US-France Cooperative Research: Rheology of the Transition Zone of Earth's Mantle

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This award will support cooperative research in geophysics between Dr. Robert Liebermann, State University of New York at Stony Brook and Dr. Jean-Paul Poirier, Institut de Physique du Globe, University of Paris VI. The objective of this research is a better understanding of the rheological behavior of the high-pressure phases of mantle minerals. Specifically, the investigators propose to synthesize specimens of high pressure phases of olivine and pyroxene in the large-volume, uniaxial split-sphere apparatus at Stony Brook and to study their deformation using tranmission electron microscopy in Paris. Special attention will be devoted to phase assemblages which contain mixtures of spinel and garnet and to specimens synthesized at P-T conditions which straddle the garnet-ilmenite phase boundary. These new data will be utilized to interpret the dynamic processes occurring in the transition zone of the Earth's mantle. These investigations also have relevance for the dynamics of the subduction processes and the occurrence of deep focus earthquakes beneath island arc regions. The U.S. and French laboratories are well qualified to pursue this project. Dr. Poirier and his colleagues have developed techniques to produce co-existing phases at high pressures and temperatures in diamond-anvil-cell apparatus and used transmission election microscopy to examine the microstructure of high pressure phases produced synthetically in the laboratory or naturally by meteorite impact. The U.S. laboratory at Stony Brook is an international center for high pressure measurement.