Rheology and seismic properties of polyphase rocks

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The long-term goals of my research program are to improve our understanding of deformation behavior, rheology and seismic properties of polymineralic rocks in lithosphere, and to apply the improved knowledge to genuine problems in pure and applied Earth Sciences. The short-term objectives are mainly two-fold: (1) Rheology and seismic properties of metastable polymineralic rocks. Metamorphism of rocks in the lithosphere is often dominated by far-from-equilibrium and controlled by fluid-mediated transport processes under differential stress. Mapping the degree of disequilibrium metamorphism within the lithosphere, which must lead to significant changes in thought in geosciences, pre-requires the understanding of how fluid-mediated phase transformation affects physically observable quantities (e.g., velocities, anisotropy and attenuation of seismic waves). We will perform an innovative, concerted study of field mapping, structural analysis, microstructures (TEM, SEM, EBSD and FTIR), petrophysics (measurements at high pressures) and rheology (HT-HP experimental deformation) of HP and UHP eclogites and peridotites as well as their retrograde metamorphic rocks from the Dabie-Sulu orogenic belt (deep drill core samples and key surface outcrops), China. (2) Rheology and seismic properties of the crust-mantle transition (CMT) zone. Although the year 2009 marked one century since the discovery of the Moho, its exact nature, origin and role in orogenic processes remain a major unresolved issue in geodynamics since the CMT beneath the present-day continents is far less accessible. A novel approach is to investigate carefully a surface-exposed, exhumed cross section of such a CMT zone (i.e., the Yushugou-Tonghuashan massif, Xinjiang, Northwest China) which represents a compressional uplift consisting of interlayered foliated mafic granulites and peridotites extruded into greenschist to lower amphibolite-facies middle crustal metasediments along intracontinental thrust shear zones at the northern margin of the South Tianshan. The research results will promise broad impacts and innovative contributions to the better understanding of seismic properties and anisotropy, composition, rheology and structure of the Moho in other parts of the world, and ultimately improve assessment of the Moho's role in the plate tectonics and continental evolution. The proposed program has also an important educational component as the students benefit from challenging interdisciplinary research.