One of the most critical experimental data in developing our understanding of dynamics and evolution of Earth and other terrestrial planets are the data on rheological properties of their constituent materials. The physical and chemical conditions in planetary interior are very broad particularly in terms of pressure. The major challenge in the experimental studies on rheological properties is to develop techniques to obtain quantitative data on rheological under the conditions of planetary interiors. Well-accepted rheological data in the previous studies were limited to those obtained at pressure less than 0.5 GPa. In the previous funding period, the investigators have extended this to ~15 GPa and obtained initial results on rheological properties under the transition zone conditions of Earth''s mantle. However, their studies have also underlined several important challenges: (i) even at relatively low pressures (<10 GPa) there is a large discrepancy in the experimental results (on olivine) among different laboratories, (ii) water fugacity in the previous experiments were not controlled, and (iii) the maximum pressure of quantitative deformation experiments is still limited and virtually nothing quantitative is known about the rheology of the lower mantle of the Earth. The goals of this new phase of the grand challenge project are: (i) to establish a strategy for quantitative deformation experiments under pressures through improved x-ray diffraction and inter-laboratory comparisons, (ii) to develop new methods of controlling water fugacity under high-pressures, and (iii) to expand the pressure (and temperature) range of these studies. The experimental studies will be conducted as a team effort involving experts in this research area across the country. Post-docs and students will be involved in this group effort and the results will be open to the community both through technical reports and through direct collaborations.
The results of this project will provide us with a new tool by which we can determine rheological properties of minerals under a broad range of conditions (under high pressures and controlled water fugacity), and the scientific results that will come out using these techniques will form the basis for geodynamic studies of Earth and planetary interiors.
