Palaeomagnetic results from Palaeogene red beds of the Chuan-Dian Fragment, southeastern margin of the Tibetan Plateau: implications for the displacement on the Xianshuihe-Xiaojiang fault systems

The mechanism of deformation associated with the Cenozoic collision of India with Asia along the eastern boundary remains a poorly understood aspect of the tectonic evolution of the southwestern South China Block (SCB). Consequently, we carried out a palaeomagnetic investigation of Palaeogene red beds of the Dayao area of Yunnan Province in order to contribute to understanding the Palaeogene evolution of the SCB. A characteristic higher temperature magnetic component (HTC), with an unblocking temperature from 660 degrees C to 680 degrees C, was determined by principal component analysis (PCA), and positive fold tests indicated that the remanence was a primary magnetization. The mean direction of the HTC from the Dayao area is Ds=27.8 degrees Is=33.1 degrees =64.8, (95)=4.3 degrees after tilt correction. Compared with other palaeomagnetic results from the SCB, our data suggest that the central part of the Chuan-Dian Fragment (CDF) experienced approximately 16.3 +/- 4.7 degrees clockwise rotation with respect to East Asia. Rotation of the CDF occurred along the left-lateral Xianshuihe-Xiaojiang Fault Systems (XSF-XJF), which exhibit an arc-shaped curve centred on the Eastern Himalayan Syntaxis. The XSF-XJF was approximated by a circle centred on a Euler pole at Lat.=26.5 degrees N, Lon.=97.2 degrees E ((95)=0.2 degrees), based on 11 reference points selected from the fault system. The clockwise rotation of the CDF resulted in left-lateral shearing along the XSF-XJF system, with a left-lateral displacement of similar to 200km. The nature of diverse intense local deformation along the Xianshuihe-Xiaojiang left-lateral strike-slip fault systems is also discussed.