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Le Touquet – Paris-Plage, France

Betto D.,Trinity College Dublin | Thiyagarajah N.,Trinity College Dublin | Lau Y.-C.,Trinity College Dublin | Piamonteze C.,Paul Scherrer Institute | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

The site-specific magnetic properties of thin films of the Heusler compound Mn2RuxGa, 0.6 Source

Malvoisin B.,Ecole Normale Superieure de Paris | Malvoisin B.,Joseph Fourier University | Chopin C.,Ecole Normale Superieure de Paris | Brunet F.,Ecole Normale Superieure de Paris | And 2 more authors.
Journal of Petrology | Year: 2012

In the Alpine blueschist- to eclogite-facies meta-ophiolitic units of northern Corsica, the contact between a serpentinite body and an immediately overlying siliceous marble is remarkable for the occurrence of wollastonite and, on the marble side, a dark halo around the serpentinite. The refolded, continuous contact is a rodingite-type reaction zone with a centimetre-thick nephritic selvage of diopside + andradite/grossular ± perovskite on the serpentinite side, followed towards the marble by a 1-5 cm thick zone of massive wollastonite (± grossular), followed by a 5-20 cm thick dark zone (the halo) consisting of wollastonite + quartz + graphitic material (± grossular ± diopside), with no carbonate. The transition to the overlying wollastonite-free, calcite + quartz-bearing layers is sharp. Considering the stability of calcite + quartz everywhere else in the regional metamorphic series, this low-temperature occurrence of wollastonite (c. 400-450°C) requires unusual conditions. A clue to its origin is the abundance of graphitic matter with the wollastonite within a few decimetres of the serpentinite body. We interpret this observation as evidence for local reduction of Ca-carbonate to form elemental carbon and wollastonite according to the reactionA similar carbonate + mica reduction reaction is responsible for the disappearance of phengite and the appearance of grossular + carbon within a narrow zone in the marble above the wollastonite-quartz zone. Textural and solubility considerations suggest that the development of the zonal sequence is an essentially diffusive process. Thermochemical modelling of mineral stability in the successive reaction zones suggests a positive oxygen-fugacity gradient from the serpentinite to the marble (-6 < ΔFMQ < -1), mediated through a CH. 4- and H. 2-bearing aqueous intergranular fluid. In line with the field evidence, it is calculated that a serpentinite body equilibrated at ΔFMQ -4 after oceanic serpentinization can still impose, through Fe. 2+-bearing serpentine oxidation, highly reducing conditions while entrained at depth in a subduction wedge and channel. This may contribute to the presence of H. 2 ± CH. 4 in the fluid and cause the destabilization of calcite in favour of graphite. In addition to the consequences for wollastonite and elemental carbon formation at low temperature, this finding has direct implications for redox conditions in subduction zones. © The Author 2011. Published by Oxford University Press. All rights reserved. Source

Sautter V.,IMPMC | Toplis M.J.,IRAP | Beck P.,Institute Of Planetologie Et Dastrophysique | Mangold N.,LPG Nantes | And 16 more authors.
Lithos | Year: 2016

Until recently, Mars was considered a basalt-covered world, but this vision is evolving thanks to new orbital, in situ and meteorite observations, in particular of rocks of the ancient Noachian period. In this contribution we summarise newly recognised compositional and mineralogical differences between older and more recent rocks, and explore the geodynamic implications of these new findings. For example the MSL rover has discovered abundant felsic rocks close to the landing site coming from the wall of Gale crater ranging from alkali basalt to trachyte. In addition, the recently discovered Martian regolith breccia NWA 7034 (and paired samples) contain many coarse-grained noritic-monzonitic clasts demonstrably Noachian in age, and even some clasts that plot in the mugearite field. Olivine is also conspicuously lacking in these ancient samples, in contrast to later Hesperian rocks. The alkali-suite requires low-degree melting of the Martian mantle at low pressure, whereas the later Hesperian magmatism would appear to be produced by higher mantle temperatures. Various scenarios are proposed to explain these observations, including different styles of magmatic activity (i.e. passive upwelling vs. hotspots). A second petrological suite of increasing interest involves quartzo-feldspathic materials that were first inferred from orbit, in local patches in the southern highlands and in the lower units of Valles Marineris. However, identification of felsic rocks from orbit is limited by the low detectability of feldspar in the near infrared. On the other hand, the MSL rover has described the texture, mineralogy and composition of felsic rocks in Gale crater that are granodiorite-like samples akin to terrestrial TTG (Tonalite-Trondhjemite-Granodiorite suites). These observations, and the low average density of the highlands crust, suggest the early formation of 'continental' crust on Mars, although the details of the geodynamic scenario and the importance of volatiles in their generation are aspects that require further work. © 2016 Elsevier B.V. Source

Amadou N.,Ecole Polytechnique - Palaiseau | Brambrink E.,Ecole Polytechnique - Palaiseau | Benuzzi-Mounaix A.,Ecole Polytechnique - Palaiseau | Huser G.,French Atomic Energy Commission | And 12 more authors.
High Energy Density Physics | Year: 2013

The study of iron under quasi-isentropic compression using high energy lasers, might allow to understand its thermodynamical properties, in particular its melting line in conditions of pressure and temperature relevant to Earth-like planetary cores (330-1500 GPa, 5000-8000 K). However, the iron alpha-epsilon solid-solid phase transition at 13 GPa favors shock formation during the quasi-isentropic compression process which can depart from the appropriate thermodynamical path. Understanding this shock formation mechanism is a key issue for being able to reproduce Earth-like planetary core conditions in the laboratory by ramp compression. In this article, we will present recent results of direct laser-driven quasi-isentropic compression experiments on iron samples obtained on the LULI 2000 and LIL laser facilities. © 2013 Elsevier B.V. Source

Drouin S.,University of Tours | Boussafir M.,University of Tours | Robert J.-L.,IMPMC | Alberic P.,University of Tours | Durand A.,University of Tours
Organic Geochemistry | Year: 2010

In order to investigate the role of clay minerals in organic matter preservation, the fixation of pure organic compounds on two synthetic low charge and high charge saponites was investigated in laboratory experiments simulating marine water conditions. The clays were exposed to four carboxylic acids: pentadecanoic, docosanoic, 5β-cholanic acid and ursolic, dissolved in treated natural sea water. Characterization of the resulting organo-clay association indicates that, under marine water column conditions, the organic fixation is only a sorption process, no intercalation being observed. The surface coverage, similar for the two clays (ca. 0.04 mg organic carbon m-2), demonstrates that the sorption is controlled by the surface properties of clays rather than their cation exchange capacity. The weaker sorption of docosanoic acid underlines the major role of the molecular properties, but the lack of selectivity among the three others does not corroborate the influence of molecular size on the sorption process. The general failure of a chemolysis treatment performed on the organo-clay associations demonstrates the high stability of these complexes. Results suggest that the bonding mechanisms are dominated by ligand exchange and not by hydrophobic effects, cation bridges or cation exchange. The minor extractable organic fraction consists of acid molecules connected to clay surfaces by van der Waals interactions. The high stability of the bonds formed in this environment, close to that observed in previous studies of marine sediments, could explain in part organic matter preservation during transfer across marine water columns, especially metabolisable material. © 2009 Elsevier Ltd. All rights reserved. Source

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