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    Insight into volatile behavior at Nyamuragira volcano (D.R. Congo, Africa) through olivine-hosted melt inclusions

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    2011GC003699.pdf (1.736Mb)
    Date
    2011-10-04
    Author
    Head, Elisabet M.  Concept link
    Shaw, Alison M.  Concept link
    Wallace, Paul J.  Concept link
    Sims, Kenneth W. W.  Concept link
    Carn, Simon A.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4885
    As published
    https://doi.org/10.1029/2011GC003699
    DOI
    10.1029/2011GC003699
    Keyword
     Effusive volcanism; Eruption mechanisms; Excess sulfur; Melt inclusions; Volcanic gases 
    Abstract
    We present new olivine-hosted melt inclusion volatile (H2O, CO2, S, Cl, F) and major element data from five historic eruptions of Nyamuragira volcano (1912, 1938, 1948, 1986, 2006). Host-olivine Mg#'s range from 71 to 84, with the exception of the 1912 sample (Mg# = 90). Inclusion compositions extend from alkali basalts to basanite-tephrites. Our results indicate inclusion entrapment over depths ranging from 3 to 5 km, which agree with independent estimates of magma storage depths (3–7 km) based on geophysical methods. Melt compositions derived from the 1986 and 2006 Nyamuragira tephra samples best represent pre-eruptive volatile compositions because these samples contain naturally glassy inclusions that underwent less post-entrapment modification than crystallized inclusions. Volatile concentrations of the 1986 and 2006 samples are as follows: H2O ranged from 0.6 to 1.4 wt %, CO2 from 350 to 1900 ppm, S from 1300 to 2400 ppm, Cl from 720 to 990 ppm, and F from 1500 to 2200 ppm. Based on FeOT and S data, we suggest that Nyamuragira magmas have higher fO2 (>NNO) than MORB. We estimate the total amount of sulfur dioxide (SO2) released from the 1986 (0.04 Mt) and 2006 (0.06 Mt) Nyamuragira eruptions using the petrologic method, whereby S contents in melt inclusions are scaled to erupted lava volumes. These amounts are significantly less than satellite-based SO2 emissions for the same eruptions (1986 = ∼1 Mt; 2006 = ∼2 Mt). Potential explanations for this observation are: (1) accumulation of a vapor phase within the magmatic system that is only released during eruptions, and/or (2) syn-eruptive gas release from unerupted magma.
    Description
    Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 12 (2011): Q0AB11, doi:10.1029/2011GC003699.
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    • Geology and Geophysics (G&G)
    Suggested Citation
    Geochemistry Geophysics Geosystems 12 (2011): Q0AB11
     

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