North Africa’s spine was built in three slow collisions
The Atlas Mountains run about 2,500 kilometres across Morocco, Algeria, and Tunisia, fencing the Sahara from the Mediterranean and Atlantic. Named with Berber mountain words that echo Atlas, they crest at Toubkal’s 4,167 metres—yet geologists still puzzle over how such height rose with so little crustal thickening.
Africa's ancient basement rock formed in the Precambrian, long before the Atlas existed. The range itself was assembled in three distinct episodes. First, around 300 million years ago, continental collisions raised the Anti-Atlas as part of the Alleghenian mountain-building event, when Africa and North America were joined. That chain once rivalled the Himalayas, and its worn remnants survive across the ocean in the Fall Line of the eastern United States and within the Appalachians.
In the second episode, during the Mesozoic, the crust stretched and tore apart, separating those continents and opening deep sedimentary basins. Most of the rock now exposed on the High Atlas was laid down on the sea floor during that time. Third, between about 66 and 1.8 million years ago, Europe and Africa collided near the southern tip of Iberia, pushing up today's chains; the same convergence helped close the Strait of Gibraltar and build the Alps and Pyrenees.
A puzzle remains. Collisions normally thicken the crust and squeeze it horizontally, but the Atlas shows surprisingly little of either despite its height, and evidence for subduction beneath it is thin. Recent studies suggest that processes deep in the mantle helped lift the High and Middle Atlas.
Geographers split the range into regions, including the Anti-Atlas, High Atlas and Middle Atlas in Morocco. The Anti-Atlas runs roughly 500 kilometres from the Atlantic in south-west Morocco towards Ouarzazate and Tafilalt, bordering the Sahara, with the volcanic Djebel Siroua reaching 3,304 metres. Its people are mainly Berber, and the Berber words adrar and adras for mountain are thought to be related to the name Atlas. The mountains hold iron, lead, copper, silver, mercury, rock salt, phosphate, marble, anthracite and natural gas, and they shelter mostly African plants and animals, some also found in Europe, many now endangered and a few already lost.
Source: Atlas Mountains
