Hydrous Intermediate Magmas

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Carmichael EAR-0125159 Although the simple expression representing the solubility of water in magmas as a function of P,T and liquid composition, is adequate for many hydrous phase-equilibrium experiments, its extrapolation to iron-rich basalts and to higher pressures is problematic. Using our internally heated pressure vessel, it is proposed to measure the water solubility in two Columbia River basalts as a function of P & T to make secure the compositional extrapolation of the solubility algorithm to Fe-rich liquids of varying silica concentration. Published direct measurements of the volume of dissolved water in magmas will be included in the revised algorithm (a regressed variable in the early formulation) to ensure that the pressure dependence of the solubility relationship extrapolate to published high pressure experiments. Hornblende-bearing intermediate lavas associated with subduction are always more oxidized than their hornblende-free associates. The reasons for this are unknown and could indirectly result from the expulsion of dissolved water on eruption in combination with a sulfur species. This will be tested by using a newly developed X-Ray fluorescence technique to measure the sulfur concentration in a large collection of sub-aerial crystalline lavas for which the redox state is well known.