Abstract

The lower mantle is the largest continuous layer within Earth. It plays a dominant role in the thermochemical and geodynamic evolution of the planet. Seismic studies have revealed numerous heterogeneities with different length scales in the lower mantle, including the small-scale seismic scatterers and the Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific in the lowermost mantle. Seismic models suggest that the thickness of scatterers is only several or tens of kilometers with a velocity perturbation of < 1% throughout the mantle, but the shear velocity could be up to ~ 12% lower than the surrounding mantle in the mid mantle. Meanwhile, the systematic observations in seismic properties indicate that the LLVS Ps are likely composed of distinct chemical materials from the surrounding mantle. Their origins have long been debated, with hypotheses ranging from subducted oceanic crust and to primordial materials. In this talk, I’ll discuss whether subducted oceanic crust can explain the lower-mantle heterogeneities or not based on our recent theoretical results. I’ll also show our experimental findings to help understand how the early magma redox reaction would have produced distinct materials that may be responsible for LLSV Ps.