Abstract
During continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.
Highlights
The Ma’Alalta volcanic field (MVF hereafter) is located in Afar (Ethiopia), ~ 50 km north of Dabbahu volcano (Fig. 1)
Little is known about the petrology, geochemistry and tectonics of MVF and how they relate to the tectonics of continental breakup in Afar
Holocene rift marginal volcanism has produced large volumes of lavas, such as those erupted by the silicic stratovolcanoes of the Nabro-Mallahle alignment or from basaltic shield volcanoes, such as Dabbayra (Fig. 1a)
Summary
The Ma’Alalta volcanic field (MVF hereafter) is located in Afar (Ethiopia), ~ 50 km north of Dabbahu volcano (Fig. 1). Volcanism in Afar initiated ~ 30 Ma ago and was initially dominated by flood basalts (Hofmann et al 1997). Since at least ~ 1 Ma, active rifting and volcanism have focused to en-echelon axial magmatic segments (~ 70-km-long, ~ 20-km-wide) marking the current plate boundary of the rift (e.g. Dabbahu segment, Manda Hararo segment and Erta Ale segment) (Fig. 1a) (Oppenheimer and Francis 1998; Wright et al 2012; Medynski et al 2013). Holocene rift marginal volcanism has produced large volumes of lavas, such as those erupted by the silicic stratovolcanoes of the Nabro-Mallahle alignment (marginal volcanism) or from basaltic shield volcanoes, such as Dabbayra (transverse volcanism) (Fig. 1a). Despite the peculiarity of the marginal volcanism, current knowledge about marginal volcanoes, their magma sources and plumbing system and the relationships with
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