Carbonate-Capped Seamount Subduction Accelerates CO2-Rich Arc Magma Ascent: Insights from Pagan Volcano, Mariana Arc

Subduction of oceanic plates drives carbon cycling between Earth’s interior and surface, yet the influence of subducted carbon on arc magma ascent dynamics remains poorly understood. Here we integrate volatile analyses of olivine-hosted melt inclusions and 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 CO ₂ contents (2000-6000 ppm), and storage at Moho depths (20 km). Diffusion profiles of Fo, Ni, and Mn in olivine constrain magma ascent from the Moho to the surface to have occurred within ~100 days. Elevated CaO/Al ₂ O ₃ ratios (>1) in melts, heavy δ ¹³ C values (~0.5‰) in volcanic gases, and the presence of seamount carbonate in the forearc mud volcano collectively indicate subducted seamount carbonates as the main source of CO ₂ -rich magma at Pagan. We propose that early CO ₂ exsolution at Moho depths generates overpressure, enabling hydrous arc magmas to bypass stalling within crust. This mechanism provides a new perspective on CO ₂ -driven arc eruptions and highlights the role of seamount subduction in deep carbon cycling.