Zircon U-Pb ages of mesozoic volcanic rocks in Chifeng area

Abstract

The Mesozoic volcanic rocks in Chifeng area consist of rhyolites, trachyandesite ignimbrites and trachyandesites. Zircons from these Mesozoic volcanic rocks are of euhedral-subhedral shapes and high Th/U ratios (0.50-2.26), implying their magmatic origin. Zircon U-Pb ages of two volcanic rocks in the Manketouebo Formation are (156±2) Ma (n=24) and (157±3) Ma (n=19) respectively, suggesting these volcanic rocks were formed in the Late Jurassic; zircon U-Pb age of volcanic rock in the Manitu Formation is (147±2) Ma (n=18), suggesting the volcanic rock was also formed in the Late Jurassic; zircon U-Pb ages of volcanic rocks in the Baiyingaolao Formation are (132±1) Ma (n=23) and (138±3) Ma (n=18) respectively, suggesting these volcanic rocks formed in the Early Carboniferous. It is proposed that the volcanic rocks in Chifeng area were formed under an extensional environment related to subduction of the Paleo-Pacific plate beneath the Eurasian continent.