Geochemical characteristics and genetic analysis of Huayingshan Emeishan basalt in Sichuan Basin

Huayingshan basalt was overlain the top of Middle Permian Maokou Formation, and intruded into the black, greyish green and dark purple shales and mudstones in the bottom of Upper Permian Longtan Formation in Huangkongcao outcrop, Sichuan Basin. The rock type is mainly composed of gray-black dolerite. There are numerous vesicles and amygdaloids at the top of Huayingshan basalt, but not found any of them in the bottom. The TAS diagram shows that Huayingshan basalt belongs to the transitional series tholeiite between alkaline and subalkaline. The content of TiO2 varies from 2.92%~3.63%, and the ratio of Ti/Y varies from 465~567 which reflects typical features of high-Ti basalt(HT). The ratios of LREE/HREE in Huayingshan basalt range between 3.25 and 3.96, slightly rich in light rare earth elements (LREE), presenting a right-leaning smooth trends in REE patterns. The geochemical characteristics of Huayingshan basalt are similar to those of Emeishan basalt in Binchuan area and Hezhang area, indicating an origin of mantle plume and the same mantle source. Moreover, the geological position of Huayingshan basalt in Huangkongcao outcrop is consistent with regional record of the eruption of Emeishan basalt in Southwest China. Therefore, Huayingshan basalt is believed to be a part of Emeishan mantle plume. The Ce/Yb of Huayingshan basalt is between 22.65 and 27.93, which is resembled with the Ce/Yb ratio range of high-Ti basalt (HT) reported by other regions. The data points of basalt in(Tb/Yb)N-(La/Sm)N diagram fall on the boundary of garnet stabilization zone and spinel stabilization zone. Ratios of Th/Ta, Nb/U and La/Ta reflect a relative low mixing degree with crust materials, indicating that Huayingshan basalt was possibly sourced from the axis of mantle plume.