Structural interpretation of gravity anomalies from the Kribi–Edea zone, South Cameroon: a case study

The analyses of established gravimetric anomaly maps, the multi-scale evaluation of the maxima of gradients and the quantitative interpretation of residual anomalies by spectral analysis, by the ideal body solution and by 2.5D modelling suggest the presence of contacts between rocks of different densities at different depths and a dense intrusive igneous body in the upper crust of the Kribi–Edea zone. The model obtained along our study profile shows two blocks of the same type of igneous rock with a density contrast of 0.167 g cm-3 in comparison with the density of the surrounding metamorphic rocks. The upper surfaces of these igneous blocks locally lie at depths between 0.9 and 1 km, but generally lie between depths of 3.5 and 4 km. Their lower surfaces, which are flat, lie between depths of 9 and 9.3 km. The multi-scale evaluation of the maxima of gradients reveals three contacts oriented SSW–NNE, one contact oriented N–S and one contact oriented SSE–NNW. We have given, after the analysis of the results of the multi-scale evaluation of maxima of gradients, the limit values that estimate the depth interval over which the depth to the bottom of each contact is found.