LA-ICP-MS zircon U-Pb dating, geochemical features and geological significance of the Daru Co granite porphyry in Baingoin County, Tibet

Located in the middle part of the Bangong Co-Nujiang River suture zone, the Daru Co granite porphyry was intruded into the ophiolite of this suture zone. In this study, the authors performed detailed field investigation, petrological and geochemical study, and zircon U-Pb and Hf isotopic analysis of the Daru Co granite porphyry. Using the LA-ICP-MS technique, the authors obtained the U-Pb age of 110±1Ma for the Daru Co granite porphyry, and this age is interpreted as the formation age of granite porphyry. The Daru Co granite porphyry has pronounced negative zircon εHf(t) values in the range of -5.5~-2.6. Whole-rock geochemical data show that it is characterized by high K calc-alkaline series, A/CNK higher than 1.1, enrichment of LREE, Rb, Ba, Pb and Th, and depletion of Ta, Nb and Ti. All samples show negative Eu anomaly. These features indicate that the Daru Co granite porphyry belongs to the peraluminous S-type granite. It is considered that the Daru Co granite porphyry might have been formed by partial melting of the thickened continental crust in a syn-collision setting, and it was probably related to the hot asthenosphere upwelling under the Lhasa block. The ocean basin had been closed and continental collision started before 110Ma in the middle part of the Bangong Co-Nujiang River suture zone. Furthermore, the ophiolite in this area should be formed before 110Ma in terms of the relationship between the Daru Co granite porphyry and ophiolite.