What is it about?
The leucite basanites of the Visoke and Muhavura volcanoes from the province of Virunga (Western Branch of the East African Rift) were investigated in detail. The major and trace element contents and Sr, Nd and Pb isotopic composition in the whole rocks were determined.
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Why is it important?
The isotope ratios (87Sr/86Sr: 0.70644–0.70793; 143Nd/144Nd: 0.51233–0.51243) show that these rocks are far from the bulk Earth on the “mantle trend” and enriched in radiogenic Sr. The major element compositions reveal that they are not primary mantle melts as they have Mg# = 0.50–0.59. Moreover the leucite basanites are enriched by LILE and LREE relative to PM which may indicate an enriched mantle source. Pb isotopes of the studied leucite basanites (206Pb/204Pb: 19.112–19.438, 207Pb/204Pb: 15.737–15.783, 208Pb/204Pb: 40.509–40.866) along with the data of Karisimbi volcano form trends on isotope diagrams towards the EM II or ancient continental crust. The position of leucite basanite data on the 87Sr/86Sr - 208Pb*/206Pb* correlation line suggests that they can be a result of melt enrichment/vein metasomatism within the mantle.
Perspectives
We identify melts from two different sources at Visoke edifice: ugandite and its possible derivatives were formed from the mantle source, whereas the leucite basanites are enriched in radiogenic strontium and could be contaminated by deep metamorphic rocks. The origin of the studied leucite basanites is the result of a combination of various processes: melting of the metasomatized mantle, fractional crystallization, magma mixing and crustal contamination.
Boris V Belyatsky
Karpinsky Geological Institute (VSEGEI)
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This page is a summary of: Leucite basanites of Virunga (East African Rift): some insights into petrogenesis and source composition, Lithos, March 2021, Elsevier,
DOI: 10.1016/j.lithos.2021.105972.
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