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Kinetics of mafic magma ascent leading to monogenetic eruptions (Chaîne des Puys, France).

Thomas Pereira1, Lydéric France1,2, Fidel Costa3, Etienne Deloule1

  • 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: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 276

  • Programme No: 1.3.20

  • Theme 1 > Session 3

Abstract

Monogenetic volcanic fields are governed by a complex multi-reservoir plumbing system with common magma transfers and recharges that eventually trigger eruptions. Diffusion chronometry can reveal ascent timescales by using chemical elements that diffuse fast enough to be affected by decompression and associated loss of volatiles. Here we use the hydrogen content of olivines (SIMS measurements) to quantify such ascent rates for six scoria cones representing the mafic endmember of the Chaîne des Puys (France), an archetypal monogenetic intracontinental volcanic province (last eruption 6.7 kyr ago). We investigated the distribution of hydrogen in around twenty olivines from those edifices, and modeled the obtained profiles to derive ascent rates. H contents range from below detection limit (<3 ppm) to 20 ppm. The initial H concentrations in olivines were determined from coexisting melt inclusions. Solubility models highlight bubble nucleation depths of less than 5 km for water concentrations of 2 wt.% in the magma which rises from depths of ≥18 km. The measured H profiles vary from one crystal to another, with rims depleted in water compared to the core, reflected degassing water loss upon ascent. However, other H profiles are rather flat suggesting limited time for diffusion, complete homogenization or more complex degassing processes than simply water loss. Modeling diffusive re-equilibration of the H indicate mafic magma ascent range from few hours to about 2 days and ascent rates of around 0.13 m/s. These timescales are similar or slower than for stratovolcanoes in subduction zones or hot spots, for example.