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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 ~80° 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.

[1] Temporal and spatial variations of high and low contents of Ti basalts in the Permian Emeishan large igneous province (ELIP) of southwest China and Vietnam are crucial for modeling of continental basalt formation and the nature of mantle-lithosphere interaction. A combined geochemical and magnetostratigraphic study was carried out at Yanyuan in the inner zone of the ELIP. Geochemical results indicate that the basalts are low-Ti (LT) basalts (Ti/Y ∼ 484.2-511.4) in the Luomapu section and high-Ti (HT) basalts (Ti/Y ∼ 558.2-658.9) in the Gongmushan section. Systematic paleomagnetic sampling and stepwise thermal demagnetization demonstrate that the higher temperature component shows two distinct characteristic remanent magnetizations with northeasterly upward and SWW downward directions. These results indicate a simple magnetostratigraphic normal and reversed polarity pattern from the lower and upper parts of the section, respectively. By comparing with available magnetostratigraphic and paleomagnetic data carried out in the ELIP, these results imply that the eruption of the Emeishan basalts can be divided into early (normal polarity subchron) and late (reversal subchron) stages. The early stage included LT basalts in the inner zone and most of the HT basalts in the intermediate and outer zones, and the late stage contained a part of LT and HT basalts in the upper parts of the sections in the inner zone and a few in the intermediate zone of the ELIP. Correlating with available Middle-Late Permian magnetostratigraphy and the Permian magnetic time scale, the new magnetic polarity sequence result suggests that the ELIP formed over a very short time interval (<1 Myr).

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Paleomagnetic studies were carried out on the Paleocene sedimentary rocks at Dingri, Tibet (28°42'N, 86°50'E) along the northern margin of the Indian plate. Thirteen sites (about 120 cores) were sampled from limestone of the Zongpu Formation. Three magnetic components were identified after stepwise thermal demagnetization. The middle-temperature component records a remagnetization event, which is inferred to be a consequence of thermal remagnetization during the collision between India and Eurasia. The age of remagnetization, ~54.0 Ma, was estimated by comparing the measured paleolatitude and the expected paleolatitude from the apparent polar wander path (APWP) of the Indian plate, which corresponds to the time of final suturing between India and Eurasia. The preliminary result for the high-temperature component was determined by the intersection of great circles, which passed a regional fold test. The magnetic remanence reflects the primary origin, and probably was acquired at ~65.5--61.7 Ma. By comparing our Paleocene results with those from the stable Indian plate, we infer that the Dingri area was a stable part of the Indian block, and crustal shortening across the Main Central thrust (MCT) and the Main Boundary fault (MBF) in the southern Himalayas was paleomagnetically insignificant. The extension of greater India is estimated as ~1000 km.

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