bombardment history of asteroid 4 vesta recorded by brecciated eucrites large impact event clusters at 4 50 ga and discreet bombardment until 3 47 ga abstract the thermal impact histories of sixteen eucrite meteorites were investigated three monomict eucrites nwa 999 a 87272 87 and stannern five polymict eucrites nwa 1000 nwa 1666 nwa 5601 y 980066 100 and y 980255 100 three quench textured eucrite melt rocks y 981646 21 y 981651 105 and mil 0766214 one eucrite dominantly comprised of quench textured clasts que 99005 11 three unclassified eucrite breccias lap 031316 9 lar 06870 5 que 99799 4 and one unbrecciated eucrite eet 92004 17 included here due to its shock features we have measured fifteen high precision new 40 ar 39 ar plateau ages on plagioclase and matrix for ten of these meteorites with a tight cluster of nine ages obtained from three different polymict breccias these ages range from 4534 56 ma to 4491 16 ma resulting in a concordant age population p 0 16 the fact that such a cluster of ages is recorded in unrelated breccias which are made of a priori unrelated components leads us to propose that those ages recorded a single heating event on a large scale and is interpreted here as a high energy impact event early in the history of vesta at 4500 4 ma we propose that the debris was ejected and isolated from subsequent large impacts in a secondary rubble pile asteroid where the energy of the outgoing shock wave from an impact is significantly reduced as it compacts the target material holsapple et al 2002 and references therein the other analyses define a spread of five plateau ages ranging from 3851 21 ma to 3469 35 ma over 380 ma an additional apparent plateau age of 4288 38 ma but with a diffusion profile of cumulative 39 ar release along with published u pb apatite age of 4 14 ga suggests that the data might either define a true continuum normal background bombardment from 4 5 ga to 3 47 ga or cluster between 3 85 ga and 3 47 ga excavation of a fresh surface at 3 85 ga continuously bombarded until 3 47 ga both scenarios are compatible with a final ejection age of 3 47 ga when a major impact liberates the bulk of the brecciated meteorites into another secondary rubble pile asteroid where the brecciated eucrites stayed relatively well protected from subsequent major impacts based on these results and recent crater counting measurements we propose that the excavation and bulk ejection were caused by the rheasilvia ca 3 47 ga basin forming impact diffusion models on plagioclase crystals with different ar age spectrum signatures from a single breccia nwa1666 4501 7 ma suggest that either 1 the formation of the breccia is very young or 2 different plagioclase crystals have different diffusion characteristics and or 3 the porosity caused heterogeneous temperatures during an impact heating event particularly likely if the 4 5 ga brecciated eucrites were stored in a rubble pile asteroid many or possibly most large asteroids being re accumulated rubble piles with potential large porosity holsapple et al 2002 scenarios 2 and 3 preclude the usage of multi grain aliquots to decipher the time temperature history of most impact breccia using 40 ar 39 ar thermochronology

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

radiative transfer mixing models of meteoritic assemblages 1 a spectral mixing model for the expected conditions on asteroid surfaces based on hapke s radiative transfer theory for intimate mixtures is presented this model calculates the visible near infrared reflectance spectrum of an intimate mixture incorporating the modal mineralogy the mineral chemistry the particle size and the degree of space weathering as factors and includes an improved treatment for the spectral effects of coarse grained fe ni metal this model can reproduce the spectra of geologically plausible mixtures of silicate components and meteorites with known mineral abundances chemistry and particle sizes we compare the model spectral effects of the coarse grained fe ni metal naturally present on asteroid surfaces to the spectral effects of submicroscopic iron produced by lunar style space weathering the model spectral effects of large asteroid surface concentrations of coarse grained fe ni metal are similar to the spectral effects of smfe in some cases we model the composition of asteroid 4 vesta and find it to be consistent with a minimally space weathered eucritic composition finally we predict the spectral properties of some example of ordinary chondrite parent bodies when modeled with particle sizes matching the optically dominant particle size of the lunar surface and minimal abundances of smfe these model ordinary chondrite parent bodies plot outside the s iv asteroid field on a band area ratio versus band i center plot we find that a combination of larger particle sizes and increased smfe abundances is the most effective way to move these models into the s iv field

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

the origin of vesta s crust insights from spectroscopy of the vestoids high quality vnir spectra of 15 vestoids small asteroids that are believed to originate from vesta were collected and compared to laboratory spectra and compositional data for selected hed meteorites a combination of spectral parameters such as band centers and factors derived from modified gaussian model fits band centers band strengths calculation of the low to high ca pyroxene ratio were used to establish if each vestoid appeared most like eucrite or diogenite material or a mixture of the two howardite this resulted in the identification of the first asteroid with a ferroan diogenite composition 2511 patterson this asteroid can be used to constrain the size of diogenite magma chambers within the crust of vesta the vestoids indicate that both large scale homogeneous units 5 km and smaller scale heterogeneity 1 km exist on the surface of vesta as both monomineralogic eucrite or diogenite material alone and mixed both eucrite and diogenite spectra are observed the small scale of the variation observed within the vestoid population is predicted by the partial melting model which has multiple intrusions penetrating into the crust of vesta it is much more difficult to reconcile the observations here with the magma ocean model which would predict much more homogeneous layers on a large scale both at the surface and with depth

the geologically recent giant impact basins at vesta s south pole since 17 july 2011 nasa s spacecraft dawn has been orbiting the asteroid vesta the second most massive and the third largest asteroid in the solar system see the cover russell et al p 684 1 use dawn s observations to confirm that vesta is a small differentiated planetary body with an inner core and represents a surviving proto planet from the earliest epoch of solar system formation vesta is also confirmed as the source of the howardite eucrite diogenite hed meteorites jaumann et al p 687 2 report on the asteroid s overall geometry and topography based on global surface mapping vesta s surface is dominated by numerous impact craters and large troughs around the equatorial region marchi et al p 690 3 report on vesta s complex cratering history and constrain the age of some of its major regions based on crater counts schenk et al p 694 4 describe two giant impact basins located at the asteroid s south pole both basins are young and excavated enough amounts of material to form the vestoids a group of asteroids with a composition similar to that of vesta and hed meteorites de sanctis et al p 697 5 present the mineralogical characterization of vesta based on data obtained by dawn s visual and infrared spectrometer revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle the global color variations detailed by reddy et al p 700 6 are unlike those of any other asteroid observed so far and are also indicative of a preserved differentiated proto planet 1 lookup doi 10 1126 science 1219381 2 lookup doi 10 1126 science 1219122 3 lookup doi 10 1126 science 1218757 4 lookup doi 10 1126 science 1223272 5 lookup doi 10 1126 science 1219270 6 lookup doi 10 1126 science 1219088

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

geochemistry hydrology and mineralogy of the sand bulge area laguna madre flats south texas abstract the sand bulge area of the laguna madre flats is a silicoclastic coastal sabkha lying between padre island and the intracoastal waterway on the gulf coast of southwest texas the sabkha is sporadically inundated by wind tidal flooding of water from an adjacent lagoon laguna madre saline interstitial brines are formed by infiltration of partially evaporated ponded flood water manometric data indicate that the brine seeps downward through the sabkha and laterally west toward the intracoastal waterway icww some of the brine may flow seaward east through incised pleistocene stream valleys most of the sabkha in this area is covered with blue green algal mat precipitation of microcrystalline mg calcite algal micrite in brine ponds or within the algal mat induced by algal or bacterial action removes much of the calcium from recharge water before it reaches the sabkha watertable thus though brine salinities reach 240 per mil low calcium concentrations prevent the precipitation of gypsum and thermodynamic calculations indicate that the brines are undersaturated with respect to gypsum gypsum does not presently occur in the sabkha sediments in this area contrary to earlier observations fisk 1959 it is suggested that emplacement of the icww altered the rate and direction of water flow through the sabkha leading to less saline brines and possibly to the dissolution of previously formed gypsum

stable isotope mapping in messinian evaporative carbonates of central sicily mapping stable isotope isolines in both modern and ancient evaporative carbonate formations demonstrates that regional variations of 18 o values exist in the case of the messinian central sicilian basin an ancient evaporite basin the distribution pattern of the 18 o isolines can be related to the paleogeometry and paleohydrology of the basin isolines of equal 13 c values also show large regional variations possibly reflecting the domination of different bacterial processes oxidation sulfate reduction or methanogenesis in different regions the potential application for stable isotope mapping in evaporative carbonate formations deposited in both marine and lacustrine environments lies in its ability to predict the location of depositional centers in ancient evaporite basins

vesta s shape and morphology vesta s surface is characterized by abundant impact craters some with preserved ejecta blankets large troughs extending around the equatorial region enigmatic dark material and widespread mass wasting but as yet an absence of volcanic features abundant steep slopes indicate that impact generated surface regolith is underlain by bedrock dawn observations confirm the large impact basin rheasilvia at vesta s south pole and reveal evidence for an earlier underlying large basin veneneia vesta s geology displays morphological features characteristic of the moon and terrestrial planets as well as those of other asteroids underscoring vesta s unique role as a transitional solar system body

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

the violent collisional history of asteroid 4 vesta vesta is a large differentiated rocky body in the main asteroid belt that accreted within the first few million years after the formation of the earliest solar system solids the dawn spacecraft extensively imaged vesta s surface revealing a collision dominated history results show that vesta s cratering record has a strong north south dichotomy vesta s northern heavily cratered terrains retain much of their earliest history the southern hemisphere was reset however by two major collisions in more recent times we estimate that the youngest of these impact structures about 500 kilometers across formed about 1 billion years ago in agreement with estimates of vesta asteroid family age based on dynamical and collisional constraints supporting the notion that the vesta asteroid family was formed during this event

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

pyroxene spectroscopy revisited spectral compositional correlations and relationship to geothermometry the authors wish to thank the various agencies which have provided the necessary support for this project including grants in aid of research from sigma xi the scientific research society to e a c the geological society of america grant 3741 87 to e a c and nasa planetary geology and geophysics grant nagw 642 to m j g

the genesis of diogenites and hed parent body petrogenesis abstract samples of clasts and whole rocks from eighteen of the twenty four known diogenites orthopyroxenite breccia meteorites have been studied by combined inaa empa in order to elucidate their petrogenetic history the incompatible elements a12o3 and tio2 are positively correlated in diogenite orthopyroxenes these elements determined by empa are also positively correlated with incompatible trace elements such as yb determined by inaa on bulk samples these correlations indicate that most diogenites may form a single igneous fractionation sequence the incompatible minor and trace elements are decoupled from the major elements for essentially constant mg tio2 varies by about 4 times and yb by about 8 times hence there is no strong evidence for igneous fractionation preserved in the major element composition of orthopyroxenes geothermometry calculations using two pyroxene and spinelorthopyroxene thermometers show that these phases in diogenites maintained equilibrium to temperatures in the range 650 880 c far below likely magmatic temperatures in some diogenites orthopyroxenes of differing composition are in breccia contact therefore the low equilibration temperatures were achieved in the diogenites prior to brecciation decoupling of major and trace elements was most likely caused by slow subsolidus cooling in the diogenite pluton which allowed ca fe and mg to reach diffusive equilibration incompatible trace elements likely have much lower diffusivities in orthopyroxene and therefore may have largely preserved their magmatic distributions the extensive variation in incompatible trace elements indicates that either the diogenites were formed through an extensive crystallization interval or that partition coefficients greatly increased during crystallization if the former were true one would expect to find substantial amounts of plagioclase in the diogenites if they are comagmatic with eucrites this is contrary to observations a model in which diogenites crystallized from one or more melts of approximately orthopyroxenitic composition can satisfy both the mineralogie and trace element constraints

composition of the northern regions of vesta analyzed by the dawn mission abstract the surface composition of the northern regions of vesta observed by the dawn spacecraft offers the possibility to test several hypotheses related to impact related processes we used mostly imaging spectrometry in the visible and near infrared to assess the distribution of mafic lithologies hydrated components and albedo properties and use the link with howardite eucrite and diogenite meteorites heds to investigate the origin of those materials we established that rheasilvia ejecta reached part of the northern regions and have a diogenitic rich composition characteristic of the lower crust investigations of the antipodes of the two major impact basins rheasilvia and veneneia did not reveal any correlation between geographic location geological features and the surface composition the northern wall of mamilia crater which is one of the freshest craters above 22 n contains relatively pure eucritic rich diogenitic rich and dark hydrated materials which are representative of the rest of the northern regions and most of vesta with the exception of an olivine like component found in bellicia crater by ammannito et al ammannito e et al 2013a nature 504 7478 122 125 we determined that similar types of materials are found in various proportions over a large region including bellicia arruntia and pomponia craters and their origin does not seem to be related to rheasilvia ejecta these materials are hydrated which could indicate an exogenous origin and not as dark as expected for carbonaceous chondrites which likely compose the majority of dark hydrated materials on vesta spectral mixture analysis reveals that mixtures of pyroxenes hypersthene pigeonite and diopside could offer an alternative interpretation to olivine in this area

spectroscopic characterization of mineralogy and its diversity across vesta the mineralogy of vesta based on data obtained by the dawn spacecraft s visible and infrared spectrometer is consistent with howardite eucrite diogenite meteorites there are considerable regional and local variations across the asteroid spectrally distinct regions include the south polar rheasilvia basin which displays a higher diogenitic component and equatorial regions which show a higher eucritic component the lithologic distribution indicates a deeper diogenitic crust exposed after excavation by the impact that formed rheasilvia and an upper eucritic crust evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta this is broadly consistent with magma ocean models but spectral variability highlights local variations which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates overall vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle

posteucritic magmatism on vesta evidence from the petrology and thermal history of diogenites we report on the petrology and the thermal histories of 13 diogenites in order to constrain the formation processes of the vestan crust we classify diogenites into unequilibrated and equilibrated diogenites in a scheme similar to that for basaltic eucrites pyroxenes in unequilibrated diogenites are chemically zoned indicating that they crystallized rapidly from melts and escaped from global crustal metamorphism the presence of unequilibrated diogenites casts doubt on the fact that all the diogenites formed at depth in the parent body as commonly thought some diogenites probably crystallized in shallow intrusions or were extruded on the surface these facts strengthen the geochemical evidence that diogenites and eucrites are not directly cogenetic and suggest that at least some diogenites have intruded the early formed eucritic crust thus diogenites are certainly not the products of the crystallization of the magma ocean that triggered the differentiation of vesta but are more likely cumulates associated with a later stage of magmatism furthermore the intrusion of diogenites could have significantly thickened the early formed crust making it difficult to excavate deep seated olivine mantle by moderate impact events

origin and implications of troilite orthopyroxene intergrowths in the brecciated diogenite northwest africa 7183 abstract troilite orthopyroxene intergrowths are present as a common material in the brecciated diogenite northwest africa nwa 7183 in this study we report on the petrographic mineralogical and rare earth element abundances of the troilite orthopyroxene intergrowths to constrain their origin and assess their implications for the diverse petrogenesis of diogenites two groups of troilite orthopyroxene intergrowths with various grain sizes and mineral chemistry have been observed in nwa 7183 one group of intergrowths contains fine grained

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

photometric mapping of asteroid 4 vesta s southern hemisphere with hubble space telescope abstract we present the surface mapping of the southern hemisphere of asteroid 4 vesta obtained from hubble space telescope hst from 105 images of vesta through four filters in the wavelengths best to characterize the 1 m pyroxene band we constructed albedo and color ratio maps of vesta these new maps cover latitudes 50 to 20 the southern hemisphere of vesta displays more diverse albedo and color features than the northern hemisphere with about 15 new albedo and color features identified the overall longitudinal albedo and color variations in the southern hemisphere are comparable with that of the northern hemisphere with a range of about 20 and 10 respectively the eastern hemisphere is brighter and displays more diogenitic minerals than the western hemisphere correlations between 1 m band depth and band width as well as between 1 m band depth and albedo are present on a global scale attributed to pyroxene composition variations the lack of correlations between albedo and the spectral slope indicates the absence of globalized space weathering the lack of a global correlation between 1 m band depth and topography suggests that the surface composition of vesta is not completely controlled by a single impact the distribution of compositional variation on vesta suggests a possible large impact basin evidence of space weathering is found in regions including the bright rim of the south pole crater where the steepest gravitational slope on vesta is and a dark area near a gravitationally flat area we propose to divide the surface of vesta into six geological units different from the background according to their 1 m absorption features and spectral slopes including two eucrite rich units a low ca eucrite unit a diogenite rich unit a space weathered unit and a freshly exposed unit no evidence of olivine rich area is present in these data

high velocity collisions from the lunar cataclysm recorded in asteroidal meteorites lunar samples suggest that the inner solar system was bombarded by asteroids about 4 gyr ago radiometric ages of meteorites suggest an unusual number of high velocity asteroids at this time consistent with a dynamical origin of the bombardment in which the asteroids were pushed by outer planet migration onto highly eccentric orbits

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

vesta vestoids and the howardite eucrite diogenite group relationships and the origin of spectral differences spectra of asteroid 4 vesta and 21 small estimated diameters less than 10 km asteroids with vesta like spectral properties vestoids were measured at visible and near infrared wavelengths similar to0 44 to similar to1 65 mum all of the measured small asteroids except for 2579 spartacus have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from vesta none of the observed asteroids have spectra similar to diogenites we find no spectral distinction between the 15 objects tabulated as members of the vesta dynamical family and 6 of the 7 sampled non family members that reside just outside the semi major axis a eccentricity e and inclination i region of the family the spectral consistency and close orbital a e i match of these non family objects to vesta and the vesta family imply that the true bounds of the family extend beyond the subjective cut off for membership asteroid 2579 spartacus has a spectrum consistent with a mixture of eucritic material and olivine spartacus could contain olivine rich material from vesta s mantle or may be unrelated to vesta altogether laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes finer particle sizes lead to an increase in the slope which is usually referred to as reddening this range of spectral variation for the best known meteoritic analogs to the vestoids regardless of whether they are actually related to each other suggests that the extremely red spectral slopes for some vestoids can be explained by very fine grained eucritic material on their surfaces

dawn the vesta hed connection and the geologic context for eucrites diogenites and howardites the dawn mission has provided new evidence strengthening the identification of asteroid vesta as the parent body of the howardite eucrite and diogenite hed meteorites the evidence includes vesta s petrologic complexity detailed spectroscopic characteristics unique space weathering diagnostic geochemical abundances and neutron absorption characteristics chronology of surface units and impact history occurrence of exogenous carbonaceous chondritic materials in the regolith and dimensions of the core all of which are consistent with hed observations and constraints global mapping of the distributions of hed lithologies by dawn cameras and spectrometers provides the missing geologic context for these meteorites thereby allowing tests of petrogenetic models and increasing their scientific value

various types of olistostromes in a closing ocean basin tethyan himalaya cretaceous tibet abstract the cretaceous rocks of the central tethyan himalayas display different types of deep sea olistostromes and chaotic deposits which are accompanied by turbidites the deposits were incorporated into an accretionary prism and more or less deformed according to the composition and provenance of their clasts we distinguish four types of olistostromes 1 p type derived from the passive indian continental margin 2 po type derived from both the passive indian margin and ocean floor pelagic sediments and oceanic crust 3 poa type with clasts from the same sources as the po type but also containing material from the active margin along the lhasa block and 4 a and oa type mainly derived from the active margin accretionary prism and magmatic arc the occurrence of these different types of deep sea chaotic deposits in space and time is closely related to the evolution of the neo tethyan basin from a wide open ocean basin to a narrowing remnant and trench basin prior to collision whereas pure p type olistostromes formed when the basin was still wide predominating a type deposits characterize a late stage of basin evolution prior to collision mixed type olistostromes record an intermediate stage of basin evolution and require specific syn sedimentary tectonic activity

comparative analysis of sulfur isotope behavior in the basins with evaporites of chloride and sulfate types abstract the pripyat trough and the caspian depression are examples of basins with chloride and sulfate type evaporite formations respectively patterns of sulfur isotope distribution in these basins are essentially different sulfur isotopic composition of sulfate minerals in the caspian depression becomes lighter from the gypsum stage 34 s 13 9 0 3 toward the chloride stage 12 7 0 2 an opposite isotopic trend occurs in the pripyat trough 34s are respectively 22 8 1 0 and 25 3 0 5 pyrite formed in the chloride stage in the caspian depression is significantly depleted in 34s with respect to the initial sulfate of the basin 34 s sulfate py 22 5 2 1 34s sulfate py in the pripyat trough is lower 17 6 1 2 diagenetic anhydrites from the intersaliferous and subsaliferous formations are enriched in 34s relative to the sulfur isotope values measured from the anhydrites in the main salts this enrichment is higher in the pripyat trough average 34s 2 7 5 2 than in the caspian depression 0 9 2 1 the above differences are well explained in the terms of chemical systems that are limited or unlimited with respect to sulfur during the sulfate reduction process brines act as sulfur limited systems in chloride type basins and as sulfur unlimited systems in sulfate type ones

oxygen isotope composition of diagenetic calcite in organic rich rocks evidence for 18o depletion in marine anaerobic pore water upper cretaceous organic rich carbonates in israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite the sparry calcite has oxygen isotope values down to 9 5 pdb that are significantly lower than those of the coexisting skeletal calcite averaging 2 pdb low 18o values are very common in carbonates that are associated with organic matter these occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and or elevated temperature on the basis of petrographic data and local geologic evidence however none of the conventional explanations can be applied in this case we advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18o in pore water of normal salinity the proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate reducing zone being inherent to reducing marine environments this model can be applied to many organic rich rock associations

vestan lithologies mapped by the visual and infrared spectrometer on dawn we present global lithological maps of the vestan surface based on dawn mission s visible infrared vir spectrometer acquisitions with a spatial sampling of 200 m the maps confirm the results obtained with the data set acquired by vir with a spatial sampling of 700 m that the reflectance spectra of vesta s surface are dominated by pyroxene absorptions that can be interpreted within the context of the distribution of howardites eucrites and diogenites heds the maps also partially agree with the ground and hubble space telescope observations they confirm the background surface being an assemblage of howardite or polymict eucrite as well as the location of a diogenitic rich spot however there is no evidence of extended olivine rich regions in the equatorial latitudes diogenite is revealed on the rheasilvia basin floor indicating that material of the lower crust mantle was exposed vir also detected diogenites along the scarp of matronalia rupes and the rims of severina and a nearby unnamed crater and as ejecta of antonia crater the diogenite distribution is fully consistent with petrological constraints although the mapped distribution does not provide unambiguous constraints it favors the hypothesis of a magma ocean

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

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

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

vesta s mineralogical composition as revealed by the visible and infrared spectrometer on dawn the dawn spacecraft mission has provided extensive new and detailed data on vesta that confirm and strengthen the vesta howardite eucrite diogenite hed meteorite link and the concept that vesta is differentiated as derived from earlier telescopic observations here we present results derived by newly calibrated spectra of vesta the comparison between data from the dawn imaging spectrometer vir and the different class of hed meteorites shows that average spectrum of vesta resembles howardite spectra nevertheless the vesta spectra at high spatial resolution reveal variations in the distribution of hed like mineralogies on the asteroid the data have been used to derive hed distribution on vesta reported in ammannito et al 2013 and to compute the average vestan spectra of the different hed lithologies reported here the spectra indicate that not only are all the different hed lithologies present on vesta but also carbonaceous chondritic material which constitutes the most abundant inclusion type found in howardites is widespread however the hydration feature used to identify carbonaceous chondrite material varies significantly on vesta revealing different band shapes the characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered the relative proportion of heds on vesta s surface is computed and results show that most of the vestan surface is compatible with eucrite rich howardites and or cumulate or polymict eucrites a very small percentage of surface is covered by diogenite and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the hed suite the largest abundance of diogenitic material is found in the rheasilvia region a deep basin where it clearly occurs below a basaltic upper crust however diogenite is also found elsewhere although the depth to diogenite is consistent with one magma ocean model its lateral extent is not well constrained

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

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

diogenites as polymict breccias composed of orthopyroxenite and harzburgite abstract a few relatively unbrecciated olivine rich diogenites consist of an equilibrium assemblage of olivine and magnesian orthopyroxene harzburgite more common diogenites with smaller amounts of olivine are breccias containing two distinct orthopyroxenes one magnesian and one ferroan these diogenites are mixtures of a harzburgite lithology that is more magnesian with the normal orthopyroxenite lithology that is ferroan and may contain small amounts of plagioclase both lithologies likely formed by fractional crystallization in multiple plutons emplaced within the crust of asteroid 4 vesta minor element trends in orthopyroxenes indicate that these plutons exhibited a range of compositions we propose a revised taxonomy for the hed howardites eucrites and diogenites suite where all ultramafic samples are referred to as diogenites within this group the prefixes dunitic harzburgitic and orthopyroxenitic are used to distinguish diogenites consisting of more than or equal to 90 olivine olivine orthopyroxene and more than or equal to 90 orthopyroxene respectively the prefix polymict is used to describe brecciated mixtures of any of these rock types the recognition that olivine is a significant phase in some diogenites is consistent with spectral interpretations of olivine in a deeply excavated crater on vesta and has important implications for the bulk composition and petrogenesis of that body

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

carbon and oxygen isotopic composition of carbonates from saliferous deposits of the pripyat trough belarus abstract 18o and 13c in accessory calcite and dolomite from salt rock and in intrasalt carbonate beds of the upper frasnian and upper famennian evaporite formations of the pripyat trough vary over a wide range within all the intrasalt carbonate interbeds four distinct groups of rocks have been recognised on the basis of their isotopic composition the ranges of variation of 13c pdb and 18o smow within these groups are respectively a 0 7 to 0 8 and 35 4 to 36 4 b 4 5 to 0 9 and 30 0 to 32 2 c 7 0 to 2 8 and 19 8 to 25 5 d 17 5 to 9 7 and 20 9 to 26 4 the isotopic composition of accessory carbonates is more uniform the main body of values falls within the range 11 to 3 for 13c and 18 to 25 for 18o the carbonate matter with the observed combinations of 13c and 18o could have been formed during sedimentation and diagenesis in sabkhas on subaetially exposed islands on evaporite depression slopes washed by sea water and freshwater and in stagnant zones with hot brines the carbon isotopic composition of intrasalt carbonate rocks is on the average lighter than that of accessory carbonates from the salts this shows that the organic matter was most readily accumulated in evaporite basins during non salt sedimentation

composition of the rheasilvia basin a window into vesta s interior 1 the estimated excavation depth of the huge rheasilvia impact basin is nearly twice the likely thickness of the vestan basaltic crust so the mantle should be exposed spectral mapping by the dawn spacecraft reveals orthopyroxene rich materials similar to diogenite meteorites in the deepest parts of the basin and within its walls significant amounts of olivine are predicted for the mantles of bulk chondritic bodies like vesta and its occurrence is demonstrated by some diogenites that are harzburgite and dunite however olivine has so far escaped detection by dawn s instruments spectral detection of olivine in the presence of orthopyroxene is difficult in samples with 25 olivine and olivine in rheasilvia might have been diluted during impact mixing or covered by the collapse of basin walls the distribution of diogenite inferred from its exposures in and around rheasilvia provides a geologic context for the formation of these meteorites but does not clearly distinguish between a magmatic cumulate versus partial melting restite origin for diogenites the former is favored by geochemical arguments and crystallization in either a magma ocean or multiple plutons emplaced near the crust mantle boundary is permitted by dawn observations

first disk resolved spectroscopy of 4 vesta abstract vesta the second largest main belt asteroid will be the first to be explored in 2011 by nasa s dawn mission it is a dry likely differentiated body with spectrum suggesting that is has been resurfaced by basaltic lava flows not too different from the lunar maria here we present the first disk resolved spectroscopic observations of an asteroid from the ground we observed 4 vesta with the eso vlt adaptive optics equipped integral field near infrared spectrograph sinfoni as part of its science verification campaign the highest spatial resolution of 90 km on vesta s surface was obtained during excellent seeing conditions 0 5 in october 2004 we observe spectral variations across vesta surface that can be interpreted as variations of either the pyroxene composition or the effect of surface aging we compare vesta s 2 m absorption band to that of howardite eucrite diogenite hed meteorites that are thought to originate from vesta and establish particular links between specific regions and hed subclasses the overall composition is found to be mostly compatible with howardite meteorites although a small area around 180 e longitude could be attributed to a diogenite rich spot we finally focus our spectral analysis on the characteristics of vesta s bright and dark regions as seen from hubble space telescope s visible and keck ii s near infrared images

the structure of the asteroid 4 vesta as revealed by models of planet scale collisions three dimensional simulations of the global evolution of asteroid 4 vesta under two overlapping planet scale collisions closely reproduce its observed shape but expected large areas of olivine rich rocks and pure diogenites are not observed on the surface possibly implying that the outer 100 km is composed mainly of a basaltic crust eucrites with ultramafic intrusions diogenites nasa s dawn mission to the asteroid 4 vesta revealed some unexpected surface features including a huge crater named veneneia underlying the even larger crater rheasilvia that was formed about a billion years ago the juxtaposition of these two impact basins provides an opportunity to develop an accurate model of vesta s topography martin jutzi et al report three dimensional simulations of vesta s global evolution through two successive planet scale collisions their model closely reproduces vesta s observed shape and provides a firm basis for the interpretation of the surface mineralogy and geology of vesta and by extension other small solar system bodies asteroid 4 vesta seems to be a major intact protoplanet with a surface composition similar to that of the hed howardite eucrite diogenite meteorites1 2 3 4 the southern hemisphere is dominated by a giant impact scar5 but previous impact models6 7 8 have failed to reproduce the observed topography the recent discovery that vesta s southern hemisphere is dominated by two overlapping basins9 provides an opportunity to model vesta s topography more accurately here we report three dimensional simulations of vesta s global evolution under two overlapping planet scale collisions we closely reproduce its observed shape and provide maps of impact excavation and ejecta deposition spiral patterns observed in the younger basin rheasilvia9 about one billion years old10 are attributed to coriolis forces during crater collapse surface materials exposed in the north come from a depth of about 20 kilometres according to our models whereas materials exposed inside the southern double excavation come from depths of about 60 100 kilometres if vesta began as a layered completely differentiated protoplanet then our model predicts large areas of pure diogenites and olivine rich rocks these are not seen11 12 13 possibly implying that the outer 100 kilometres or so of vesta is composed mainly of a basaltic crust eucrites with ultramafic intrusions diogenites