Redetermination of the age of granitic stocks in Silingtou area, Xiuning Country, southern Anhui Province

The small granitic stocks in Xiuning granodiorite have K-Ar age of 133.4Ma, suggesting that these stocks were formed in Early Cretaceous. During recent field geological survey, the authors found that these small stocks contain aluminum mineral cordierite, and their lithologic characteristics are very similar to those of Xiuning granodiorite. They are all coarse grained granodiorite with local deformation and obvious schistosity. Samples collected from both internal Xiuning granodiorite and Waiye stock yielded LA-ICP-MS zircon U-Pb age of 835.4±32Ma for Xiuning granodiorite and 841±29Ma for Waiye rock, showing that they were formed during the same period. In addition, these small granitic stocks have similar geochemical characteristics to Xiuning granodiorite. Whole-rock geochemical data show that both samples are characteristics by lower HFSE Nb, Ta, Sr and higher K, Ru, Ba, U, Th, and thus belong to the peraluminous S-type granite. By comparative analysis of lithology characteristics, U-Pb age and geochemical data from previous study and this paper, the authors confirm that these stocks should intruded during the Neoproterozoic as a part of the Jinningian Xiuning pluton, not in the Early Cretaceous as previously thought. And the northern boundary of Xiuning pluton must have migrated northward for about 2km. The sandstone (no conglomerate) of Xiuning Formation resulted from the transgressive deposition on these stocks.