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New Research Published in Nature Geoscience

Deep inside Earth, scientists have long puzzled over two giant mysterious regions above the planet’s core known as “large low shear-wave velocity provinces” (LLSVPs), along with smaller patches called “ultra-low velocity zones” (ULVZs). These regions look very different from the rest of the mantle in seismic images, but their origin has remained unclear. Our new research suggests they may have formed from an ancient “basal magma ocean” at the bottom of Earth’s mantle, which was gradually mixed with material exsolved from the core. This process, which we call a “basal exsolution contaminated magma ocean” (BECMO), prevented the buildup of unrealistic iron-rich layers and instead produced mantle structures that match what seismologists observe today. Computer models show that solidified BECMO material could explain both the vast LLSVPs and the smaller ULVZs. The BECMO also carries distinctive chemical signals—such as silicon, tungsten, and helium isotopes—that are often detected in volcanic rocks at ocean islands like Hawaii and Iceland. This means the same process may connect Earth’s deepest mantle to the volcanic activity we see at the surface, offering a unified explanation for some of the planet’s most enduring geochemical and geophysical mysteries.