Rift related magmatism and the petrogenesis of lavas from the Kiejo eruptive, Rungwe Volcanic Province, SW Tanzania

Abstract

Structural trends inferred from volcanological features display a dominantly N-NW alignment within the province. Volcanic episodes data from late Tertiary (10 Ma) through to Recent, with the last eruption occurring approximately 190 years ago from the Kiejo eruptive. Compositions from the Fiteko and Sarabwe vents of Kiejo range from alkali basalt/basanite to tephrite. In the Sengereti region south of Kiejo, picritic lavas dominate. Evidence from nickel content and Mg-values suggest that the picrobasalts show signs of olivine accumulation from "primitive' magma. Projection into appropriate phase diagrams indicates that alkali basalts and basanites from the Sarabwe vent are transitional lavas of intermediate to low pressure evolution, with variable degrees of crustal contamination. Tephrite from the Fiteko vent shows signs of clinopyroxene + olivine fractionation at low pressure from more "primitive' magma. -from Authors