Objective The Permian to Triassic is a key period in the evolution of the Central Asian Orogenic Belt (CAOB), forming a series of deformation with different properties, mechanisms, and stages, which may represent the products of three important stages of evolution in the Paleo Asian Ocean (PAO): subduction, collision and intracontinental deformation. In recent years, a large number of Permian−Triassic deformation have been identified in the Alxa area in the southern margin of the CAOB. However, disputations regarding the interpretation and understanding of the deformation lead to significant differences in the determination of the closure time of the PAO.

Methods Based on systematic introduction of the Permian−Triassic deformation in different regions of Alxa, the deformation sequences and characteristics of the Alxa region during this period are determined.

Results In the late Middle Permian (approximately 270~260 Ma), widespread linear fold and thrust belts were formed in the northern part of Alxa. At the end of the Late Permian to the Early Triassic, the entire Alxa Block and the Central Asian Orogenic Belt were involved into a large−scale dextral ductile shear system, which was cut by left lateral strike−slip shear zones formed in the Late Triassic. The cutting relationships are clear in Langshan in the northeastern Alxa, Hangwula in the northern Alxa, and Houbuhaer in the northwestern Alxa. Based on an integrative analysis of the different deformation characteristics between the collision stage and the intracontinental stage, it is believed that the late Permian deformation formed at the collision stage after the final closure of the PAO, while the deformation from the Late Permian to the Early Triassic represents the giant shear deformation formed during the formation of the Pangea Supercontinent after the formation of the orogenic belt, which is the first intracontinental deformation record after the final assemblage of the CAOB. The late Triassic deformation represents a far−field effect induced by the collision at continental margins to the south.

Conclusions The differences between the deformation formed at the collision stage and at the intracontinental stage can effectively constrain the evolution of different stages of the PAO from the perspective of deformation. The CAOB, represented by the Alxa region, underwent successive superposition of deformation in different properties and directions during the ocean−continent transition, which is an important feature of accretionary orogenic belts.