Formation of deep mantle heterogeneities through basal exsolution contaminated magma ocean

Abstract

Earth’s mantle harbors two large low shear-wave velocity provinces (LLSVPs) with patches of ultra-low velocity zones (ULVZs) distributed in the bottom. These structures exhibit distinct seismic and geochemical signatures compared to the surrounding mantle. Yet, their origin remains enigmatic. One proposed explanation is the differentiation of an early basal magma ocean (BMO). However, the presence of an excessively thick layer of iron-rich ferropericlase in the crystallized BMO conflicts with seismic tomography. Here, we investigate the crystallization of a BMO continuously contaminated by oxide exsolutions from the core, termed BECMO, and find significant suppression of ferropericlase crystallization and consequently a mineralogical profile consistent with LLSVPs and ULVZs. In addition, diapirs of core exsolution entrained into the solid mantle may cause small-scale scattering. The BECMO inherits the light silicon isotope composition from the core and exhibits trace element enrichments, suggesting its potential role as a source material for ocean island basalts potentially sampling the lowermost LLSVPs, pointing to a unified mechanism for forming deep mantle heterogeneities.