The Magmatic Evolution of Dabbahu Volcano, Afar, Ethiopia

Dabbahu is situated in the western region of Afar, Ethiopia, at the northern end of the Manda Hararo rift segment. This volcano came back to life in 2005 with a small rhyolitic eruption from the Da'Ure vent, the first such eruption in Africa for a century. This coincided with the start of a major rifting event which has been modelled as a basalt dyke injection (Wright et al 2006). The aim of this research is to provide an insight into the history and evolution of a silicic magmatic centre in the rift, and to contribute to the wider aims of the NERC Afar Consortium to track the creation, migration, evolution and emplacement of magma from the asthenosphere to the crust. Here we report the results of recent fieldwork in the northern, ESE and summit areas of the volcano, the first geological expedition to the area for over 30 years (Barberi et al, 1975). The volcano is characterised by a wide range of magma types from alkali-basalts, through trachytes to pantellerites. Initial mapping has revealed that the volcano has not evolved through eruptions from a central vent but mainly through a series of N-S trending fissures located across the volcano, sub-parallel to the current rift axis. At least four generations of rifting have been identified, each associated with obsidian flows and pyroclastic deposits, some of which contain pumices and obsidian-pumice bombs ranging from ~0.08 to 2 m in length. Dabbahu shows several signs of rejuvenation, including substantial fumaroles activity. Geodetic surveys reveal subsidence of Dabbahu and nearby Gabho following the 2005 event, and subsequent inflation, consistent with emplacement of a shallow magma body. Our new SIMS data from feldspar hosted melt inclusions, suggests crystallisation occurs from depths of ~12 km. However, many inclusions are trapped between 3.5 and 6 km, suggesting magma is typically stored in this region prior to eruption. Whole rock and micro-analytical data of our samples will allow us to comprehensively characterise the magma which will provide information on the relationship between Dabbahu's sub-volcanic system and the magmas involved in the dyking events. Many of these erupted units will be dated using 40Ar-39Ar techniques.