Rapid crustal transit of magma drives magmatic rifting in Ethiopia

The evolution of a continental rift towards an ocean ridge appears to be strongly controlled by the magmatic architecture of the rifting crust. Geophysical evidence from magmatically rifted margins and active continental rifts suggests that a key stage of rift maturation is localisation of extensional activity to narrow magmatic rift zones. The dynamics of magma ascent beneath these rift zones is key to driving further crustal extension and eventual breakup. Here we constrain the dynamics and timescales of magma ascent beneath two magmatic rift zones in the Main Ethiopian Rift (MER). At both locations we find that magmas move rapidly through the crust, replenishing mid-crustal reservoirs only weeks to months before intrusive-eruptive events. Our results suggest that upper crustal rifting in the MER occurs during transient magmatic events, mediated by dynamic mid-crustal magma reservoirs. These timescales of melt ascent are notably similar to the return times of dykes observed during rifting episodes at more mature rift zones, suggesting that the onset of oceanic-style magmatic rifting of the crust can occur relatively early in the development of a continental rift system, prior to significant attenuation of the lithosphere.