Neoproterozoic Passive Margin Formation And Evolution During The Rodinia–Gondwana Supercontinent Cycle At The Eastern Margin Of The West African Craton.

Abstract

Petrographical and geochemical data from the Togo structural unit (TSU), also referred to as the Atacora structural unit, are presented together with the existing dataset; geochemical and age data from the sedimentary and metasedimentary rocks from the passive margin sequences of the Dahomeyide belt in Ghana to infer their provenance and depositional setting and expand the discussion on the Rodina–Gondwana supercontinent assembly during the Pan-African orogeny. The metasedimentary rocks of the TSU are quartzites and phyllites. The framework grains of the quartzites consisting dominantly of quartz and small amounts of feldspar grains and relict lithic fragments classify them as quartz arenite, subarkose and sublitharenite. Generally, the studied rocks show similar rare-earth element and multi-element patterns, which imply derivation from similar sources. Elemental ratios, including (La/Lu)N, Th/Sc and La/Sc, suggest sediments sourced from intermediate to felsic rocks. Provenance and depositional setting indicators of the TSU suggest deposition in a passive margin setting, with the West African and Amazonian cratons’ granitoids and granitic gneisses as possible provenance, akin to siliciclastic rocks of the Buem structural unit and the Voltaian Supergroup of the Volta Basin. The deformational history of the TSU is similar to those of the Buem structural unit and the eastern margin of the Voltaian Supergroup, indicating the effect of the Pan-African orogeny on the passive margin of the Dahomeyide belt. We, therefore, propose the formation and evolution of a Neoproterozoic passive margin unit, which was tectonically deformed during the Rodinia– Gondwana supercontinent cycle.