PETROGENESIS OF SCHISTS IN SOUTHEAST LOKOJA, CENTRAL NIGERIA

Abstract

Schists in southeast Lokoja, central Nigeria are enriched in Si02 and AI203. Cr, Ni and Tio2 are also relatively high in these rocks. The chemical compositions of the schists indicate that they were derived from a shale-greywacke sequence of sedimentary rocks. As a result, they have high Ti02/Al203 and variable K20/ Na20 ratios. The grey wackes had a granodioritic provenance. The high Ti02 and Ni content of these metasediments suggest that mafic debris were possibly mixed in their source- rocks. The schists are products of metamorphism of immature sediments which were deposited in an intracratonic extensional basin. Available geochronological data indicate that most intensive reworking of these sedimentary rocks occurred ca. 687±13 Ma ago during the Pan African orogency. Earlier metamorphism of the sediments could have occurred ca. 1315 Ma ago during the Kibaran orogeny.


Keywords: Lokoja, shale-greywacke, immature-sediments, Pan-African, Kibaran


[Global Jnl Geol. Sci. Vol.1(1) 2003: 29-42]