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Reevaluation of metal interconnectivity in a partially molten silicate matrix using 3D microtomography

Néri, Adrien and Guignard, Jérémy and Monnereau, Marc and Bystricky, Misha and Perrillat, Jean-Philippe and Andrault, Denis and King, Andrew and Guignot, Nicolas and Tenailleau, Christophe and Duployer, Benjamin and Toplis, Michael J. and Quitté, Ghylaine Reevaluation of metal interconnectivity in a partially molten silicate matrix using 3D microtomography. (2020) Physics of the Earth and Planetary Interiors, 308. 106571. ISSN 0031-9201

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Official URL: https://doi.org/10.1016/j.pepi.2020.106571

Abstract

Understanding metal-silicate differentiation in small rocky bodies that accreted early in solar system history requires quantification of the effects of variable amounts of silicate melt and molten metal on the connectivity of metal-rich liquids. To shed light on this question, the equilibrium geometry and textural ripening of metal grains in the vicinity of the metal interconnection threshold have been determined experimentally. High pressure and temperature experiments were performed in the three-phase system forsterite + silicate melt + nickel at conditions of 1 GPa and up to 2080 K using piston-cylinder and Paris-Edinburgh presses. Sample textures were analyzed by 3D X-Ray microtomography either in-situ at the PSICHE beamline of the SOLEIL synchrotron, or on quenched samples using a laboratory Computed Tomography scan. Although dihedral angles point to textural equilibrium at the scale of individual grains at the end of each experiment, the attainment of textural equilibrium at sample scale is not straightforward. Depending on the relative proportions of the phases, different states of textural maturation are revealed. A particularly important issue is that time-resolved in-situ microtomography data show that cold (subsolidus) compression at the beginning of the experiment leads to soft metal grains being squeezed between silicates, leading to a forced interconnectivity of nickel. High temperature experiments with metal contents ≤20 vol% resulted in disruption of these forced networks, while the networks persisted in time for metal contents ≥25 vol%. This is taken to indicate that the stable interconnection threshold of pure nickel in a partially molten silicate matrix lies between 20 and 25 vol%. Therefore, we conclude that care must be taken when defining the interconnection threshold: not only should there be existence of a network of touching grains, but this network must persist in time in the absence of external forces and at pressure-temperature conditions that permit grain-boundary movement (i.e. excluding kinetically arrested systems). Growth of silicate grains is identified as the process driving textural maturation, and may explain the variability of interconnection thresholds reported in the literature. In addition, these considerations shed light on the diversity of textures observed in natural meteoritic samples (e.g. carbonaceous and ordinary chondrites and primitive achondrites), providing textural arguments to constrain the processes that affected these meteorites.

Item Type:Article
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National d'Études Spatiales - CNES (FRANCE)
French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Other partners > Ecole Normale Supérieure de Lyon - ENS de Lyon (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
French research institutions > Institut de Recherche pour le Développement - IRD (FRANCE)
Other partners > Synchrotron SOLEIL - SSOLEIL (FRANCE)
Other partners > Université Clermont Auvergne - UCA (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
Other partners > Université de Nantes (FRANCE)
Other partners > Université Claude Bernard-Lyon I - UCBL (FRANCE)
Other partners > Université Jean Monnet - St Etienne (FRANCE)
Other partners > Université d'Angers (FRANCE)
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Funders:
Agence Nationale de la Recherche - ANR
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Deposited On:09 Dec 2020 15:42

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