Rift Focusing and Magmatism During Late-Stage Rifting in Afar

Processes that facilitate the transition between continental rifting and sea-floor spreading remain unclear. Variations in the spatial distribution of extension and magmatism through Afar and into the Red Sea are indicative of temporal evolution of the rifting process. We develop a time series of Sentinel-1 interferometric synthetic aperture radar (InSAR) observations of ground deformation covering the whole Afar rift zone from 2014 to 2019, to study the distribution of extension. By incorporating Global Navigation Satellite System observations, we resolve 3D average velocities in the vertical, rift-perpendicular, and rift-parallel directions. Results show the spatial distribution of long-wavelength deformation over the rift zone, as well as deformation at individual volcanic centers, including Dallol, Nabro, and Erta ’Ale. We find that in northern and central Afar, the majority of extension is accommodated close to the rift axis (±15–30 km). In southern Afar, near the Nubia-Arabia-Somalia triple junction, amagmatic extension is distributed over 80–160 km, which may indicate an increase in rift focusing with rift maturity. We also observe rapid surface uplift and rift-perpendicular extension at the Dabbahu-Manda-Hararo rift segment with velocities of 33 ± 4 mm/yr and 37 ± 4 mm/yr respectively. These are higher than the background extension rate of 18–20 mm/yr, but have decreased by 55%–70% since 2006–2010. The data suggests that this is due to an ongoing long-lived response to the 2005–2010 rifting episode, with potential continued processes below the rift segment including a lower-crustal viscous response and magma movement. Continued observations of surface deformation provide key constraints on tectono-magmatic processes involved in rift development.