40Ar diffusion in phlogopite: P V T atomistic calibration and implications for Ar–melt–solid kinetic interactions and ascent dynamics of mantle xenoliths and kimberlites - INSU - Institut national des sciences de l'Univers Accéder directement au contenu
Article Dans Une Revue Geochimica et Cosmochimica Acta Année : 2024

40Ar diffusion in phlogopite: P V T atomistic calibration and implications for Ar–melt–solid kinetic interactions and ascent dynamics of mantle xenoliths and kimberlites

Résumé

40Ar/39Ar ages of phlogopite from kimberlite-hosted mantle xenoliths are commonly older than the kimberlite eruption, despite the fact that argon is supposed not to be retained by phlogopite at temperatures above hydrothermally-derived Ar closure temperatures (). Combining Molecular Dynamics (MD) with Nudged Elastic Band (NEB) and Transition State Theory (TST), we investigate 40Ar (PressureVolumeTemperature) relationships in pristine, defect-free, phlogopite and show that 40Ar diffusivity is several orders of magnitude slower than existing estimates with a strong effect of pressure on diffusion rates and retention of 40Ar at mantle conditions. These results imply to fundamentally revise residence- and transit-time estimates based on Ar kinetics in phlogopite assuming simple diffusive relaxation during upwelling. When accounting for pressure, 40Ar retention trends in phlogopite predict substantially slower kimberlite ascent rates than documented by independent chronometers, indicating that 40Ar resetting during ascent in phlogopite does not result from simple decompression-driven diffusive relaxation. We argue that 40Ar remobilization probably involves secondary structural–textural modifications induced by reaction-driven recrystallization or rim overgrowth. These findings have far-reaching consequences in terms of argon isotopic mobility at mantle depths as well as for dating and tracing metasomatic events during crustmantle interactions in the evolution of the subcontinental mantle.
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Dates et versions

insu-04675027 , version 1 (22-08-2024)

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Jehiel Nteme, Stéphane Scaillet, Pascal Brault, Laurent Tassan-Got, Florian Duval. 40Ar diffusion in phlogopite: P V T atomistic calibration and implications for Ar–melt–solid kinetic interactions and ascent dynamics of mantle xenoliths and kimberlites. Geochimica et Cosmochimica Acta, 2024, ⟨10.1016/j.gca.2024.07.008⟩. ⟨insu-04675027⟩
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