Structure of Tendaho Graben and Manda Hararo Rift: Implications for the evolution of the southern Red Sea propagator in Central Afar

摘要

The Red Sea and Aden rifts (or propagators) meet in Afar. Here we use remote sensing and field analyses to define the geology and structure of the southern part of the Red Sea propagator in Central Afar. This consists of the NW-SE trending Tendaho Graben (TG) and the younger and active NW-SE trending Manda Hararo Rift (MHR), partly within TG. Tectonic and volcanic activity within TG developed mostly between ～1.8 and ～0.6 Ma, with a stretching factor β ～ 1.1, an extension rate ～3.6 mm/yr and the fissural eruption of part (～7000 km~3/Ma) of the Afar Stratoid sequence (mainly basaltic lava flows and ignimbrites). MHR, before terminating southward, has a β ～1.04 and an extension rate ～1.2 mm/yr, and is associated with the emission of ～600 km~3/Ma of basalts in the last ～0.2 Ma. These data suggest that after the exceptional amount of magma erupted between ～1.8 and ～0.6 Ma, magmatic and tectonic activity significantly decreased along the southern part of the Red Sea propagator in the last ～0.2 Ma. This decrease coincides with the on-land development and migration of the more active (inferred extension rate in the order of ～10 mm/yr, as proposed in previous studies) Aden propagator, suggesting that spreading in Central Afar mainly occurred along one active propagator at any one time.