CSEDI:Collaborative Research: Experimental and SIMS investigation of H2O storage capacity of the mantle

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.