How Africa's Shape Was Determined By Competing Tectonic-Plate Movements

By Shweta Iyer on March 2, 2014 12:12 PM EST

west africa
Competing expansion between the tectonic plates that made up Africa and South America led to West Africa's shape. (Photo: NASA)

What would the Earth have looked like if the great supercontinent Gondwana had split differently 130 million years ago? Geography, as we know it would have been completely different. Africa and South America would have had different shapes, and there would have been an ocean south of the Sahara desert, according to a group of geoscientists. They discovered this using sophisticated plate tectonic and three-dimensional modeling to highlight the importance of rift orientation (where tectonic plates split) relative to extension direction (how much they stretch before they break) as a key factor in deciding if an ocean basin opens or an aborted rift forms - usually appearing as a lake, river or stream - in the continental interior. .

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Millions of years ago, there was only a single supercontinent, called Pangea. It eventually split into the two supercontinents Laurasia and Gondwana, of which the latter eventually became South America, Africa, Antarctica, Australia, India, and other landmasses that make up today's Southern Hemisphere - the reasons behind these tectonic plate separations are still debated. But what is known, is that the first split took place along the East African Coast, forming a western and eastern half. The western half, which constituted Africa and South America, fragmented further, separating the two landmasses.

Looking for insights into the processes that shaped present day West Africa and eastern  South America, researchers from the University of Sydney and the GFZ German Research Centre for Geosciences investigated the continental margins - where oceanic crust meets continental crust - and the subsurface graben structure - essentially a valley - forming the West African Rift, which stretches between Nigeria and Libya. They were specifically looking at why the South Atlantic part of this giant rift system evolved into an ocean, while its northern part, along the West African Rift, became stuck.

"Extension along the so-called South Atlantic and West African rift systems was about to split the African-South American part of Gondwana north-south into nearly equal halves, generating a South Atlantic and a Saharan Atlantic ocean," geoscientist Sascha Brune said in a statement. "In a dramatic plate tectonic twist, however, a competing rift along the present-day equatorial Atlantic margins, won over the West African rift, causing it to become extinct, avoiding the break-up of the African continent and the formation of a Saharan Atlantic ocean."

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