Cenozoic Cooling History And Fluvial Terrace Development Of The Western Domain Of The Eastern Kunlun Range, Northern Tibet

The growth of the Tibetan Plateau resulted primarily from Cenozoic India-Asia collision and continued convergence, and thus the deformation timing and geomorphic evolution of northern Tibet are critical to understanding the dynamics of orogenic plateau growth. Although previous studies have suggested that the Altyn Tagh Shan and the Eastern Kunlun Range of northern Tibet have experienced differential faulting and exhumation history, our knowledge of the temporal and spatial distribution of the growth of the northwestern Tibetan Plateau is still lacking. In this study, we integrate new geologic mapping, low-temperature themochronometry (18 apatite-fission track ages), and Optically Stimulated Luminescence (OSL) dating to provide constraints on the Cenozoic cooling history of northwestern Tibet and late Quaternary fluvial terrace development. We focus on where Altyn Tagh Shan structures are juxtaposed against Eastern Kunlun Range structures. New fission-track cooling ages from one traverse along the Aksu River yielded three cooling age domains: Paleocene, Miocene, and early Pliocene. With this new knowledge of similar to 12-10 Ma initiation of Jianxiashan thrusting and exhumation, we suggest a refined N-S shortening rate of this thrust system of 2.0-2.4 mm/yr and strain rates of 8-9x10(-16) s(-1). Thermal history modeling suggests that the study area experienced two broad events, including slow cooling through the AFT PAZ since the early Eocene and rapid cooling during the late Miocene. Our OSL dating results from the Aksu drainage reflect two separate processes of aggradation and incision that occurred during the late Pleistocene and Holocene, respectively, which are interpreted to result from long-term forcing of incision by a constant rate of tectonic uplift modulated by late Quaternary climatic variations. We interpret that this incision occurred at a rate of similar to 1 mm/yr, which is faster than exhumation rates inferred from the AFT data (0.3-0.5 mm/yr). These Quaternary exhumation rates may reflect faster recent exhumation or uplift associated with the proximal Altyn Tagh fault. In accordance with previous studies, we present a refined Cenozoic tectonic model for the evolution history of northern Tibet. The deformation pattern of northern Tibet results from clockwise rotation of preexisting weaknesses and transpressional deformation along the Kunlun fault and the Haiyuan fault.