Nd-Sr-Pb isotopes of Emeishan basalt in the Zhaotong area of northeastern Yunnan—Coupling relationship between source of Emeishan mantle plume and Rodinia supercontinent

The latest Nd-Sr-Pb isotopes study of Emeishan basalt in the Zhaotong area of northeastern Yunnan Province shows that the basalt samples generally have a 1000~900 Ma Nd model age of depleted mantle. The source could be generated by mixing of different proportions of a recycled ancient oceanic crust component(EM1-like, 60%~90%) and a peridotite component from the lower mantle(FOZO-like component, 10%~40%). The sample satisfies the Dupal anomaly boundary condition, suggesting that the latitude of Emeishan basalt magma formation and emplacement is quite different from the current latitude, and there may exist a large space distance between them. Therefore, a new model for the formation of the Emeishan mantle plume is proposed. During 1000~900 Ma, the oceanic crust derived from the Rodinia supercontinent event subducted and subsided, and the remnants of the oceanic crust piled on the 660 km mantle transition zone to form relatively cold refractory megaliths. In the Late Permian(~260 Ma), these megaliths(probably eclogite facies super-compressive metamorphic rocks) further subsided down to the "D" layer of the core-mantle transition, and resulted in the transformation from perovskite to post-perovskite, which was a strong exothermic reaction resulting in partial melting of lower mantle and subducting plate accumulations themselves, leading to upwelling of high temperature iron and titanium to form the mantle plume. The large scale upwelling and eruption of these magmas formed the large-scale Emeishan Igneous Province(LIPs) in the west of Yangtze block. At this time, the paleogeographic location was still in a certain position in the southern hemisphere. After the closure of the Paleotethys, these basalts bearing the unique geochemical imprint of the southern hemisphere(Dupal anomaly) drifted northward along with the Yangtze plate and reached the present position.