Discovery of new force driving Earth’s tectonic plates

Plumes of hot magma from deep inside the Earth could propel tectonic plate motions around the globe, according to Scripps scientists.

Scientists have known for decades that the ongoing pull and push movements of tectonic plates are responsible for sculpting continental features around the planet. Volcanoes, for example, are generally located at areas where plates are moving apart or coming together. Scripps scientists Steve Cande and Dave Stegman have now discovered a new force that drives plate tectonics: plumes of hot magma pushing up from Earth’s deep interior. Their research is published in the July 7, 2011 issue of the journal Nature.

Bends of the fracture zones on the Southwest Indian Ridge caused by the slowdown of Africa in response to the Reunion plume head. The image shows the gravity field. Via Scripps News

Using analytical methods to track plate motions through Earth’s history, Cande and Stegman’s research provides evidence that such mantle plume “hot spots,” which can last for tens of millions of years and are active today at locations such as Hawaii, Iceland and the Galapagos, may work as an additional tectonic driver, along with push-pull forces.

Reconstruction of the Indo-Atlantic Ocean 63 million years ago, during the time of the superfast motion of India which Scripps scientists attribute to the force of the Reunion plume head. The arrows show the relative convergence rate of Africa (black arrows) and India (dark blue) relative to Eurasia before, during and after (from left to right) the period of maximum plume head force. The jagged red and brown lines northeast of India show two possible positions of the trench (the subduction zone) between India and Eurasia depending on whether the India-Eurasia collision occurred 52 million years ago or 43 million years ago. Via Scripps News

Their new results describe a clear connection between the arrival of a powerful mantle plume head around 70 million years ago and the rapid motion of the Indian plate that was pushed as a consequence of overlying the plume’s location. The arrival of the plume also created immense formations of volcanic rock now called the Deccan flood basalts in western India, which erupted just prior to the mass extinction of dinosaurs. The Indian continent has since drifted north and collided with Asia, but the original location of the plume’s arrival has remained volcanically active to this day, most recently having formed Réunion island near Madagascar.

The team also recognized that this “plume-push” force acted on other tectonic plates, and pushed on Africa, as well, but in the opposite direction.

Stegman, an assistant professor of geophysics in Scripps’ Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, said:

Prior to the plume’s arrival, the African plate was slowly drifting but then [stopped] altogether, at the same time the Indian [sped] up. It became clear the motion of the Indian and African plates [was] synchronized, and the Réunion hotspot was the common link.

Images of the satellite-derived gravity field over the Central Atlantic (top) and Southwest Indian Ridge (right) showing the zones of rough topography and sharp bends in the fracture zones that were caused by the slowing of Africa’s motion as the Reunion plume head reached its maximum force. The inset globe shows the location of the gravity maps as well as the extent of the parallel zones of rough topography (outlined in red) on the flanks of the Mid-Atlantic and Southwest Indian ridges caused by the change in Africa’s motion. Via Scripps News

After the force of the plume had waned, the African plate’s motion gradually returned to its previous speed while India slowed down.

Cande, a professor of marine geophysics in the Geosciences Research Division at Scripps, said:

There is a dramatic slow down in the northwards motion of the Indian plate around 50 million years ago that has long been attributed to the initial collision of India with the Eurasian plate. An implication of our study is that the slow down might just reflect the waning of the mantle plume—the actual collision might have occurred a little later.

Summary: Scripps scientists Steve Cande and Dave Stegman have discovered a new force that is likely a driver of plate tectonics: plumes of hot magma pushing up from Earth’s deep interior. Their research is published in the July 7, 2011 issue of the journal Nature.

Via Scripps Institution of Oceanography

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