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Microstructural evolution in deforming olivine-serpentine aggregates at subduction zones conditions using in-situ X-ray tomography

Abstract : Rheology and deformation of serpentinized peridotite play and important role in the flow and dynamicsof thesubducting slab. Antigorite, the high-temperature variety mineral of serpentinegroup, coexists with olivine in serpentinized peridotite at conditions of subduction zones.It is generally accepted that antigorite mechanical strength is lower than olivine at geological strain rates. Therefore,in a bimineralic rock comprising olivine and antigorite, deformation localization is expected to occur in the weaker antigoriterather than in olivine. Based on polymineralic rocks mechanical and microstructural behaviours (e.g., Handy, 1990), two mainend-member configurations arepossible: the strong olivine crystals form a loadbearing framework(LBF) that contains spaces filled with antigorite; or the antigorite governsthe bulk rheology of the aggregate by forming an interconnected weak layer(IWL), while the olivine crystals behave as clasts.The aim of this study is to observe at which conditions an IWL stage may be achieved under simple shear deformation in serpentinized peridotite at subduction zones conditions.Wecarried out torsion experiments at high pressures (HP, > 2 GPa) and high temperatures (HT, 400-600°C) on antigorite + olivine aggregates asaproxy for partially serpentinized peridotite. The experiments are coupled with in-situX-ray tomography on the PSICHE beamline at SOLEIL synchrotron. Weretrieve and quantify 2-D and 3-D information on fabricsand/or microstructureevolutionsunder HP-HT, extent of interconnection(or connectivity), preferred microstructural directions and morphologyof the weak antigorite phase. We also perform post-mortemelectron microscopy analysis onrecovered samplesof interestto link our X-ray tomography observations to the plastic propertiesand/or deformation mechanism of the phases.Our results suggest that the total connectivity of the weak antigorite increases with thestrain extenttransferred to the samples, with antigorite minerals forming, in some cases, clear interconnected weak layers in agreement with IWL behaviour.The stronger olivinethen shows localized lattice bending/rotation in clasts indicating local deformation accommodated by intracrystalline low-temperature plasticity.
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https://hal.univ-lille.fr/hal-03164202
Contributeur : Lilloa Université de Lille <>
Soumis le : mardi 9 mars 2021 - 17:11:36
Dernière modification le : mercredi 7 juillet 2021 - 03:42:04

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  • HAL Id : hal-03164202, version 1

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Tommaso Mandolini, Nadege Hilairet, Julien Chantel, Sébastien Merkel, Yann Le Godec, et al.. Microstructural evolution in deforming olivine-serpentine aggregates at subduction zones conditions using in-situ X-ray tomography. 17th International Symposium on Experimental Mineralogy, Petrology and Geochemistry (EMPG), Mar 2021, Online, Germany. ⟨hal-03164202⟩

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