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

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

mn cr dating of fe and ca rich olivine from quenched and plutonic angrite meteorites using secondary ion mass spectrometry this research was supported by grants dp034277 and dp0666751 from the australian research council to tri and ya and an australian national university phd research scholarship

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

experimental partial melting of the st severin ll and lost city h chondrites we have performed melting experiments between 1170 1325 c and at an oxygen fugacity of iw 1 on the ordinary chondrites lost city h and st severin ll in order to investigate the origin of diogenites and their possible relationship to eucrites low ca pyroxene disappears from the lost city residuum just above 1220 c at a mg near 66 accordingly lost city does not have a sufficiently large stability field for orthopyroxene to be a likely parent composition for melts which could crystallize diogenites in contrast orthopyroxene in st severin persists up to about 1325 c at which point it has a mg similar to that of typical diogenites 75 this is only marginally compatible with diogenite origins as the most magnesian pyroxenes from diogenites mg 82 and howardites mg 85 are more mgo rich than any pyroxene formed from a st severin melt accordingly if diogenites formed from a source having the bulk composition of an ordinary chondrite than either the fo2 had to be lower than that inferred for eucrite formation or more likely the parent body had a lower fesi ratio than that of an ll chondrite also low temperature melts of st severin are depleted in elements compatible with pyroxene and so while broadly eucritic do not closely match the compositions of eucrites that are thought to be primary partial melts hence it doesn t appear possible to produce both diogenites and eucrites from the same source region composition if eucrites are primary partial melts reconnaiss mce experiments at higher oxygen fugacity iw 2 produce broadly angritic melts for lost city as was observed for murchison and allende in contrast our na2o poor st severin charge produced a broadly eucritic melt at this higher fo2 this difference in melting behavior is probably because ll chondrites have a much lower bulk fesi ratio than the h cm or cv chondrites

mineralogy and petrology of the angrite northwest africa 1296 we report on a new angrite northwest africa nwa 1296 a fine grained rock with a magmatic texture of rapid cooling dendritic olivine fo50 crystallized first in association with anorthite microcrysts an98100 forming composite chains separated from one another by intergrown al fe diopside hedenbergite pyroxenes in addition some olivines with lower mg and increased cao up to 12 are found between the chains as equant microphenocrysts pyroxenes and olivines are both normally zoned from mg 0 52 to less than 0 01 in the rims ca rich olivines are surrounded by intergrown with or replaced by subcalcic kirschsteinite they appear after plagioclase crystallization stopped at the end of the crystallization sequence minor phases are pyrrhotite fapatite and titanomagnetite pyroxene is the last silicate phase to grow interstitial to idiomorphic olivine kirschsteinite numerous small vesicles and some channels are filled with microcristalline carbonate the mode vol is about 28 olivine 3 kirschsteinite 32 anorthite 34 pyroxene and 3 of the minor phases close to that reported previously for d orbigny and sahara sah 99555 the bulk chemical composition of nwa 1296 is similar to d orbigny and sah 99555 nwa 1296 differs by its texture and mineralogy which are interpreted as resulting from rapid crystallization an evidence of impact melting angrites cannot be produced by partial melting of a cv source because segregation of a planetary core is necessary to explain the low feo mgo ratio of magnesian olivines neither the odd ca al ratio nor the very low sio2 content can be explained by conventional partial melting scenarios we suggest that carbonate is the key to angrite genesis this is supported by the striking similarities with terrestrial melilitites low sio2 superchondritic ca al ratio presence of carbonate the lack of alkalies could be the result of either loss after impact melting or absence of alkalies in the source

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

calcareous nannoplankton response to late albian oceanic anoxic event 1d in the western north atlantic well preserved nannofossil and stable isotope records from the mid cretaceous of ocean drilling project leg 171b western north atlantic indicate cyclical productivity based variations in surface water characteristics suggesting orbitally paced changes in upwelling intensity and the strength of deep mixing associated with oceanic anoxic event oae 1d paleontologic and isotopic evidence suggest that collapse of upper water column stratification associated with oae1d was preceded by approximately 1 m y of progressively decreasing water column stability and increasing surface water fertility thirteen species went extinct during a short ca 200 k y interval associated with oae1d nine of these have morphological characters suggesting adaptation to specific depths in the photic zone simultaneous extinction of these depth zoned species suggests that stratification collapse disrupted the habitat space for these specialized forms resulting in extinction a cyclostratigraphic model provides age estimates of several important nannofossil datums including the first appearances of eiffellithus turriseiffelii 100 95 ma and corollithion kennedyi 99 55 ma

carbonate compositions in cm and ci chondrites and implications for aqueous alteration abstract carbonate minerals in fourteen cm chondrites and two ci chondrites have been analyzed by electron microprobe to provide a better understanding of the aqueous processes that affected carbonaceous chondrite parent bodies calcites in cm chondrites and dolomites and magnesites in ci chondrites display the compositions expected of stable phases formed at low temperatures dolomites in cm chondrites identified here for the first time in five members of the group have small amounts of excess ca which may reflect metastable growth the distribution of fe between dolomite and coexisting serpentine differs in the two chondrite groups if the distributions reflect an approach to chemical equilibrium then the difference implies higher alteration temperatures for the ci group than the cm group in agreement with the results of previously published oxygen isotope thermometry and mineral solubility modeling of the alteration process dolomite fe contents are relatively uniform in the two chondrite groups dolomite mn contents by contrast vary widely the variations may reflect transport controlled coprecipitation of mn resulting from a heterogeneous distribution of the element in the anhydrous precursor material if this interpretation is correct then the altering fluids were essentially immobile while hydration reactions proceeded on the meteorite parent bodies the near closed system character of the alteration process long known from bulk chemical analyses of the meteorites is a direct consequence of the limited mobility of dissolved species

a petrologic chemical and isotopic study of monument draw and comparison with other acapulcoites evidence for formation by incipient partial melting abstract we have conducted petrologic chemical and isotopic studies of acapulcoites acapulco monument draw yamato 74063 alh a77081 alh a81261 alh a81315 alh 78230 alh a81187 and alh 84190 in an attempt to constrain their genesis acapulcoites have distinctly different oxygen isotopic compositions than silicate inclusions in iab and iiicd irons winonaites and ureilites and thus formed on a different parent body oxygen isotopic compositions which are slightly heterogeneous within the group overlap with lodranites indicating a likely origin on a common parent body these groups can be distinguished on the basis of mafic silicate grain size all acapulcoites have mafic silicate compositions intermediate between e and h chondrites roughly chondritic mineralogies achondritic equigranular textures micrometer to centimeter sized veins of fe ni fes which cross cut silicate phases rapid metallographic cooling rates at 600 400 c 103 105 c myr and trapped noble gas abundances comparable to type 3 4 ordinary chondrites they exhibit variable mafic silicate zoning abundance of fe ni fes veins ree abundances and patterns and possibly cosmic ray exposure ages 5 7 ma momument draw and yamato 74063 retain rare relict chondrules phosphates are associated with fe ni fes veins or form separate veins in monument draw and acapulco heating and cooling of acapulcoites occurred very early in the history of the solar system as evidenced by the 39ar 40ar ages of 4 51 ga these ages appear distinctly younger than the likely formation time for acapulco of 4 557 ga but are older than analogous 39ar 40ar ages for most chondrites acapulcoites formed from a precursor chondrite which differs from known chondrites in mineral and oxygen isotopic compositions heating to 950 1000 c resulted in melting at the fe ni fes cotectic but silicates did not melt silicate textures resulted from extensive solid state recrystallization heating was by noncollisional sources e g 26al electromagnetic induction despite uncertainties owing to a lack of data acapulcoites may have experienced a three stage thermal history of slow cooling at high temperature rapid cooling at intermediate temperatures and slow cooling at low temperatures possibly resulting from breakup and gravitational reassembly of the parent body the complex thermal history is also reflected in disequilibrium ree abundances one or at most two impact events 7 ma and possibly 5 ma ago are consistent with the cosmic ray exposure ages of all four acapulcoites for which cosmogenic noble gas data exist

oxygen isotope variation in stony iron meteorites asteroidal material delivered to earth as meteorites preserves a record of the earliest stages of planetary formation high precision oxygen isotope analyses for the two major groups of stony iron meteorites main group pallasites and mesosiderites demonstrate that each group is from a distinct asteroidal source mesosiderites are isotopically identical to the howardite eucrite diogenite clan and like them are probably derived from the asteroid 4 vesta main group pallasites represent intermixed core mantle material from a single disrupted asteroid and have no known equivalents among the basaltic meteorites the stony iron meteorites demonstrate that intense asteroidal deformation accompanied planetary accretion in the early solar system

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

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

metamorphic angrite northwest africa 3164 5167 compared to magmatic angrites abstract northwest africa nwa 3164 and 5167 are two angrites with a granulitic texture unlike that of other angrites with a variable up to millimeter grain size besides mineralogical and chemical similarities to other angrites nwa 3164 and 5167 exhibit unique characteristics ca rich olivine dominates in nwa 3164 49 vol fo57 nwa 5167 40 vol fo59 fassaitic clinopyroxene is the second major phase in nwa 3164 29 vol in nwa 5167 36 vol with a significant tschermak component in addition two al rich phases are present plagioclase an99 and hercynitic spinel 6 and 7 vol respectively for nwa 3164 17 and 4 vol respectively for nwa 5167 heavily weathered iron sulfide and kamacite 9 wt in nwa 3164 4 wt in nwa 5167 are the remaining minor phases a unique feature among angrites all mineral phases are homogeneous like other angrites nwa 3164 and 5167 exhibit a superchondritic ca al ratio with negligible amounts of alkalis and very low silica content the presence of metal results from the incorporation of exogenous iron following impact subsequent annealing resulted in the observed granulitic texture major element composition indicates that both nwa 3164 and 5167 are derived from a picritic angrite precursor after incorporation of metal and annealing after correction for iron and fo90 olivine incorporation bulk rock ree abundances of both nwa 3164 and nwa 5167 appear lower than those of quenched angrites showing the lowest absolute abundances among angrites laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of clinopyroxene olivine and anorthite indicate that difference of rare earth element ree abundances between nwa 3164 and nwa 5167 can be explained by adding traces of phosphate to nwa 3164 nwa 3164 5167 trace elements abundances are similar showing depletion in volatile elements and enrichment in refractory lithophile elements such as ca ti and al the most incompatible elements are depleted as well unlike other angrites this indicates that the source of these younger angrites was more depleted in incompatible elements when compared to the older magmatic angrites the low hf w is understood as the result of exogenous iron incorporation and therefore the hf w and w isotopic heterogeneity of the angrite parent body apb mantle is secondary comparison with other angrites suggests that iron incorporation may be necessary to explain their low hf w and w isotopic compositions

fracture mechanical behavior of red sandstone containing a single fissure and two parallel fissures after exposure to different high temperature treatments it is well known to us that the stability and safety of deep underground mining excavations and nuclear waste depositories rely on accurate knowledge of the physical and mechanical properties of representative rocks under the action of high temperature zhang et al in int j plast 34 93 113 2012

phase equilibrium constraints on angrite petrogenesis parameterizations of liquidus boundaries and solid solution in the cmas fe system shi 1992 have been employed to depict the liquidus equilibria relevant to the petrogenesis of angrites angrites are basaltic achondrites characterized by highly aluminous augite fassaite intermediate mg fe olivine and late stage cafe olivine kirschsteinite two important features of the equilibria on the olivine liquidus surface relevant to angrite petrogenesis are 1 the presence of a thermal divide on the ol aug plag liq boundary curve which separates the compositions of source materials that produce low silica angritic melts that crystallize highly aluminous augite from those that produce higher silica melts with tholeiitic to eucritic crystallization patterns and 2 the change in the pseudo invariant point on the low silica side of the thermal divide from a plagioclase peritectic involving spinel ol aug plag sp liq at high to intermediate mg mg mg fe to two pseudo eutectics involving kirschsteinite ol aug plag kir liq and ol kir plag sp liq at low mg the fassaitic aluminous augite pyroxene composition in angra dos reis ador the presence of minor green spinel and the absence of primary kirschsteinite prinz et al 1977 indicate that crystallization of the ador parental liquid was governed by the intermediate mg set of equilibria such that following crystallization of ol aug plag the plagioclase reacted completely at the plagioclase peritectic with the interstitial liquid which subsequently crystallized beyond the plagioclase peritectic onto the ol aug sp liquidus boundary curve the ador bulk composition is consistent with trapping 10 of the parental liquid in a cumulate with cotectic proportions of fassaite and olivine lewis cliff lew 86010 crystallized from a liquid with mg similar to that of ador but on the ol plag cotectic closer to the thermal divide such that the first pyroxene to crystallize had much lower al content than that of ador in the late stages of crystallization the 86010 residual liquid and that of lew87051 encountered the low mg set of equilibria involving kirschsteinite these relationships require either a higher degree of melting for the 86010 parent magma or source region different than ador s these relationships are also consistent with compositionally dependent ree partition coefficients between fassaite and the ador liquid being as much as 1 5 2 times higher than those for the 86010 liquid at the onset of pyroxene crystallization the combination of a trapped liquid component higher partition coefficients and smaller degrees of melting help to explain the observation that ador an apparent cumulate has ree concentrations twice as high as those in 86010 mittlefehdlt and lindstrom 1990 an apparent chilled liquid the absence of a strong negative eu anomaly in the ador parent liquid however requires relatively high degrees of partial melting to eliminate plagioclase in the source region resorption of plagioclase at the peritectic eliminates the eu anomaly that develops during crystallization so ultimately different source regions are required progressive iron loss from devolatilized primitive chondrites allende murchison produces source regions capable of producing a wide range of melt compositions with angritic to eucritic crystallization behavior the compositions of carbonaceous and ordinary chondrite provide a similar range of potential source region compositions however primitive chondrite fe source regions that produce angrite like melts have mg that is too low whereas chondrite fe sources that have mg sufficiently high to yield the mg in angrite minerals have too much silica or orthopyroxene component to yield angrite like liquids no single group of meteorites fe simultaneously satisfies the constraints of mg and silica component however mixtures of fe depleted chondrite plus a low silica component similar to ca al rich inclusions cais can satisfy the constraints the absence in angrites of 48ca and 50ti anomalies typical of cais lugmair and galer 1992 suggests that the low silica component was not simply an enrichment of cais but was the result of direct accretion of high temperature condensate grossman 1972 into sizable thermally shielded planetesimals thus angrites cryptically record mixing of planetesimal sized heterogeneities in the early solar system

a partial melting study of an ordinary h chondrite composition with application to the unique achondrite graves nunataks 06128 and 06129 melting experiments of a synthesized alkali bearing h chondrite composition were conducted at ambient pressure with three distinct oxygen fugacity conditions iw 1 iw and iw 2 oxygen fugacity conditions significantly influence the compositions of partial melts partial melts at iw 1 are distinctly enriched in sio2 relative to those of iw and iw 2 melts the silica enriched reduced iw 1 melts are characterized by high alkali contents and have silica oversaturated compositions in contrast the silica depleted oxidized iw melts which are also enriched in alkali contents have distinctly silica undersaturated compositions these experimental results suggest that alkali rich felsic asteroidal crusts as represented by paired achondrites graves nunataks 06128 and 06129 should originate from a low degree relatively reduced partial melt from a parent body having near chondritic compositions based on recent chronological constraints and numerical considerations as well as our experimental results we propose that such felsic magmatism should have occurred in a parent body that is smaller in size and commenced accreting later than those highly differentiated asteroids having basaltic crusts and metallic cores

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

the non igneous genesis of angrites support from trace element distribution between phases in d orbigny d orbigny is an exceptional angrite chemically it resembles other angrites such as asuka 881371 sahara 99555 lewis cliff lew 87051 and lew 86010 but its structure and texture are peculiar it has a compact and porous lithology abundant glasses augite bearing druses and chemical and mineralogical properties that are highly unusual for igneous rocks our previous studies led us to a new view on angrites they can possibly be considered as cais that grew to larger sizes than the ones we know from carbonaceous chondrites thus angrites may bear a record of rare and special conditions in some part of the early solar nebula here we report trace element contents of d orbigny phases trace element data were obtained from both the porous and the compact part of this meteorite we have confronted our results with the popular igneous genetic model according to this model if all phases of d orbigny crystallized from the same system as an igneous origin implies a record of this genesis should be expressed in the distribution of trace elements among early and late phases our results show that the trace element distribution of the two contemporaneous phases olivine and plagioclase which form the backbone of the rock seem to require liquids of different composition abundances of highly incompatible elements in all olivines including the megacrysts indicate disequilibrium with the bulk rock and suggest liquids very rich in these elements 10 000 x ci which is much richer than any fractional crystallization could possibly produce in addition trace element contents of late phases are incompatible with formation from the bulk systems residual melt these results add additional severe constraints to the many conflicts that existed previously between an igneous model for the origin of angrites and the mineralogical and chemical observations this new trace element content data reported here corroborate our previous results based on the shape structure mineralogy chemical and isotopic data of the whole meteorite as well as on a petrographic and chemical composition study of all types of glasses and give strength to a new genetic model that postulates that d orbigny and possibly all angrites could have formed in the solar nebula under changing redox conditions more akin to chondritic constituents e g cais than to planetary differentiated rock

petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites

geochemistry and genesis of the angrites the angrites angra dos reis lew86010 and lew87051 are petrologically and compositionally similar achondrites all angrites have high feomno ratios of 80 94 and very low ci normalized na sm ratios of 0 001 0 003 high abundances of oxidized fe and low abundances of moderately volatile na most likely resulted from parent body processes such as magmatic outgassing rather than nebular processes all angrites have fractionated ca al ratios with angra dos reis exhibiting the most extreme ratio 3 1 ci this ca al fractionation may be due to small amounts of residual spinel in the source region after removal of the angrite melts or to crystallization of spinel from precursor melts for lew86010 and lew87051 the fractionated ca al ratios are not caused by the presence of significant cumulus material for angra dos reis cumulus material may be the cause of the high ca al ratio refractory element ca eu al sc la ce sm tb yb lu ti hf th and ta abundances of lew86010 and lew87051 show similar patterns while angra dos reis has both greater enrichments in these elements and more fractionated patterns compositional and petrologic constraints indicate that lew86010 and lew87051 are related via olivine control the refractory element abundances and mg of lew86010 can be approximated by removal of olivine from lew87051 suggesting that lew86010 may be a residual melt from a lew87051 like precursor alternatively lew87051 may have formed via olivine accumulation from a lew86010 like precursor the origin of the unusual refractory element pattern in angra dos reis remains obscure the differences between the lew86010 lew87051 duo and angra dos reis suggest that either the angrite parent body was heterogeneous or that angra dos reis was formed on a separate parent body based on feomno ratios and normative mineralogies the angrite parent body ies may be similar in bulk composition to one of the carbonaceous chondrite groups particularly ci cm co

petrogenesis of d orbigny like angrite meteorites and the role of spinel in the angrite source this research was supported by an australian national university phd scholarship to smck who is currently a postdoctoral fellow of the research foundation flanders

petrology and mineralogy of the angrite northwest africa 1670 northwest africa nwa 1670 contains olivines of up to 5 mm in size representing about 30 of the studied section with subordinate clinopyroxene and chrome spinel microphenocrysts 0 2 0 5 mm they represent a xenocrystic association phenocrysts are surrounded by a groundmass predominantly comprising bundles of plagioclase and clinopyroxene typically 20 x 200 m crystals olivine and kirschsteinite are present in the groundmass in lesser amounts the olivine xenocrysts fo90 are significantly fractured and show mosaicism for their major part the remaining showing faint undulatory extinction they are surrounded with a rim of 100200 m zoned down to fo80 and overgrown with serrated olivine fo80 to fo60 about 100 m olivine in the groundmass is zoned from mg 0 55 to 0 15 its cao content ranges 2 0 to 8 4 subcalcic kirschsteinite is zoned from mg 0 13 to 0 03 cao increasing from 15 8 to 21 3 pyroxenes xenocrysts mg 0 77 are superseded in the groundmass by less magnesian pyroxenes mg 0 61 to 0 17 with an average feo mno of 98 their compositions range from en30fs22wo27al ts28ti ts2 to en2fs37wo22al ts40ti ts1 anorthite microcrysts an99 100 are restricted to the groundmass accessories are pyrrhotite kamacite ca phosphate titanomagnetite hercynite and ca carbonate the bulk chemical composition confirms that nwa 1670 corresponds to a normal angrite melt that incorporated olivine high mg olivine xenocrysts and the associated mineralogy are typical of angrites we suggest that it is an impact melt with relict phenocrysts the strong silica undersaturation the presence of fo90 olivine xenocrysts and carbonate support their derivation as melilite like melts in the presence of carbonate

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