Central African Shear Zone

The Central African Shear Zone (CASZ) (or Shear System) is a wrench fault system extending in an ENE direction from the Gulf of Guinea through Cameroon into Sudan. The structure just isn't nicely understood. The shear zone dates to at the least 640 Ma (million years in the past). Motion occurred along the zone throughout the break-up of Gondwanaland within the Jurassic and Cretaceous periods. A number of the faults within the zone were rejuvenated more than once before and throughout the opening of the South Atlantic in the Cretaceous period. It has been proposed that the Pernambuco fault in Brazil is a continuation of the shear zone to the west. In Cameroon, the CASZ cuts across the Adamawa uplift, a post-Cretaeous formation. The Benue Trough lies to the north, and the Foumban Shear Zone to the south. Volcanic activity has occurred alongside most of the size of the Cameroon line from 130 Ma to the present, and may be associated to re-activation of the CASZ.



The lithosphere beneath the CASZ on this area is thinned in a relatively slim belt, with the asthenosphere upwelling from a depth of about 190 km to about 120 km. The Mesozoic and Tertiary movements have produced elongated rift basins in central Cameroon, northern Central African Republic and southern Chad. The CASZ was previously thought to increase eastward solely to the Darfur region of western Sudan. It is now interpreted to increase into central and eastern Sudan, with a total length of 4,000 km. Within the Sudan, the shear zone might have acted as a structural barrier to growth of deep Cretaceous-Tertiary sedimentary basins within the north of the area. Objections to this principle are that the Bahr el Arab and Blue Nile rifts prolong northwest beyond one proposed line for the shear zone. However, the alignment of the northwestern ends of the rifts on this areas helps the theory. Ibrahim, Ebinger & Fairhead 1996, pp.



Dorbath et al. 1986, pp. Schlüter & Trauth 2008, pp. Foulger & Jurdy 2007, pp. Plomerova et al. 1993, pp. Bowen & Jux 1987, pp. Bowen, Robert; Jux, Ulrich (1987). Afro-Arabian geology: a kinematic view. Dorbath, C.; Dorbath, L.; Fairhead, J. D.; Stuart, G. W. (1986). "A teleseismic delay time examine across the Central African Shear Zone within the Adamawa area of Cameroon, West Africa". Foulger, Gillian R.; Jurdy, Donna M. (2007). Plates, plumes, and planetary processes. Geological Society of America. Ibrahim, A. E.; Ebinger, C. J.; Fairhead, J. D. (20 April 1996). "Lithospheric extension northwest of the Central African Shear Zone in Sudan from potential subject studies". Pankhurst, Robert J. (2008). West Gondwana: pre-Cenozoic correlations across the South Atlantic Region. Plomerova, J; Babuska, V; Dorbath, C.; Dorbath, L.; Lillie, cordless power shears R. J. (1993). "Deep lithospheric construction throughout the Central African Shear Zone in Cameroon". Geophysical Journal International. 115 (2): 381-390. Bibcode:1993GeoJI.115..381P. Selley, Richard C. (1997). African basins. Schlüter, Thomas; Trauth, Martin H. (2008). Geological atlas of Africa: with notes on stratigraphy, tectonics, financial geology, geohazards, geosites and geoscientific training of every country. シュプリンガー・ジャパン株式会社.



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