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

摘要

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 bio-tite 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).