The Iriba alkaline basalts, an expression of mantle-derived Cretaceous magmatism of the Cameroon-Chad volcanic line along the Central Africa Rift System

Abstract

The poorly documented volcanic rocks of the Ouaddai massif in Chad are a continuity of the ones of the Cameroon Volcanic Line further to the SE, located within the Central African rift system. New mineralogical and geochemical data from the Iriba basanites (SiO2: 41–45 wt%) show depletion in HREE, slight negative Sm anomaly and high LREE/HREE ratios, which is typical of OIB. The main differentiation process is fractional crystallization with a complete lack of crustal contamination. These features, similar to basanites exposed in southern Cameroon, reflect the partial melting of a metasomatized subcontinental lithospheric root reworked during the formation of the Cenozoic Central Africa Rift System. We propose to define by Cameroon-Chad Volcanic Line this continental scale structure controlling the emplacement of alkaline magmas.

Keywords

• Chad volcanic activity
• Iriba basanite
• Fractional crystallization
• HIMU-type mantle
• Alkaline magmatism
• Central Africa rift system