Late Early Permian (266 Ma) N–S compressional deformation of the Turfan basin, NW China: the cause of the change in basin pattern

Previous studies suggested an important, but yet poorly-understood, tectonic transition in the Altaids (also termed the Central Asian Orogenic Belt, CAOB) in the Permian. This tectonic transition, clearly documented by published stratigraphic data and provenance analyses, suggested a unified Junger–Turfan basin in northwest China in Permian time and it further indicated that extension dominated Early Permian tectonics in the region, whereas flexural, foreland subsidence controlled Late Permian basin evolution. Our new structural observations, microtectonic analyses, and 40Ar/39Ar geochronological data from southwest of the Turfan basin reveal that in the late Early Permian (266 Ma) a NS-directed contractional deformation operated along the southern border of the unified Junger–Turfan basin, which was probably related to the transition in basin evolution. The contraction gave rise to a NW-striking right-lateral transpressional, rather than simple-shear dextral, ductile shear zone along the southwestern border of the Turfan basin, and to an interference fold pattern together with closely-spaced, concentrated cleavage and thrusts in a constrictional strain regime in the basin interior. After the Late Permian the tectonic evolution of the CAOB changed from Paleozoic continental amalgamation to Mesozoic–Cenozoic intracontinental orogenic reactivation.