Relative active tectonic in the metamorphic rocks of the Yaounde group: insights from geomorphic indices and topographic analysis

The Yaounde Group (YG), representing the southern edge of the North Equatorial Pan-African Belt, consists of quartzites, schists, micaschists, amphibolites, gneisses and migmatites. Tectonism has formed a landscape characterized by the development of linear and folded valleys and ridges, fault scarps, V-shaped valleys, incised rivers and knickpoints. These landforms constitute important markers of the regional tectonic activity, which have been computed from spatial sources such as SRTM, DEM, hydrographical networks and geomorphic indices such as AF, T, Smf, Vf, Bs, Hi, U, SI and Li. The results highlighted a mature relief consisting of asymmetric basins generated by tilting and uplift phenomena. The relative index of active tectonics (RIAT) has been estimated from an average of eight geomorphic indices evaluated on 24 sub-basins, in the study area. Four classes have been defined: class 1 (1.38), very high active (1.0 ≤ RIAT < 1.5); class 2 (1.50–1.88), high active (1.5 ≤ RIAT < 2.0); and class 3 (2.00–2.13) moderate active (2.0 ≤ RIAT < 2.5). These three classes, respectively covering 10.20% (458 km 2 ), 80.10% (3595 km 2 ) and 9.69% (435 km 2 ) of the study area, have shown a highly active tectonic zone, and imply the existence of a neotectonic event in the YG. This tectonic unit (YG) was also affected by the dextral NW-SE strike-slip faulting, which cross-cut the Sanaga Shear Zone (SSZ) at Ebebda and the foliation oriented NW-SE. The tilting and uplift of rocks related to Moho ascending are responsible for crustal thinning in the Cameroon basement, more important to the Adamawa Plateau from the Cretaceous age and the reactivation of existing tectonic accidents. The presence of hills, fault scarps, reverse faults, knickpoints, V and U shaped valleys and rounded mountains testify to the interaction between tectonic uplift, lithology, climate, weathering and erosion.