Saharan Metacraton
The Saharan Metacraton is a term used by some geologists to describe a large area of continental crust in the north-central part of Africa. Whereas a craton is an old and stable part of the lithosphere, the term "metacraton" is used to describe a craton that has been remobilized during an orogenic event, but where the characteristics of the original craton are still identifiable. The geology of the continent has only been partially explored, and other names have been used to describe the general area that reflect different views of its nature and extent. These include "Nile Craton", "Sahara Congo Craton", "Eastern Saharan Craton" and "Central Saharan Ghost Craton". This last term is because the older rocks are almost completely covered by recent sediments and desert sands, making geological analysis difficult.
The "metacraton" covers an area of about 5,000,000 km2. It lies between the Tuareg shield to the west, the Congo craton to the south, the Arabian-Nubian Shield to the east, and the northern African continental margin. The southern boundary is not well-defined, but may be considered to run along the northern edge of the Oubangides orogenic belt in the southwest and the Aswa Shear Zone further east. It lies under southern Egypt and Libya and western Sudan, northern Kenya, Uganda and Congo, the Central African Republic, Cameroon and eastern Nigeria and Chad.
The craton may have formed during a period of accelerated crustal growth between 3000 Ma and 2000 Ma (Ma: million years ago). The oldest rocks in Egypt date to about 2700 Ma. Rocks in southern Libya and eastern Chad have been dated between 2900 Ma and 2600 Ma. Some geologists date a rifting episode to between 1200 Ma and 950 Ma.
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