Early Cretaceous Tuffs From the Southwestern Ordos Basin, North China Craton: Geochronology, Geochemistry and Geological Significance

Abstract

Tuffs are the significant medium to figure out volcanic activities, explore regional tectonic evolution and constrain the depositional ages in basins. Tuff intervals are found in the Early Cretaceous successions from the southwestern Ordos Basin, southwestern part of the North China Craton, which supplies new geochronological and geochemical evidence to understand the Early Cretaceous tectonic setting. In this work, whole-rock and zircon geochemistry, zircon U–Pb dating and Hf isotopic analyses were conducted. Zircon U–Pb dating results yielded ages of 125.32, 121.71 and 118.20 Ma, which have recorded the erupting of rhyolites and constrained the depositional age precisely to belong to the Aptian. Two groups of zircons Hf isotopic data are ε_Hf(t) of 8 with T_DM2 of 693–570 Ma and ε_Hf(t) of −11.7 with T_DM2 of 1908 Ma. Westerlies or southwesterlies were prevailing in the Early Cretaceous and can bring cinerites from the western or southwestern part of China. Comparative analysis of geochemistry and zircon Hf isotopes exhibited that the volcanoes from the Qiangtang Block and the Qingling Orogen were the most potential sources for the tuffs. These Early Cretaceous volcanic eruptions were triggered by the subduction of the Bangong-Nujiang Ocean and the Paleo-Pacific Ocean with plate roll-back and lithospheric destruction.