partition coefficients for calcic plagioclase implications for archean anorthosites by the use of a multiple aliquot technique combined with statistical calculations to overcome effects of alteration and contamination we have determined partition coefficients d s for rare earth elements rees between natural high ca plagioclase megacrysts and their basaltic matrices some of the basalts that we investigated are shown experimentally to crystallize only high ca plagioclase over approximately a 20 30 c temperature interval below the liquidus the ree d s agree well with experimentally determined values and predict equilibrium melts for archean anorthosites that agree well with coeval basaltic flows and dikes furthermore the d s appear to be valid for both tholeiitic and alkali basalts over a range of mg numbers 34 58 and ree concentrations la from 3 50 ppm similarly calculated d s for co sc cr rb sr cs ba hf ta and th also predict equilibrium melts for anorthosites that agree reasonably well with coeval basaltic flows and dikes the apparent values for co sc and ta seem good to better than 50 whereas the standard deviations for rb and th are equal to their means making the d s of questionable value the others are useful probably to within a factor of 2 experimental studies of the d for total fe as feot indicate a value of about 04 at an oxygen fugacity slightly below that of the qfm buffer a by product of the feot experiments was the experimental d s for mgo tio2 and k2o which could be compared with the d s from natural assemblages from the d s that were determined we suggest that plagioclase megacrysts in the bad vermilion lake anorthosite were in equilibrium with melts having the composition of tholeiitic basalts at an oxygen fugacity slightly below the qfm buffer the predicted melts have an feot content of about 13 k2o of about 15 tio2 of about 1 3 a chondrite normalized ree pattern that is nearly flat at 10 to 20 chondrites with a slight depletion of lrees other incompatible trace elements at 10 to 20 chondrites and cr and co at 0 01 to 0 1 chondrites this range of compositions is essentially identical to the tholeiitic flows and dikes in archean greenstone belts we therefore suggest that the moderately fe rich tholeiites that are hosts to plagioclase megacrysts in greenstone belts form the parental melts for megacrysts which make up the bad vermilion lake anorthositic complex and probably other similar archean anorthositic complexes

la reunion island dunites as analogs of the martian chassignites tracking trapped melts with incompatible trace elements abstract fractional crystallization of basalts produces a variety of ultramafic cumulates poor in incompatible elements in order to discuss the effect of trapped liquids on the concentrations of incompatible elements in these cumulates we studied a series of dunites and pyroxenites from the piton de la fournaise la reunion island indian ocean these rocks have a high variability in the abundance of these elements which is only partially explained by their proportions of olivines and pyroxenes mass balance calculations indicate that 0 25 to 1 wt of trapped melts are required to account for the budget of the highly incompatible element abundances such as u rb nb or light rare earth elements ree using our results we revisited the ree geochemistry of chassignites a grouplet of martian meteorites chassignites are mineralogically texturally and chemically very similar to the dunites from la reunion island which can be seen as very close terrestrial analogs the variations of ree abundances and ratios in chassigny one of the three known chassignites can be explained by inhomogeneous distribution of trapped melts in this meteorite at the scale of the size of the fragments typically

an ion microprobe study of the intra crystalline behavior of ree and selected trace elements in pyroxene from mare basalts with different cooling and crystallization histories abstract to study the effects of crystallization sequence and rate on trace element zoning characteristics of pyroxenes we used combined electron microprobe ion microprobe techniques on four nearly isochemical apollo 12 and 15 pigeonite basalts with different cooling rates and crystallization histories major and minor element zoning characteristics are nearly identical to those reported in the literature all the pyroxenes have similar chondrite normalized ree patterns negative eu anomalies positive slopes as defined by yb ce and slopes of ree patterns from ce to sm much steeper than from gd to yb the characteristics of the ree patterns of pigeonite and augite can be rationalized in terms of ree size and charge and m2 site characteristics numerous ree and other trace element v sr zr na sc cr zoning characteristics can be correlated with quadrilateral composition the total ree abundances increase with increasing ca in the m2 site and indicate that the distribution coefficients of ree between pyroxene and melt vary systematically with the wo component the total ree abundances also increase with decreasing mg mg fe and increasing al prior to plagioclase crystallization the eu anomaly in pyroxene is not substantially affected by plagioclase crystallization because eu3 is effectively partitioned into pyroxene relative to eu2 eu 2 eu 3 03 in pigeonite and the plagioclase effect is diluted by the low eu distribution coefficient for the more abundant pyroxene the cr and v components behave similarly in that cr and v decrease with increasing ti al in basalt sample 15058 and decrease with crystallization and at similar ti al na and sc increase in abundance from pigeonite to augite with similar ti al in both 15058 and 15499 in 15058 na decreases coherently with increasing ti al whereas sc shows a limited variability sr and zr in 15058 are somewhat more enriched in the augite with low ti al relative to pigeonite the augite does not become enriched in zr or sr until the pyroxene has high ti al and low mg mg fe in 15499 sr and zr show slight enrichment in augite relative to pigeonite these trace element zoning characteristics in pyroxene and the partitioning of trace elements between pyroxene and the melt are intimately related to the interplay among the efficiency of the crystallization process the kinetics at the crystal melt interface the kinetics of plagioclase nucleation and the characteristics of the crystal chemical substitutions within both the pyroxene and the associated crystallizing phases i e plagioclase

the igneous crystallization history of an ancient martian meteorite from rare earth element microdistributions rare earth element ree and other selected trace and minor element concentrations were meas ured in individual grains of orthopyroxene feldspathic glass of plagioclase composition and merrillite of the alh 84001 martian meteorite unlike in other martian meteorites phosphate is not the main ree car rier in alh 84001 the ree pattern of alh 84001 bulk rock is dependent on the modal abundances of three ree bearing phases namely orthopyroxene which contains most of the heavy rare earth elements hrees feldspathic glass which dominates the eu abundances and merrillite which contains the majority of the light rare earth elements lrees variations in the ree abundances previously observed in different splits of alh 84001 can easily be explained in terms of small variations in the modal abundances of these three minerals without the need to invoke extensive redistribution of lrees at least some orthopyroxenes i e those away from contacts with feldspathic glass in alh 84001 appear to have preserved their original ree zonation from igneous fractionation an estimate of the alh 84001 parent magma composition from that of the unaltered orthopyroxene core i e zoned orthopyroxene with the lowest ree abundances indicates that it is lree depleted this implies that the martian mantle was already partly depleted within 100 ma of solar system formation which is consistent with rapid accretion and differentiation of mars although equilibration and exchange of rees between phases in particular transport of lrees into the interstitial phases feldspathic glass and merrillite cannot be ruled out our data suggest that the lree enrichment in melts in equilibrium with these interstitial phases is most likely the result of late stage infil tration of the cumulate pile by a lree enriched melt

the perils of partition difficulties in retrieving magma compositions from chemically equilibrated basaltic meteorites abstract the chemical compositions of magmas can be derived from the compositions of their equilibrium minerals through mineral magma partition coefficients this method cannot be applied safely to basaltic rocks either solidified lavas or cumulates which have chemically equilibrated or partially equilibrated at subsolidus temperatures i e in the absence of magma applying mineral melt partition coefficients to mineral compositions from such rocks will typically yield magma compositions that are strongly fractionated and unreasonably enriched in incompatible elements e g rees in the absence of magma incompatible elements must go somewhere they are forced into minerals e g pyroxenes plagioclase at abundance levels far beyond those established during normal mineral magma equilibria further using mineral magma partition coefficients with such rocks may suggest that different minerals equilibrated with different magmas and the fractionation sequence of those melts i e enrichment in incompatible elements may not be consistent with independent constraints on the order of crystallization subsolidus equilibration is a reasonable cause for incompatibleelement enriched minerals in some eucrites diogenites and martian meteorites and offers a simple alternative to petrogenetic schemes involving highly fractionated magmas or magma infiltration metasomatism

rb sr and sm nd isotopic and ree studies of igneous components in the bulk matrix domain of martian breccia northwest africa 7034 the bulk matrix domain of the martian breccia nwa 7034 was examined petrographically and isotopically to better understand the provenance and age of the source material that make up the breccia both 147sm 143nd and 146sm 142nd age results for mineral separates from the bulk matrix portion of breccia nwa 7034 suggest that various lithological components in the breccia probably formed contemporaneously 4 44 ga ago this old age is in excellent agreement with the upper intersection ages 4 35 4 45 ga for u pb discordia and also concordia defined by zircon and baddeleyite grains in matrix and igneous textured clasts consequently we confirm an ancient age for the igneous components that make up the nwa 7034 breccia substantial disturbance in the rb sr system was detected and no age significance could be gleaned from our rb sr data the disturbance to the rb sr system may be due to a thermal event recorded by bulk rock k ar ages of 1 56 ga and u pb ages of phosphates at about 1 35 1 5 ga which suggest partial resetting from an unknown thermal event s possibly accompanying breccia formation the nwa 7034 bulk rock is lree enriched and similar to kreep rich lunar rocks which indicates that the earliest martian crust was geochemically enriched this enrichment supports the idea that the crust is one of the enriched geochemical reservoirs on mars that have been detected in studies of other martian meteorites

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

petrography and bulk chemistry of martian orthopyroxenite alh84001 implications for the origin of secondary carbonates abstract new petrologic and bulk geochemical data for the snc related martian meteorite alh84001 suggest a relatively simple igneous history overprinted by complex shock and hydrothermal processes alh84001 is an igneous orthopyroxene cumulate containing penetrative shock deformation textures and a few percent secondary extraterrestrial carbonates rare earth element ree patterns for several splits of the meteorite reveal substantial heterogeneity in ree abundances and significant fractionation of the rees between crushed and uncrushed domains within the meteorite complex zoning in carbonates indicates nonequilibrium processes were involved in their formation suggesting that co2 rich fluids of variable composition infiltrated the rock while on mars we interpret petrographic textures to be consistent with an inorganic origin for the carbonate involving dissolution replacement reactions between co2 charged fluids and feldspathic glass in the meteorite carbonate formation clearly postdated processes that last redistributed the ree in the meteorite

crystal accumulation in a 4 2 ga lunar impact melt abstract the ages of lunar impact basins and the role of fractional crystallization in producing compositional heterogeneity of lunar melt sheets are long standing problems with significant implications for solar system dynamics and the petrologic evolution of the lunar crust here we document the formation of a basin scale impact on the moon at 4 20 0 07 ga based on the 147 sm 143 nd isochron age of a magnesian noritic anorthosite melt rock from lunar breccia 67955 major element compositions of plagioclase and mafic silicates in the melt rock imply a substantial component of primary mg suite cumulates or related lithologies in the pre impact crustal stratigraphy trace element compositions of the plagioclase including diagnostic ratios such as sr ba are also mostly similar to those in plagioclase from mg suite cumulates with a small number of grains trending toward compositions observed in ferroan anorthosites mineral melt distribution coefficients applied to trace element compositions of the 67955 plagioclase and pyroxene predict parental melt compositions that contrast strongly with the bulk rock compared to the whole rock parental melts calculated from the plagioclase are enriched in ree ree la yb 131 885 average 619 ppm vs 39 8 ppm and they have more fractionated ree patterns la yb n 1 2 9 8 average 4 9 vs 1 5 with deep negative eu anomalies eu eu 0 09 0 40 vs 1 36 trace element data for the pyroxenes also imply incompatible element enriched parental melts subsolidus equilibration between the plagioclase and the pyroxene apparently rotated the ree patterns but the conclusion that the parental melt was highly enriched in ree relative to the whole rock appears robust quantitative modeling shows that fractional crystallization of the 67955 whole rock composition cannot reproduce the range of ba sr ti and la concentrations measured in the 67955 plagioclase rather the models require an initial melt composition that was strongly enriched in these elements and they suggest that fractional crystallization became less efficient as crystallization proceeded the contrast between the inferred parental melt composition and the bulk rock implies formation of the 67955 noritic anorthosite as a crystal cumulate and that the cogenetic residual melt was strongly enriched in incompatible elements if so this would be the first documented example of fractional crystallization in a lunar impact melt sheet the petrological and geochemical characteristics of the 67955 noritic anorthosite suggest that it formed by an impact in the procellarum kreep terrane and was transported to the apollo 16 site as imbrium ejecta inheritance of ejecta related to this pre imbrium basin may contribute to the common occurrence of 4 2 ga 40 ar 39 ar plateau ages in breccia clasts and regolith fragments from the rim of north ray crater in that case those data may provide no constraints on the age of the nectaris basin despite its proximity to the apollo 16 site

evidence of chemical heterogeneity within lunar anorthosite parental magmas abstract lunar anorthosites are known for displaying a limited range of plagioclase an content an 94 to 98 here we demonstrate that plagioclase trace element variations from apollo ferroan anorthosites fan samples collected by the apollo 15 and 16 missions display more significant chemical heterogeneity e g chondrite normalized la sm 0 33 5 42 than previously reported we report mineral plagioclase pyroxene and olivine major and trace element abundances for a suite of apollo fan samples in addition to anorthositic clasts within apollo 16 regolith breccias this suite of data extends the compositional range currently reported for apollo anorthosites and for anorthositic clasts previously found within lunar meteorites petrological classifications of the regolith breccia clasts e g anorthosite versus noritic anorthosites cannot always be accurately assessed due to the limited size

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

crystallization of accessory phases in magmas by local saturation adjacent to phenocrysts abstract accessory minerals commonly occur attached to or included in the major crystalline phases of felsic and some intermediate igneous rocks apatite is particularly common as inclusions but fe ti oxides pyrrhotite zircon monazite chevkinite and xenotime are also known from silicic rocks accessories may nucleate near the host crystal liquid interface as a result of local saturation owing to formation of a differentiated chemical boundary layer in which accessory mineral solubility would be lower than in the surrounding liquid differentiation of this boundary layer would be greatest adjacent to ferromagnesian phenocrysts especially fe ti oxides it is with oxides that accessories are most commonly associated in rocks a boundary layer may develop if the crystal grows more rapidly than diffusion can transport incorporated and rejected elements to and from the phenocryst diffusion must dominate over convection as a mode of mass transfer near the advancing crystal liquid interface in order for a boundary layer to exist accumulation of essential structural constituent elements of accessory minerals owing to their slow diffusion in evolved silicate melt also may force local saturation but this is not a process that applies to all cases local saturation is an attractive mechanism for enhancing fractionation during crystallization differentiation if accessory minerals attached to or included in phenocrysts formed because of local saturation their host phenocrysts must have grown rapidly when accessories nucleated in comparison to lifetimes of magma reservoirs some inconsistencies remain in a local saturation origin for accessory phases that cannot be evaluated without additional information

subsolidus ree partitioning between pyroxene and plagioclase in cumulate eucrites an ion microprobe investigation abstract in an attempt to elucidate the relationship between the cumulate eucrites and the noncumulate main series eucrites we have examined the trace element systematics of plagioclase grains that coexist with inverted pigeonites of the cumulate eucrites analyses were done by secondary ion mass spectrometry sims plagioclase compositions are uniform in trace element abundances within grains from each cumulate eucrite but are variable between the four analyzed moama moore county serra de mage and binda shapes of ci normalized trace element abundance patterns of the plagioclase grains of the cumulates are typical of plagioclase showing a lree enriched pattern with positive eu anomalies reflecting the site preference of eu 2 in the feldspar structure using trace element concentrations of the pyroxenes orthopyroxene pigeonite augite pun and papike 1995 and plagioclase this study we calculate the subsolidus partition coefficients ds for the rees and y between plagioclase and pyroxenes in the examined cumulate eucrites trace element systematics suggest that igneous trace element signatures have been altered by subsolidus exchange for both the plagioclase and pyroxene calculated hypothetical parental melt patterns determined from pyroxene and plagioclase are different and can differ by a factor of 4 5 for individual rees

geochemistry of intermediate olivine phyric shergottite northwest africa 6234 with similarities to basaltic shergottite northwest africa 480 and olivine phyric shergottite northwest africa 2990 the newly found meteorite northwest africa 6234 nwa 6234 is an olivine ol phyric shergottite that is thought based on texture and mineralogy to be paired with martian shergottite meteorites nwa 2990 5960 and 6710 we report bulk rock major and trace element abundances including li abundances of highly siderophile elements re os isotope systematics oxygen isotope ratios and the lithium isotope ratio for nwa 6234 nwa 6234 is classified as a martian shergottite based on its oxygen isotope ratios bulk composition and bulk element abundance ratios fe mn al ti and na al the li concentration and d 7 li value of nwa 6234 are similar to that of basaltic shergottites zagami and shergotty the rare earth element ree pattern for nwa 6234 shows a depletion in the light ree la nd compared with the heavy ree sm lu but not as extreme as the known depleted shergottites thus nwa 6234 is suggested to belong to a new category of shergottite that is geochemically intermediate in incompatible elements the only other basaltic or ol phyric shergottite with a similar intermediate character is the basaltic shergottite nwa 480 rhenium osmium isotope systematics are consistent with this intermediate character assuming a crystallization age of 180 ma we conclude that nwa 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in mars

a rock magnetic study of the lower massive sandstone moenkopi formation triassic gray mountain area arizona this paper describes the results of rock magnetic and petrographic studies of the lower massive sandstone of the moenkopi formation north central arizona which heretofore has been considered to be a reliable magnetostratigraphic unit the rock magnetic studies included stepwise thermal demagnetization of samples of intraformational mudstone clasts and a deformed shale lens both of which occur within the lower part of the sandstone and stepwise thermal and selective destructive demagnetization sdd of samples of the sandstone containing black sand laminae composed largely of opaque grains in samples both from the claystone clasts and deformed shale lens two secondary components one of modern normal polarity and one of triassic normal polarity were unambiguously identified and a third crm component of triassic reversed polarity was tentatively identified there is no evidence in samples of either the claystone clasts or deformed shale lens of a remanence acquired prior to deposition or to deformation respectively sdd by means of which the small scale homogeneity of remanence within samples of the lower massive sandstone containing black sand laminae could be assessed shows that each sample primarily contains a heterogeneous three dimensional mixture of triassic normal and reversed components the triassic normal direction that is characteristic of the lower massive sandstone is a vector resultant of almost balanced proportions of the two nearly antiparallel components averaging about 55 to 60 normal and 45 to 40 reversed the local variability in both direction and intensity of remanence within and between individual black sand laminae confirms that acquisition of the remanence took place over a geologic time interval that spanned at least two and probably several polarity intervals and that on a small scale the remanence was sporadically acquired more or less randomly probably in response to local conditions in the interstitial physicochemical environment that affected the growth of authigenic hematite no primary component of remanence acquired at or soon after deposition could be identified the remanence in the black sand bearing lower massive sandstone is largely carried by the black sand grains which as determined from reflected light petrographic studies are primarily martite 67 and altered ilmenite grains 20 composed of complex intergrowths of hematite and iron titanium minerals these data strongly suggest that these grains deposited initially as unaltered to only moderately altered magnetite and ilmenite subsequently underwent oxidation during which they acquired their remanence

metamorphic diogenite grosvenor mountains 95555 mineral chemistry of orthopyroxene and spinel and comparisons to the diogenite suite abstract grosvenor mountains gro 95555 is a relatively newly discovered and unique metamorphic diogenite it does not show the usual brecciated appearance of other diogenites or wide compositional variability of orthopyroxene or spinel electron microprobe analysis empa and secondary ion mass spectrometer sims analysis of orthopyroxene and empa of spinel show limited compositional variability compositions for orthopyroxene for fe fe mg atomic al zr y and yb fall in the middle of the compositional ranges of the diogenite suite apparently gro 95555 formed at sufficient depth or location to escape brecciation by meteorite bombardment and in a thermal regime that led to high grade metamorphism resulting in homogeneous mineral compositions the believed introduction howardite eucrite and diogenite hed lithologies are to have originated on asteroid 4 vesta during an extensive melting event at 4 6 ga consolmagno and drake

accessory silicate mineral assemblages in the bilanga diogenite a petrographic study the petrographic relationships in diogenites between orthopyroxene and minor phases such as chromite troilite diopside plagioclase and silica are often obscured by the intense brecciation that characterizes these meteorites although brecciated bilanga preserves numerous clasts displaying primary textural relations between orthopyroxene and these minor phases that are large enough to analyze by electron microprobe in this study we focus on the distribution composition and origin of the minor phases in bilanga to provide new insights into the crystallization and metamorphic history of these rocks the samples examined consist mainly of orthopyroxene grains plus five types of assemblages containing diopside a fe rich phase chromite troilite and or fe ni metal plagioclase silica we interpret type 1 assemblages as being remnants of intercumulus melt trapped in the interstices between orthopyroxene grains after crystal settling in a magma chamber type 2 assemblages appear to have formed by heterogeneous exsolution during thermal metamorphism type 3 assemblages are believed to be remnants of other assemblages that have been shocked melted and rapidly recrystallized by impact events type 4 assemblages consist of veins that also appear to have formed from trapped intercumulus melt regions of silica rich mesostasis type 5 appear to be larger patches of more evolved intercumulus melt that have been significantly affected by late stage impact melting finally large clasts containing plagioclase diopside are interpreted to be exotic fragments of a different but possibly related rock type incorporated in the bilanga breccia

basaltic volcanism on the eucrite parent body petrology and chemistry of the polymict eucrite alha80102 the polymict eucrite meteorite alha80102 i s an unequilibrated breccia of basaltic and gabbroic clasts in a fragmental matrix clasts include basalts of many textural types cumulate gabbro black glass and ferroan troctolite plagioclase silica fe rich olivine ilmenite mesostasis ferroan troctolite has not been previously reported from eucrites or howardites it is interpreted as the end product of fractional crystallization of eucritic magmas bulk and trace element compositions by electron microprobe and inaa of clasts and matrix from alha80102 are similar to those of other eucrites the meteorite contains clasts similar to juvinas and to stannern a clast of cumulate eucrite gabbro is enriched in the light rare earths la lu 2xci this clast is interpreted as an unrepresentative sample of metamorphically equilibrated gabbro lree enriched magmas need not be invoked alha80102 is similar to other polymict eucrites from the allan hills and may be paired with alha76005 alha77302 and alha78040

the parent magma of the nakhla snc meteorite inferred from magmatic inclusions abstract the nakhla meteorite one of the snc group of putative martian origin is an igneous rock a cumulate of augite and olivine that does not represent a magma composition samples of its parent magma were trapped as magmatic inclusions in its cumulus olivine crystals the inclusions range from 10 350 m in diameter and consist of augite rich in ti and al silica rich glass iron oxides ilmenite apatite and rare amphibole each inclusion has a rind of augite and chromite against its host olivine and a core of radiating sprays of augite set in glass and feldspar these textures are consistent with an origin as trapped silicate liquid twenty four inclusions were analyzed by electron microprobe by averaging series of rastered beam analyses on average the analyses are independent of the size of the inclusion most clearly for inclusions larger than 70 m diameter and variations among analyses are consistent with small differences in the proportions of augite glass and iron oxides exposed on thin section surfaces the average inclusion analysis is calculated to represent 28 host olivine and 72 inclusion composition the inclusion rinds are calculated to be 13 of the inclusion composition for which a small correction is made the inclusion composition is then corrected for mg fe exchange with the host olivine to chemical equilibrium with the cumulus augite cores and crystallization of 13 olivine onto the host crystal to yield a magma composition with the proper mgo feo ratio and with olivine and augite on its liquidus this composition nk93 is an estimate of nakhla s parent magma originally trapped in the inclusions nk93 is basaltic rich in iron and poor in aluminum compared to terrestrial basalts its abundances of al ti and na are consistent with the geochemistry of the snc meteorites as a whole nk93 is similar to the parent magmas proposed in an independent study of magmatic inclusions in nakhla but unlike other proposed compositions one proposed parent magma based on mass balance and the assumption that nakhla was a closed system after crystal accumulation is inconsistent with the magmatic inclusion studies and nakhla s petrography this suggests that nakhla was not a closed system but was infiltrated by post cumulus basaltic magmas another suggested parent magma was derived from element distribution between augite and basaltic magma but that calculation relied on an incorrect augite composition using a correct augite composition in that calculation yields a parent magma much closer in composition to nk93 thus three independent approaches converge in requiring that nakhla originally formed from a low al low mgo feo basalt like nk93

patterns of quaternary uplift of the corinth rift southern border n peloponnese greece revealed by fluvial landscape morphometry abstract the rift of corinth is a world class example of young active rifting and as such is an ideal natural laboratory of continental extension however though much investigated for two decades several aspects of the mechanisms at work are still poorly understood the aim of this paper is a detailed morphometric study of the fluvial landscape response to the tectonic uplift of the rift southern shoulder in order to reconstruct the rift s quaternary evolution with special attention to timing location and intensity of uplift episodes based on the use of a large set of catchment and long profile metrics complemented by the new r sr integrative approach of the regional drainage network we identified three distinct episodes of uplift of the northern peloponnese coastal tract of which the intermediate one dated around 0 35 0 4 ma is only recorded in the topography of the central part of the rift shoulder and the youngest one appears to have propagated from east to west over the last 10 20 ka while net uplift remained minimum in the eastern part of the study area during the whole quaternary it shows a clear maximum in the central part of the rift shoulder since 0 4 ma and an eastward shift of this maximum in recent times maximum uplift rates calculated from the morphometric data are of 1 05 and 2 5 mm year 1 for the mid middle pleistocene and holocene uplift episodes respectively the morphometric evidence reveals an onshore uplift history remarkably consistent with the rift evolution reconstructed from other data sets in the long term it shows a stable pattern of maximum activity in the central part of the rift confirming previous conclusions about the absence of rift propagation in the short term it sheds light on a possible e w migration of the zone of recent uplift suggesting that in the near future fault activity and seismic hazard might concentrate in the heliki aegion area at the western tip of this uplift wave

mesosiderite clasts with the most extreme positive europium anomalies among solar system rocks pigeonite plagioclase gabbros that occur as clasts in mesosiderites brecciated stony iron meteorites show extreme fractionations of the rare earth elements rees with larger positive europium anomalies than any previously known for igneous rocks from the earth moon or meteorite parent bodies and greater depletions of light rees relative to heavy rees than known for comparable cumulate gabbros the ree pattern for merrillite in one of these clasts is depleted in light rees and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates the extreme ree ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system melting of the crust by large scale impacts or electrical induction from an early t tauri phase sun may be responsible for these processes

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

basaltic diversity at the apollo 12 landing site inferences from petrologic examinations of the soil sample 12003 a detailed petrologic survey has been made of 17 basaltic chips sized between 1 and 10 mm from the 12003 soil sample as part of an ongoing study of basaltic diversity at the apollo 12 landing site an attempt has been made to classify these samples according to the well established grouping of olivine pigeonite ilmenite and feldspathic basalts particular attention has been paid to variations in major minor and trace element mineral chemistry determined by electron microprobe analysis and laser ablation icp ms which may be indicative of particular basaltic suites and less susceptible to sampling bias than bulk sample characteristics examples of all three main olivine pigeonite and ilmenite basaltic suites have been identified within the 12003 soil one sample is identified as a possible new addition to the feldspathic suite which currently consists of only one other confirmed sample identification of additional feldspathic basalts strengthens the argument that they represent a poorly sampled basaltic flow local to the apollo 12 site rather than exotic material introduced to the site by impact mixing processes three samples are identified as representing members of one or two previously unrecognized basaltic suites

determination of parental magmas of hed cumulates the effects of interstitial melts an evaluation of trapped melts effects during crystallization and subsolidus equilibration of cumulates is necessary to constrain the composition of their parental magmas in this paper a simple mass balance approach is described it allowes to estimate trace element abundances in these parental melts from phase compositions it is used to discuss the genesis of cumulate eucrites and diogenites the ree behavior is in full agreement with the view that cumulate eucrites formed from melts similar to noncumulate eucrites trapped melt fractions ranging from 10 wt for moama to 30 wt for moore county were involved the origin of diogenites is more complex the assumption that eucrites and diogenites shared the same parental melts cannot satisfactorily explain the diversity of incompatible trace element ratios e g dy yb observed in diogenitic orthopyroxenes even if interstitial melt effects are taken into account moreover some diogenites unambiguously crystallized from magmas displaying significant hree heavy rare earth elements enrichments more likely diogenites formed from distinct batches of parental magmas as previously proposed by mittlefehldt 1994 fowler et al 1995 and shearer 1997

portales valley petrology of a metallic melt meteorite breccia portales valley pv is an unusual metal veined meteorite that has been classified as an h6 chondrite it has been regarded either as an annealed impact melt breccia as a primitive achondrite or as a meteorite with affinities to silicated iron meteorites we studied the petrology of pv using a variety of geochemical mineralogical techniques our results suggest that pv is the first well documented metallic melt meteorite breccia mineral chemical and other data suggest that the protolith to pv was an h chondrite the composition of feni metal in pv is somewhat fractionated compared to h chondrites and varies between coarse vein and silicate rich portions it is best modeled as having formed by partial melting at temperatures of 940 1150 c with incomplete separation of solid from liquid metal solid metal concentrated in the coarse vein areas and s bearing liquid metal concentrated in the silicate rich areas possibly as a result of a surface energy effect both carbon and phosphorus must have been scavenged from large volumes and concentrated in metallic liquid graphite nodules formed by crystallization from this liquid whereas phosphate formed by reaction between p bearing metal and clinopyroxene components depleting clinopyroxene throughout much of the meteorite and growing coarse phosphate at metal silicate interfaces some phosphate probably crystallized from p bearing liquids but most probably formed by solid state reaction at 975 725 c phosphate forming and feo reduction reactions were widespread in pv and entailed a change in the mineralogy of the stony portion on a large scale portales valley experienced protracted annealing from supersolidus to subsolidus temperatures probably by cooling at depth within its parent body but the main differences between pv and h chondrites arose because maximum temperatures were higher in pv a combination of a relatively weak shock event and elevated pre shock temperatures probably produced the vein and breccia texture with endogenic heating being the main heat source for melting and with stress waves from an impact event being an essential trigger for mobilizing metal portales valley is best classified as an h7 metallic melt breccia of shock stage s1 the meteorite is transitional between more primitive chondritic and evolved achondrite iron meteorite types and offers clues as to how differentiation could have occurred in some asteroidal bodies

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

lunar mg suite thermobarometry and petrogenesis of parental magmas using compilations of internally consistent thermodynamic data on minerals and advances in quantifying the energetics of crystalline solid solutions we have recalculated the pressures and temperatures of equilibration of troctolite sample 76535 and a number of spinel cataclasites the five phase assemblage olivine orthopyroxene clinopyroxene cr spinel plagioclase which occurs in symplectite assemblages in 76535 gives equilibration temperatures from 800 900 c and pressures from 200 to 250 mpa indicating a deep 40 50 km crustal source spinel cataclasite assemblages give minimum pressures of 100 mpa mg suite magmas were apparently intruded throughout the lunar crust early in lunar history the textures and equilibration temperatures in many mg suite samples are consistent with sub solidus recrystallization and the mg rich minerals of some refractory troctolites and dunites may be residues of a crustal melting process or products of subsolidus elemental redistribution the sm nd age of 4 26 0 06 ga of troctolite 76535 most likely represents the time of sub solidus recrystallization and or partial melting in an attempt to identify the primary source material for the mg suite magmas a variety of models were tested using the melts and magfox codes a good fit between mineral compositions and crystallization sequences is obtained by 20 batch melting at 0 5 gpa of an average whole moon composition with an mg of 0 85 melts formed by batch melting at higher pressures and melts formed by poly baric partial fusion over the pressure range from 2 0 to 0 3 gpa were either too poor in mg and or crystallized clinopyroxene before orthopyroxene mixing with 10 20 urkreep which is required to satisfy the ree constraints of the mg suite reduces the mg of the parental magmas and requires a whole moon mg closer to that of the terrestrial mantle

petrogenesis of lunar highlands meteorites dhofar 025 dhofar 081 dar al gani 262 and dar al gani 400 the petrogenesis of four lunar highlands meteorites dhofar 025 dho 025 dhofar 081 dho 081 dar al gani 262 dag 262 and dar al gani 400 dag 400 were studied for dho 025 measured oxygen isotopic values and fe mn ratios for mafic minerals provide corroboratory evidence that it originated on the moon similarly fe mn ratios in the mafic minerals of dho 081 indicate lunar origin lithologies in dho 025 and dho 081 include lithic clasts granulites and mineral fragments a large number of lithic clasts have plagioclase an and coexisting mafic mineral mg that plot within the gap separating ferroan anorthosite suite fan and high magnesium suite hms rocks this is consistent with whole rock ti sm ratios for dho 025 dho 081 and dag 262 which are also intermediate compared to fan and hms lithologies although ion microprobe analyses performed on dho 025 dho 081 dag 262 and dag 400 clasts and minerals show far stronger fan affinities than whole rock data suggest most clasts indicate admixture of 12 hms component based on geochemical modeling in addition coexisting plagioclase pyroxene ree concentration ratios in several clasts were compared to experimentally determined plagioclase pyroxene ree distribution coefficient ratios two dho 025 clasts have concordant plagioclase pyroxene profiles indicating that equilibrium between these minerals has been sustained despite shock metamorphism one clast has an intermediate fan hms composition these lunar meteorites appear to represent a type of highland terrain that differs substantially from the kreep signatured impact breccias that dominate the lunar database from remote sensing data it is inferred that the lunar far side appears to have appropriate geochemical signatures and lithologies to be the source regions for these rocks although the near side cannot be completely excluded as a possibility if these rocks are indeed from the far side their geochemical characteristics may have far reaching implications for our current scientific understanding of the moon

petrology and provenance of a very low titanium picrite clast in lunar highland regolith breccia 15295 clast 100 in regolith breccia 15295 could be a key to resolving the relationship s between mare basalts and lunar picritic glasses the clast is basaltic with texture mineralogy mineral compositions and calculated bulk composition suggesting that it crystallized in a thick lava flow or shallow intrusive body from a very low titanium vlt basaltic magma the estimated bulk composition of clast 15295 100 is primitive i e magnesian compared to those of known vlt basalts and is very close to those of vlt picritic green glasses especially the apollo 14 a green glass from these similarities we infer that clast 15295 100 is a crystalline product of a picritic magma similar to the apollo 14 a glass clementine and m3 remotely sensed data of the lunar surface were used to find areas that have chemical compositions consistent with those of clast 15295 100 not only near the apollo 15 site but in a broad region surrounding the site two regions are consistent with clast s 15295 100 compositional data the larger region is in southern mare imbrium and a smaller region is in the eastern half of sinus aestuum these locations should be considered as candidates for future missions focusing on sample science

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

comparative petrology of silicates in the udei station iab and miles iie iron meteorites implications for the origin of silicate bearing irons abstract the textures and mineral chemistries of silicate inclusions in the udei station iab and miles fractionated iie iron meteorites were studied using optical and electron microscopy sem empa and la icp ms techniques to better understand the origin of silicate bearing irons inclusions in udei station include near chondritic basaltic gabbroic feldspathic orthopyroxenitic and harzburgitic lithologies in miles most inclusions can be described as feldspathic pyroxenite or pyroxene enriched basalt gabbro the trace element compositions of both orthopyroxene and plagioclase grains are similar in different lithologies from udei station whereas in different inclusions from miles the compositions of orthopyroxene grains are similar while those of clinopyroxene plagioclase and especially cl apatite are variable orthopyroxene in miles tends to be enriched in ree compared to that in udei station but the reverse is true for plagioclase and clinopyroxene the data can be explained by models involving partial melting of chondritic protoliths silicate melt migration and redox reactions between silicate and metal components to form phosphate the extent of heating melt migration and phosphate formation were all greater in miles silicates in miles were formed from liquids produced by 30 partial melting of a chondritic precursor brought to a peak temperature of 1250 c this silicate melt crystallized in two stages during stage 1 crystallizing minerals orthopyroxene clinopyroxene chromite and olivine were largely in equilibrium with an intercumulus melt that was evolving by igneous fractionation during slow cooling with a residence time of 20 ka at 1150 c during stage 2 following probable re melting of feldspathic materials and after the silicate mush was mixed with molten metal plagioclase and phosphate fractionally crystallized together during more rapid cooling down to the solidus in udei station despite a lower peak temperature we suggest that a model involving major collisional disruption and mixing of partly molten endogenically heated planetesimals can best explain the data for iab and fractionated iie silicate bearing irons the extent of endogenic heating was different less for the iabs and the amount of parent body disruption was different scrambling with collisional unroofing for the iab iiicd winonaite body more complete destruction for the fractionated iie body but both bodies were partly molten and incompletely differentiated at the time of impact we suggest that the post impact secondary body for iab iiicd winonaite meteorites was mineralogically zoned with ni poor metal in the center and that the secondary body for fractionated iie meteorites was a relatively small melt rich body that had separated from olivine during collisional break up

lunar ferroan anorthosite petrogenesis clues from trace element distributions in fan subgroups the rare earth elements ree and selected other trace elements were measured in plagioclase and pyroxene from nine samples of the lunar ferroan anorthosite fan suite of rocks samples were selected from each of four fan subgroups previously defined by james et al 1989 plagioclase compositions are homogeneous within each sample but high and low ca pyroxenes from lithic clasts typically have different ree abundances from their counterparts in the surrounding granulated matrices measured plagioclase low ca pyroxene concentration ratios for the ree have steeper patterns than experimentally determined plagioclase low ca pyroxene partition coefficients in most samples textural and trace element evidence suggest that although subsolidus equilibration may be responsible for some of the discrepancy plagioclase compositions in most samples have been largely unaffected by intermineral redistribution of the ree the ree systematics of plagioclase from the four subgroups are broadly consistent with their derivation through crystallization from a single evolving magma however samples from some of the subgroups exhibit a decoupling of plagioclase and pyroxene compositions that probably reflects the complexities inherent in crystallization from a large scale magmatic system for example two anorthosites with very magnesian mafic minerals have highly evolved trace element compositions major element compositions in plagioclase also do not reflect the evolutionary sequence recorded by their ree compositions finally a noritic anorthosite breccia with relatively ferroan mafic minerals contains several clasts with high and variable ree and other trace element abundances although plagioclase ree compositions are consistent with their derivation from a magma with a kreepy trace element signature very shallow ree patterns in the pyroxenes suggest the addition of a component enriched in the light ree

magnesian anorthositic granulites in lunar meteorites allan hills a81005 and dhofar 309 geochemistry and global significance abstract fragments of magnesian anorthositic granulite are found in the lunar highlands meteorites allan hills alh a81005 and dhofar dho 309 five analyzed clasts of meteoritic magnesian anorthositic granulite have mg molar mg mg fe 81 87 feo 5 wt al2o3 22 wt rare earth elements abundances 0 5 2 ci except eu 10 ci and low ni and co in a non chondritic ratio the clasts have nearly identical chemical compositions even though their host meteorites formed at different places on the moon these magnesian anorthositic granulites are distinct from other highlands materials in their unique combination of mineral proportions mg ree abundances and patterns ti sm ratio and sc sm ratio their mg is too high for a close relationship to ferroan anorthosites or to have formed as flotation cumulates from the lunar magma ocean compositions of these magnesian anorthositic granulites cannot be modeled as mixtures of or fractionates from known lunar rocks however compositions of lunar highlands meteorites can be represented as mixtures of magnesian anorthositic granulite ferroan anorthosite mare basalt and kreep meteoritic magnesian anorthositic granulite is a good candidate for the magnesian highlands component inferred from apollo highland impactites magnesian feldspathic and ree poor bulk compositions of meteorite magnesian anorthositic granulites are comparable to those inferred for parts of the lunar farside the feldspathic highlands terrane 4 5 wt feo 28 wt al2o3 and th 1 ppm thus magnesian anorthositic granulite may be a widespread and abundant component of the lunar highlands

cr and sr keys to parental magmas and processes in the bushveld complex south africa abstract large layered intrusions are almost certainly periodically replenished during their protracted cooling and crystallization the exact composition s of the replenishing magma s in the case of the bushveld complex south africa has been debated mainly on the basis of major element composition and likely crystallization sequences the intrusion is dominated by orthopyroxene and plagioclase and so their cr and sr contents and likely partition coefficient values can be used to re investigate the appropriateness of the various proposed parental magmas one magma type with about 12 mgo 1000 ppm cr and 180 ppm sr can explain the genesis of the entire lower and critical zones a number of other magma compositions proposed to produce the critical zone fail to match these trace element constraints by being too poor in cr a fundamentally different magma type was added at the base of the main zone but none of the proposed compositions is consistent with the trace element requirements specifically the cr contents are higher than predicted from pyroxene compositions a further geological constraint is demonstrated from a consideration of the cr budget at this level there is an abrupt decrease from about 0 4 to 0 1 cr 2 o 3 in orthopyroxene across this critical zone main zone transition no realistic proportions of mixing between the residual magma at the top of the critical zone and any proposed added magma composition can have produced a composition that could have crystallized these low cr orthopyroxenes instead it is suggested that the resident magma from the upper critical zone was expelled from the chamber possibly as sills into the country rocks during influx of a dense differentiated magma near the level of the pyroxenite marker in the main zone there is further addition of a ferrobasaltic magma with 6 mgo 111 ppm cr and 350 ppm sr that is consistent with the geochemical requirements

petrology of the western highland province ancient crust formation at the apollo 14 site plutonic rocks found at the apollo 14 site comprise four lithologic suites the magnesian suite the alkali suite evolved lithologies and the ferroan anorthosite suite fan rocks of the magnesian suite include troctolite anorthosite norite dunite and harzburgite they are charaterized by plagioclase an95 and mafic minerals with mg s 82 92 alkali suite rocks and evolved rocks generally have plagioclase an90 to an40 and mafic minerals with mg s 82 40 lithologies include anorthosite norite quartz monzodiorite granite and felsite ferroan anorthosites have plagioclase an96 and mafic minerals with mg s 45 70 whole rock geochemical data show that most magnesian suite samples and all alkali anorthosites are cumulates with little or no trapped liquid component norites may contain significant trapped liquid component and some alkali norites may represent cumulate enriched near liquid compositions similar to kreep basalt 15386 evolved lithologies include evolved partial cumulates related to alkali suite fractionation quartz monzodiorite immiscible melts derived from these evolved magmas granites and impact melts of preexisting granite felsite plots of whole rock mg versus whole rock ca ca na k show a distinct gap between rocks of the magnesian suite and rocks of the alkali suite suggesting either distinct parent magmas or distinct physical processes of formation chondrite normalized rare earth element ree patterns show that rocks of both the magnesian suite and alkali suite have similar ranges despite the large difference in major element chemistry current models for the origin of the magnesian suite call for a komatiitic parent magma derived from early magma ocean cumulates these melts must assimilate plagiophile elements to form troctolites at low pressures and must assimilate a highly enriched kreep component so that the resulting mixture has ree concentrations similar to high k kreep there are as yet no plausible scenarios that can explain these unusual requirements we propose that partial melting of a primitive lunar interior and buffering of these melts by ultramagnesian early magma ocean cumulates provides a more reasonable pathway to form magnesian troctolites alkali anorthosites and norites formed by crystallization of a parent magma with major element compositions similar to kreep basalt 15386 if the parent magma of the alkali suite and evolved rocks is related to the magnesian suite then that magma must have evolved through combined assimilation fractional crystallization processes to form the alkali suite cumulates

the origin of aubrites evidence from lithophile trace element abundances and oxygen isotope compositions abstract we report the abundances of a selected set of lithophile trace elements including lanthanides actinides and high field strength elements and high precision oxygen isotope analyses of a comprehensive suite of aubrites two distinct groups of aubrites can be distinguished a the main group aubrites display flat or light ree depleted ree patterns with variable eu and y anomalies their pyroxenes are light ree depleted and show marked negative eu anomalies b the mount egerton enstatites and the silicate fraction from larned display distinctive light ree enrichments and high th sm ratios mount egerton pyroxenes have much less pronounced negative eu anomalies than pyroxenes from the main group aubrites leaching experiments were undertaken to investigate the contribution of sulfides to the whole rock budget of the main group aubrites sulfides contain in most cases at least 50 of the rees and of the actinides among the elements we have analyzed those displaying the strongest lithophile behaviors are rb ba sr and sc the homogeneity of the 17 o values obtained for main group aubrite falls 17 o 0 009 0 010 2 suggests that they originated from a single parent body whose differentiation involved an early phase of large scale melting that may have led to the development of a magma ocean this interpretation is at first glance in agreement with the limited variability of the shapes of the ree patterns of these aubrites however the trace element concentrations of their phases cannot be used to discuss this hypothesis because their igneous trace element signatures have been modified by subsolidus exchange finally despite similar o isotopic compositions the marked light ree enrichments displayed by mount egerton and larned suggest that they are unrelated to the main group aubrites and probably originated from a distinct parent body

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

clinopyroxene ree distribution coefficients for shergottites the ree content of the shergotty melt abstract ree distribution coefficients were measured between synthetic pyroxenes and melts similar in composition to the inferred shergotty intercumulus liquid by in situ analysis with the electron microprobe using samples doped to per cent concentration levels these coefficients exhibit a strong positive correlation with pyroxene wollastonite content recommended values for augites similar in composition to the shergotty cumulus augite cores wo32en48 are d la 0 023 d ce 0 039 d nd 0 10 d sm 0 17 d eu 0 16 d gd 0 20 d yb 0 29 and d lu 0 30 recommended values for pigeonites similar in composition to the shergotty cumulus pigeonite cores wo12en58 are d la 0 002 d ce 0 004 d nd 0 019 d sm 0 031 d yb 0 13 and d lu 0 13 these values resemble distribution coefficients measured for terrestrial basalts of higher mg fe than the shergotty melt rather than those of more evolved siliceous rocks of similar mg fe to the shergotty melt thus it appears that mg fe is considerably less important than other factors in determining distribution coefficient values for pyroxenes ree abundances were computed for the shergotty intercumulus melt using distribution coefficients measured for the natural phase compositions these computed abundances display lree depletion such lree depleted abundance patterns cannot be generated by simple partial melting of a mafic mineral assemblage having the lree enriched patterns required for a two stage sm nd evolution history this result implies that either 1 the melting process was complex e g continuous melting 2 the source region had a more complex history than that of the simple 2 stage model or 3 shergotty does not satisfy the closed system assumption of the calculation and has suffered post magmatic lree enrichment

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms

relative chronology of crust formation on asteroid vesta insights from the geochemistry of diogenites abstract the eucrites and diogenites are meteorites that probably originate from asteroid 4 vesta the upper part of the crust of this body is certainly composed of eucrites which are basaltic or gabbroic rocks diogenites are ultramafic cumulates whose relationships with eucritic lithologies are unknown here we show that the orthopyroxenes of some diogenites display very deep negative eu anomalies eu eu close to 0 1 or lower the contamination of the parental magmas of diogenites by melts derived by partial melting of the eucritic crust can satisfactorily explain the range of the eu anomalies displayed by diogenites thus these anomalies are the first firm indication that parental melts of diogenites have intruded the eucritic crust and consequently are younger than eucrites