Déformations très grandes longueurs d’onde de l’Afrique au cours du Cénozoique
Résumé
The African continent is characterized by a bimodal topography. The
900-1100 m elevation peak mainly corresponds to the Southern African
(Kalahari Plateau) and the East African Domes, whereas the 300-400 m
peak is the mean elevation of the Sahara. Those reliefs are characterized
by very long wavelength (x1000 km), similar to the scale of mantle
dynamics. The origin of this relief, dynamic topography or more local
controls (e.g. old lithospheric inheritance), are highly debated and more
geological controls are required.
To answer those questions - in the frame of the TopoAfrica project -
we performed a geomorphical study of Africa coupled with the tectonosedimentary
study of the sedimentary basins or the magmatism.
(1) Most of the African reliefs are younger than the Early-Middle Eocene
(55-40 Ma).
(2) The only significative old relief of Africa is the Southern African
Plateau that experienced a two steps evolution, a first uplift during Late
Cretaceous contemporaneous with high erosion under humid climatic
conditions, followed by a second uplift during Late Eocene - Early Oligocene.
The present-day arid to semi-arid climate could explain its preservation.
(3) Most of Africa is uplifted during Miocene times (20-10 Ma), age of
most of the present-day reliefs.
(4) The African magmatic provinces (Virunga-Kivu, Cameroon Volcanic
Line, Hoggar, Aïr...) are associated with local uplifts that started
around Late Eocene times (40-35 Ma).
The relationships of those reliefs with the migration of the African plate
over the African superswell will be discussed.