Dating Strike‐Slip Ductile Shear Through Combined Zircon‐, Titanite‐ and Apatite U–Pb Geochronology Along the Southern Tan‐Lu Fault Zone, East China

Abstract

AbstractDating the timing of ductile shear deformation is critical to the understanding of complex, multi‐episode kinematics that commonly occur within the study of continental tectonics. The Tan‐Lu fault zone (TLFZ) in East China is a lithospheric discontinuity that records multistage sinistral strike‐slip shearing during Mesozoic time. Herein, based on field mapping, pressure‐temperature estimates via microstructures, quartz lattice preferred orientations, and geothermobarometer analysis, and U–Pb geochronology, we present a detailed examination of a portion of the southern TLFZ known as the Fucha Shan ductile shear zone. Two phases of sinistral ductile shear deformation in the shear zone are identified. The main phase occurred under amphibolite‐facies metamorphic conditions (500°C–650°C, 2.8–5.2 Kbar). U–Pb dating of synkinematic titanite indicate deformation occurred ca. 142–140 Ma. This age information is consistent with U–Pb dating of zircon from crosscutting granitic dikes that provide an upper limit of the shearing of ca. 134 Ma. A later, but less well‐developed phase of sinistral ductile shearing variably overprints older structures within the Fucha Shan shear zone at greenschist‐facies metamorphic conditions. U–Pb dating of apatite grains in rocks that record this later event are interpreted to indicate that shearing occurred ca. 118–108 Ma. These results provide new insight into Early Cretaceous shear deformation history within the southern TLFZ in the context of the late Mesozoic intracontinental deformation in East Asia.