The intermediate step in fractionation trends of mildly alkaline volcanic suites: An experimental insight from the Pavin trachyandesite (Massif Central, France)

Morgane Rondet (1, 2) , Caroline Martel (1, 2) , Jean-Louis Bourdier (1, 2)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 Magma - UMR7327

We examined magma storage conditions and eruptive dynamics for the trachyandesite (~58 wt% SiO2, 9–10 wt% alkalis) of the Pavin monogenetic volcano, a maar-like explosive crater belonging to a small group of youngest volcanoes in the Massif Central. By confronting the natural samples to experimental products, we constrained pre-eruptive conditions around 950–975 °C, 150–200 MPa (~5.5–7.0 km in depth), NNO+1.5, and 4.5–5.5 wt% melt H2O. There is petrological evidence of magma crystallization in the conduit up to shallow levels (~50 MPa; 2 km in depth) before fragmentation into pumice clasts in the last kilometre of ascent. The experiments highlight the role of biotite and of crystallization pressure in defining separate compositional trends of residual liquids, i.e. alkaline (trachytes) versus sub-alkaline (dacite-rhyolite).

Mots clés: trachyandesite; Pavin; experimental petrology; differentiation

Domaines: Planète et Univers [physics]; Sciences de la Terre; Minéralogie

Morgane Rondet, Caroline Martel, Jean-Louis Bourdier. The intermediate step in fractionation trends of mildly alkaline volcanic suites: An experimental insight from the Pavin trachyandesite (Massif Central, France). Comptes Rendus Géoscience, 2019, 351, pp.525-539. ⟨10.1016/j.crte.2019.07.003⟩. ⟨insu-02310393⟩