Structure of the Tibetan Crust and Upper Mantle and Its Geodynamic Implications

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This research will study the large-scale structure of the crust and upper mantle beneath Tibet andinvestigate its geodynamic implications. Two features of a preliminary 3-D seismic model motivate this work and define the primary questions that the work proposes to address.First, a coherent 3-D pattern of high and low speed anomalies in the mantle underlies the Tibetan plateau. What geodynamic processes can account for this pattern? Second, strong mid-crustal radial anisotropy characterizes the Tibetan crust, and preliminary analysis implies coherent, period-dependent azimuthal anisotropy. Which models of the development of finite strain in the Tibetan crust are consistent with these observations?The work will improve the current seismic model and investigate its geodynamical implications.The model will be improved by adding more surface wave dispersion measurements and by introducing new kinds of measurements into the inversion; e.g., crustal and mantle overtone measurements and receiverfunctions. The inversion generates an ensemble of acceptable models, rather than a single best-fitting model, thereby producing meaningful uncertainty information needed to test hypotheses. Several geodynamic scenarios that may explain aspects of the pattern of velocity anomalies in the upper mantlebeneath Tibet will be investigated, including; the underthrusting of Indian lithosphere, southwestwardthrusting of Asian lithosphere, and the detachment or convective removal of Tibetan lithosphere.In addition, the relation between inferred crustal anisotropy and three models of the development of finitestrain in the Tibetan crust will be investigated.A graduate student will receive training at the interface between seismic tomography andgeodynamics. The seismic models will be placed in a form that is useful in the classroom. Collaborators in this effort include researchers at the Digital Library for Earth Systems Education (DLESE, www.dlese.org) and UNAVCO, who are also part of the GEON large scale information technology research project (www.geongrid.org).