The origin of EMI component in the Shikoku back-arc spreading center, Philippine Sea Plate

Abstract

The Mesozoic-Cenozoic geological evolution of the East Asian continental margin and a series of Cenozoic back-arc basins (South China Sea, West Philippine Sea, Sea of Japan and Shikoku Basin) developing in the West Pacific region have been predominately resulted from the westward subduction of Pacific plate, accompanying with the effects of some intraplate processes. However, how the intraplate processes work remains unclear. Here we present new geochemical and Sr-Nd-Pb-Hf isotope data for the lava samples collected from Deep Sea Drilling Project Expeditions 6, 58, and 59 in the Shikoku Basin (SKB) and its adjacent region. High Nb/La ratio and enriched Sr-Nd-Pb-Hf isotopic compositions indicate that the spreading-related lavas in the SKB were affected by the enriched mantle type I (EMI) component, which can be solely produced by mixing enriched mantle components and ambient mantle. We suggested that EMI components in the asthenosphere mantle beneath the region from northeast China to Sea of Japan may be involved in the back-arc spreading processes by means of asthenospheric toroidal flow around the subducting Philippine Sea slab, or the EMI components have preexisted in the asthenospheric mantle beneath the SKB prior to the northward migration of the Philippine Sea Plate since Equator.