How did Gondwana Break Up?

Posted by Joshua S. Hill

March 26, 2008

The history of Earth’s supercontinents is one that will never end to fill me with wonder. A theorized cyclical phenomenon, supercontinents are thought to form roughly every 250 million years. In fact, we currently have a supercontinent of our own today; Eurasia. And though due to the wonders of modern day politics it has been separated in to innumerable countries, its geological structure qualifies it as a supercontinent.

But take us back some 180 million years, and we’ll find ourselves on the last major supercontinent; Gondwana.

But it is theorized that it would be about this time that Gondwana began to break up. The question however has stood, how did Gondwana break up? Several theories have been presented ranging from lithospheric stretching in response to subduction to the action of deep-seated mantle plumes.

Before moving on to the most recent theory that has gained support, I want to stop and explain the first two theories.

A lithosphere is the solid outermost shell of a rocky planet, and in the Earth’s case, includes the curst and the uppermost mantle. If the lithosphere is caused to stretch horizontally a twofold action is theorized to occur. The lower, hotter part of the lithosphere will flow slowly away from the focal point of the stretching, leaving the upper and more brittle crust to fault and fracture.

These two actions cause the earth’s surface to subside, and create a geological depression. This can often lead to the influx of water to fill in the new basin as in the example of the North Sea.

When related to the breakup of Gondwana, the influx of water would enhance the fracturing and possibly force the land masses away from each other.

The second theory is that of deep-seated mantle plumes, a less developed theory due to the necessity to redevelop plate-tectonics to explain it. A mantle plume is the upwelling of hot rock within the Earth’s mantle. It is theorized that these mantle plumes are the creators of volcanic hotspots, and volcanic island chains such as Hawaii.

In the case of Hawaii, the island chain stretches over a distance in the direction of its drift. Known to be a volcanic hotspot, the most active of the Hawaiian volcanic islands is always in the same location. The theory exists that as the underwater seabed drifted across this particular mantle plume, the islands were created through the upwelling of geological structure.

All of this leads us to our third and most recently popular theory; that Gondwana simply cracked in two due to its massive size and weight.

Graeme Eagles, from Royal Holloway, University of London and Matthias König, from the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, have acquired magnetic and gravity anomaly data from what are known to be Gondwana’s earliest cracking points; fracture zones in Mozambique Basin and the Riiser-Larsen Sea off Antarctica.

Eagles and König input the data into a computer model that potted the path that different parts of the now split Gondwana took as it broke apart. The model supports the idea that Gondwana split in to only two large plates. This simple split is already a more approved theory over deep-seated mantle plumes due to its simplicity. “It doesn’t require us to re-invent plate tectonics at break-up times,” says Eagles.

The pair suggests that large continents like Gondwana are naturally and inherently unstable because they have such a thick crust. Compared to the oceans this allows the mass to spread outwards under their own weight and, eventually, split apart.

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