Collaborative Research: A plan to determine if the core can be the ultimate high 3He/4He source

Studies of noble gases, such as helium (He), suggest that parts of the mantle have largely escaped melting at, or near, the Earth’s surface. These mantle domains are characterized by high ratios of the isotopes 3He to 4He (3He/4He). Much work has been done to understand how these mantle domains within Earth’s interior have escaped melting in the face of billions of years of mantle convection and plate tectonics.

New observations of these high 3He/4He domains suggest that, rather than reflecting previously unmelted portions of the mantle, these domains may be the result of Earth’s core leaking into the mantle. Through this leak, pristine noble gases from the core imprint their helium ratios on mantle rocks that sit above the core-mantle boundary. Subsequently, the mantle rocks are transported to the surface and sampled by intraplate volcanism.

This project will involve experiments using metal and magma at temperatures and pressures similar to the Earth’s core to explore the question of whether the core is the source of the high 3He/4He found in parts of the mantle. If true, and the core is the source, this would provide new information about the chemistry of the core and would mean that high 3He/4He mantle domains may not, in fact, be unmelted and pristine. This helps us understand Earth’s early evolution.

This proposal seeks to test the hypothesis that the core can be the ultimate high 3He/4He source. Experiments will be conducted that react metal and magma under controlled conditions that range up to the pressures and temperatures directly applicable to core formation within Earth. The noble gas distribution in the experiments will be analyzed using laser-ablation mass spectrometry.

These analyses will yield constraints regarding the ability of the core to incorporate noble gases during its creation. These constraints will be applied towards developing a core formation model that predicts the isotopic composition of the core for both He and Xe for various plausible formation conditions. Important model parameters include core formation timing, nature of Earth’s primordial atmosphere, the prevailing redox state associated with core formation, and core formation pressure-temperature conditions.

Model predictions will be compared to existing geochemical analyses to identify if the core is a plausible source of high 3He/4He noble gases. This proposal will support the training of two PhD students in cutting-edge experimental and analytical methods, the production and characterization of noble gas analytical standards that will be made available to the community, and summer internships for college students in and around New Orleans.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.