Paleomagnetic result of the Cenozoic volcanic rocks from the Tuoyun Basin, southwest Tien Shan of China and its tectonic implications

摘要

Paleomagnetic study on the Cenozoic volcanic rocks from the Tuoyun Basin of the southwest Tien Shan indicates that most samples could isolate a stable characteristic remanent magnetization with reversed polarity. The positive fold test suggests that the characteristic component is very likely to be a primary magnetization acquired in the formation of rocks. Comparison with the reference Eurasia poles at 60 Ma indicates little or insignificant N-S convergence between the south edge of southwest Tien Shan and Siberia since the onset of the India/Asia collision at the Eocene. Furthermore, the Cretaceous and Tertiary paleomag-netic results suggest that the Tuoyun Basin was subjected to a local clockwise rotation of 20 deg -- 35 deg with respect to Eurasia since the Paleocene time, which is probably subsequent to the Cenozoic northward compression of the Pamir arc.