Ca‑carbonate mantle metasomatism and rapid melt ascent recorded in xenoliths from the Northern Andean Volcanic Zone (Colombia): A window into mantle wedge dynamics

Mantle xenoliths from the Mercaderes–Río Mayo volcanic area (SW Colombia) provide rare evidence of carbonate–silicate interactions within the sub-arc mantle of the Northern Andean Volcanic Zone. We describe metasomatized high-pressure garnet-peridotites containing up to 51 vol% carbonate, mainly aragonite, calcite, and dolomite, indicating extensive Ca‑carbonate metasomatism. Microstructural observations, together with mineral chemistry, stable isotope data and thermodynamic models, suggest that these carbonates originated from carbonatitic melts derived from the decarbonation or partial melting of subducted Nazca sediments. Thermobarometric calculations indicate equilibration at 3.0–3.7 GPa and 1200–1250 °C, consistent with a hot mantle wedge environment. Reaction textures between carbonates and silicates indicate a multistage carbonation history, involving initial olivine consumption, followed by carbonate partial melting and melt–rock interaction with orthopyroxene during exhumation. The associated CO₂ release may have promoted rapid, buoyancy-driven magma ascent. Preservation of aragonite and disequilibrium microstructures indicates ascent rates on the order of hours to days, far exceeding those of ductile or porous flow.