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We report new high-precision stable K isotope data for three martian meteorites, one lunar meteorite, one ordinary chondrite, four terrestrial igneous United States Geological Survey (USGS) reference materials, and twenty howardite–eucrite–diogenite [HED] meteorites. The three martian meteorites define a relatively narrow δ41K range with an average of −0.36 ± 0.12‰ (2 SD) that is slightly heavier than the Bulk Silicate Earth (BSE) K isotopic composition (−0.48 ± 0.03‰). Except for the four Northwest Africa samples which were terrestrially contaminated, all HED meteorites reveal substantial 41K enrichment compared to BSE, lunar samples, martian meteorites, and chondrites. We propose that the average δ41K (+0.36 ± 0.16‰) obtained from HED meteorites is representative of Bulk Silicate 4-Vesta. The coupled volatile depletion and heavy K isotope enrichment in 4-Vesta could be attributed to both nebula-scale processes and parent-body events. The asteroid 4-Vesta is likely to have accreted from planetary feedstocks that have been significantly volatile-depleted prior to the major phases of planetary accretion in the early Solar System, with secondary effects of K loss during accretionary growth and magma ocean degassing.

Kersantite is the international designation for hypabyssal lamprophyres essentially made up of dark micas and plagioclase. Kersantites from the type locality (Kersanton hamlet) and the W-Armorican surrounding area are Serpukhovian/Bashkirian in age. They are systematically associated in the field with hypabyssal microgranodiorites, both types being intruded synchronously as syn-compressional magmatic bodies that postdated pre-tectonic Tournaisian/Visean dolerites. The kersantitic amphibole compositions can be used to constrain the crystallization pressures and oxygen fugacities (redox conditions much more oxidizing than the Ni-NiO buffer). The oscillatory zoning observed in clinopyroxene phenocysts is consistent with a magma chamber repeatedly refilled by mafic liquid. The melting source of the W-Armorican kersantites corresponded to a lithospheric mantle located in the spinel-garnet transition zone (75–85 km depth), highly metasomatized by fluids probably released by a subducted sediment-bearing slab. Microgranodiorites could result from intimate mixing between mantle- and crust-derived magmas, with cordierite as possibly melting phase. The emplacement of dolerites with anorogenic geochemical signature prior to kersantites/microgranodiorites implies upwelling of the asthenospheric mantle up to a relatively high level, probably as the result of an extension induced by either roll back of the subducted lithospheric slab or delamination of the overriding plate. The heat input associated to the long-lasted asthenosphere rise could have favored (1) the formation of early dolerites between 347 and 330 Ma; and then, (2) the genesis of syn-compressional kersantites and microgranodiorites between 330 and 310 Ma, once the overlying lithospheric mantle was metasomatized by crust-derived fluids. This magmatic sequence marked the beginning of the Avalonia-Armorica collision, just prior to the main Variscan compressional event in this zone at c. 315 Ma.

International audience; Glassy ejecta are associatedto a limited number of impact craters, and yet hold key information about hypervelocity impact processes. Here we report on the discovery of a similar to 650 km(2) impact glass strewnfield in the Central Depression of the Atacama Desert. These cm-sized splash-form objects, that we refer to as atacamaites, are essentially composed of a dacitic glass formed by high-temperature melting of local magmatic rocks, with the addition of a variable iron meteorite contamination, 5 wt.% on average. The most likely nature for the impactor is the IIAB iron group. The fission-track plateau method, on two samples, yielded a mean formation age of 7.83 +/- 0.26 Ma. No associated impact crater has been discovered so far, suggesting it may be a relatively small, km-sized crater. The glassy nature, aerodynamic shapes, elevated formation temperature, and low water content are reminiscent of tektites. However, their small size, heterogeneity, oxidation state, significant contamination by the impactor, and likely more proximal provenance distinguish them from tektites. Atacamaites have no equivalent among the few known terrestrial ejected impact glasses, and increase the intriguing diversity of such products that we propose to name "tektoids".

Basaltic rocks generated by upwelling mantle plumes display a range of trace element and isotope compositions indicative of strong heterogeneity in deep material brought to Earth surface. Helium isotopes are an unrivalled tracer of the deep mantle in plume-derived basalts. It is frequently difficult to identify the composition of the deep mantle component as He isotopes rarely correlate with incompatible trace element and radiogenic isotope tracers. It is supposed that this is due to the high He concentration of the deep mantle compared to degassed/enriched mantle reservoirs dominating the He in mixtures, although this is far from widely accepted. The modern Afar plume is natural laboratory for testing the prevailing paradigm.The 3He/4He of basalt glasses from 26°N to 11°N along the Red Sea spreading axis increases systematically from 7.9 to 15 Ra. Strong along-rift relationships between 3He/4He and incompatible trace element ratios are consistent with a binary mixture between moderately enriched shallow asthenospheric mantle in the north and plume mantle evident in basalts from the Gulf of Tadjoura, Djibouti (the Ramad enriched component of Barrat et al. 1990). The high-3He/4He basalts have trace element-isotopic compositions that are similar, but not identical, to the high 3He/4He (22 Ra) high Ti (HT2) flood basalts erupted during the initial phase of the Afar plume volcanism (Rogers et al. in press). This suggests that the deep mantle component in the modern Afar plume has a HIMU-like composition. From the hyperbolic 3He/4He-K/Th-Rb/La mixing relationships we determine that the upwelling deep mantle has 3-5 times higher He concentration than the asthenosphere mantle beneath the northern Red Sea.Barrat et al. 1990. Earth and Planetary Science Letters 101, 233-247.

International audience; Radiogenic strontium isotopes are routinely used in provenance studies, but their application to sediments is often complicated by various grain size and weathering effects, which can influence measured 87Sr/86Sr ratios. Here, we report Sr isotopic data for a large number of sediment samples (n = 61) from the world's largest rivers and other river catchments draining particular geological and climatic settings; using both clay-rich (20 °C, intense feldspar weathering leads to the preferential incorporation of unradiogenic Sr into secondary clay minerals; a process which results in negative Δ87Sr/86Sr Clay-Silt values. In addition to climate forcing, the degree of size-dependent Sr isotope decoupling is also shown to be dependent on the type of weathering regime in watersheds, being more pronounced in low-elevation environments (< 2000 m), where transport-limited conditions and the presence of thick soil sequences can be associated with intense silicate weathering, than in high mountain regions (> 4000 m) dominated by kinetically-limited weathering regimes.While further studies will be required to test the validity of these conclusions at the local scale of weathering profiles, these findings suggest that combined Sr isotopic analyses of separate size fractions could be used as a new weathering proxy in sediment records, ideally complementing the conventional use of radiogenic Sr isotopes as provenance tracers. Finally, our results are also used to re-assess the mean Sr flux and 87Sr/86Sr composition of the suspended sediment exported to the ocean yearly, yielding a global flux-weighted average of 0.7160, identical to that proposed earlier in the seminal study of Goldstein and Jacobsen (1988).

Main-group pallasites (MGPs) are meteorites mainly composed of Fe-Ni metal and olivines, the latter being considered as one of the largest sampling of extraterrestrial mantle material available for study on Earth. We analysed the rare earth element (REE) concentrations of olivines from six MGPs to understand better the processes of formation of their parent mantle. All the investigated samples display very low REE abundances, and enrichments in both light REEs and heavy REEs. We interpret the light REE enrichments as a fingerprint of terrestrial contamination. The least contaminated olivines have higher heavy REE enrichments than those inferred for olivines directly crystallised in a magma ocean. Such enrichments in heavy REEs are possible if the mantle of the MGPs parent body is a residue of partial melting from a chondritic source. Alternatively, re-melting of magma ocean cumulates would explain both the homogeneity of the Ä17O values of MGPs, and the heavy REE enrichments of the olivines.

A major breakthrough in the field of rare earth element (REE) geochemistry has been the recent discovery of their utility to microbial life, as essential metalloenzymes catalyzing the oxidation of methanol to formaldehyde. Lanthanide-dependent bacteria are thought to be ubiquitous in marine and terrestrial environments, but direct field evidence of preferential microbial utilization of REE in natural systems is still lacking. In this study, we report on the REE and trace element composition of the tube of a siboglinid worm collected at a methane seep in the Gulf of Guinea; a tube-dwelling annelid that thrives in deep-sea chemosynthetic ecosystems. High-resolution trace element profiles along the chitin tube indicate marked enrichments of lanthanum (La) and cerium (Ce) in its oxic part, resulting in REE distribution patterns that depart significantly from the ambient seawater signature. Combined with various geochemical and microbiological evidence, this observation provides direct support for an active consumption of light-REE at cold seeps, associated with the aerobic microbial oxidation of methane. To further evaluate this hypothesis, we also re-examine the available set of REE data for modern seep carbonates worldwide. While most carbonate concretions at cold seeps generally display REE distribution patterns very similar to those for reduced pore waters in marine sediments, we find that seafloor carbonate pavements composed of aragonite commonly exhibit pronounced light-REE enrichments, as inferred from high shale-normalized La/Gd ratio (>~0.8), interpreted here as possibly reflecting the signature of lanthanide-dependent methanotrophic activity. This finding opens new perspectives for revisiting REE systematics in ancient seep carbonates and other microbialites throughout the Earth's history. In particular, the geochemical imprint of aerobic methane oxidation could be possibly traced using REE in Archaean stromatolites and other archives of Precambrian seawater chemistry, potentially providing new insights into the oxygenation of early Earth's oceans and associated microbiogeochemical processes.

International audience; Methane is an important greenhouse gas whose emissions into the oceans and atmosphere are regulated by relatively unconstrained anaerobic and aerobic microbial processes. The aerobic pathway for methane oxidation is thought to be largely dependent upon the use of rare earth elements (REE), but to date the effects of this process on their abundances in bacteria or in organisms living in symbiosis with methanotrophs remain to be evaluated. Here we show that deep sea chemosynthetic mussels prospering at methane seeps display distinctive lanthanum enrichments linked to the enzymatic activities of their symbionts. These results demonstrate that methanotrophy is able to fractionate efficiently REE distributions in organisms and possibly in the environment. Lanthanum anomalies recorded in ancient sediments are potential chemical fossils that could be used in the geological record for tracking early evidence of microbial life.

International audience; The origin(s) of the chassignites and nakhlites, closely related martian olivine and augite cumulates, respectively, are much debated. Northwest Africa (NWA) 8694 is the third chassignite to be discovered and the most ferroan, containing 85% olivine (Fo54). Its O-isotope compositions (δ18O ∼ 4.4‰, Δ17O ∼ 0.30‰) are typical of other martian meteorites. It has adcumulate texture and contains cumulus chromite, poikilitic pigeonite (En56Fs37Wo7) and mesostasis (trapped interstitial liquid). The latter contains pyroxene and plagioclase (An23 Ab70 Or8) plus rare K- feldspar (Or74), and has a trachyandesitic to trachytic bulk composition. Melt inclusions in olivine contain a variety of phases including biotite and rare amphibole. Olivine, chromite, and pigeonite compositions are intermediate between those of the other chassignites and those of the nakhlites. Augite, which appears to mantle pigeonite, has a composition overlapping that in nakhlite NWA 998 and some other nakhlites at (En41-40Wo38-39). The augite lamellae in pigeonite 1–2 μm in apparent width, and the survival of Ca zoning in olivine, suggest a near-surface cooling environment. The bulk-rock REE concentrations in the three chassignites do not correlate with Mg# but depend on the abundance of trapped liquid. The form of REE patterns calculated for olivine subtraction is very like those of nakhlite mesostases, but the observed concentrations of LREE in NWA 8694 trapped liquid have a very steep slope. This is explained by undersampling of baddeleyite and zirconolite that occur near olivine contacts with mesostasis. Though pyroxene is unzoned, its trace element variations indicate fractional crystallization. The range of olivine compositions in the three chassignites (Fo79-54) is too large to result from the crystallization sequential growth of olivine from a single magma undergoing fractional crystallization. The Ge/Si ratios show degassing of NWA 8694 which sets this chassignite apart from other chassignites and nakhlites, implying a unique batch of magma for its genesis. Many potential parent liquids are capable of generating the NWA 8694 olivine composition, though not its alkaline mesostasis. We calculated that Nakhla parent liquid NA01a (Stockstill et al., 2005) with 10% Nakhla core olivine added would produce both olivine crystals and alkaline daughter liquids with compositions matching those of NWA 8694. This meteorite is a chassignite cumulate containing nakhlitic mesostasis, a direct link between the chassignites and the nakhlites and the association of dunitic to trachytic compositions is reminiscent of terrestrial shield volcanoes. Chassignites and nakhlites were possibly formed when solidification fronts on chamber walls were disrupted, mainly as side eruptions of olivine-charged magmas from the deeper zones, and augite-charged fractionated magmas from nearer the summit of a volcano resembling Piton de la Fournaise on Earth.

We analyzed the C isotopic compositions of 32 unbrecciated ureilites, which represent mantle debris from a now disrupted, C-rich, differentiated body. The δ 13 C values of their C fractions range from −8.48 to +0.11‰. The correlations obtained between δ 13 C, δ 18 O and Δ 17 O values and the compositions of the olivine cores, indicate that the ureilite parent body (UPB) accreted from two reservoirs displaying distinct O and C isotopic compositions. The range of Fe/Mg ratios shown by its mantle was not the result of melting processes involving reduction with C (“smelting”), but was chiefly inherited from the mixing of these two components. Because smelting reactions are pressure-dependent, this result has strong implications for the size of the UPB, and points to a large parent body, at least 690 km in diameter. It demonstrates that C-rich primitive matter distinct from that represented by carbonaceous chondrites was present in some areas of the early inner Solar System, and could have contributed to the growth of the terrestrial planets. We speculate that differentiated, C-rich bodies, or debris produced by their disruption, were an additional source of volatiles during the later accretion stages of the rocky planets, including Earth.

International audience; Fractional crystallization of basalts produces a variety of ultramafic cumulates poor in incompatible elements. Inorder 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 Réunion Island, Indian Ocean).These rocks have a high variability in the abundance of these elements, which is only partially explained by theirproportions of olivines and pyroxenes. Mass balance calculations indicate that≈0.25 to 1 wt% of trapped meltsare required to account for the budget of the highly incompatible element abundances such as U, Rb, Nb orlight Rare Earth Elements (REE). Using our results, we revisited the REE geochemistry of chassignites, a groupletof Martian meteorites. Chassignites are mineralogically, texturally and chemically very similar to the dunitesfrom La Réunion Island, which can be seen as very close terrestrial analogs. The variations of REE abundancesand ratios in Chassigny, one of the three known chassignites, can be explained by inhomogeneous distributionof trapped melts in this meteorite at the scale of the size of the fragments (typicallyb1 g) used for the chemicalanalyses. Using these variations, we deduced the shape of the REE pattern and abundances of the Chassigny par-ent melt.

On February 6, 2016 at 21:07:19 UT, a very bright fireball was seen over the eastern part of Denmark. The weather was cloudy over eastern Denmark, but many people saw the sky light up-even in the heavily illuminated Copenhagen. Two hundred and thirty three reports of the associated sound and light phenomena were received by the Danish fireball network. We have formed a consortium to describe the meteorite and the circumstances of the fall and the results are presented in this paper. The first fragment of the meteorite was found the day after the fall, and in the following weeks, a total of 11 fragments with a total weight of 8982 g were found. The meteorite is an unbrecciated, weakly shocked (S2), ordinary H chondrite of petrologic type 5/6 (Bouvier et al. 2017). The concentration of the cosmogenic radionuclides suggests that the preatmospheric radius was rather small similar to 20 cm. The cosmic ray exposure age of Ejby (83 +/- 11 Ma) is the highest of an H chondrite and the second highest age for an ordinary chondrite. Using the preatmospheric orbit of the Ejby meteoroid (Spurny et al. 2017) locations of the recovered fragments, and wind data from the date of the fall, we have modeled the dark flight (below 18 km) of the fragments. The recovery location of the largest fragment can only be explained if aerodynamic effects during the dark flight phase are included. The recovery location of all other fragments are consistent with the dark flight modeling.

Northwest Africa (NWA) 5958 is a carbonaceous chondrite found in Morocco in 2009. Preliminary chemical and isotopic data leading to its initial classification as C3.0 ungrouped have prompted us to conduct a multi-technique study of this meteorite and present a general description here. The petrography and chemistry of NWA 5958 is most similar to a CM chondrite, with a low degree of aqueous alteration, apparently under oxidizing conditions, and evidence of a second, limited alteration episode manifested by alteration fronts. The oxygen isotopic composition, with $\Delta^{17}$O = -4.3 $\permil$, is more 16O-rich than all CM chondrites, indicating, along with other compositional arguments, a separate parent body of origin. We suggest that NWA 5958 be reclassified as an ungrouped carbonaceous chondrite related to the CM group., Comment: 32 pages, 12 figures

Seeping of methane-rich fluids at submarine cold seeps drives intense microbial activity and precipitation of authigenic carbonates. Some trace elements play an important role in the biogeochemical processes operating at cold seeps, especially as specific enzymatic co-factors related to methanogenesis and the anaerobic oxidation of methane (AOM). However, it is unclear whether microbial trace metal utilization can be traced by the geochemical composition of seep carbonates. In this study, we analyzed a series of authigenic carbonate samples recovered from various seep settings worldwide and report for the first time trace element concentrations for total lipid fractions, combined with biomarker analyses and determination of elemental abundances in associated inorganic mineral phases (carbonate phases, sulfides, organic compounds and detrital fractions). Our results indicate marked enrichments of Co, Ni, Cu, Mo and W in the archaeal and bacterial lipids associated with authigenic carbonates, which can all be ascribed to previously identified enzymatic pathways. In addition to the microbial communities involved in AOM, which most likely control specific lipid-bound enrichments of Co, Ni, Mo and W in seep carbonates, Cu was found to display higher concentrations in the lipid fractions extracted from a few authigenic carbonate samples formed closer to the sediment-water interface, hence possibly related to the presence of aerobic methane-oxidizing bacterial assemblages in the near seafloor environment. While the above mentioned trace metals are relatively enriched in all studied inorganic and organic fractions, the very low W concentrations measured in carbonate phases, combined with their pronounced enrichment in associated lipid fractions and inferred microbial requirement, suggest that tungsten depletion in pore waters could possibly act as a limiting factor on AOM at cold seeps. Finally, two other trace elements (Li and Ti) also displayed particular enrichments in studied lipid fractions, which, despite no reported evidence, could possibly indicate that they are also involved as metalloenzymes in microbial methane oxidation processes at cold seeps.

We show that the bulk of Earth’s water was delivered before the high-energy collision that led to the formation of the Moon., The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Δ17O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Δ17O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post–giant impact additions to Earth. On the basis of this assumption, our data indicate that post–giant impact additions to Earth could have contributed between 5 and 30% of Earth’s water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth’s water was accreted before the giant impact and not later, as often proposed.

International audience; The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in D 17 O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the D 17 O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post-giant impact additions to Earth. On the basis of this assumption, our data indicate that post-giant impact additions to Earth could have contributed between 5 and 30% of Earth's water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth's water was accreted before the giant impact and not later, as often proposed.

The unique achondrite NWA 7325 is an unusual olivine gabbro composed chiefly of calcic plagioclase (An(85-93)), diopsidic pyroxene (En(50.1-54.0) Wo(44.8-49.3) Fs(0.6-1.3)), and forsteritic olivine (Fo(97)). It is Al and Mg-rich and Fe and Na-poor and displays very low concentrations of incompatible trace elements, much below 0.3 x CI abundances for many of them. It is also characterized by huge Eu and Sr anomalies (Eu/Eu* = 65, Sr-n/Ce-n = 240). Although the O isotopic composition of NWA 7325 and some ureilites (those with olivine cores in the range Fo(75)-Fo(88)) are similar, a genetic relationship between them is unlikely due to the Fe-poor composition of NWA 7325. It is almost certainly derived from a distinct planetesimal, not previously sampled by other achondrites. The low Na/Al, Ga/Al, Zn/Al ratios as well as the low K, Rb and Cs shown by NWA 7325, suggest a volatile-depleted parent body. This unique gabbro is demonstrably a cumulate, but the composition of its parental melt cannot be precisely assessed. However, the liquid from which NWA 7325 crystallized would have been very poor in incompatible trace elements (Yb in the range of 0.25-1.5 x CI abundance) with a very large positive Eu anomaly. Such a melt cannot be the product of the early magmatic activity on a small parent body. Instead, we propose that the parental melt to NWA 7325 formed as a consequence of the total melting of an ancient gabbroic lithology, possibly upon impact, in agreement with the systematics of highly siderophile elements and Al-26-Mg-26. Based on recent dating, the crustal material that was parental to NWA 7325 must have been older than 4562.8 Ma, and formed possibly approximate to 4566 Ma ago. If this scenario is correct, NWA 7325 provides evidence of one of the earliest crusts on a differentiated body so far studied. (C) 2015 Elsevier Ltd. All rights reserved.

Cr isotopic compositions have been measured on carbonaceous chondrites (CC): Tafassasset, Paris, Niger I, NWA 5958, NWA 8157 and Jbilet Winselwan. In bulk samples, the 54 Cr/ 52 Cr ratios (expressed as e 54 Cr) range from 0.93 to 1.58 e units. These values are in agreement with values characteristic for distinct petrologic types. Despite this 54 Cr heterogeneity, the variability in the 53 Cr/ 52 Cr ratios (expressed as e 53 Cr) of 0.2 e units and the Mn/Cr ratios is consistent with the previous finding of an isochron in the Mn–Cr evolution diagram. The Mn/Cr ratio in CC corresponds to variable abundances of high-T condensate formed and separated at the beginning of the solar system, thus the canonical 53 Mn/ 55 Mn ratio can be defined. Based on a consistent chronology for U–Pb and Mn–Cr between the earliest objects formed in the solar nebula and the D’Orbigny angrite we define a canonical 53 Mn/ 55 Mn ratio and e 53 Cr i of 6.8 × 10 −6 and −0.177, respectively. The internal Mn/Cr systematics in Tafassasset and Paris were studied by two approaches: leaching technique and mineral separation. Despite variable e 54 Cr values (up to >30 e) linear co-variations were found between e 53 Cr and Mn/Cr ratio. The mineral separates as well as the leachates of Tafassasset fall on a common isochron indicating that (1) cooling of the Tafassasset’s parent body occurred at 4563.5 ± 0.25 Ma, and that (2) 54 Cr is decoupled from the other isotopes even though temperatures >900 °C have been reached during metamorphism. In the case of Paris, the leachates form an alignment with a 53 Mn/ 55 Mn ratio higher than the canonical value. This alignment is not an isochron but rather a mixing line. Based on leachates from various CM and CI, we propose the occurrence of three distinct Cr reservoirs in meteoritic material: PURE54, HIGH53 and LOW53 characterized by a e 53 Cr and e 54 Cr of 0 and 25,000, −2.17 and 8, and 0.5 and −151, respectively. PURE54 has already been described and is carried by highly refractory nano-spinel; HIGH53 is Mn-rich and most probably carried by sulfides in the matrix, whereas LOW53 is characterized by low Mn/Cr ratios and it is sensitive to metamorphism. This component could correspond to mineral phases such as refractory oxides and carbide. Variable mixing proportions of HIGH53 and LOW53 would explain the larger-than-expected uncertainty (MSWD of 5.5) on the CC bulk regression line. A Monte Carlo simulation allows us to evaluate the impact of the dispersion of the initial Cr isotopic ratios (as a function of variable HIGH53). The co-variation of the Mn/Cr ratio and the e 53 Cr defined by the mineral separates from Paris corresponds to an age of 4566.44 +0.66 / −0.75 Ma, while their e 54 Cr still differ by at least 0.42 e. This age is likely to date the segregation of forsteritic olivines (most probably from type I chondrules) from fayalitic olivines (from type II chondrules) and, given the sampling procedure by handpicking of hundreds of grains, corresponds to the average age of chondrule formation.

On March 6, 2016 at 21:36:51 UT, extended areas of Upper Austria, Bavaria (Germany) and the southwestern part of the Czech Republic were illuminated by a very bright bolide. This bolide was recorded by instruments in the Czech part of the European Fireball Network and it enabled complex and precise description of this event including prediction of the impact area. So far six meteorites totaling 1473 g have been found in the predicted area. The first pieces were recovered on March 12, 2016 on a field close to the village of Stubenberg (Bavaria). Stubenberg is a weakly shocked (S3) fragmental breccia consisting of abundant highly recrystallized rock fragments embedded in a clastic matrix. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivine (Fa31.4) and pyroxene (Fs25.4) clearly indicate that Stubenberg is an LL6 chondrite breccia. This is consistent with the data on O, Ti, and Cr isotopes. Stubenberg does not contain solar wind-implanted noble gases. Data on the bulk chemistry, IR spectroscopy, cosmogenic nuclides, and organic components also indicate similarities to other metamorphosed LL chondrites. Noble gas studies reveal that the meteorite has a cosmic ray exposure (CRE) age of 36 ± 3 Ma and that most of the cosmogenic gases were produced in a meteoroid with a radius of at least 35 cm. This is larger than the size of the meteoroid which entered the Earth's atmosphere, which is constrained to

International audience; Volcanism is a substantial process during crustal growth on plane-tary bodies and well documented to have occurred in the early Solar System from the recognition of numerous basaltic meteorites. Considering the ureilite parent body (UPB), the compositions of magmas that formed a potential UPB crust and were complemen-tary to the ultramafic ureilite mantle rocks are poorly constrained. Among the Almahata Sitta meteorites, a unique trachyandesite lava (with an oxygen isotope composition identical to that of common ureilites) documents the presence of volatile-and SiO 2 -rich magmas on the UPB. The magma was extracted at low degrees of disequilib-rium partial melting of the UPB mantle. This trachyandesite extends the range of known ancient volcanic, crust-forming rocks and docu-ments that volcanic rocks, similar in composition to trachyandesites on Earth, also formed on small planetary bodies ∼4.56 billion years ago. It also extends the volcanic activity on the UPB by ∼1 million years (Ma) and thus constrains the time of disruption of the body to later than 6.5 Ma after the formation of Ca–Al-rich inclusions. differentiation | meteorite parent body | achondrites | differentiated

The asteroid 4 Vesta was recently found to have two large impact craters near its south pole exposing subsurface material. Modelling suggested that surface material in the northern hemisphere of Vesta came from a depth of about 20 kilometres whereas the exposed southern material comes from a depth of 60 to 100 kilometres. Large amounts of olivine from the mantle were not seen suggesting that the outer 100 kilometres or so is mainly igneous crust. Here we analyse the data on Vesta and conclude that the crust mantle boundary (or Moho) is deeper than 80 kilometres. © 2014 Macmillan Publishers Limited. All rights reserved.

International audience; Mandler and Elkins-Tanton () recently proposed an upgraded magma ocean model for the differentiation history of the giant asteroid 4 Vesta. They show that a combination of both equilibrium crystallization and fractional crystallization processes can reproduce the major element compositions of eucritic melts and broadly the range of mineral compositions observed in diogenites. They assert that their model accounts for all the howardites, eucrites, and diogenites (HEDs), and use it to predict the crustal thickness and the proportions of the various lithologies. Here, we show that their model fails to explain the trace element diversity of the diogenites, contrary to their claim. The diversity of the heavy REE enrichment exhibited by the orthopyroxenes in diogenites is inconsistent with crystallization of these cumulates in either shallow magma chambers replenished by melts from a magma ocean or in a magma ocean. Thus, proportions of the various HED lithologies and the crustal thickness predicted from this model are not necessarily valid.

International audience; Oxygen isotope measurements of a suite of 22 diogenites demonstrate that they have a restricted range of Δ17O values: View the MathML source−0.246±0.014(2σ). These results indicate that the diogenites form a single population consistent with a single parent body source, rather than multiple sources as has recently been suggested. Our previously published analysis of eucrites and cumulate eucrites (n=34n=34) give very similar results to the diogenites, with View the MathML sourceΔO17=−0.241±0.016‰(2σ) and confirm that diogenites and eucrites are from the same parent asteroid. The isotopic homogeneity displayed by diogenites, eucrites and cumulate eucrites, provides strong evidence for an early large-scale melting event on the HED parent body, possibly resulting in the formation of a magma ocean. The paradox, whereby diogenites show isotopic evidence in favor of global melting, but also geochemical features indicative of late stage interaction with eucritic crust, may reflect a rapid transition from global to serial magmatism on their parent body. The fact that all the lithologically varied HED units have an isotopically homogeneous composition supports the proposal that they are derived from a single, large, diverse asteroid, most likely 4 Vesta. The recent suggestion that the HEDs are not from Vesta, but instead represent material from the same asteroidal source as the main-group pallasites and IIIAB irons can be excluded by our oxygen isotope data.

International audience; Core formation is the main differentiation event in the history of a planet. However, the chemical composition of planetary cores and the physicochemical conditions prevailing during core formation remain poorly understood. The asteroid 4-Vesta is the smallest extant planetary body known to have differentiated a metallic core. Howardite, Eucrite, Diogenite (HED) meteorites, which are thought to sample 4-Vesta, provide us with an opportunity to study core formation in planetary embryos. Partitioning of elements between the core and mantle of a planet fractionates their isotopes according to formation conditions. One such element, silicon, shows large isotopic fractionation between metal and silicate, and its partitioning into a metallic core is only possible under very distinctive conditions of pressure, oxygen fugacity and temperature. Therefore, the silicon isotope system is a powerful tracer with which to study core formation in planetary bodies. Here we show through high-precision measurement of Si stable isotopes that HED meteorites are significantly enriched in the heavier isotopes compared to chondrites. This is consistent with the core of 4-Vesta containing at least 1 wt% of Si, which in turn suggests that 4-Vesta's differentiation occurred under more reducing conditions (ΔIW∼−4) than those previously suggested from analysis of the distribution of moderately siderophile elements in HEDs.

Three-dimensional simulations of the global evolution of asteroid 4 Vesta under two overlapping planet-scale collisions closely reproduce its observed shape; but expected large areas of olivine-rich rocks and pure diogenites are not observed on the surface, possibly implying that the outer ∼100 km is composed mainly of a basaltic crust (eucrites) with ultramafic intrusions (diogenites). NASA's Dawn mission to the asteroid 4 Vesta revealed some unexpected surface features, including a huge crater, named Veneneia, underlying the even larger crater, Rheasilvia, that was formed about a billion years ago. The juxtaposition of these two impact basins provides an opportunity to develop an accurate model of Vesta's topography. Martin Jutzi et al. report three-dimensional simulations of Vesta's global evolution through two successive planet-scale collisions. Their model closely reproduces Vesta's observed shape and provides a firm basis for the interpretation of the surface mineralogy and geology of Vesta, and by extension, other small Solar System bodies. Asteroid 4 Vesta seems to be a major intact protoplanet, with a surface composition similar to that of the HED (howardite–eucrite–diogenite) meteorites1,2,3,4. The southern hemisphere is dominated by a giant impact scar5, but previous impact models6,7,8 have failed to reproduce the observed topography. The recent discovery that Vesta’s southern hemisphere is dominated by two overlapping basins9 provides an opportunity to model Vesta’s topography more accurately. Here we report three-dimensional simulations of Vesta’s global evolution under two overlapping planet-scale collisions. We closely reproduce its observed shape, and provide maps of impact excavation and ejecta deposition. Spiral patterns observed in the younger basin Rheasilvia9, about one billion years old10, are attributed to Coriolis forces during crater collapse. Surface materials exposed in the north come from a depth of about 20 kilometres, according to our models, whereas materials exposed inside the southern double-excavation come from depths of about 60–100 kilometres. If Vesta began as a layered, completely differentiated protoplanet, then our model predicts large areas of pure diogenites and olivine-rich rocks. These are not seen11,12,13, possibly implying that the outer 100 kilometres or so of Vesta is composed mainly of a basaltic crust (eucrites) with ultramafic intrusions (diogenites).

International audience; The Northwest Africa (NWA) 1664 and 1769 howardites contain fragments of low-Mg lithologies. These clasts consist of plagioclase, Fe-rich pyroxenes (high-Ca pyroxene and an Fe-rich pigeonite (or pyroxferroite) partially to totally converted to a silica-fayalite-hedenbergite symplectite), K-Ba-feldspars (hyalophane), silica, troilite, phosphates (merrillite and apatite), ilmenite, baddeleyite and zircon. Textural considerations and phase compositions show that these clasts cannot be unrepre- sentative debris of mesostasis-rich areas from eucrites, but are instead remnants of evolved rocks. The occurrence of hyalo- phane and the modal abundances of phosphates in the largest of them suggest that their source rocks were much more K- and P-rich than regular HEDs. Moreover, the rare earth element abundances of the pyroxenes indicate that their parental melts were rich in incompatible trace elements (possibly at the level of 100 ﰀ CI or much higher for heavy REEs), with variable negative Eu anomalies. Although, their petrogenesis is uncertain, they demonstrate that magmatic activity on Vesta has been able to generate a diversity of rocks greater than generally thought, and local lithologies with possible KREEP affinities.

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.\ud 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.\ud The homogeneity of the Δ17O values obtained for main-group aubrite falls [Δ17O = +0.009 ± 0.010‰ (2σ)] 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.

International audience; Ureilites are among the most common achondrites and are widely believed to sample the mantle of a single, now-disrupted, C-rich body. We analyzed 17 ureilite samples, mostly Antarctic finds, and determined their incompatible trace element abundances. In order to remove or reduce the terrestrial contamination, which is marked among Antarctic ureilites by light-REE enrichment, we leached the powdered samples with nitric acid. The residues display consistent abundances, which strongly resemble those of the pristine rocks. All the analyzed samples display light-REE depletions, negative Eu anomalies, low (Sr/Eu∗)n, and (Zr/Eu∗)n ratios which are correlated. Two groups of ureilites (groups A and B) are defined. Compared to group A, group B ureilites, which are the less numerous, tend to be richer in heavy REEs, more light-REE depleted, and display among the deepest Eu anomalies. In addition, olivine cores in group B ureilites tend to be more forsteritic (Mg# = 81.9-95.2) than in group A ureilites (Mg# = 74.7-86.1). Incompatible trace element systematics supports the view that ureilites are mantle restites. REE modelling suggests that their precursors were rather REE-rich (ca. 1.8-2 x CI) and contained a phosphate phase, possibly merrillite. The REE abundances in ureilites can be explained if at least two distinct types of magmas were removed successively from their precursors: aluminous and alkali-rich melts as exemplified by the Almahata Sitta trachyandesite (ALM-A), and Al and alkali-poor melts produced after the exhaustion of plagioclase from the source. Partial melting was near fractional (group B ureilites, which are probably among the least residual samples) to dynamic with melt porosities that did not exceed a couple of percent (group A ureilites). The ureilite parent body (UPB) was almost certainly covered by a crust formed chiefly from the extrusion products of the aluminous and alkali-rich magmas. It is currently uncertain whether the Al and alkali-poor melts produced during the second phase of melting reached the surface of the body. The fact that initial silicate melting of ureilitic precursors would have produced relatively low density liquids capable of forming an external crust to the UPB casts doubt on models that invoke chondritic outer layers to achondritic asteroids.

International audience; Northwest Africa 5790, the latest nakhlite find, is composed of 58 vol.% augite, 6% olivine and 36% vitrophyric intercumulus material. Its petrology is comparable to previously discovered nakhlites but with key differences: (1) Augite cores display an unusual zoning between Mg# 54 and 60; (2) Olivine macrocrysts have a primary Fe-rich core composition (Mg#= 35); (3) the modal proportion of mesostasis is the highest ever described in a nakhlite; (4) It is the most magnetite-rich nakhlite, together with MIL 03346, and exhibits the least anisotropic fabric. Complex primary zoning in cumulus augite indicates resorption due to complex processes such as remobilization of former cumulates in a new magma batch. Textural relationships indicate unambiguously that olivine was growing around resorbed augite, and that olivine growth was continuous while pyroxene growth resumed at a final stage. Olivine core compositions (Mg#= 35) are out of equilibrium with the augite core compositions (Mg# 60-63) and with the previously inferred nakhlite parental magma (Mg#= 29). The presence of oscillatory zoning in olivine and augite precludes subsolidus diffusion that could have modified olivine compositions. NWA 5790 evidences at least two magma batches before eruption, with the implication that melt in equilibrium with augite cores was never in contact with olivine. Iddingsite is absent.

Thulium is a heavy rare earth element (REE) whose geochemical behavior is intermediate between Er and Yb, and that is not expected to be decoupled from these elements during accretion of planetary bodies and geological processes. However, irregularities in REE volatilities at higher temperature could have decoupled the REEs relative to one another during the early stages of condensation of the solar nebula. Indeed, positive Tm anomalies are found in some refractory inclusions from carbonaceous chondrites, and it is possible that large scale nebular reservoirs displaying positive or negative Tm anomalies were formed during the early history of the solar system. We analyzed a series of meteorites and terrestrial rocks in order to evaluate the existence of Tm anomalies in planetary materials. Relative to CIs (Ivuna-type carbonaceous chondrites), carbonaceous chondrites display unresolved or positive Tm anomalies, while most of the noncarbonaceous chondrites show slightly negative Tm anomalies. Quantification of these anomalies in terrestrial samples is complicated when samples display fractionated heavy REE patterns. Taking this effect into account, we show that the Earth, Mars, Vesta, the aubrite and ureilite parent bodies display small negative anomalies (Tm/Tm* approximate to 0.975), very similar to those found in ordinary and enstatite chondrites. We suggest that a slight negative Tm anomaly relative to CI is a widespread feature of the materials from the inner solar system. This finding suggests that CI chondrites may not be appropriate for normalizing REE abundances of most planetary materials as they may be enriched in a high-temperature refractory component with non-solar composition. The presence of Tm anomalies at a bulk planetary scale is, to this day, the strongest piece of evidence that refractory lithophile elements are not present in constant CI proportions in planetary bodies. (C) 2015 Elsevier Ltd. All rights reserved.

International audience; Over the past decades, rare earth elements (REE) and their radioactive isotopes have received tremendous attention in sedimentary geochemistry, as tracers for the geological history of the continental crust and provenance studies. In this study, we report on elemental concentrations and neodymium (Nd) isotopic compositions for a large number of sediments collected near the mouth of rivers worldwide, including some of the world's major rivers. Sediments were leached for removal of non-detrital components, and both clay and silt fractions were retained for separate geochemical analyses. Our aim was to re-examine, at the scale of a large systematic survey, whether or not REE and Nd isotopes could be fractionated during Earth surface processes. Our results confirmed earlier assumptions that river sediments do not generally exhibit any significant grain-size dependent Nd isotopic variability. Most sediments from rivers draining old cratonic areas, sedimentary systems and volcanic provinces displayed similar Nd isotopic signatures in both clay and silt fractions, with Delta epsilon Nd(clay-silt) < vertical bar 1 vertical bar. A subtle decoupling of Nd isotopes between clays and silts was identified however in a few major river systems (e.g. Nile, Mississippi, Fraser), with clays being systematically shifted towards more radiogenic values. This observation suggests that preferential weathering of volcanic and/or sedimentary rocks relative to more resistant lithologies may occur in river basins, possibly leading locally to Nd isotopic decoupling between different size fractions. Except for volcanogenic sediments, silt fractions generally displayed homogeneous REE concentrations, exhibiting relatively flat shale-normalized patterns. However, clay fractions were almost systematically characterized by a progressive enrichment from the heavy to the light REE and a positive europium (Eu) anomaly. In agreement with results from previous soil investigations, the observed REE fractionation between clays and silts is probably best explained by preferential alteration of feldspars and/or accessory mineral phases. Importantly, this finding clearly indicates that silicate weathering can lead to decoupling of REE between different grain-size fractions, with implications for sediment provenance studies. Finally, we propose a set of values for a World River Average Clay (WRAC) and Average Silt (WRAS), which provide new estimates for the average composition of the weathered and eroded upper continental crust, respectively, and could be used for future comparison purposes. (C) 2015 Elsevier Ltd. All rights reserved.

We report on the bulk chemical composition, petrology, oxygen isotopic composition, trace element composition of silicates, and degree of self-irradiation damage on zircon grains of the eucrite Northwest Africa (NWA) 5073 to constrain its formation and postcrystallization thermal history, and to discuss their implications for the geologic history of its parent body. This unequilibrated and unbrecciated meteorite is a new member of the rare Stannern-trend eucrites. It is mainly composed of elongated, zoned pyroxene phenocrysts up to 1.2 cm, plagioclase laths up to 0.3 cm in length, and is rich in mesostasis. The latter contains zircon grains up to 30 μm in diameter, metal, sulfide, tridymite, and Ca-phosphates. Textural observations and silicate compositions, coupled with the occurrence of extraordinary Fe-rich olivine veins that are restricted to large pyroxene laths, indicate that NWA 5073 underwent a complex thermal history. This is also supported by the annealed state of zircon grains inferred from μ-Raman spectroscopic measurements along with U and Th data obtained by electron probe microanalyses.

We studied the mineralogy, petrology, and bulk, trace element, oxygen, and noble gas isotopic compositions of a composite clast approximately 20 mm in diameter discovered in the Larkman Nunatak (LAR) 04316 aubrite regolith breccia. The clast consists of two lithologies: One is a quench-textured intergrowth of troilite with spottily zoned metallic Fe,Ni which forms a dendritic or cellular structure. The approximately 30 μm spacings between the Fe,Ni arms yield an estimated cooling rate of this lithology of approximately 25–30 °C s−1. The other is a quench-textured enstatite-forsterite-diopside-glass vitrophyre lithology. The composition of the clast suggests that it formed at an exceptionally high degree of partial melting, perhaps approaching complete melting, and that the melts from which the composite clast crystallized were quenched from a temperature of approximately 1380–1400 °C at a rate of approximately 25–30 °C s−1. The association of the two lithologies in a composite clast allows, for the first time, an estimation of the cooling rate of a silicate vitrophyre in an aubrite of approximately 25–30 °C s−1. While we cannot completely rule out an impact origin of the clast, we present what we consider is very strong evidence that this composite clast is one of the elusive pyroclasts produced during pyroclastic volcanism on the aubrite parent body (Wilson and Keil 1991). We further suggest that this clast was not ejected into space but retained on the aubrite parent body by virtue of the relatively large size of the clast of approximately 20 mm. Our modeling, taking into account the size of the clast, suggests that the aubrite parent body must have been between approximately 40 and 100 km in diameter, and that the melt from which the clast crystallized must have contained an estimated maximum range of allowed volatile mass fractions between approximately 500 and approximately 4500 ppm.

The eucritic meteorites are basaltic rocks that originate from the upper part of the crust of some small bodies as exemplified possibly by asteroid 4-Vesta. A few eucrites appear to have been modified by different degrees of a late stage alteration process that caused significant variations in mineralogy. Three distinct alteration stages are identified: 1/ Fe-enrichment along the cracks that cross cut the pyroxene crystals ("Fe-metasomatism"); secondary olivine and minute amounts of troilite are found only occasionally in cracks at this stage; 2/ deposits of Fe-rich olivine (Fa64-86) and minor amounts of troilite are frequent inside the cracks; sporadic secondary Ca-rich plagioclase (An97-98) is associated with the fayalitic olivine; 3/ at this stage, the Fe-enrichment of the pyroxene is accompanied by a marked Al-depletion; moreover, secondary Ca-rich plagioclase is more frequent and partly fills some cracks or rims of the primary plagioclase crystals. The composition of the secondary phases on one hand, the lack of incompatible trace element enrichment in the metasomatized pyroxenes on the other hand, rule out a silicate melt as the metasomatic agent. Although no hydrous phase has been yet identified in the studied samples, aqueous fluids are plausible candidates for explaining the deposits of ferroan olivine and anorthitic plagioclase inside the fractures of the studied unequilibrated eucrites.

International audience; 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.

Major and trace element abundances were determined on powders prepared from four distinct chips from ALH84001 in order to constrain the bulk rock composition, and to assess the trace element abundances of orthopyroxen es and phosphates. Our new determinations were used to evaluate the compositio n of the parental melt of this stone. An unrealistic light-REE enriched parental melt is calculated from the composition of the orthopyroxene and relevant equilibrium partition co efficients. The involvement of a small amount of trapped melt and subsolidus reequilibrati ons between orthopyroxene and the interstitial phases can account for this discrepanc y. A parental melt that displays a trace element pattern (REE, Zr, and Hf) that closely res embles enriched shergottites such as Zagami or Los Angeles is calculated if these effect s are taken into account. These results suggest that some shergottitic melts were already e rupted on Mars during the Noachian. 1. Introduction

International audience; The howardite–eucrite–diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired. The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.

The howardite-eucrite-diogenite (HED) clan is a group of meteorites that probably originate from the asteroid Vesta. Some of them are complex breccias that contain impact glasses whose compositions mirror that of their source regions. Some K-rich impact glasses (up to 2 wt% K2O) suggest that in addition to basalts and ultramafic cumulates, K-rich rocks are exposed on Vesta's surface. One K-rich glass (up to 6 wt% K2O), with a felsic composition, provides the first evidence of highly differentiated K-rich rocks on a large asteroid. They can be compared to the rare lunar granites and suggest that magmas generated in a large asteroid are more diverse than previously thought.

We report on the major and trace element abundances of 18 diogenites, and O-isotopes for 3 of them. Our analyses extend significantly the diogenite compositional range, both in respect of Mg-rich (e.g., Meteorite Hills [MET] 00425, MgO = 31.5 wt%) and Mg-poor varieties (e.g., Dhofar 700, MgO = 23 wt%). The wide ranges of siderophile and chalcophile element abundances are well explained by the presence of inhomogeneously distributed sulfide or metal grains within the analyzed chips. The behavior of incompatible elements in diogenites is more complex, as exemplified by the diversity of their REE patterns. Apart from a few diogenite samples that contain minute amounts of phosphate, and whose incompatible element abundances are unlike the orthopyroxene ones, the range of incompatible element abundances, and particularly the range of Dy/Yb ratios in diogenites is best explained by the diversity of their parental melts. We estimate that the FeO/MgO ratios of the diogenite parental melts range from about 1.4 to 3.5 and therefore largely overlap the values obtained for non-cumulate eucrites. Our results rule out the often accepted view that all the diogenites formed from parental melts more primitive than eucrites during the crystallization of a magma ocean. Instead, they point to a more complex history, and suggest that diogenites were derived from liquids produced by the remelting of cumulates formed from the magma ocean.

International audience; We report on the petrology of a new eucrite belonging to the Stannern trend and discuss the origin of this trend. The eucrite Northwest Africa 4523 (NWA 4523) is an equilibrated eucrite consisting of dark clasts embedded in a fine-grained crystallized matrix. Two types of clasts have been observed: medium-grained ophitic/subophitic clasts, and very fine-grained clasts. Despite textural differences, the clasts display the same mineralogy, in particular the same kind of pyroxenes with pigeonitic cores containing sparse exsolution lamellae, and augitic rims, zoned plagioclases and the occurrence of K-feldspar. The major and trace element abundances of a large medium-grained clast are very similar to Stannern or Bouvante. The Stannern trend eucrites are characterized by high incompatible trace element abundances. Their trace element patterns normalized to a representative Main Group eucrite, exhibit significant Eu, Sr and Be negative anomalies. In this paper, we show that contamination of Main Group eucritic magmas by melts derived by partial melting of the asteroid's crust can successfully explain both the high incompatible trace elements concentrations and the distinctive Eu, Sr, Be anomalies shown by the Stannern trend eucrites. This model is in agreement with the view that Stannern and some Main Group-Nuevo Laredo trend eucrites have been contemporaneously erupted, and with the probable assumption that Stannern trend eucrites formed rather late in the history of the 4-Vesta's crust.

Evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in Solar System history. These bodies should have had well-developed olivine-rich mantles and consequentially such materials ought to be abundant both as asteroids and meteorites, which they are not. To investigate this "Great Dunite Shortage" we have undertaken a geochemical and oxygen isotope study of main-group pallasites and dunitic rocks from mesosiderites.Oxygen isotope analysis of 24 main-group pallasites (103 replicates) yielded a mean Delta17O value of -0.187 ± 0.0160/00 (2sigma), which is fully resolved from the HED Delta17O value of -0.246 ± 0.014 (2sigma) obtained in our earlier study and demonstrates that both groups represent distinct populations and were derived from separate parent bodies. Our results show no evidence for Delta17O bimodality within the main-group pallasites, as suggested by a number of previous studies.Olivine-rich materials from the Vaca Muerta, Mount Padbury and Lamont mesosiderites, and from two related dunites (NWA 2968 and NWA 3329), have Delta17O values within error of the mesosiderite average. This indicates that these olivine-rich materials are co-genetic with other mesosiderite clasts and are not fragments from an isotopically distinct pallasite-like impactor. Despite its extreme lithologic diversity the mesosiderite parent body was essentially homogeneous with respect to Delta17O, a feature best explained by an early phase of large-scale melting (magma ocean), followed by prolonged igneous differentiation.Based on the results of magma ocean modeling studies, we infer that Mg-rich olivines in mesosiderites formed as cumulates in high-level chambers and do not represent samples of the underlying mantle. By analogy, recently documented Mg-rich olivines in howardites may have a similar origin.Although the Dawn mission did not detect mesosiderite-like material on Vesta, evidence linking the mesosiderites and HEDs includes: (i) their nearly identical oxygen isotope compositions; (ii) the presence in both of coarse-grained Mg-rich olivines; (iii) both have synchronous Lu-Hf and Mn-Cr ages; (iv) there are compositional similarities between the metal in both; and (v) mesosiderite-like material has been identified in a howardite breccia. The source of the mesosiderites remains an outstanding question in meteorite science.The underrepresentation of olivine-rich materials amongst both asteroids and meteorites results from a range of factors. However, evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early, catastrophic destruction of planetesimals in the terrestrial planet-forming region and the subsequent preferential loss of their olivine-rich mantles. Evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in Solar System history. These bodies should have had well-developed olivine-rich mantles andconsequentially such materials ought to be abundant both as asteroids and meteorites, which they are not. To investigate this "Great DuniteShortage" we have undertaken a geochemical and oxygen isotope study of main-group pallasites and dunitic rocks from mesosiderites.Oxygen isotope analysis of 24 main-group pallasites (103 replicates) yielded a mean Δ17O value of -0.187 ±0.016‰ (2σ), which is fully resolved from the HED Δ17O value of -0.246 ± 0.014 (2σ) obtained in our earlier study and demonstrates that both groups represent distinct populations and were derived from separate parent bodies. Our results show no evidence for Δ17O bimodality within themain-group pallasites, as suggested by a number of previous studies.Olivine-rich materials from the Vaca Muerta, Mount Padbury and Lamont mesosiderites, and from two related dunites (NWA 2968 and NWA 3329), have Δ17O values within error of the mesosiderite average. This indicates that these olivine-rich materials are co-genetic with other mesosiderite clasts and are not fragments from anisotopically distinct pallasite-like impactor. Despite its extreme lithologic diversity the mesosiderite parent body was essentially homogeneous with respect to Δ17O, a feature best explained by an early phase of large-scale melting (magma ocean), followed by prolonged igneous differentiation. Based on the results of magma ocean modeling studies, we infer that Mg-rich olivines in mesosiderites formed as cumulates in high-levelchambers and do not represent samples of the underlying mantle. By analogy, recently documented Mg-rich olivines in howardites may have a similar origin. Although the Dawn mission did not detect mesosiderite-like material on Vesta, evidence linking the mesosiderites and HEDs includes: (i) theirnearly identical oxygen isotope compositions; (ii) the presence in both of coarse-grained Mg-rich olivines; (iii) both have synchronous Lu-Hf and Mn-Cr ages; (iv) there are compositional similarities between the metal in both; and (v) mesosiderite-like material has been identified in a howardite breccia. The source of the mesosiderites remains an outstanding question in meteorite science. The underrepresentation of olivine-rich materials amongst both asteroidsand meteorites results from a range of factors. However, evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early, catastrophic destruction ofplanetesimals in the terrestrial planet-forming region and the subsequent preferential loss of their olivine-rich mantles.

International audience; We performed a petrological and geochemical study of an olivine diogenite, Northwest Africa (NWA) 5480. NWA 5480 is a crystalline stone, but shows a heterogeneous texture. Olivine aggregates and grains of olivine and chromite display resorption textures set in a crystalline pyroxene matrix. Large olivine aggregates are penetrated by pyroxene matrix. Flow textures are observed near olivine aggregates. Olivine, chromite, and pyroxene show minor chemical zoning, implying relatively rapid cooling. NWA 5480 contains a significant amount of platinum group elements with chondritic relative proportions. All this evidence supports that NWA 5480 is an impact-melt breccia from a target composed of olivine and pyroxene-rich lithologies. Such impact melt would have formed by melting crustal materials, possibly during one of the impacts that formed the South Pole basins on Vesta.

International audience; Ureilites displays  56 Fe values higher than average chondrite. 29-Segregation of Fe-sulfide melts explains the high  56 Fe values in ureilites. 30-Formation of a core can begin at very low degrees of melting through the circulation of a Fe-S melt 31 through a silicate mantle. 32 33 Earth and Planetary Science Letters, in press (11/3/15). 34 2 35 Abstract 36 37 Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated asteroid rich in carbon. They provide a unique opportunity to study the differentiation 39 processes of such a body. We analyzed the iron isotopic compositions of 30 samples from the Ureilite 40 Parent Body (UPB) including 29 unbrecciated ureilites and one ureilitic trachyandesite (ALM-A) 41 which is at present the sole large crustal sample of the UPB. The  56 Fe of the whole rocks fall within a 42 restricted range, from 0.01 to 0.11‰, with an average of +0.056 ± 0.008 ‰, which is significantly 43 higher than that of chondrites. We show that this difference can be ascribed to the segregation of S-44 rich metallic melts at low degrees of melting at a temperature close to the Fe-FeS eutectic, and 45 certainly before the onset of the melting of the silicates (< 1100 °C), in agreement with the marked S 46 depletions, and the siderophile element abundances of the ureilites. These results point to an efficient 47 segregation of S-rich metallic melts during the differentiation of small terrestrial bodies. 48 49

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.

Ion-microprobe was used to measure Li abundances and isotopic compositions in pyroxenes from three Martian meteorites belonging to the nakhlite family. The profiles performed across augite crystals from Northwest Africa 817 show a large isotopic zoning from crystal cores (delta Li-7 similar to 0 parts per thousand) to rims (delta Li-7 similar to +20 parts per thousand) while Li abundances are almost constant (similar to 9.2 mu g/g). Unlike NWA 817, the pyroxene studied in the Miller Range 03346 nakhlite shows a zoning in Li abundance, with concentrations increasing from similar to 2.5 mu g/g in the core to similar to 9 mu g/ g in the rim. The augite rim (delta Li-7 = +7 parts per thousand) is slightly enriched in Li-7 with regard to the core (delta Li-7 = +4 parts per thousand), but most of the isotopic variations observed occur at an intermediate position along the profile, where 67 Li falls down to similar to-11 parts per thousand. In the case of Nakhla, Li concentrations in augite increase from cores (similar to 3.5 mu g/g) to rims (similar to 6.5 mu g/g), while the delta Li-7 variation is restricted (i.e., between delta Li-7 = +6.0 and +12.6 parts per thousand). For the three meteorites the Li abundances were also measured in the groundmass, which was found to be enriched in lithium (similar to 10 mu g/g). Conventional magmatic and post-magmatic processes such as alteration and fractional crystallization, fail to explain the dataset obtained on nakhlites. Degassing processes, which were previously proposed to explain the Li distribution in shergottite crystals, cannot result in the strong decoupling between Li abundances and isotopic composition observed in nakhlites. We suggest that the original magmatic Li distributions (concentrations and isotopic compositions) in nakhtites have been modified by diffusion of Li from the Li-rich groundmass towards the pyroxene crystals during sub-solidus cooling. Diffusion appears to have been efficient for NWA 817 and MIL 03346 but. apparently, did not produce a significant migration of Li in Nakhla, possibly because of the lower abundance of groundmass in the latter. Diffusion induced Li redistributions may also affect terrestrial porphyric rocks but very specific cooling rates are required to quench the diffusion profiles as observed in two of the present nakhlites. (c) 2006 Elsevier Inc. All rights reserved.

We report noble gas data for the second chassignite, Northwest Africa (NWA) 2737, which was recently found in the Moroccan desert. The cosmic ray exposure (CRE) age based on cosmogenic 3He, 21Ne, and 38Ar around 10-11 Ma is comparable to the CRE ages of Chassigny and the nakhlites and indicates ejection of meteorites belonging to these two families during a discrete event, or a suite of discrete events having occurred in a restricted interval of time. In contrast, U-Th/He and K/Ar ages