Earth's Ancient Rock Isn't as Stable as Once Thought: Cratons are Unstable

First Posted: Sep 10, 2015 08:09 AM EDT

Over the course of billions of years, continents break up, drift apart, and are pushed back together again. The cores of continents, though, are geologically extremely stable. Called cratons, these cores are the oldest known geological features on our planet. Now, though, scientists have found that these cratons are not as solid as once thought.

"We combined and analyzed several data sets from Earth's gravity field, topography, seismology, and crustal structure and constructed a three dimensional density model of the composition of the lithosphere below North America," said Mikhail Kaban, one of the researchers, in a news release. "It became apparent that the lower part of the cratonic root was shifted by about 850 kilometers."

Previously, researchers believed that cratons were solid, and that these continental roots did not undergo substantial changes after their formation about 2.5 to 3.8 billion years ago. In this latest study, though, this traditional view is contradicted.

What causes the deformation of the stable and solid craton? Scientists created a model of the flows in Earth's mantle below North America. This revealed that the mantle material below 200 kilometers flows westward at a velocity of about 4 millimeters per year. This is in concordance with the movement of the tectonic plate. Due to the basal drag of this flow, the lower part of the cratonic lithosphere is shifted.

"This indicates that the craton is not as solid and as insensitive to the mantle flow as was previously assumed," said Kaban

The findings are published in the journal Nature Geoscience.

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