Division of the geotectonic units of the middle-western area of north Tibet and its geological significance
The research area is located in the north margin of Gondwana. Since Mesozoic , the Bangong Lake-Lu River ocean and the Yaluzangbu River ocean have subducted toward each other, leading to the transformation of poly-island arc-basin and the intracontinental convergence-the plateau uplift, and forming a extreme complex pattern of geological structure. On the basis of the 1∶250 000 Bangduo Chuomai geologic maps of North Tibet and the previous regional geological data in the theory of the poly-island arc-basin orogency model ,it is believed that geotectonic unit Ⅰ--the Banggong Lake-Lu River junction zone and Ladake-Gangdisi-Lasa-Tengchong continental block from north to south can be divided further into such geotectonic units Ⅱ such as the late Jurassic foreland basin, the Cretaceous residual sea basin, the Asuo tectonic melange, the Yanshanian magma arc,the Mesozoic compound back-area basin and fault-uplift zone , late Yanshanian-Himalayan magma arc and the Neogene Quaternary S-N graben and so on.The result shows that complex orogenesis reminders are very well arranged in a time-space seqaence