Petrology and Geodynamic Context of Metabasic Rocks of Nemba Complex in the West Congo fold Belt (Republic of Congo)

Abstract

The West Congo belt contains Paleoproterozoic and Neoproterozoic Units which are deformed during Panafrican event. The Neoproterozoic Unit contains rift and post rift deposits. The rift formation is made of metabasite, volcanic and volcano-sedimentary rocks. The metabasite constitutes the Nemba Complex which is considered put into place in a continental or oceanic context. Samples from Nemba Complex collected along the “Congo ocean railway realignment” are analyzed. Major elements indicate a low potassic subalkaline affinity of the samples. Classification diagrams based of major elements shows that the rocks are a tholeiitic serie constituted of andesitic basalts, sub-alkaline andesitic basalts and a sub-alkaline to alkaline basalts. Some samples with a calc-alkaline signature indicate a crustal contamination. The traces elements plots indicate that the rocks are the MORB. The spectrum of multi-elements is characteristic of continental rocks with a lithospheric origin. This is an agreement with many works on the Nemba Complex and the alkali plutons and acid volcanic rocks associated which attribute there a rift context.