Geochronology, Petrogeochemistry, and Tectonic Setting of Cretaceous Granitoids in the Zanzongcuo Zone, Northern Tibet, China

Magmatic rock plays a key role in controlling tectonics. By determining the chronology, petrogenesis and tectonic significance of newly discovered granite porphyry and granite units, this study documents the Bangong-Nujiang Neo-Tethys ocean evolution and the tectonic environment of the Zanzongcuo zone. Based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of zircons, the ages of the granite porphyry and the granite are 113.74 ± 0.68 and 79.58 ± 0.83 Ma, respectively. Thus, these intrusive rocks formed at different times in the Cretaceous. The two studied intrusive bodies are I-type granitoids with peraluminous characteristics. The granite porphyry and the granite belong to the medium- to high-K calc-alkaline and low-K calc-alkaline series, respectively. These rocks are enriched in large ion lithophile elements (LILEs, e.g., Rb, U, and Th) and light rare earth elements (LREEs) but depleted in high field strength elements (HFSEs, e.g., Nb, Ta, and Ti). The granite porphyry and the granite have δEu values of 0.69–0.82 and 0.6–0.73, respectively, and have moderately negative Eu anomalies. The granite porphyry formed in a subduction-related structural environment and represents an arc-type granite. The granite formed in a collisional tectonic environment and represents a granite that formed in a within plate setting. The geochronologic and tectonic characteristics of these two intrusive rocks indicate that the Zanzongcuo zone experienced a series of tectonic events in the Cretaceous, including oceanic crust subduction in the late Early Cretaceous, continent-continent collision, and intraplate compression in the late Late Cretaceous. Furthermore, the Bangong-Nujiang Neo-Tethys ocean closed in the late Early Cretaceous.