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Kinetics of mafic magma transfer and destabilization of the deep plumbing system in monogenetic volcanic provinces (Chaîne des Puys, France).

Thomas Pereira 1, Lydéric France1,2, Fidel Costa3, Johan Villeneuve1

  • Affiliations: 1Centre de Recherches Pétrographiques et Géochimiques, UMR 7358 (CNRS-Université de Lorraine), 54500 Vandœuvre-lès-Nancy, France. 2Institut Universitaire de France (IUF). 3Institut de Physique du Globe de Paris, UMR 7154 (CNRS-Université Paris Cité), 75005 Paris, France. 

  • Presentation type: Talk

  • Presentation time: Monday 09:00 - 09:15, Room R280

  • Programme No: 1.2.3

  • Theme 1 > Session 2

Abstract

Volcanism results from magmatic processes that are governed by the plumbing system architecture and the timescales of magma migration. While large stratovolcanoes are believed to be fed by transcrustal magmatic systems with crystals and melts erupted from a range of reservoir depths, mafic monogenetic volcanoes are commonly considered to be fed directly from the mantle, with strong implications on the timescales of unrest and magma transport to the surface. Here we address these issues by a petrological study of six scoria cones representing the mafic endmember of the Chaîne des Puys (France). This monogenetic volcanic province dominates the Clermont-Ferrand agglomeration (400,000 inhabitants), with the last eruption occurring only 6.7 kyr ago. We investigated the composition and textures of several hundred clinopyroxene and olivine phenocrysts and applied crystal system analyses, and diffusion chronometry. We found that scoria cones were fed by two to three magmatic reservoirs and that crystal circulated between them before eruption at a range of timescales. We propose that magmas migrate repetitively from the deepest basaltic reservoir (R1; ~25 km depth) partly in the mantle, to slightly more evolved and shallower reservoirs (R2) where they interact with the host magma before eruption onset. Occasionally, magmas from R2 migrate and interact with trachy-basaltic R3 reservoirs (~18 km). The timescale of eruptions triggering when magma is transferred from R1 to R2 ranges from about six months to a few years, while it ranges from about one week to five months for magma transfer from R2 to R3.