Zircon U-Pb age and geochemical characteristics of Langding intrusion of Shangri-La, Yunnan Province

The west porphyry belt and east porphyry belt in Shangri-La are mainly composed of Indosinian intermediate-acidic intrusive complex rocks.In the western porphyry belt, there are Luanitang porphyry, Xuejiping porphyry, Chundu porphyry, Are porphyry and Langding porphyry from north to south.In the eastern porphyry belt, there are Disuga porphyry, Songnuo porphyry, Pulang porphyry and Lanzhong porphyry from north to south.The Langding porphyry is mainly composed of hornblende diorite porphyrite, quartz diorite porphyrite and pyroxene diorite porphyrite.The zircon U-Pb age indicates that the intrusive rock has an age of 206.4±3.9 Ma.Geochemical characteristics of the Langding porphyry are similar to those of adakite, whose SiO₂ is higher than 56.66, averaging 60.42%, and whose δEu is not distinct (0.90~1.23, averaging 1.08).Chondrite-normalized REE patterns show right-inclined feature, and are characterized by enrichment of LREE and LILE, heavy depletion of HREE, high Sr (490×10^-6~1165×10^-6, averaging 842×10^-6), Sr/Y (37.4~77.2, averaging 56.9) and La/Yb (21.7~28.4, averaging 25.6), but low Y (13.1×10^-6~17.4×10^-6, averaging 14.6×10^-6) and Yb (1.20×10^-6~1.61×10^-6, averaging 1.37×10^-6).The results of the studies of major oxides, REEs, trace elements and zircon U-Pb age show that the Langding rock body was formed in an island arc environment, and its formation was related to the partial melting of the low-angle subduction of Garze-Litang oceanic crust slab.