| Abstract: | The formation of the Tibetan Plateau is closely related to the evolution of Tethys. There have been many researchers and articles concerning the Tethys since E.Suess proposed the concept in 1893. It means a large ocean which lies between Eurasia and Gondwanaland. With the development of Tethyan research, some new terms, appeared such as Neo\|Tethys, Paleo\|Tethys, and Proto\|Tethys, representing the Tethys in Mesozoic—Cenozoic, late Paleozoic and early Paleozoic respectively. The trace of an ocean from Sinian to Ordovician was discovered during the scientific expedition and Proto\|Tethys was proposed to name the ocean. Therefore, the Tibetan Plateau is the main scope of the Eastern Tethys. It can be divided c losely related into three zones which represent the main oceanic locations in th ree different stages.The Northern Tethyan Region lies in the Kunlun and Qilian Mountains, its remnant is the Fifth Suture Zone. It is also the northern boundary of the Tibetan Plateau The rift initiated after the continental basement had been formed in Sinian and gradually developed into an ocean, which was named Proto\|Tethys, the earliest Tethyan ocean known up to now. The petrochemical compositions of pillow lava in this zone show the characteristics of mid\|ocean ridge tholeiite basalt and the pelagic ophiolitic flysch were well developed, indicating a matured ocean. It was closed in Ordovician and Silurian. |
