Abstract:Objectives:The Late Carboniferous Dulongbao granodiorite pluton located in the north of Hongshishan—Baiheshan—Pengboshan ophiolite mlangen belt have important geological significance for constraining the tectonic evolution of the Beishan Orogenic Belt, but no report on isotope and tectonic setting about granites.Methods: Based on the field work, through the microscope observation, the wholerock geochemical analysis and the LAICPMS zircon UPb dating of the granodiorite.Results: Zircon grains from these granodiorite are euhedral subhedral in shape, display finescale oscillatory growth zonong with high Th/U ratios of 0.42~0.75,indicating a magmata origin. UPb dating results show that the pluton was emplaced with the age of 303.4±2.1Ma. The granodiorite have high SiO2 contents of 63.73%~69.12% and Al2O3 contents of 14.83%~15.89%, Na2O concentrations of 3.69%~4.03%, and K2O concentrations of 2.23%~2.73%, with (Na2O+K2O) concentrations of 6.08%~6.44% and K2O/Na2O ratios of 0.58~0.74, A/NCK values of 0.91~0.99, Mg# values of 48.27~50.93. They are enriched in light rare earth elements(LREEs) and large ion lithophile elements(LILE),such as Rb， Th， U， Pb, and depleted in heavy rare earth elements(HREEs) and high field strength elements(HFSE), such as Nb， Ta， P， Ti, with (La/Yb)N ratios of 4.77~6.35 and weak negative Eu anomalies(δEu=0.79~0.94) .Conclusions: These granodiorites chemically belong to metaluminous and caclalkaline Itype ones, and their primary magma could be mixed by mantle and crust, formed under the tectonic setting of continental arc in late Carboniferous. Combining neighborhood characteristics, We propose that the ocean basin represented by Hongshishan—Baiheshan—Pengboshan ophiolite mlangen belt may have subducted to north and south in late Carboniferous.
