Age Migrations of Anorogenic Ring Complexes in Northern Nigeria

Rahaman, M.A.; Breemen, O. van; Bowden, Peter; Bennett, J. N.

doi:10.1086/628847

Cited by 73 publications

(49 citation statements)

References 24 publications

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“…The ring complexes are roughly orientated along a N-S axis and give Rb-Sr ages ranging from 213 Ma in the north to 141 Ma in the south (Rahaman et al, 1984;Vail, 1989). They comprise a wide variety of rock types including alkali granite, syenite and trachyte with minor gabbro, dolerite, rhyolite and ignimbrite.…”

Section: Nigeria-jos Plateaumentioning

confidence: 99%

“…Earlier hypotheses suggested that the magmatism was triggered by the northward migration of the African plate over a mantle plume (Bowden and Turner, 1974;Bowden et al, 1976;Karche and Vachette, 1976). However, more recently it has been suggested that they are linked to shear movements along pre-existing ENE-WSW trending wrench faults in the Pan African basement (Rahaman et al, 1984;Black et al, 1985). To the north of the Jos Plateau, there are similar alkali granite ring complexes in southern Niger and Air which are Palaeozoic in age (Vail, 1989).…”

Section: Nigeria-jos Plateaumentioning

confidence: 99%

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Magmatism and rifting in Western and Central Africa, from Late Jurassic to Recent times

Wilson¹,

Guiraud²

1992

Geodynamics of Rifting

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Section: Nigeria-jos Plateaumentioning

confidence: 99%

Section: Nigeria-jos Plateaumentioning

confidence: 99%

Magmatism and rifting in Western and Central Africa, from Late Jurassic to Recent times

Wilson¹,

Guiraud²

1992

Geodynamics of Rifting

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“…When we take into account that the ages of these granites decreased from north (e.g. 307 Ma for Daura granite) to south (141 Ma for Afu granite) (KARCHE & VACHETTE, 1978;RAHAMAN et al, 1984), and that the dyke we studied is 24 Ma older than the adjacent Mada granite, whose age is 147 Ma, it becomes clear that the rhyolite studied does not fit into the sequence of the age migration trend of the alkaline granites. Moreover, the Nassarawa-Egon rocks are calc-alkalic, as suggested by our preliminary geochemical investigation, whereas the Mada granite and the thin feeder rhyolites surrounding it are alkalic (ABAA, 1985b Measurements were carried out in the geochronological laboratory at Clermont-Ferrand.…”

Section: Discussionmentioning

confidence: 91%

“…Although it has been proposed by RAHAMAN et al (1984) that the emplacement of the Nigerian alkaline granite complexes was guided by ancient lineaments, there has been no documentation known to the authors of a shear zone associated with any of the alkaline granite centers. The dyke of this report is, therefore, peculiar.…”

Section: Discussionmentioning

confidence: 99%

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Geochronology of a rhyolite dyke from Nassarawa-Egon in Central Nigeria

Umeji

Caen-Vachette

1991

Geol Rundsch

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Ein 50 m mfichtiger Rhyolithgang, der das kristalline Basement des pan-afrikanischen Komplexes bei Nassarawa-Egon in Zentral-Nigeria schneidet, wurde auf ein Gesamtgesteins-Isochronalter von 171 • 3 Ma datiert und das 87Sr/86Sr Ausgangsverh/iltnis auf 0,71137 + 0,00020 bestimmt. Die Gesteinspetrographie und die Geochemie der wichtigsten Oxide lassen auf eine kalk-alkalische Verwandtschaft schliessen. Der Rhyolithgang verlfiuft entlang einer frtiheren Mylonit-Scherungszone, die am Rand der Benue Riftzone liegt. Die Streichrichtung des Rhyolithgangs und der Mylonitzone bilden mit der L/ingsachse der Riftzone einen stumpfen Winkel. Diese Beobachtungen ffihrten uns zu der Annahme, dab die Intrusion des Rhyolitganges mit der Dombildung in Zusammenhang steht, die die Benue Riftphase vordatiert (OLADE, 1975). Das berechnete Alter des Rhyolithganges ergibt ein welt h6heres Alter als das der nahe gelegenen jurassischen Granite (z. B. der Mada-Komplex mit 147 Ma). AuBerdem sind die Jura-Granite und die mit ihnen assoziierten Vulkanite ohne Ausnahme alkalisch.Die Ergebnisse dieser Arbeit liefern weitere Hinweise dafiir, dab saurer mitteljurassischer Vulkanismus die Riftphase vordatiert, obwohl die filtesten aufgeschlossenen Sedimentgesteine aus der Mittelkreide stammen. AbstractA 50-m thick rhyolite dyke which cuts the PanAfrican crystalline basement complex at NassarawaEgon, in central Nigeria, yielded a 10-point Rb-Sr whole-rock isochron age of 171 _+ 3 Ma and an initial 87Sr/86Sr ratio of 0.71137 _+ 0.00020. The petrography and major oxide geochemistry of the rock indicate that it has a calc-alkalic affinity. The dyke occupies the axis of an ancient mylonitic shear zone situated at the edge of the Benue Rift, and both strike at a high angle with respect to the long axis of the rift. We therefore consider that the emplacement of the dyke is related to the doming which predated the formation of the Benue Rift (OLADE, 1975). The calculated age of the dyke is much older than those of the Jurassic Younger Granites in the closest neighbourhood (e.g. Mada complex; 147 Ma). Furthermore, the Jurassic Granites and their associated volcanics and subvolcanics are all alkalic. This work provides further evidence that acid, pre-rift volcanism began by mid-Jurassic, although the oldest exposed sedimentary fill is mid-Cretaceous in age. R6sum6Une isochrone Rb-Sr comportant dix points a 6t6 6tablie sur roches totales pour un filon rhyolitique de 50 m d'dpaisseur qui recoupe le socle cristallin PanAfricain ~ Nassarawa-Egon dans le Nig6ria central. Un fige de 171 _ 3 Ma et un rapport initial 87Sr/86Sr de 0.71137 + 0,00020 (MSWD = 1,2) ont 6t6 obtenus. La g6ochimie des 616ments majeurs et la p6tro-graphic soulignent l'affinit6 calco-alcaline de cette roche. Ce filon, situ6 sur le bord du rift, est presque perpendiculaire ~ l'allongement du rift et dans l'axe d'une zone mylonitis6e. Nous considdrons donc que

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Nigerian rare-metal pegmatites and their lithological framework

Matheis

1987

Geol. J.

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Most of Africa's rare-metal potential is linkcd to Proterozoic pegmatite fields exccpt for the Jurassic tin-bearing ring complees of the Jos Plateau Nigeria. In order to establish the position of the Nigerian tin province in terms of economic rare-metal mineralization, occurrences of mineralized pegmatitic phases of the Nigerian basement complex. including the so-called 'Older Tin-Ficlds'. have been investigated. RbiSr geochronology confirms the end Pan-African ages for the pegmatites in the range 580-530 Ma. Although emplaced within the same time span. the mineralogy. geochemistry. and mineralization of these pegmatites differ according to the lithology of their host-rock. Pegmatite occurrences from southwest Nigeria. which are emplaced into Proterozoic metasedimentary-metavolcanic sequences, are enriched in tantalum relative to niobium. These geochemical characteristics are also displayed by the composition of eluvial heavy-mineral concentrates as well as by the trace-element distribution in cassiterites.Although Pan-African granites with an age range of 70(l-S20 Ma are dispersed throughout Nigeria, associated rare-metal mineralized pegmatites are known almost exclusively along a southwest-northeast striking belt about 400 km long, which interwets the Jos Plateau tin-fields. A direct genetic link between the rare-mctal hearing pegmatites and proximal granite occurrences was never obscrved. I t is suggested that reactivation of old tectonic lineaments during the Pan-African orogcny provided excess heat and fluid to concentrate rare-metal pegmatites by partial melting with selective leaching lrom the country rocks, i.e. their lithological framework.

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Age Migrations of Anorogenic Ring Complexes in Northern Nigeria

Cited by 73 publications

References 24 publications

Magmatism and rifting in Western and Central Africa, from Late Jurassic to Recent times

Magmatism and rifting in Western and Central Africa, from Late Jurassic to Recent times

Geochronology of a rhyolite dyke from Nassarawa-Egon in Central Nigeria

Nigerian rare-metal pegmatites and their lithological framework

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