Geochronology of the Orosirian Shear Zones in the Wulashan–Daqingshan Complex, Khondalite Belt, North China Craton: Apatite, Zircon U–Pb Ages and Their Tectonic Implications

The NE- to E-trending ductile shear zones are well-exposed in the Wulashan–Daqingshan Complex of the Khondalite Belt, an Orosirian collisional orogen in the northwestern North China Craton. However, the timing of the shear zone activity remains ambiguous. In this study, we performed field-based structural observations and apatite and zircon U–Pb geochronology on these shear zones. The results show that the pre- and post-kinematic intrusions yielded magmatic zircon U–Pb ages of 1967 ± 24 Ma and 1812 ± 18 Ma, interpreted to broadly provide the maximum and minimum age constraints for shearing. Meanwhile, eight samples of mylonites gave a range of apatite U–Pb ages between 1878 ± 34 Ma and 1798 ± 29 Ma, considered to record the timing of shear deformation. Moreover, a similar metamorphic zircon U–Pb age of 1876 ± 38 Ma was also obtained from another mylonite. Combined with available data, we summarized that orogen-parallel ductile shear zones in the Helanshan, Qianlishan, Wulashan–Daqingshan and Jining Complexes of the Khondalite Belt have comparable deformation ages of 1904–1823 Ma, 1902–1801 Ma, 1906–1798 Ma and ~1866 Ma, respectively. These late Orosirian (1.90–1.80 Ga) shear zones were inferred to result from the prolonged orogenic processes of the Khondalite Belt, in response to the collision between the Yinshan and Ordos Blocks.