Geochemistry and zircon U-Pb age of granite porphyry in the Yabunuma region close to the southern margin of the Asuo structural melange belt, Gangdise, Tibet

The granite porphyry vein in the Yabunuma area is located in Asuo and Nyima area of northern Central Gangdise. LAICP-MS zircon U-Pb age of 161.2±5.9Ma indicates emplacement during the Late Jurassic. The bulk rock geochemical analyses indicate the characteristics of high silica, rich alkali and Al, suggesting alkali metaluminous granite porphyry. The granite porphyry samples are rich in LREE, the fractionation between LREE and HREE is strong and shows obvious negative Eu anomalies, with the characteristics of enrichment of Rb and Pb, depletion of Ba, Sr, Nb, Ta, Ti and U, suggesting an island-arc setting. The granite porphyry is likely to root in anatexis of thickened lower crust. Considering coeval magma event in the vicinity, the authors hold that granite porphyry from Yabunuma region should have formed in an active epicontinental environment on the background of the southern subduction of Bangong Co-Nujiang Tethyan Ocean crust.