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The drift history of the Lhasa terrane plays an essential role in understanding the tectonic evolution of the Bangong-Nujiang Tethyan Ocean and the Neo-Tethyan Ocean, as well as the evolutionary history of the Tibetan Plateau. Here, a combined rock magnetic, petrographic, and palaeomagnetic study is performed on the Upper Permian–Lower Triassic limestones (∼259–251 Ma) in the western Lhasa terrane. The site-mean direction for the 28 sites is D g = 32.1°, I g = 50.3°, k g = 47.9 and α 95 = 4.0° in situ and D s = 342.9°, I s = 32.7°, k s = 43.2 and α 95 = 4.2° after tilt-correction, yielding a palaeopole at 68.9°N, 314.4°E with A 95 = 4.3°, corresponding to a palaeolatitude of 18.0° ± 4.3°N. The fold tests are not significant because the sampling section shows monoclinic features with minor variations in their bedding attitudes. The palaeopoles for the directions before and after tilt-correction are compared with reliable Late Permian–Palaeogene palaeopoles obtained from the Lhasa terrane. Based on these comparisons, the studied limestones were remagnetized prior to tilting and this remagnetization most likely occurred during the Early Cretaceous. The depositional environment of the limestones may have changed from anoxic to suboxic and oxic during the Early Cretaceous, leading to the oxidation of iron sulphide to authigenic magnetite. Meanwhile, the Late Jurassic–Early Cretaceous convergence between the western Lhasa and Qiangtang terranes may have resulted in tectonic fluid migration and the formation of calcite veins and stylolites in the limestones. This is supported by the presence of small calcite veins and stylolites in some samples, as well as the fact that the framboidal oxides were formerly sulphides (mostly pyrite), implying that the majority of the iron oxides observed in the limestones were authigenic. These processes indicate that chemical remanent magnetization caused by the growth of magnetic minerals related to tectonic fluid migration was most likely the mechanism for the limestone remagnetization. [ABSTRACT FROM AUTHOR]

To further constrain the India–Asia collisional process, a combined paleomagnetic and geochronologic study has been carried out on the Upper Cretaceous Jingzhushan Formation redbeds and the Lower Cretaceous Dianzhong Formation volcanic rocks dated at ~ 121–117 Ma from the Cuoqin area in the central Lhasa terrane. Stepwise thermal demagnetization successfully isolated reliable characteristic remanent magnetization (ChRM) directions that include dual polarity and pass positive fold tests at 95% and 99% confidence levels, indicating prefolding primary magnetizations. The tilt-corrected site-mean direction for 33 redbed sites is D = 316.8°, I = 30.2° with α 95 = 5.4°, corresponding to a paleopole at 49.0°N, 344.3°E with A 95 = 5.3°, and the other for 12 volcanic sites is D = 350.5°, I = 25.5° with α 95 = 7.7°, corresponding to a paleopole at 70.5°N, 292.9°E with A 95 = 7.4°. Our new paleomagnetic results, together with reliable Cretaceous paleomagnetic data obtained from the Lhasa terrane, demonstrate that the southern margin of Asia was located at ~ 15.1°N during the Cretaceous. Comparison with the apparent polar wander paths (APWP) of India and the Cretaceous–Paleocene paleopoles of the Himalayan terrane suggests that the India–Asia collision was likely a complex process, which consists of the collision of the Lhasa and Himalayan terranes at 54.0 ± 2.1 Ma, the longtime subduction of an intra-oceanic basin between the Himalayan terrane and the Indian craton from ~ 54.0 to ~ 40.4 Ma, and the collision of the Himalayan terrane and the Indian craton at 40.4 ± 4.1 Ma. Comparing with the Late Cretaceous average pole of the East Asia APWP reveals that a latitudinal convergence of 780 ± 240 km has taken place between the Lhasa terrane and East Asia (the Hexi corridor) since the India–Asia collision; the amount of latitudinal shortening deduced from paleomagnetic data is very consistent with the 600–1000 km accommodated by the Cenozoic fold and thrust belts between the Lhasa terrane and Hexi corridor. [ABSTRACT FROM AUTHOR]