Paleomagnetic Results Of The Late Cretaceous Strata From Zhongba,Dingri And Gyangze Areas,Southern Tibet And Their Tectonic Implications

India-Eurasia collision is one of the most significant geologic events in the Cenozoic.Different from the India-Eurasia archetypical continental collision model,a dual continent-continent collision model has recently been proposed.In this model,an oceanic Greater Indian basin was hypothesized to have formed between?120 Ma and?70 Ma by 2675±700 km of North-South extension that separated the cratonic India from its northern margin of Tethyan Himalaya(TH),and TH first collided with Lhasa block and then India craton collided with TH.However,the lack of high quality paleomagnetic data from this critical time interval in the TH marks an important gap in our knowledge about the tectonic evolution of the Greater India.To better constrain the structure relationship between TH and India,we have conducted detail paleomagnetic studies of Late Cretaceous strata in Zhongba section of Zhongba area,Gongzha section and Anba section of Dingri area and Yongla section of Gyangze area in Southern Tibet.Based on the new results,the following conclusions can be drawn:(1)The paleomagnetic results from the Gongzha section and Anba section of Dingri area and Yongla section of Gyangze area failed to yield reliable primary remanent magnetization;the HTCs of samples from Zhongba section exhibit dual polarities that passed a reversed test at 95%confidence level,suggesting a primary origin of the remanence.(2)With chronologic constraints from the combined analysis of the lithostratigraphy,magnetostrati graphic and radiolarian data,the HTCs of Zhongba section yield a mean of Ds=336.9°,Is=-50.70,ks=18.0,?95= 5.3°for the?120.8-93.9 Ma interval of the TH,which corresponds to a paleopole at 25.0°N,285.7°E(dp/dm?4.8/7.10).(3)The apparent polar wander path(APWP)of the TH overall resembles that of cratonic India,suggesting no polarward separation that is sufficiently large to merit an oceanic basin between the TH and cratonic India.Therefore,our new reliable paleomagnetic data from the critical time interval do not support the Greater Indian Basin hypothesis and its implied dual collisional processes between India and Asia.On the other hand,the APWPs exhibit relative shifts for the post-120 Ma segment and the pre-130 Ma segment,indicating relative motions between the TH and cratonic India that most likely resulted from sinistral or dextral shearing along boundary-parallel faults after the initial India-Eurasia collision.