Evidence for an active, transcrustal magma system in the last 60 ka and eruptive degassing budget (H2O, CO2, S, F, Cl, Br) : The case of Dominica

Evidence for an active, transcrustal magma system in the last 60 ka and eruptive degassing budget (H2O, CO2, S, F, Cl, Br) : The case of Dominica

d’Augustin, T. ; Balcone-Boissard, H. ; Boudon, G. ; Martel, E. ; Deloule, E. ; Bürckel, P.

Geochemistry, Geophysics, Geosystems, 2020, e2020GC009050

Abstract :

The Morne Trois Pitons‐Micotrin volcanic complex on the island of Dominica (Lesser Antilles) emitted a series of plinian eruptions between 18 and 9 ka BP. We studied it to constrain magma storage conditions and volatile degassing balances, by comparison with the three previous ignimbrites ( 60–24 ka BP). Volatile concentrations in glass inclusions and mineral‐melt thermobarometry indicate storage at ≤200 MPa ( 6–8 km) and 860–880°C. The magmas feeding these plinian eruptions were stored at a shallower depth than those that older ignimbrites from the same volcanic complex and stored at 16 km. Close magma composition and similar halogen ratios, however, suggest a common source for the magmas feeding both the plinian eruptions and the ignimbrites. The large eruptive fluxes of F, Cl, and Br to the atmosphere (up to 1.4–2.8 × 10−1 Mt/km3, 1.5–4.0 Mt/km3, and 2–4 × 10−2 Mt/km3, respectively), estimated by the petrological method, support the potentially important role of volcanic halogens in modifying the chemistry of the atmosphere, though Cl is underestimated here because of buffering in a fluid phase. The behavior of S, potentially partitioned in the same fluid phase, prevents here the calculation of an eruptive outgassing budget.