Extensive CO2 degassing in the upper mantle beneath oceanic basaltic volcanoes: First insights from Piton de la Fournaise volcano (La Réunion Island)

Based on the modeling developed in this study, we propose a new estimation of the CO2 content (up to 3.5 ± 1.4 wt%) in primary basaltic melts at PdF leading to a carbon content in the mantle source of 716 ± 525 ppm. This new estimation is considerably higher than the few previous calculations performed for Ocean Island Basalts (OIB) systems. Another implication of this work involves the possible bias between the δ13C measured in volcanic gas emissions (<−6‰) and that of primary vapour phase (−0.5 ± 0.5‰) constrained in this work. This bias would confirm the early step of extensive CO2 degassing within the upper mantle and could represent an alternative for the hypotheses of carbon recycling or mantle heterogeneity in support of the low δ13C signature of some mantle reservoirs. This study bears significant implications on the global budget of volcanic volatile emissions, chiefly regarding the contribution of past and future emissions of volcanic CO2 to climate dynamics, and on volcanic gas monitoring.