Papers by Philippe GILLET
Meteoritics & Planetary Science, 2014
Two petrographic settings of carbonaceous components, mainly filling open fractures and occasiona... more Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ13C = −12.8 to −33.1‰) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insolu...
Minerals, 2021
Both seismic observations of dense low shear velocity regions and models of magma ocean crystalli... more Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between coexisting lower mantle phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO3 bridgmanite, and (Mg,Fe)SiO3 post-perovskite. The partitioning of iron between these phases was investigated in synthetic ferrous-iron-rich olivine compositions (Mg0.55Fe0.45)2SiO4 and (Mg0.28Fe0.72)2SiO4 at lower mantle conditions ranging from 33–128 GPa and 1900–3000 K in the laser-heated diamond anvil cell. The resulting phase assemblages were characterized by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy. The exchange coefficient between bridgmanite and magnesiowüstite decreases with pressure and bulk Fe# and increases with temperature. Thermodynamic modeling determines that...
Nature Communications, 2018
Planetary formation models show that terrestrial planets are formed by the accretion of tens of M... more Planetary formation models show that terrestrial planets are formed by the accretion of tens of Moon- to Mars-sized planetary embryos through energetic giant impacts. However, relics of these large proto-planets are yet to be found. Ureilites are one of the main families of achondritic meteorites and their parent body is believed to have been catastrophically disrupted by an impact during the first 10 million years of the solar system. Here we studied a section of the Almahata Sitta ureilite using transmission electron microscopy, where large diamonds were formed at high pressure inside the parent body. We discovered chromite, phosphate, and (Fe,Ni)-sulfide inclusions embedded in diamond. The composition and morphology of the inclusions can only be explained if the formation pressure was higher than 20 GPa. Such pressures suggest that the ureilite parent body was a Mercury- to Mars-sized planetary embryo.
Meteoritics & Planetary Science, 2017
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Proceedings of the National Academy of Sciences of the United States of America, Jan 4, 2016
We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron ... more We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth's lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth's mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D" layer. The succession of layers could dynamically decouple the mantle above 2,000 km from th...
Science, 2006
The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them ... more The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.
Proceedings of the National Academy of Sciences, 2008
Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pr... more Peace River is one of the few shocked members of the L-chondrites clan that contains both high-pressure polymorphs of olivine, ringwoodite and wadsleyite, in diverse textures and settings in fragments entrained in shock-melt veins. Among these settings are complete olivine porphyritic chondrules. We encountered few squeezed and flattened olivine porphyritic chondrules entrained in shock-melt veins of this meteorite with novel textures and composition. The former chemically unzoned (Fa 24–26 ) olivine porphyritic crystals are heavily flattened and display a concentric intergrowth with Mg-rich wadsleyite of a very narrow compositional range (Fa 6 –Fa 10 ) in the core. Wadsleyite core is surrounded by a Mg-poor and chemically stark zoned ringwoodite (Fa 28 –Fa 38 ) belt. The wadsleyite–ringwoodite interface denotes a compositional gap of up to 32 mol % fayalite. A transmission electron microscopy study of focused ion beam slices in both regions indicates that the wadsleyite core and ri...
Mineralogical Magazine, 1998
Meteoritics & Planetary Science, 2009
The howardite-eucrite-diogenite (HED) clan is a group of meteorites that probably originate from ... more The howardite-eucrite-diogenite (HED) clan is a group of meteorites that probably originate from the asteroid Vesta. Some of them are complex breccias that contain impact glasses whose compositions mirror that of their source regions. Some K-rich impact glasses (up to 2 wt% K 2 O) suggest that in addition to basalts and ultramafic cumulates, K-rich rocks are exposed on Vesta s surface. One K-rich glass (up to 6 wt% K 2 O), with a felsic composition, provides the first evidence of highly differentiated K-rich rocks on a large asteroid. They can be compared to the rare lunar granites and suggest that magmas generated in a large asteroid are more diverse than previously thought.
Geochimica et Cosmochimica Acta, 2006
Ion-microprobe was used to measure Li abundances and isotopic compositions in pyroxenes from thre... more Ion-microprobe was used to measure Li abundances and isotopic compositions in pyroxenes from three Martian meteorites belonging to the nakhlite family. The profiles performed across augite crystals from Northwest Africa 817 show a large isotopic zoning from crystal cores (delta Li-7 similar to 0 parts per thousand) to rims (delta Li-7 similar to +20 parts per thousand) while Li abundances are almost constant (similar to 9.2 mu g/g). Unlike NWA 817, the pyroxene studied in the Miller Range 03346 nakhlite shows a zoning in Li abundance, with concentrations increasing from similar to 2.5 mu g/g in the core to similar to 9 mu g/ g in the rim. The augite rim (delta Li-7 = +7 parts per thousand) is slightly enriched in Li-7 with regard to the core (delta Li-7 = +4 parts per thousand), but most of the isotopic variations observed occur at an intermediate position along the profile, where 67 Li falls down to similar to-11 parts per thousand. In the case of Nakhla, Li concentrations in augite increase from cores (similar to 3.5 mu g/g) to rims (similar to 6.5 mu g/g), while the delta Li-7 variation is restricted (i.e., between delta Li-7 = +6.0 and +12.6 parts per thousand). For the three meteorites the Li abundances were also measured in the groundmass, which was found to be enriched in lithium (similar to 10 mu g/g). Conventional magmatic and post-magmatic processes such as alteration and fractional crystallization, fail to explain the dataset obtained on nakhlites. Degassing processes, which were previously proposed to explain the Li distribution in shergottite crystals, cannot result in the strong decoupling between Li abundances and isotopic composition observed in nakhlites. We suggest that the original magmatic Li distributions (concentrations and isotopic compositions) in nakhtites have been modified by diffusion of Li from the Li-rich groundmass towards the pyroxene crystals during sub-solidus cooling. Diffusion appears to have been efficient for NWA 817 and MIL 03346 but. apparently, did not produce a significant migration of Li in Nakhla, possibly because of the lower abundance of groundmass in the latter. Diffusion induced Li redistributions may also affect terrestrial porphyric rocks but very specific cooling rates are required to quench the diffusion profiles as observed in two of the present nakhlites.
Earth and Planetary Science Letters, 2008
The transformation of pyroxene to its high-pressure polymorph akimotoite (MgSiO 3 ilmenite type s... more The transformation of pyroxene to its high-pressure polymorph akimotoite (MgSiO 3 ilmenite type structure) is documented in the shock-induced melt veins of the L6 Tenham chondrite. Four textural relationships between pyroxene and akimotoite are observed in former pyroxene grains entrained in the shear melt vein and in pyroxene grains attached to the wall of the melt vein. In one of the entrained enstatite grains the transformation to akimotoite is partial. One third of the grain is transformed to a polycrystalline aggregate of akimotoite with a scalloped interface with enstatite. Akimotoite (Fe 0,4 Mg 1,24 Ca 0.07 Na 0,12 Al 0,14)(Si 1,963 Al 0,037)O 6 is slightly enriched in Ca (CaO = 1.74%), Al and Na with respect to enstatite (CaO = 0.71%). Narrow bands of polycrystalline akimotoite with three crystallographic orientations and a chemical composition similar to the surrounding enstatite intersect the other part of the grain. In a second grain entrained in the shear melt vein, tablets of akimotoite are interwoven with a pyroxene glass with a lower Na and Fe content and a higher Mg content compared to the adjacent akimotoite. This pyroxene glass is probably the product of (Mg,Fe)SiO 3-perovskite amorphization. Polycrystalline akimotoite is also formed at the expense of enstatite at the vein wall of the shear melt vein. In that case akimotoite is also enriched in Ca (CaO = 2.85%) Na (NaO = 1.72%) and Al (Al 2 O 3 = 4.14%). All these observations suggest that akimotoite is mainly formed by solid-state transformation of former pyroxenes with subsequent diffusion of calcium, aluminum and sodium from the chondritic melt of the shear melt vein. Finally, the first complete X-ray diffraction pattern of natural akimotoite is presented.
Earth and Planetary Science Letters, 2007
![Research paper thumbnail of A new natural high-pressure (Na,Ca)-hexaluminosilicate [(CaxNa1−x)Al3+xSi3−xO11] in shocked Martian meteorites](https://attachments.academia-assets.com/111430480/thumbnails/1.jpg)
Earth and Planetary Science Letters, 2004
A (Ca,Na)-hexaluminosilicate, whose Ca end member was previously synthesized in numerous high-pre... more A (Ca,Na)-hexaluminosilicate, whose Ca end member was previously synthesized in numerous high-pressure experiments, has been identified by Raman spectroscopy in heavily shocked Martian meteorites. This mineral has a structural formula close to (Ca x Na 13x)Al 3þx Si 33x O 11 and is similar to the calcium aluminum silicate phase previously synthesized in high-pressure experiments performed on anorthite and rocks of basaltic composition. This new mineral occurs in shock melt pockets in two distinct settings and is intimately intergrown with SiO 2-stishovite. The first setting, encountered in Zagami, consists of idiomorphic equant crystals overgrown by acicular stishovite that crystallized from a melt of labradorite composition. The second setting contains the (Na,Ca)-hexaluminosilicate phase intergrown with stishovite and hollandite and was formed during partial melting at high pressures. The mineralogical association (Na,Ca)-hexaluminosilicate+stishovite was observed in shock melt pockets, which have distinct bulk compositions in seven Martian shergottites. This new mineral represents, after majorite, the second natural occurrence of a silicate mineral with silicon in both four and six coordination. The assemblage stishovite+(Na,Ca)hexaluminosilicate sets constraints on the pressure and temperature conditions that prevailed during shock in some of the studied meteorites. The (Na,Ca)-hexaluminosilicate mineral is a potential carrier of Al and Na during subduction of oceanic crust in the lower mantle of the Earth.
Earth and Planetary Science Letters, 2002
North West Africa (NWA 817) is a single stone of 104 g found in the Sahara (Morocco) by meteorite... more North West Africa (NWA 817) is a single stone of 104 g found in the Sahara (Morocco) by meteorite hunters in November 2000. The meteorite is an unbrecciated, medium-grained olivine-bearing clinopyroxenite with a cumulate texture. It consists of zoned euhedral subcalcic augite (Wo 42 En 38À22 Fs 20À36), olivine spanning a wide range of compositions (from Fa 56 in the core to Fa 86) with rare magmatic inclusions and an intercumulus mesostasis made of Febearing albitic plagioclase, Si-rich glass, Ti-magnetite with unusual skeletal growth morphologies containing ilmenite exsolutions, acicular pyroxene, olivine and cristobalite. Trace minerals are sulfide droplets and Cl-apatite. Mineral modes (in vol%) are augite 69%, olivine 10%, mesostasis 20% and Fe^Ti oxides 1%. Pervasive alteration produced a reddish clay mineral (hydrous ferrous silicate) in both olivine crystals and the mesostasis. The major element composition of NWA 817 is very similar to that of the other nakhlites: high FeO, MgO and CaO concentrations reflect the abundance of cumulus augite and olivine. Key element ratios such as FeO/MnO (= 37), Na/Al (= 0.40), K/La (= 449), Ga/Al (= 3.9U10 34) and oxygen isotopic composition (v 17 O = +0.37x) are clear evidence for a Martian origin. The incompatible trace element pattern as in Nakhla displays a strong light rare earth element enrichment relative to chondrite (La n /Yb n = 4.89). However, when compared to the other nakhlites, NWA 817 has specific features: (1) a higher modal proportion of mesostasis; (2) quench textures of Ti-magnetite and Fe-rich clinopyroxene; (3) more Mg-rich olivine core compositions whereas the augite core composition is identical for all nakhlites; (4) a stronger Fe enrichment toward crystal rims of these cumulus minerals. The intercumulus minerals (Ti-magnetite with skeletal growth morphology, acicular chains of clinopyroxene and Fe 3-rich feldspar) indicate rapid crystallization in response to a high degree of undercooling at the end of the sample story.
Chemical Geology, 1998
Long-term evolution of the Earth's water cycle is investigated t... more Long-term evolution of the Earth's water cycle is investigated to predict potential variations in the hydrogen stable isotope composition of seawater. Mass balance calculations are used to estimate the δD value of the early ocean before storage of water (about 20% of the present-day size) in the biosphere, cryosphere, sediments, and metamorphic rocks. The early ocean was plausibly deuterium-depleted (δD=− 18±6‰) in comparison with the present-day oceans (δD= 0‰). A kinetic treatment of the long-term water cycle suggests that hydrogen ...
Annual Review of Earth and Planetary Sciences, 2013
Impacts are central to the origin and evolution of planets of the Solar System. The shapes of cra... more Impacts are central to the origin and evolution of planets of the Solar System. The shapes of craters, which can reach up to 1,000 km in diameter on the Moon, provide critical information on the large-scale dynamics of the impact and related shock. Minerals formed at high pressure and temperature found in shocked terrestrial rocks and meteorites give additional and complementary insights on the shock process at a smaller scale, typically from a few micrometers to a few millimeters. Local flaws in rocks, such as voids and mineral interfaces, are the preferential sites for the formation of high-pressure melts and minerals. Calculations based on the physics of shocks and the thermodynamics and kinetics of mineral transformations provide orders of magnitude for the duration, transient pressure, and prevailing temperature conditions of shock events. Case studies on shocked terrestrial and extraterrestrial materials illustrate the links between these parameters and impact duration. Many o...
Journal of Geophysical Research: Solid Earth, 1998
Melting and subsolidus relations in the (Mg,Fe)SiO3‐(Mg,Fe)CO3, (Mg,Fe) 2SiO4‐(Mg,Fe)CO3, and (Mg... more Melting and subsolidus relations in the (Mg,Fe)SiO3‐(Mg,Fe)CO3, (Mg,Fe) 2SiO4‐(Mg,Fe)CO3, and (Mg,Fe)O‐(Mg,Fe)CO3 systems have been investigated at 14, 15, 16 and 25 GPa, 1973 K and 2173 K, using a 1000 t uniaxial multi anvil split sphere apparatus. The iron‐magnesium partition coefficients between magnesite and silicates or oxides have been measured in subsolidus assemblages. Iron is always partitioned preferentially in the silicate and oxide phases, the order of increasing partitioning being pyroxene, olivine, silicate perovskite, wadsleyite and magnesiowüstite. A thermodynamic model of iron‐magnesium distribution between magnesite and all these phases, based on Gibbs free energy minimization, is established. Melting of pyroxene‐magnesite and olivine‐magnesite pseudo binary systems is eutectic, with eutectic points close to 1973 K and 60 mol % carbonate at 15 GPa in both systems. In the more complex mantle system, it is likely that such melts would form in the transition zone by h...
Nature, 1998
Acknowledgements. We acknowledge grant support from the NSF (D.M.R.
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Papers by Philippe GILLET