Paleomagnetism of Miocene sediments from the Turfan Basin Northwest China: no significant vertical-axis rotation during neotectonic compression within the Tian Shan Range, Central Asia

Paleomagnetic results are reported from 377 samples of Miocene red sediments in the Turfan Basin of East Tian Shan, Northwest China. Thermal demagnetization for most specimens isolates a low-temperature component that groups around the present geomagnetic field. A high-temperature characteristic component is isolated from four localities and interpreted as primary remanent magnetization from apparent pre-folding origin and positive reversal test. As for previous results obtained from Tertiary rocks in central Asia, the magnetic inclination is significantly shallower than the reference field computed from the Eurasian APW path at 10 and 20 Ma. Magnetic susceptibility measured in 324 specimens exhibits low anisotropy of less than 1.05 for > 80% of the sample. The low anisotropy degrees, AMS shape and orientations suggest that the studied rocks are unlikely to have undergone significant strain during compaction or tectonism. We argue that the shallow inclination is likely to result from an initially shallow detrital remanent magnetization. Comparison of the paleomagnetic declination from Eurasia, North China, and Tarim suggests that the Turfan Basin has been subjected to little or no vertical-axis rotation since the Miocene. Together with paleomagnetic declinations on both sides of the Talas-Ferghana fault, we propose that the Tian Shan to the east of the Talas-Ferghana fault has remained relatively stationary with respect to adjacent blocks since the Miocene. (C) 2004 Elsevier B.V. All rights reserved.