Lower crustal earthquakes near the Ethiopian rift induced by magmatic processes

Keir, Derek; Bastow, I. D.; Whaler, Kathryn A.; Daly, Eve; Cornwell, David G.; Hautot, Sophie

doi:10.1029/2009gc002382

Cited by 90 publications

(135 citation statements)

References 81 publications

(98 reference statements)

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“…These spatial variations in crustal thickness in Ethiopia correlate well with variations in effective elastic plate thickness (Te), with strongest plate (Te ≈ 60 km) beneath the plateaus, and weakest plate (Te ≈ 6 km) beneath the Danakil depression Pérez-Gussinyé et al, 2009). Both crustal thickness and plate strength also correlate with variations in seismogenic layer thickness, which is 25-30 km beneath the Ethiopian plateau (Keir et al, 2009a) and~5 km beneath the Danakil depression (Craig et al, 2011).…”

Section: Crustal Structurementioning

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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Section: Crustal Structurementioning

confidence: 99%

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

et al. 2013

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“…These intrusions combined with faulting and fracturing of the crust, likely accommodated most of the extension (Keir et al, 2006(Keir et al, , 2011a. High conductivities observed at both~2-km and~15-km-depth in a magnetotelluric survey across Boset volcano (Whaler and Hautot, 2006;Keir et al, 2009), combined with b10-km-deep magma bodies beneath Corbetti, Aluto, Bora, Haledebi and Ayelu-Amoissa volcanoes modelled from InSAR data (Biggs et al, 2011;Keir et al, 2011b), suggests persistence of meltrich zones in both mid-and upper crust beneath many QuaternaryRecent volcanic centres.…”

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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“…45-30 Ma) and modifi ed by subsequent Miocene-to-Holocene rifting in the Main Ethiopian Rift. Recent analyses of earthquake data in Ethiopia also highlight the absence of seismicity on the Somalian plate (SE) and its relative abundance on the Nubian plate (NW; Keir et al, 2009b). In places, seismicity on the NW side of the Main Ethiopian Rift is anomalously deep and most likely caused by ongoing magmatic processes (Fig.…”

Section: Rifting In Ethiopia: Geophysical Studies Of Crustal Structurmentioning

confidence: 99%

“…The cluster of deep earthquakes also coincides with a zone of particularly high conductivity (attributed to presence of fl uids such as partial melt and hydrous fl uids; Whaler and Hautot, 2006;Whaler, 2006) in the lower crust, which is positioned directly above the slowest-velocity P-wave uppermost mantle (Keir et al, 2009b). These lowercrustal earthquakes are interpreted as related to either the emplacement of magma or release of fl uids during magma crystallization (Keir et al, 2009b). Keir et al (2006bKeir et al ( , 2009b.…”

Section: Seismicitymentioning

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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Lower crustal earthquakes near the Ethiopian rift induced by magmatic processes

Cited by 90 publications

References 81 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

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

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