Experimental studies of trace water in the mantle

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Under this award, the PIs propose to continue experimental studies at upper mantle conditions centered around understanding the mineralogical, petrological, and geochemical implications of mantle water at low bulk concentration. Specific goals are to determine the concentration of OH in olivine saturated with water and the accurate determination of the solidus of slightly hydrous peridotite. This work will also be extended to pyroxenes, garnet, and low- degree high-pressure melts, placing each phase on a common calibrated OH concentration scale. The PIs will test the hypothesis that in undersaturated experiments the mineral-melt bulk D for water does not follow Henry's law but decreases with water concentration. The PIs will use a newly developed trace element technique for studying low-degree melts to study the region below the dry solidus in the range 2-6 GPa. They will focus first on accurate determinations of the solidus as a function of water content; second on precise measurement of extents of melting between the "damp" solidus and the "dry" solidus; and third on measurements of liquid compositions in equilibrium with peridotite residua at high pressure, relatively low temperature, and slightly hydrous conditions.