The Logone Birni Basin in Northern Cameroon: Transition Between the West African Rift Sub-System (WAS) and the Central African Rift Sub-System (CAS); Tectonic and Geophysical Models
Jean-Pierre Loule1 and Pospisil Lumbomil2
1SNH, Yaounde, Cameroon
2Brno University of Technology, Brno, Czech Republic
The Logone Birni Basin (LBB) situated in northern Cameroon and to the south of Lake Chad covers a total area of 27,000 sqkm and geographically belongs to the West and Central African Rift System (WCAS). The WCAS is divided into two coeval Cretaceous genetically related but physically separated rift sub-systems (Fairhead, 1986), namely the West African Rift sub-System (WAS) and the Central African Rift sub-System (CAS). Genik (1992) indicated that these two rift sub-systems, although genetically related, decipher some structural differences.
To unravel the tectonic and geophysical models of the inter-locked LBB, geophysical analyses and interpretation have been realized as an accompanying program of the 2D non-exclusive seismic survey carried out jointly by Geofyzika, a.s. and SNH. The seismic reflection data coupled with Grav/Mag and Remote Sensing data were used to model basement architecture, structural conditions of basin filling and distribution of buried volcanic bodies. The results arrived at confirm former basic knowledge on the tectonic and geophysical models of the WCAS, but also offer new insights on the peculiar tectonic conditions in the LBB.
The structural styles observed in the LBB include NE-SW mainly pre-Tertiary extensional faults, normal synthetic tilted fault blocks, NNE-SSW antithetic normal faults associated with sinistral wrenching, WNW-ESE normal faults, ENE-WSW fault blocks associated with dextral transtensional movement of Borogop fault zone to the south, transpressional draped anticlines, transpressed basement blocks, traspressed basement blocks with associated transtensional negative flower structures,and positive flower structures.
This blending of structural styles is attributed to the importance of strike-slip deformation within the LBB, compared to the adjacent CAS and WAS basins.
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