Magma Mixing in Arc Contexts

Magma reservoirs are frequently replenished, in particular in ac contexts. The result of such a recharge is the juxtaposition of different magmas with varied chemical and physical properties: the replenishing magma is typically hot, crystal-free and mafic whereas the host magma is differentiated, colder and may contain crystals. Arc volcanoes and plutons exhibit a range of mixing and mingling features, from layered magmas, enclaves, crystals in disequilibrium in their host to perfect hybrids. However, the conditions for magma mixing are still poorly assessed, principally due to difficulties to gather all magmatic conditions (temperature, pressure, water content, crystal fraction, strain rate). We have experimentally investigated the textural and rheological properties of magma mixing to constrain their favorable conditions. Magma mixing is ruled by a viscosity threshold (η ≈ 10^7 Pa.s) and a viscosity contrast (Log Δη < 0.5) resulting from the crystal fraction in one or both magmas. From theses results, we simulate the fraction of mafic injected magma into a reservoir to get favorable condition for magma mixing. The recharge style of magma chambers appears to be determinant to the production of intermediate magmas and possibly to continental crust formation.