Full-waveform tomography reveals iron spin crossover in Earth lower mantle

TL;DR

This study uses full-waveform tomography to investigate the Earth's lower mantle, revealing that an iron spin crossover in (Mg,Fe)O better explains wave speed data between 1000 and 2500 km depth, and silica enrichment explains deeper wave speed variations.

Contribution

It demonstrates that incorporating an iron spin crossover in mantle models improves the fit to seismic data and provides insights into deep mantle composition and temperature.

Findings

Spin crossover models fit wave-speed data better between 1000-2500 km depth.

Silica enrichment explains wave speed variations below 2500 km.

Results suggest a complex, chemically diverse lower mantle.

Abstract

Joint interpretation of bulk and shear wave speeds constrains the chemistry of the deep mantle. At all depths, the diversity of wave speeds cannot be explained by an isochemical mantle. Between 1000 and 2500 km depth, hypothetical mantle models containing an electronic spin crossover in (Mg,Fe)O provide a significantly better fit to the wave-speed distributions, as well as more realistic temperatures and silica contents, than models without a spin crossover. Below 2500 km, wave speed distributions are explained by enrichment in silica towards the core-mantle-boundary. This silica enrichment may represent the fractionated remains of an ancient basal magma ocean.