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.

The Alxa Block is a significant tectonic unit in the middle part of the southern Central Asian Orogenic Belt that was affected by multiple Paleozoic and Meso-Cenozoic deformation events. In this study, the results from detailed mapping and structural analysis coupled with new U-Pb zircon ages indicate that the northeastern Alxa Block has experienced ten deformation events since the late Paleozoic. Four separate structural domains are identified in the study area, and these domains contain intrusive and structural crosscutting relationships that allow the complex deformational history to be determined. Each deformation phase can be related to regional tectonic events associated with the consolidation of Central Asia's crust and subsequent intraplate reactivation. The first three events are tied to convergence between the Alxa Block, the North China and the Yangtze Cratons prior to and during closure of the Paleo-Asian Ocean in the Mid-Late Permian. Subsequently, sinistral displacement occurred between the Alxa Block and the North China Craton during the Triassic. Since the late Mesozoic, reactivation of the northeastern Alxa Block occurred repeatedly as an intraplate response to the subduction of the Paleo-Pacific Plate, the closure of the Mongol-Okhotsk Ocean, the collision between the Qiangtang and Lhasa blocks and the later collision between India and Eurasia. The Alxa Block provides a superb case study of how continental interior regions that evolve from plate boundaries to intraplate settings may remain susceptible to reactivation in different kinematic modes in response to distant plate margin-derived forces and internal gravitational forces that evolve through time.