Stratigraphy and eruptive history of Gedemsa caldera volcano, Central Main Ethiopian Rift

Gedemsa caldera is a peralkaline volcanic depression located in the Central sector of the Main Ethiopian Rift. An integrated volcanological study of stratigraphic sections was carried out in order to constrain the eruptive history of Gedemsa caldera volcano (GCV), Ethiopia. Textural analyses on plagioclase crystals together with field observations shed light on magma chamber processes feeding the volcanic complex. A multi-vent eruption is ascribed to the pre-caldera volcanic products, as can be seen from the varying caldera wall sequences comprising lavas and pyroclastic deposits. At least three major caldera-forming eruptions are identified producing: 1) a lower ignimbrite, 2) extensive pumice fall and pyroclastic density current deposits, and 3) an upper ignimbrite exposed in different areas of the caldera, indicating a sector collapse. We identified 20 individual pyroclastic deposits found outside and within the caldera that erupted after the climactic caldera collapse. The most recent volcanic activity at Gedemsa is characterized by rhyolitic lava domes and pyroclastic deposits from eruptions through numerous vents aligned with WNW-ESE pre-existing cross-cutting structures. Macrocryst disequilibrium textures such as fine-scale oscillatory zoning (FOZ), sieve textures, glomerocryst, and synneusis indicate that magma reservoir is characterized by repeated magma injection, convection flows, and mixing.