Mapping transpressional and transtensional relay zones by coupling geological and geophysical field data: The case of the central Cameroon shear zone in the Mbere administrative division of the Adamawa region in Cameroon

Abstract

The aim of this study was to map the transpressional and transtensional relay zones of the Central Cameroon Shear Zone in the Mbere Administrative Division of the Adamawa Region of Cameroon using, geological and geophysical data analysis. The central Cameroon Shear Zone (CCSZ) is characterised by several large strike-slip faults oriented between N030E and N070E. The geological and structural field data analysis revealed two deformation regimes (strike-slip and tensile) that exhibit characteristic deformation markers identified in the field. The dextral movements on the strike-slip faults of the CCSZ were associated with these markers, the two regimes were found to be associated with the D3 deformation along the CCSZ. The tensile regime generated transtensional structures and led to the formation of the Cretaceous Mbere and Djerem basins, whereas the transcurrent regime caused the transpressional tectonics. Structural analysis of the joints and veins of the D4 deformation shows that their directions describe those of the major axes of the CCSZ. As the D4 deformation is controlled by transcurrent tectonics, to show that the vein intrusions constitute transpressional relay zones and to derive different models, processing, and interpretation methods (spectral analysis, shaded relief analysis, magnetic signal filtering, upward continuation, horizontal gradient magnitude, analytical signal, and 2.5D inversion) have been applied to the geophysical data. Magnetic residual analysis shows that the transpressional relay zones are characterised by high-frequency rectilinear magnetic anomalies (207.12–305.809 nT) and interference along the strike-slip faults. Through the superimposition of the geophysical interpretations, a structural model integrating the two deformation regimes with relay and Cretaceous basin models was developed.