Magnetostratigraphy Of Cretaceous Sediments In Lanzhou-Minhe Basin And Its Implications On The Uplift Of The Northern Tibetan Plateau

The research on the tectonic deformation history of the northern Tibetan Plateau provides great significance to understand the formation of Tibetan Plateau and its influence on the environmental system in the East Asia.In the last decades the researchers have better approached to well constrain the Cenozoic formation of the Tibetan Plateau.But the tectonic evolution prior to the collision of India with Asian such as that in the Cretaceous is unclear. The Longzhong basin,located in the northern Tibetan Plateau and filled with more than 3690 meters nonmarine sediments,is a good place to reconstruct the Cretaceous tectonic history and its effect on the formation of present-day Tibetan Plateau and East Asian environmental system.The Minhe-lanzhou sub-basin of the Longzhong basin holds the most widely exposed and seccussive Cretaceous sediment.In this paper paleomagnetic and rock-magnetic sampling and measurement tie with the sedimentary facies,paleocurrent,pebble analysis and susceptibility along the typical sections Hekou,Yanguoxia and Lamagou have conducted.We find that the ChRM were loaded by the hematite in the red lithos and magnetite in the green lithos.The 28 normal polarities and 27 reversed polarities are observed in the sediments,and can be reasonably correlated to the M15 thorough M-"2r" below,this yields an age control to the Hekou Group 139-106Ma.Seven sedimentary facies including the alluvial fan facies,fan delta facies,braided fluvial facies,shore-lake facies,shore-shallow lake facies,semi-deep lake facies and delta facies have been found,indicative of that the basin has undergone initial compression-rifted (139-120.4 Ma),intermediate stage of expansion(120.4-108.3 Ma)and last stage of extinction(108.3-106 Ma).The susceptibility data shows that the tectonic uplift of the Cretaceous Qilianshan Mount spanned following three stage:the early stage of fast and strong uplift between 139 and 120.4 Ma,the intermediate stage of stable uplift spanned from 120.4 Ma to 108.3 Ma and the last fast uplift stage from 108.3 Ma to 106Ma.