Palaeomagnetic Results And Their Tectonic Significance From Late Mesozoic To Cenozoic Sedimentary Strata Of The Chuan-Dian Fragment,Southeastern Margin Of The Tibetan Plateau

In order to contribute to the understanding of the kinematic mechanism and dynamic models for intracontinental deformation associated with the Cenozoic collision of India with Asia along the eastern boundary,we carried out a systematic paleomagnetic research in the Jurassic-Paleogene sedimentary basin in the Chuan Dian Fragment,and a magnetostratigraphy research in the lacustrine strata sedimentology along the Jinshajiang River.The paleomagnetic investigation of Paleogene red beds of the Dayao area of Yunnan province in order to contribute to understanding the Paleogene evolution of the Chuan Dian Fragment.A characteristic higher temperature magnetic component,with an unblocking temperature from 660?to 680?,was determined by principal component analysis,and positive fold tests indicated that the remanence was a primary magnetization.The mean direction of the higher temperature magnetic component from the Dayao area is Ds=27.8°,Is=33.1°,?=64.8,?95=4.3° after tilt correction.Compared with other paleomagnetic results from the South Chian Block,our data suggest that the central part of the Chuan Dian Fragment experienced approximately 16.3±4.7° clockwise rotation with respect to East Asia.Rotation of the CDF occurred along the left-lateral Xianshuihe-Xiaojiang Fault Systems,which exhibit an arc-shaped curve centered on the Eastern Himalayan Syntaxis.The Xianshuihe-Xiaojiang Fault Systems was approximated by a circle centered on an Euler pole at Lat.=26.5°N,Lon.=97.2°E(?95=0.2°),based on eleven reference points selected from the fault system.The clockwise rotation of the Chuan Dian Fragment resulted in left-lateral shearing along the Xianshuihe-Xiaojiang Fault Systems system,with a left-lateral displacement of?200 km.The nature of diverse intense local deformation along the Xianshuihe-Xiaojiang left-lateral strike-slip fault systems is also discussed.The paleomagnetic investigation of Jurassic-Cretaceous red beds to the east of Chenghai Fault shows the mean direction of the high temperature magnetic component from the Xiaongyun area is Ds=359.3°,Is=53.2°,?=60.1,?95=4.8° after tilt correction;the mean direction of the high temperature magnetic component from the Rende-Dongshan area is Ds=3.6°,Is=56.1°,?=69.3,?95=8.1° after tilt correction;the mean direction of the high temperature magnetic component from the Binchuan Jurassic stratum and Cretaceous stratum are Ds=12.7°,Is=54.7°,?=49.3,?95=6.2°and Ds=29.9°,Is=45.7°,?=90.2,?95=5.1° after tilt correction,respectively.All the positive fold tests indicated that the remanences were the primary magnetizations.Compared with other paleomagnetic results from the South Chian Block,the counterclockwise rotation result suggest that Xiangyun and Rende-Dongshan areas had been affected by Yupaojiang Fault before Paleogene.The same clockwise rotation of Binchuan Cretaceous red beds indicated the Chenghai Fault is a brittle fault system.The magnetostratigraphy researche in the lacustrine strata sedimentology along the Jinshajiang River was carried out,be better constrain the timing of Changhai Fault activity.The Taiji Taiji lacustrine strata deposited silty clay with fine sand rocks up to?360 meters thick,but only there is a normal polarity.Compared with the zircons U-Pb age,apatite fission track and Cyclostratigraphy results,our data suggest that the persistent depositional time should be 370 Kyr and the age of sedimentary sequence in Taiji area can thus be paleomagnetically constrained in early Bmnhes normal polarity ehron.Macroscopic millimetre-sized horizontal bedding should be better annually laminated sediments(varve).During early Brunhes normal polarity chron associated tectonic the lacustrine strata sedimentology resulted in Chenghai strike-slip fault.