Experiments on Hydrous Intermediate Magmas

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CarmichaelEAR-0228919Andesitic lava and ash (52-63% SiO2) erupts along the 35,000 km global volcanic arc system, which is associated with the subduction of an oceanic plate at an oceanic trench. This material contains water and represents one of the principal return fluxes of water from the earth's mantle to the crust and to the surface. Thus estimating the concentration of water in intermediate magma is a first order problem, as it not only affects the conditions of melting in the andesite source region, as well as the order and variety of the crystalline phases (as the magmas decompress on ascent), but it also is one of the fundamental controls on explosive volcanism. Moreover constraints on the amount of water in arc related magmas affects the global water budget and the question of whether more water is being subducted in comparison to that released by magmatism. This project will assess the concentration of water in Mexican andesitic magmas over a wide whole composition range, and will provide a thermodynamically based expression for the solubility of water in andesitic magma as a function of pressure, temperature and composition.