The Afar Rift

Afar has been created by the separation of the Nubian, Arabian, and Somalian Plates during the past 30 Ma (Fig. 1) [Barberi and Varet, 1977; Courtillot, 1980; Ebinger et al., 2010]. Extension occurs along three rift branches, the Red Sea, the Gulf of Aden, and the Main Ethiopian Rift (MER). Current full spreading velocities are 18 mm/yr between Nubia and Arabia, 16 mm/yr for the Somalian–Arabian Plates, and 6 mm/yr for Nubia–Somalia [McClusky et al., 2010; Saria et al., 2014; Vigny et al., 2006]. 

The Red Sea and Gulf of Aden rifts are extending in a NE-SW direction, and are effectively decoupled from the much slower, E-W extension in the MER. Rifting along the southern Red Sea started at ~30 Ma after a major pulse of flood magmatism. Extension was initially accommodated on large border faults (thick black lines in Fig. 1) but later (last ~4 Ma) it localized to < 30 km-wide, ~50 km-long axial magmatic segments, which mark the axis of the active plate boundary from latitude ~15 to 12N in the Red Sea rift, and south of 11N in the MER (red fillings in Fig.1). Similar patterns occur in the Gulf of Aden rift (Asal-Ghoubbet rift) (Fig. 1). Between the clear segmentation of the Red Sea and Gulf of Aden rifts, from latitude 12 to 11N, mainly tectonic extensional rifts without recent (Holocene) volcanism occur (black lines in Fig. 1).

References

✔ Barberi, F., and J. Varet (1977), Volcanism of Afar - Small-Scale Plate Tectonics Implications, Geol Soc Am Bull, 88(9), 1251-1266.

✔ Courtillot, V. E. (1980), Opening of the Gulf of Aden and Afar by progressive tearing, Physics of the Earth and Planetary Interiors, 21(4), 343-350.

✔ Ebinger, C., A. Ayele, D. Keir, J. Rowland, G. Yirgu, T. Wright, M. Belachew, and I. Hamling (2010), Length and Timescales of Rift Faulting and Magma Intrusion: The Afar Rifting Cycle from 2005 to Present, Annual Review of Earth and Planetary Sciences, 38(1), 439-466.

✔ McClusky, S., et al. (2010), Kinematics of the southern Red Sea-Afar Triple Junction and implications for plate dynamics, Geophys Res Lett, 37.

✔ Saria, E., E. Calais, D. S. Stamps, D. Delvaux, and C. J. H. Hartnady (2014), Present-day kinematics of the East African Rift, Journal of Geophysical Research: Solid Earth, 119(4), 3584-3600.

✔ Vigny, C., P. Huchon, J. C. Ruegg, K. Khanbari, and L. M. Asfaw (2006), Confirmation of Arabia plate slow motion by new GPS data in Yemen, J Geophys Res-Sol Ea, 111(B2).