Paleomagnetic Constraints And Implications Of The Big Bend In The Eastern Part Of The Qiangtang Terrane

Qiangtang terrane,located at the east of the Tethys Himalaya tectonic domain,has been one of the major part of Qinghai-Tibet Plateau.The study on the evolution of Qiangtang terrane that referred to a great many perspectives such as the formation,evolution and Dynamics of the Qinghai-Tibet Plateau and its predecessor has played an important role in the evolution of Tethys Ocean,Qinghai-Tibet Plateau and its predecessor.However owing to the fact that the tectonic evolutionary history of Qinghai-Tibet Plateau has been so complicated and relevant geologic data was limited,there was a huge argument about the tectonic evolutionary regarding Cenozoic era of Qiangtang terrane such as the division of Gondwana land and Eurasian continent as well as the position of the Cenozoic era that belonged to Qiangtang terrane.Therefore,the research on the tectonic evolutionary history of Qinghai-Tibet Plateau and its components since the Cenozoic era was unsatisfactory,thus there is a great need of the acknowledgement and study on its predecessor.In the eastern part of the Qiangtang terrane,the extension of Qiangtang terrane has transformed from the east-to-west extension in the central part of Qinghai-Tibet Plateau to the south-to-north extension within Yunan province.The degree of the difference in terms of the east-to-west extension has reached 90° degree.In respect of the formation in this turn,the former researchers showed that since the late Cretaceous the eastern part of Qiangtang terrane has witnessed the 40° degree clockwise rotation.However there wasn't any report concerning the tectonic rotation before the late Cretaceous.However Qiangtang terrane has been one of the crucial part of Qinghai-Tibet Plateau.The tectonic evolution was considered as an important issue in researching the formation and evolution of the Qinghai-Tibet Plateau and its predecessor.This major research methodology was based on Paleomagnetism,with the sedimentary strata in the Permian System in Mangkang region in the eastern part of Qiangtang terrane as the target layer.Thus a series of accurate data parameter of paleomagnetism and reliable paleomagnetic outcome could be acquired after the experiment.Then two sets of paleomagnetism data gained in the layers provided the restriction of quantitative data for the formation of the huge turn in the eastern part of Qiangtang terrane and tectonic evolution in order to present the rotation process in the geological striation in this region.After the discovery of Permain system in Tuoba layer of the sandstone,here are the magnetic carrier minerals: hematite,small amount of magnetite and a little or non-magnetic hematite.The major magnetic carrier minerals in the Jingxing set ofCretaceous and Nanxin set of violet red sandstone are hematite and a little or non-magnetic hematite.Based on the type of the major magnetic carrier minerals in each layer,demagnetization process that targeted at our aim and procedure in the experiment was put forward.The principal component analysis(Kirschvink)analyzed the remanence property obtained in the experiment.With the help of statistical methodology Fisher,the data from each sampling spot of each layer was statistically analyzed.Moreover the component of sandstone samples in the Permain system of Tuoba set at high temperature have passed the reversal test.After the sample of the read sandstone in Cretaceous has passed the fold test(Mc Elhiny),the component of remanence in high temperature was normally regarded as the primary component of remanence.After the analysis and calculation of the experiment above,the average direction about the component of remanence in high temperature concerning the Permain system of Tuoba set: Ds=162.25°,Is=46.13°,k=2.92,?95=19.88°;the average direction regarding the component of remanence in high temperature in terms of Cretaceous strata(Nanxin set,Jinxing set): Ds=45.35°,Is=53.83°,K=15.12,?95=6.27°;compared with the stable region of Eurasian continent,since the Permian period,due to the collision and matching of Qiangdong terrane and Qiangtang terrane,the collision of Songpan-Ganzi terrane and Lhasa terrane and the influence from the collision between India-Eurasian Continent in the Cenozoic era,there was clockwise rotation(107.9±16.9°)and movement(12.5±14.9°)to the north.Moreover the clockwise rotation(33.3±5.9°)and the southward movement(6.4±4.9°)were caused by the collision of India and Eurasian Continent.