Precambrian lithospheric controls on the development of the East African rift system

Nyblade, A.; Brazier, Richard

doi:10.1130/0091-7613(2002)030<0755:plcotd>2.0.co;2

Cited by 123 publications

(95 citation statements)

References 28 publications

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“…The fast directions for the on-craton stations are roughly perpendicular to these predicted directions, but because there are few signs of current or recent extensional deformation penetrating through the craton [Nyblade and Brazier, 2002], it is likely that the rough anticorrelation between NW fast directions and the NE MHCS direction is a mere coincidence.…”

Section: Mantle Anisotropy Due To Extensionmentioning

confidence: 99%

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

et al. 2004

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[1] East Africa is a tectonically complex region owing to the presence of a rigid craton, paleothrust belts and shear zones, active magmatism and rifting, and possibly even a mantle plume. We present new splitting results of teleseismic shear phases recorded by 21 broadband seismic stations in Tanzania, seven broadband stations in Kenya, and three permanent broadband Global Seismic Network stations in Kenya and Uganda. Inconsistent apparent splitting is observed beneath the craton and along its southern and southeastern flank in Tanzania. Splitting at stations elsewhere in the rifts and orogenic belts is more consistent. We test between different models of anisotropy for stations with inconsistent splitting (single layer with horizontal fast axis, single layer with dipping fast axis, and two layers with horizontal fast axes). However, we show that these more complicated models do not reasonably explain the data. The data are explained better by a laterally (and/or in some places vertically) varying single-layer model with a horizontal fast axis. We arrive at a conceptual model of anisotropy in Tanzania and Kenya that is controlled by (1) active shear along the base of the plate associated with asthenospheric flow beneath and around the moving craton keel, (2) asthenospheric flow from a plume north of central Kenya, (3) fossilized anisotropy in the lithosphere due to past orogenic events, and possibly (4) aligned magma-filled lenses beneath the rifts. Our most robust conclusion is that we can rule out an extension-induced lattice preferred orientation of olivine as a dominant factor, which is surprising given the long history of extension in the region. This indicates that mantle-lithospheric extension in East Africa occurs via dikeintrusion and/or ductile thinning within narrow rift zones and is possibly facilitated by a mechanical lithospheric anisotropy imparted by fossilized north/south structural or mineralogical fabrics.

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Section: Mantle Anisotropy Due To Extensionmentioning

confidence: 99%

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

et al. 2004

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“…The onset of rifting in East Africa has been associated with a southward-directed migration of volcanism, which in turn has been inferred to be linked with the northward motion of the African plate over a mantle plume [Ebinger and Sleep, 1998;Nyblade and Brazier, 2002]. Accordingly, the onset of tectonic activity in the eastern branch of the rift is also thought to have followed this temporal trend from Ethiopia to northern Tanzania [Nyblade and Brazier, 2002].…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly, the onset of tectonic activity in the eastern branch of the rift is also thought to have followed this temporal trend from Ethiopia to northern Tanzania [Nyblade and Brazier, 2002]. In contrast, Zeyen et al [1997] proposed that the onset of extension was less systematic, and largely dictated by the spatially variable mechanical properties of the lithosphere and crust.…”

Section: Introductionmentioning

confidence: 99%

Cenozoic extension in the Kenya Rift from low‐temperature thermochronology: Links to diachronous spatiotemporal evolution of rifting in East Africa

et al. 2015

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Key points: Data and modeling show Paleogene and middle Miocene cooling episodes  Cooling episodes separated by stable conditions, slow exhumation or subsidence  Extension pattern is compatible with random rift initiation above a plume This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/2015TC003949 ©2015 American Geophysical Union. All rights reserved. AbstractThe cooling history of rift shoulders and the subsidence history of rift basins are cornerstones for reconstructing the morphotectonic evolution of extensional geodynamic provinces, assessing their role in paleoenvironmental changes, and evaluating the resource potential of their basin fills. Our apatite fission-track and zircon (U-Th)/He data from the Samburu Hills and the Elgeyo Escarpment in the northern and central sectors of the Kenya Rift indicate a broadly consistent thermal evolution of both regions. Results of thermal modeling support a three-phased thermal history since the early Paleocene. The first phase (~65-50 Ma) was characterized by rapid cooling of the rift shoulders and may be coeval with faulting and sedimentation in the Anza Rift basin, now located in the subsurface of the Turkana depression and areas to the east in northern Kenya. In the second phase, very slow cooling or slight reheating occurred between ~45 and 15 Ma as a result of either stable surface conditions, very slow exhumation, or subsidence. The third phase comprised renewed rapid cooling starting at ~15 Ma. This final cooling represents the most recent stage of rifting, which followed widespread flood-phonolite emplacement and has shaped the present-day landscape through rift shoulder uplift, faulting, basin filling, protracted volcanism, and erosion. When compared with thermochronologic and geologic data from other sectors of the East African Rift System, extension appears to be diachronous, spatially disparate, and partly overlapping, likely driven by interactions between mantle-driven processes and crustal heterogeneities, rather than the previously suggested north-south migrating influence of a mantle plume.

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“…This would suggest that there were different (higher) geothermal gradients during Group 1 kimberlite emplacement in the Mozambique Belt than into the Kaapvaal Craton. Nyblade & Brazier (2002) show that the thick depleted Analysed olivine grains are fosteritic with over 45% MgO and less than 14% total iron as FeO ( Figure 7 and Table 2). The single analysis of a groundmass clinopyroxene is typical of the 'pure' diopside found in kimberlite groundmasses, as recorded by Mitchell (1986).…”

Section: Reconnaissance Sem Chemistry Resultsmentioning

confidence: 99%

“…The western arm of the East African Rift System began to develop at between 12 and 10 Ma (Nyblade & Brazier, 2002). The East African Rift System thus largely post-dates kimberlite emplacement.…”

Section: Rb-sr Geochronology and Other Isotope Studiesmentioning

confidence: 99%

Kimberlites in a Karoo graben of northern Mozambique: Tectonic setting, mineralogy and Rb-Sr geochronology

Bingen

Barton

Daudi

et al. 2007

South African Journal of Geology

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Kimberlites occur as dykes up to 3 m thick and isometric bodies in the southern explored part of a NE-SW trending Karoo graben across the Mozambique Belt in northern Mozambique. The kimberlites are reported along four NW-SE-trending zones, and one ENE-WSW-trending zone. The kimberlites are macrocrystic hypabyssal Group Ia kimberlites based on their mineralogy and whole rock geochemistry. The kimberlites show a typical crystallization history with early olivine, perovskite, ilmenite and phlogopite growth succeeded by rutile and spinel

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Precambrian lithospheric controls on the development of the East African rift system

Cited by 123 publications

References 28 publications

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

On the relationship between extension and anisotropy: Constraints from shear wave splitting across the East African Plateau

Cenozoic extension in the Kenya Rift from low‐temperature thermochronology: Links to diachronous spatiotemporal evolution of rifting in East Africa

Kimberlites in a Karoo graben of northern Mozambique: Tectonic setting, mineralogy and Rb-Sr geochronology

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