Rifts in Sudan and Kenya
The Central African Shear Zone (CASZ) (or Shear System) is a wrench fault system extending in an ENE directionfrom the Gulf of Guinea throughCameroon into Sudan.[1] The structureis not well understood. As of 2008 therewas still no general agreement about how the individual shearsalong the lineamentlink up.[2]
Description
The shear zone dates to at least 640 MA (million years ago).[3] Motion occurred along the zone during the break-up of Gondwanaland in the
Jurassic and Cretaceousages.[1] Some of the faults in the zone were rejuvenated more than oncebeforeand during the opening of the
South Atlanticin the Cretaceousera.[3]
The Pernambuco fault in Brazil is a continuation of the shear zone to the west.[3] 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.[4] Volcanic activity has occurred along most of the length of the Cameroon line from 130 MA to the present, and may be related to re-activation of the CASZ.[5] The lithospherebeneath the CASZ in this area is thinnedin a relatively narrow belt, with the
asthenosphereupwelling from a depth of about 190 km to about 120 km.[6] The Mesozoic and
Tertiarymovements have produced elongated
riftbasins in central Cameroon, northern
Central African Republic and southern Chad.[3]
Sudan
The CASZ was formerlythoughtto extend eastward only to the Darfur regionof western Sudan.[3] It is now known to extend into central and eastern Sudan, with a total length of 4,000 km.[1] In the Sudan, the shear zone may have acted as a structuralbarrier to development of deep Cretaceous-Terriary sedimentarybasins in the north of the area. Objectionsto this theoryare that the Bahr el Arab and Blue Nile rifts extend northwest beyond one proposed line for the shear zone.[7] However, the alignment of the northwestern ends of the rifts in this areas supports the theory.[8]
References1
Ibrahim, Ebinger & Fairhead 1996 , pp. Pankhurst2008 , pp. 404.
3. ^ a b c d e Dorbath et al. 1986 , pp. 751-766.
4. ^ Schlüter& Trauth 2008 , pp. 60.
5. ^ Foulger & Jurdy 2007 , pp. 16.
6. ^ Plomerova et al. 1993 , pp. 381–390.
7. ^ Selley 1997 , pp. 113.
8. ^ Bowen& Jux 1987 , pp. 143.
الرئيسية 