Tianxin Cretaceous Volcanic Rock in Xingguo, South Jiangxi: Zircon U-Pb Dating and Its Tectonic Setting

The Nanling area is famous for its widely distributed granites. There are also many volcanic rocks there, but cretaceous volcanic rocks are rare. In this paper, based on field survey, we investigate the rock formation time of Tianxin andesitic-porphyrite by Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICPMS) zircon U-Pb dating, and determine its age to be (102.3±0.5) Ma. This result indicates that the stratum relation considered before should be adjusted, the Tianxin andesitic-porphyrite must have erupted in the late Cretaceous but not the late Jurassic period, the included sandstone breccia belongs to the early cretaceous Ganzhou group and the stratum covering on the andesitic-porphyrite belongs to the Nanxiong group, not the Ganzhou group. However, this result also indicates that, in this area, the magma activity from early to late was a reverse evolution from acid to neutral to mafic-ultra mafic during the Yanshanian period, and this might be related to the magma activity of the deep mantle, and possibly a production of tectonic event in the South China continental crust from thickening to thinning.