Tectonically, the area bordering Sichuan, Yunnan and Xizang is the central sector of the Sanjiang Indosinides, the Bitu and Jinshajiang suture zones being northward elongation of the Changning-Menglian and Mojiang geosutures, respectively, in SW Yunnan. Owing to thrusting-nappe structuring of Indosinian orogenics and reformation of Himalayan movement, the area is a complicated orogenic collage. To distinguish the arc volcanics from the volcanic rocks of passive continental margin, seamount oceanic island and delamination-related rift in collisional region, and to distinguish the sediments of active continental margin from the deposits on block, two arc volcanics suites are determined. Based on the field and petrochemical data, the temporal spatial constraints for the Paleotethyan evolution are discussed. The Jidonglong Formation, in age of Early Permian and with chemical features of island arc tholeiite, is the record of eastward subduction, beneath the Chaya Mangkang Block, of the Bitu Ocean. The back-arc basin is represented by the calcareous turbidites, which is overthrust by the Yugong Formation originally deposited on the Chaya Mangkang Block. The radiolarias from chert in the fore-arc trench indicate that the subduction may last to early Late Permian. The Late Permian Xiayacun Formation, with majority of continental eruption, is tholeiite related to westward subduction of the Jinshajiang Ocean (southern sector). The Tuoba coal-measures are synchronous deposits in the back-arc region, which may comprehend a transitional continental margin between the West Pacific and the Andean. The subduction continues in Early Triassic evidenced by the Malasongduo Formation, which consists of acidic lava only, and may be an Andean-type continental margin, with the back-arc region being compressing-uplifting.