Hotspots are magma plumes that emerge from deep within the Earth and erupt at the surface. They are believed to help form large volcanic islands such as Hawaii and Iceland. These hotspots are also popular with geochemical travelers.
Natural processes throughout Earth’s history have transmitted measurable geochemical signals, from the deep interior of the metallic core to the thick middle layer and all the way to the surface, where they have been identified as magma-‘ hot spots’.
Amy Ferrick, the lead author of a new study, said: “Magma hotspots are home to some of the most unique geochemistry found on the Earth’s surface.”
“Where hotspots come from and what makes magma hotspots so unique is not entirely clear, but studying their geochemistry may give us clues.”
The tungsten and helium isotopes detected in the crystallized magmas near these hot spots are one such clue.
Isotopes are two or more different types of atoms with the same atomic number but different neutron counts.
The ratios of tungsten and helium isotopes in magma hotspots differ from those in the mantle, the planet’s rocky middle layer.
Instead, the ratios match isotopes discovered much deeper, in the planet’s metallic, tungsten-rich core.
Ferrick and Jun Korenaga, a professor of earth and planetary sciences at Yale’s Faculty of Arts and Sciences, noted: “The convective processes of the Earth’s mantle are so powerful — and were especially true during Earth’s early years, when it was hotter and partially molten — that helium is highly unlikely to become trapped in reservoirs emanating from the mantle. “
For this study, scientists developed a computer model that shows how the tungsten and helium isotopes can make the journey from the center of the Earth.
They argue that isotope diffusion, the movement of atoms that depends on temperature and the size of the particles being displaced, can produce a hotspot highway.
Korenaga said, “I initially thought that diffusion might be too slow to be effective, so I was surprised when Amy showed that this process was more than enough to explain the anomalous tungsten and helium compositions of basalts on ocean islands.”
“The research has far-reaching implications for understanding early Earth conditions, such as the vastness of magma oceans. It could also help scientists understand the evolution of regions of the Earth’s interior that have been hidden from view for billions of years.”
- A. Ferrick and J. Korenaga. Long-term core-mantle interaction explains the heterogeneities of W-He isotopes. PNAS, 17 January 2023. DOI: 10.1073/pnas.2215903120