The state of the upper mantle beneath southern Africa

Priestley, Keith; McKenzie, Dan; Debayle, E.

doi:10.1016/j.tecto.2005.11.024

Cited by 84 publications

(55 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, James et al (2001) and Fouch et al (2004), using near-vertical body wave analyses, find that the lithosphere varies in thickness between 250 and 400 km, but predict that it is probably closer to 250 km or 300 km (Wittlinger and Farra, 2007). Others using surface and Rayleigh wave data find the lithosphere to be at most 200 km Ritsema et al, 1999;2004;Priestley et al, 2006;Merrer et al, 2007). Converted P-S waves studies (Stankiewicz et al, 2002) reported seismic velocities ~6% higher compared to global model averages for the upper 300 km, followed by a lower velocity section down to 400 km, with speeds of ~3% higher than the same global average model.…”

Section: The Deep Lithosphere Of Cratonic Southern Africamentioning

confidence: 99%

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Wit

2007

South African Journal of Geology

View full text Add to dashboard Cite

Southern Africa's high Kalahari plateau and its flanking mountain ranges formed over an extended period of ~200 million years through vertical tectonic processes different from those at convergent plate boundaries. We refer to this as the Kalahari epeirogeny. Episodic uplift and erosion during the Kalahari epeirogeny is inferred from thermo-chronology and from stratigraphy of sediment accumulated around its continental margin. A total thickness of 2 to 7 km of rock (of which basalt was a major component) was eroded from the subcontinent's surface during two punctuated episodes of exhumation, in the early-Cretaceous and in the mid-Cretaceous. Major exhumation was over by the end of the Cretaceous, and the rate of erosion decreased by more than an order of magnitude to remove less than 1 km thickness of rock during the Cenozoic. Cosmogenic dating shows that erosion rates today are almost an order of magnitude less still.The cause for the Kalahari epeirogeny remains elusive, but three striking observations stand out: (i) major exhumation occurred during the late Mesozoic break-up of Gondwana; (ii) large scale basaltic magmatism closely match two accelerated episodes of exhumation: first along the west coast (~132 Ma, Etendeka large igneous province [LIP], associated with vast amounts of underplating along this entire passive margin), and the second flanking the sheared south coast margin (~90 Ma, Agulhas oceanic LIP). Yet exhumation that might have accompanied the vast Karoo LIP (~180 Ma) is not readily detected; (iii) the two main regional episodes of accelerated exhumation and coastal sediment accumulation are near synchronous with two regional 'spikes' of kimberlite intrusions: >450 kimberlites at ~90 Ma, and >200 kimberlites at ~120 Ma. Southern Africa is underlain by an anomalous warm region in the lowermost ~1500 km of the mantle that is linked to core to mantle heat loss. This warm region was inherited from a large Cretaceous thermo-chemical anomaly in the mantle created during long-lived subduction beneath Gondwana. Associated Mesozoic kimberlite genesis and basaltic magmatism may have been sufficient to cause volatile/heat-induced density changes in the lithospheric mantle of southern Africa to sustain the Kalahari plateau. In addition, such changes may have been induced by tectonic uplift and decompressional melting resulting from far-field collision processes between Africa and Europe, and/or final continental lithosphere decoupling between the Falkland plateau and southern Africa. CO 2 released into the ocean-atmosphere system during the Kalahari epeirogeny contributed to the global mid-Cretaceous hot-house conditions. However, because the CO 2 -consumption rate associated with basalt weathering is about eight times that of granite, atmospheric CO 2 was also efficiently sequestrated during the rapid erosion of Karoo basalt. Thus, the Kalahari epeirogeny also may have catalysed the onset of long-term global Cenozoic cooling.

show abstract

Section: The Deep Lithosphere Of Cratonic Southern Africamentioning

confidence: 99%

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Wit

2007

South African Journal of Geology

View full text Add to dashboard Cite

show abstract

“…Substantial progress has recently been made in deriving seismic tomography models that approach the horizontal resolution needed to address the modelling challenges outlined above (Priestley et al 2006;Simmons et al 2007;Fishwick et al 2007). In this study we focus on the geodynamic implications of a new joint inversion of combined global seismic and surface geodynamic data sets, in which mineral physical constraints on mantle thermal properties are also included (Simmons et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Joint seismic–geodynamic-mineral physical modelling of African geodynamics: A reconciliation of deep-mantle convection with surface geophysical constraints

Forte

Quéré

Moucha

et al. 2010

Earth and Planetary Science Letters

192

244

View full text Add to dashboard Cite

“…6). Surface-wave studies of southern Africa also show a similar east-to-west gradient in the shallow mantle velocity (PRIESTLEY et al, 2006). It is unlikely that the lid difference is due to temperature variations since the lid is confined to very shallow depths.…”

Section: Lithospheric and Shallow Structure Above 410 Kmmentioning

confidence: 74%

Upper Mantle Seismic Structure Beneath Southern Africa: Constraints on the Buoyancy Supporting the African Superswell

Brandt

Grand

Nyblade

et al. 2011

Pure Appl. Geophys.

View full text Add to dashboard Cite

We present new one-dimensional SH-wave velocity models of the upper mantle beneath the Kalahari craton in southern Africa obtained from waveform inversion of regional seismograms from an Mw = 5.9 earthquake located near Lake Tanganyika recorded on broadband seismic stations deployed during the 1997-1999 Southern African Seismic Experiment. The velocity in the lithosphere beneath the Kalahari craton is similar to that of other shields, and there is little evidence for a significant low velocity zone beneath the lithosphere. The lower part of the lithosphere, from 110 to 220 km depth, is slightly slower than beneath other shields, possibly due to higher temperatures or a decrease in Mg number (Mg#). If the slower velocities are caused by a thermal anomaly, then slightly less than half of the unusually high elevation of the Kalahari craton can be explained by shallow buoyancy from a hot lithosphere. However, a decrease in the Mg# of the lower lithosphere would increase the density and counteract the buoyancy effect of the higher temperatures. We obtain a thickness of 250 ± 30 km for the mantle transition zone, which is similar to the global average, but the velocity gradient between the 410 and 660 km discontinuities is less steep than in global models, such as PREM and IASP91. We also obtain velocity jumps of between 0.16 ± 0.1 and 0.21 ± 0.1 km/s across the 410 km discontinuity. Our results suggest that there may be a thermal or chemical anomaly in the mantle transition zone, or alternatively that the shear wave velocity structure of the transition zone in global reference models needs to be refined. Overall, our seismic models provide little support for an upper mantle source of buoyancy for the unusually high elevation of the Kalahari craton, and hence the southern African portion of the African Superswell.

show abstract

The state of the upper mantle beneath southern Africa

Cited by 84 publications

References 50 publications

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Joint seismic–geodynamic-mineral physical modelling of African geodynamics: A reconciliation of deep-mantle convection with surface geophysical constraints

Upper Mantle Seismic Structure Beneath Southern Africa: Constraints on the Buoyancy Supporting the African Superswell

Contact Info

Product

Resources

About