Kohlstedt 9526925 An experimental investigation of three central issues in upper mantle rheology is proposed: (I) the dependence of viscosity on water concentration, (ii) the dependence of creep behavior on mineralogy and (iii) the dependence of creep rate on pressure. The proposed experiments are designed to gain a basic physical understanding of the roles of water, mineralogy and pressure on the flow behavior of mantle rocks. An important goal of this research is to determine quantitative constitutive equations for plastic flow that permit reliable extrapolation of laboratory results to upper mantle environments.