白垩纪以来中国西部地体运动的古地磁证据和问题

THE TERRANES MOTION IN WESTERN CHINA: PALEOMAGNETIC EVIDENCES AND THEIR PROBLEMS

地质证据表明中国西部各地体在白垩纪之前已经增生到欧亚大陆之上 ,但这些地体自白垩纪以来的古地磁极位置与稳定欧亚大陆的古地磁极位置存在较大差异 ,对其最可能的解释是发生在晚白垩世与古新世之交 (约 6 5Ma)印度板块和欧亚大陆之间的碰撞及其后印度板块的持续北向挤压 ,使得这些地体之间以及这些地体与稳定欧亚大陆之间发生了相对位移和地体内部的变形。文中利用现有的古地磁研究成果 ,计算了自白垩纪以来中国西部各地体与欧亚稳定大陆之间的南北向相对位移量。塔里木地块和柴达木地体的古地磁数据表明 ,阿尔金断裂至少经历了四期活动。在欧亚地区普遍存在的第三纪磁倾角偏缓现象 ,很可能反映了在该地区长期存在非偶极子场。

The geological evidences indicate that the terranes in Western China have been accreted by the Cretaceous. However, there is a great discrepancy in the paleomagnetic results of these terranes and Eurasia. The most plausible interpretation is that the collision between India and Eurasian, which started around the boundary of Cretaceous and Tertiary (about 65 Ma), resulted in the crustal shortening among the tectonic units. Based on the paleomagnetic results of the terranes in Western China, the amount of the crustal shortening between each terrane and Eurasia are calculated. The crustal shortenings between Eurasia and Junggar, Tarim, northern Lasha and southern Lasha are 655 km, 1 043 km, 1 265 km and 1 631 km, respectively. The paleomagnetic results of Tarim and Qaidam indicate that Altyn Taugh fault has experienced complicated tectonic activity. The shallow inclination phenomenon which have been observed in many paleomagnetic studies in Asia may be induced by the existence of long-term non-dipole field in the Tertiary.