The South Altun orogenic belt is an important subduction—collision complex belt in northwest China. In this paper, we study the petrological, geochemical, zircon U- Pb and Lu—Hf isotopic characteristics of the Manya diorites, to discuss its petrogenesis and tectonic environment. Based on our research, the Manya diorites are depleted in Nb, Ta, Ti, P, Th, U, HREEs, Ba and Sr, while enriched in LREEs and Rb, indicating geochemical characteristics of subduction- related island arc magmatic rocks. The zircon U- Pb ages are in the range of 494 Ma to 461 Ma, and the ε Hf (t) are in the range of 0. 01 to 3. 90, with tDM2 ranging from 1496 Ma to 1447 Ma, and some negative values ranging from -2. 22 to -0. 03 (tDM2 =1453~1254 Ma) are also included, indicating that the diorites were derived from Mesoproterozoic (1453~1254 Ma) juvenile crustal materials, mixed with small amount of Mesoproterozoic (1496~1447 Ma) ancient crustal materials, triggered by underplating of mantle magma. Thus, the Southern Altyn orogenic belt was in break off and exhumation stage of the deep~subduction continental crust in <494 Ma, accompanied by underplating of large-scale mantle-derived magma, and the Manya diorites were magmatic response to the exhumation of the deep-subduction continental crust.