The African Superswell

Nyblade, A.; Robinson, Scott

doi:10.1029/94gl00631

Cited by 305 publications

(225 citation statements)

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“…Using the system of Clifford (1986) (Schlüter, 2006). Another significant influence for the continent is the African Superswell (Nyblade and Robinson, 1994). This large feature has elevated significant portions of the African continent along a swath running from south of Africa to the middle of the Arabian Peninsula, and has been observed seismically down to the core-mantle boundary (Ritsema et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

“…These three rift zones form a triple junction in the Afar. This area also sits at the northern edge of the African Superswell, a buoyant region under eastern and southern Africa responsible for high residual topography (Nyblade and Robinson, 1994). Rifting in the south continues along the Moving further to the south, the Katanga Belt runs east-west between the Congo and Kalahari Cratons.…”

Section: Introductionmentioning

confidence: 99%

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A top to bottom lithospheric study of Africa and Arabia

2007

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We study the lithospheric structure of Africa, Arabia and adjacent oceanic regions with fundamental-mode surface waves over a wide period range. Including short period group velocities allows us to examine shallower features than previous studies of the whole continent.In the process, we have developed a crustal thickness map of Africa. Main features include crustal thickness increases under the West African, Congo, and Kalahari cratons. We find crustal thinning under Mesozoic and Cenozoic rifts, including the Benue Trough, Red Sea, and East, Central, and West African rift systems. Crustal shear wave velocities are generally faster in oceanic regions and cratons, and slower in more recent crust and in active and formerly active orogenic regions. Deeper structure, related to the thickness of cratons and modern rifting, is generally consistent with previous work. Under cratons we find thick lithosphere and fast upper mantle velocities, while under rifts we find thinned lithosphere and slower upper mantle velocities. There are no consistent effects in areas classified as hotspots, indicating that there seem to be numerous origins for these features. Finally, it appears that the African Superswell has had a significantly different impact in the north and the south, indicating specifics of the feature (temperature, time of influence, etc.) to be dissimilar between the two regions. Factoring in other information, it is likely that the southern portion has been active in the past, but that shallow activity is currently limited to the northern portion of the superswell.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A top to bottom lithospheric study of Africa and Arabia

2007

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“…It sits between two other regions of anomalous topography and bathymetry, the East African Plateau to the north, and the southeastern Atlantic Ocean basin to the southwest, and together, these regions form the African Superswell [Nyblade and Robinson, 1994] ( Figure 1). By removing the mean global continental elevation from the observed elevations in Africa, and by removing the age-predicted bathymetry from the observed bathymetry in the ocean basins around Africa, Nyblade and Robinson [1994] showed that the long wavelength (i.e., > a few hundred km) anomalous topography and bathymetry associated with the African Superswell is about 500 m. Many shorter wavelength topographic and bathymetric features are superimposed on this long wavelength swell.…”

Section: Introductionmentioning

confidence: 99%

“…Pysklywec and Mitrovica [1999] suggested that dynamic rebound after slab detachment following the cessation of subduction below the Cape Fold Belt at the end of the Triassic may have contributed to present-day elevations over much of southern Africa. And van der Beek et al [2002], citing work by Lowry et al [2000] for the western United States, offered as a possible uplift mechanism the underplating of lowdensity melts, chemically depleted of their basaltic constituents, to the underside of the lithosphere at Nyblade and Robinson, 1994]. Continental shelves and areas where the bathymetry was not corrected for sediment thickness are shown in white.…”

Section: Introductionmentioning

confidence: 99%

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

Nyblade

Sleep

2003

Geochem Geophys Geosyst

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We investigate under what conditions the present-day long wavelength anomalous elevation ($500 m) of the southern African Plateau can be attributed to Mesozoic plume events. The anomalous, long wavelength topography of the southern African Plateau cannot be easily explained by recent heating of the upper mantle, as opposed to other areas of the African Superswell, and geomorphological studies provide few hard constraints on the timing of the uplift. A Mesozoic origin for the plateau uplift is attractive in that southern Africa experienced several large magmatic events in the Mesozoic. We formulate numerical and scaling models to investigate if plume material ponded beneath cratonic lithosphere in the Mesozoic could produce 500 m of present-day elevation. We find that starting plume heads are ineffective at producing much long lasting uplift because the material spreads into a thin layer, tens of km thick. The ponded plume material also suppresses secondary convection by having a stable boundary at its base. Over time, heat continues to flow out of the top of the lithosphere, and a net imbalance of heat flow in the lithosphere develops, resulting in subsidence. Even after the plume material has cooled to the temperature of the mantle adiabat, secondary convection supplies less heat to the lithosphere than is lost upward by conduction. The cratonic lithosphere returns to its original thermal structure on a timescale of less than 200 m.y. Even two mantle starting plume heads, one at the time of Karoo volcanism (ca.183 Ma) and the other at the time of kimberlite eruption (ca. 80-90 Ma) in our models, cannot produce much (<200 m) of the present-day anomalous elevation. However, significant uplift can be generated by plume tails, provided they linger beneath the lithosphere for $25-30 m.y., and if the uplift effects of Mesozoic plume heads and tails are considered together, then it is possible to account for $500 m of present-day elevation. Consequently, a Mesozoic plume model for plateau uplift in southern Africa appears to be a viable model, if plume tails delivered heat to the southern African lithosphere over a period of 25 m.y. or more.Components: 15,106 words, 15 figures, 1 table.

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“…The mean elevation of these areas is -1 km, -500 m higher than the global average of similar continental areas. Nyblade and Robinson [ 1994] used the term "African superswell" to refer to these areas together with a contiguous, bathymetrically elevated region in the southeastern Atlantic Ocean. The origin of the African superswell is not well understood.…”

Section: Introductionmentioning

confidence: 99%

Upper mantle velocity structure beneath southern Africa from modeling regional seismic data

et al. 1999

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Abstract. The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data which come from a large mine tremor in South Africa (mb 5.6) recorded by the Tanzania broadband seismic experiment and by several stations in southern Africa. The waveform data show upper mantle triplications for both the 410-and 670-km discontinuities between distances of 2100 and 3000 km. Auxiliary travel time data along similar profiles obtained from other moderate events are also used. P wave travel times are inverted for velocity structure down to -800-km depth using the Wiechert-Herglotz technique, and the resulting model is evaluated by perturbing it at three depth intervals and then testing the perturbed model against the travel time and waveform data. The results indicate a typical upper mantle P wave velocity structure for a shield. P wave velocities from the top of the mantle down to 300-km depth are as much as 3% higher than the global average and are slightly slower than the global average between 300-and 420-km depth. Little evidence is found for a pronounced low-velocity zone in the upper mantle. A high-velocity gradient zone is required above the 410-km discontinuity, but both sharp and smooth 410-km discontinuities are permitted by the data. The 670-km discontinuity is characterized by high-velocity gradients over a depth range of *-80 km around 660-km depth. Limited S wave travel time data suggest fast S wave velocities above -150-km depth. These results suggest that the bouyant support for the African superswell does not reside at shallow depths in the upper mantle.

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The African Superswell

Cited by 305 publications

References 21 publications

A top to bottom lithospheric study of Africa and Arabia

A top to bottom lithospheric study of Africa and Arabia

Long lasting epeirogenic uplift from mantle plumes and the origin of the Southern African Plateau

Upper mantle velocity structure beneath southern Africa from modeling regional seismic data

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