Earth's mantle illustration

A slice through the Earth’s mantle, cutting across major mantle upwelling locations. (Image courtesy of C. Conrad)

A study by Clinton Conrad, associate professor of geology at the University of Hawaiʻi at Mānoa’s School of Ocean and Earth Science and Technology, and colleagues shows that large-scale upwelling within Earth’s mantle mostly occurs in only two places—beneath Africa and the Central Pacific. More importantly, the study revealed that these upwelling locations have remained remarkably stable over geologic time, despite dramatic reconfigurations of tectonic plate motions and continental locations on the Earth’s surface. The paper, “Stability of active mantle upwelling revealed by net characteristics of plate tectonics” was published in Nature.

Conrad has studied patterns of tectonic plates throughout his career, and has long noticed that the plates were, on average, moving northward. “I was curious if I could determine a single location in the Northern Hemisphere toward which all plates are converging, on average,” said Conrad.

After locating this point in eastern Asia, Conrad then wondered if other special points on Earth could characterize plate tectonics. “With some mathematical work, I described the plate tectonic ‘quadrupole,’ which defines two points of ‘net convergence’ and two points of ‘net divergence’ of tectonic plate motions.”

When the researchers computed the plate tectonic quadruople locations for present-day plate motions, they found that the net divergence locations were consistent with the African and central Pacific locations where scientists think that mantle upwellings are occurring today.

Conrad headshot

Clinton Conrad

“Next, we applied this formula to the time history of plate motions and plotted the points. I was astonished to see that the points have not moved over geologic time,” said Conrad.

Because plate motions are merely the surface expression of the underlying dynamics of the Earth’s mantle, Conrad and his colleagues were able to infer that upwelling flow in the mantle must also remain stable over geologic time.

Earth’s mantle dynamics govern many aspects of geologic change on the Earth’s surface. This recent discovery provides a framework for understanding how mantle dynamics can be linked to surface geology over geologic time. For example, the researchers can now estimate how individual continents have moved relative to these two upwelling locations. This allows them to tie specific events that are observed in the geologic record to the mantle forces that ultimately caused these events.

Read more about the discovery in the School of Ocean and Earth Science and Technology news release.

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