关键词: 青藏高原, 羌塘盆地, 三叠纪, 古地磁, 构造

Abstract:

The Qiangtang terrane is located in the central part of the Tibetan Plateau, where the Mesozoic geological evolution has great significance for revealing the closure of Paleotethyan ocean and the disintegration of Gondwanaland. In order to find out the Mesozoic evolution of the Qiangtang terrane, more than 200 paleomagnetic samples were collected from the Upper Trassic Tumengela Formation and Zala Formation both in the north and in the south Qiangtang. Most samples contained two components of magnetization in thermal demagnetization experiments. The most stable high-unblocking temperature components were isolated and passed positive reversal tests at the 95% confidence level, which suggested that these high-temperature components could be regarded as primary characteristic remanent magnetization. The mean characteristic magnetization directions of the samples from north Qiangtang and south Qiangtang were D/I=28°/45.5° (a₉₅＝3.6°) and D/I=35.3°/46.5° (a₉₅＝4.0°), respectively.Nearly similar paleomagnetic polar and palaeolatitude, obtained from the north Qiangtang and the south Qiangtang, indicated that they had already belonged to one plate in the Late Triassic. The Late Triassic paleolatitude of Qiantang terrane was 27° in the Northern Hemisphere. Combined with previously reported paleomagnetic results, the paleomagnetic polar wandering paths were obtained. According to the paleomagnetic polar wandering paths, the Qiangtang terrane was located in the Southern Hemisphere during the Late Paleozoic and very close to the Equator in Late Permian. It drifted fast northward from the northeast Gondwanaland from the Late Paleozoic to the Mesozoic. The Qiangtang-Tarim plate collision finished at the end of the Triassic, and the Qiangtang-Lhasa collision might finish in the Middle Cretaceous. By then, all suture movements between Qiangtang terrane and other blocks had finished.

Key words: Tibetan Plateau, Qiangtang terrane, Triassic, paleomagnetic, tectonics