Petrogenesis of Late Cretaceous I-type granites in the southern Yidun Terrane: New constraints on the Late Mesozoic tectonic evolution of the eastern Tibetan Plateau

Abstract

Abstract The collision between the Lhasa and Qiangtang terranes, prior to the Indo–Asian collision, is a critical aspect in terms of development of the Tibetan Plateau. It has been demonstrated that the occurrence of the Late Cretaceous granites (110–80 Ma) in the Yidun Terrane, eastern Tibetan Plateau (ETP) associates with the Lhasa–Qiangtang collision. The Xiuwacu Late Cretaceous pluton in the southern Yidun Terrane, consists three phases including biotite granitic porphyry (phase 1), monzogranite (phase 2), and alkali–feldspar leucogranite (phase 3), which have zircon U–Pb ages ranging from 85.5 Ma to 84.4 Ma. All these three phases are metaluminous or slightly peraluminous granites (A/CNK = 0.96–1.07), with high SiO2 (70.0–76.0 wt.%), K2O + Na2O (7.5–10.7 wt.%), and Ga/Al (2.5–4.7), and relatively low CaO (0.39–1.67 wt.%), MgO (0.01–0.57 wt.%), and P2O5 (0.01–0.17 wt.%). The granites are enriched in light rare earth elements (LREEs), Rb, Th, U and Ta, but depleted in heavy REEs (HREEs), Ba, Sr, P, and Ti, with significantly negative Eu anomalies (Eu/Eu* = 0.24–0.59). Comparing to classic A-type granites, these samples present higher Sr (10.1–256 ppm, mostly > 100 ppm) and lower FeO*/MgO ratios (1.2–9.9) and Zr + Nb + Ce + Y (248–483 ppm, mostly