Petrogenesis of the Daquandian granitoids in the Dabie orogenic belt, eastern China: Tectonic shift from compression to extension caused by the Paleo-Pacific Plate in the early Cretaceous

Abstract

This paper discusses the petrogenesis of the Daquandian granitoid pluton exposed in northern Dabie Mts. and the tectonic implications for the Dabie orogen. Rocks of this pluton yield Early Cretaceous ²⁰⁶Pb/²³⁸U ages between 133 and 129 Ma. They are high-K calc-alkaline and of I-type affinity, with A/CNK values ranging from 0.95 to 1.12, and variable (La/Yb)_N, Eu/Eu^⁎ and Sr/Y values. Rock samples with Sr/Y values <20 show remarkable variations in Sr/Y and Eu/Eu^⁎ ratios due to the fractional crystallization of feldspar, while those with Sr/Y ratios >20 also show variations in Sr/Y ratios, but have relatively consistent Eu/Eu^⁎ ratios, which is linked to the change in the crustal architecture and thickness and the appearance of plagioclase as a residual mineral phase. Whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios range from 0.7075 to 0.7085, initial ε_Nd values from −21.9 to −16.1, and initial Pb isotope ratios vary from ²⁰⁶Pb/²⁰⁴Pb = 16.24–16.84, ²⁰⁷Pb/²⁰⁴Pb = 15.27–15.41, and ²⁰⁸Pb/²⁰⁴Pb = 37.22–37.89. These isotopic characteristics are similar to those of other Cretaceous granitoids in the Dabie Mts. Inherited zircon grains of different ages (Archean, Neoproterozoic, and Triassic) were identified in the Daquandian pluton, indicating a multi-source origin. By integrating existing geological, chronological, and geochemical data, we propose that the magma(s) of the Daquandian pluton were sourced from different crustal lithologies, mainly from the Northern Dabie Complex with a contribution from the Yangtze and/or North China lower crust. Crustal anatexis responsible for the generation of the granitoid magmas is proposed to have taken place in a post-collision extensional setting.