Coupling of basaltic magma evolution and lithospheric seismic structure in the Emeishan Large Igneous Province: MELTS modeling constraints

Abstract

Seismic tomography and deep sounding reveal high-velocity upper mantle (HVUM), high-velocity lower crust (HVLC) and crustal strips beneath the Emeishan Large Igneous Province (ELIP). Such a lithospheric structure is similar to that of typical large igneous provinces (LIPs) elsewhere, such as Ontong Java oceanic plateau and Columbia River LIP (Furumoto et al., 1976; Catchings and Mooney, 1988). This study models the formation mechanism of the lithospheric structure and its relationship with the magmatic evolution of the ELIP. Petrological modeling package MELTS is used and the simulation results show that crystal fractionation can account for the main magmatic processes related to the Emeishan mantle plume. It is suggested that the partial melting of the plume head generated the picritic magma, which then finally evolved into high-Ti basalts after undergoing a two-stage differentiation at Moho and in the upper crust. The Sub-continental Lithosphere Mantle (SCLM)-derived magmas experienced fractionation at the Moho boundary and their residual melt fits well with the low-Ti basalts both in oxides composition and evolutionary trends. Calculated fractionated mineral assemblages at Moho match well with the HVLC both in P-wave velocity (Vp) and in inferred mineral phases (olivine pyroxenite with Vp of 7.53–7.84 km s − 1 and clinopyroxenite with Vp of 7.32–7.55 km s − 1 ). Some residual melts may have also been emplaced in the crustal weak layers and formed the high-Vp gabbroic cumulates. Moreover, the HVUM was probably crystallized from the upwelling deep komatiitic magma as the plume's thermal anomaly gradually decayed. The differentiation mode of Emeishan basaltic magmas couples well with the lithospheric seismic structure and may shed lights on the understanding of mafic–ultramafic intrusions and associated ore deposits in the ELIP area.