Chronology, Geochemistry, and Tectonic Implications of Early Cretaceous Granitoids in the Ranwu Area, Eastern Gangdese Belt

The Gangdese Belt is sandwiched between the Yarlung–Zangbo Suture Zone (YZSZ) and the Bangong–Nujiang Suture Zone (BNSZ), and witnessed large-scale magmatic activity during the Early Cretaceous period. Currently, controversies remain regarding the petrogenetic mechanism and tectonic setting of the Early Cretaceous magmatism in the eastern Gangdese Belt. To clarify these controversies, this study conducted systematic petrogeochemical analysis on the Ranwu pluton in the eastern Gangdese Belt. The results show that the main rock types of the Ranwu pluton are monzogranite and granodiorite. The LA-ICP-MS zircon U-Pb ages of the monzogranite (sample CZTW1105) and granodiorite (sample CZTW2051) are 116.3 ± 0.5 Ma and 114.6 ± 0.6 Ma, respectively, collectively indicating that the Ranwu pluton formed during the Early Cretaceous period. The results of in situ zircon Hf isotope analysis show that the εHf(t) values range from −5.0 to 0.5, with corresponding Hf crustal model ages (TDMC) of 1139–1494 Ma. The Ranwu pluton belongs to the high-K calc-alkaline series and is classified as I-type granite. Combined with geochemical characteristics and tectonic setting discrimination diagrams, it is determined that the granites of this period have geochemical signatures of post-collisional granites and formed in a tectonic setting during the transition from a compressional to an extensional regime. The occurrence of Early Cretaceous post-collisional granites marks the end of the main orogenic stage in the Bangong–Nujiang Suture Zone, and the Gangdese Belt has since transitioned into a tectonic environment of the post-orogenic extensional stage.