关键词: 五垛山岩体, 花岗岩, 锆石U-Pb年龄, 地球化学, 北秦岭

Abstract: The Wuduoshan pluton, located in the eastern segment of the North Qinling terrane, is a large-scale composite granitic intrusion formed via multi-stage emplacement. Zircon U-Pb dating yields crystallization ages of 441-430 Ma for representative samples of biotite granite and monzogranite, and inherited zircons have been identified in some samples with ages ranged from Proterozoic to Neoproterozoic. Granites from the Wuduoshan pluton exhibit high silica, low magnesium, alkaline-rich, and weakly to strongly peraluminous signatures. On the primitive mantle-normalized trace element spidergrams, they show enrichment of Rb, Ba, K and Pb and depletion of Nb, Ta, P and Ti. Chondrite-normalized REE distribution patterns exhibit distinct fractionation between LREE and HREE, and with δEu values of 0.36-1.45. 87Sr/ 86Sr(i) and εNd(t) values for granites from the Wuduoshan pluton are 0.70304-0.71290 and -4.6- -1.9 respectively, with two-stage Nd model ages of 1.34-1.58 Ga. These granites were likely formed via a partial melting process by using REE discrimination diagram. Isotopic compositions indicate that they were originated from a source characterized by mixing of metasedimentary rocks from the North Qinling terrane and mantle-derived materials. Among them, one part of granites were formed in lower crust, and another part were generated in middle-upper crust. The mantle-derived materials in source region may be intermediate-basic plutons that intruded into the crust during an early stage. Combined with crustal evolution of the North Qinling terrane during Early Paleozoic, we suggest that the granites from the Wuduoshan pluton likely reflect the collapse process of the thickened North Qinling crust under a post-collisional setting during Early Silurian.