Experimental Constraints on the Formation of Silicic Magmas

Bruno Scaillet (1, 2) , Francois Holtz (3) , Michel Pichavant (1, 2)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 Magma - UMR7327
3 Institut für Mineralogie [Hannover]

A rich history of experimental petrology has revealed the paths by which silicic igneous rocks follow mineral–melt equilibria during differentiation. Subdividing these rocks by ‘molar Al versus Ca + Na + K’ illustrates first-order differences in mineralogy and gives insight into formation mechanisms. Peraluminous magmas, formed by partial melting of sediments, largely owe their attributes and compositions to melting reactions in the protoliths, whereas most metaluminous felsic magmas record both continental and mantle inputs. Peralkaline rhyolites are mainly derived from either protracted crystallization or small degrees of partial melting of basalt, with only a marginal crustal contribution. Most silicic magmas hold 3–7 wt% H2Omelt, which is inversely correlated with pre-eruptive temperature (700 °C to >950 °C) but unrelated to their reduced/oxidized state.

Keywords: granite; rhyolite; phase equilibria; water; redox state; metaluminous peraluminousper; alkaline; viscosity

Domains: Sciences of the Universe [physics]; Earth Sciences; Volcanology

Bruno Scaillet, Francois Holtz, Michel Pichavant. Experimental Constraints on the Formation of Silicic Magmas. Elements, 2016, 12 (2), pp.109-114. ⟨10.2113/gselements.12.2.109⟩. ⟨insu-01310808⟩