P-V-T-X Evolution of Olivine-hosted Melt Inclusions and Implications for Interpretation of Homogenization Experiments

Abstract : Olivine-hosted melt inclusions (MIs) provide unique insights into physico-chemical conditions of magma at depth. MIs are often rehomogenized in laboratory to bring them back (or close) to the original state. At homogenization temperature (Th), the last bubble disappears and MI becomes a homogeneous liquid phase. However, during 1-atm experiments in heating stages, homogenization is usually achieved at Th higher than expected entrapment T and systematic increase of Th with time is observed. This reveals occurrence of physico-chemical processes that irreversibly lower internal pressure (Pint) (relative to entrapment P) during magma ascent and laboratory treatments. We combined theoretical modeling with experimental observations on H2O-poor and H2O-rich basaltic MIs in order to: a) identify the reversible (olivine elastic deformation and olivine dissolution-crystallization on MI walls) and irreversible (water loss from MIs and olivine plastic deformation) processes responsible for evolution of MI volume, Pint and composition upon heating, and b) examine how these processes affect the results of typical homogenization experiments. Due to Pint drop caused by olivine elastic deformation, performing experiments at 1 atm prevents achievement of homogenization at Th equal to entrapment T. Predicted increase of Th ranges from some to tens of degrees depending on entrapment conditions, melt composition and volatile contents. Presence of a gas bubble must be considered for the correct prediction of P-volume evolution. In H2O-rich MIs, faster increase of Th with time shown by small MIs is consistent with increase of Th mainly driven by water loss. In H2O-poor MIs, occurrence of olivine elastoplastic deformation is mainly responsible for the increase of Th with time. Distance from MI wall to olivine rim is a critical parameter to take into account, as short distances enhance depressurization related with both elastoplastic deformation and water loss and contribute to increase Th.
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https://hal.uca.fr/hal-02404844
Contributor : Federica Schiavi <>
Submitted on : Wednesday, December 11, 2019 - 3:22:51 PM
Last modification on : Thursday, December 19, 2019 - 2:06:24 AM

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Federica Schiavi, A. Provost, P. Schiano, N. Cluzel. P-V-T-X Evolution of Olivine-hosted Melt Inclusions and Implications for Interpretation of Homogenization Experiments. American Geophysical Union, Fall Meeting 2015, Dec 2019, San Francisco, United States. ⟨hal-02404844⟩

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