Caldera-forming eruptions of the Quaternary Kone Volcanic Complex, Ethiopia

Abstract

Quaternary volcanism in the northern Main Ethiopian Rift is characterized by rift-axis eruptive centres with complicated collapse structures. Despite their association with major explosive eruptions, few modern studies have been carried out on them. We present the results of fieldwork and laboratory analyses of one of the largest of these centres, the Kone Volcanic Complex (KVC). It consists of nested calderas, trachyte lava flows, trachyte and alkali rhyolite pyroclastic deposits, alkali rhyolite lava domes and numerous small transitional to alkali basalt lava vents and flows. The largest subsidence structure, Birenti Caldera, has a diameter of ∼11 km and an area of ∼95 km 2. Post-collapse volcanism in the interior of Birenti Caldera produced a predominantly trachytic cone that was partially destroyed by a further eruption, forming the well-preserved but irregularly-shaped Kone Caldera (diameter of ∼8 km and an area of ∼24 km 2). Rhyolite lava dome eruptions and tectonically-controlled basalt lava effusion represent the most recent volcanism in the KVC. We report here the first detailed geologic map, along with petrologic and stratigraphic analyses, in order to reconstruct the eruptive history of this large but previously little-known volcanic complex. The findings have implications for understanding the relationships between rifting, tectonics and volcanism in the northern Main Ethiopian Rift, and for future efforts to trace widespread tephra horizons for regional stratigraphic correlation.