ABSTRACT

Quantitative tectonic models that explain the evolution of deep-crustal rocks in the Tibet-Himalayan orogen call upon processes which link them to the suture zone between India and Asia. Inherent in all models that describe the dynamics of the suture zone are predictions of the kinematic history, origin, and pressure-temperature-time evolution of suture zone rocks. This project, carried out by a research team from the University of Houston in collaboration with scientists from the Chinese Academy of Sciences, exploits a rare exposure of the deep and shallow portions of the suture between India and Asia, the Indus-Yalu suture zone, in south-central Tibet afforded by the Lopukangri rift, a rift that extends approximately 150 km from the Lhasa terrane into the Indian subcontinent. Reconnaissance studies of the rift show that its uplifted footwall provides a window into the deformation history of deep suture zone rocks, while the history of the shallow portion of the suture zone is archived in its hanging wall. The goals are to determine: 1) the crustal architecture and kinematics of deformation within the India-Asia suture zone; 2) the derviation of the suture zone rocks (subducted Indian plate or Asia); 3) determine the nature and timing of metamorphism in the suture; 4) the exhumation rate of the metamorphic suture zone rocks; 5) the relationship between the geologic history recorded in deep suture zone rocks to that of the shallow crustal regions and the Himalayan thrust belt. The deformation history, petrogenesis, and thermal history of suture zone rocks will be examined using a variety of techniques including field mapping and structural analysis, thermobarometry, Nd isotope geochemistry, 40Ar/39Ar thermochronology, and Sm-Nd garnet geochronology. The resulting data will directly address the predictions of models for Tibet-Himalayan orogenesis and suture zone dynamics.

The Tibet-Himalayan orogen is a paradigm for active continental collision; hence studies of its evolution have played a major role in shaping the conceptual understanding of mountain-building processes and continental growth by accretion. While numerous geodynamic models of mountain building have emerged from geologic and geophysical studies of the Tibet-Himalayan Range, their predictions for the behavior of middle and lower crust remain largely untested because access to deep rocks is, in general, limited to the frontal regions in the High Himalaya. This project exploits an unusual exposure of these deep rocks in the interior of the range and employs techniques in isotope geochemistry, geochronology, and geological mapping of the to address processes hypothesized to operate during intercontinental collision, such as, the deep structure of suture zones, and the rates at which suture zone rocks are translated from great depths to the surface. Integration and analysis of these new observations with existing geologic and geophysical data from other parts of the Himalaya and Tibet will significantly impact the conceptual understanding of the evolution of mountains belts and continents. The project involves a significant collaboration with Chinese scientists, supports early career researchers, and actively promotes participation of underrepresented groups in earth science research.

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