The lithospheric architecture of Africa: Seismic tomography, mantle petrology, and tectonic evolution

Begg, Graham; Griffin, William L.; Natapov, Lev M.; O’Reilly, Suzanne Y.; Grand, S. P.; O’Neill, Craig; Hronsky, Jon; Djomani, Yvette Poudjom; Swain, Christopher J.; Deen, T.; Bowden, Peter

doi:10.1130/ges00179.1

Cited by 492 publications

(253 citation statements)

References 157 publications

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“…Resolution is similar for both the P and S models and indicates that there can be at most only 200 km of separation between an upper and a lower mantle anomaly in order to explain a LWA that extends through the transition zone into the lower mantle, as seen in Figures 5 and 8. [32] At shallow mantle depths, the LWA beneath northwestern Zambia may represent a secondary Western rift branch extending southwestward from Lake Tanganyika, as suggested by O'Donnell et al [2013], and the fast wave speed anomaly imaged beneath the eastern and central parts of Zambia may represent a southeastward extension of the Bagweulu Block [O'Donnell et al, 2013]. To the north, the fast wave speed anomaly observed beneath the Uganda Basement Complex is likely thick Archean lithosphere [Begg et al, 2009;Adams et al, 2012]. The fast wave speed anomaly along the very northern edge of the P and S wave models extending to depths > 300 km is probably not well resolved and may be caused by vertical smearing of fast upper most mantle beneath the Uganda Basement Complex.…”

Section: Discussionmentioning

confidence: 99%

“…[6] The Precambrian tectonic framework of eastern Africa is comprised of the Archean Tanzania Craton, which likely includes the Basement Complex of northern Uganda, the Paleoproterozoic Bangweulu Block, and several Proterozoic mobile belts [Cahen et al, 1984;Begg et al, 2009] (Figure 1). This framework has been affected by two primary episodes of rifting, first during the Karoo (Permian-Jurassic) caused by the breakup of Gondwana, and then in the Cenozoic.…”

Section: Regional Geology and Tectonic Settingmentioning

confidence: 99%

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The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

Mulibo

Nyblade

2013

Geochem Geophys Geosyst

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P and S relative arrival time residuals from teleseismic earthquakes recorded on over 60 temporary AfricaArray broadband seismic stations deployed in Uganda, Tanzania, and Zambia between 2007 and 2011 have been inverted, together with relative arrival time residuals from earthquakes recorded by previous deployments, for a tomographic image of mantle wave speed variations extending to a depth of 1200 km beneath eastern Africa. The image shows a low‐wave speed anomaly (LWA) well developed at shallow depths (100–200 km) beneath the Eastern and Western branches of the Cenozoic East African rift system and northwestern Zambia, and a fast wave speed anomaly at depths ≤ 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia. At depths ≥350 km the LWA is most prominent under the central and southern parts of the East African Plateau and dips to the southwest beneath northern Zambia, extending to a depth of at least 900 km. The amplitude of the LWA is consistent with a ∼150–300 K thermal perturbation, and its depth extent indicates that the African superplume, originally identified as a lower mantle anomaly, is likely a whole mantle structure. A superplume extending from the core‐mantle boundary to the surface implies an origin for the Cenozoic extension, volcanism, and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle.

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Section: Discussionmentioning

confidence: 99%

Section: Regional Geology and Tectonic Settingmentioning

confidence: 99%

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

Mulibo

Nyblade

2013

Geochem Geophys Geosyst

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“…Today Africa is surrounded on three sides by divergent plate boundaries. Despite some compression on its northern edge, it is essentially stationary (Begg et al, 2009), however, along the East African Rift Zone the African continent is beginning to break apart (e.g. Rosendahl, 1989).…”

Section: Evolution Of the African Continentmentioning

confidence: 99%

“…After several episodes of extension and compression, continental fragments formed the first super-continents in the Proterozoic (Begg et al, 2009;Bleeker, 2003, and references therein), followed by the formation of the most recent super-continent, Gondwana in the Paleozoic. After the assemblage of Gondwana, a period of predominantly "breaking" followed.…”

Section: Introductionmentioning

confidence: 99%

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Weckmann

2011

Surv Geophys

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The African continent inherits a long history of continental accretion and breakup. The stage of "making" a continent goes back to the Archean, when the first continental masses formed cratons which mostly remained stable ever since. Subsequent collision of weaker continental masses was followed by several extension and compression episodes that resulted in the formation of supercontinents. After the assemblage of Gondwana, a period of predominantly "breaking" , i.e. the breakup of supercontinents, took over. The modern day African continent exhibits different types of margins; continental rifting occurs side by side with recent collision. Since the late 1960's Magnetotelluric (MT) experiments have played an important role in studies of the electrical conductivity structure of Africa. The early results significantly shaped the MT community's understanding of continental scale conductivity belts and basic characteristics of cratons and mobile belts on both crustal and lithospheric mantle scale for some decades. Modern MT studies in Africa have generally supported earlier results with high resistivities observed on cratons and low resistivities observed across mobile belts. Advances in instrumentation, data processing and interpretation resulted in higher resolution images of the lithosphere which in consequence induce an improved understanding of tectonic processes and geological prerequisites for the occurrence of natural resources. The high electrical conductivity of mobile belts and their relation to reactivated fault and detachment zones were often interpreted to characterize mobile belts as tectonic weak zones, which can accommodate stress and constitute zones along which continents can break. Recent breaking of the African continent can be studied on land across the East African rift; however, the lack of amphibian MT experiments across today's margins does not allow for good resolution of remnants of continental break-up processes. Naturally, the regions and the focus of the MT studies in Africa are diverse, but they all contribute to the story of making and breaking a continent.

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“…Reconstructions of past plate motion come from surface geological mapping, geochemical, geochronological, and geophysical studies [Abdelsalam et al, 2011;Begg et al, 2009;De Waele et al, 2009;Johnson et al, 2006;Pasyanos and Nyblade, 2007;Ritsema et al, 1998;Ritsema and van Heijst, 2000]. However, substantial uncertainties in reconstructing continents over geologic timescales exist as continental tectonic elements experienced heavy structural alteration, high degrees of metamorphism, erosion and sedimentary cover [Abdelsalam et al, 2002;Artemieva and Mooney, 2001;Daly, 1986;De Waele et al, 2008;Johnson et al, 2005;Liégeois et al, 2013].…”

Section: Oceanic Plate Motionmentioning

confidence: 99%

Geophysical and petrological constraints on ocean plate dynamics

Sarafian¹

2017

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This thesis investigates the formation and subsequent motion of oceanic lithospheric plates through geophysical and petrological methods. Ocean crust and lithosphere forms at mid-ocean ridges as the underlying asthenosphere rises, melts, and flows away from the ridge axis. In Chapters 2 and 3, I present the results from partial melting experiments of mantle peridotite that were conducted in order to examine the mantle melting point, or solidus, beneath a mid-ocean ridge. Chapter 2 determines the peridotite solidus at a single pressure of 1.5 GPa and concludes that the oceanic mantle potential temperature must be ~60 ºC hotter than current estimates. Chapter 3 goes further to provide a more accurate parameterization of the anhydrous mantle solidus from experiments over a range of pressures. This chapter concludes that the range of potential temperatures of the mantle beneath mid-ocean ridges and plumes is smaller than currently estimated. Once formed, the oceanic plate moves atop the underlying asthenosphere away from the ridge axis. Chapter 4 uses seafloor magnetotelluric data to investigate the mechanism responsible for plate motion at the lithosphere-asthenosphere boundary. The resulting two dimensional conductivity model shows a simple layered structure. By applying petrological constraints, I conclude that the upper asthenosphere does not contain substantial melt, which suggests that either a thermal or hydration mechanism supports plate motion. Oceanic plate motion has dramatically changed the surface of the Earth over time, and evidence for ancient plate motion is obvious from detailed studies of the longer lived continental lithosphere. In Chapter 5, I investigate past plate motion by inverting magnetotelluric data collected over eastern Zambia. The conductivity model probes the Zambian lithosphere and reveals an ancient subduction zone previously suspected from surface studies. This chapter elucidates the complex lithospheric structure of eastern Zambia and the geometry of the tectonic elements in the region, which collided as a result of past oceanic plate motion. Combined, the chapters of this thesis provide critical constraints on ocean plate dynamics.

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The lithospheric architecture of Africa: Seismic tomography, mantle petrology, and tectonic evolution

Cited by 492 publications

References 157 publications

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Geophysical and petrological constraints on ocean plate dynamics

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