帕米尔-西昆仑地区新生代古地磁结果及其构造意义

通过对帕米尔-西昆仑地区新生代地层51个采点古地磁样品系统的古地磁测试,获得了研究区新生代较可靠的古地磁数据。尽管上述研究剖面因为单斜地层无法对所获得的古地磁结果进行褶皱检验,但从实验结果可以看出,其地理坐标下平均的高温特征剩磁方向远离现代地磁场方向,且和田朗如乡古近纪、策勒恰恰古近纪、叶城柯克亚乡新近纪剖面所获得的古地磁结果具有正、反2种极性,由此,我们认为以上剖面的高温特征剩磁很可能代表了岩石形成时的原生剩磁方向。结合研究区已有的古地磁数据,认为在新生代印度板块向北挤压作用下,塔里木地块西缘地区(帕米尔高原东北缘)早白垩世-晚白垩世始相对欧亚大陆在古地磁误差范围内并没有发生明显的构造旋转作用(1°~1.6°),而始新世以来相对欧亚大陆则发生了明显的逆时针旋转(22°~38°),该地区的逆时针旋转作用可能与塔拉斯-费尔干纳断裂新生代以来的右旋走滑作用有关,而在帕米尔高原以东则主要以沿大型走滑断裂的走滑作用为主,并没有发生明显的旋转作用。

Paleomagnetic study of Cenozoic sediments from western Kunlun-Pamir and its tectonic implications

To help understand the deformational history of the western Kunlun and adjacent regions in response to the India-Asia collision, paleomagnetic samples were collected from 51 sites in the Cenozoic sedimentary distributed in five general regions adjacent to the western Kunlun mount. Though the monoclinal bedding attitudes of the studied sections do not allow the fold test to be applied with any significance, however, the mean direction of this high-temperature component (HTC) is distinguishable from the present-day field direction. Also, the results of magnetic polarity from Hetian, Cele, Yecheng sections possess both normal and reversal polarities. Thus, we consider that the HTC magnetization of the studied sections may represent the primary remanence. Combined with existing regional paleomagnetic data, the mean paleomagnetic declinations indicates no significant Early Cretaceous to Late Cretaceous vertical-axis rotation (1°~1.6°), and significant Cenozoic counter clockwise rotation (22°~38°) of the western Tarim basin (the northeastern Pamir Plateau) relative to Eurasia due to the penetration of India into Asia. We suggest that the large-scale right-slip movement of the Talas-Ferghana Fault may be responsible for rotation of blocks. Occurrence of slip-movement without significant rotation along large-scale faults may be an important tectonic model in the eastern Pamir Plateau after the initial collision of India with Asia.