Paleomagnetism Research On Jiushidaoban Layer’s Extrusive Rock Of Middle Permian In North Tanggula

Northern Qiangtang-Qamdo block is located between Xijinwulan-Jinshajiang suture zone and Bangonghu-Nujiang suture zone, which is divided into two relatively independent ’plots by northern Lantcang spreading from northwest to southeast in current tectonic framework. However, it hasn’t been decided that the two plots are formed from one block by late reformation or from two relatively independent plots’splice. Therefore, it is one of the critical problems about Qinghai-Tibet plateau’s tectonic evolution to determine northern Qiangtang block and Qamdo block’s paleogeographic position and tectonic evolution. Late Paleozoic to Mesozoic whose paleomagnetic data can provide basis for research on Qiangtang-Qamdo block is the key period of Qiangtang and Qamdo block’s geological evolution. However, the paleomagnetic data is few and disperse. In the paper, paleomagnetism about Jiushidaoban formation of Kaixinling group belonging to Tuotuo river north to Tanggula mountain in Permain was studyed and reliable datas were obtained. Contrasting with circumjacent datas, the result can provide basis for tectonic movement of two blocks.The mining points were lacated in north of kaixinling coal mine in region of Tuotuo river. 19sites of Jiushidaoban formation in middle permian were setted and 175 paleomagnetic samples orientated were gotten. Through rock magnetic experiment, we can know the magnetic mineral of the roak mainly include three types:only magnetite, only hematite, magnetite and hematite. Methods of thermal demagnetization and alternating demagnetization were used to clear the residual magnetic. Demagnetizing curves of most samples showed characteristics of two-component of which the high temperature components passed the fold at the 95% confidence level, so the high temperature components of Jiushidaoban formation represented the original residual magnetism.The average direction for original residual magnetism component is Ds=252.9°, Is=24.3°, ks=6.9,α95=14.6; the paleomagnetic pole position isλ(°N)=6.6°, φ(°E)=202°, dp/dm=15.6/8.4; Paleolatitude is 12.7°N.According to the experimental result and comparision with previous datas, it is known that northern Qiangtang block was relatively independent of Qamdo block before early Mesozoic in low latitudes of southern hemisphere. In terminal late paleozoic, northern Qiangtang block drifted slowly while Qamdo block drifed drastically to north.. From terminal late paleozoic to early Mesozoic, the distance between two blocks became shorter and shorter. In late Triassic, the two blocks collided to be one block whose center is northern Lantcang suture zone.