No abstract

No abstract

No abstract

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°w ith α 95 = 2.3°, corresponding to a paleopole at 61. 4°N, 192.9°E (A 95 = 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.

No abstract