Paleomagnetic Results Of The Red Bed Of Early Cretaceous Duoni Formation From The Lhasa Terrane And Their Tectonic Implications

The Tibetan Plateau,which formed by muitl-period collisions of the micro-terrane from the Gondwana continent and the south edge of the Eurasia continent is youngest and most spectacular collisional belt on Earth by tectonic activities.Therefore,there are residual sutures between this micro-terrane after the collision.The formation time of these sutures and collision process between the terranes which have critical instruction for illustrative the origin and evolution of theTibetan Plateau.Although the predecessors have carried out extensive geological and geophysical studies on the Tibetan Plateau,the specific collision time for the Lhasa-Qiantang terrane,the initial collision time of the India-Eurasia,and the crustal shortening of the Eurasia after the collision.There are still major differences in scientific problem such as the amount of crustal shortening.The Lhasa terrane which adjacent to the Bangonghu-Nujiang Suture zone in north and the Yarlung Zangbo Suture zone in south is one of the key terranes on the Tibetan Plaetua.The paleo-geographic evolution of the Lhasa terrane since the Cretaceous period is essential for understanding these scientific problems.In this paper,the paleomagnetic study of Lower Cretaceous Duoni formation in the Baoji of the eastern Lhasa terrane,based on the available paleomagnetic data for the Tibetan Plateau and geological evidence,several conclusions can be summarized as follows:1.The main magnetic mineral of high temperature characteristic remanence in the Duoni formation red layer of Baoji area is hematite.The site mean direction of 154 samples,22 sites is Ds=348.1°,Is=11.6°,k=152.5,a₉₅=2.5°after tilt-correction,and it pass both the McElhinny?1964?and McFadden?1990?fold test at 99%and 95%confident level,Ds=23.7°after E/I correction,corresponding to a paleopole at 62.6°N;296.6°E,A₉₅=1.8°.2.Combine with previously paleomagnetic and geology result form Lhasa and Qiangtang The Lhasa terrane were stable at¹7.0°N,during the Cretaceous to Eocene,the paleolatitude of the eastern and western parts were basically the same,and it was concluded that the Lhasa terrane and the Qiangtang terrane collision at about 113 Ma.3.Combine with previously study result form The Tibetan Plateau,this paper reconstruct the evolution process of Bangong-Nujinag Ocean between Permian to Cretaceous.We conclude that Bangong-Nujiang Ocean may be the Late Permian-Early Triassic,and Late Triassic this basin matured and reached its maximum.During the Jurassic,the Bangong-Nujiang ocean basin was shrinking.At the early Cretaceous?¹13Ma??Lhasa terrane had collided with the Qiangtang terrane and came together with the closure of the Bangong-Nujiang Ocean.