Paleogeomagnetic Study Of The Early Carboniferous-Late Triassic In The Qamdo Block, Qiangtang-Tibet Plateau,China

It is generally believed that the Tibet Plateau is formed by the northward drift of several micro-blocks separated by the northern margin of the Gondwana continent and the continuous southward expansion of the Eurasian continent.It is represented by a complex tectonic unit composed of multiple plots.Since the Paleozoic,there have been more than 20 collisional zones of varying scales.The Qamdo block is located in the mid-eastern part of the hinterland of the Qinghai-Tibet Plateau and is sandwiched between the Xijinwulan-Jinshajiang-Ailaoshan belt,the Wulanwula-Liangjiang belt and the Bangonghu-Nujiang-Changning belt.In the northeast,the neighboring area is the Bayan Hara block,and the west is adjacent to the Nanqiantang and Beitangtang blocks.There is a relatively complete Late Paleozoic in the block,which is characterized by the Triassic and Jurassic-Cretaceous in the whole area.A continental margin volcanic-magmatic arc?P₁-T₃?is symmetrically developed on the east and west sides.In the past studies of paleomagnetic research,most of the researchers believe that the Qamdo block,the northern Qiangtang and the Nanqiantang may originate from a certain position on the edge of the Gondwana continental margin,and the Paleozoic rupture and begin to drift northward,and combine the early and middle generations.To the southern margin of Eurasia,but the latest geological evidence suggests that these blocks may not form a unified whole at least in the Late Paleozoic.In order to more accurately depict the trajectories of the Late Paleozoic-Early Mesozoic in the southern and northern Qiangtang and Qamdo blocks,the relative positional changes between the Qamdo block and its surrounding micro-blocks were determined,and their evolution in Tethys was studied.In the process,the similarities and differences of the trajectories in the process,this paper attempts to carry out the paleomagnetic research work in the Late Paleozoic and Early Mesozoic strata in the hinterland of the Qamdo block,and compare the contemporary paleomagnetic data obtained from the Qinghai-Tibet and Beituntang hinterland protection stations.The relative paleo-position relationship and its trajectory between the micro-blocks in the hinterland of the Tibet Plateau are comprehensively determined,which provides a reference for the study of Tethys evolution in the Late Paleozoic and Mesozoic in the Qinghai-Tibet Plateau.QamdoIn this paper,we selected 24 sites in the Early Carboniferous-Late Triassic limestone strata in the Toba Township area of the Qamdo block.A total of more than 220 paleomagnetic samples were collected and detailed rock magnetism and system demagnetization work were carried out.The resulting data was subjected to a calibration analysis.The results of rock magnetism show that the magnetic minerals contained in the early Carboniferous Wuqingna Formation,the Late Carboniferous Aoqu group,and the Late Triassic Gongyeong Formation are mainly magnetite;In the limestone samples of the Tuoba group,the magnetic minerals contained are magnetite with a little hematite.The characteristic remanence results after tilt correction are:The average direction of the early Carboniferous Wuqingna group?C₁w?after tilt correction is D_s=297.9°,I_s=39.6°,?95_s=4.8°,K=47.5,paleomagnetic?=-34.6°N,?=194.8°E,A95=4.9°;the average direction of the Late Carboniferous Aoqu group?C₂a?is D_s=330.1°,I_s=44.4°,?95_s=7.1°,K=90.4,paleomagnetic?=-63.5°N,?=181°E,A95=1.26°;the average direction of the Late Permian Tuoba group?P₃t?after tilt correction is D_s=61.7°,I_s=9.8°,?95_s=6.1°,K=43.7,paleomagnetic?P₃T??=26.6°N,?=198.5°E,A95=4.3°;the average direction of the Late Triassic Gongyenong group?T₃g?after tilt correction is D_s=184.8°,I_s=42.1°,?95_s=7.4°,K=21.5,paleomagnetic is?=92.7°N,?=-33.6°E,A95=7.1°.By comparing with the collected paleomagnetic data of the predecessors,the following conclusions are drawn:?1?The Carboniferous in the Qamdo block is basically stable at-25.5°±4.8°N,and no large-scale zonal motion has occurred.The drift is limited to 2.3°?253km?,with a counterclockwise rotation of 32.9°±6.7°;in the Late Permian Changdu block,it is located at-4.8°±2.5°N;the drift amount reaches 7000 km;The Late Triassic Changdu block is located at²5.8°±6.9°N.?2?During the Early Carboniferous to Late Carboniferous period,the Qamdo block and the Beitangtang block remained independent of each other,with an ancient latitude difference of¹1.2°±2.9°;to the Late Permian,the Qamdo block reached the equator equator Nearby,while the North Qiangtang block is in the mid-latitudes of the southern hemisphere,the two plots are not combined to maintain a latitude difference of¹2°,and the latitudinal gap is smaller than that of the Carboniferous period;After the World War,the Qamdo block continued to move northward and reached the mid-latitudes of the Northern Hemisphere in the Late Triassic.At this time,there is no significant difference in the latitude of the North Qiangtang block,so we believe that during the Early Triassic period.The two plots began to piece together.?3?This paper attempts to correct the ancient locations of the Carboniferous-Triassic in the Qamdo and Beitangtang blocks using the paleomagnetic results in the reconstructed East Asian continental paleogeographic map?Huang et al 2018?.