Tensional fissures and crustal extension rates in the northern part of the Main Ethiopian Rift

Williams, Frances; Williams, Martin; Aumento, F.

doi:10.1016/j.jafrearsci.2003.10.007

Cited by 123 publications

(93 citation statements)

References 47 publications

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“…This lends some support to the importance of aseismic processes (e.g., diking) in accommodating strain (Hofstetter and Beyth, 2003). Localized, rift-axial brittle failure in the Main Ethiopian Rift is manifest in development of extensional fi ssures at the surface and associated fault growth in the upper crust (e.g., Asfaw, 1982;Acocella and Korme, 2002;Acocella et al, 2003;Williams et al, 2004;Soliva and Schultz, 2008;Kidane et al, 2009). In addition to brittle strain, magma intrusion and extrusion processes in the Main Ethiopian Rift are known to have occurred episodically since historical times to the present day (e.g., Gibson, 1969;Tadesse et al, 2003;Williams et al, 2004).…”

Section: The Ethiopia Afar Geoscientifi C Lithospheric Experiments (Eamentioning

confidence: 71%

“…Localized, rift-axial brittle failure in the Main Ethiopian Rift is manifest in development of extensional fi ssures at the surface and associated fault growth in the upper crust (e.g., Asfaw, 1982;Acocella and Korme, 2002;Acocella et al, 2003;Williams et al, 2004;Soliva and Schultz, 2008;Kidane et al, 2009). In addition to brittle strain, magma intrusion and extrusion processes in the Main Ethiopian Rift are known to have occurred episodically since historical times to the present day (e.g., Gibson, 1969;Tadesse et al, 2003;Williams et al, 2004). Asfaw et al (1992) postulated that deformation in the Main Ethiopian Rift occurs primarily during episodic, magma-dominated rifting episodes similar to those observed in Iceland and the subaerial Red Sea and Aden Rifts in Afar (e.g., Abdallah et al, 1979;Björnsson et al, 1977;Wright et al, 2006;Ayele et al, 2007a;Rowland et al, 2007;Hamling et al, 2009;Keir et al, 2009a;Ebinger et al, 2010).…”

Section: The Ethiopia Afar Geoscientifi C Lithospheric Experiments (Eamentioning

confidence: 99%

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The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

Bastow¹,

Keir²,

Daly³

2011

Volcanism and Evolution of the African Lithosphere

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The Miocene-Holocene East African Rift in Ethiopia is unique worldwide because it subaerially exposes the transition between continental rifting and seafl oor spreading within a young continental fl ood 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 multidisciplinary, multi-institutional effort to understand geological processes in the region: The Ethiopia Afar Geoscientifi c Lithospheric Experiment (EAGLE). In 2001-2003, dense broadband seismological networks probed the structure of the upper mantle, while controlled-source wide-angle profi les illuminated both along-axis and across-rift crustal structure of the Main Ethiopian Rift. These seismic experiments, complemented by gravity and magnetotelluric surveys, provide important constraints on variations in rift structure, deformation mechanisms, and melt distribution prior to breakup. Quaternary magmatic zones at the surface within the rift 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 magmaassisted rifting. Mantle tomographic images reveal an ~500-km-wide low-velocity zone at ≥ ≥75 km depth in the upper mantle that extends from close to the eastern edge of the Main Ethiopian Rift westward beneath the uplifted and fl ood basaltcapped NW Ethiopian Plateau. The low-velocity zone does not interact simply with the Miocene-Holocene (rifting-related) base of lithosphere topography, but it also provides an abundant source of partially molten material that assists extension of the seismically and volcanically active Main Ethiopian Rift to the present day.

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Section: The Ethiopia Afar Geoscientifi C Lithospheric Experiments (Eamentioning

confidence: 71%

Section: The Ethiopia Afar Geoscientifi C Lithospheric Experiments (Eamentioning

confidence: 99%

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

Bastow¹,

Keir²,

Daly³

2011

Volcanism and Evolution of the African Lithosphere

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“…Seismicity within the magmatic segments of the MER is likely controlled by episodic injection of dikes . Although a major rifting event has not yet been directly observed in the MER, structural data suggest that episodes of surface fissuring and volcanic eruptions have occurred in MER magmatic segments during the last ϳ10,000 years (e.g., Asfaw, 1982Asfaw, , 1998Williams et al, 2004). Despite the current period of quiescence, hazards associated with seismicity and volcanic eruptions pose a serious risk to life and economy in the MER.…”

Section: Discussionmentioning

confidence: 99%

Local Earthquake Magnitude Scale and Seismicity Rate for the Ethiopian Rift

Keir¹,

Stuart²,

Jackson³

et al. 2006

Bulletin of the Seismological Society of America

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A calibrated local earthquake magnitude scale is essential for quantitative analyses of seismicity. In Ethiopia, effective monitoring of earthquakes and resulting assessment of seismic hazard are especially important as regions with seismic and volcanic activity coincide with regions of economic significance and population growth. We have developed a local magnitude (M L ) scale for the northern Main Ethiopian rift (MER) using earthquake data collected during 2001-2003 on 122 three-component broadband seismic stations. Waveform data from 2139 local earthquakes were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response appropriate for the original definition of local magnitude. The hypocentral distances considered are 5 to 800 km, with the best represented range from 5 to 150 km. A total of 30,908 maximum zero-to-peak amplitudes (A WA ) were incorporated into a direct linear inversion for individual earthquake local magnitudes (M L ), 244 station factors (C), and 2 linear distance-dependent factors (n, K) in the distance correction term, log (A o ), of the equation for local magnitude: M L ‫ס‬ log(A WA ) ‫מ‬ log(A o ) ‫ם‬ C. The resulting distance correction is given by ‫מ‬log(A o ) ‫ס‬ 1.196997log(r/17) ‫ם‬ 0.001066(r ‫מ‬ 17) ‫ם‬ 2, which implies that ground-motion attenuation is relatively high, consistent with ongoing magma intrusion and the presence of shallow magma reservoirs beneath the MER. Station corrections significantly reduce M L residuals and range between ‫24.0ע‬ M L units. The catalog of earthquakes is complete above M L ϳ2.1 and the annual cumulative seismicity rate follows the relation log N ‫ס‬ 4.5 ‫מ‬ 1.13 M L . Our results are critical for accurate routine quantitative analysis of past, current and, future seismicity in Ethiopia.

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“…1 and 2). These encapsulate active volcanoes (Biggs et al, 2011), aligned monogenetic cones (e.g., Ebinger and Casey, 2001;Mazzarini, 2008;Williams et al, 2004), and small-offset faults striking perpendicular to the direction of extension (Fig. 2) (e.g., Agostini et al, 2011a,b;Corti, 2008Corti, , 2009Hayward and Ebinger, 1996;Keir et al, 2011a).…”

Section: Localisation Of Strainmentioning

confidence: 99%

The development of extension and magmatism in the Red Sea rift of Afar

et al. 2013

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Despite the importance of continental breakup in plate tectonics, precisely how extensional processes such as brittle faulting, ductile plate stretching, and magma intrusion evolve in space and time during the development of new ocean basins remains poorly understood. The rifting of Arabia from Africa in the Afar depression is an ideal natural laboratory to address this problem since the region exposes subaerially the tectonically active transition from continental rifting to incipient seafloor spreading. We review recent constraints on along-axis variations in rift morphology, crustal and mantle structure, the distribution and style of ongoing faulting, subsurface magmatism and surface volcanism in the Red Sea rift of Afar to understand processes ultimately responsible for the formation of magmatic rifted continental margins. Our synthesis shows that there is a fundamental change in rift morphology from central Afar northward into the Danakil depression, spatially coincident with marked thinning of the crust, an increase in the volume of young basalt flows, and subsidence of the land towards and below sea-level. The variations can be attributed to a northward increase in proportion of extension by ductile plate stretching at the expense of magma intrusion. This is likely in response to a longer history of localised heating and weakening in a narrower rift. Thus, although magma intrusion accommodates strain for a protracted period during rift development, the final stages of breakup are dominated by a phase of plate stretching with a shift from intrusive to extrusive magmatism. This late-stage pulse of decompression melting due to plate thinning may be responsible for the formation of seaward dipping reflector sequences of basalts and sediments, which are ubiquitous at magmatic rifted margins worldwide.

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Tensional fissures and crustal extension rates in the northern part of the Main Ethiopian Rift

Cited by 123 publications

References 47 publications

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

Local Earthquake Magnitude Scale and Seismicity Rate for the Ethiopian Rift

The development of extension and magmatism in the Red Sea rift of Afar

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