This project is a collaboration between experimental petrologists at U. Minnesota and analytical geochemists at Arizona State to address two of the chief goals of the CSEDI initiative: (1) to understand the Earth's deep water cycle and (2) to understand the influence of H2O on melting, phase transitions, and physical properties of the mantle. Experiments to determine the H2O storage capacity of peridotite under upper mantle, transition zone, and lower mantle conditions will be performed using high temperature high pressure devices at the University of Minnesota. The storage capacity is the maximum H2O that can be retained in solid peridotite at a given temperature and pressure. Storage capacities constrain possible regions of H2O-rich mantle reservoirs and possible loci of hydrous melting. Owing to the large effect of H2O on mantle properties such as creep strength, elasticity, and conductivity, they also provide critical constraints on mantle dynamics. Experimental products will be analyzed at Arizona State for trace quantities of H2O using newly-developed low-blank secondary ion mass spectrometry techniques. Four related experimental problems will be addressed: (1) To investigate recent indications that the upper mantle has a larger storage capacity than previously appreciated, experiments at 3-13 Gigapascals will determine peridotite H2O storage capacities. (2) To determine the influence of H2O on deep melting beneath oceanic ridges and oceanic islands and the consequences for dehydration of the upper mantle, mineral/melt H2O partitioning will be determined at 3-8 GPa. (3) To better understand transport of H2O across the 410 km discontinuity, including the effect of H2O on melting and phase transitions, inter-mineral partitioning of H2O and the storage capacity will be determined at 13-15 GPa over a range of temperatures. (4) To help resolve controversy about the storage capacity of the lower mantle, experiments will be performed at 22-25 GPa, pressures relevant to in the region of the 670 km discontinuity.
