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

Abstract

[1] 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.

The time scales of continental rifting: Implications for global processes

“…Recent and ongoing multidisciplinary projects are beginning to provide threedimensional constraints on the distribution of strain and magmatism in the lower crust within active rifts needed to develop the next generation of rift models (e.g., Keranen et al, 2004;Thybo and Nielsen, 2009;Hammond et al, 2011;Delph et al, 2011). Systematic measurements of volatile degassing in rift zones will help constrain their fl ux through stretching lithosphere, and inform models and experiments of mantle lithospheric deformation where partial pressures of CO 2 are elevated (e.g., Fischer et al, 2009;Head et al, 2011).…”

New lava lake at Nyamuragira volcano revealed by combined ASTER and OMI SO2 measurements

“…An alternative hypothesis would be residual degassing of unerupted magma from the 2011–2012 eruption. We consider this hypothesis less likely for three reasons:The SO 2 emissions marked a distinct decrease toward the end of the eruptions before picking up again after it had ended.The total SO 2 mass released by the eruption, 1.2 Tg calculated using the data of Theys et al [], is smaller than the 2 Tg amount estimated using the erupted lava volume of 0.2 km 3 reported by Coppola and Cigolini [], an initial south content of 2000 ppm [ Head et al , ], a density of 2.8, and a vesicularity of 15%. This suggests that the magma from the 2011–2012 eruption was already partly degassed.The degassing of unerupted magma should have taken place from the eruption location, whereas ASTER imagery shows that it was taking place in the summit caldera.…”

River geochemistry, chemical weathering, and atmospheric CO2 consumption rates in the Virunga Volcanic Province (East Africa)

“…We carried out monthly sampling on 13 rivers in the VVP (all located in the DRC) from December 2010 to February 2013; eight are located in the Kabuno bay basin (a subbasin of Lake Kivu) while the five others drain into Lake Edward (Figure 1). Temperature, specific conductivity, pH, and dissolved oxygen (%O 2 ) were measured in situ with a Hanna (Hi 9828) multiparameter probe between December 2010 and December 2011, 1912, 1938, 1948, 1977, 1982, 1986, 2006eruptions after Denaeyer [1972, 1975, Pouclet [1974], Aoki and Kurasawa [1984], Aoki et al [1985], Hertogen et al [1985], Marcelot et al, 1989, Head et al [2011, and Smets et al [2013].…”