Petrochemistry of the Ilesha amphibolites and Precambrian crustal evolution in the Pan-African domain of SW Nigeria

Abstract

Major and trace element characteristics of Proterozoic amphibolites and talc-tremolite schists from the Ilesha area in the Pan-African orogenic domain of SW Nigeria suggest that they are metamorphosed tholeiitic basalts and associated peridotite flows or sills. The rather 'primitive' nature of these metabasalts as indicated by extremely low K, Rb and Rb/Sr values and high K/Rb ratios are interpreted as reflecting magma generation from a deep-seated subcrustal region due to rifting of a thinned sialic crust. The tholeiitic rather than alkaline affinity is attributed to partial melting at shallow depths in the mantle with only minor crustal contamination. The Nigerian Schist Belt is therefore envisaged as a Pan-African ensialic mobile belt derived from an aulacogen connected with an ocean lying to the west in the Dahomeyan-Pharusian belt during Late Precambrian times. © 1979.