Lithostratigraphy of the chole section, Southeastern Ethiopian volcanic province

Abstract

This study presents a detailed flow-by-flow petrographic modal description and major element data integrated into the stratigraphic framework for the central part of the southeastern Ethiopian plateau (the Chole Section). The stratigraphic data are placed in the context of the regional stratigraphic framework and correlated with existing geochronology of the province, allowing us to estimate the timing and duration of volcanic activity in the area. Based on petrographic variations and physical volcanological features, the Chole section is divided into: (1) lower basalt; (2) middle basalt; and (3) upper basalt. The phase assemblages and major element data show that the lower and upper basalts underwent possible fractionation involving olivine, plagioclase, and augite. In contrast, the middle basalt equilibrium phase and major element data exhibits low-degree fractionation involving olivine, clinopyroxene, and orthopyroxene at greater depths. The stratigraphic position and the petrographic data suggests, the lower and middle basalt successions likely correlate with the Oligocene to Early Miocene basaltic succession (28–15.5 Ma) of the southeastern Ethiopian volcanic province. The presence of several volcanic hiatuses and the decrease in flow thickness in the middle basalt suggest a waning of magmatic activity during this period. The upper basalt of the Chole section correlates with the upper Miocene basalt of the southeastern volcanic province (15.5–11 Ma). From this, we determine that volcanic activity in the southeastern Ethiopian volcanic province is well constrained within the broader tectono-magmatic framework of the East African volcanic province.