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

Abstract

AbstractTo 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.