Rift structure in southern Ethiopia

Moore, John M.; Davidson, A

doi:10.1016/0040-1951(78)90111-7

Cited by 76 publications

(50 citation statements)

References 6 publications

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“…This region is at the eastern edge of a broadly rifted zone in southern Ethiopia that accommodated extension from Oligocene-Recent times (e.g. Moore and Davidson, 1978;Davidson and Rex, 1980;Woldegabriel and Aronson, 1987;Ebinger et al, 2000). In the MER, the WFB south of 8°N exhibits geochemical characteristics that suggest a melting column at depths similar to Arba Minch, however the source heterogeneity inferred between the two regions ( Fig.…”

Section: Lithospheric Thinning In the Rift As A Function Of Latitudementioning

confidence: 94%

Insights into extensional processes during magma assisted rifting: Evidence from aligned scoria cones

Rooney

Bastow

Keir

2011

Journal of Volcanology and Geothermal Research

125

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Mechanical and magmatic processes exert first-order control on the architecture and evolution of rifts. As a continental rift develops towards a new oceanic spreading centre, extension that is initially accommodated in a broad zone of faulting and ductile stretching must transition towards a narrow zone of focused magmatic intrusion. The Main Ethiopian Rift (MER), part of the East African Rift System, is an ideal location to study this transition because it captures rifting processes during continental breakup. In this contribution we synthesise geochemical data from scoria cones in the Wonji Fault Belt (WFB) and Silti-Debre Zeyit Fault Zone (SDFZ) in the MER to provide new constraints on the development of mantle melting columns and magmatic plumbing systems since the onset of rifting. We utilize the extensive geophysical and geochemical databases, collected in the Ethiopian Rift, to show that geochemical evidence of heterogeneity in the depth of the mantle melting column which produced Quaternary rift basalts correlates with lithospheric structure. When combined with existing observations of asymmetry across the rift in terms of depth of melting column and magmatic plumbing systems, it is evident that the mechanical structure of the rift, defined during the initial stages of breakup, has played a dominant role in the initial development of magma assisted rifting in the MER. Surface structures and crustal-scale geophysical studies have suggested the WFB is analogous to a sea-floor spreading centre. However, the geochemical characteristics of rift basalts are consistent with mantle tomography that shows no evidence beneath the MER for passive magmatic upwelling beneath discrete rift segments as is observed in the ocean basins. Collectively, the Ethiopian data show that the distribution of mantle melts during the initiation of magma assisted rifting is fundamentally influenced by lithospheric structures formed during earlier syn-rift stretching.

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Section: Lithospheric Thinning In the Rift As A Function Of Latitudementioning

confidence: 94%

Insights into extensional processes during magma assisted rifting: Evidence from aligned scoria cones

Rooney

Bastow

Keir

2011

Journal of Volcanology and Geothermal Research

125

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“…Most of these, however, can be eliminated. Shear zones and metamorphic fabric within Precambrian basement rocks, where they are exposed, strike N-S, and Mesozoic rift structures strike NW 20,21 . Thus, pre-existing deformation fabric cannot explain the strong NE alignment we observe.…”

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confidence: 99%

Magma-assisted rifting in Ethiopia

Kendall

Stuart

Ebinger

et al. 2005

Nature

330

323

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The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick continental lithosphere 1,2 . However, Buck 1 has proposed that lithospheric heating by mantle upwelling and related magma production could promote lithospheric rupture at much lower stresses. Such models of mechanical versus magma-assisted extension can be tested, because they predict different temporal and spatial patterns of crustal and upper-mantle structure. Changes in plate deformation produce strain-enhanced crystal alignment and increased melt production within the upper mantle, both of which can cause seismic anisotropy 3 . The Northern Ethiopian Rift is an ideal place to test break-up models because it formed in cratonic lithosphere with minor far-field plate stresses 4,5 . Here we present evidence of seismic anisotropy in the upper mantle of this rift zone using observations of shear-wave splitting. Our observations, together with recent geological data, indicate a strong component of melt-induced anisotropy with only minor crustal stretching, supporting the magma-assisted rifting model in this area of initially cold, thick continental lithosphere.The data we analysed were collected as part of the EAGLE project (Ethiopian Afar Geophysical Lithospheric Experiment), an international multi-institutional experiment designed to investigate rifting processes in Ethiopia 6 . The Miocene-Recent Ethiopian Rift (Fig. 1) constitutes the northern part of the East African Rift system and forms one arm of a triple junction that formed on or near a mantle plume. Our study region is transitional between continental and incipient oceanic, with strain localized to ,20-km-wide zones of dyking, faulting and volcanism 6,7 . It is an ideal place to study magmatism and plate rupture, because up to 25% of the crust is extruded lava or intrusive magma 7,8 and mantle lithosphere is thin (,50 km) beneath the rift valley 9 . Seismic data were acquired in three phases of the EAGLE project 6 , two of which were designed to record passive seismicity. In phase I, 29 broad-band seismometers were deployed for 16 months with a nominal station spacing of 40 km and covering a 250 km £ 350 km region centred on the transitional part of the rift (Fig. 1). In phase II, a further 50 instruments were deployed for three months in a tighter array (nominal station spacing of 10 km) in the rift valley. Our study of mantle anisotropy is based on evidence of shear-wave splitting in the teleseismic phases SKS, SKKS and PKS recorded by these two arrays. With the longer duration array, 15 events produced usable splitting results, and with the shorter duration rift-valley array, three events produced usable results (list of events given in Supplementary Information).Shear-wave splitting analysis of the seismic phases SKS, SKKS and PKS is now a standard tool for studyi...

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“…The Omo basin is an extensional basin (Moore and Davidson, 1978;WoldeGabriel and Aronson, 1987) of half-graben system and lies within the topographic depression that separates the Ethiopian dome from the Kenyan dome. It is also situated in between the NWeSW trending prolific Muglad-Melut rift basins of south Sudan and the similarly trending highly prospective Anza basin of Kenya (Fig.…”

Section: Tectonic and Geological Settingmentioning

confidence: 99%

Analysis of gravity field to reconstruct the structure of Omo basin in SW Ethiopia and implications for hydrocarbon potential

Mammo

2012

Marine and Petroleum Geology

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Rift structure in southern Ethiopia

Cited by 76 publications

References 6 publications

Insights into extensional processes during magma assisted rifting: Evidence from aligned scoria cones

Insights into extensional processes during magma assisted rifting: Evidence from aligned scoria cones

Magma-assisted rifting in Ethiopia

Analysis of gravity field to reconstruct the structure of Omo basin in SW Ethiopia and implications for hydrocarbon potential

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