Tectonics of the Eastern Kunlun Range: Cenozoic Reactivation of a Paleozoic-Early Mesozoic Orogen

摘要

The Eastern Kunlun Range in north Tibet, located along the northern margin of the eastern Tethyan orogenic system, records evidence for continental break-up and ocean development in the Neoproterozoic, Paleozoic-early Mesozoic subduction and continental collision, Mesozoic intracontinental extension, and Cenozoic contractional deformation. The Kunlun region is marked by active left-lateral strike-slip deformation of Kunlun fault system, one of the major intracontinental strike-slip faults in Tibet that developed in response India-Asia. To better constrain the tectonic evolution of the Eastern Kunlun Range and the closure of the various Kunlun oceans, we conducted detailed investigation integrating new geologic mapping, geochronology, and whole-rock geochemistry with a synthesis of existing datasets across north Tibet. The Eastern Kunlun Range experienced three major deformation events in the Neoproterozoic, early Paleozoic, and Late Paleozoic-early Mesozoic, which were associated with collision of the Proto-, Paleo-, and Neo-Kunlun arcs, respectively. Our new detrital zircon analyses from Mesoproterozoic-Cenozoic strata constrain stratigraphic age and sediment provenance and highlight the importance of three periods of arc activity. Our stratigraphic synthesis, including new field observations, provides new insights into connections between sediment dispersal and changes in tectonism and paleogeography. Miocene-to-present strike-slip activity on the Kunlun fault and the associated strain pattern can be explained by clockwise rotation of the Kunlun fault and its wall rock as a bookshelf-fault system, which has been proposed for northern Tibet as a result of distributed north-south right-lateral shear. The development of this fault system was facilitated by the presence of a Triassic suture that provided a preexisting weakness.Plain Language Summary The Eastern Kunlun Range in northern Tibet is located within the interior high-elevation Tibetan Plateau. Its current morphology and geologic structure reflect Cenozoic faulting related to India-Asia convergence since the early Cenozoic. Active deformation across the Eastern Kunlun Range reactivates complex older geologic relationships that record prior oceanic subduction and continental collision events. We present field and analytical observations from key sites along the Kunlun and Xiangride Rivers across the Eastern Kunlun Range to establish the pre-Cenozoic geologic history of this region. Our dating of arc-related intrusions and sedimentary rocks reveals that three distinct ocean-closure-related collisions occurred here over the last billion years. This repeated focused deformation has been reactived most recently in the Cenozoic to for the left-slip Kunlun fault.