Post-collisional Pan-African granitoids and rare metal pegmatites in western Nigeria: age, petrogenesis, and the ‘pegmatite conundrum’

Goodenough, K.M.; Lusty, P.A.J.; Roberts, N.M.W.; Key, R.M.; Garba, A.. 2014 Post-collisional Pan-African granitoids and rare metal pegmatites in western Nigeria: age, petrogenesis, and the ‘pegmatite conundrum’. Lithos, 200-201. 22-34.

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The Minna area of western Nigeria lies within a Pan-African orogenic belt that extends along the margin of the West African Craton, from Algeria southwards through Nigeria, Benin and Ghana, and into the Borborema Province of Brazil. This belt is characterised by voluminous post-collisional granitoid plutons that are well exposed around the city of Minna. In this paper we present new information about their age and petrogenesis. The Pan-African plutons around Minna can be divided into two main groups: a group of largely peraluminous biotite–muscovite granites that show varying levels of deformation in late Pan-African shear zones; and a younger group of relatively undeformed, predominantly metaluminous hornblende granitoids. Pegmatites, including both barren and rare-metal types, occur at the margins of some of the plutons. New U–Pb zircon dating presented here, in combination with published data, indicates an early phase of magmatism at c. 790–760 Ma in the Minna area. This magmatism could be related either to continental rifting, or to subduction around the margins of an existing continent. The peraluminous biotite–muscovite granites were intruded at c. 650–600 Ma during regional shearing in the orogenic belt, and are likely to have formed largely by crustal melting. Subsequent emplacement of metaluminous granitoids at c. 590 Ma indicates the onset of post-orogenic extension in this area, with a contribution from mantle-derived magmas. The rare-metal pegmatites represent the youngest intrusions in this area and thus are likely to have formed in a separate magmatic episode, post-dating granite intrusion.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 00244937
Date made live: 24 Jul 2014 09:00 +0 (UTC)

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