Degassing of CO2 and H2O in submarine lavas from the Society hotspot

We analyzed CO2–δ13C–H2O–δD in vesicles of a suite of 23 vesicular submarine volcanic glasses (4 alkalic basalts and 19 trachytes) from Teahitia, Volcano 4 and Rocard seamounts and Mehetia Island in the active area of the Society hotspot (French Polynesia, South Pacific). e C and H2O concentrations ([Cvesicle] and [H2Ovesicle]) vary in the range 1–1487 ppm C and ∼0–5431 ppm H2O, respectively. The δ13C of CO2 in vesicles (δ13Cvesicle) vary from − 3.8‰ to − 9.7‰ and the δD of H2O in vesicles (δD vesicle) vary from − 32‰ to − 71‰. 3Cvesicles values are correlated with the vesicularity, Log([Cvesicle]) and the δDvesicle values. The Log([H2Ovesicle]) is also correlated to the δDvesicle values and Log([Cvesicle]). These observations show that late-stage open-system degassing, following a first stage of closed-system degassing, is the chief process controlling the concentration and isotopic ratio variations observed in the vesicles. ghest measured δ13Cvesicle values fall in a typical mantle range (− 4.0 ± 0.5‰). Taking into account the effect of vesicle bursting and crystal fractionation, the reconstructed pre-eruptive carbon and water concentrations in the alkalic basalt parental magma are ∼3810 ppm C and 14,360 ppm H2O (1.43 wt.%). These concentrations correspond to carbon and water fluxes for the Society hotspot during the last 900 kyr of 2.57 × 104 tons C yr− 1 and 97 × 103 tons H2O yr− 1 and volatile concentrations of the source of 190 ppm C and 720 ppm H2O. These values are similar in magnitude to previous estimates for other hotspots. udy emphasizes that H2O degassing must be taken into account before discussing H2O content and δD value variations in the lavas in terms of source variation in the case of the Society hotspot.