Isotopic fractionation between gaseous and dissolved Carbon in silicate melts; assessing the C content and d13C signature of Earth's Upper Mantle

Understanding the Earth's interior remains a top research priority in the geosciences. How much carbon is in the Earth's mantle, how much goes in and how much comes out - these questions remain unanswered despite decades of dedicated research. Yet the answers to these questions have profound implications for how the Earth's interior must function and how our planet has evolved over geological time. This project aims to precisely quantify the carbon content and its isotopic signature (δ13C) in the upper mantle to constrain how much of the Earth's carbon is contained in the upper mantle and in which regions of the mantle it accumulates. This research will not only advance our fundamental knowledge of Earth's interior but also support education by training a graduate student in state-of-the-art experimental and analytical techniques. The project seeks to determine the carbon content and δ13C signature of the upper mantle through a two-pronged approach. First, the researchers will experimentally determine the mass-dependent isotopic fractionation of carbon during the degassing of silicate melts. High-pressure/high-temperature experiments will be conducted using internally heated pressure vessels and piston-cylinder apparatuses to simulate conditions in the upper mantle. These experiments will measure the isotopic fractionation coefficients (α) as a function of melt composition, temperature, and pressure. Second, the team will directly measure δ13C in deep mantle melts using melt inclusions from volcanoes such as Etna, Erebus, and El Hierro. By combining experimental data with natural observations, the researchers will back-calculate the original carbon content and isotopic signature of the mantle. The project will utilize recent advances in secondary ion mass spectrometry. The results will provide a comprehensive understanding of the carbon cycle in the upper mantle, contributing to our knowledge of Earth's deep carbon reservoirs and their impact on global geodynamics. 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.