Carbonate-capped seamount subduction accelerates CO2-rich arc magma ascent

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Abstract
Subduction transports carbon into Earth's interior, yet how subducted carbon influences arc magma ascent dynamics remains unclear. Here we combine volatile compositions of olivine-hosted melt inclusions with olivine diffusion chronometry at Pagan volcano (Mariana arc) to reveal a direct link between carbonate-capped seamount subduction and rapid magma ascent. Melt inclusions record high CO2 contents (2000-6000 ppm), and magma storage near Moho depths (~20 km). Olivine zoning profiles constrain magma ascent from near-Moho to the surface on timescales of weeks to months. Elevated CaO/Al2O3 ratios (>1) in erupted volcanics, heavy δ13C values (~0.5‰) in monitored volcanic gases, and the occurrence of seamount carbonate in the forearc mud volcano collectively point to subducted seamount carbonates as the dominant CO2 source feeding Pagan magmatism. We propose that early CO2 exsolution near the Moho generates overpressure that enables hydrous arc magmas to bypass crustal stalling. These results identify CO2 as a key driver of rapid magma ascent in arcs and highlight carbonate-capped seamount subduction as an efficient pathway for deep carbon cycling.
Funding Information
  • National Natural Science Foundation of China (42322604)

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