TheTuareg Shield is a geological formation lying between theWest African craton and theSaharan Metacraton inWest Africa. Named after theTuareg people, it has complex a geology, reflecting the collision between thesecratons and later events. The landmass covers parts ofAlgeria,Niger andMali.
The Tuareg Shield is mainly composed ofArchean orPaleoproterozoicterranes andNeoproterozoic terranes that amalgamated during the Pan African orogeny when the West African craton and the Saharanmetacraton converged.
The shield originated in oceanicisland 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, theTilemsi 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 thePan-African orogeny.[2]The western part of theHoggar Mountains (Ahaggar Mountains) is made of material from thePharusian 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]
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 inAlgeria,Adrar des Ifoghas inMali andAïr Mountains inNiger.[1]
The Trans-Saharanorogenic belt which lies along the eastern margin of the West African craton is generally thought to have been caused by the collision between that craton and the Tuareg shield.[2]
At the start of thePhanerozoic the shield was eroded and covered byOrdovician sandstones. More recently, around 95 Ma - 90 Ma, the area was partly submerged by a seaway linking theMediterranean and the proto-Atlantic. Since then, starting around 30 Ma the area rose by as much as 3000 meters.
Volcanic activity started around 35 Ma - 30 Ma, and continues sporadically to this day.[1]The higher areas consist of the upliftedPrecambrian basement overlaid with volcanic rocks.[4]