科希斯坦-拉达克弧及其周缘地块的古地磁学研究进展
摘要
<p indent="0mm">Understanding the nature of the Kohistan-Ladakh arc before the India-Asia collision is crucial for reconstructing the Tethyan paleogeography, deciphering geodynamic process of the India-Asia collision, and restoring Asia’s history of intracontinental deformation. However, there are two opposing views dealing with nature of the Kohistan-Ladakh arc: The continental marginal arc and intra-oceanic island arc. Based on the accumulated published paleomagnetic data for the Kohistan-Ladakh arc and its surrounding terranes during the Cretaceous-Paleocene, we reconstruct paleogeography of the Kohistan-Ladakh arc and its surrounding terranes, and explore the nature of the Kohistan-Ladakh arc. The Karakoram terrane was situated on the southern edge of Asia at a paleolatitude consistent with that of the western Lhasa terrane in the late Cretaceous. The Kohistan-Ladakh arc was situated in the equatorial Neo-Tethys Ocean (southern hemisphere) in the early Late Cretaceous (ca. <sc>90 Ma)</sc> before drifting northward to reach the low-latitude northern hemisphere in the early Paleocene (ca. <sc>64 Ma).</sc> The central and eastern parts of the Tethyan Himalaya, as the northern margin of India prior to the collision, were located at paleolatitudes of 16.7° and 19.4°S at ca. <sc>75 Ma,</sc> respectively. The Kohistan-Ladakh arc was separated from the western Lhasa terrane by an ocean basin with a north-south extent of <sc>~900 km</sc> at ca. <sc>64 Ma.</sc> The above analyses suggest that the Kohistan-Ladakh arc demonstrated intra-oceanic characteristics prior to the India-Asia collision. Therefore, the Kohistan-Ladakh arc should be considered in the India-Asian collision system. Recently published paleomagnetic data obtained from the Tethyan Himalaya terrane, data obtained from the Kohistan-Ladakh arc, and the apparent polar wander path of India inspired us to propose a triple-stage India-Asia collision model. The first collision occurred at ca. <sc>64 Ma</sc> betwee