Kinematics, temperature and geochronology of the Qingyi ductile shear zone: Tectonic implications for late Neoarchean microblock amalgamation in the Western Shandong Province, North China craton

摘要

The Qingyi ductile shear zone is located in the Western Shandong Province, North China Craton, and it strikes NNW-SSE with a nearly vertical mylonitic foliation and horizontal stretching lineation. This shear zone is characterized by dextral strike-slip shearing. The estimated kinematic vorticity numbers of the studied mylonites ranging from 0.79 to 0.99 indicate that the shear zone is dominated by simple shear. Microstructures, quartz fabrics and mineral assemblages reveal that this shear zone is developed in upper greenschist facies with deformation temperatures of 400-500 ?. Zircon U-Pb data of mylonites and a late-kinematic vein constrain the timing of shearing at ~2501 Ma. Biotite Ar-40/Ar-39 age data of the late-kinematic vein suggest the end of late tectono-thermal events and crustal stabilisation at ~1878 Ma. Based on the geometry, kinematics and geochronology, the Qingyi ductile shear zone is interpreted to result from microblock amalgamation and indicates a horizontal tectonic regime of the Western Shandong Province during the late Neoarchean period.