Zircon U-Pb Dating of Dayishan and Tashan Plutons in Hunan Province and Its Tectonic Implications

The distribution and intrusion of Early Mesozoic granites in central South China such as Dayishan pluton and Tashan pluton are closely related to folded structure in this region. Precise chronologic studies can constrain the age of the tectonic deformation. This paper report zircon U-Pb LA-ICP-MS ages of the southern part of Dayishan pluton based on dating of 3 samples: the age of the eastern margin is(171.8±1.9) Ma, that of the western margin is(169.9±1.8) Ma and that of the central part is(164.2±2.6) Ma. The zircon U-Pb LA-ICP-MS age of the eastern part of Tashan pluton is(247±5.9) Ma. Dayishan pluton experienced two phases of intrusion between 164.2 and 171.8 Ma and formed a composite pluton; after that, it experienced rapid uplift prior to 125 Ma, and then it was rapidly raised to the surface at the cooling rate of 1°C/Ma. Dayishan pluton and Tashan pluton recorded Indosinian and Yanshanian magmatic activities. The EW-trending structural zone controlled Indosinian granites, such as Yangmingshan and Tashan; the ages of Dayishan and Qitianling plutons constrain the Yanshanian tectonic deformation, and the formation of the NNE-trending folds in South China should be earlier than(171.8±1.9) Ma.