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.