Origin of early Triassic rift-related alkaline basalts from Southwest China: age, isotope, and trace-element constraints

Abstract

We report new analytical data regarding major and trace element geochemistry, Sr-Nd isotopic composition, and zircon LA-ICP-MS U-Pb analysis from the Kaiyuan alkaline basalts of Yunnan Province, along the southern margin of the Emeishan Large Igneous Province (ELIP). Zircon U-Pb ages and bulk-rock geochemistry indicate that the mafic lavas erupted at 248 ± 6 Ma with OIB-like trace element and isotope ratios similar to the Emeishan high-Ti basalts. These characters suggest that the Kaiyuan alkaline basalts are the products of the post-ELIP magmatism, involving remelting of the plume head after the main ELIP phase. By analogy with the Neogene Red Sea rift system, the Kaiyuan alkaline basalts may have been caused by a Red Sea-like extension along the southwestern margin of the Yangzte during the Early Triassic, during which the hypothesized rift system experienced plate–boundary forces that vanished quickly in the Late Triassic period.