Wehrmann, Heidi, Hoernle, Kaj , Portnyagin, Maxim , Wiedenbeck, M. and Heydolph, Ken (2011) Volcanic CO2 output at the Central American subduction zone inferred from melt inclusions in olivine crystals from mafic tephras. Geochemistry, Geophysics, Geosystems, 12 . Q06003. DOI 10.1029/2010GC003412.

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Abstract

The volatile contents of olivine‐hosted (Fo89–71) melt inclusion glasses in rapidly quenched mafic tephras
from volcanic front volcanoes of the Central American Volcanic Arc (CAVA) in Guatemala, Nicaragua, and
Costa Rica, were analyzed by secondary ion mass spectrometry (SIMS) in order to derive the minimum eruptive
output of CO2, along with H2O, Cl, and S. Details of the analytical method are provided that establish
melt inclusion CO2 analyses with the Cameca ims6f at the Helmholtz Centre Potsdam. The highest CO2 concentrations
(up to 1800 mg/g) are observed in Nicaraguan samples, while melt inclusions from Guatemala and
Costa Rica have CO2 contents between 50 and 500 mg/g. CO2 does not positively covary with sediment/slab
fluid tracers such as Ba/La, Ba/Th, or U/La. Instead, the highest CO2 concentrations occur in the inclusions
with the most depleted incompatible element compositions and low H2O, approaching the composition
of mid‐ocean ridge basalts (MORBs), whereas the most H2O‐rich inclusions are relatively CO2‐poor
(<800 mg/g). This suggests that CO2 degassing was more extensive in the melts with the highest slab contribution.
CO2/Nb ratios in the least degassed CAVA melt inclusions are similar to those of primitive MORBs.
These are interpreted here as recording a minimum CO2 output rate from the mantle wedge, which amounts to
2.8 × 104 g/s for the ∼1100 km long CAVA. Previously published estimates from quiescent degassing and
numerical modeling, which also encompassed the slab contribution, are 3 times higher. This comparison
allows us to estimate the proportion of the total CO2 output derived from the mantle wedge.

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