U-Pb Dating of Volcanic Rocks and Granites along the Wuyishan Belt:Constraints on Timing of Late Mesozoic Tectonic Events in Southeast China

摘要

Five volcanic rock samples and two granite samples taken from the volcanic basins in western Fujian and southern Jiangxi were dated by using the zircon laser albation-inductively coupled plasma mass spectrometry U-Pb method.Together with previously dated ages,the dates obtained provide important constraints on the timing of late Mesozoic tectonic events in SE China.The volcanic rock samples yield ages of 183.1±3.5 Ma,ca.141 Ma to 135.8+1.1 Ma,100.4±1.5 to 97.6±1.1 Ma, confirming three episodes of late Mesozoic volcanic activities,which peaked at 180±5 Ma,140±5 Ma and 100±5 Ma,respectively,along the Wuyishan belt.Moreover,based on field investigations of these volcano-sedimentary basins,we have recognized two compressional tectonic events along this belt.The early one was characterized by Upper Triassic to Middle Jurassic NNE-trending folds that were intruded by late Jurassic granites;and the late one caused the Lower Cretaceous volcano-sedimentary layer to be tilted.The dated age 152.9±1.4 Ma of the granitic samples from the Hetian granitic pluton in the Changting Basin and that from the Baishiding granitic pluton,100.2±1.8 Ma,in the Jianning Basin, give the upper boundaries of these two tectonic events respectively.Hence,the late Mesozoic tectonic evolution of SE China was alternated between extension and compression.