Late Palaeozoic Tectonic Evolution of the Northern Part of the Zhusileng-Hangwula Arc in the Middle Segment of the Central Asian Orogenic Belt: Insights From Structural Geology and Geochronology

The final closure time and tectonic evolution of the middle segment of the Paleo-Asian Ocean (PAO) remain poorly constrained. The northern part of the Zhusileng-Hangwula arc, located in the middle segment of the Central Asian Orogenic Belt, is crucial for understanding its tectonic evolution and for constraining the closure time of the middle segment of the PAO. Field structural, microstructural, and fabric analyses reveal that the NE-trending ductile shear zone within the Baishan Formation has undergone sinistral shearing. Zircon U–Pb and ³⁹Ar/⁴⁰Ar dating indicate that the shear zones formed at 216 Ma. In addition, the northern part of the Zhusileng-Hangwula arc experienced superimposed folding deformation. Kinematic studies show that the second phase of folding refolded the tightly upright NE-trending F1 folds into NE-trending asymmetric steeply plunging F2 folds under a sinistral transpression regime. ⁴⁰Ar/³⁹Ar geochronology data indicate that the first phase of folding deformation occurred at 215 Ma, while the second phase of folding deformation occurred slightly later than 215 Ma. Geochemical characteristics indicate that the Baishan Formation formed in an active magmatic arc setting during the Late Permian. Combined with published data, the final closure time of the northern part of the Yagan and Zhusileng-Hangwula arcs in the middle segment of the PAO can be constrained to the Late Permian–Early Triassic. The formation of the shear zones and the superimposed folding deformation can be attributed to the oblique convergence orogenic process between the South Gobi Zone and the Yagan and Zhusileng-Hangwula arcs during the Late Triassic.