Abstract:Objectives: Tongling area of Anhui province is a famous copper—gold polymetallic ore concentration area in the middle and lower reaches of Yangtze River of eastern China. The intermediate—acid intrusions related to largescale mineralization are widely exposed in the area. Fenghuangshan pluton is the largest one with 10 km2 exposed area in all intermediate—acid plutons from Tongling. Some copper, gold and molybdenum deposits are distributed around the body. Thus, it is of great significance to study petrology, zircon UPb chronology and geochemistry of the pluton. This paper is aimed to discuss the petrogenesis and tectonic implications of the Fenghuangshan pluton.Methods:Based on the field work, through the microscope observation, the whole rock chemical analysis and zircon UPb LA ICPMS dating of the pluton, we determine the emplacement time and geochemical affinity of the pluton.Results: Petrologically, the Fenghuangshan pluton is mainly composed of granodiorite and quartz monzodiorite. The zircon UPb LAICPMS dating yielded ages of 140.6~144.7 Ma for the granodiorite, and 142.2~143.3Ma for the quartz monzodiorite, indicating that the emplacement time of the pluton is from 144.7 Ma to 140.6 Ma. Mineralogically, both kinds of rocks in the pluton are mainly composed of plagioclase, quartz, alkaline feldspar, amphibole and biotite with different contents, and the common accessory minerals are apatite, zircon. In addition, the pluton contains a large amount of microgranular diorite enclaves, showing a magma mixing. Geochemically, the rocks show significant features of Itype granite with aluminum saturation index (A/CNK<1.1)，and Na2O>K2O. It is also enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) (such as Rb, Ba, Th, U, K), depleted in heavy rare earth element (HREE) and part of high field strength elements (HFSE) (such as Nb, Ta, P, Ti), and has LREE differentiation to be obvious but HREE, with slightly negative Eu anomaly in REE patterns.Conclusions: The Fenghuangshan pluton was emplaced at 140.6~144.7 Ma. Geochemical characteristics indicate that its source rock may be the mixed source of crust and mantle. The pluton may have been formed by the mixing of acidic magma from the partial melting of the ancient crust and alkalirich basaltic magma from the enriched mantle.
