The Yidun island arc belt, on the eastern margin of the Qinghai—Xizang Plateau and betwe en the Jinshajiang fracture zone and Garzê—Litang fracture zone, is a very importan t unit of the Sanjiang (Jinshajiang， Lancangjiang and Nujiang Rivers) fold syste m within the Tethyan tectonic realm. This area undergone a multicyclic evoluti on c haracterized by alternation of extension and compression regime, which could be divided into 10 stages. ① Permian and prePermian stage: being one part of th e panYangtze plate. At present, the Yidun island arc belt is far separated from the Y angtze landmass by the extensive Yajiang fold system, the marginal tract of the present Yangtze landmass. However, in the Permian and prePermian this are a wa s directly connected with the present Yangtze landmass, forming a unified and br oad plate, which could be called the panYangtze Plate; ② Terminal Permiane arly mi ddle Triassic stage：marginal continental rift→ocean. In the terminal Permian t he p anYangtze plate cracked and formed some land blocks such as Zhongza and Ruoerg a i blocks. These blocks drifted westward in the earlyEarly Middle Triassic and the o ceanic crust initiated, forming the Garzê—Litang ocean, which has its relics r e p resented by a sequence of basic pillow lavas, basicultrabasic cumulates and ra d iolarian siliceous rocks exposed intermittently along the Garzê—Litang fractur e zone; ③ late Middle Triassic stage: shortterm's subduction of the Garzê—Lit an g ocean and the appearance of the immature island arc in the Yidun area; ④ Earl y Carnian stage: the rifting Yidun area and the spreading GarzêLitang ocean; ⑤ late Carnian\_early Norian stage: the thorough subduction of the Garzê—Lita ng oc e an and the forming of the Yidun mature island arc; ⑥ middle\_late Norian stage: rifting on the island arc; ⑦ Terminal Norian—Rhaetian stage: collision and r e lict sea; ⑧ Jurassic—Early Cretaceous stage: intensive compression and orogen y ; ⑨ Late Cretaceous—Tertiary stage: intermontane rift—basin; \(10 Quaternar y —tod ay: rapid uprising and orogeny.