Magmatic history of Dabbahu, a composite volcano in the Afar Rift, Ethiopia
L. Field et al., School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ, UK. Posted online 25 October 2012; http://dx.doi.org/10.1130/B30560.1.
Dabbahu is a volcano in northern Ethiopia that comprises a range of lavas from basaltic to very evolved rhyolites which have a high silica content. L. Field and colleagues present 93 new whole-rock analyses, mineral analyses from 65 samples and 9 new 40Ar/39Ar dates, together with a new geological map of the volcano. They use these data to show that Dabbahu has been active for over 67 thousand years, but there is an apparent hiatus of about 20 thousand years in its eruptive history that occurred between the eruption of the most evolved magmas. Some rhyolites erupted both effusively and explosively. All magmas were erupted from a relatively closely spaced network of vents and fissures, and field evidence indicates that magmas were not erupted in a simple fractionation sequence. Some mixing occurred between magmas of less evolved compositions, together with more evolved compositions shortly prior to, or during, eruption. The differentiation of basalt to rhyolite must have occurred on timescales that were relatively short compared to the lifetime of the volcano, probably due to the small volumes of basalt intruded into the crust and consequently enhanced cooling and crystallization rates. A network of stacked sills or closely spaced dykes in the shallow to mid crust represents the most plausible configuration of the sub-volcanic plumbing system. Input of new magma batches into such a system may serve as a key eruption trigger at Dabbahu.
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