Tuareg Shield
The Tuareg Shield is a geological formation lying between the
Origins
The Tuareg Shield is mainly composed of Archean or Paleoproterozoic terranes and Neoproterozoic terranes that amalgamated during the Pan African orogeny when the West African craton and the Saharan metacraton converged.
The shield originated in oceanic island arcs that formed on the cratons during 900 Ma to 680 Ma, of which relics remain as thrust sheets on top of more rigid bodies.[1]
In Mali, the Tilemsi belt is a complex of intraoceanic arcs that formed above a subduction zone sloping down to the east and were accreted to the shield during the Pan-African orogeny.[2] The western part of the Hoggar Mountains (Ahaggar Mountains) is made of material from the Pharusian Ocean.
This comprises oceanic basalts, arc volcanic and sedimentary rocks and sediments, which were shed into the Pharusian Ocean by the West African craton and the eastern Hoggar.[3]
Fracturing
During the oblique collision of the West African craton with the Saharan metacraton the shield was torn into separate but rigid moving blocks.[1] These blocks were separated by subvertical shear zones.
The fractured shield was penetrated by volcanic magmas that formed the Hoggar Mountains in Algeria, Adrar des Ifoghas in Mali and Aïr Mountains in Niger.[1]
The Trans-Saharan
Later events
At the start of the
Volcanic activity started around 35 Ma - 30 Ma, and continues sporadically to this day.[1] The higher areas consist of the uplifted Precambrian basement overlaid with volcanic rocks.[4]
References
- ^ ISBN 0-8137-2388-4.
- ^ ISBN 0-8137-1197-5.
- ISBN 0-19-516589-6.
- ISBN 978-0-8137-2418-8.