The metabasalts from the greenstone belt of the Lebzenia group in the Tasiast complex, Mauritania, and their geodynamic implications

Abstract

Samples of metabasalts collected from the Lebzenia Group, located in the Tasiast region of Mauritania, reveal a complex geochemical signature that highlights magmatic processes related to tectonically active environments. The analyses show low concentrations of incompatible elements such as Nb, TiO 2 , and P 2 O 5 , combined with marked negative anomalies in Nb, Ta, and Ti. These characteristics, along with an enrichment of light rare earth elements (LREE) and Th, are typical of a transitional calc-alkaline affinity commonly associated with volcanic arcs. The high Th/Nb ratios, as well as the presence of specific geochemical anomalies, suggest an interaction between an enriched mantle source and a modified continental crust. This interaction reflects partial mantle melting processes at significant depths, influenced by crustal materials or fluids from intense tectonic activity. Samples such as DRAM7 and DRAM8 show a transitional calc-alkaline affinity while exhibiting similarities to tholeiitic basalts of mantle origin. These geochemical data shed light on the diversity and complexity of the tectonomagmatic processes that contributed to the formation of the Lebzenia Group. This study enhances the understanding of the geodynamic evolution of the Tasiast region and its role in crustal growth processes during the Archaean, emphasising the contribution of mantle–crust interactions in magma genesis.