A model for the structure, composition and evolution of the Kenya rift

Mechie, J.; Keller, G. Randy; Prodehl, C.; Khan, M. Aftab; Gaciri, S.J.

doi:10.1016/s0040-1951(97)00097-8

Cited by 89 publications

(61 citation statements)

References 31 publications

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“…This spatiotemporal pattern of extension is inconsistent with tectonic models of rifting in East Africa that are based on a southward-directed migration of volcanism and cogenetic extension [McConnell, 1972;Ebinger and Sleep, 1998;Ebinger et al 2000;Nyblade and Brazier, 2002;Morley, 2010]. In light of the pronounced geophysical anomalies, evidence for mantle advection, and the evolution of dynamic topography associated with regional domal uplift [i.e., White and McKenzie, 1989;Simiyu and Keller, 1997;Prodehl et al, 1997;Achauer and Masson, 2002;Mechie et al, 1997;Sepulchre et al, 2006;Moucha and Forte, 2011;Wichura et al, 2015], the timing of extension throughout East Africa likely reflects a large-scale, mantle-driven process that generated differential stresses [e.g., Crough, 1983;Zeyen et al, 1997] and the formation of rift basins in areas characterized by pronounced lithospheric and crustal-scale anisotropies and weaknesses [i.e., Ashwal and Burke, 1989;Ebinger and Sleep, 1998;Smith and Mosley, 1993;Smith, 1994]. As such, our new data from the Kenya Rift, combined with the synopsis of geological and thermo-chronological studies in East Africa, is compatible with recent numerical modeling results [Koptev et al, 2015] that predict a regionally overlapping initiation of amagmatic and magmatic rifting sectors in East Africa following the asymmetric impingement of a single mantle plume [i.e., Halldórsson et al, 2014] at the base of the lithosphere of the eastern sector of the Tanzania Craton.…”

Section: Regional Implications For Rifting In East Africamentioning

confidence: 66%

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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Section: Regional Implications For Rifting In East Africamentioning

confidence: 66%

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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“…The xenolith-bearing basanites and alkali basalts represent the youngest volcanic products (1.8-0.5 Ma; Brotzu et al 1984;Key et al 1987) and thus potentially sampled mafic lithologies accumulated earlier. The presence of such material is supported by seismic studies providing evidence for presence of mafic material underplating the lowermost crust beneath the rift flanks of the Kenya rift (Mechie et al 1997) and by the occurrence of pyroxenite xenoliths in South Ethiopian basanites interpreted to have formed during Quaternary alkaline magmatic activity (Orlando et al 2006).…”

Section: Origin Of the Grt Websteritesmentioning

confidence: 96%

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Kaeser

Olker

Kalt

et al. 2008

Contrib Mineral Petrol

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Garnet-bearing and garnet-free pyroxenite xenoliths from Quaternary basanites of Marsabit, northern Kenya, were analysed for microstructures and mineral compositions (major and trace elements) to constrain the thermal and compositional evolution of the lithospheric mantle in this region. Garnet-bearing rocks are amphibolebearing websterite with *5-10 vol% orthopyroxene. Clinopyroxene is LREE-depleted and garnet has high HREE contents, in agreement with an origin as cumulates from basaltic mantle melts. Primary orthopyroxene inclusions in garnet suggest that the parental melts were orthopyroxene-saturated. Rock fabrics vary from weakly to strongly deformed. Thermobarometry indicates extensive decompression and cooling (*970-1,100°C at *2.3-2.6 GPa to *700-800°C at *0.5-1.0 GPa) during deformation, best interpreted as pyroxenite intrusion into thick Paleozoic continental lithosphere subsequently followed by continental rifting (i.e., formation of the Mesozoic Anza Graben). During continental rifting, garnet websterites were decompressed (garnet-to-spinel transition) and experienced the same P-T evolution as their host peridotites. Strongly deformed samples show compositional overlaps with cpx-rich, initially garnet-bearing lherzolite, best explained by partial re-equilibration of peridotite and pyroxenite during deformation and mechanical mingling. In contrast, garnet-free pyroxenites include undeformed, cumulate-like samples, indicating that they are younger than the garnet websterites. Major and trace element compositions of clinopyroxene and calculated equilibrium melts suggest crystallisation from alkaline basaltic melt similar to the host basanite, which suggests formation in the context of alkaline magmatism during the development of the Kenya rift.

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“…1). This was followed by normal faulting and extension, estimated currently to be 35±40 km, which corresponds to a stretching ( -) factor of 1.6 (Hendrie et al 1994;Mechie et al 1997). Since its inception, magmatism has subsequently migrated southwards with time, reaching northern Tanzania c. 5±8 Ma.…”

Section: Magmatism Of the Kenya Riftmentioning

confidence: 98%

“…The relevant crustal layer may be the high-velocity seismic layer (6¢8±7¢1 km s ¡1 ) identi®ed at 25±35 km depth, i.e. at the base of the crust beneath the central rift, which has been interpreted as a mix of high-grade metamorphic rocks and underplating ma®c and ultrama®c material (Mooney & Christensen 1994;Hay et al 1995a,b;Mechie et al 1997).…”

Section: Partial Melting Of Deep Crustmentioning

confidence: 99%

Magmatism of the Kenya Rift Valley: a review

MacDonald

2002

Transactions of the Royal Society of Edinburgh: Earth Sciences

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Tertiary±Recent magmatism in the Kenya Rift Valley was initiated c. 35 Ma, in the northern part of Kenya. Initiation of magmatism then migrated southwards, reaching northern Tanzania by 5±8 Ma. This progression was accompanied by a change in the nature of the lithosphere, from rocks of the Panafrican Mozambique mobile belt through reworked craton margin to rigid, Archaean craton. Magma volumes and the geochemistry of ma®c volcanic rocks indicate that magmatism has resulted from the interaction with the lithosphere of melts and/or¯uids from one or more mantle plumes. Whilst the plume(s) may have been characterised by an ocean island basalttype component, the chemical signature of this component has everywhere been heavily overprinted by heterogeneous lithospheric mantle. Primary ma®c melts have fractionated over a wide range of crustal pressures to generate suites resulting in trachytic (silica-saturated and -undersaturated) and phonolitic residua. Various Neogene trachytic and phonolitic¯ood sequences may alternatively have resulted from volatile-induced partial melting of underplated ma®c rocks. High-level partial melting has generated peralkaline rhyolites in the south±central rift. Kenyan magmatism may, at some future stage, show an increasing plume signature, perhaps associated ultimately with continental break-up. KEY WORDS: Plume±lithosphere interactionsThe Red Sea and the Gulf of Aden are two arms of a postulated triple junction centred on the Afar region (Fig. 1). Oceanic crust began to form under these arms c. 10 Ma. The third arm, the East African Rift System (EARS), extends southwards through Ethiopia, Kenya and Tanzania into Mozambique. Whilst lithospheric extension is occurring beneath the EARS, the rift has not developed to the stage of ocean crust formation. The EARS has come to be seen, therefore, as a prime location in which to investigate the early stages of continental break-up.This review focuses on the magmatism of the Kenya Rift section, used here to indicate that section of the EARS extending from northern Kenya to northern Tanzania. The primary aim is to demonstrate the complex polybaric evolutionary history of the magmatism, starting with the postulated plume-induced generation of primary magmas by variable degrees of partial melting of heterogeneous, metasomatised lithosphere, through to generation of salic magmas by assimilation±crystal fractionation processes over a range of crustal pressures and by partial melting of crustal protoliths, also over a range of pressures.

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A model for the structure, composition and evolution of the Kenya rift

Cited by 89 publications

References 31 publications

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

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

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Magmatism of the Kenya Rift Valley: a review

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