Petrology and zircon U-Pb geochronology of metamorphic massifs around the middle segment of the Tan-Lu fault to define the boundary between the North and South China blocks

Abstract

The Tan-Lu fault (TLF) is a significant linear structure of eastern China. The middle segment of the TLF in the northern Anhui Province separates the North China Block (NCB) and South China Block (SCB). Lack of geological work makes the plate boundary here ambiguous. Detailed field survey and laboratory analyses have been conducted to constrain the formation and evolution of the TLF. To the west of the TLF, the Wuhe massif underwent a granulite facies metamorphism with T=778–836°C, P=1.0–1.2GPa during 2.41–2.43Ga according to LA-ICP-MS U-Pb zircon dating. On the contrary, to the east of the TLF, the Zhangbaling massif suffered a greenschist to lower amphibolite facies metamorphism with the average metamorphic temperature at around 340–440°C, with the protolith igneous ages of ca. 750Ma. These differences indicate that the two massifs belong to the different blocks. Furthermore, the granitic gneiss in the central part of TLF gives three populations of zircon U-Pb age at 667–504Ma, 228±2Ma and 211±2Ma, respectively. The later two groups of spectra correspond to the periods of subduction and exhumation of the Dabie massif (245–200Ma). Combined with previous study, the precise plate boundary between NCB and SCB has been delineated as the Zhuding-Shimenshan fault, and the initial time of the motion for the TLF is also discussed.