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| Central African Shear Zone | |
|---|---|
| Name | Central African Shear Zone |
| Other name | C.A.S.Z. |
| Country | Central African Republic, Chad, Cameroon, Sudan, Nigeria, Gabon |
| Region | Central Africa |
| Epoch | Proterozoic Eon, Phanerozoic Eon |
| Type | Transcurrent shear zone |
Central African Shear Zone The Central African Shear Zone is a major intracontinental transcurrent fault system that traverses multiple sovereign states across Central Africa and links cratonic blocks and mobile belts. It plays a key role in the tectonic framework connecting the West African Craton, the Sao Francisco Craton, the Congo Craton, and the East African Rift System, and has been the focus of structural, geochronological, and geophysical investigations by institutions such as the US Geological Survey, the British Geological Survey, and the Université de Yaoundé.
The shear zone lies within a mosaic of ancient terranes including the Pharusian orogeny-affected belts, the Eburnean orogeny-modified crust, and Proterozoic granitoids that abut the São Francisco Craton. It constitutes a long-lived strike-slip corridor cutting across Precambrian shield areas and Phanerozoic cover sequences, juxtaposing units correlated with the Neoproterozoic Pan-African orogeny and Mesoproterozoic rifted margins. Regional syntheses link its kinematics to plate interactions involving the breakup of Gondwana and later intraplate stress fields associated with the opening of the South Atlantic Ocean and the evolution of the East African Rift System.
The structural history records multiple reactivations from the Neoproterozoic through the Phanerozoic, with an early history tied to Pan-African collisional events documented in zircon ages from studies by teams at Imperial College London and Université Félix Houphouët-Boigny. Subsequent Mesozoic transtensional phases coincide with the seafloor spreading that formed the South Atlantic Ocean and the concomitant thermal adjustments recorded in apatite fission-track data used by researchers at the University of Cape Town. Cenozoic reactivation episodes correlate with far-field stresses transmitted from the African Plate interactions with the Eurasian Plate and the Somalia Plate during evolution of the Red Sea Rift.
The shear corridor displays right-lateral to transtensional kinematics expressed as steeply plunging mylonite zones, anastomosing fault strands, and pull-apart basins comparable to structures mapped in the East African Rift and the Tethyan fold belt. Detailed mapping by teams from the Geological Society of London and the Institut de Recherche pour le Développement reveals segmented geometry with restraining and releasing bends that localize dextral strike-slip motion and control sedimentary depocenters related to the Benue Trough and intracontinental basins such as the Chad Basin. Cross-cutting relationships tie the shear zone to major lineaments, including correlations with the Trans-Saharan Belt.
Magmatic suites spatially associated with the shear zone range from Proterozoic granitoids and syn-tectonic granites to Mesozoic alkaline provinces akin to the Cameroon Volcanic Line, with petrogenesis examined by laboratories at CNRS and ETH Zurich using U-Pb geochronology. Metamorphic gradients reveal greenschist to amphibolite facies zones within mylonites, comparable to metamorphic assemblages described in the Mozambique Belt, and reflect burial and exhumation cycles during transpressional events documented by thermochronology from groups at Leeds University.
Although largely aseismic compared to plate boundary faults, the shear zone shows intraplate seismicity recorded by networks run by the International Seismological Centre and national observatories in Nigeria and Chad, indicating episodic strain release. Aeromagnetic, gravity, and satellite-based interferometric synthetic aperture radar (InSAR) surveys by the European Space Agency and the NASA Earth Science Division have delineated deep-seated contrasts and crustal thinning along the corridor, while passive seismic tomography from collaborations with GFZ Potsdam has imaged variations in lithospheric thickness beneath cratonic and mobile belt segments.
The shear zone and adjacent terranes host diverse mineral occurrences including orogenic gold deposits analogous to those in the Ashanti Belt, base-metal sulfide mineralization reminiscent of deposits in the Central African Copperbelt, and rare-metal pegmatites studied by prospectors from Barrick Gold Corporation and regional geological surveys. Structural traps and hydrothermal fluids channeled along mylonite corridors have been targeted for exploration by companies operating under licensing regimes of the Gabonese Republic and the Republic of Cameroon, with commodity interests in gold, tin, tantalum, and associated rare earth elements.
The shear zone provides a key link in reconstructions of Proterozoic to Phanerozoic supercontinents, intersecting reconstructions produced by researchers at Caltech and the Smithsonian Institution that tie African deformational fabrics to conjugate margins in South America such as the Borborema Province. Correlative relationships with the Central African Republic Orogen and alignments with lineaments in the Amazonian Craton support hypotheses about long-lived transcontinental shear systems influencing continental assembly, basin development, and modern intraplate stress transmission across the African Plate.