Rapid crustal transit of magmas beneath the Main Ethiopian Rift

Abstract

As continental rifts evolve towards lithospheric break-up and the formation of an ocean ridge, basaltic dyke intrusion becomes the dominant mechanism of upper-crustal extension, surpassing tectonic faulting. The magmatic architecture within the rifting crust, which governs the availability and pathways of ascending magmas, therefore has a crucial role in the transition from continental- to oceanic-style rifting. Here we use olivine Fe–Mg interdiffusion chronometry to constrain the dynamics and timescales of magma ascent beneath the Main Ethiopian Rift, a continental rift of intermediate tectonic maturity. We find that magmas move rapidly through the crust, replenishing mid-crustal reservoirs only weeks to months before intrusive-eruptive events. Such ascent timescales are comparable to those of dyke intrusion recurrence observed during active phases at more mature rifts; hence, we infer that extensional activity in the Main Ethiopian Rift is probably mediated by the supply of magma from depth. The magmatic architecture and magma ascent rates we propose for the Main Ethiopian Rift indicate that well-established magma plumbing systems, capable of efficiently delivering melts to feed upper-crustal dykes, can develop in a continental rift even before substantial lithospheric thinning has occurred. Magmas beneath the Main Ethiopian Rift ascend through the crust on timescales of only weeks to months, indicating that, during continental rifting, a magmatic plumbing system can be well established before the lithosphere has thinned.