Abstract: The Songpan-Ganzi fold belt and Yidun Terrane in northern Sanjiang, Southwest China are characterized by intensive Late Triassic tectono-magmatism. The magmatism in Songpan-Ganzi fold belt occurred mainly at 228-190 Ma (peaking at 210 Ma), slightly younger than the magmatism in the Yidun Terrane (236-200 Ma, peaking at 216 Ma). The Jinshajiang Ocean may have experienced divergent subduction to the west and east and closed at the end of Late Permian to the beginning of Early Triassic. The Ganzi-Litang Ocean might be a back-arc basin associated with the eastward subduction of the Jinshajiang Ocean and closed before ca. 217 Ma. The Late Triassic magmatism in the Songpan-Garze fold belt and Yidun Terrane is assigned to post-collisional magmatism and most likely related to lithospheric delamination and the slab break-off of the Jinshajiang Ocean, respectively. Mantle components have contributed to the Late Triassic post-collisional magmatism. Fractional crystallization of mantle-derived mafic magmas played an important role in the formation of Late Triassic intermediate to felsic magmas, suggesting net crustal growth. The Triassic collisional events occurred among terranes resulted in orogenesis, and spatially varied crustal thickening and mountain uplift.