Single zircon LA-ICPMS U-Pb dating of Weishan granite (Hunan, South China) and its petrogenetic significance

A detailed microstructure analysis and LA-ICPMS U-Pb dating have been done for zircons of Weishan granite from Hunan Province, South China. The results indicate that the Weishan granite is a multistage batholith formed during the late Indosinian-early Yanshanian time. The intruded time of the late Indosinian granite is 211.0 +/- 1.6Ma and 215.7 +/- 1.9Ma (two samples), whereas that of the early Yanshanian granite is 187.4 +/- 3.5Ma and 184.5 +/- 5.1 Ma (two samples). In combination with other geochronological data for Indosinian rocks of South China and the adjacent region, it is inferred that the late Indosinian granites of South China (especially Hunan Province) are probably formed under extension regime as a consequence of post-collision stress relaxation, which is a spontaneous response to intracontinental thickening attributed to the collision and extrusion of two Indosinian seams, namely Qinling-Dabie and Song Ma. Moreover, it is also deduced that the early Yanshanian granites of Hunan Province could not be directly related with the subduction of Paleo-Pacific plate towards Eurasian continent, and they are most likely derivation of the mid- or lower-crustal materials because of decompressional melting under the continuous extension setting.