SHRIMP zircon U-Pb geochronology of Indosinian granites in Hunan Province and its petrogenetic implications

The SHRIMP zircon U-Pb geochronology of three typically Indosinian granitic plutons with peraluminous and potassium-rich affinities (Tangshi ultraunit for Weishan and Baimashan, and Longtan ultraunit for Guandimiao) is presented in Hunan Province, South China. The analyses of zircons from biotite monozonite granites for Weishan, Baimashan and Guandimiao plutons show the single and tight clusters on the concordia, and yield the weighted mean Pb-206/U-238 ages of 244 +/- 4, 243 +/- 3 and 239 +/- 3 Ma, respectively, representing the crystallized ages of these Indosinian granites. These data suggest that the Indosinian granitic plutons as previously thought formed at a narrow age span. In combination with other data, it is inferred that the Indosinian granites within the South China Block probably distributed in Hunan, Jiangxi, Guangxi and Guangdong provinces as planar shape, and were the derivation of the crustal materials in the intracontinental thickening setting. These precisely geochronologicall data provide important constraints for better understanding the spatiotemporal pattern of the Indosinian peraluminous granites and early Mesozoic tectonic evolution of the South China Block.