The northern Alxa Block occupies a key position in the southern margin of Central Asian Orogenic Belt (CAOB) and records late Paleozoic subduction and closure processes of the Paleo–Asian Ocean (PAO). However, there are still controversies regarding the timing and location of the final closure of the PAO. This study presents structural deformation data, geochronological and geochemical data for Permian volcanic rocks, as well as detrital zircon provenance analysis of Permian sedimentary rocks along the Nuoergong - Langshan Zone (NLZ) in the northern Alxa Block. During the Carboniferous to middle Permian, the Paleo-Asian Ocean (PAO) lithospheric slab subducts beneath the northern Alxa Block, rendering a continental volcanic arc in the NLZ and also giving rise to extensive folding, thrusting and crustal thickening. Subsequently, a retroarc foreland basin was developed behind the continental volcanic arc, where pyroclastic material with Carboniferous to Permian ages from the volcanic arc and sediments eroded from the Alxa Precambrian basements were deposited (Dahongshan Formation) during middle Permian (Ca. 261 Ma). A large-scale dextral ductile shear deformation in the NLZ resulting from the lateral extrusion of the thickened crust after the continental collision was constrained between 272 Ma and 249 Ma, suggesting a middle Permian tectonic transition from compression to transpression. Combining with published data, we suggest that the final consumption of the PAO occurred in the middle to late Permian, probably along the Qagan Qulu suture zone in the northern Alxa Block.