EXPERIMENTAL STUDIES OF SHEAR DEFORMATION OF MANTLE MATERIALS - TOWARDS STRUCTURAL GEOLOGY OF THE MANTLE

A brief outline is given on experimental studies carried out in the Mi nnesota Mineral and Rock Physics Laboratory of microstructural evoluti on and rheology of mantle mineral aggregates or their analogues, using a simple shear deformation geometry. A simple shear deformation geome try allows us to unambiguously identify controlling factors of microst ructural evolution and to obtain large strains at high pressures and t emperatures, and thus provides a unique opportunity to investigate the ''structural geology of the mantle.'' We have developed a simple shea r deformation technique for use at high pressures and temperatures (pr essure up to 16 GPa and temperature up to 2000 K) in both gas-medium a nd solid-medium apparati. This technique has been applied to the follo wing mineral systems: (i) olivine aggregates, (ii) olivine basaltic me lt, (iii) CaTiO3 perovskite aggregates. The results have provided impo rtant data with which to understand the dynamics of the earth's mantle , including the geometry of mantle convection, mechanisms of melt dist ribution and migration beneath mid-ocean ridges, and the mechanisms of shear localization. Limitations of laboratory studies and future dire ctions are also discussed.