Crustal tomographic imaging of a transitional continental rift: the Ethiopian rift

Daly, Eve; Keir, Derek; Ebinger, C. J.; Stuart, G. W.; Bastow, I. D.; Ayele, Atalay

doi:10.1111/j.1365-246x.2007.03682.x

Cited by 80 publications

(90 citation statements)

References 76 publications

(173 reference statements)

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“…Crustal seismic tomography and gravity analysis show zones of high seismic velocity and high density at~7-10-km-depth below discrete segments of the WFB, interpreted as composed of predominantly cooled mafic intrusions (Keranen et al, 2004;Tiberi et al, 2005;Daly et al, 2008). These intrusions combined with faulting and fracturing of the crust, likely accommodated most of the extension (Keir et al, 2006(Keir et al, , 2011a.…”

Section: Study Areamentioning

confidence: 99%

“…Local earthquakes were derived from arrival times of earthquakes at four or more seismic stations composing the 2001-2003 EAGLE seismic network (Keir et al, 2006;Bastow et al, 2011), and using a best-fit 1-D seismic velocity model (Daly et al, 2008). From October 2001 to February 2003 within the MER, 1957 earthquakes were located and local magnitudes were determined, some of which are used for focal mechanism determination (Keir et al, 2006).…”

Section: Earthquakesmentioning

confidence: 99%

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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: Study Areamentioning

confidence: 99%

Section: Earthquakesmentioning

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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“…The magmatic segments are characterised by positive Bouguer anomalies (Tessema and Antoine, 2004;Tiberi et al, 2005;Cornwell et al, 2006) and underlain by anomalously high velocity material interpreted as cooled mafic intrusions (Keranen et al, 2004;Daly et al, 2008). Keranen et al (2004) and Daly et al (2008) tomographically imaged a right-stepping pattern of high velocities between 20 km and 7 km depth in the crust beneath magmatic segments. Bastow et al (2005;2008) image a NE-trending low velocity zone in the upper mantle (75-100 km depth) beneath the Ethiopian Rift.…”

Section: Magmatic Segments In the Northern Mer And Southern Red Sea Rmentioning

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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“…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 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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Crustal tomographic imaging of a transitional continental rift: the Ethiopian rift

Abstract: 03.06.14 KB. Ok to add published paper, RAS policy

Cited by 80 publications

References 76 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

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

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