Marty, B.; Meynier, V.; Nicolini, E.; Griesshaber, Erika; Toutain, J.P.
Geochemistry of gas emanations: A case study of the Réunion Hot Spot, Indian Ocean.
In: Applied Geochemistry, Vol. 8, Nr. 2: S. 141-152
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The results of analysis of natural emanations in Réunion Island show a clear magmatic origin for CO2 and He, while N2 and Ar are predominantly derived from the atmosphere. The distribution of magmatic gases in the Piton des Neiges massif fits the local volcanotectonic context well and suggests that the areas concerned are still subject to volcanic activity at depth. A simple method is proposed for correcting gas concentration and isotope composition for water degassing. In doing so, the isotope and elemental (C, He) composition of gases is homogeneous for the two volcanoes. The isotope ratio of He (12.5 ± 0.5 R/Ra) in the present discharges is in agreement with the results of previous studies on rocks of various ages from the two volcanoes. The isotope ratio of C (δ13C = -5‰ to -4‰ vs PDB) and the C/3 He ratio (∼4 × 109) are similar to those found in other Hot Spot volcanic systems such as Kilauea (Hawaii) and Hengill (Iceland). These similarities suggest comparable volatile history for the respective mantle sources, the main differences being in the relative proportions of radiogenic 4He. In detail, Hot Spots appear enriched in C having a light composition with respect to MORB, possibly due to the addition of a C-rich (e.g. subducted) component, in addition to a relatively undegassed, 3He-rich, component.