HR: 14:55h
AN: V33D-06    [Abstracts]
TI: Is the Virunga Volcanic Province a precursor to Continental Flood Basalt eruption by Plume Volcanism?
AU: * Basu, A R
EM: abasu@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Chakrabarti, R
EM: ramananda@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Tedesco, D
V33D-06 AF: Department of Environmental Sciences, Via Vivaldi 43, Caserta, 81100 Italy
AU: Santo, A P
EM: asanto@geo.unifi.it
AF: Department of Earth Sciences, Via G. La Pira 4, Firenze, 50121 Italy
AU: Vaselli, O
V33D-06 AF: Department of Earth Sciences, Via G. La Pira 4, Firenze, 50121 Italy
AB: The Virunga Volcanic Province (VVP), located near the northern end of the western branch of the East African Rift system is characterized by silica undersaturated mafic volcanism that started to erupt at ~ 10 Ma ago with continuing activity today in two volcanoes, Nyiragongo and Nyiamuragira. These volcanoes are in a seismically active zone of the West Rift at the periphery of the Archean Tanzanian Craton. The VVP is within a large area of uplift associated with anomalously hot upwelling asthenosphere (Ebinger and Furman, 2003) and the seismic tomography images have been interpreted with a plume stem beneath the Tanzanian Craton (Weeraratnam, 2003). Lavas from the Nyiragongo Volcanic complex consisting of three alkalic ultrabasic lava- erupting volcanoes aligned along a N-S direction were analyzed for major, trace elements, Nd, Sr, Pb and He-isotopes. The bulk rocks range in SiO₂ = 38.1-39.5, Na₂O = 5.5-5.8, K₂O = 5.1-5.7. Melilite (Ak 55-70, Ge 5-13), nepheline (Ne 65-73), and olivine (75-72) occur as phenocrysts in the ultrabasic lavas which grade to basanite to picrobasalt. Primitive mantle-normalized multiple trace element patterns show strong negative Pb-anomaly with high Ba/Rb, Nb/Th and Th/Pb ratios. Ce/Pb ratios (25-90) show positive correlation with Ce contents. Sr and Nd isotopes cluster around bulk Earth values for the 2002 Nyiragongo lavas as well as for some other Virunga lavas. However the Pb-isotope composition of these lavas show radiogenic, typical HIMU-like character, contrasting with their Bulk Earth like Sr and Nd isotopic compositions. The He isotopic ratios(R/R_a) of the lava lake and fluid inclusions in minerals typically show MORB like value of 8 +/- 1 We propose that the VVP is a potential site for continental flood basalt eruption. It has similarities in structural-tectonic setting, pre-flood basalt eruptive craton-margin alkalic volcanism, and in the Nd, Sr, Pb and 'potential' He isotopic signatures with those of the pre-Deccan alkalic lavas of the Indian subcontinent. We also note that the Ethiopian flood basalts had already erupted 30 Ma ago by the Afar plume volcanism in a similar process farther NNE along the East African rift.
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005