Crustal structure of the northern Main Ethiopian Rift from the EAGLE controlled-source survey; a snapshot of incipient lithospheric break-up

Maguire, P. K. H.; Keller, G. Randy; Klemperer, S. L.; Mackenzie, G. D.; Keranen, K. M.; Harder, S. H.; O’Reilly, B. M.; Thybo, Hans; Asfaw, Laike M.; Khan, M. Aftab; Amha, Mulugeta

doi:10.1144/gsl.sp.2006.259.01.21

Cited by 140 publications

(260 citation statements)

References 69 publications

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“…Discussion has often focussed on whether the crust is completely new oceanic crust, or whether it is stretched and thinned continental crust, heavily intruded by magma (transitional crust). Constraints on crustal structure primarily come from wide-angle seismic studies (Berckhemer et al, 1975;Maguire et al, 2006;Makris and Ginzburg, 1987;Prodehl et al, 1997), teleseismic receiver function studies (Ayele et al, 2004;Dugda et al, 2005;Hammond et al, 2011;Stuart et al, 2006), and from gravity analysis (Redfield et al, 2003;Tessema and Antoine, 2004;Tiberi et al, 2005). Results achieved using these different methods are broadly consistent (e.g., Fishwick and Bastow, 2011).…”

Section: Crustal Structurementioning

confidence: 99%

“…2) (e.g., Agostini et al, 2011a,b;Corti, 2008Corti, , 2009Hayward and Ebinger, 1996;Keir et al, 2011a). In the MER, gravity and seismic imaging show that magmatic segments are underlain by dense, high seismic velocity material, interpreted as cooled gabbroic intrusions (e.g., Beutel et al, 2010;Cornwell et al, 2006;Keranen et al, 2004;Mackenzie et al, 2005;Maguire et al, 2006). Since the voluminous intrusions into the mid-upper crust appear largely restricted to beneath the Quaternary-Recent magmatic segments, it is likely that magma intrusion has only dominated extension during the past~2 Ma (Daly et al, 2008;Keranen et al, 2004).…”

Section: Localisation Of Strainmentioning

confidence: 99%

“…The crust thins abruptly to 15-30 km into Afar (Fig. 7) (e.g., Maguire et al, 2006;Stuart et al, 2006). The crust throughout Ethiopia has a consistent, unbroken layering with lower crust of Vp= 6.7-7.0 km/s, an upper crust of Vp= 6.0-6.3 km/s, and cover rocks of lava flows and sediments of Vp= 2.2-4.5 km/s (Makris and Ginzburg, 1987;Prodehl and Mechie, 1991).…”

Section: Crustal Structurementioning

confidence: 99%

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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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Section: Crustal Structurementioning

confidence: 99%

Section: Localisation Of Strainmentioning

confidence: 99%

Section: Crustal Structurementioning

confidence: 99%

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

et al. 2013

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“…Crustal structure of the MER has been imaged by recent wideangle controlled source seismic studies as well as using passive seismic techniques, both of which show crustal thickness varying from 30 to 35 km in the northern sector of the rift to about 35-40 km in the central sector (Mackenzie et al, 2005;Maguire et al, 2006;Stuart et al, 2006;Keranen and Klemperer, 2008;Keranen et al, 2009) (Fig. 2).…”

Section: Study Areamentioning

confidence: 99%

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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“…2). Beneath the MER, crustal thickness decreases from ∼ 38 km in the south to 24 km beneath Fentale volcano in the southern Afar depression, with a significant decrease north of Gedemsa volcano (Dugda et al, 2005;Maguire et al, 2006) (Fig. 3).…”

Section: Tectonic Settingmentioning

confidence: 99%

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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Crustal structure of the northern Main Ethiopian Rift from the EAGLE controlled-source survey; a snapshot of incipient lithospheric break-up

Cited by 140 publications

References 69 publications

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

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

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

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