Late Permian basalts in the Yanghe area, eastern Sichuan Province, SW China: Implications for the geodynamics of the Emeishan flood basalt province and Permian global mass extinction

Abstract

We report the finding of a ∼20m thick sequence of massive pyroxene–plagioclase–phyric basalt lava flows in the Yanghe area of the northeastern Sichuan Basin, within the Yangtze craton of SW China, which were previously considered to be located outside the Emeishan flood basalt province. This basaltic sequence above the middle Permian Maokou Formation (Fm.) is overlain by the late Permian Longtan Fm. Thus, the Yanghe basalts should be stratigraphically correlated with the Emeishan flood basalts. The Yanghe basalts show typical oceanic island basalt (OIB) affinity, and geochemically resemble Emeishan basalts, especially in the case of high-Ti (HT) basalts from the eastern domain of the Emeishan flood basalt province. The rocks have low age-corrected (87Sr/86Sr)t (t=260Ma) ratios (0.704158–0.704929) and Pb isotopic ratios [206Pb/204Pb(t) (18.264–18.524), 207Pb/204Pb(t) (15.543–15.58), and 208Pb/204Pb(t) (38.147–38.519)], and positive εNd(t) values (+3.15 to +3.61), suggesting that the lavas have not undergone any significant crustal contamination. The crystallization temperature of clinopyroxene is estimated to be 1368–1420°C, suggesting anomalously thermal inputs from a mantle source and a possible plume-head origin. The fractionation of middle rare earth elements (MREE) to heavy REE (HREE) suggests that these rocks were produced by small degrees of partial melting of mantle peridotite within the garnet–spinel transition region. The stratigraphic relationships and similar geochemical signatures with the Emeishan flood basalts suggest that the Yanghe basalts are part of the Emeishan flood basalt province and can be considered as the northeastern limit of the Emeishan flood basalt province. Our finding extends the diameter of the Emeishan flood basalt province to ∼1200–1400km, covering an area of up to ∼7×105km2, two times more than previously estimated. The larger areal extent and giant eruption volume, incorporating the Sichuan Basin, lend support to the correlation between the end-Guadalupian mass extinction and the Emeishan flood basalt province.