Experimental Investigation of Melting Relations between Bridgmanite and Davemaoite under Lower Mantle Conditions: Implications for Early Earth Differentiation

• Applicant: Professor Dr. Tomoo Katsura
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560750697

This pioneering research initiative is dedicated to the comprehensive investigation of the melting relationships between bridgmanite and davemaoite in the MgSiO3-CaSiO3 system under exceptional pressure conditions of up to 50 GPa. This study will significantly contribute to our understanding of the chemical evolution of the Earth's mantle after the magma ocean phase. Building on the fundamental insights of previous studies on eutectic melting between bridgmanite and davemaoite at 22-24 GPa, this project systematically extends the range of investigation to 23, 31, 40 and 50 GPa. This comprehensive pressure series will enable a precise characterization of the pressure dependence of the melting temperature and composition of these important mantle phases for the first time. A central aspect of the investigation is the determination of the CaSiO3 content of the eutectic composition at increasing pressure. The possible enrichment of Davemaoite could lead to the formation of a previously undiscovered geochemical reservoir in the lower mantle - a finding of fundamental importance for our understanding of mantle geochemistry. The experimental procedure is carried out using a state-of-the-art multi-anvil press that achieves impressive pressures of up to 53 GPa and temperatures above 3000 K. This advanced ultra-high pressure-temperature multi-anvil method ensures precise measurement results under the most extreme conditions. The study will also critically test the intriguing hypothesis of Ko et al. (2022) on the increased CaSiO3 solubility in bridgmanite. Promising initial results suggest a decreasing solubility with increasing pressure, which suggests the continuous presence of davemaoite in the lower mantle. Scientific excellence is ensured by an outstanding support team: Prof. Tomoo Katsura and Dr. Artem Chanyshev are leading the experimental work, while Dr. Nobuyoshi Miyajima contributes his expertise in structural and chemical analysis using SEM and TEM. This constellation provides optimal conditions for training a doctoral student in state-of-the-art high-pressure experimental techniques. The systematic series of experiments begins with validation experiments at 23 GPa and methodically progresses to higher pressures. Through detailed analyses of the texture changes and chemical compositions, fundamental insights into the melting behavior of bridgmanite and davemaoite will be gained. This pioneering research project promises not only groundbreaking insights into the melting behavior and trace element distribution in the deep mantle, but also provides an excellent platform for training the next generation of scientists in the demanding field of high-pressure research.

• DFG Programme: Research Grants