A Comparative Geophysical Study of the Sedimentary-Metamorphic Contacts in the Douala and Kribi-Campo Sub-Basins of Cameroon
The magnetotelluric method has been used in this work to compare the nature of the sedimentary-metamorphic contacts of the Douala and Kribi-Campo sub-basins in Cameroon. The results show that the sedimentary-metamorphic contact zones for the two sub-basins, marked by a subsidence of the low resistivity materials on the sedimentary formations and uplift of the high resistivity materials characterized by intrusive bodies of higher values of resistivity on the metamorphic formations, are structurally similar,. However, the very low values of resistivity of rocks in the Douala sub-basin is suggestive of high porosity, permeability and high level of saline ions dissociation leading to high conductivity. These rocks should be of unconsolidated sediments for the sedimentary formation and gneiss for the metamorphic formation. On the contrary, the very high values of resistivity for rocks in the Kribi-Campo sub-basin indicate the absence of free mobile electrons and ions and low porosity, permeability and non-conductivity. The sedimentary formation of this sub-basin should be composed of limestone and conglomerates rocks with some gneissic and unconsolidated granitic materials. The rocks in the metamorphic formation should be completely granitic in nature. The shallow depth of penetration of only 4 km of telluric current in the Douala sub-basin is enough evidence that the tectonic events responsible for the emplacement of this contact zone were limited to the earth crust. On the other hand, in the Kribi-Campo sub-basin the tectonic events should have originated from within the earth mantle as the depth of penetration of telluric current attains 150 km.
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