New insights into the Cenozoic lateral extrusion of crustal blocks on the southeastern edge of Tibetan Plateau: Evidence from paleomagnetic results from Paleogene sedimentary strata of the Baoshan Terrane

In order to characterize the lateral extrusion of crustal material during the Cenozoic, we conducted a paleomagnetic study of the Eocene-Oligocene Zhushan Formation and Paleocene Muguahe Formation in the central part of the Baoshan Terrane (BST), on the southeastern edge of Tibetan Plateau. A primary magnetic component and a remagentized component with the Miocene acquisition age were isolated from the Muguahe Formation and Zhushan Formation, respectively. These data indicate that the BST did not commence clockwise rotation in the period of the Paleocene and the Oligocene and that the BST experienced similar to 80 degrees clockwise rotation relative to East Asia, since the Miocene. Combining with the documented history of crustal boundary strike-slip faults on the southeastern edge of the Tibetan Plateau shows that the BST and Tengchong Terrane (TCT) first underwent latitudinal crustal shortening in the Oligocene, and the eastward extension was the main type of motion of the crustal material during this period, which induced the initial strike-slip movement of their boundary faults. Since the Miocene, the main form of crustal motion of BST, TCT, and Simao Terrane was gradually transformed into clockwise rotation, which possibly indicates that the fold and thrusting fault system-induced crustal shortening and thickening in the southeastern edge of the Tibetan Plateau have reached extremity, and the southeastern part of the Tibetan Plateau has already been uplifted to the similar elevation with today's elevation in the Miocene.