Abstract:
The songlinkou pluton is located in the mid-eastern Songpan-Ganzi orogenic belt. It was studied by microscopical observation, major and trace element analysis and zircon U-Pb dating, in order to determine the emplacement age and geochemical characteristics of the pluton. The results show that the Songlinkou pluton is composed of monzonitic granite and granodiorite which formed by two stages of magmatism in the late Triassic, the weighted mean age of zircon of granodiorite is 212.4±0.9 Ma (MSWD=0.66), and the weighted mean age of zircon of monzonitic granite is 222.4±1.1 Ma(MSWD=0.39). The pluton content of SiO2 is 56.56%~61.97%, A/CNK value is 0.93~1.05, total alkali 3.78~5.38, K2O/Na2O 1.02~1.68, Rittmann index 1.194~1.612, so that the rocks belong to metaperaluminous mid-high K Calc-alkaline series. The LREE/HREE is 5.22~7.13, and LaN/YbN is 6.93~8.96, light and heavy rare earths are distinct, with obvious negative Eu anomalies. The rocks have high Mg# values(50.97~61.27), w(Rb)/w(Sr) is 0.12~0.25, and the Rb-(Y+Nb) diagram shows that it belongs to post-collision environment. Therefore, Songlinkou monzonitic granite-granodiorite belongs to post-collision metaperaluminous mid-high K Calc-alkaline Ⅰ-type granite.