Rift Focusing and Magmatism During Late‐Stage Rifting in Afar. Issue 10 (16th October 2021)

• Record Type: Journal Article
• Authors: Moore, C.; Wright, T. J.; Hooper, A.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 10(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-10-16
• Subjects: rift -- InSAR -- magmatism -- Afar -- surface velocities; 1240 -- 8109 -- 8485 -- 8416 -- 3270; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2020JB021542
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: 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. Plain Language Summary: The Afar region, which includes parts of Northern Ethiopia, Djibouti and Eritrea, is located where three tectonic plates are pulling apart. This "rifting" occurs in segments, each of which is 50–100 km long. Some segments are associated with extensive volcanic activity, with intrusions of molten rock (magma) along the rift causing extension; others lack magma and extension occurs through slip on tectonic faults. Deformation is not constant in time, with "episodes" of rifting occurring periodically and magma intrusions causing sudden ground movements. We process large quantities of radar data from the European Sentinel‐1 satellites to measure very precisely the ground movements that occurred during the period 2014–2019, combining the data from different satellite tracks to produce maps of the ground movement in three directions (perpendicular to the rift zone, parallel to the rift zone, and vertical). The data show that extension is tightly focused around the volcanic segments and broadly distributed around those lacking volcanism. One segment, where a major rifting episode occurred between 2005 and 2010, still shows accelerated motions; at least four volcanic centers show evidence of subsurface magma movement. Continued observation of these time‐varying ground movements is important for understanding how continents breakup. Key Points: From Sentinel‐1 interferometric synthetic aperture radar and Global Navigation Satellite System observations, we resolve 3D average surface velocities from 2014 to 2019 across the whole Afar rift zone Extension is tightly focused around magmatic segments in northern Afar, but is distributed over 80–160 km in central and southern Afar We observe current surface deformation at the Dallol, Erta 'Ale, Nabro, and Dabbahu‐Manda‐Hararo volcanic centers, demonstrating their activity