The Afar volcanic province within the East African Rift System: introduction

Yirgu, Gezahegn; Ebinger, C. J.; Maguire, P. K. H.

doi:10.1144/gsl.sp.2006.259.01.01

Cited by 55 publications

(15 citation statements)

References 54 publications

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“…This is compatible with a manifold of geoscientific observations across the highlands of East Africa where the intense Cenozoic volcanism peaked between ~20 and ~40 Ma (e.g. Bond, 1979, Crough 1979, Smith, 1994Ebinger and Sleep, 1998;Nyblade et al, 2000 a;Yirgu et al, 2006 and references therein), but not so for high southern Africa, which is dominated by Mesozoic alkaline volcanism and was already a high region at that time (Doucouré and de Wit, 2003a).…”

Section: The Kalahari Epeirogeny and Climate Change 368supporting

confidence: 84%

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

Wit

2007

South African Journal of Geology

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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.

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Section: The Kalahari Epeirogeny and Climate Change 368supporting

confidence: 84%

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

Wit

2007

South African Journal of Geology

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“…Within the context of the plume model, the roles of lithospheric structure and process have also been called upon to explain complexities in plateau volcanism [e.g., Furman et al , 2006; Furman , 2007], uplift [e.g., Gani et al , 2007], and MER evolution [e.g., Rooney et al , 2005; Bastow et al , 2005; Yirgu et al , 2006; Keranen and Klemperer , 2007; Rooney et al , 2007; Corti , 2008]. However, even though lithospheric structural inheritance can strongly influence continental rift development, [e.g., Vauchez et al , 1997], the nature of plume‐lithosphere interactions remains poorly understood outside a 250 × 350 km area centered on the MER [ Bastow et al , 2005].…”

Section: Introductionmentioning

confidence: 99%

Upper mantle seismic structure beneath the Ethiopian hot spot: Rifting at the edge of the African low‐velocity anomaly

Bastow

Nyblade

Stuart

et al. 2008

Geochem Geophys Geosyst

203

291

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[1] The Miocene-Recent East African Rift in Ethiopia subaerially exposes the transitional stage of rifting within a young continental flood basalt province. As such, it is an ideal study locale for continental breakup processes and hot spot tectonism. We combine teleseismic traveltime data from 108 seismic stations deployed during two spatially and temporally overlapping broadband networks to present detailed tomographic images of upper mantle P and S wave seismic velocity structure beneath Ethiopia. Tomographic images reveal a $500 km wide low P and S wave velocity zone at 75 to !400 km depth in the upper mantle that extends from close to the eastern edge of the Main Ethiopian Rift (MER) westward beneath the uplifted and flood basalt-capped NW Plateau. We interpret this broad low-velocity region (LVR) as the upper mantle continuation of the African Superplume. Within the broad LVR, zones of particularly low velocity are observed with absolute delay times (dt P $ 4 s) that indicate the mantle beneath this region is amongst the slowest worldwide. We interpret these low velocities as evidence for partial melt beneath the MER and adjacent NW Plateau. Surprisingly, the lowest-velocity region is not beneath Afar but beneath the central part of the study area at $9°N, 39°E. Whether this intense low-velocity zone is the result of focused mantle upwelling and/or enhanced decompressional melting at this latitude is unclear. The MER is located toward the eastern edge of the broad low-velocity structure, not above its center. This observation, along with strong correlations between low-velocity zones and lithospheric structures, suggests that preexisting structural trends and Miocene-to-Recent rift tectonics play an important role in melt migration at the base of the lithosphere in this magmatic rift zone.

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“…[4] Whereas the distribution and style of Quaternary volcanotectonic deformation (in terms of seismic, structural and geodetic data) is known with a satisfactory approximation in the northern MER owing to the large geophysical and petrological data set obtained from the EAGLE project [e.g., Yirgu et al, 2006], this is comparatively less constrained southward. Therefore, we focus on the central sector of the MER and we present new field structural data coupled with radiometric dating of faulted rocks that shed new light on the distribution, characteristics and timing of Quaternary deformation in this rift sector and its connection with the northern MER.…”

Section: Introductionmentioning

confidence: 99%

Distribution of Quaternary deformation in the central Main Ethiopian Rift, East Africa

et al. 2011

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The Main Ethiopian Rift (MER) is a narrow continental rift characterized by an along‐axis variation in rift evolution, with early stages in the south evolving to incipient breakup in the north. Although distribution and style of Quaternary volcanotectonic deformation is well known in the northern rift sector, knowledge of these characteristics is comparatively less constrained southward. In this paper we present the results of a field structural study carried out to better constrain the time‐space distribution of faulting in the central sector of the MER (central MER). The new field structural data coupled with new 14C radiometric dating of faulted rocks suggest a localization of faulting at both rift margins of the central MER, where radiometric dating of faulted material has allowed establishing a Late Pleistocene–Holocene activity of border faults. Conversely, in‐rift faulting (Wonji Fault Belt (WFB)) is subordinate highlighting a major difference with the northern sector of the MER where deformation is essentially accommodated in the axial zone. This is consistent with an along‐axis variation in rift evolution, showing the central MER less evolved than the northern rift sector. Inversion of cumulative fault slip data reveals a variation in the extension direction between the rift margins (N105°–110°E) and the rift floor (N90°–95°E), which accords well with the current Nubia‐Somalia plate kinematics. The variation in extension direction across the rift could manifest a slip partitioning between the boundary faults and in‐rift WFB faults.

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The Afar volcanic province within the East African Rift System: introduction

Cited by 55 publications

References 54 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

Upper mantle seismic structure beneath the Ethiopian hot spot: Rifting at the edge of the African low‐velocity anomaly

Distribution of Quaternary deformation in the central Main Ethiopian Rift, East Africa

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