The initial time of the Tan-Lu wrench fault: In the view of geochronological data of the basement rocks, northern Anhui Province

Abstract

As the most conspicuous structure of Eastern China, the Tan-Lu fault arouses the most controversies on its initial time of the sinistral strike-slip movement. In the northern Anhui Province, the Bengbu uplift, which consists of basement rocks of the North China Craton, is situated to the west of the Tan-Lu fault, and the Weigang granitic gneiss is located to the east. Three samples were analyzed by in situ zircon U-Pb dating and P-T calculation from the Bengbu uplift: WS055-1 (albite granitic gneiss), WS055-3 (amphibolite) and WS021-1 (granitic gneiss). All of them have experienced medium-high grade metamorphism with the P-T condition about 0.53±0.01 GPa and 742±5℃. LA-ICP-MS U-Pb zircon dating results suggest a main crystallization age at Late Mesoarchean to Paleoproterozoic. New geochronological data from zircons of the basement rocks can be preliminarily divided into four groups around (1) 2886±28 Ma, (2) 22481±18 Ma to 2440±28 Ma, (3) 2163±55 Ma, and (4) 1944±89 Ma, respectively. The oldest age indicates the presence of the oldest juvenile crustal materials at the late Mesoarchean (2.89 Ga). These age groups correspond well to the tectonic events of the North China Craton. One granitic gneiss (FD019-1) was collected from the west of the Zhangbaling group. Zircons of the Sample FD019-1 have structure of core-mantle-rim, which yield ages at 667-271 Ma for core, 228±3 Ma for mantle, and 211±2 Ma for rim, respectively. According to the regional tectonic framework, FD019-1 can be considered as derived from the Qinling-Dabie-Sulu orogenic belt along the northern margin of the Yangtze Block. Hence, as the boundary between the North China Craton and the Yangtze Block, the western boundary of the Tan-Lu fault in northern Anhui Province is the Zhuding-Shimenshan fault. Combined with previous work, the initial time of the Tan-Lu wrench fault is also discussed.