Alumina nanoparticle-induced decarbonation at subduction-zone conditions

The evolution of calcium carbonate in subduction zones exerts profound effects on Earth’s long-term climate dynamics and planetary habitability. Here, we report the first experimental study to elucidate the influence of aluminum oxide particle size on carbonate stability under high pressure-temperature (P-T) conditions using a piston-cylinder press. CaCO3 remains thermodynamically stable across the investigated P-T conditions when coexisting with micron-sized Al2O3 and Al(OH)3. In contrast, Al2O3 nanoparticles destabilize calcium carbonate at 0.5–2.8 GPa and 350–1050 °C, forming CaAl4O7, CO2, and trace graphite. Our results reveal that the grain size effect of Al2O3 strongly regulates calcium carbonate stability in subduction-zone environments, driven by ultrahigh specific surface areas and elevated defect densities inherent to nanoparticles. This work fundamentally revises the current understanding of the spatiotemporal distribution of decarbonation in this region, yielding a pattern of shallower, more heterogeneous carbon release. Alumina (Al2O3)-bearing minerals are hosted in carbonate-rich sediments, potentially interacting with CaCO3 during subduction. Here, the authors study the influence of Al2O3 particle size on carbonate stability at 0.5–2.8 GPa and 350–1050 °C, showing that CaCO3 remains thermodynamically stable when coexisting with micron-sized Al2O3 and Al(OH)3, whereas Al2O3 nanoparticles trigger decarbonation, forming CaAl4O7, CO2, and trace graphite.