Petrostructural and Geochemical Characteristics of the Metamagmatites in the External Zone of the Dahomeyides Belt: Case of the KantèSerpentinites (Northern Togo)

Thanks to detailed field investigations, microstructural and geochemical analysis and relationship with enclosing rocks, microfabrics, magmatic typology and metamorphic evolution of the Kantè sepentinites have been specified for the first time. The Kantè serpentinites in northern Togo constitute a mega-lens of ultrabasic rocks tectonically intercalated in the sericite chlorite schists of the Atacora structural unit. The brecciated, schitotose or massive rock facies are strongly marked by an S1 schistocity plane superimposed by a flat C shear plane linked to a west vergence thrusting movement. The parageneses that compose the metamagmatites are essentially serpentinous, containing plagioclase, opaque minerals (magnetite, chromite, spinel) and pyroxene porphyroblasts. These microfabrics represent relics of a probable gabbroic protolith. In fact, the geochemical characteristics of the Kantè serpentinites suggest that their magmatic typology is that of komatiites or tholeiitic basalts with oceanic arc affinities. They would have been emplaced in an active margin environment. The retromorphic evolution of the protolith corresponds to the phase of involvement in a major tangential contact during the panafrican tectogenesis.

Evidence of Atlantic Extension in South-East Togo: Case of Fracturing in the Sandstone Relics of Tohoun

The sandstone relics of probable Cretaceous age found around Tohoun show an extensional tectonics imprint associated with the Atlantic opening. This imprint consists of normal fault networks well expressed on two sites of outcrop and corresponds to three fracturing episodes materialized by families of conjugated planes striking E-W, NW-SE, and NE-SW. Striated plane data analysis shows three extensional axes successively N-S, NE-SW and NNW-SSE. The reconstructed paleostress tensors can be attributed to pre- to syn-rift phases responsible for the development of primary basin structures in the Gulf of Guinea. This preliminary analysis, concerning only fractures in the basal sequence relics, remains to be extended to the entire Togolese coastal basin to a better definition of the Atlantic dynamic.