Paleomagnetic Study Of The Paleocene Redbeds In The Tethyan Himalaya And Its Geological Significance

The collision and ongoing convergence between the India and Asia continents have produced the Himalayan-Tibetan Orogen.Therefore,the India-Asia collisional time and collisional process are very important to understand the tectonic evolution of the Tibetan Plateau.However,disputes still remain concerning these two problems.Paleomagnetism is one of the principal techniques for reconstructing continental drift and plate tectonics,and thus is very helpful to solve the above two problems.A combined paleomagnetic and rock-magnetic study has been carried out on the Sangdanlin and Zheya Formation redbeds,which were dated at 60-58.5 Ma,in the Saga area of the Tethys Himalaya.Based on the new paleomagnetic results,as well as previous paleomagnetic poles from the Indian craton,Tethyan Himalaya and Lhasa terrane,several conclusions can be summarized as follows:?1?Thirty-six Paleocene redbed sites provide a tilt-corrected site-mean direction of D=178.3°,I=9.8°with?₉₅=5.5°,corresponding to a paleopole at 55.6°N,268.5°E with A₉₅=4.9°.This reliable paleomagnetic dataset passes positive fold tests and shows that the Saga area?29.3°N,85.3°E?was located at⁵.1°S during 60-58.5 Ma.?2?Comparing the Paleocene?60-58.5 Ma?paleomagnetic results observed from the Tethyan Himalaya with those expected from the Indian APWP indicates a paleolatitude difference of?2.1°,which,combined with that the early Cretaceous paleomagnetic results obtained from the Tethyan Himalaya and India craton also showed a similar paleolatitude difference,suggests that neither a great north-south crustal shortening occurred between the Indian craton and the Tethyan Himalaya after the India-Asia collision,nor that a wide ocean extended between them after the early Cretaceous.?3?Based on our new Paleocene results obtained from the Tethyan Himalaya and the reliable Cretaceous-Early Eocene paleomagnetic results observed from the Lhasa terrane,as well as extrapolating a constant Indian northward velocity of 18.8 cm/yr,the India-Asia collision was at¹1.4°N and⁴9.2 Ma for the reference point at 29.3°N,85.3°E.