COLLABORATIVE RESEARCH: Mesozoic Nonmarine Sedimentary Record of Transition from Contractile to Extensional Deformation, Southern Mongolia

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9614555 Hendrix The Mesozoic tectonic evolution of southern Mongolia includes a poorly understood transition from contractile to extensional tectonism and associated sedimentary basin development. Only in its broadest outline has this transition become apparent in recent years, as a consequence of recognition of a major north-verging early Mesozoic fold-thrust belt in adjacent north-central China, reconnaissance description of syn-tectonic coarse-grained strata in southern Mongolia, and limited geophysical and geological documentation of late Mesozoic rift basins in southern Mongolia. Major aspects of the kinematics, rates, and styles of structural and sedimentary systems associated with the tectonic transition remain unresolved, and form the basis for this research proposal. From such issues stem a suite of exciting questions: How do sedimentary basin systems formed atop heterogeneous crust respond to fundamental changes in tectonic deformational style? Do previously unrecognized basin types occur, as recently documented for collisional foreland basins formed atop accreted terranes in western China? What role to metamorphic core complexes, documented across the border in north-central China and apparently structurally continuous with similar though undocumented structures in the proposed field area, play in the transition from a contractile to extensional tectonics? These questions are but several among many to be addressed by this proposal. Specifically, this proposal seeks three years of funding to investigate and document the sedimentary response to a rapid and fundamental transition from compressional tectonics of early Mesozoic age to extensional tectonism of late Mesozoic age. In answering each of the above questions, we propose first to document the fundamental geology of the contractile and extensional systems to fill the very large gaps which exist presently in the geologic understanding of Mesozoic southern Mongolia. The principal tools and means of investigation we propose to employ involve an integrated structural and sedimentary geologic approach in which structural data and detailed mapping will serve as backdrop for detailed depositional systems and stratigraphic architectural analysis, provenance analysis, and reconnaissance thermochronologic studies. Importantly, subsurface data will be incorporated into the investigation, thanks to access to vital core material from a small oil field currently in development. After fundamental documentation of each tectonic system and its sedimentary record has been completed, the important broader scientific questions posed above can be addressed. Beyond its scientific importance, the proposed research will enable continued scientific exchange between U.S. institutions and the Mongolian Academy of Sciences. An important additional educational dimension of the proposal lies in its support for one Post-doctoral Research Associate, one Ph.D. student, and two M.S. students.