Fault architecture in the Main Ethiopian Rift and comparison with experimental models: Implications for rift evolution and Nubia–Somalia kinematics

Abstract

The Main Ethiopian Rift (MER) offers a complete record of the time-space evolution of a continental rift. We have characterized the brittle deformation in different rift sectors through the statistical analysis of a new database of faults obtained from the integration between satellite images and digital elevation models, and implemented with field controls. This analysis has been compared with the results of lithospheric-scale analogue models reproducing the kinematical conditions of orthogonal and oblique rifting. Integration of these approaches suggests substantial differences in fault architecture in the different rift sectors that in turn reflect an along-axis variation of the rift development and southward decrease in rift evolution. The northernmost MER sector is in a mature stage of incipient continental rupture, with deformation localised within the rift floor along discrete tectono-magmatic segments and almost inactive boundary faults. The central MER sector records a transitional stage in which migration of deformation from boundary faults to faults internal to the rift valley is in an incipient phase. The southernmost MER sector is instead in an early continental stage, with the largest part of deformation being accommodated by boundary faults and almost absent internal faults. The MER thus records along its axis the typical evolution of continental rifting, from fault-dominated rift morphology in the early stages of extension toward magma-dominated extension during break-up. The extrapolation of modelling results suggests that a variable rift obliquity contributes to the observed along-axis variations in rift architecture and evolutionary stage, being oblique rifting conditions controlling the MER evolution since its birth in the Late Miocene in relation to a constant post ca. 11 Mã N100°E Nubia-Somalia motion.

Structural controls on fluid pathways in an active rift system: A case study of the Aluto volcanic complex

“…Geodetic and seismic data (Bendick et al, 2006;Keir et al, 2006;Stamps et al, 2008) indicate that the current E-W (~N100°E) extension rates are 4-6 mm yr -1 . The MER is usually divided into three sectors (northern, central, and southern) that reflect differences in terms of the spatial pattern of the faulting (Agostini et al, 2011), the timing of the major faulting episodes (Woldegabriel et al, 1990;Wolfenden et al, 2004;Bonini et al, 2005), and the thermal-mechanical state of the lithosphere (e.g., Keranen and Klemperer , 2008). This pattern is consistent with rift maturity increasing northward along the MER toward Afar, where the overall physiology changes from continental rifting to incipient oceanic spreading (Beutel et al, 2010;Ebinger et al, 2010;Ferguson et al, 2013).…”

“…For example, Acocella et al (2003) identified a number of E-W-oriented pre-rift tectonic structures on the flanks of the MER and invoked these to explain elongate calderas at Fentale, Kone, and Gedemsa. We investigated fault maps of the MER presented by Acocella et al (2003), Abebe et al (2007), and Agostini et al (2011), as well as our own satellite imagery and could not highlight any clear E-W structures on the rift plateau adjacent to Aluto. On the other hand, however, the E-W elongation of the Aluto caldera is almost orthogonal to the active Wonji faults of the central MER (Fig.…”

Influence of regional tectonics and pre-existing structures on the formation of elliptical calderas in the Kenyan Rift

“…Further complexity is observed in the MER, where the reactivation of pre-existing lithospheric weaknesses during extension has led to the development of rift border faults that are oblique to both the main rift trend and the extension direction (e.g. Agostini et al 2011). For MER segments that have a low/ moderate obliquity angle between the rift trend and the extension orientation (15 -458), the intra-rift fault orientation tends to form orthogonal to the 4.…”

Spatial relationship between earthquakes and volcanic vents in the central-northern Main Ethiopian Rift

“…At the northern end of the EARS, the volcanically active Main Ethiopian Rift (MER) records the transition from continental rifting to seafloor spreading in the Red Sea and Gulf of Aden (Hayward and Ebinger, 1996;Ebinger and Casey, 2001;Bonini et al, 2005;Corti, 2009;Agostini et al, 2011a). The rift valley in the MER separates the Ethiopian and Somalian plateaus, which are capped with Eocene-Oligocene flood basalts, isolated OligoceneMiocene shield volcanoes and Quaternary scoria cone fields (Kieffer et al, 2004;Rooney et al, 2011).…”