Exceptionally High Emplacement Rate of the Afar Mantle Plume Head

Abstract

We investigated a 1-km-thick sequence of lava flows that erupted over the Afar plume axis in order to better understand the emplacement history of the ∼30 Ma Ethiopia-Yemen Traps. Geochemical analyses reveal high-titanium concentrations (TiO2 3.9 ± 0.5 wt%) in basalts close to picritic compositions. Indistinguishable 40Ar/39Ar ages throughout the section define a weighted-mean of 31.18 ± 0.28 Ma (95% confidence). This date, together with solely normal polarity magnetization directions in 68 geomagnetically independent horizons, constrain the eruption to within chron C12n, with a maximum duration of a few hundreds of kyr for the entire 1-km-thick section. The rate of geomagnetic secular variation used as a chronometer refines the duration to only a few tens of kyr, leading to a local extrusion rate of 4–13 km3/yr for the Afar plume head, which greatly exceeds the average rate of 0.3–1.2 km3/yr for the entire Ethiopia-Yemen Traps.