Why is Africa rifting?

Kendall, J.‐M.; Lithgow‐Bertelloni, Carolina

doi:10.1144/sp420.17

Cited by 43 publications

(55 citation statements)

References 112 publications

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“…Although gaps remain in our knowledge of the Western rift and beneath the Indian Ocean, the lowest P and S wave velocity regions underlie the Main Ethiopian Rift (MER) and the Eastern rift zone and the isolated volcanic provinces of the Western rift (e.g., Adams et al, ; Bastow et al, ; Fishwick, ; O'Donnell et al, ). The Ethiopia‐Yemen and East African Plateaux are separated by an ~300 km wide topographic depression that is underlain by crust stretched during Mesozoic rifting, allowing the possibility that the two plateaux are actually one uplifted region extending from southern Africa to the Red Sea: the African superplume province (e.g., Kendall & Lithgow‐Bertelloni, ; Nyblade & Robinson, ; Ritsema et al, ).…”

Section: Geodynamic Settingsmentioning

confidence: 99%

Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

et al. 2017

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The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow‐moving African continent, which last experienced orogeny during the Pan‐African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas‐rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises ~20% new magmatic material ponded in the lower crust and intruded as sills and dikes at shallower depths. In the Main Ethiopian Rift, intrusions comprise 30% of the crust below axial zones of dike‐dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow‐spreading ridges. Our comparisons suggest that transitional crust, including seaward dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15–20 km thick crust. In the 30 Ma Recent CVL, which lacks a hot spot age progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hot spot toward the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology, and contributing significantly to global carbon and water fluxes.

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Section: Geodynamic Settingsmentioning

confidence: 99%

Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

et al. 2017

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“…Active faulting and magmatism occur across a large part of the African continent above one of Earth's largest mantle upwellings, the African Superplume [e.g., Nyblade and Robinson , ; Mulibo and Nyblade , ; Kendall and Lithgow‐Bertelloni , ]. The Eastern (Gregory) rift marks the divergent plate boundary between the slowly opening (≤6 mm yr −1 ) Nubia and Somalia plates [e.g., Saria et al ., ; Birhanu et al ., ] (Figure and supporting information Figure SM1).…”

Section: Introductionmentioning

confidence: 99%

Fault‐magma interactions during early continental rifting: Seismicity of the Magadi‐Natron‐Manyara basins, Africa

Weinstein

Oliva

Ebinger

et al. 2017

Geochem Geophys Geosyst

100

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Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2‐D studies. We analyze seismicity data from a 13 month, 39‐station broadband seismic array to determine the role of magma intrusion on state‐of‐stress and strain localization, and their along‐strike variations. Precise earthquake locations using cluster analyses and a new 3‐D velocity model reveal lower crustal earthquakes beneath the central basins and along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6–10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b‐value of 0.87 ± 0.03. Focal mechanisms for 65 earthquakes, and 13 from a catalogue prior to our array reveal an along‐axis stress rotation of ∼60° in the magmatically active zone. New and prior mechanisms show predominantly normal slip along steep nodal planes, with extension directions ∼N90°E north and south of an active volcanic chain consistent with geodetic data, and ∼N150°E in the volcanic chain. The stress rotation facilitates strain transfer from border fault systems, the locus of early‐stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Results indicate that earthquakes are largely driven by stress state around inflating magma bodies.

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“…Preexisting variations in lithospheric thickness, such as unusually thick Archaean cratons, can enhance or modify mantle flow and melt production (e.g., Sleep et al, 2002). Horizontal and vertical forces induced by the dynamic flow lead to lithospheric thinning and heating as well as melt generation, but the spatial distribution of the forces remains debated (e.g., Birhanu et al, 2016;Kendall & Lithgow-Bertelloni, 2016;Stamps et al, 2014). In some areas, the mantle plume transfers heat, magma, and volatiles to the African plate, changing its composition and structure over time (e.g., Bastow & Keir, 2011;Ebinger & Sleep, 1998;Lee et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Seismic Anisotropy of the Upper Mantle Below the Western Rift, East Africa

et al. 2018

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Although the East African rift system formed in cratonic lithosphere above a large‐scale mantle upwelling, some sectors have voluminous magmatism, while others have isolated, small‐volume eruptive centers. We conduct teleseismic shear wave splitting analyses on data from 5 lake‐bottom seismometers and 67 land stations in the Tanganyika‐Rukwa‐Malawi rift zone, including the Rungwe Volcanic Province (RVP), and from 5 seismometers in the Kivu rift and Virunga Volcanic Province, to evaluate rift‐perpendicular strain, rift‐parallel melt intrusion, and regional flow models for seismic anisotropy patterns beneath the largely amagmatic Western rift. Observations from 684 SKS and 305 SKKS phases reveal consistent patterns. Within the Malawi rift south of the RVP, fast splitting directions are oriented northeast with average delays of ~1 s. Directions rotate to N‐S and NNW north of the volcanic province within the reactivated Mesozoic Rukwa and southern Tanganyika rifts. Delay times are largest (~1.25 s) within the Virunga Volcanic Province. Our work combined with earlier studies shows that SKS‐splitting is rift parallel within Western rift magmatic provinces, with a larger percentage of null measurements than in amagmatic areas. The spatial variations in direction and amount of splitting from our results and those of earlier Western rift studies suggest that mantle flow is deflected by the deeply rooted cratons. The resulting flow complexity, and likely stagnation beneath the Rungwe province, may explain the ca. 17 Myr of localized magmatism in the weakly stretched RVP, and it argues against interpretations of a uniform anisotropic layer caused by large‐scale asthenospheric flow or passive rifting.

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Why is Africa rifting?

Cited by 43 publications

References 112 publications

Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

Fault‐magma interactions during early continental rifting: Seismicity of the Magadi‐Natron‐Manyara basins, Africa

Seismic Anisotropy of the Upper Mantle Below the Western Rift, East Africa

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