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

Zhao, Minghui; Langston, Charles A.; Nyblade, A.; Owens, Thomas

doi:10.1029/1998jb900058

Cited by 59 publications

(71 citation statements)

References 30 publications

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“…In southern Africa, we find fast mantle velocities in the Kalahari Craton, but slower velocities at the southern edge of the continent. The fast velocities are consistent with previous studies of the region (Zhao et al, 1999;James et al, 2001), with the latter also finding slower velocities in the Cape Fold Belt. There does not seem to be any systematic difference in the uppermost mantle velocities of Archean and post-Archean terranes.…”

Section: Bysupporting

confidence: 82%

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: Bysupporting

confidence: 82%

A top to bottom lithospheric study of Africa and Arabia

2007

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“…Clouser and Langston [1990], Nyblade et al [1996], Zhao et al [1999], and Simon et al [2002] investigated upper mantle structure beneath the Archean nucleus and surrounding Proterozoic mobile belts by modeling regional P travel times and waveforms. The former two studies found fast P wave velocities and positive velocity gradients to depths of 150-170 km, while the latter two studies found fast P wave velocities extending to much greater depth (>300 km), all consistent with the tomographic images of James et al [2001].…”

Section: Geophysical and Geochemical Backgroundmentioning

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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“…On the other hand, the recent body wave studies of Zhao et al (1999) and James et al (2001) find the high velocity upper mantle beneath southern Africa extends to 300-400 km depth. Hence, there is still no consensus on the state of the upper mantle beneath southern Africa.…”

Section: Introductionmentioning

confidence: 99%