Paleomagnetic insights into the Neogene evolution of the Guide and Jiuxi Basins, NE Tibetan Plateau.

One of the major hotly debated issues in current geo-science studies is the evolution of the Tibetan Plateau, because the mechanisms and processes by which the plateau reached its present configuration remain unclear. Two end models exist for the uplift of the Tibetan Plateau, each of them seeking confirmation from a still inadequate database. Our studies yield magnetostratigraphic data from the Guide and the Jiuxi Basins, northeastern Tibetan Plateau, which provide detailed age constraints on the Neogene sedimentary infilling of the two basins, and aid in increasing our understanding of the evolution of the region. We find that the formation of the two basins began as early as the Oligocene, followed by complex multiple tectonic deformation and uplift processes. Significant and repeated uplifts began around Late Miocene, and increased in the Pliocene after 3.6 Ma. We believe that the deformation history within the northeastern Tibetan Plateau is more complex than simple northeastward thrust propagation resulting Plio-Quaternary uplift. Paleomagnetic declinations reveal diachronous rotations of the NE Tibetan Plateau and show that the Guide Basin has rotated clockwise ∼25° during the Mid-Miocene, and the Longzhong Basin has rotated clockwise ∼30° before 29Ma, whereas the Jiuxi Basin rotated counterclockwise by >15° during 8.5--3.6Ma. The deformation history of the NE Tibetan Plateau evidently impacted different basins at different times. The observed mean inclinations within the entire NE Tibetan Plateau are 10--30° shallower than expected, but they can be corrected by a recently proposed method that uses the elongation of the distributions of directions as a measure of inclination shallowing. We therefore conclude that post-deformation compaction is the main cause of inclination shallowing in the NE Tibetan Plateau.Ph.D.Earth SciencesGeologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125605/2/3208320.pd