| The study on the Emeishan Basalt and theory of Mantle plume
Cai Keqin, Chen Baoguo, Yun Xuemei, Lin Shanyuan, Ge Wensheng ,Mu Xingtong
School of Earth Science and Resources, China University of Geosciences(Beijing) , Beijing 100083
Abstract: Emeishan Basalt covers about 300,000 square kilometers with the maximum thickness up to 5384 m. Since Zhao Yazeng has created “Series of Emeishan Basalt” in 1928, the basalt of Emeishan Basalt became independent lithostratigraphic unit area of Sichuan, Yunnan and Guizhou provinces in China and appeared in all types of geological maps. Regional geology research indicates that the basalt eruption ocurred in the Yangtze platform in western China, giving priority to with a huge amount of overflow basalt. The whole rock has ages of 219 ~ 237 Ma by the K-Ar method, suggesting that the volcanic eruption began in the early Permian, and continued till the late Permian. The whole Emeishan Basalt can be divided into three areas from the east to the west: the basalt rock in east area has the chemical characteristics of the lower crust; middle rock area, known as the Panxi Rift bi-model volcanic set, was crust-mantle type because of the continental crustal contamination; the rock in the west area has the chemical characteristics of the mantle source type. The center of the thickness and direction changes of basalt area is consistent with the main deep fault belt. Integrated geophysical studies of earth's crust and mantle confirm that the Panxi Rift is located on the Kang-Dian uplift plume area and is the thinning crust belt. The top of the upper mantle in this area has a thickness of 12 ~ 22 kilometers, with P wave speed of 7.6 ~ 7.8 km/s, low speed, low density and low resistance of abnormal mantle shows. Based on the studies of the geological evolution, petrological, geochemical and geophysical data of the whole basalt series, it is concluded that the Emeishan Basalt area can be classified as an ancient mantle activity area. Studying, analyzing and summarizing the research history of Emeishan Basalt is effectively conducted by the Chinese geologists. This situation also suggest these geologists participate the study of mantle plume, which is a modern hot spot and frontier topic issue in the world and will open up a new field of mantle plume and its related mineralization.
Key words: Emeishan Basalt; tectonic setting; geological evolution; mantle plume; mineralization