Johan Villeneuve

@article{Piralla_etal2023,

title = {A unified chronology of dust formation in the early solar system},

author = {M. Piralla and J. Villeneuve and N. Schnuriger and D. V. Bekaert and Y. Marrocchi},

doi = {10.1016/j.icarus.2023.115427},

year  = {2023},

date = {2023-01-01},

urldate = {2023-01-01},

journal = {Icarus},

volume = {394},

pages = {115427},

abstract = {The chronology of dust formation in the early solar system remains controversial. Chondrules are the most abundant high-temperature objects formed during the evolution of the circumsolar disk. Considering chondrule formation, absolute lead‑lead (Pb--Pb) ages and aluminum‑magnesium (26Al--26Mg) ages relative to calcium‑aluminum-rich inclusions (CAIs) provide inconsistent chronologies, with Pb--Pb ages showing early and protracted chondrule formation episodes whereas 26Al--26Mg ages suggest that chondrule production was delayed by \>1.5 Ma. Here, we develop a new method to precisely determine in situ 26Al--26Mg ages of spinelbearing chondrules, which are not affected by secondary asteroidal processes. Our data demonstrate that 26Al--26Mg chondrule formation ages are actually 1 Ma older than previously thought and extend over the entire lifetime of the disk. This shift in chondrule formation ages relative to CAIs, however, is not sufficient to reconcilethe Pb--Pb and 26Al--26Mg chronologies of chondrule and achondrite formation. Thus, either chondrules’Pb--Pb ages and volcanic achondrites’ 26Al--26Mg ages are incorrect or the age of CAIs should be reevaluated at 4,568.7 Ma to ensure consistency between chronometers. We favor the second hypothesis, given that (i) thecanonical age of CAIs was determined using only 4 specimens and (ii) older ages of 4,568.2 Ma have also been measured. We show that the adoption of 4,568.7 Ma as the new canonical age of CAIs and the use of our new spinel-derived 26Al--26Mg ages enable reconciling the Pb--Pb and 26Al--26Mg ages of chondrules and achondrites.This new chronology implies the existence of a 0.7--1 Ma gap between the formation of refractory inclusions and chondrules, and supports the homogeneous distribution of 26Al in the circumsolar disk.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bouilhol_etal2022,

title = {Decoupling of inorganic and organic carbon during slab mantle devolatilisation},

author = {P. Bouilhol and B. Debret and E. Inglis and M. Warembourg and T. Grocolas and T. Rigaudier and J. Villeneuve and K. W. Burton},

doi = {10.1038/s41467-022-27970-0},

year  = {2022},

date = {2022-01-01},

journal = {Nature Communications},

volume = {13},

number = {308},

abstract = {Serpentinites are an important sink for both inorganic and organic carbon, and their behavior during subduction is thought to play a fundamental role in the global cycling of carbon. Here we show that fluid-derived veins are preserved within the Zermatt-Saas ultra-high pressure serpentinites providing key evidence for carbonate mobility during serpentinite devolatilisation. We show through the O, C, and Sr isotope analyses of vein minerals and the host serpentinites that about 90% of the meta-serpentinite inorganic carbon is remobilized during slab devolatilisation. In contrast, graphite-like carbonaceous compounds remain trapped within the host rock as inclusions within metamorphic olivine while the bulk elemental and isotope composition of organic carbon remains relatively unchanged during the subduction process. This shows a decoupling behavior of carbon during serpentinite dehydration in subduction zones. This process will therefore facilitate the transfer of inorganic carbon to the mantle wedge and the preferential slab sequestration of organic carbon en route to the deep mantle.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marrocchi_etal2022,

title = {Isotopic evidence for two chondrule generations in CR chondrites and their relationships to other carbonaceous chondrites},

author = {Y. Marrocchi and M. Piralla and M. Regnault and V. Batanova and J. Villeneuve and E. Jacquet},

doi = {10.1016/j.epsl.2022.117683},

year  = {2022},

date = {2022-01-01},

journal = {Earth and Planetary Science Letters},

volume = {593},

pages = {117683},

abstract = {Among primitive meteorites, CR chondrites have peculiar isotopic compositions, the origin of which is uncertain and may have involved contributions from primordial molecular cloud material or the chondrites’ formation and agglomeration late during the evolution of the protoplanetary disk. Here, we report a comprehensive textural and isotopic characterization of type I CR chondrules and provide new insights on their formation conditions. We find that two chondrule populations characterized bydifferent sizes and oxygen isotopic compositions co-exist in CR chondrites. The typically larger, 16O-poor (17O \> -4) chondrules (type I-CR chondrules) appear to have formed late out of a CR reservoir already populated by typically smaller, 16O-rich (17O \< -4) chondrules (type I-CO chondrules). Before formation of type I-CR chondrules, the CR reservoir was likely dominated by CI-like dust, in line with the proximity of CR with CI chondrites for many isotopic ratios. The CR reservoir thus may have largely belonged to the continuum shown by other carbonaceous chondrites, although some isotopic ratios maintain some originality and suggest isotopic variation of CI-like dust in the outer disk. Combined with literature data,our data (i) demonstrates that recycling processes are responsible for the singular compositions of CR chondrites and their chondrules for isotopic systems with drastically different geochemical behaviors (O, Cr, Te) and (ii) support the homogeneous distribution of 26Al throughout the protoplanetary disk.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Morin_etal2022,

title = {16O-rich anhydrous silicates in CI chondrites: Implications for the nature and dynamics of dust in the solar accretion disk},

author = {G. L. F. Morin and Y. Marrocchi and J. Villeneuve and E. Jacquet},

doi = {10.1016/j.gca.2022.06.017},

year  = {2022},

date = {2022-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {332},

pages = {203--219},

abstract = {CI chondrites have nonvolatile chemical compositions closely resembling that of the Sun’s photosphere and are thus considered to have the most primitive compositions of all known solar system materials. They have, however, experienced pervasive parent-body alteration processes that transformed their primary constituents, obscuring the nature and origin of primordial CI dust. We used in-situ quantitative microprobe and secondary ion mass spectrometry techniques to characterize the chemistry and oxygen isotopic compositions of anhydrous silicates in two sections of the CI chondrites Ivuna and Alais, which contain higher abundances of those than other CI samples. These silicates are Mg-rich olivine and low-Ca pyroxene crystals mostly occurring as aggregates within sub-mm Fe-rich clasts. Our data reveal mass-independent oxygen isotopic variations with D17O values ranging from -23.63 to -0.57texttenthousand, representing the first evidence of extremely 16O-rich (D17O \< -20texttenthousand) olivine and pyroxene grains in CI chondrites. Two of these olivines are characterized by MnO/FeO textasciitilde 1,typical of low-iron, Mn-enriched silicates commonly observed in amoeboid olivine aggregates. Other anhydrous silicate grains have D17O values ranging from -6 to 0texttenthousand, probably representing chondrule fragments. Combined, these results indicate that chondrule and refractory inclusion material were incorporated into the CI parent body(ies). This conclusion is consistent with recent models showing that refractory inclusions could have formed and/or been transported at larger heliocentric distances than previously thought during the concomitant injection of material from the molecular cloud and outward extension of the disk by viscous spreading. The CI chondrules are presumably of local origin, with their isotopic systematics suggesting an affinity with the CR clan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Regnault_etal2022,

title = {Oxygen isotope systematics of chondrules in Rumuruti chondrites : Formation conditions and genetic link with ordinary chondrites},

author = {M. Regnault and Y. Marrocchi and M. Piralla and J. Villeneuve and V. Batanova and N. Schnuriger and E. Jacquet},

doi = {10.1111/MAPS.13778},

year  = {2022},

date = {2022-01-01},

journal = {Meteoritics \& Planetary Science},

volume = {57},

number = {1},

pages = {122--135},

abstract = {Rumurutiites (R chondrites) are rare, highly oxidized chondrites belonging to the noncarbonaceous superclan and characterized by low chondrule abundances. Although textural and chemical features of Rumurutiite chondrules resemble those of ordinary chondrites (OCs), their formation conditions and potential genetic link remain debated. Here, we report high-resolution elemental X-ray mapping analyses and in situ O isotopic measurements of olivine grains from five chondrules and eight isolated olivine grains (IOGs) in the NWA 12482 R3 chondrite. The chondrules show chemical zonings similar to their counterparts in ordinary and carbonaceous chondrites (CCs), implying that gas--melt interaction processes between chondrule precursors and SiO- and Mg-rich gas were operative throughout the circumsolar disk. Our isotopic data show that R chondrules are isotopically similar to ordinary chondrules, although differences in their abundances of relict olivine grains and chondrule textural characteristics suggest different formation environments, with R chondrules being formed from 16O-poorer precursors. As with chondrules in OCs, the O isotopic characteristics of R chondrules and IOGs suggest limited transport between CC and noncarbonaceous reservoirs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Schnuriger_etal2022,

title = {Spinel in CV chondrules : Investigating precursor legacy and chondrule thermal histories},

author = {N. Schnuriger and C. Cartier and J. Villeneuve and V. Batanova and M. Regnault and Y. Marrocchi},

doi = {https://doi.org/doi:10.1111/maps.13802},

year  = {2022},

date = {2022-01-01},

journal = {Meteoritics \& Planetary Science},

volume = {57},

number = {5},

pages = {1018--1037},

abstract = {In carbonaceous chondrites, Mg-spinel (MgAl2O4) grains are ubiquitous in refractory inclusions but rarely reported in chondrules, where they may correspond to minerals either (i) inherited from chondrule precursors or (ii) crystallized from chondrule melts. Here, we report high-current quantitative electron microprobe measurements and secondary ion mass spectrometry oxygen isotopic analyses of Mg-spinel-bearing chondrules in the CV3 carbonaceous chondrites Northwest Africa 10235 and Allende. Compared to spinels in refractory inclusions, chondrule spinels are characterized by higher Cr contents and 16O-poorer oxygen isotopic signatures ($Delta$17O \^{a}‰¡ $delta$17O\^{a}ˆ’0.52 texttimes $delta$18O, from \^{a}ˆ’2 to \^{a}ˆ’6texttenthousand). Because the similar $Delta$17O values of chondrule olivine and spinel crystals imply their comagmatic origin, we applied a geothermometer based on the Al-Cr distribution between these minerals to determine their crystallization temperatures. The calculated temperatures range from 1200 to 1640 textdegreeC (mean = 1470 textdegreeC), most being lower than the estimated liquidus temperature of porphyritic chondrules ( 1600 textdegreeC). Our results suggest that chondrules experienced relatively slow cooling rates (slower than a few hundreds of textdegreeC h\^{a}ˆ’1), which is in good agreement with models of chondrule formation invoking nonlinear or twostage cooling rates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ferrando_etal2022,

title = {Brown amphibole as tracer of tectono-magmatic evolution of the Atlantis Bank Oceanic Core Complex (IODP Hole U1473A)},

author = {C. Ferrando and R. Tribuzio and C. J. Lissenberg and L. France and C. J. MacLeod and V. Basch and J. Villeneuve and E. Deloule and A. Sanfilippo},

doi = {10.1093/petrology/egac089},

year  = {2022},

date = {2022-01-01},

journal = {Journal of Petrology},

volume = {63},

pages = {1--27},

abstract = {Brown amphibole is a minor but common mineral component in lower oceanic crust. It is generally interpreted as products of migrating SiO2 and H2O-rich fluids or melts, which can be either residual melts from advanced magmatic differentiation of Mid-Ocean Ridge Basalt (MORB), or hydrothermal fluids including a seawater component. Within the lower oceanic crust exhumed at the Atlantis Bank Oceanic Core Complex, along the ultraslow Southwest Indian Ridge, brown amphibole is ubiquitous in all lithologies from olivine- to oxide-gabbros and diorites, including both undeformed and plastically deformed varieties. We here show the results of a systematic petrological study conceived to unravel the nature of the H2O-rich component recorded in brown amphiboles and document: (i) the evolution of migrating melts during the magmatic stage and (ii) different extents of melt-bearing deformation events recorded throughout the entire crustal transect. The low Cl contents and the light over heavy rare earth elements (LREE/HREE) ratios and high Ti contents in brown amphiboles indicate they crystallized from melts with a magmatic hydrous component. Consistently, their $delta$18O values are in equilibrium with Mid-Ocean Ridge Basalt (MORB) composition, except for diorite amphiboles that possibly record the local assimilation of altered minerals. In undeformed olivine gabbros, interstitial pargasite crystallized at hypersolidus conditions (textasciitilde1000textdegreeC) from the melt residual after late stages of MORB differentiation. We speculate that before the olivine gabbro crystal mush reached fully solid state, some aliquots of residual melts were extracted and accumulated within discrete intervals. There, ferrobasaltic melts differentiated through the early crystallization of Fe-Ti oxides and clinopyroxene as liquidus phases, ultimately forming the oxide gabbros. This process promoted rapid Si enrichment and depletion in Fe, Ti, V in the residual melt, later extracted to form the crosscutting diorite veins. The mylonitic olivine gabbros record high-temperature plastic deformation (textasciitilde900textdegreeCthinspacetextpmthinspace50textdegreeC) under hypersolidus conditions, involving melts residual from previous crystallization of the gabbroic rock. Further solid-state plastic deformation led to substantial grain size reduction and, consequently, to an increase in porosity. This created pathways for subsequent melt focusing, which likely represent late-stage differentiated melts migrating throughout the lower crustal section. This study shows that brown amphibole in the Atlantis Bank lower oceanic crust is the crystallization product of melts residual from advanced magmatic differentiation, which are also locally involved in the plastic deformation events during crustal accretion.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rudraswami_etal2022,

title = {In-situ O-isotope analysis of relict spinel and forsterite in small (\<200 $mu$m) Antarctic micrometeorites -- Samples of chondrules \& CAIs from carbonaceous chondrites},

author = {N. G. Rudraswami and M. D. Suttle and Y. Marrocchi and S. Taylor and J. Villeneuve},

doi = {10.1016/j.gca.2022.03.015},

year  = {2022},

date = {2022-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {325},

pages = {1--24},

abstract = {We report high-precision secondary ion mass spectrometer triple oxygen isotope systematics (95 individual analyses) from 37 micrometeorites (MMs) collected from South Pole Water Well (SPWW), Antarctica. The study population focuses on unmelted coarse-grained (Cg) MMs (n = 23) with both multiple (n = 14) and single-mineral (n = 9) varieties investigated. We also analysed relict minerals in porphyritic cosmic spherules (n = 13) and the relict matrix in a single scoriaceous fine-grained (Fg) MM. The target minerals investigated are primarily olivine (Fo \^{a}`u 43--99%) and spinel. Textural, chemical and isotopic data confirm that both olivine and spinel grains have retained their pre-atmospheric O-isotope compositions, allowing inferences to be drawn about their formation and parent body affinities. We separate the study population into three groups: spinel-free particles (consisting of the CgMMs and PO cosmic spherules), spinel-bearing MMs and the single FgMM.Olivine grains in spinel-free MMs vary between $delta$17O: \^{a}ˆ’12.6texttenthousand and +3.5texttenthousand, $delta$18O: \^{a}ˆ’9.6texttenthousand and +7.5texttenthousand, and $Delta$17O: \^{a}ˆ’9.5texttenthousand and +1.3texttenthousand and define a slope-1 profile in $delta$18O--$delta$17O isotope space. They are most likely fragmented chondrules, with both type I and type II varieties represented. Their observed Mg#-$Delta$17O distribution is best explained by a mixture of CM chondrules and either CR chondrules, Tagish Lake chondrules or WILD2 cometary silicates. One of these chondrule-like MMs has an isotopically heterogeneous composition, characterised by a single olivine grain with a markedly 16O-rich composition ($Delta$17O: \^{a}ˆ’16.3texttenthousand), suggesting it is a relict silicate fragment of AOA material that was incorporated into the chondrule precursor.We analysed 11 spinel grains in five spinel-bearing MMs. In all instances spinels are nearly pure MgAl2O4 with isotopically light (16O-rich) compositions (ranging from $delta$17O: \^{a}ˆ’34.4texttenthousand to \^{a}ˆ’0.9texttenthousand, $delta$18O: \^{a}ˆ’30.8texttenthousand to +11.0texttenthousand, and $Delta$17O: \^{a}ˆ’18.3texttenthousand to \^{a}ˆ’4.4texttenthousand). They are therefore 16O-poor relative to spinel found in unaltered CAIs, indicating a different origin. Grains with high Cr2O3 contents (\>0.5 wt.%) are interpreted originating from Al-rich chondrule precursors, while low Cr2O3 spinels (\<0.5 wt.%) are interpreted as CAI-derived material affected by parent body aqueous alteration.Finally, we report a single FgMM with a 16O-poor composition ($Delta$17O \> 0texttenthousand and $delta$18O \> +15.0texttenthousand). This particle adds to our growing inventory of water-rich C-type asteroid samples united by their formation history which is characterised by accretion of abundant heavy water.Our work strongly supports findings from earlier in-situ O-isotope studies, concluding that small MMs overwhelmingly sample material from CC parent bodies and that CgMMs largely sample chondrules and, to a lesser extent, CAI material. The analysis of CgMMs therefore provides insights into the primitive O-isotope reservoirs that were present in the early solar system and how they interacted.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bouden_etal2021,

title = {Triple oxygen isotope measurements by multi-collector secondary ion mass spectrometry},

author = {N. Bouden and J. Villeneuve and Y. Marrocchi and E. Deloule and E. F\"{u}ri and A. Gurenko and L. Piani and E. Thomassot and P. Peres and F. Fernandes},

doi = {doi: 10.3389/feart.2020.601169},

year  = {2021},

date = {2021-01-01},

journal = {Frontiers in Earth Science},

pages = {8:601169},

abstract = {Secondary ion mass spectrometry (SIMS) is a powerful technique for in situ triple oxygen isotope measurements that has been used for more than 30 years. Since pioneering works performed on small-radius ion microprobes in the mid-80s, tremendous progress has been made in terms of analytical precision, spatial resolution and analysis duration. In this respect, the emergence in the mid-90s of the large-radius ion microprobe equipped with a multi-collector system (MC-SIMS) was a game changer. Further developments achieved on CAMECA MC-SIMS since then (e.g., stability of the electronics, enhanced transmission of secondary ions, automatic centering of the secondary ion beam, enhanced control of the magnetic field, 1012$\Omega$ resistor for the Faraday cup amplifiers) allow nowadays to routinely measure oxygen isotopic ratios (18O/16O and 17O/16O) in various matrices with a precision (internal error and reproducibility) better than 0.5texttenthousand (2$sigma$), a spatial resolution smaller than 10 $mu$m and in a few minutes per analysis. This paper focuses on the application of the MC-SIMS technique to the in situ monitoring of mass-independent triple oxygen isotope variations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Deng_etal2021,

title = {Simultaneous determination of mass-dependent Mg isotopic variations and radiogenic 26Mg by laser ablation-MC-ICP-MS and implications for the formation of chondrules},

author = {Z. Deng and M. Chaussidon and D. S. Ebel and J. Villeneuve and J. Moureau and F. Moynier},

doi = {10.1016/j.gca.2021.01.015},

year  = {2021},

date = {2021-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {299},

pages = {163--183},

abstract = {Improvements in our understanding of the formation of chondrules requires a better knowledge of the thermal histories and the nature of their solid precursors. We present an in situ nanosecond laser ablation multi-collector inductively-coupled-plasma mass-spectrometry (LA-MC-ICP-MS) technique to measure simultaneously mass-dependent Mg isotopic fractionations and radiogenic 26Mg in chondritic components, thus allowing us to investigate within a chronological framework the thermal processes redistributing Mg in chondrules and their precursors. The internal 26Al-26Mg isochrons provide initial 26Al/27Al ratios from 5.46 (textpm 0.38) texttimes 10−5 to 6.14 (textpm 0.92) texttimes 10−5 for amoeboid olivine aggregates (AOAs) and Ca-, Al-rich inclusions (CAIs), and from 0.16 (textpm 0.08) texttimes 10−5 to 1.87 (textpm 0.92) texttimes 10−5 for chondrules from Allende and Leoville chondrites, which are consistent with the previously reported values. The combination of these values with up to 2.5texttenthousand variation of the 25Mg/24Mg ratio within the studied chondrules shows that: (i) AOAs and the precursors of chondrules were likely formed via condensation of rapid-cooling gas reservoirs, and (ii) Mg stable isotopes are probably at disequilibrium between olivines and mesostases in some chondrules, likely due to Mg loss by vaporization during chondrule formation. We use these new observations to propose that Mg isotopes can likely serve as a tracer for the thermal histories of chondrules. We present here a scenario taking into account Mg loss by vaporization from chondrule melt and Mg gain into the melt by olivine dissolution. The existing Mg isotopic observations in chondrule melts and olivines can be explained in a scenario with a homogeneous distribution of Mg isotopes and initial 26Al in the accretion disk, provided that chondrule precursors have been heated up to sufficiently high peak temperatures (up to 2123 K) and stayed above 1800 K for several tens of minutes to allow for significant Mg evaporation. These conditions are most consistent with a shock wave model for the origin of chondrules.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Piralla_etal2021_2,

title = {Conditions of chondrule formation in ordinary chondrites},

author = {M. Piralla and J. Villeneuve and V. Batanova and E. Jacquet and Y. Marrocchi},

doi = {10.1016/j.gca.2021.08.007},

year  = {2021},

date = {2021-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {313},

pages = {295--312},

abstract = {Chondrules are sub-millimetric spheroids that are ubiquitous in chondrites and whose formation mechanism remains elusive. Textural and oxygen isotopic characteristics of chondrules in carbonaceous chondrites (CCs) suggest that they result from the recycling of isotopically heterogeneous early-condensed precursors via gas--melt interactions. Here, we report high-resolution X-ray elemental maps and in situ O isotopic analyses of FeO-poor, olivine-rich chondrules from ordinary chondrites (OCs) to compare the conditions of chondrule formation in these two main classes of chondrites. OC chondrules show minor element (e.g., Ti, Al) zonings at both the chondrule and individual olivine grain scales. Considering the entire isotopic data set, our data define a mass-independent correlation, with olivine grains showing O isotopic variations spanning more than 40texttenthousand. Though 16O-rich relict olivine grains were identified in OC chondrules, they are much less abundant than in CC chondrules. They appear as two types : (i) those with low minor element abundances and D17O \< -15texttenthousand and (ii) those with varying minor element abundances and less negative D17O values averaging -5.5texttenthousand. The host olivine grains exhibit massdependent O isotopic variations within individual chondrules. Our results reveal that similar processes (precursor recycling and interactions between chondrule melts and a SiO- and Mg-rich gas) established the observed features of OC and CC chondrules. The mass-dependent isotopic variations recorded by host olivine grains result from kinetic effects induced by complex evaporation/recondensation processes during the gasmelt interactions. This suggests that OC chondrules formed through enhanced recycling processes, in good agreement with the lower abundances of relict olivine grains in OC chondrules compared to CC chondrules. We use the D18O = d18O ?\u{I} d17O parameter to demonstrate that there is no genetic relationship between CC and OC chondrules, suggesting limited radial transport in the protoplanetary disk. Finally, to the first order, the D18O--D17O diagram may allow the non-carbonaceous vs. carbonaceous origin of a given chondrule to be deciphered.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Casola_etal2020,

title = {No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa},

author = {V. Casola and L. France and A. Galy and N. Bouden and J. Villeneuve},

doi = {10.1130/G47629.1},

year  = {2020},

date = {2020-01-01},

journal = {Geology},

volume = {48},

pages = {971--975},

abstract = {Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (\<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The $delta$18O values vary little, from 19texttenthousand to 29texttenthousand, whereas $delta$13C values are more variable, ranging from --23texttenthousand to +0.5texttenthousand. We show that such carbonate $delta$18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed $delta$13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Decraene_etal2020,

title = {High spatial resolution measurements of iron isotopes in pyrites by SIMS using the new Hyperion‐II Radio‐Frequency Plasma source},

author = {M. N. Decraene and J. Marin-Carbonne and A. S. Bouvier and J. Villeneuve and N. Bouden and B. Luais and E. Deloule},

doi = {10.1002/rcm.8986},

year  = {2020},

date = {2020-01-01},

journal = {Rapid Communications in Mass Spectrometry},

pages = {e8986},

abstract = {RationaleIron isotopic signatures in pyrites are considered as a good proxy to reconstruct paleoenvironmental and local redox conditions. However, the investigation of micro‐pyrites less than 20$mu$m in size has been limited by the evaluable analytical techniques. The development of the new brighter radio‐frequency plasma ion source (Hyperion‐II source) enhances the spatial resolution by increasing the beam density 10 times compared with the Duoplasmatron source.MethodsHere we present high spatial resolution measurements of iron isotopes in pyrites using a 3nA‐3$mu$m primary 16O‐ beam on two Cameca IMS 1280‐HR2 ion microprobe instruments equipped with Hyperion sources at CRPG‐IPNT (France) and at SwissSIMS (Switzerland). We tested analytical effects, such as topography and crystal orientation that could induce analytical biases perceptible through variations of the Instrumental Mass Fractionation (IMF).ResultsThe $delta$56Fe reproducibility for the Balmat pyrite standard is textpm0.25texttenthousand (2SD, standard deviation) and the typical individual internal error is textpm0.10texttenthousand (2SE, standard error). The sensitivity on 56Fe+ was 1.2x107cps/nA/ppm or better. Tests on Balmat pyrites revealed that neither the crystal orientation nor channeling effects seem to significantly influence the IMF. Different pyrite standards (Balmat and SpainCR) were used to test the accuracy of the measurements. Indium mounts must be carefully prepared with sample topography \< 2$mu$m, which was checked using an interferometric microscope. Such a topography is negligible for introducing change in the IMF. This new source increases the spatial resolution while maintaining the high precision of analyses and the overall stability of the measurements compared with the previous Duoplasmatron source.ConclusionsWe developed a reliable method to perform accurate and high‐resolution measurements of micrometric pyrites. The investigation of sedimentary micro‐pyrites will improve our understanding of the processes and environmental conditions during pyrite precipitation, including contribution of primary (microbial activities or abiotic reactions) and secondary signatures (diagenesis and/or hydrothermal fluid circulation).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Deng_etal2020,

title = {Early oxidation of the martian crust triggered by impacts},

author = {Z. Deng and F. Moynier and J. Villeneuve and N. K. Jensen and D. Liu and P. Cartigny and T. Mikouchi and J. Siebert and A. Agranier and M. Chaussidon and M. Bizzarro},

doi = {10.1126/sciadv.abc4941},

year  = {2020},

date = {2020-01-01},

journal = {Science Advances},

volume = {6},

number = {44},

pages = {eabc4941},

abstract = {Despite the abundant geomorphological evidence for surface liquid water on Mars during the Noachian epoch (\>3.7 billion years ago), attaining a warm climate to sustain liquid water on Mars at the period of the faint young Sun is a long-standing question. Here, we show that melts of ancient mafic clasts from a martian regolith meteorite, NWA 7533, experienced substantial Fe-Ti oxide fractionation. This implies early, impact-induced, oxidation events that increased by five to six orders of magnitude the oxygen fugacity of impact melts from remelting of the crust. Oxygen isotopic compositions of sequentially crystallized phases from the clasts show that progressive oxidation was due to interaction with an 17O-rich water reservoir. Such an early oxidation of the crust by impacts in the presence of water may have supplied greenhouse gas H2 that caused an increase in surface temperature in a CO2-thick atmosphere.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gauriau_etal2020,

title = {Chemical and boron isotope composition of tourmaline from the Kiaka orogenic gold deposit (Burkina Faso, West African Craton) as a proxy for ore-forming processes},

author = {J. Gauriau and M. Harlaux and A. S. Andr\'{e}-Mayer and A. Eglinger and A. Richard and A. Fontaine and M. G. Lefebvre and D. B\'{e}ziat and J. Villeneuve and D. Lemarchand},

doi = {10.1007/s00126-020-01002-7},

year  = {2020},

date = {2020-01-01},

journal = {Mineralium Deposita},

abstract = {The Kiaka orogenic gold deposit (Burkina Faso), located in the Paleoproterozoic domain of the West African Craton, is characterized by a two-stage gold mineralization hosted in volcano-sedimentary metamorphic rocks that was formed during the Eoeburnean (2.20--2.13 Ga) and Eburnean (2.13--2.05 Ga) orogenic cycles. These two stages include an early disseminated low-grade gold mineralization and a late vein-hosted high-grade gold mineralization. Paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline. The aim of this paper is twofold: (i) to determine the processes responsible for deposition of the economic disseminated gold mineralization and (ii) to identify the source of the mineralizing fluids. For this purpose, we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes. Hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different $delta$11B values falling within the two intervals of −thinspace25.1 to −thinspace22.0texttenthousand and −thinspace19.6 to −thinspace15.1texttenthousand, respectively. Our results suggest that tourmaline formed from a distal, high-temperature (ca. 400 textdegreeC), reduced, and low-salinity hydrothermal fluid that interacted with the local host rocks. Based on the modeling of tourmaline--fluid boron isotope fractionation, we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca. 2.13 Ga. This metamorphic fluid--rock interaction model may possibly extend to other orogenic gold deposits in the West African Craton.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Piralla_etal2020,

title = {Primordial water and dust of the Solar System: Insights from in situ oxygen measurements of CI chondrites},

author = {M. Piralla and Y. Marrocchi and M. J. Verdier-Paoletti and L. G. Vacher and J. Villeneuve and L. Piani and D. V. Bekaert and M. Gounelle},

doi = {10.1016/j.gca.2019.10.041},

year  = {2020},

date = {2020-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {269},

pages = {451--464},

abstract = {As the chemical compositions of CI chondrites closely resemble that of the Suntextquoterights photosphere, their oxygen isotopic compositions represent a powerful tool to constrain the origin and dynamics of dust and water ice grains in the protoplanetarydisk. However, parent-body alteration processes make straightforward estimation of the primordial isotopic compositions of CI chondritic water and anhydrous minerals difficult. In this contribution, we used in situ SIMS measurements to determinethe oxygen isotope compositions of mechanically isolated olivine and carbonate grains from the CI chondrite Orgueil and carbonates in a polished section of the CI chondrite Ivuna. Most CI olivine grains have Earth-like O isotopic compositions(D17O ≈ 0texttenthousand) plotting at the intersection of the terrestrial fractionation line and the primitive chondrule minerals line. Ca-carbonates from Orgueil and Ivuna define a trend with d17O = (0.50 textpm 0.05) x d18O + (0.9 textpm 1.4) that differs from massindependent variations observed in secondary phases of other carbonaceous chondrites. These data show that CIs are chemically solar but isotopically terrestrial for oxygen isotopes. This supports models suggesting that primordial Solar System dust was 16O-poor (D17O ≈ 0texttenthousand) relative to the 16O-rich nebular gas. Based on results, mass balance calculations reveal that the pristine O isotopic compositions of carbonaceous chondrite matrices differ significantly from the CI composition, except for CR chondrites (calculated D17O values of CM, CO, CV and CR matrices being --3.97 textpm 1.19texttenthousand, --4.33 textpm 1.45texttenthousand, --7.95textpm 1.95texttenthousand, and --0.07 textpm 1.16texttenthousand, respectively). This confirms an open chondrule-matrix system with respect to oxygen isotopes where chondrule compositions reflect complex processes of chondrule precursor recycling and gas-melt interactions. As the Mg-Si-Fe chondrule budget is also partially controlled by gas-melt interactions, the complementary formation of chondrules and matrix from a single solar-like reservoir -if it exists- require that (i) this reservoir must have been in a closed system with the gas or (ii) the gas had a CI composition to satisfy the elemental mass balance.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rudraswami_etal2020,

title = {The oxygen isotope compositions of large numbers of small cosmic spherules : Implications for their sources and the isotopic composition of the upper atmosphere},

author = {N. G. Rudraswami and M. J. Genge and Y. Marrocchi and J. Villeneuve and S. Taylor},

doi = {10.1029/2020JE006414},

year  = {2020},

date = {2020-01-01},

journal = {Journal of Geophysical Research (Planets)},

volume = {125},

pages = {e2020JE006414},

abstract = {Cosmic spherules are micrometeorites that melt at high altitude as they enter Earthtextquoterights atmosphere, and their oxygen isotope compositions are partially or completely inherited from the upper atmosphere, depending on the amount of heating experienced and the nature of their precursor materials. In this study, the three oxygen isotope compositions of 137 cosmic spherules are determined using 277 in situ analyses by ion probe. Our results indicate a possible correlation between increasing average $delta$18O compositions of silicate -dominated (S-type) spherules along the series scoriaceous \< porphyritic 0texttenthousand) and are largely derived from ordinary chondrite (OC)-like sources related to S (IV)-type asteroids. Glass and CAT spherules have variable �'u17O values indicating they formed by intense entry heating of both CC and OC -like materials. I-type cosmic spherules have a narrow range of $delta$17O ( 20--25texttenthousand) and $delta$18O ( 38--48texttenthousand) values, with �'u17O ( 0texttenthousand) suggesting their oxygen is obtained entirely from the Earthtextquoterights atmosphere, albeit with signicant mass fractionation owing to evaporative heating. Finally, G-type cosmic spherules have unexpected isotopic compositions and demonstrate little mass fractionation from a CC-like source. The results of this study provide a vital assessment of the wider population of extraterrestrial dust arriving on Earth.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Villeneuve_etal2020,

title = {Silicon isotopic compositions of chondrule silicates in carbonaceous chondrites and the formation of primordial solids in the accretion disk},

author = {J. Villeneuve and Y. Marrocchi and E. Jacquet},

doi = {10.1016/j.epsl.2020.116318},

year  = {2020},

date = {2020-01-01},

journal = {Earth and Planetary Science Letters},

volume = {542},

pages = {116318},

abstract = {We determined the silicon isotopic compositions of silicates (olivine and low-Ca pyroxene) in type I and type II chondrules of the carbonaceous chondrites Allende, Kaba, NWA (Northwest Africa) 5958, and MIL (Miller Range) 07342. Type I chondrule silicates show large, mass-dependent Si isotopic fractionations, with Si values ranging from −7texttenthousand to +2.6texttenthousand, whereas the Si values of type II chondrule silicates are close to zero and vary by less than 2texttenthousand. When present, Mg-rich relict olivine grains in type II chondrules show larger Si variations than their FeO-rich counterparts. In type I chondrules, low-Ca pyroxenes yield systematically lighter Si values than Mg-rich olivines. Our results show that type I chondrules are complex objects whose Si isotopic compositions derived from their precursors and SiO-rich gas-melt interactions. This corroborates that type I chondrules are nebular products that formed under open-system conditions. Our data also suggest that at least some type II chondrules derived from their type I counterparts. Overall, this demonstrates that recycling was common during the evolution of the protoplanetary disk},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gigon_etal2019,

title = {Insights into B-Mg-Metasomatism at the Ranger U Deposit (NT, Australia) and Comparison with Canadian Unconformity-Related U Deposits},

author = {J. Gigon and R. G. Skirrow and M. Harlaux and A. Richard and J. Mercadier and I. R. Annesley and J. Villeneuve},

doi = {10.3390/min9070432},

year  = {2019},

date = {2019-01-01},

journal = {Minerals},

volume = {9},

number = {432},

abstract = {The Ranger deposit (Northern Territory, Australia) is one of the largest uranium deposits inthe world. Uranium mineralisation occurs in crystalline basement rocks and is thought to belong tothe unconformity-related category. In order to address the sources of magnesium and boron, and thetemperature of the fluids related to boron and magnesium metasomatism that occurred shortly beforeand during the main uranium stage, in situ analyses of chlorite and tourmaline were carried out. Thechemical composition of tourmaline shows an elevated X-site vacancy and a low Fetot/(Fetot+Mg)ratio typical of Mg-foitite. Uranium-related chlorite has relatively low Fe content (0.28--0.83apfu) andhigh Mg content (3.08--3.84apfu), with Si/Al=1.08−1.22 and Mg/(Mg+Fetot)=0.80−0.93 indicating acomposition lying between the clinochlore and Mg-amesite fields. Chlorite composition indicatescrystallisation temperature of 101--163◦C. The boron isotopic composition of tourmaline shows arange of$delta$11B values of 1--9textdegree/00. A model is proposed involving two boron sources that contributeto a mixed isotopic signature : (i) evaporated seawater, which is typically enriched in magnesiumand boron ($delta$11B 40textdegree/00), and (ii) boron from the crystalline basement ($delta$11B −30 to+10textdegree/00), whichappears to be the dominant source. Collectively, the data indicate similar tourmaline chemistry butsignificant differences of tourmaline boron isotopic composition and chlorite chemistry betweenthe Ranger deposit and some of the Canadian unconformity-related uranium deposits. However,lithogeochemical exploration approaches based on identification of boron- and magnesium-enrichedzones may be usefully applied to uranium exploration in the Northern Territor},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Harlaux_etal2019,

title = {Origin of the atypical Puy-les-Vignes W breccia pipe (Massif Central, France) constrained by trace element and boron isotopic composition of tourmaline},

author = {M. Harlaux and J. Mercadier and C. Marignac and J. Villeneuve and B. Mouthier and M. Cuney},

doi = {10.1016/j.oregeorev.2019.103132},

year  = {2019},

date = {2019-01-01},

journal = {Ore Geology Reviews},

volume = {114},

pages = {103132},

abstract = {The Puy-les-Vignes W deposit is an atypical wolframite-bearing hydrothermal breccia pipe hosted in migmatitic biotite-sillimanite gneisses in the northwestern French Massif Central. The deposit is characterized by volumetrically important tourmaline alteration allowing to investigate the fluid evolution of the ore-forming hydrothermal system. Four generations of hydrothermal tourmaline (Tur 1--Tur 4) formed during pre-, syn-, and post-mineralization stages were identified based on detailed petrographic observations and were analyzed in situ for their chemical and boron isotopic compositions. At the grain scale, tourmaline commonly shows oscillatory zoning and dissolution textures resulting from a multi-stage crystallization in a fluid-dominated system. The different generations of hydrothermal tourmaline have dravite-schorl compositions and show similar major and trace element contents falling into the field of metamorphic rocks. High concentrations of V, Cr, Sr and low concentrations of Li, Sn in tourmaline suggest a metamorphic-dominated origin of these elements. The boron isotopic compositions of tourmaline range between −13.3texttenthousand and −7.8texttenthousand and cannot unambiguously distinguish between a magmatic and a metamorphic fluid origin. Our data indicate that the chemical and boron isotopic composition of tourmaline was dominantly controlled by high-temperature fluid-rock interactions between the metamorphic basement and boron-rich, reduced, and low-salinity hydrothermal fluids. Based on these results, we propose a fluid evolution scenario for the Puy-les-Vignes ore-forming hydrothermal system. Release of magmatic-hydrothermal fluids from an unexposed peraluminous leucogranite at ca. 324 Ma is proposed as the main mechanism responsible for early greisenization and formation of disseminated Tur 1. This episode was followed by massive tourmalinization and hydraulic brecciation of the overlying gneisses producing a tourmaline-rich (Tur 2) crackle breccia by interactions with boron-rich hydrothermal fluids. Fluid-assisted reopening and collapse of the former tourmalinite at ca. 318 Ma yielded a matrix-supported quartz-tourmaline breccia pipe and formation of wolframite-bearing quartz veins accompanied by deposition of Tur 3. Finally, post-ore hydraulic fracturing at ca. 300 Ma led to formation of tourmaline-rich microbreccias (Tur 4) possibly from metamorphic fluids.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Legros_etal2019,

title = {U-Pb isotopic dating of columbite-tantalite minerals : Development of reference materials and in situ applications by ion microprobe},

author = {H. Legros and J. Mercadier and J. Villeneuve and R. L. Romer and E. Deloule and M. Van Lichtervelde and S. Dewaele and P. Lach and X. D. Che and R. C. Wang and Z. Y. Zhu and E. Gloaguen and J. Melleton},

doi = {10.1016/j.chemgeo.2019.03.001},

year  = {2019},

date = {2019-01-01},

journal = {Chemical Geology},

volume = {512},

pages = {69--84},

abstract = {Columbite-tantalite group minerals are the most common Nb-Ta minerals. Columbite-tantalite is particularly suitable for U-Pb dating due to its high U and low common Pb contents. In situ isotopic dating of columbite-tantalite by LA-ICP-MS or SIMS requires certified reference material to properly account for potential matrix effects linked to substitutions between Nb and Ta and between Mn and Fe. Our study has two objectives : i) establish a database of reference materials for in situ U-Pb isotopic dating of columbite-tantalite minerals and ii) test the capability of SIMS to in situ U-Pb date columbite-tantalite minerals of different chemical composition. Tests of in situ U-Pb dating demonstrate that SIMS can easily be used to date columbite-tantalite minerals with errors and precisions overlapping the reference ID-TIMS age. There are, however, significant matrix effects for non-matching Nb-Ta-Fe-Mn compositions of sample and reference material. Matrix effects are highly correlated with the Ta/(Ta + Nb) ratio of columbite-tantalite, due to the significant difference in the atomic mass of Nb and Ta. The Mn/(Mn + Fe) ratio does not significantly contribute to the observed matrix effect as the two elements have similar atomic masses. The linear correlation between Ta/(Nb + Ta) and ((206Pb/238U)SIMS/(206Pb/238U)ID-TIMS) obtained for columbite-tantalite minerals of known ID-TIMS age demonstrates that the SIMS matrix-effect can be properly accounted for by using the chemical composition as determined by EMPA. The ability to measure 204Pb by SIMS also allows the use of reference materials with a small common lead contribution and to calculate accurate and precise ages for columbite-tantalite minerals with contributions of common lead.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mari_etal2019,

title = {Syneruptive incorporation of martian surface sulphur in the nakhlite lava flows revealed by S and Os isotopes and highly siderophile elements: implication for mantle sources in Mars},

author = {N. Mari and A. J. V. Riches and L. J. Hallis and Y. Marrocchi and J. Villeneuve and P. Gleissner and H. Becker and M. R. Leese},

doi = {10.1016/j.gca.2019.05.025},

year  = {2019},

date = {2019-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {266},

pages = {416--434},

abstract = {Martian lava flows likely acquired S-rich material from the regolith during their emplacement on the planettextquoterights surface. We investigated five of the twenty known nakhlites (Nakhla, Lafayette, Miller Range (MIL) 090032, Yamato 000593, and Yamato 000749) to determine whether these lavas show evidence of regolith assimilation, and to constrain the potential implications that this process has on chemical tracing of martian mantle source(s). To establish the proportionate influence of atmospheric, hydrothermal, and volcanic processes on nakhlite isotopic systematics we obtained in situ sulphur isotope data (D33S and d34S) for sulphide grains (pyrrhotite and pyrite) in all five nakhlite samples. For Nakhla, Lafayette, and MIL 090032, these data are integrated with highly siderophile element (HSE) abundances and Os-isotope compositions, as well as textural information constrained prior to isotopic analysis. This work thereby provides the first Re-Os isotope systematics for two different nakhlites, and also the first Re-Os isotope data for martian sample for which detailed petrographic information was constrained prior to digestion. We report the largest variation in d34S yet found in martian meteorites (-13.20texttenthousandto +15.16texttenthousand). The relatively positive D33S and d34S values of MIL 090032 (d34S = +10.54 textpm 0.09texttenthousand ; D33S = -0.67 textpm 0.10texttenthousand) indicate this meteorite assimilated sulphur affected by UV-photochemistry. In contrast, the strongly negative values of Lafayette (d34S = -10.76 textpm 0.14texttenthousand ; D33S = -0.09 textpm 0.12texttenthousand) are indicative of hydrothermal processes on Mars. Nakhla, Yamato 000593, and Yamato 000749 sulphides have a narrower range of sulphur isotope compositions (D33S and d34S 0) that is consistent with no assimilation of martian surface materials during lava flow emplacement. Consequently we used this second group of D33S values to approximate the D33S of the nakhlite source, yielding a D33S value of -0.1texttenthousand. Nakhlite HSE patterns result from a sulphide-saturated melt where Ru-Os-Ir alloys/sulphide were likely crystallized during earlier phases of magmatic processing in Mars to result in the fractionated HSE patterns of the nakhlites. Our data, alongside a synthesis of previously published data, suggest assimilation of an enriched component to the primary nakhlite melt, potentially a late-stage crystallization cumulate from the martian magma ocean stage. In the context of this model, and within large uncertainties, our data hint at perturbation and potential decoupling of nakhlite Re-Os isotope systematics from other isotopic systems as a result of small degrees of assimilation of a regolith component with highly radiogenic 187Os/188Os.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marrocchi_etal2019,

title = {Formation of CV chondrules by recycling of amoeboid olivine aggregate-like precursors},

author = {Y. Marrocchi and R. Euverte and J. Villeneuve and V. Batanova and B. Welsch and L. Ferri`ere and E. Jacquet},

doi = {10.1016/j.gca.2018.12.038},

year  = {2019},

date = {2019-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {247},

number = {2},

pages = {121--141},

abstract = {We have studied porphyritic olivine-rich chondrules of the carbonaceous chondrite Kaba (CV3) by combined high-resolution X-ray mapping, quantitative electron microprobe analyses, and oxygen isotopic analyses via secondary ion mass spectrometry. These chondrules contain smaller inner-chondrule olivine grains characterized by low refractory element (Ca, Al, Ti) contents, and larger outer-chondrule olivine crystals that are enriched in refractory elements and show complex Ti and Al oscillatory zonings. Our O isotopic survey revealed that many of the inner-chondrule olivines are 16O-richer than the relatively isotopically uniform outer-chondrule olivines. Inner-chondrule olivine crystals---only a minority of which may be derived from earlier generations of chondrules---are likely mostly inherited from nebular condensates similar to AOAs, as they share similar isotopic and chemical features and are thus interpreted as relict grains. Still, being 16O-poorer than most AOAs, they may have experienced significant exchange with a 16O-poor reservoir prior to chondrule formation (even if to a lesser degree than relicts in CM2 and ungrouped C2 chondrites). Subsequent incomplete melting of the relict grains produced Ca-Al-Ti-rich melts that engulfed the remaining relict olivine grains. The complex Ti and Al zoning patterns in outer chondrule (host) olivines, in particular the systematic dilution near the margin, seem to reflect gas-melt interactions (with e.g. SiO (g), Mg (g)) which also buffered the O isotopic composition of chondrule hosts. Together, these results demonstrate that important episodes of recycling of nebular condensates occurred in the solar protoplanetary disk.https://doi.org/10.1016/j.gca.2018.12.038},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marrocchi_etal2019_2,

title = {Rapid condensation of the first Solar System solids},

author = {Y. Marrocchi and J. Villeneuve and E. Jacquet and M. Piralla and M. Chaussidon},

doi = {/10.1073/pnas.1912479116},

year  = {2019},

date = {2019-01-01},

journal = {PNAS},

volume = {116},

number = {47},

pages = {23461--23466},

abstract = {Chondritic meteorites are composed of primitive components formed during the evolution of the Solar protoplanetary disk. The oldest of these components formed by condensation, yet little is known about their formation mechanism because of secondary heating processes that erased their primordial signature. Amoeboid Olivine Aggregates (AOAs) have never been melted and underwent minimal thermal annealing, implying they might have retained the conditions under which they condensed. We performed a multiisotope (O, Si, Mg) characterization of AOAs to constrain the conditions under which they condensed and the information they bear on the structure and evolution of the Solar protoplanetary disk. High-precision silicon isotopic measurements of 7 AOAs from weakly metamorphosed carbonaceous chondrites show large, mass-dependent, light Si isotope enrichments (--9texttenthousand \< $delta$30Si \< --1texttenthousand). Based on physical modeling of condensation within the protoplanetary disk, we attribute these isotopic compositions to the rapid condensation of AOAs over timescales of days to weeks. The same AOAs show slightly positive $delta$25Mg that suggest that Mg isotopic homogenization occurred during thermal annealing without affecting Si isotopes. Such short condensation times for AOAs are inconsistent with disk transport timescales, indicating that AOAs, and likely other high-temperature condensates, formed during brief localized high-temperature events.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Martz_etal2019,

title = {Post-crystallization alteration of natural uraninites : Implications for dating, tracing, and nuclear forensics},

author = {P. Martz and J. Mercadier and J. Perret and J. Villeneuve and E. Deloule and M. Cathelineau and D. Quirt and A. Doney and P. Ledru},

doi = {10.1016/j.gca.2019.01.025},

year  = {2019},

date = {2019-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {249},

pages = {138--159},

abstract = {This study presents systematic chemical (U, Pb, Ca, Si, Fe) mapping coupled with in situ analyses of major, minor and trace elements, U/Pb, 207Pb/206Pb, and O isotopic compositions of natural uraninites (UO2) from two samples of the high-grade uranium ore from the Cigar Lake unconformity-related uranium deposit (Athabasca Basin, Saskatchewan, Canada).The studied uraninites are characterized by major chemical and isotopic heterogeneities expressed at small scale (textmum to tens of textmum), from almost pristine zones to strongly altered material. The 206Pb/238U and 207Pb/235U ratios of the different areas are widely spread and depict two similar and well-defined Discordia, providing an upper intercept age of crystallization at ca. 1300 Ma (1299 textpm 4 and 1308 textpm 14 Ma, respectively) and lower intercepts at 38 textpm 13 and 72 textpm 22 Ma, respectively.The freshest areas are characterized by sub-concordant 206Pb/238U and 207Pb/235U ratios, identical chemical compositions and similar very low $delta$18O values (−39.3 to −31.4texttenthousand). These data indicate that the two uraninites both crystallized at ca. 1300 Ma, from the same fluid and under identical physico-chemical conditions.Alteration is characterized by (i) the progressive incorporation of Ca, Si, and Fe, reaching several wt.%, which substitute to the radiogenic Pb and cause a progressive decrease in the Pb/U isotopic ratios. The radiogenic Pb is also substituted by water during the alteration, (ii) concomitant variations in trace element contents (As, Mn, V, LREEs, Sr, Th, B, Ba, Nb, for example) and (iii) heavier $delta$18O signatures (−22.5 to −8.91texttenthousand), typical of meteoric waters, in the altered zones. This combined approach demonstrates that fluid-driven post-crystallization exchanges affected each uraninite during recent fluid flow events (ca. 40 Ma and 70 Ma respectively). The relatively high dispersion of the Pb/U ratios in relation to the Discordia for both samples is considered as linked to a local (nm to textmum-scale) differential mobility between lead and uranium within the uranium oxides.The chemical changes affecting elements previously considered as immobile in uraninite, such as REEs, indicate that these elements are not preserved during the post-crystallization alteration process studied here. Alteration processes may therefore have a major impact on the classical geochemical tracers, such as REE patterns or LREE/HREE ratios, currently used in nuclear forensic studies. The isotopic and chemical tracers currently used to track back the origin, age and history of natural uraninites should therefore be considered with a high degree of caution to avoid misleading and erroneous conclusions.Moreover, the comparison of calculated U-Th-Pb chemical, 207Pb/206Pb, and Pb/U isotopic ages shows that the use of age clustering for determining U-Th-Pb chemical ages and 206Pb/207Pb ages is not appropriate for constraining crystallization stage(s) of altered uraninites and for deciphering the different fluid events that potentially altered or recrystallized the uraninites over time. This study also indicates that estimation of the crystallization age of uraninite from substitution trends of Pb to Ca is not applicable to unconformity-related U deposits and results in overestimated ages because of an initial integration of calcium in the uraninite lattice at the time of crystallization.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Prcigout_etal2019,

title = {Excess water storage induced by viscous strain localization during high-pressure shear experiment},

author = {J. Pr\'{e}cigout and H. St\"{u}nitz and J. Villeneuve},

doi = {10.1038/s41598-019-40020-y},

year  = {2019},

date = {2019-01-01},

journal = {Science Report},

volume = {9},

pages = {1--9},

abstract = {Strain localization in viscously deformed rocks commonly results in fine-grained shear zones where massive fluid circulation is regularly observed. Recently attributed to strain-induced pumping, this phenomenon may have major implications for the distribution of ores deposits and rock rheology. However, although grain size reduction and/or creep cavitation have been proposed as important processes, the source mechanism of fluid concentration remains unresolved, particularly at high pressure. Here we use secondary ion mass spectrometry to document the H2O content of fine-grained olivine across an experimental shear zone, which developed with grain size reduction during a H2O-saturated shear experiment at 1.2thinspaceGPa and 900thinspacetextdegreeC. Through data interpolation, the olivine matrix reveals high fluid concentrations where shear strain is localized. These concentrations far exceed the predicted amount of H2O that grain boundaries can contain, excluding grain size reduction as a unique source of water storage. Instead, we show that H2O increases per unit of grain boundary across the shear zone, suggesting that cavitation and textquotelefttextquotelefthealingtextquoterighttextquoteright processes compete with each other to produce a larger pore volume with increasing strain rate. This provides an alternative process for fluids to be collected where strain rate is the highest in deep shear zones.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rudraswami_etal2019,

title = {Oxygen isotopic and chemical composition of chromites in micrometeorites: Evidence of ordinary chondrite precursors},

author = {N. G. Rudraswami and Y. Marrocchi and M. Shyam Prasad and D. Fernandes and J. Villeneuve and S. Taylor},

doi = {10.1111/maps.13281},

year  = {2019},

date = {2019-01-01},

journal = {Meteoritics \& Planetary Science},

volume = {54},

number = {6},

pages = {1347--1361},

abstract = {We identified 66 chromite grains from 42 of textasciitilde5000 micrometeorites collected from Indian Ocean deep‐sea sediments and the South Pole water well. To determine the chromite grains precursors and their contribution to the micrometeorite flux, we combined quantitative electron microprobe analyses and oxygen isotopic analyses by high‐resolution secondary ion mass spectrometry. Micrometeorite chromite grains show variable O isotopic compositions with $delta$18O values ranging from −0.8 to 6.0texttenthousand, $delta$17O values from 0.3 to 3.6texttenthousand, and $Delta$17O values from −0.9 to 1.6texttenthousand, most of them being similar to those of chromites from ordinary chondrites. The oxygen isotopic compositions of olivine, considered as a proxy of chromite in chromite‐bearing micrometeorites where chromite is too small to be measured in ion microprobe have $Delta$17O values suggesting a principal relationship to ordinary chondrites with some having carbonaceous chondrite precursors. Furthermore, the chemical compositions of chromites in micrometeorites are close to those reported for ordinary chondrite chromites, but some contribution from carbonaceous chondrites cannot be ruled out. Consequently, carbonaceous chondrites cannot be a major contributor of chromite‐bearing micrometeorites. Based on their oxygen isotopic and elemental compositions, we thus conclude with no ambiguity that chromite‐bearing micrometeorites are largely related to fragments of ordinary chondrites with a small fraction from carbonaceous chondrites, unlike other micrometeorites deriving largely from carbonaceous chondrites.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Villeneuve_etal2019,

title = {High‐precision in situ silicon isotopic analyses by multicollector secondary ion mass spectrometry in olivine and lowcalcium pyroxene},

author = {J. Villeneuve and M. Chaussidon and Y. Marrocchi and Z. Deng and E. B. Watson},

doi = {10.1002/rcm.8508},

year  = {2019},

date = {2019-01-01},

journal = {Rapid Communications in Mass Spectrometry},

volume = {33},

pages = {1589--1597},

abstract = {High‐precision determination of silicon isotopes can be achieved by in situ multi‐collector secondary ion mass spectrometry (MS‐SIMS). The accuracy of the analyses is, however, sensitive to ion yields and instrumental mass fractionations (IMFs) induced by the analytical procedure. These effects vary from one instrument to another, with the analytical settings, and with the composition and nature of the sample. Because ion yields and IMF effects are not predictable and rely on empirical calibrations, high‐accuracy analyses require suitable sets of standards. Methods : Here, we document calibrations of ion yields and matrix effects in a set of 23 olivine standards and 3 low‐Ca pyroxene for silicon isotopic measurements in both polarities using Cameca IMS 1270 E7 and IMS 1280 HR2 ion probes set with the cesium (Cs) or radiofrequency (RF) source. Results : Silicon ion yields show (i) strong variations with the chemical composition, and (ii) an opposite behavior between the secondary positive and negative polarities. The magnitude of IMF along the fayalite‐forsterite (olivine) series shows a complex behavior, increasing overall by ≈7texttenthousand (secondary positive) and ≈15texttenthousand (secondary negative) with increasing olivine Mg#. A drastic change in olivine IMF occurs at Mg#≈70 in both polarities. The magnitude of IMF for low‐Ca pyroxene from Mg#= 70--100 is almost constant in both polarities, i.e. ≈0.1texttenthousand in secondary positive and ≈0.15texttenthousand in secondary negative. The analytical uncertainties on individual analyses were textpm 0.05--0.15texttenthousand (2 S.E.) with both sources, and the external errors for each standard material were ≈ textpm0.05--0.5texttenthousand (2 S.E.) with the Cs source and ≈ textpm0.03--0.15texttenthousand (2 S.E.) with the RF source. Conclusions : The IMF effect of Si isotopes in silicates shows complex behaviors that vary with the chemistry and the settings of the instrument. We developed a suitable set of standards in order to perform high‐accuracy in situ measurements of Si isotopes in olivine and low‐Ca pyroxene characterized by varying chemical compositions by MC‐SIMS.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bonnetti_etal2018,

title = {The genesis of granite-related hydrothermal uranium deposits in the Xiazhuang and Zhuguang ore fi elds, North Guangdong Province, SE China: Insights from mineralogical, trace elements and U-Pb isotopes signatures of the U mineralisation},

author = {C. Bonnetti and X. Liu and J. Mercadier and M. Cuney and E. Deloule and J. Villeneuve and W. Liu},

doi = {https://doi.o10.1016/j.oregeorev.2017.12.010},

year  = {2018},

date = {2018-01-01},

journal = {Ore Geology Reviews},

volume = {92},

pages = {588--612},

abstract = {Granite-related hydrothermal U deposits from the Xiazhuang and Zhuguang ore fields are located within the Nanling Metallogenic Belt in South China. These deposits are hosted in Triassic and Jurassic granites that were emplaced during the Indosinian orogeny and the Yanshanian post-orogenic extension. Four main types of granitic host rocks were identified based on geochemical characteristics as the most favourable sources of U for the mineralisation in the district : (i-ii) Indosinian peraluminous S-type (Maofeng) and L-type leucogranite (Baishuizhai) ; (iii) Indosinian highly fractionated high-K calc-alkaline A2-type granite (Xiazhuang, Maofeng and Youdong) and (iv) early Yanshanian highly fractionated high-K, (Fe) calc-alkaline A2-type granite (Sundong, Siqian and Changjiang). They contain high U concentrations ranging from 15 to 28 ppm indicating the crystallisation of uraninite, which is a source of U easily leachable by oxidised fluids for the formation of hydrothermal mineralisation.This study characterises the mineralogical, chemical and isotopic signatures of the U mineralisation from five representative deposits and occurrences in the Xiazhuang (Baishuizhai, Shituling, Xiwang and Xianshi) and Zhuguang (Mianhuakeng) ore fields. The 175 textpm 16 Ma Baishuizhai occurrence and 162 textpm 27 Ma Shituling deposit represent an early stage of U mineralisation (175--145 Ma) that occurred during the early Yanshanian. Disseminated Th-bearing uraninite at Baishuizhai and the association of U oxides with alteration minerals such as epidote and chlorite in both Baishuizhai and Shituling indicate temperatures \>250 textdegreeC for the hydrothermal system. The early Yanshanian granites (190--150 Ma) provided the heat source and magmatic fluids to the hydrothermal system while U-rich Indosinian granites provided U for the Zr-Th-Ta-bearing U mineralisation. In contrast, the mineralisation from Xiwang, Mianhuakeng and Xianshi deposits (107 textpm 16, 93 textpm 15 and 79 textpm 11 Ma, respectively) represent several pulses of the main mineralisation stage (110--50 Ma) that occurred during the late Yanshanian crustal extension. The mineralisation occurred at relatively low temperatures (\<250 textdegreeC) as W-Y-Nb-Ti-rich pitchblende and uraninite veins associated with quartz, fluorite, calcite and pyrite. During Cretaceous-early Cenozoic crustal extension, oxidising meteoric and/or basinal waters percolated downward into the granitic basement through deep faults and mixed with CO2-rich magmatic fluids. These thermal solutions circulated along opening fractures and leached U from Indosinian and early Yanshanian U-rich granites and also possibly from early Yanshanian U mineralisation. After heating, the ore-forming fluids ascended along structures leading to the decrease of the hydrostatic fluid pressure, which promoted the deposition of U in veins. Therefore, granite-related hydrothermal U mineralisation in the province, formed over a long time span (\>100 Ma) in two major stages related to different genetic conditions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Holycross_etal2018,

title = {Diffusive fractionation of Li isotopes in wet, highly silicic melts},

author = {M. E. Holycross and E. B. Watson and F. M. Richter and J. Villeneuve},

doi = {10.7185/geochemlet.1807},

year  = {2018},

date = {2018-01-01},

journal = {Geochemical Perspectives Letters},

volume = {6},

pages = {39--42},

abstract = {The discovery of large lithium isotopic gradients in geologic media has motivated recent work examining the kinetic fractionation of Li isotopes in silicate materials. Here, piston-cylinder experiments were used to determine Li diffusivities in rhyolitic melts containing 6 wt. % H2O at 1 GPa pressure and 790-875 textordmasculineC. Lithium transport in wet rhyolitic melt is almost an order of magnitude faster than diffusion in dry obsidian glass over the investigated temperature range. Li isotope profiles collected by ion microprobe show that the kinetic exponent $beta$ = 0.228 for diffusive fractionation of Li isotopes in wet rhyolite. This value is very close to $beta$ = 0.215 determined by Richter et al. (2003) for Li isotope diffusion in a dry basalt-rhyolite couple at 1350 textdegreeC. The similarity of the two values indicates little or no dependence of $beta$Li in silicate melts on either temperature or melt composition. The new data confirm a very high potential for diffusive fractionation of 6Li from 7Li and can be confidently used to model deviations in $delta$7Li to determine the time-temperature histories of natural rhyolite samples.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Marrocchi_etal2018_2,

title = {Oxygen isotopic diversity of chondrule precursors and the nebular origin of chondrules},

author = {Y. Marrocchi and J. Villeneuve and V. Batanova and L. Piani and E. Jacquet},

doi = {10.1016/j.epsl.2018.05.042},

year  = {2018},

date = {2018-01-01},

journal = {Earth and Planetary Science Letters},

volume = {496},

pages = {132--141},

abstract = {FeO-poor (type I) porphyritic chondrules formed by incomplete melting of solid dust precursors viaa yet-elusive mechanism. Two settings are generally considered for their formation: (i) a nebular setting where primordial solids were melted, e.g. by shock waves propagating through the gas and (ii) a collisional planetary setting. Here we report a method combining high-current electron microprobe X-ray mapping and quantitative measurements to determine the chemical characteristics of relict olivine grains inherited from chondrule precursors. We find that these olivine crystals are Ca--Al--Ti-poor relative to host olivine crystals. Their variable $Delta$17O, even in individual chondrule, is inconsistent with derivation from planetary interiors as previously argued from 120◦triple junctions also exhibited by the chondrules studied herein. This indicates that chondrule precursors correspond to solid nebular condensates formed under changing physical conditions.We propose that porphyritic chondrules formed during gas-assisted melting of nebular condensates comprising relict olivine grains with varying $Delta$17O values and Ca--Al--Ti-rich minerals such as those observed within amoeboid olivine aggregates. Incomplete melting of chondrule precursors produced Ca--Al--Ti-rich melts (CAT-melts), allowing subsequent crystallization of Ca--Al--Ti-rich host olivine crystalsviaepitaxial growth on relict olivine grains. Incoming MgO and SiO from the gas phase induced (i)the dilution of CAT-melts, as attested by the positive Al--Ti correlation observed in chondrule olivine crystals, and (ii) buffering of the O-isotope compositions of chondrules, as recorded by the constant $Delta$17O values of host olivine grains. The O-isotopic compositions of host olivine grains are chondrule-specific, suggesting that chondrules formed in an array of environments of the protoplanetary disk with different $Delta$17O values, possibly due to variable solid/gas mixing ratios.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vacher_etal2018,

title = {Collisional and alteration history of the CM parent body},

author = {L. Vacher and Y. Marrocchi and J. Villeneuve and M. J. Verdier-Paoletti and M. Gounelle},

doi = {10.1016/j.gca.2018.08.006},

year  = {2018},

date = {2018-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {239},

pages = {213--234},

abstract = {Boriskino is a little studied CM2 chondrite composed of millimeter-sized clasts of different lithologies and degrees of alteration. Boriskino thus offers a good opportunity to better understand the preaccretionary alteration history and collisional evolution that took place on the CM parent body. The least altered lithology displays 16O-poor Type 1a calcite and aragonite grains (d18O textasciitilde 30--37texttenthousand, d17O textasciitilde 15--18texttenthousand and D17Otextasciitilde-2 to 0texttenthousand, SMOW) that precipitated early, before the establishment of the petrofabric, from a fluid whose isotopic composition was established by isotopic exchange between a 16O-poor water and 16O-rich anhydrous silicates. In contrast, the more altered lithologies exhibit 16O-rich Type 2a and veins of calcite (d18O textasciitilde 17-- 23texttenthousand, d17O textasciitilde 6--9texttenthousand and D17Otextasciitilde-4 to -1texttenthousand, SMOW) that precipitated after establishment of the deformation, from transported16O-rich fluid in preexisting fractures. From our petrographic and X-ray tomographic results, we propose that the more altered lithologies of Boriskino were subjected to high intensity impact(s) (10--30 GPa) that produced a petrofabric, fractures and chondrule flattening. Taking all our results together, we propose a scenario for the deformation and alteration history of Boriskino, in which the petrographic and isotopic differences between the lithologies are explained by their separate locations into a single CM parent body. Based on the d13C-d18O values of the Boriskino Type 2a calcite (d13C textasciitilde 30--71texttenthousand,PDB), we propose an alternative d13C-d18O model where the precipitation of Type 2a calcite can occurred in an open system environment with the escape of 13C-depleted CH4 produced from the reduction of C-bearing species by H2 released during serpentinization or kamacite corrosion. Assuming a mean precipitation temperature of 110 textdegreeC, the observed d13C variability in T2a calcite can be reproduced by the escape of textasciitilde15--50% of dissolved carbon into CH4 by Rayleigh distillation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Chaussidon_etal2017,

title = {In situ analysis of non-traditional isotopes by SIMS and LA--MC--ICP--MS: key aspects and the example of Mg isotopes in olivines and silicate glasses},

author = {M. Chaussidon and Z. Deng and J. Villeneuve and J. Moureau and B. Watson and F. Richter and F. Moynier},

doi = {10.2138/rmg.2017.82.5},

year  = {2017},

date = {2017-01-01},

journal = {Reviews in Mineralogy and Geochemistry},

volume = {182},

pages = {127--163},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sossi_etal2017,

title = {Early Solar System irradiation quantified by linked vanadium and beryllium isotope variations in meteorites},

author = {P. A. Sossi and F. Moynier and M. Chaussidon and J. Villeneuve and C. Kato and M. Gounelle},

doi = {10.1038/s41550-017-0055},

year  = {2017},

date = {2017-01-01},

journal = {Nature Astronomy},

volume = {1},

number = {55},

abstract = {X-ray emission in young stellar objects (YSOs) is orders of magnitude more intense than in main sequence stars1,2, suggestive of cosmic ray irradiation of surrounding accretion disks. Protoplanetary disk irradiation has been detected around YSOs by the Herschel Space Observatory3. In our Solar System, short-lived 10Be (with a half-life of 1.39 Myr)4, which cannot be produced by stellar nucleosynthesis, was discovered in the oldest Solar System solids, the calcium--aluminium-rich inclusions (CAIs)5. The high 10Be abundance, as well as the detection of other tracers6,7, suggest 10Be likely originates from cosmic rayirradiation caused by solar flares8--10. Nevertheless, the nature of these flares (gradual or impulsive), the target (gas or dust), and the duration and location of irradiation remain unknown. Here we use the vanadium isotopic composition, together with the initial 10Be abundance to quantify irradiation conditions in theearly Solar System11. For the initial 10Be abundances recorded in most CAIs, 50V excesses of a few per mil (texttenthousand) relative to chondrites have been predicted8,9. We report 50V excesses in CAIs up to 4.4texttenthousand that co-vary with 10Be abundance. Their co-variation dictates that excess 50V and 10Be were synthesized through irradiationof refractory dust. Modelling of the production rate of 50V and 10Be demonstrates that the dust was exposed to solar cosmic rays produced by gradual flares for less than 300 years at ≈0.1 au from the protosun.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vacher_etal2017,

title = {Petrographic and C \& O isotopic characteristics of the earliest stages of aqueous alteration of CM chondrites},

author = {L. Vacher and Y. Marrocchi and J. Villeneuve and M. J. Verdier-Paoletti and M. Gounelle},

doi = {10.1016/j.gca.2017.06.049},

year  = {2017},

date = {2017-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {213},

pages = {271--290},

abstract = {CM chondrites form the largest group of hydrated meteorites and span a wide range of alteration states, with the Paris meteorite being the least altered CM described to date. Ca-Carbonates are powerful proxies for the alteration conditionsof CMs because they are direct snapshots of the chemical and isotopic compositions of the parent fluids. Here, we report a petrographic and a C isotope and O isotope survey of Ca-carbonates in Paris in order to better characterize the earlieststages of aqueous alteration. Petrographic observations show that Paris contains two distinct populations of Cacarbonates: Type 1a Ca-carbonates, which are surrounded by rims of tochilinite/cronstedtite intergrowths (TCIs), and newType 0 Ca-carbonates, which do not exhibit the TCI rims. The TCI rims of Type 1a Ca-carbonates commonly outline euhedral crystal faces, demonstrating that these Ca-carbonates were (i) partially or totally pseudomorphosed by TCI and (ii) precipitated at the earliest stages of aqueous alteration, before Type 0 Ca-carbonates. Isotopic measurements show that Paristextquoteright Ca-carbonates have d13C values that range from 19 to 80texttenthousand (PDB), d18O values that range from 29 to 41%, and d17O values that range from 13 to 24texttenthousand (SMOW). According to the d13C--d18O values of Paristextquoteright Ca-carbonates, we developed a new alteration model that involves (i) the equilibration of a primordial 17,18O-rich water (PW) with 16O-rich anhydrous silicates and (ii) varying contribution of 12C- and 13C-rich soluble organic matter (SOMs). It also suggests that many parameters control the C and O isotopic composition of Ca-carbonates, the principles being the degree of isotopic equilibration between the PW and the anhydrous silicates, the respective contribution of 12C and 13C-rich SOMs as well as the thermal evolution of CM parentbodies. Consequently, we suggest that CM Ca-carbonates could record both positive and negative d13C--d18O relationships, but a systematic correspondence is probably absent in CM chondrites due to the large number of factors involved in generatingthe isotopic characteristics of Ca-carbonates. From recent reports of the C-isotopic compositions of SOM in CM chondrites, we propose that water-soluble organic compounds were the most probable source of 13C enrichment in the majority of CM carbonates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vacher_etal2017_2,

title = {Erratum: textquotelefttextquoteleftInward Radial Mixing of Interstellar Water Ices in the Solar Protoplanetary Disktextquoterighttextquoteright (2016, ApJL, 827, L1)},

author = {L. G. Vacher and Y. Marrocchi and M. J. Verdier-Paoletti and J. Villeneuve and M. Gounelle},

year  = {2017},

date = {2017-01-01},

journal = {The Astrophysical Journal Letters},

volume = {836},

number = {1},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Vacher_etal2016,

title = {Inward radial mixing of interstellar water ices in the solar protoplanetary disk},

author = {L. Vacher and Y. Marrocchi and M. J. Verdier-Paoletti and J. Villeneuve and M. Gounelle},

doi = {10.3847/2041-8205/827/1/L1},

year  = {2016},

date = {2016-01-01},

journal = {The Astrophysical Journal Letters},

volume = {826},

pages = {1--6},

abstract = {The very wide diversity of asteroid compositions in the main belt suggests significant material transport in the solar protoplanetary disk and hints at the presence of interstellar ices in hydrated bodies. However, only a few quantitative estimations of the contribution of interstellar ice in the inner solar system have been reported, leading to considerable uncertainty about the extent of radial inward mixing in the solar protoplanetary disk 4.56 Ga ago. We show that the pristine CM chondrite Paris contains primary Ca-carbonates whose O-isotopic compositions require an 8%--35% contribution from interstellar water. The presence of interstellar water in Paris is confirmed by its bulk D/H isotopic composition that shows significant D enrichment (D/H = (167textpm0.2)texttimes10−6) relative to the mean D/H of CM chondrites ((145textpm3)texttimes10−6) and the putative D/H of local CM water((82textpm1.5)texttimes10−6). These results imply that (i) efficient radial mixing of interstellar ices occurred from the outer zone of the solar protoplanetary disk inward and that (ii) chondrites accreted water ice grains from increasingheliocentric distances in the solar protoplanetary disk},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Villeneuve_etal2015,

title = {Relationships between type I and type II chondrules: Implications on chondrule formation processes},

author = {J. Villeneuve and G. Libourel and C. Souli\'{e}},

doi = {10.1016/j.gca.2015.03.033},

year  = {2015},

date = {2015-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {160},

pages = {277--305},

abstract = {In unequilibrated chondrites, the ferromagnesian silicates in chondrules exhibit wide ranges of mg# = Mg/(Mg + Fe),allowing to sub-divide porphyritic chondrules into either type I (mg# \> 0.9) or type II (mg# \< 0.9). Although both chondruletypes formed under oxidizing conditions relative to the canonical solar nebula, it is generally inferred that type II chondrules formed in more oxidizing conditions than type I. In order to check whether this redox difference was established during chondrule formation, or reflects differences in their precursors, we have undertaken a set of experiments aimed at heating type I olivine-rich (A) chondrule proxy, i.e. forsterite + Fe metal + Ca--Mg--Si--Al glass mixtures, under oxidizing conditions. We show that high temperature (isothermal) oxidation of type IA-like assemblages is a very efficient and rapid process (e.g.few tens of minutes) to form textures similar to type IIA chondrules. Due to the rapid dissolution of Fe metal blebs, a FeO increase in the melt and in combination with the dissolution of magnesian olivine allows the melt to reach ferroan olivine saturation. Crystallization of ferroan olivine occurs either as new crystal in the mesostasis or as overgrowths on the remaining unresorbed forsterite grains (relicts). Interruption of this process at any time before its completion by rapid cooling allows to reproduce the whole range of textures and chemical diversity observed in type A chondrules, i.e. from type I to type II. Several implications on chondrule formation processes can be inferred from the presented experiments. Type I chondrules or fragments of type I chondrules are very likely the main precursor material involved in the formation of most type II chondrules. Formation of porphyritic olivine type II chondrules is very likely the result of processes generating crystal growth by chemical disequilibrium at high temperature rather than processes generating crystallization only by cooling rates. This questionsthe reliability of chondrule thermal history (e.g. cooling rate values) hitherto inferred for producing porphyritic textures from dynamical cooling rate experiments only. Type A chondrule formation can be a very fast process. After periods of subisothermal heating or slow cooling (\<50 K/h) as short as several tens of minutes and no longer than few hundreds of minutes at 1500--1800 C, type A chondrules terminates their formation by a fast cooling (\>103--104 K/h) in order to preserve their glassy mesostasis. Such inferred thermal history being at odds with nebular shock models, we thus advocate that impacts on planetesimals causing rapid melting and vaporization may provide the high density and highly volatile-enriched gaseous environments required to form chondrules. In this scenario, chondrules and their diversity should result from various degrees of interaction of the ejected fragments with the impact vapor plume; the most oxidizing conditions recorded in type IIA chondrules being very likely the closest to those imposed by the impact vapor plume.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Luu_etal2013,

title = {High precision Mg isotope measurements of meteoritic samples by secondary ion mass spectrometry},

author = {T. H. Luu and M. Chaussidon and R. K. Mishra and C. Rollion-Bard and J. Villeneuve and G. Srinivasan and J. L. Birck},

doi = {10.1039/C2JA30187C},

year  = {2013},

date = {2013-01-01},

journal = {Journal of Analytical Atomic Spectrometry},

volume = {28},

number = {1},

pages = {67--76},

abstract = {The possibility of establishing an accurate relative chronology of the early solar system events based on the decay of short-lived 26Al to 26Mg (half-life of 0.72 Myr) depends on the level of homogeneity (or heterogeneity) of 26Al and Mg isotopes. However, this level is difficult to constrain precisely because ofthe very high precision needed for the determination of isotopic ratios, typically of 
5 ppm. In this study, we report for the first time a detailed analytical protocol developed for high precision in situ Mg isotopic measurements (25Mg/24Mg and 26Mg/24Mg ratios, as well as 26Mg excess) by MC-SIMS. As the data reduction process is critical for both accuracy and precision of the final isotopic results, factors such as the Faraday cup (FC) background drift and matrix effects on instrumental fractionation have been investigated. Indeed these instrumental effects impacting the measured Mg-isotope ratios can be as large or larger than the variations we are looking for to constrain the initial distribution of 26Al and Mg isotopes in the early solar system. Our results show that they definitely are limiting factors regarding the precision of Mg isotopic compositions, and that an under- or over-correction of both FC background instabilities and instrumental isotopic fractionation leads to important bias on d25Mg, d26Mg and D26Mgvalues (for example, olivines not corrected for FC background drifts display D26Mg values that can differ by as much as 10 ppm from the truly corrected value). The new data reduction process described here can then be applied to meteoritic samples (components of chondritic meteorites for instance) to accurately establish their relative chronology of formation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Villeneuve_etal2012,

title = {Lack of relationship between 26Al ages of chondrules and their mineralogical and chemical compositions},

author = {J. Villeneuve and M. Chaussidon and G. Libourel},

doi = {10.1016/j.crte.2012.07.005},

year  = {2012},

date = {2012-01-01},

journal = {Comptes Rendus. G\'{e}oscience},

volume = {344},

number = {9},

pages = {423--431},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Villeneuve_etal2011,

title = {Magnesium isotopes constraints on the origin of Mg-rich olivines from the Allende chondrite: Nebular versus planetary?},

author = {J. Villeneuve and M. Chaussidon and G. Libourel},

doi = {10.1016/j.epsl.2010.10.025},

year  = {2011},

date = {2011-01-01},

journal = {Earth and Planetary Science Letters},

volume = {301},

pages = {107--116},

abstract = {High precision Mg isotope measurements by multi-collector ion microprobe show that refractory olivines from the Allende chondrite, either olivines isolated in the matrix (2 samples studied) or olivines in type I chondrules (6 samples studied), have variable $delta$26Mg* enrichments and deficits (calculated in permil as the26Mg deviation from the instrumental mass fractionation line) relative to the Earth. Most average $delta$26Mg* (noted $delta$26Mg*av) values (between 10 and 20 analyses per chondrule) are negative but the total range is from −0.029 (textpm0.010) texttenthousand (2 sigma errors) to +0.011 (textpm0.011) texttenthousand with an exception of one olivine at +0.043(textpm0.023) texttenthousand. These variations in $delta$26Mg*av reflect the formation of the olivines from reservoirs enriched in various amounts of 26Mg by the decay of short-lived 26Al (T1/2=0.73 Ma). Similarly, 30 analyses of olivines from the Eagle Station pallasite show a $delta$26Mg*av value of −0.033textpm0.008texttenthousand, as negative as some olivines from Allende chondrules and the Solar system initial $delta$26Mg* value of −0.038textpm0.004texttenthousand (defined at the time of formation of type B Ca--Al-rich inclusions -- CAIs -- when 26Al/27Al=5.23texttimes10−5, Jacobsen et al., 2008). Because olivines are Al-poor and because their Mg isotopic compositions are not reset during the chondruleforming events, their $delta$26Mg*av can be used to calculate model crystallization ages relative to various theoretical Mg isotope growth curves. The two end-member scenarios considered are (i) a textquotelefttextquoteleftnebulartextquoterighttextquoteright growth in which the Al/Mg ratio remains chondritic and (ii) a textquotelefttextquoteleftplanetarytextquoterighttextquoteright growth in which a significant increase of the Al/Mg ratio can be due to, for instance, olivine magmatic fractionation. The low $delta$26Mg*av value of olivines from the Eagle Station pallasite demonstrate that metal-silicate differentiation occurred as early as textasciitilde0.15-0.23 +0.29 Ma after CAIsin either of the growth scenarios. Similarly the variable $delta$26Mg*av values of refractory olivines can be understood if they were formed in planetesimals which started to differentiate as early as the Eagle Station parent body. Accretion of these planetesimals must have been coeval to the formation of CAIs and theirdisruption could explain why their fragments (Mg-rich olivines) were distributed in the chondrule forming regions of the disk.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Villeneuve_etal2009,

title = {Homogeneous distribution of 26Al in the solar system from the Mg isotopic composition of chondrules},

author = {J. Villeneuve and M. Chaussidon and G. Libourel},

doi = {10.1126/science.1173907},

year  = {2009},

date = {2009-01-01},

journal = {Science},

volume = {325},

number = {5943},

pages = {985--988},

keywords = {},

pubstate = {published},

tppubtype = {article}

}