Paleomagnetism and U‐Pb zircon geochronology of Lower Cretaceous lava flows from the western Lhasa terrane: New constraints on the India‐Asia collision process and intracontinental deformation within Asia

To better understand the India-Asia collisional process and intracontinental deformation within Asia, a paleomagnetic study has been conducted on the Qushenla Formation lava flows dated at ~132–120 Ma from the Yanhu area in the western Lhasa terrane. Stepwise thermal demagnetization isolates stable characteristic remanent magnetizations, which include dual polarity and pass fold tests at a 99% confidence level, indicating primary magnetizations. The tilt-corrected site-mean direction for 51 sites is D = 28.2°, I = 34.5°, and k = 74.3° with α95 = 2.3°, corresponding to a paleopole at 61.4°N, 192.9°E (A95 = 2.1°). Our new paleomagnetic data, combined with previous Cretaceous volcanic paleomagnetic data from the Lhasa terrane, show that the precollisional southern margin of Asia was at ~16.8°N with a relatively E-W alignment and that the Lhasa terrane did not experience significantly discrepant north-south movement although local vertical axis rotations did take place after the Cretaceous. Comparison with the apparent polar wander paths (APWPs) of India and the Cretaceous-Paleocene paleopoles of the Tethyan Himalaya shows that the India-Asia collision was at ~54.3 Ma and the Greater India during the Paleocene had a large northern extent of ~2000 km (~18.1°) beyond its present northern margin. Comparison with the Cretaceous Eurasian APWP indicates that a latitudinal convergence of ~1000 km has taken place between the Lhasa terrane and Eurasia since the India-Asia collision. The amount of north-south shortening deduced from Cretaceous paleomagnetic data is consistent with that accommodated by the Cenozoic fold and thrust belts between the Lhasa terrane and the Hexi corridor.