Paleomagnetism And Geochronology Of Cretaceous Rocks From The Lhasa Terrane And The Tethyan Himalaya

The India-Asia collision created the Himalayan-Tibetan Orogen, which is a key area for the study of the continent-continent collision and intracontinental deformation. The Lhasa terrane and Tethyan Himalaya were the leading edges of the stable Asia and India craton prior to the Cenozoic India-Asian collision, respectively. Their pre-collisional paleogeographic evolutions are essential to understand the topics mentioned above. A combined paleomagnetic and U-Pb zircon geochronological study has been carried out on the Cretaceous rocks from the western part of the Lhasa terrane and the southeastern part of the Tethyan Himalaya. Based on new paleomagnetic and geochronologic results, combined with previous geologic and geophysical data, several conclusions can be summarized as follows:(1) The volcanic rocks from the Cuoqin and Shiquanhe sampling sections were dated at ~117–121 Ma and ~67.7 Ma, respectively. The Sangxiu formation volcanic rocks from the Gongbuxue sampling areas in Tethyan Himalaya were dated at ~124–135 Ma.(2) Three reliable Cretaceous paleopoles have been obtained from the western part of the Lhasa terrane. Theses new paleomagnetic data, combined with previous Cretaceous paleomagnetic results from Lhasa terrane, suggest that the southern margin of Asia was at ~16.8°N with a relatively E-W alignment during the whole Cretaceous.(3) Two Early Cretaceous paleopoles have been obtained from the Tethyan Himalaya, and they show that the southestern part of the Tethyan Himalaya(28.5°N, 92.0°E) was located at 50.5°S at ~130 Ma, and that the Tethyan Himalaya should be a contiguous part of the Indian subcontinent at ~130 Ma.(4) The Neo-Tethyan Ocean, which opened up to several thousand kilometers width at ~130 Ma, lay between the Tethyan Himalaya and the Lhasa terrane during 134–130 Ma.(5) A Cretaceous extension, represented perhaps by a small post-Neo-Tethyan Ocean, occurred between the Indian craton and the Tethyan Himalaya after 130 Ma.(6) The India-Asia collision should be a dual-collision process, which includes a first collision between the Tethyan Himalaya and the Lhasa terrane(Asia) at ~54.8 Ma and a final continent-continent collision between the Indian craton and the Tethyan Himalaya at ~41.7 Ma.(7) A north-south shortening amount of ~800–1000 km has taken place between the Lhasa terrane and Eurasia/East Asia(the Hexi corridor) since the India-Asia collision.