Large‐Scale Mesozoic Thrusting in the Central Segment of the Central Asian Orogenic Belt: A Reappraisal

Abstract

Large‐scale intracontinental deformation within the framework of plate tectonics is common, yet difficult to explain reasonably. The Central Asian Orogenic Belt (CAOB) not only experienced large‐scale shortening deformation during the closure of Paleo‐Asian Ocean, but also underwent polyphasic, intense intracontinental deformation. There currently exist many debates regarding the scale, timing, extent of these deformations, and their tectonic backgrounds. Through structural mapping in the Zhusileng area of the central southern CAOB and regional analysis, our study shows that the previously identified large‐scale thrust structure along the Sino‐Mongolian border is the result of the superposition of three thrusting events that had different vergence directions. The main deformation period ranges from Late Permian to Early Triassic (280–255 Ma), rather than the previously well‐known Middle to Late Jurassic or Late Triassic. The main structures in the mapping area consist of a nearly east–west striking and top‐to‐the‐south thrust belt, a north–south striking and top‐to‐the‐east thrust belt, a large ring‐shaped ductile shear zone, and scattered north‐ or south‐trending thrust faults that cut through the above‐mentioned structures. The early nearly east–west trending thrust belt is consistent in orientation and timing with deformations in other regions of the CAOB, resulting from the final closure of the Paleo‐Asian Ocean during the Late Permian. The later eastward‐directed thrusting is related to the clockwise rotation of a large composite batholith caused by widespread ductile shearing along the entire CAOB dated after ca 255 Ma. During the middle to late Mesozoic, the CAOB was affected by the Mongol‐Okhotsk orogeny to the north, but the resulting thrust displacement was limited.