Kinematics, rheology, and cooling of the continental-scale Chongshan strike-slip shear zone on the southeast of the Tibetan plateau

Quantitative analysis is crucial for understanding the tectonic evolution of continental-scale shear zones. To unravel the deformation history and processes of a continental strike-slip shear zone, we examined a range of deformed rocks from the Chongshan shear zone (CS-SZ) on the southeast of the Tibetan plateau. The detailed field observations, microstructural, and EBSD texture analyses reveal that the CS-SZ experienced early high-temperature (500–650 °C) deformation overprinted by a low-temperature (300–400 °C) deformation during the shearing and exhumation process. Our vorticity data indicate that the pure shear dominated flow (Wm = 0.32–0.65) of the bulk non-coaxial deformation history overprinted by later increase of simple shear (Wm = 0.68–1) during the later increments of ductile deformation. The bulk strain rates of CS-SZ ranged from 3.9 × 10−15 to 1.5 × 10−11 s−1, while the northernmost region experienced higher differential stress (35 to 81 MPa) and higher strain rates (3.9 × 10−12 to 2.6 × 10−11 s−1). Both sinistral and dextral shear senses occurred in the north segment of CS-SZ, but dextral kinematics was prevalent. The opposing shear senses in the northern segment could be explained by a large amount of pure shear during deformation. The southern segment was dominated by sinistral kinematics. To account for the opposing shear senses in the northern and southern segments of the CS-SZ, we propose a new model called the dextral closing zipper. Geochronology and structural data suggest that the CS-SZ underwent high-temperature ductile deformation beginning at 33–29 Ma and continued until 19 Ma. Subsequently, from 19 Ma to 13 Ma, the shear zone experienced rapid cooling, accompanied by the coeval exhumation of the metamorphic rocks and shearing.