The PI will examine the influence of grain size, temperature, oxygen fugacity, bulk composition, and melt fraction on the grain boundary electrical response. Of particular importance will be the comparison of natural rocks with ground- and-pressed compacts because natural grain boundaries may be quite different than those in the laboratory-prepared materials. Initial experiments will be performed at 1-bar total pressure. Subsequent efforts will extend this work to elevated temperatures and pressures in internally-heated argon gas pressure vessels and piston cylinder devices. The results will be interpreted in terms of equivalent electrical circuits that can be related to models of ionic processes. This results of this study will be important for the interpretation and modeling of magnetotelluric data and will also shed new light on grain boundary transport processes in variety of geological environments.
