Abstract
Lithospheric controls on alkaline volcanism; evidence from Nyiragongo and Nyamulagira Volcanoes, Virunga volcanic province, DR Congo
Abstracts with programs - Geological Society of America, Vol.55(5)
Geological Society of America, Rocky Mountain Section, 73rd annual meeting
05/2023
DOI: 10.1130/abs/2023RM-388091
Abstract
The active volcanoes Nyiragongo and Nyamulagira, DR Congo have very different physical and geochemical characteristics, despite being situated 15 km apart. Nyiragongo's foiditic lavas are some of the most silica-undersaturated on earth, whereas Nyamulagira erupts primarily basanites and tephrites. To better understanding the magmatic sources, processes, and eruptive characteristics of these two volcanoes, we have measured major and trace element concentrations, Sr, Nd, Hf, and Pb isotopes, and (super 238) U- (super 230) Th- (super 226) Ra- (super 210) Pb- (super 210) Po and (super 232) Th- (super 228) Ra- (super 228) Th nuclides. Nyiragongo lavas are clearly distinct from Nyamulagira lavas in terms of their Sr, Nd, Hf, and Pb isotope compositions, indicating long-lived and small-scale heterogeneity beneath these two volcanoes. Invariant (super 206) Pb/ (super 204) Pb, (super 208) Pb/ (super 204) Pb, and ( (super 230) Th/ (super 232) Th) ratios for Nyamulagira lavas compared to Nyiragongo imply different controls on the long-term U/Pb and Th/Pb within the sources of the two volcanoes. The marked relationship between eruption age and Sr, Nd, and Hf isotope compositions at Nyamulagira emphasizes the short time scale on which these lavas change geochemically. Nyiragongo lavas are affected by carbonate metasomatism to a greater degree than Nyamulagira lavas. Carbonate metasomatism in Nyiragongo lavas is evidenced by high ( (super 230) Th/ (super 232) Th) and variable ( (super 230) Th/ (super 238) U). The source of both volcanoes likely contains residual garnet evidenced by the relatively high DyN/YbN ratios and (super 230) Th excesses. Additionally, there appears to be spatial mixing between these two volcanoes, as samples collected from parasitic cones in between the two have intermediate isotopic compositions. We posit that each volcano's composition is being controlled by lithospheric metasomes of carbonate for Nyiragongo and phlogopite for Nyamulagira, and that their respective plumbing systems overlap such that there is significant mixing between the two volcanoes.
Details
- Title: Subtitle
- Lithospheric controls on alkaline volcanism; evidence from Nyiragongo and Nyamulagira Volcanoes, Virunga volcanic province, DR Congo
- Creators
- Kenneth Sims - University of WyomingGregory J. StarkErin PhillipsJanne Blichert-ToftMark K. ReaganSean R. ScottDario TedescoPaul WallaceLissie Connors
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.55(5)
- Conference
- Geological Society of America, Rocky Mountain Section, 73rd annual meeting
- DOI
- 10.1130/abs/2023RM-388091
- ISSN
- 0016-7592
- Publisher
- Geological Society of America (GSA)
- Alternative title
- Geological Society of America, Rocky Mountain Section, 73rd annual meeting
- Language
- English
- Date published
- 05/2023
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984962544202771
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