LAUSR

Knowledge of the evolution of the Altyn Tagh Fault (ATF) has significant implications for our understanding of the tectonic deformation of the Tibetan Plateau. Controversy exists regarding the formation of the orocline-like arcuate structures or curved thrust faults south of the ATF. In this paper, we conducted a paleomagnetic rotation study of the Akatengnengshan (AK) and Youshashan (YSS) anticlines to determine whether the changes in the anticlines' axes were caused by frictional drag associated with sinistral strike-slip faulting along the ATF. No significant paleomagnetic rotations during the last 20Ma were observed at the Xichagou and Laomangai localities, which are situated along the YSS anticline, whereas significant counterclockwise (CCW) rotations of similar to 50 degrees that occurred between similar to 16.2 and 11.1Ma were noted at the Yitunbulake locality, which lies along the western edge of the AK anticline. This amount of CCW rotation is consistent with the difference in axes between the AK and YSS anticlines. Combined with other geological evidence, we believe that the middle ATF was active between similar to 16 and 11Ma. Frictional drag associated with sinistral strike-slip motion likely resulted in the similar to 50 degrees CCW rotation of the AK anticline, which was originally straight or parallel to the YSS anticline. There was concentrated or insignificant strike-slip faulting along the middle ATF before similar to 16Ma, but rapid and distributed (< 40km) strike-slip faulting occurred between similar to 16 and 11Ma at a rate of 10mm/yr, and the minimum displacement was similar to 50km.