LA-ICPMS U-Pb ages of zircons from Mesozoic volcanic rocks and their significance in Fanchang basin, Anhui Province, China
安徽繁昌盆地中生代火山岩错石LA-ICPMS U-Pb年龄及其意义

The Fanchang basin is one of the important continental volcanic fault basins in the Middle-Lower Reaches of Yangtze River, where the volcanic rocks can be generally subdivided into four formations, i.e., Zhongfencun Formation, Chisha Formation, Kedoushan Formation and Sanliangshan Formation. The LA-ICPMS U-Pb ages of zircons from trachyandesite of Zhongfencun Formation, biotite trachytic porphyry of Chisha Formation, rhyolite of Kedoushan Formation and biotite trachyte of Sanliangshan Formation are 134.4±2.9Ma, 131.3±1.8Ma, 130.8±2.2Ma and 128.1±3.1Ma respectively. Hence, the ages of volcanic rocks in the Fanchang basin range from 134~128Ma, corresponding to the Early Cretaceous. Many inherited or captured zircons occur in the volcanic rocks, the oldest one is 2894Ma age which may correspond to the 2.7Ga peak age of global magma activities and continental developments. It is implies the existence of Archean basement under the Fanchang basin. The forming period of volcanic rocks in the Fanchang basin is nearly similar to those in the other continental volcanic basins in Middle-Lower Reaches of Yangtze River, and the four volcanic circles of Fanchang basin can entirely correspond with those of Luzong basin and Ningwu basin. The 135Ma is considered as the beginning of the Early Cretaceous volcanic activities in the continental volcanic fault basins in Middle-Lower Reaches of Yangtze River. The period of Mesozoic volcanic activities, 135~128Ma, in Fanchang basin, correspond to the fastigium of the lithospheric thinning in eastern China, which constrained the volcanic activities in Fanchang basin.