The Origin of Carbonate Magmas Predating and Accompanying Main‐Phase LIPs Eruptions

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Abstract
Some large igneous provinces (LIPs) are associated with precursory carbonatite eruptions. Models for precursory carbonatites invoking partial melting of a carbonate metasomatized lithosphere appear implausible, given the long time needed for heat conduction from the plume head. Instead, we consider that the plume, not the lithosphere, is the source of carbon. We explore a range of carbon concentrations in the plume source (196 C 440 ppm) and various melting depths of carbonate‐bearing peridotite, depending on the mantle redox state. Our numerical simulations provide a fluid dynamically consistent evolution of the plume‐lithosphere system and enable us to calculate the ascent velocity of carbonate melts. Moreover, we advect millions of passive tracers to follow the 3‐D trajectories of melts. The term “precursory‐C” indicates plume carbon that has reached sub‐lithospheric depths (140 km) before the onset of anhydrous silicate melting. For models with carbonatite melt produced at great depths (200 km), we find that the precursory‐C flux can be up to 6 × mol(C)/yr during a time period of ∼2 Myr preceding the onset of anhydrous silicate melting. The considerable mass of precursory‐C, up to 2 × kg(C), can explain carbonatite complexes predating main phase volcanism in the Paraná province and the Deccan Traps. For some LIPs, environmental and biotic perturbations, indicated by negative carbon isotope excursions and mass extinctions, predate the main phase LIPs eruptions. For the Central Atlantic Magmatic Province (CAMP) we suggest that precursory‐C could represent a non‐negligible carbon source for the earliest volcanism, likely synchronous with the end‐Triassic extinction.

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