Geological evolution of the Boset-Bericha Volcanic Complex, Main Ethiopian Rift: 40 Ar/ 39 Ar evidence for episodic Pleistocene to Holocene volcanism

Siegburg, M., Gernon, T. M., Bull, J. M., Keir, D., Barfod, D. N. , Taylor, R. N., Abebe, B. and Ayele, A. (2018) Geological evolution of the Boset-Bericha Volcanic Complex, Main Ethiopian Rift: 40 Ar/ 39 Ar evidence for episodic Pleistocene to Holocene volcanism. Journal of Volcanology and Geothermal Research, 351, pp. 115-133. (doi: 10.1016/j.jvolgeores.2017.12.014)

Abstract

The Boset-Bericha Volcanic Complex (BBVC) is one of the largest stratovolcanoes of the northern Main Ethiopian Rift (MER). However, very little is known about its eruptive history, despite the fact that approximately 4 million people live within 100 km of the complex. Here, we combine field observations, morphometric analysis using high-resolution LiDAR data, geochemistry and 40Ar/39Ar geochronology to report the first detailed account of the geological evolution of the BBVC, with a focus on extensive young lava flows covering the two edifices, Gudda and Bericha. These lavas exhibit a bimodal composition ranging dominantly from basaltic rift floor lavas and scoria cones, to pantelleritic trachytes and rhyolite flows at Gudda, and comenditic rhyolites at Bericha. Further, several intermediate compositions are associated with fissure vents along the Boset-Kone segment that also appear to link the silicic centres. We divide the BBVC broadly into four main eruptive stages, comprising: (1) early rift floor emplacement, (2) formation of Gudda Volcano within two main cycles, separated by caldera formation, (3) formation of the Bericha Volcano, and (4) sporadic fissure eruptions. Our new 40Ar/39Ar geochronology, targeting a representative array of these flows, provides evidence for episodic activity at the BBVC from ~ 120 ka to the present-day. We find that low-volume mafic episodes are more frequent (~ 10 ka cyclicity) than felsic episodes (~ 100 ka cyclicity), but the latter are more voluminous. Over the last ~ 30 ka, mafic to intermediate fissure activity might have reinvigorated felsic activity (over the last ~ 16 ka), manifested as peralkaline lava flows and pyroclastic deposits at Gudda and Bericha. Felsic episodes have on average a higher eruption rate (2–5/1000 years) and productivity at Gudda compared to Bericha (1–2/1000 years). The young age of lavas and current fumarolic activity along the fault system, suggest that the BBVC is still potentially active. Coincident episodic activity within the BBVC and at several rift segments in the MER is observed, and facilitates continental rifting.

• Item Type: Articles
• Additional Information: We would like to thank the NERC Airborne Research and Survey Facility (grant ET12-14) for undertaking a LiDAR survey over the BBVC. We thank staff of the Institute of Geophysics, Space Science and Astronomy and Department of Earth Science at Addis Ababa University, Ethiopia for support during data collection (2012) and field work (2015). We thank R. Dymock and J. Imlach of the AIF laboratory at SUERC, and E. Roberts from University of Southampton for their assistance with sample preparation and 40Ar/39Ar measurement. We acknowledge the NERC Isotope Geosciences Facilities Steering Committee for funding to undertake 40Ar/39Ar dating at the Argon Isotope Facility (grant IP1569-1115). We thank W. Hutchison and F. Illsley-Kemp for their helpful assistance with the GMT script for lava volume measurement. DK is supported by NERC grant NE/L013932.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Barfod, Dr Dan
• Authors: Siegburg, M., Gernon, T. M., Bull, J. M., Keir, D., Barfod, D. N., Taylor, R. N., Abebe, B., and Ayele, A.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Journal of Volcanology and Geothermal Research
• Publisher: Elsevier
• ISSN: 0377-0273
• Published Online: 29 December 2017
• Copyright Holders: Copyright © 2018 The Authors
• First Published: First published in Journal of Volcanology and Geothermal Research 351:115-133
• Publisher Policy: Reproduced under a Creative Commons License