New Late Cretaceous Paleomagnetic Data From Volcanic And Red Beds From The Lhasa Terrane And Its Implications For The Paleolatitude Of The Southern Margin Of Eurasia Prior To The Collision With India

Collision of the Indian and Eurasian continents is considered to be one of the major tectonic events of the Cenozoic time. It resulted in the formation of the Himalayas and the Tibetan Plateau, which have had major repercussions on regional environments and possibly global climate. Despite its importance and decades of research, the precise time of the initial India–Asia contact and the amount of crustal shortening remains controversial until recently. The proposed initial time of collision mainly ranges from ~34 Ma to ~70 Ma. The most direct evidence of approximately North-South direction collision between India and Asia continents is whether terranes distributed in both sides of suture zone have comparable paleolatitudes.Paleomagnetism is the one effective method which can directly determine paleolatitudes.In this study, we report the paleomagnetic and chronologic data from volcanic and red beds from the Linzhou basion in Lhasa block, and discuss the initial time and the amount of crustal shortening by the way of tectonics and paleomagnetism. In this study, we gets some conclusions as follows:(1) Potassium-argon(K-Ar) dating indicates that the basalt sequences are of late Cretaceous age(63.75-73.75 Ma).(2) The consistent inclination recorded in red beds and basalt lava flows from Lhasa terrane shows that no significant inclination shallowing caused by deposition compaction in red beds from the studied section. The tilt-corrected mean direction is Ds=0.5°, Is=20.2°, k=25.5° with α95=6.4° and N=21 sites, corresponding to apaleopole at 70.5°N, 269.6°E with A95=4.9°, yielding a paleolatitude of 10.4° N for the southern margin of Eurasia in late Cretaceous period.(3) Based on previous Cretaceous and Paleogene results within Lhasa terrane, we can obtain that the latitude position of the southern margin of Eurasia is located at about 11-15°N, and it yields a stable position of the Lhasa terrane during Cretaceous and Paleogene. The initial age of the collision between India and Eurasia was determined at about 54- 47 Ma.(4) Compared with expected paleolatitude calculated from newest APWP of the Asia and India, the difference suggests that the latitudinal distance of the Lhasa with respect to Eurasia since ~70Ma is 1300 ± 450 km.