Open AccessVolcanic CO 2 output at the Central American subduction zone inferred from melt inclusions in olivine crystals from mafic tephras
Author(s) -
Wehrmann H.,
Hoernle K.,
Portnyagin M.,
Wiedenbeck M.,
Heydolph K.
Publication year - 2011
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2010gc003412
Subject(s) - melt inclusions , geology , mafic , geochemistry , olivine , mantle (geology) , volcano , basalt , subduction , mantle wedge , incompatible element , slab , magma chamber , volcanic rock , inclusion (mineral) , mineralogy , partial melting , magma , seismology , geophysics , tectonics
The volatile contents of olivine‐hosted (Fo 89–71 ) 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 CO 2 , along with H 2 O, Cl, and S. Details of the analytical method are provided that establish melt inclusion CO 2 analyses with the Cameca ims6f at the Helmholtz Centre Potsdam. The highest CO 2 concentrations (up to 1800 μ g/g) are observed in Nicaraguan samples, while melt inclusions from Guatemala and Costa Rica have CO 2 contents between 50 and 500 μ g/g. CO 2 does not positively covary with sediment/slab fluid tracers such as Ba/La, Ba/Th, or U/La. Instead, the highest CO 2 concentrations occur in the inclusions with the most depleted incompatible element compositions and low H 2 O, approaching the composition of mid‐ocean ridge basalts (MORBs), whereas the most H 2 O‐rich inclusions are relatively CO 2 ‐poor (<800 μ g/g). This suggests that CO 2 degassing was more extensive in the melts with the highest slab contribution. CO 2 /Nb ratios in the least degassed CAVA melt inclusions are similar to those of primitive MORBs. These are interpreted here as recording a minimum CO 2 output rate from the mantle wedge, which amounts to 2.8 × 10 4 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 CO 2 output derived from the mantle wedge.