Timing, geometry, and kinematics of the Yilan-Yitong fault zone in the Northern Tan-Lu fault system of Northeast Asia

Abstract

The largest Tan-Lu active fault system in northeastern Asia, spans approximately 3500 km in length and varies in width from 10 km to 200 km. In 1668, an earthquake with a magnitude of 8.5 occurred in Tancheng, causing the loss of over 50000 lives. To constrain the timing and process of the Tan-Lu fault system on eastern Asian margin, this study presents the field mapping, thin section observation, geochronology, and microanalysis of Weiyuanpu-Yehe ductile shear zone (WYSZ) of the northern Tan-Lu fault system. Kinematic indicators and microstructures suggest a sense of sinistral strike-slip. The deformation temperature of the mylonite is mediate to high based on the quartz deformation, c-axis fabrics. The differential stress of the shear zone is 20‒40 MPa using quartz paleopiezometry. The dikes within the shear zone yielded zircon U-Pb ages of 165‒163 Ma. However, due to the ambiguous geological relationship between the dikes and shear zone, additional geochronology is warranted. Since the Mesozoic era, based on the exposure of mylonite and dikes, the upper crust has been extensively eroded, exposing the ductile shear zone. Moreover, the understanding of the geometry and process of pre-existing structures has fundamental implications for predicating the potential earthquakes for the Tan-Lu fault system.