CHICAGO, Feb. 19 (Xinhua) -- Geologic activity within stable portions of the Earth's uppermost layer may have occurred more recently than previously believed.

A research team led by the University of Illinois (UI) has identified unexpected geophysical signals underneath tectonically stable interiors of South America and Africa.

The findings was published in the latest issue of the Nature Geoscience, the University of Illinois said in a website press release on Monday.

It is not clear if and how craton-plume interaction may affect modern-day earthquake activity and volcanism in areas thought of as geologically inactive.

But the study marks new thinking in how geologists may understand the so-called stable cratons.

The researchers processed geophysical data with the Blue Waters supercomputer at the National Center for Supercomputing Applications at Illinois, hoping to better understand these high-elevation regions.

The new data indicate that the cold mantle that lies below these regions in South America and Africa, once joined as part of the supercontinent Pangea, has a layered structure and that the lower layer was more dense in the past than it is today.

This density difference could be the result of a process called mantle delamination.

During delamination, the denser lower mantle layer peels away from the buoyant upper layer under the crust of the craton after interacting with hot magma from mantle plumes, the researchers said.

"From several types of seismic imaging data, we can see what we think are delaminated mantle slabs sinking into the hot, viscous deep mantle," said UI professor of geology and study co-author Lijun Liu.

"The material that subsequently grows back at the roots of the cratons after delamination, due to cooling from above, is probably compositionally much less dense than what was there before," said UI geology professor Craig Lundstrom.

"That adds buoyancy, and that force from buoyancy could be what forms the anomalously high topography," said Craig Lundstrom.

There is also evidence to support other locations of craton-plume interaction during other times in Earth's history.

"The rock record shows that uplift and erosion events have taken place during previous supercontinent cycles," said UI geology professor and School of Earth, Society and Environment Director Stephen Marshak. Enditem

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