Geochemistry, zircon U-Pb chronology of the Triassic granites in the Changning-Menglian suture zone and their implications
滇西昌宁-孟连带三叠纪花岗岩地球化学、年代学及其意义

Located in the middle and north sections of Changning-Menglian suture zone,Lailitoushan,Yunling and Gengma plutons are mainly composed of monzogranites.The zircon LA-ICP-MS U-Pb dating indicates that the three granitoid plutons intruded simultaneously at about 231Ma.The three plutons have 65.65% ～ 67.68% SiO2,with high K2O(K2O/Na2O = 2.71% ～ 1.42%) and low CaO(1.35% ～ 2.98%).These granitoids are high in A/CNK(1.10 ～ 1.22),and are enriched in Rb,Ba,Th,U,K,La and LREE,but depleted in Nb,Ta,Ti,Zr and Hf.These geochemical signatures indicate that the three plutons are high-K calcalkaline peraluminous S-type granites.The wide and negative zircon εHf(t) values(-26.8 ～-8.2) and ancient Hf-isotope crust model ages(1.2 ～ 2.7Ga) indicate that these three plutons originated mainly from anatexis of ancient crust materials(such as feldspar-and biotite-bearing lithic greywacke) with varying contributions of mantle-derived materials.These plutons probably formed in a post-collisional setting,which may imply that the Burma-Thai-Malaysia microcontinent collided with the Simao block before 232Ma(prior to Late Triassic).