Open AccessInsight into volatile behavior at Nyamuragira volcano (D.R. Congo, Africa) through olivine‐hosted melt inclusions
Author(s) -
Head Elisabet M.,
Shaw Alison M.,
Wallace Paul J.,
Sims Kenneth W. W.,
Carn Simon A.
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 - 10.1029/2011gc003699
Subject(s) - melt inclusions , olivine , geology , tephra , volcano , basalt , geochemistry , lava , inclusion (mineral) , magma , mineralogy , magma chamber
We present new olivine‐hosted melt inclusion volatile (H 2 O, CO 2 , 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: H 2 O ranged from 0.6 to 1.4 wt %, CO 2 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 FeO T and S data, we suggest that Nyamuragira magmas have higher f O 2 (>NNO) than MORB. We estimate the total amount of sulfur dioxide (SO 2 ) 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 SO 2 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.