Structural analysis of ductile shear zones in the North Qinling Orogen and its implications for the evolution of the Proto‐Tethys Ocean

Abstract

The ductile shear zones in the North Qinling Orogen, such as the Luonan‐Luanchuan, Guanpo‐Qiaoduan, Zhuyangguan‐Xiaguan, and Shangdan shear zones, play an important role in the preclosure and postclosure evolution of the Proto‐Tethys Ocean. On the basis of detailed macrostructural/microstructural analysis and quartz C‐axis electron backscattered diffraction fabric analysis, the sense and formation environment of the 4 shear zones have been obtained. The Luonan‐Luanchuan and Guanpo‐Qiaoduan shear zones mainly present as dextral and sinistral shearing under low temperature, respectively. The Zhuyangguan‐Xiaguan shear zone mainly presents as dextral shearing under medium temperature. The Shangdan shear zone underwent an early dextral shearing under medium temperature and a late sinistral shearing under low temperature. The Qinling Group and the Taibai region were intensively affected by the late sinistral shearing of the Shangdan shear zone. According to published metamorphic ages, the 4 shear zones should have been formed during the collision between the North China Block and the South China Block. Due to the opening of the Mianlue and the Paleo‐Tethys oceans since ~380 Ma, the North China Block and the South China Block departed from northern Gondwanaland and drifted northward along transform faults, which led to the arrangement between the North China Block and the South China Block that transited from an east–west direction to a north–south direction. Since ~320 Ma, the scissors‐type closure between the North China Block and the South Qinling Terrane led to the westward extrusion of the North Qinling Orogen, and the dextral shearing of the Luonan‐Luanchuan and the Zhuyangguan‐Xiaguan shear zones and the sinistral shearing of the Guanpo‐Qiaoduan and the Shangdan shear zones.