Correlations between morphoneotectonic parameters and Precambrian tectonic structures in the Nyong Group greenstone belts: Example of the Kopongo area (NW of the Congo Craton, Southwestern Cameroon)

Abstract

The satellite image processing techniques used (filtering, enhancements, slope and elevation analysis) and morphoneotectonic analysis were applied to the topography and hydrographic network draining the Paleoproterozoic iron formations of Kopongo in SW Cameroon. Morphostructural investigations have shown that this domain is marked by an elongated relief of NNE-SSW direction, composed of asymmetric hills, plateaus and plains. The typology of the relief, slopes and hydrographic network, in addition to the structural axes, reflect well the lithostructural characteristics of these iron formations. The analysis and interpretation of morphometric data, coupled with literature review, field and drill-core mapping investigations, have resulted in logical morphoneotectonic and geological maps illustrating the correlations between the iron formations and buried structures. The information obtained relates in part to the tectonic relationship between geological structures, morphological units and iron formations. In addition, the spatial distribution of drain lengths and elevation appear to indicate the presence of buried geological basement megastructures. The waviness of the Sn foliation, Sn+1 foliations and the concordance of the Sn+1 and Sn/Sn+1 foliations in this area at the megascopic scale are marked respectively by Fn, Fn+1 and Fn+2 map folds corresponding to tectonic scales from the multiple compressive tectonics that affected these iron formations. These observations also show that the Kopongo iron formations are controlled by polyharmonic Fn+1 and Fn+2 map folds whose surface traces of their respective axial planes are oriented NE-SW to NNE-SSW and NE-SW, NW-SE to NNW-SSE. On the other hand, Digital Terrain Model data and geographical information system (GIS) were used in the evaluation of morphometric parameters such as linear, aerial and relief features. Besides, swath profiles helped in the interpretation of the regional topographic patterns and topographic stream profiles allowed to recognise vertical deformations affecting the drainage network. It appears that, the investigated terrain has been rejuvenated due to the interaction between climatic, lithological and tectonic factors. The lithopackage from the top to the base stratigraphy comprises three units in this study area. The upper unit consists of a mixture of colluvium and pisolitic laterite material, while, the middle unit is represented by alternating magnetite, magnetite-pyroxene and enriched magnetite-pyroxene gneisses, and the lower unit is made up of amphibolites and hypersthene-bearing gneisses.