The NS-trending structures in the southwestern part of the Qinghai-Xizang Plateau: New insights

Nunerous studies conducted in the southwestern part of the Qinghai-Xizang Plateau in the last decades have revealed that there has been considerable progress but still debate concerning the NS-trending structures in this vast area. These NS-trending structures represent an important part of the Cenozoic intracontinental convergent deformation on the Plateau. Some aspects of views from the author in the present paper are suggested as follows. (1) The NS-trending structures consist of not only the extensional structures but also the compressional structures such as folds, overthrust faults and superimposed structures. (2) The terminology rift systems can't be applied to represent all of the extensional structures,and the rift systems and graben systems also can't represent all of the NS-trending structural features. Instead, the NS-trending structures are herein suggested. (3) The NS-trending structures in the study area were initiated during the Eocene to the Oligocene. (4) The NS-trending extensional structures were initiated in the northern Xizang to southern Qinghai zone rather than in the Himalayas. (5) A phase of temporary EW-trending compressional stress field once occurred on the Plateau during the latest Oligocene to the earliest Miocene, and resulted in the formation of various compressional structures. The NS-trending structures outlined above show a long and complex history, with early initiation and development spanning three phases of extension during the middle and late Eogene, compression during the latest Eogene to the earliest Neogene, and reextension during the Miocene or later.