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Can destabilization rims of hydrous minerals be used to constrain magma ascent kinetics at lava dome volcanoes ?

France, L., Bulletin of Volcanology

Can destabilization rims of hydrous minerals be used to constrain magma ascent kinetics at lava dome volcanoes ?

France, L.

Bulletin of Volcanology, 2020, 82, 66

Abstract :

Time constraints on igneous processes related to eruption triggering, e.g., magma mixing or ascent in the conduit, are needed in any risk mitigation attempt. In this context, magma ascent rate and kinetics are key parameters as they may correspond to the response time available to civil protection during volcanic unrest. Several tools available to quantify such durations include diffusion chronometry, isotopic geochemistry, and hydrous mineral destabilization related to magma degassing during ascent through the conduit. Here I discuss the possible limitations of the widely used hydrous mineral destabilization chronometry applied to minerals within large lava bodies that cool relatively slowly (over days or weeks) such as thick lava flows and lava domes. Based on the type case of the Sarcoui dome (Chaîne des Puys, France) and its associated phreatomagmatic outbreak deposits, I suggest that hydrous mineral destabilization rims may, in some cases, develop at the surface during dome emplacement. From this perspective, preeruptive timescales calculated based on disequilibrium kinetics will be greatly underestimated, leading to a serious issue in the reconstruction of the eruption dynamics and its possible applications to emergency management for future eruptions. More generally, hydrous mineral destabilization chronometry should be used with great caution. Nevertheless, it remains a choice tool to quantify magma ascent rates for eruptions during which magmas quench upon arrival at the surface (e.g., Plinian, Vulcanian, or phreatomagmatic eruptions), with pumiceous textures being a good indicator of quenching. In the case of lava dome emplacement, I suggest that the minerals embedded in pumiceous clasts emitted during explosive phases are more reliable candidates for chronometry studies than crystals within the dome itself as those clasts might represent the fresh magma that triggered the explosion.

Voir en ligne : https://doi.org/10.1007/s00445-020-...




publié mardi 6 octobre 2020