Periodical Thickening of Continental Crust in Northern Xizang (Tibet), SW China: Insights From Late Mesozoic Magmatism in the Middle Bangong–Nujiang Suture Zone
Ming Zheng, Yang Song, Juxing Tang, Zhibo Liu, Qin Wang, Bo Liu, Faqiao Li, Yiling HuABSTRACT
The middle Bangong–Nujiang suture zone (MBN) has emerged as the most intensely debated area in recent studies on the tectonic dynamics and geological evolution of the Bangong–Nujiang Ocean. This study presents an integrated analysis of geochemical, geochronological and isotopic data for the Leibao intrusions in the MBN and aims to clarify its petrogenesis and tectonic settings. The Leibao intrusions (77–79 Ma) are monzodiorite to granite in composition with a wide range of SiO 2 (52.5–81.5 wt%) and high K 2 O content, affiliated with high‐K calc‐alkaline I‐type granites. Leibao intrusions were formed by partial melting of the juvenile lower crust. They were subjected to varying degrees of middle–upper crustal contamination and fractional crystallisation during ascent and emplacement in a post‐collisional extensional setting. We propose that the MBN experienced three distinct magmatic episodes during the Mesozoic: Late Jurassic (> 150 Ma), Early Cretaceous (125–105 Ma) and Late Cretaceous (< 95 Ma), with two apparent magmatic gaps of 150–125 and 105–95 Ma. Periodic fluctuations in the Sr/Y ratio, ε Hf ( t ), and T Zr (°C) values of the Late Mesozoic rocks indicate possible periodic thickening of the continental crust, similar to the Cordilleran orogenic systems.