ZIRCON U-Pb DATING AND GEOCHEMISTRY OF THE EARLY CRETACEOUS GRANITIC ROCKS IN THE MIDDLE SECTION OF DAXINGANLING MOUNTAINS

The Phanerozoic granites are widely distributed in the Daxinganling region, but the research on Mesozoic granites was relatively poor. The paper conducts a geochronological and geochemical study on the Early Cretaceous granites collected from Bijiadian pluton and Shenshan pluton on the west of Zhalantun in the middle section of Daxinganling Mountains, and discusses the petrogenesis and tectonic setting of the granitic rocks. The LA-ICP-MS zircon U-Pb dating indicates that the Bijiadian pluton is mainly composed of syenogranite and granite porphyry, with ages of 136±3 Ma, 139.5±0.9 Ma and 128.1±0.8 Ma, whereas the Shenshan pluton consists of mainly alkali-feldspar granites, with age of 119.3±0.8 Ma, which indicate that both of them were formed in the Early Cretaceous. The two plutons are geochemically characterized by high Si, low Ca, rich Alkali, negative Eu anomalies, enrichment of Rb, Th and U, and depletion of Nb and Ta, belonging to the weakly peraluminous high-K calc-alkaline series and quite similar to highly fractionated I-type granitoids. Combined with the petrological and geochronological features of the coeval granitoids in Daxinganling region, it is proposed that the formation of the Early Cretaceous granitic rocks was closely related to the delamination induced by the subduction of the Pacific plate.