Structure of the Ethiopian lithosphere: Xenolith evidence in the Main Ethiopian Rift

Rooney, Tyrone O.; Furman, Tanya; Yirgu, Gezahegn; Ayalew, Dereje

doi:10.1016/j.gca.2005.03.043

Cited by 109 publications

(147 citation statements)

References 81 publications

(111 reference statements)

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“…Vent self-similar clustering along the central MER has an upper cut off of~11 km (Table 1), in accordance with estimates by and Mazzarini et al (2013). Controlled source seismic imaging shows that along the volcanic belts below~7-10 km depth the crust is heavily modified by dense gabbroic intrusions (Keranen et al, 2004;Rooney et al, 2005;Maguire et al, 2006;Keranen et al, 2009). Above these, the uppermost crust is intruded by basaltic sheeted dykes to a lesser extent, with these intrusions feeding vent eruptions (Ebinger and Casey, 2001).…”

Section: Self-similar Clusteringsupporting

confidence: 77%

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

Mazzarini

Keir

Isola

2013

Journal of Volcanology and Geothermal Research

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During the breakup of continents extension is commonly accommodated by connected networks of fluid filled fractures (dykes) and by faults. Despite the importance of these two extension mechanisms their spatial relationship in three dimensions is poorly understood primarily because it is difficult to quantify the subsurface distribution of faulting and intrusion. In order to address this problem, we conduct a quantitative analysis of the spatial distribution and clustering of earthquakes and volcanic vents in the Main Ethiopian Rift in East Africa in order to understand how extension by faulting and intrusion is distributed throughout the volcanic rift. We use fractal analysis of earthquake epicentres in order to infer the 2D characteristics of the subsurface fault network, and directly test our model results against the 3D distribution of earthquake hypocentres. Our results show that fractal analysis of these features is a reliable means to characterise the 3D properties of the fault network. In addition, the strong similarity between the properties of the fault network derived from earthquakes and properties of the magma-filled fracture network derived from fractal analysis of volcanic vents strongly suggests that these are genetically linked. We then explore their spatial link using computation of earthquake and vent density, which shows that the zone of seismicity is generally around 20-30-km-wide, while the zone of vents is narrower and centred within the zone of seismicity. This spatial relationship suggests that the faults, which form rift axial grabens, are induced above a narrower and central zone of diking. We also demonstrate significant along-rift variation in degree of magmatism and faulting with regions of increased degree of diking inferred from a higher cone density characterised by reduced degree of faulting.

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Section: Self-similar Clusteringsupporting

confidence: 77%

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

Mazzarini

Keir

Isola

2013

Journal of Volcanology and Geothermal Research

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“…P-and S-wave tomography models indicate that the lithosphere-asthenosphere boundary lies at ∼ 70 km below the surface with anomalous low velocity zones in the upper asthenosphere 2008). Major element compositions of Quaternary mafic lavas from the MER are derived from parental melts generated at depths of 60-75 km (Rooney et al, 2005;Furman et al, 2006), consistent with the tomographic estimates of the lithosphere-asthenosphere boundary. Analyses of SKS and crustal splitting observations indicate that partial melt accumulates in vertically oriented dykes that cross-cut the lithosphere Keir et al, 2005).…”

Section: Tectonic Settingsupporting

confidence: 65%

Formation and stability of magmatic segments in the Main Ethiopian and Afar rifts

Beutel

Wijk

Ebinger

et al. 2010

Earth and Planetary Science Letters

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Editor: R.D. van der HilstKeywords: East African Rift continental rifting magmatic intrusion stress lithospheric extension rupturing continental lithosphere As rifting progresses to seafloor spreading, extension within the continental crust commonly is accommodated by a combination of fault slip and dike intrusion. Consistent patterns in the spatial arrangement of long-lived magma intrusion zones in the Ethiopian and Afar rift sectors, East Africa, suggest that the magma intrusions help to localize strain during repeated rifting episodes. Within the broad Main Ethiopian Rift, extensional deformation has localized since ∼ 3 m.y. in narrow magmatic segments, that are oriented oblique to the orientation of the Miocene border faults, but (sub-) orthogonal to the extension direction. Numerical models combined with geophysical and geological observations from East Africa are used to examine the viability of self-sustaining magmatic segmentation. Initiation of the magmatic segments is shown to result from magma injections, which focus strain in narrow elongated zones. During magmatic phases of segment evolution the segments are weak, and extensional stresses localize at the rift tips, promoting along-axis lengthening. During amagmatic phases of extension, the numerical models predict strain localization within the magmatic segments and, to a lesser extent, broadly distributed extension within the rift zone. This promotes segment stability; the segments remain the preferred location for magma intrusion during new magmatic phases. These results are applied to the formation and maintenance of MER segmentation. The Fentale-Dofen segment is currently in a non-magmatic phase of extension; the Dabbahu segment in the Red Sea Rift is currently experiencing a rifting episode and therefore is in a transient magmatic cycle. The observed patterns of instantaneous localized deformation, seismicity, and dike intrusions sometimes propagating beyond the tip of the magmatic segments occur as predicted by the models.

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“…Patterns between both series broadly correlate though Group 2 samples extend to depleted values of the more compatible elements, and higher values of Nb-Ta in comparison to other HT-1 basalts. (c) Group 3 basalts are shown in comparison to Quaternary volcanic rocks from the Main Ethiopian Rift (Rooney et al, 2005;Furman et al, 2006;Rooney et al, 2007;Rooney, 2010). Our Group 3 differs markedly from the Quaternary rift-floor volcanic in the MER by having much more enriched values of HREE and an overall flatter trace element profile.…”

Section: Group 4 Dikes ($25-12 Ma)mentioning

confidence: 74%

“…(Pik et al, 1999;Kieffer et al, 2004;Beccaluva et al, 2009) and Yemen (Baker et al, 1996b). (a) MgO-X diagrams illustrating the variance between our Group 3 and the 10 MaRecent activity in MER of Ethiopia (Rooney et al, 2005;Furman et al, 2006;Rooney et al, 2007;Rooney, 2010), Pliocene-Quaternary Djibouti, Quaternary Asal Rift, and 4-9 Ma Dahla series (Deniel et al, 1994). (b) MgO-X diagrams illustrating the variance between the rift margin and shield building phase of the Ethiopian plateau and Group 4 of this study.…”

Section: Group 4 Dikes ($25-12 Ma)mentioning

confidence: 87%

“…Thus, the initial phase of rifting above a mantle plume may be marked by a pulse of widespread dike intrusion (e.g., Renne et al, 1996;Fialko and Rubin, 1999;Klausen and Larsen, 2002). During the later stages of continental rifting, extension occurs principally by dike intrusion into a thinned lithosphere (Ebinger and Casey, 2001;Keranen et al, 2004;Rooney et al, 2005;Daly et al, 2008;Keir et al, 2009;Bastow et al, 2010;Ebinger et al, 2010;Wright et al, 2012), before a final stage of plate stretching and associated decompression melting characterizing the final stages of continentocean transition (e.g., Bastow and Keir, 2011). Key unresolved questions remain concerning the geochemical signature(s) of the melt sources during the initial stages of continental rifting, and the evolution of these sources as rifting continues.…”

Section: Introductionmentioning

confidence: 99%

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Geochemical evidence of mantle reservoir evolution during progressive rifting along the western Afar margin

Rooney

Mohr

Dosso

et al. 2013

Geochimica et Cosmochimica Acta

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evidence of mantle reservoir evolution during progressive rifting along the western Afar margin. Geochimica et Cosmochimica Acta, Elsevier, 2013Elsevier, , 102, pp.65-88. 10.1016Elsevier, /j.gca.2012 Geochemical evidence of mantle reservoir evolution during progressive rifting along the western Afar margin AbstractThe Afar triple junction, where the Red Sea, Gulf of Aden and African Rift System extension zones converge, is a pivotal domain for the study of continental-to-oceanic rift evolution. The western margin of Afar forms the southernmost sector of the western margin of the Red Sea rift where that margin enters the Ethiopian flood basalt province. Tectonism and volcanism at the triple junction had commenced by $31 Ma with crustal fissuring, diking and voluminous eruption of the EthiopianYemen flood basalt pile. The dikes which fed the Oligocene-Quaternary lava sequence covering the western Afar rift margin provide an opportunity to probe the geochemical reservoirs associated with the evolution of a still active continental margin. 40 Ar/ 39 Ar geochronology reveals that the western Afar margin dikes span the entire history of rift evolution from the initial Oligocene flood basalt event to the development of focused zones of intrusion in rift marginal basins. Major element, trace element and isotopic (Sr-Nd-Pb-Hf) data demonstrate temporal geochemical heterogeneities resulting from variable contributions from the Afar plume, depleted asthenospheric mantle, and African lithosphere. The various dikes erupted between 31 Ma and 22 Ma all share isotopic signatures attesting to a contribution from the Afar plume, indicating this initial period in the evolution of the Afar margin was one of magma-assisted weakening of the lithosphere. From 22 Ma to 12 Ma, however, diffuse diking during continued evolution of the rift margin facilitated ascent of magmas in which depleted mantle and lithospheric sources predominated, though contributions from the Afar plume persisted. After 10 Ma, magmatic intrusion migrated eastwards towards the Afar rift floor, with an increasing fraction of the magmas derived from depleted mantle with less of a lithospheric signature. The dikes of the western Afar margin reveal that magma generation processes during the evolution of this continental rift margin are increasingly dominated by shallow decompressional melting of the ambient asthenosphere, the composition of which may in part be controlled by preferential channeling of plume material along the developing neo-oceanic axes of extension.

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Structure of the Ethiopian lithosphere: Xenolith evidence in the Main Ethiopian Rift

Cited by 109 publications

References 81 publications

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

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

Formation and stability of magmatic segments in the Main Ethiopian and Afar rifts

Geochemical evidence of mantle reservoir evolution during progressive rifting along the western Afar margin

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