Paleomagnetic Research On The Late Triassic Xujiahe Formation And Early Jurassic Baitianba Formation In The Yangtze Block

The Yangtze Block is an important and stable tectonic unit in East Asia.The history of tectonic evolution has always been the focus of geology research.It is of great significance to understand and comprehend the collision and consolidation process between major blocks in the mainland of China by clarifying the law of motion drift of the Yangtze Block.We sampled 89 Late Triassic Xujiahe Formation sandstone samples and 97 Early Jurassic Baitianba sandstone and siltstone samples form Majiaoba area of Jiangyou,Sichuan,and conducted on the systematic rock magnetic and paleomagnetism studies to these samples in this paper.The rock magnetism results of representative samples show that the main magnetic minerals of the sandstone and siltstone samples in the Xujiahe Formation and the Baitianba Formation are magnetite.Through the system's thermal demagnetization experiment,the high-temperature characteristic components separated from the Xujiahe sample were statistically analyzed.The average direction in the geographic coordinate system was close to the current geomagnetic field direction,and the high-temperature characteristic components after stratigraphic correction were more scattered,indicating that The high temperature component obtained in the Xujiahe sandstone sample may have been remagnetized.After the thermal demagnetization experiments of the sandstone and siltstone samples of Baitianba,the low-temperature viscous component of a present geomagnetic field and a stable high-temperature characteristic component were separated from the demagnetization results.The high-temperature characteristic component of the Baitianba Formation passed the C-level inversion test at the 95% confidence level,indicating that the high temperature component of the Baitianba Formation may be the original remanent magnetization.After the formation correction,the average direction is Ds = 44.6°,and Is = 43.9°.k = 14.9,?95 = 7.8°;paleomagnetic pole position is ?p =-50.7°,?p = 192.5°,A95 = 7.7°;the corresponding ancient latitude is 25.7°N.Compared the high-temperature characteristic components of the Xujiahe Formation obtained in this study with the polar locations since the Mesozoic of the Yangtze Block.The results shows that the position of the paleomagnetic pole in this research is relatively close to that of the Cenozoic position obtained in the Yangtze block.It indicates that the Late Triassic Xujiahe sample collected in the Majiaoba area of Jiangyou,Sichuan Province may be remagnetized since the Himalayan movement.In addition,combined the results of this early Jurassic study with previous scholars' research on paleomagnetic properties of the Yangtze block and North China block,this paper plots the ancient latitudes of the Phanerozoic in the Yangtze Block and the North China Block.It can be seen that the old latitudes of the Early Jurassic Yangtze block and the North China block are already close to coincide with each other.Depict the paleomagnetic poles in the Early Jurassic of the Yangtze block obtained in this study into the Paleozoic polarographic shift curve of the existing Phanerozoic in the Yangtze block,we found the new APWP shows no significant movement during the Late Triassic to Early Jurassic of the Yangtze block.