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Partage des halogènes entre silicates hydroxylés en zone de subduction : modélisation ab initio et analyse in situ par LA-ICP-MS/MS

Abstract : The distribution of halogens in hydrous silicates representative of subduction zones is quantified by ab initio modelling and in situ analysis. The quantification of the energetic cost of the substitution of OH groups by halogens by an ab initio modelling allows studying the impact of crystal chemistry on halogen partitioning. Calculations are carried out in large systems where halogens are treated as point defects, in minor to trace concentrations. Results highlight the competition between the effects of electrostatic interactions and steric hindrance for incorporation of halogens. Interaction with alkalis, along with octahedral site occupancy, plays a major role in controlling halogen incorporation, especially in mica and amphibole. Calculation of partition coefficients predicts fractionation between halogens, and shows that pargasite, biotite and lizardite are favoured hosts for all three halogens, followed by clinochlore, tremolite and carpholite. Incorporation of halogens in dioctahedral phyllosilicates or epidote is unfavourable. A protocol for LA-ICP-MS/MS (with electron microprobe) has been proposed to quantify F, Cl and Br in metamorphic and refertilized mantle rocks from the Mont Albert ophiolitic complex (Quebec, Canada). The presence of halogen-bearing amphibole in the peridotite highlights refertilization of the mantle wedge by Cl-, Br-enriched fluids derived from the metamorphic rocks of the slab. This study sheds light on the behaviour of halogens at depth, with F mostly stored in the minerals of the slab (in mica and amphibole), whereas Cl and Br are also abundantly found in refertilized mantle rocks.
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Submitted on : Wednesday, July 6, 2022 - 1:02:29 PM
Last modification on : Tuesday, August 2, 2022 - 4:03:36 AM

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  • HAL Id : tel-03715374, version 1

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Sarah Figowy. Partage des halogènes entre silicates hydroxylés en zone de subduction : modélisation ab initio et analyse in situ par LA-ICP-MS/MS. Géochimie. Sorbonne Université, 2022. Français. ⟨NNT : 2022SORUS088⟩. ⟨tel-03715374⟩

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