Zircon U-Pb ages and geochemistry of volcanic rocks in the Nie'er Co-Laguo Co area of the western Bangong Co-Nujiang suture zone

In order to ascertain the formation age, rock genesis and tectonic setting of volcanic rocks in the Nie'er Co and Laguo Co areas of the western Bangong Co-Nujiang suture zone, the authors mainly carried out zircon U-Pb dating and petrogeochemical analysis of volcanic rocks. The zircon U-Pb dating results show that the rhyolites in the Nie'er Co area were formed at 112.5Ma, and the dacite in the Laguo Co area was formed at 112.3Ma, respectively, consistent with the age of the magmatism extensively distributed in the study area. The characteristics of the main trace elements of the whole rock show that both the dacite and rhyolite samples belong to the calc-alkaline series, and are obviously enriched in Th, U, and depleted in high field strength elements such as Nb, Ta and Ti. Geochemical characteristics indicate that the dacite originated from the partial melting of the thickened lower crust, whereas rhyolite was formed by the extensive crystallization differentiation of the lower crust melts. The authors hold that the largescale magmatism in the late Early Cretaceous in central Tibet formed a background after collision, and the deep dynamic mechanism was probably related to the slab break-off of the northward subduction of Bangong Co-Nujiang oceanic floor.