First identification of Late Permian mafic dykes in the nucleus of Yangtze Craton: Emeishan large igneous province doubled?

Abstract

ABSTRACT The Emeishan large igneous province (ELIP) is known to have a relatively small-exposed area with a radius no longer than 700 km. New zircon U-Pb and plagioclase and pyroxene 40Ar/39Ar age determinations from mafic dykes in the nucleus of Yangtze Craton, located more than 1000 km away from the inner zone of ELIP, reveal that they were emplaced at ~260 Ma. This is synchronous with the ELIP. The zircon εHf(t) values of the dolerite dyke vary between +5.4 and +8.9. These mafic dykes have low Ti/Y ratios (299–413) and are enriched in light rare-earth elements (LREE) and depleted in heavy rare-earth elements (HREE) and high field strength elements (HFSE). These dykes bear similarities to the Emeishan high-Ti basalts despite their relatively low Ti/Y ratios. Whole-rock Sr-Nd isotopes gave highly radiogenic initial 87Sr/86Sr (0.710033–0.710371) and extremely low initial 143Nd/144Nd (0.511515–0.511641) and εNd(t) of −15.4 to −12.9. Electron microprobe analysis of concentric-zoned pyroxenes yielded increasing Mg# and Cr2O3 from core to rim. Bulk rock geochemistry, Sr-Nd isotopes, and mineral chemistry indicate that recharge of a new batch of ascending plume-derived magma into an enriched lithosphere generated the mafic dykes. The synchronous emplacement and geochemical and isotopic similarities between the examined Huangling mafic dykes and Emeishan flood basalts, as well as the presence of titanaugite, all point to the genetic link between the Huangling mafic dykes to the ELIP. The Emeishan-age of the Huangling dykes permits a substantial increase of at least 3 × 105 km2 in the spatial extent of the ELIP.