New Cretaceous paleomagnetic poles from the Tarim Basin, Northwestern China

摘要: Most paleomagnetic studies of the Tarim have been focused on Paleozoic, with little data published for Mesozoic rocks. However, ancient configuration this part Asia has affected by Indian-Eurasian collision. During second French-Chinese Karakorum expedition, from Kashkar to Kunjerab, in Autumn 1990, we sampled about 500 cores 53 sites Upper and Lower Cretaceous red sandstones three areas near Uytak, Yingjisha Wuqia (38.5-39.5'N, 75-76.5"8). Isothermal remanent magnetization acquisition indicates presence minerals high magnetic coercivity. Stepwise thermal demagnetization confirms that hematite is dominant carrier allowed separation low temperature components (LTC, 600"C) most samples. The mean direction LTCs aligned present Earth field. Normal reversed polarities found HTCs each age group. show positive fold tests at least one sub-study where attitudes bedding were sufficiently different allow test be performed. More important, four sub-studies give fully compatible results. Results Uytak area a wide dispersion declinations, as could expected rather severe deformation proximity major thrust strike-slip faults. Data obtained Kuche northern Li co-workers southern Junggar Chen are statistically identical new Wuqia. Paicheng appear subject local rotation. Excluding those which study significantly rotated, calculated pole basin 69.1'N', 223.88 (Ass:3.5", N:5). This result total post-Cretaceous rotation relative Eurasia negligible (2.6 + 6.1" 0.4 4.6', respectively). Continental shortening between Junggar, within Tien Shan, not resolved paleomagnetism although values (400 t 600 km, 3 6") tectonic models range. A discrepancy, warranting further geological investigation, North China block poles, would imply some 1400 1060 km north-south displacement.