An Early Cretaceous record of trachyte from the red bed basin of the southwest Dabie Orogen, Central China: Implications for tectonic evolution and geodynamics

Abstract

Zircon U–Pb ages of approximately 130 Ma were obtained from trachytes in Xiaochang County, at the southwestern margins of the Dabie Mountains, in Central China. The SiO2 and K2O contents of these trachytes range between 56.78–63.77% and 3.76–5.07%, respectively, while Rittmann indexes (δ) range between 3.7 and 6.8. These characteristics indicate that the trachytes belong to the alkaline series. The trachytes are enriched in large‐ion lithophile elements (LILEs) but are depleted in high‐field‐strength elements (HFSEs). The initial 87Sr/86Sr values of the trachytes range from 0.7060 to 0.7072, with negative εNd(t) values varying from −10.43 to −12.88. The weighted averages of the zircon εHf(t) and TDM2 values are −11.7 ± 0.5 and 1921 ± 28 Ma, respectively. The presence of Early Cretaceous K‐rich volcanic rocks at the southwestern margins of the Dabie Mountains has been confirmed for the first time. This finding fills a gap regarding the presence of Mesozoic volcanic rocks in this region and limits the earliest possible formation age of the red bed basin at the southwestern margins of the Dabie Mountains to the Early Cretaceous. The trachytes originate from partial melting of enriched mantle. They are closely related to major regional faults and represent the eastern extension of the Qinling–Daba alkaline rock belt.