Abstract
Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic gneiss. This rock has been dated by LA-ICP-MS yielding a concordant U-Pb zircon age of 2207 ± 20 Ma indicating the crystallization age of the granite protolith. This early Rhyacian age and its affinity with within-plate granites indicates emplacement during crustal extension and rifting presceding the main phase of the Eburnean orogeny. The strong, early, shear fabric, S1, in the rock is interpreted to be also of Paleoproterozoic age i.e. imprinted during the Eburnean orogeny. The Jebba granitic gneiss is thus correlatable with the widely abundant Paleoproterozoic granitic magmatism now represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil.
Highlights
The Nigerian basement complex forms the southern part of the Trans-Saharan Pan-African mobile belt [1] of Neoproterozoic (500 - 750 Ma) age situated between the Archean-Paleoproterozoic blocks of the West African craton to the west, the East Saharan block to the east and the Congo craton to the southeast (Figure 1)
The Jebba granitic gneiss is correlatable with the widely abundant Paleoproterozoic granitic magmatism represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil
This paper reports the first data on the geochronology of the leucocratic Jebba granitic gneiss, a very strongly deformed and folded unit in the area and examines its significance in the Paleoproterozoic crustal evolution of the area and discusses it correlation with other parts of the Nigeria basement complex and western Gondwana, especially Brazil
Summary
The Nigerian basement complex forms the southern part of the Trans-Saharan Pan-African mobile belt [1] of Neoproterozoic (500 - 750 Ma) age situated between the Archean-Paleoproterozoic blocks of the West African craton to the west, the East Saharan block to the east and the Congo craton to the southeast (Figure 1) This basement complex comprises gneisses, migmatites and supracrustals which have yielded Archean and Proterozoic ages [2,3] and bears the imprints of Liberian (ca 2700 Ma), Eburnean (ca 2000 Ma) and Pan-African (ca 600 Ma) orogenic events [3,4,5,6,7,8,9]. This paper reports the first data on the geochronology of the leucocratic Jebba granitic gneiss, a very strongly deformed and folded unit in the area and examines its significance in the Paleoproterozoic crustal evolution of the area and discusses it correlation with other parts of the Nigeria basement complex and western Gondwana, especially Brazil
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