The Miocene–Recent East African rift in Ethiopia is unique worldwide because it exposes subaerially the transition between continental rifting and sea-floor spreading within a young continental flood basalt province. As such, it is an ideal study locale for continental breakup processes and hotspot tectonism. Here we review the results of a recent multi-disciplinary, multi-institutional effort to understand geological processes in the region: The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE). In 2001–3 dense broadband seismological networks probed the structure of the upper-mantle, while controlled source wide-angle profiles illuminated both along-axis and across-rift crustal structure of the Main Ethiopian rift (MER). These seismic experiments, complemented by gravity and magnetotelluric surveys, have provided important constraints on variations in rift structure, deformation mechanisms, and melt distribution prior to break-up. Quaternary magmatic zones at the surface within the MER are underlain by high-velocity, dense gabbroic intrusions that accommodate extension without marked crustal thinning. A magnetotelluric study illuminated partial melt in the Ethiopian crust, consistent with an overarching hypothesis of magma assisted rifting. Mantle tomographic images reveal a ~500 km wide low-velocity zone at ≥75 km depth in the upper-mantle that extends from close to the eastern edge of the MER westwards beneath the uplifted and flood basalt-capped NW Plateau. The low-velocity zone does not interact simply with the Miocene–Recent (rifting-related) base of lithosphere topography, but provides an abundant source of partially molten material that assists extension of the seismically and volcanically active MER to the present day.

Some of my Publications Related to Project EAGLE

2011


• T.O. Rooney, C. Herzberg & I.D. Bastow. Elevated mantle temperature beneath East Africa. Geology, G32382, doi: 10.1130/G32382.1, in press 2011.


• J. Biggs, I.D. Bastow, D. Keir & E. Lewi. Pulses of deformation reveal frequently recurring shallow magmatic activity beneath the Main Ethiopian Rift. Geochem. Geophys. Geosyst., doi:10.1029/2011GC003662, 2011.


• I.D. Bastow & D. Keir. The protracted development of the continent-ocean transition in Afar. Nature Geoscience, doi:10.1038/NGEO01095, 2011.


• I.D. Bastow, D. Keir & E. Daly, The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading, in Beccaluva, L., Bianchini, G., and Wilson, M., eds., Volcanism and Evolution of the African Lithosphere: Geological Society of America Special Paper 478, 1-26, doi:10.1130/2011.2478(04), 2011.


• T.O. Rooney, I.D. Bastow & D. Keir. Insights into Extensional Processes During Magma Assisted Rifting: Evidence from Aligned Scoria Cones and Maars. J. Volcanol. Geotherm. Res., doi:10.1016/j.jvolgeores.2010.07.019, 83-96, 2011.


• S. Fishwick & I.D. Bastow. Towards a better understanding of African topography: A review of passive-source seismic studies of the African crust and upper mantle, in Out of Africa: a synopsis of 3.8 Ga of Earth History, eds. van Hinsbergen, D.J.J., Buiter, S., Torsvik, T.H., Gaina, C. and Webb, S., Geol. Soc. Lond. Spec. Pub., 357, 343-371, doi:10.1144/SP357.19, 2011.


• D. Keir, C. Pagli, I.D. Bastow & A. Ayele. The magma-assisted removal of Arabia in Afar: evidence from dike injection in the Ethiopian rift captured using InSAR and seismicity. Tectonics, doi:10.1029/2010TC002785, 2011.



2010


• T.O. Rooney, I.D. Bastow, D. Keir. Insights into Extensional Processes During Magma Assisted Rifting: Evidence from Aligned Scoria Cones and Maars. J. Volcanol. Geotherm. Res., doi:10.1016/j.jvolgeores.2010.07.019, 2010.


• I.D. Bastow, S. Pilidou, J-M., Kendall, G.W. Stuart. Melt-Induced Seismic Anisotropy and Magma Assisted Rifting in Ethiopia: Evidence from Surface Waves. Geochem. Geophys. Geosyst., Q0AB05, doi:10.1029/2010GC003036, 2010.



2009


• D.B. Keir, I.D. Bastow, E. Daly, D. Cornwell and K.A. Whaler. Lower-crustal earthquakes near the Ethiopian rift induced by magmatic processes. Geochem. Geophys. Geosyst., doi:10.1029/2009GC002382, 2009.



2008


• I.D. Bastow, A.A. Nyblade, G.W. Stuart, T. Rooney and M.H. Benoit. Upper Mantle Seismic Structure Beneath the Ethiopian Hotspot: Rifting at the Edge of the African Low Velocity Anomaly. Geochem. Geophys. Geosyst., 9(12), doi:10.1029/2008GC002107), 2008.
  Additional images from the tomographic models presented in this paper are available here.


• E. Daly, D. Keir, C.J. Ebinger, G.W. Stuart, I.D. Bastow and A. Ayele. Crustal tomographic imaging of a transitional continental rift: the Ethiopian Rift. Geophys. J. Internat., 10.1111/j.1365-246X.2007.03682.x, 2008.



2007




• A. Ayele, G.W. Stuart, I.D. Bastow, and D. Keir. The August 2002 earthquake sequence in north Afar: insights into the neotectonics of the Danakil microplate. J. Afr. Earth Sci., 48, 70-79, doi:10.1016/j.jafrearsci.2006.06.011, 2007.


• T.O. Rooney, T. Furman, I.D. Bastow, D. Ayalew, and G. Yirgu. Lithospheric modification during crustal extension in the Main Ethiopian Rift. J. Geophys. Res., 112, B10201, doi:10.1029/2006JB004916, 2007.



2006


• J.-M. Kendall, S. Pilidou, D. Keir, I.D. Bastow, Stuart G.W., and A. Ayele. Mantle upwellings, melt migration and the rifting of Africa: Insights from seismic anisotropy, in The Structure and Evolution of the East African Rift System in the Afar Volcanic Province, eds. Yirgu, G., Ebinger, C.J. & Maguire, P.K.H. Geol. Soc. Lond. Spec. Pub., 259:271–293, 2006. (note - 22Mb).


• G.W. Stuart, I.D. Bastow, and C.J. Ebinger. Crustal structure of the northern Main Ethiopian rift from receiver function studies, in The Structure and Evolution of the East African Rift System in the Afar Volcanic Province, eds. Yirgu, G., Ebinger, C.J. & Maguire, P.K.H. Geol. Soc. Lond. Spec. Pub., 259:271–293, 2006.



2005


• I.D. Bastow, G.W. Stuart, J-M. Kendall, and C.J. Ebinger. Upper-mantle seismic structure in a region of incipient continental breakup: northern Ethiopian rift. Geophys. J. Internat., doi: 10.1111/j.1365-246X.2005.02666.x, 2005.


• J.-M. Kendall, G.W. Stuart, C.J. Ebinger, I.D. Bastow, and D. Keir. Magma assisted rifting in Ethiopia. Nature, doi:10.1038/nature03161 433:146–148, 2005.