sr whole rock age of chondrites and are in agreement with 206pb 207pb and sm nd ages of ordinary monomict eucrites for 87rb 0 01402 b y 1 based on a comparison of the rb sr and u th pb ages of chondrites minster et al 1982 the good precision obtained for the rb sr ages of both clast and matrix is due to the presence of a mesostasis phase in which the rb sr ratio is enriched 3 4 times above that of any eucrite phase previously analysed the initial 87sr 86sr ratios of clast and matrix are 0 69894 2 and 0 69896 3 respectively and are in satisfactory agreement with the babi value papanastassiou and wasserburg 1969 there is evidence of isotopic disturbance in both the rb sr and sm nd systems of the most magnetic separate analysed a sm nd internal isochron of 4 55 0 14 b y for the combined data from both clast and matrix exclusive of the most magnetic separate is in agreement with the more precise rb sr age the corresponding initial 143nd 144nd 0 50587 19 normalized to 148nd 144nd 0 24308 the clast data alone exclusive of the most magnetic separate define an isochron age of 4 52 0 16 b y and initial 143nd 144nd 0 50593 19 the isochron error limits quoted here for the sm nd data are 2 from the york 1966 program and include the factor s n 2 used in that program to compensate for geological error however this factor is not appropriate for the rb sr isochrons and has been omitted from the quoted error limits the initial 143nd 144nd of the pristine clast at 4 56 b y ago is 0 505877 25 in agreement within error limits with the chur value jacobsen and wasserburg 1984 clast y75011 84 represents the oldest pristine unambiguously basaltic lava as yet recovered from a solar system object rare earth element abundance measurements shimizu and masuda 1985 show it to be one of the most differentiated eucrites thus moderately evolved basaltic lavas were produced very early in the history of the hed parent body their preservation as clasts in the polymict eucrites suggests derivation from a different geologic setting on the parent body than that occupied by the more thermally metamorphosed monomict eucrites we suggest that the preservation of pristine clasts in polymict eucrites may be due to their impact excavation to the surface of the parent body away from heat sources concentrated within impact craters the monomict eucrites may be derived from the floors of craters where they were thermally metamorphosed by shock heating and by the presence of overlying impact melts and nearly molten breccias

age of a eucrite clast from the bholghati howardite 39ar 40ar rb sr and sm nd investigations of the large eucrite clast 1 studied by the bholghati consortium show that it crystallized from a melt 4 51 ga ago the crystallization age is given most precisely by a sm nd internal isochron of 4 510 0 034 ga 2 error limits for 147sm 0 00654 ga 1 142nd144nd measurements show that the clast contained live 146sm at the time of crystallization a solar system initial 146sm144sm0 0 00431 0 0039 0 0026 at 4 555 ga ago can be calculated from a 146sm 142nd isochron and the age of the clast alternatively using 146sm144sm 0 0 0045 as previously reported in the literature a 146sm142nd formation interval of 0 05 0 12 0 08 ga can be calculated which is concordant with the 147sm 143nd isochron age and in agreement with pu u xe and pu nd xe formation intervals reported in a companion consortium paper the initial 143nd144nd ind of the clast was ind 0 505958 50 2 error limits normalized to 146nd 144nd 0 724140 and is consistent with the chur reference value for evolution in a source having chondritic relative ree abundances prior to magma generation however when interlaboratory bias is considered the data are also permissive of a lree depleted source as suggested in a companion consortium paper a primary rb sr isochron yields an age of 4 54 0 06 ga 2 error limits for 87rb 0 01402 ga 1 in agreement with the more precise sm nd age the initial 87sr86sr isr of the clast was isr 0 699006 21 and was the same within error limits as isr previously determined for a pristine eucrite clast from polymict eucrite y75011 compatible with a common parent body the 39ar 40ar data and some of the rb sr data show that bholghati was affected by a major thermal event 2 3 ga ago and also provide weak evidence for a minor thermal event 1 ga ago the age and isotopic systematics of the clast are consistent with those of other eucrites and support the widely held assumption of a common parent body for howardites and eucrites the isotopic investigations of polymict eucrites and howardites point to a prolonged cratering record on the howardite eucrite diogenite hed parent body and suggest that it survived the cataclysm affecting the moon 3 8 4 0 ga ago

the antarctic achondrite alha 76005 a polymict eucrite abstract alha 76005 is a basaltic achondrite containing few if any orthopyroxenes its bulk major and trace element composition is like that of a non cumulate eucrite and unlike that of a howardite it contains a variety of igneous clasts which differ in their textures pyroxene plagioclase ratios and pyroxene and plagioclase compositions one clast no 4 was found to have the ree pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite both the chemical and oxygen isotopic composition of clast no 4 suggest that it was derived from a source different from its host these observations lead to the conclusion that alha 76005 is a polymict eucrite

geologic mapping of vesta from 1994 hubble space telescope images we utilize the 56 images of asteroid 4 vesta obtained through four mineralogically diagnostic filters by the hubble space telescope zellneret al 1997 icarus to construct a geologic map vesta s surface is found to be geologically diverse and to be dichotomous at a hemispheric scale the eastern hemisphere longitude definition from thomaset al 1997 icarus is dominated by units interpreted to be impact excavated plutonic material composed of magnesium rich and calcium poor pyroxene the mineralogy of this region is most analogous to diogenite meteorites several eastern hemisphere units which have the deepest and broadest 1 m absorption bands may contain a substantial olivine component the locations of these units are consistent with a previous map based on rotationally resolved groundbased spectroscopy gaffey 1997 icarus the western hemisphere is dominated by units interpreted to consist of a single component of iron rich and relatively calcium rich pyroxene analogous to surface basalts such as eucrite meteorites we investigate the spectral properties of 20 representative surface regions and find a correlation between the 1 m absorption band depth and albedo the units with lower albedos have shallower band depths such a relation could arise from differences in lithologies differences in surface particle sizes or from a weathering effect which decreases albedo and band depth over time because of vesta s geologic diversity and hemispheric dichotomy it is apparent that any major impact events such as those possibly related to the formation of the vesta family binzel and xu 1993 science260 186 191 did not globally resurface the planet the spectral evidence for remnants of a basaltic crust implies that the oldest units on the surface date back to the time of their emplacement most likely 4 5 byr ago if a weathering process exists which alters the albedo then the lowest albedo units such as the feature with the proposed name olbers most likely represent remnants of vesta s ancient basaltic crust

complexities in pyroxene compositions derived from absorption band centers examples from apollo samples hed meteorites synthetic pure pyroxenes and remote sensing data we reexamine the relationship between pyroxene composition and near infrared absorption bands integrating measurements of diverse natural and synthetic samples we test an algorithm plc involving a two part linear continuum removal and parabolic fits to the 1 and 2 m bands a computationally simple approach which can easily be automated and applied to remote sensing data employing a suite of synthetic pure pyroxenes the plc technique is shown to derive similar band centers to the modified gaussian model plc analyses are extended to natural pyroxene bearing materials including 1 bulk lunar basalts and pyroxene separates 2 diverse lunar soils and 3 hed meteorites for natural pyroxenes the relationship between composition and absorption band center differs from that of synthetic pyroxenes these differences arise from complexities inherent in natural materials such as exsolution zoning mixing and space weathering for these reasons band center measurements of natural pyroxene bearing materials are compositionally nonunique and could represent three distinct scenarios 1 pyroxene with a narrow compositional range 2 complexly zoned pyroxene grains or 3 a mixture of multiple pyroxene or nonpyroxene components therefore a universal quantitative relationship between band centers and pyroxene composition cannot be uniquely derived for natural pyroxene bearing materials without additional geologic context nevertheless useful relative relationships between composition and band center persist in most cases these relationships are used to interpret m3 data from the humboldtianum basin four distinct compositional units are identified 1 mare humboldtianum basalts 2 distinct outer basalts 3 low ca pyroxene bearing materials and 4 feldspathic materials

revisiting spectral parameters of silicate bearing meteorites visible and near infrared reflectance spectra of a sample of silicate bearing meteorites have been used to evaluate the spectral parameters space defined in the pioneering work of gaffey et al 1993 the studied sample consisted of 91 ordinary chondrites 47 basaltic achondrites and 21 different laboratory mixtures obtained from the relab database our results indicate that the spectral parameter space in particular the bar versus band i center is not suitable enough to identify the mineralogy of meteorites and asteroids the grain size of the sample also appears as a very sensitive parameter and can play an important role in locating an object in the spectral parameter space finally the application of our study to the question of a genetic link between v type asteroids and hed meteorites shows that these bodies plot in distinct regions in the bar versus band i center space this result further confirms that those spectral parameters cannot uniquely define the mineralogy of a sample

the tatahouine diogenite mineralogical and chemical effects of sixty three years of terrestrial residence comparison between clasts of the tatahouine diogenite collected the day of the fall in 1931 and 63 years later in 1994 allows the evaluation of mineralogical and chemical effects of terrestrial residence on meteorites secondary minerals are found in the 1994 samples iron stains and carbonate rosettes major and trace element abundances have been determined on fallen and found clasts no significant differences have been observed for most elements with the exception of rb sr and in a single case the light rare earth elements lree in this case the ree pattern of a 1994 clast displays a weak positive ce anomaly probably linked to the presence of iron hydroxide the contents of rb and sr are significantly higher in the 1994 samples than in the 1931 clasts and reflect the formation of calcite inside some of the clast fractures these results demonstrate that weathering processes may change the chemistry of meteorites in a very short time

megaregolith insulation and the duration of cooling to isotopic closure within differentiated asteroids and the moon ages determined for extraterrestrial samples by the sm nd and rb sr techniques are commonly assumed to record igneous crystallization events because in solid silicates nd and sr diffuse at exceedingly slow rates however we find that for coarse grained igneous cumulate rocks from the moon or from a large thoroughly brecciated asteroid this assumption may not be reliable the moon and at least one asteroid the parent body of the eucrite diogenite and howardite meteorites appear to have been largely molten at or about the time they formed we have modeled global cooling of the moon and large r 40 250 km asteroids starting at or near the solidus a crucial factor in determining the prevailing interval ic of cooling between igenous crystallization and isotopic closure for any given depth in the crust is the extent to which the body is insulated by a regolith megaregolith layer of porous fragmental impact debris given plausible assumptions regarding the thicknesses of such layers on the moon and the eucrite parent asteroid and regarding the radius of the eucrite asteroid our results indicate that deep crustal regions tend to remain above the nd and sr isotopic closure temperature for intervals that are long in comparison to the precision of modern nd and sr based age measurements and in comparison to suggested chronologic scenarios of global differentiation ic intervals of as long as 100 m y may be common among available samples of primordial deep crustal cumulates from both bodies chronologies for the gross solidification of the moon and the eucrite asteroid should allow for the possibility that any single age for a coarse grained plutonic or cumulate textured rock might be many tens of millions of years younger than the igneous crystallization age

smnd systematics of a silicate inclusion in the caddo iab iron meteorite we report the first sm nd data from an iron meteorite silicate inclusion mineral separates from an inclusion in the caddo iab iron define a 147 sm 143 nd age of 4 53 0 02 ga and an initial 146 sm 144 sm of 0 0086 0 0021 a plagioclase separate from the inclusion yields the lowest 142 nd 144 nd ratio measured to date which provides an absolute maximum initial solar system 142 of 2 1 0 4 when the 146 sm 142 nd data are combined with the 147 sm 143 nd data we obtain our preferred initial solar system 142 value of 3 2 u which corresponds to an initial 146 sm 144 sm of 0 009 rare earth element data from the caddo silicate inclusion suggest that it was derived by partial melting of a chondritic source prior to incorporation into the metal therefore differentiation of the silicate portion of the parent body must have started approximately within the first 30 ma of solar system history the data reported here clearly show that iab meteorites preserve a record of very early planetary differentiation processes modeling of element diffusion indicates that if the silicate material was incorporated into its feni host at a time much later than 4 53 ga then the mixing must have taken place at shallow levels i e 50 m in the parent body in order to preserve the sm nd systematics it is more likely that incorporation of the silicate took place at depths greater than 2 km and that it occurred within the first 30 ma of solar system history this is consistent with estimates of cooling rates determined for iab irons

acapulco and lodran like achondrites petrology geochemistry chronology and origin we have performed petrologic and geochemical studies of five primitive achondrites alha81187 and alha81261 acapulco like eet 84302 transitional but acapulco like and lew 88280 and mac 88177 lodran like we have also performed 39ar 40ar chronology on alha81187 alha81261 and eet 84302 lew 88280 and mac 88177 contain more ferroan olivines orthopyroxenes clinopyroxenes and chromites than do the acapulco like achondrites plagioclase is present in only alha81187 alha81261 and eet 84302 its composition does not track that of the mafic silicates eet 84302 with the most calcic plagioclase contains olivine and pyroxene with an mg intermediate between alha81187 and alha81261 similarly spinels in eet 84302 have the same mg as those in alha81187 while pyroxenes in the former are more ferroan than in the latter acapulco like achondrites have sm sc ratios between 0 8 1 5 times h chondrites and na sc ratios are between 0 81 0 times h chondrites indicating that silicate partial melts have not been lost from these rocks siderophile and chalcophile elements are fractionated and show a trend of increasing ir ni ratios with decreasing se co ratios this variation is consistent with fractionation by partial melting in the fe ni s system eet 84302 is very depleted in se and troilite is a accessory phase indicating essentially total loss of the low temperature fe ni s melt in contrast the lodran like achondrites are depleted in the highly incompatible lithophile elements relative to more compatible elements sm sc ratios are 0 2 0 7 times and na sc ratios are 0 04 0 18 times h chondrites these data are consistent with a model for formation of the lodran like achondrites as partial melting residues however the low ir ni and high se co ratios in two lodran like achondrites suggest the metal troilite in these rocks is dominated by the low melting fraction in the fe ni s system this metal troilite was added to the silicates after partial melting depleted them in a basaltic fraction the ar ar release spectra yield good plateau ages of 4 507 0 024 ga alha81187 4 511 0 007 ga alha81261 and 4 519 0 017 ga eet 84302 in good agreement with previously determined ar ar ages for other acapulco like achondrites together the ar ar ages demonstrate that metamorphism on the acapulco lodran parent body occurred 4 51 0 02 ga ago roughly 50 ma after its formation the geochemical and petrologic evidence on the acapulco and lodran like achondrites suggest that heating on the parent body was localized and heterogeneous in space and time the parent body was probably not subjected to parent body wide magmatism in contrast to the case for 4 vesta and the hed meteorites

chondritic models of 4 vesta implications for geochemical and geophysical properties simple mass balance and thermodynamic constraints are used to illustrate the potential geochemical and geophysical diversity of a fully differentiated vesta sized parent body with a eucrite crust e g core size and density crustal thickness the results of this analysis are then combined with data from the howardite eucrite diogenite hed meteorites and the dawn mission to constrain vesta s bulk composition twelve chondritic compositions are considered comprising seven carbonaceous three ordinary and two enstatite chondrite groups our analysis excludes ci and ll compositions as plausible vesta analogs as these are predicted to have a negative metal fraction second the melts thermodynamic calculator is used to show that the enstatite chondrites the cv ck and l groups cannot produce juvinas like liquids and that even for the other groups depletion in sodium is necessary to produce liquids of appropriate silica content this conclusion is consistent with the documented volatile poor nature of eucrites furthermore carbonaceous chondrites are predicted to have a mantle too rich in olivine to produce typical howardites and to have fe mn ratios generally well in excess of those of the heds on the other hand an na depleted h chondrite bulk composition is capable of producing juvinas like liquids has a mantle rich enough in pyroxene to produce abundant howardite diogenite and has a fe mn ratio compatible with eucrites in addition its predicted bulk silicate density is within 100 kg m 3 of solutions constrained by data of the dawn mission however oxidation state and oxygen isotopes are not perfectly reproduced and it is deduced that bulk vesta may contain approximately 25 of a cm like component values for the bulk silicate composition of vesta and a preliminary phase diagram are proposed

mineral chemistry and the petrogenesis of eucrites ii cumulate eucrites abstract we carried out an ion microprobe study of rees and other selected trace and minor element concentrations in orthopyroxene augite lamellae and plagioclase of two cumulate eucrites moama and moore county in order to reevaluate the relationships between cumulate and noncumulate eucrites and among cumulate eucrites pyroxene and plagioclase in these two meteorites are more homogeneous in major minor and trace elements than in noncumulate eucrites and trace and minor element concentrations in moore county are higher than in moama although subsolidus equilibration erased and original igneous zoning it did not affect the ree patterns of these minerals both pigeonite and plagioclase of moama and moore county have higher lree hree ratios than those phases in noncumulate eucrites this indicates that cumulate eucrites derived from melts with fractionated ree patterns and thus are not related to noncumulate eucrites in addition the inconsistency between degrees of fractional crystallization deduced from major and trace elements and the differences of lree hree ratios recorded in pigeonite and plagioclase also suggest that moama and moore county did not form in the same fractional crystallization sequence this study confirms earlier observations and conclusions of ma and schmitt 1979 and poses problems for prevalent models

comment on magnitude and profile of organic carbon isotope records from the paleocene eocene thermal maximum evidence from northern spain by manners et al earth planet sci lett 376 2013 220 230