Earth Core Instability: Is North America's Core Less Solid Than We Thought?
Beneath North America, we have some unstable rock within the Earth's crust, in an area thought to be the craton, according to a new study. Cratons are located at the cores of continents, and are generally considered stable and mostly unchanged in a long while. However, a team of researchers recently discovered that the craton's root has shifted 850 kilometers west-southwest from its center.
Having survived 38 billion years, these cores were assumed to be stable, due to their solid structure and relatively low temperatures, compared to those of the surrounding mantle. According to a news release, new findings contradict previous assumptions that these continental roots did not experience significant changes after forming between 2.5 and 3.8 billion years ago.
"We combined and analyzed several data sets from the 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," Dr. Mikhail Kaban, from the GFZ German Research Centre for Geosciences and leader of the study, said in a statement. "It became apparent that the lower part of the cratonic root was shifted by about 850 kilometers."
So what caused this deformation? The researchers modeled flows in the Earth's mantle below North America to answer this question. They found that mantle material flows westward below 200 kilometers, at roughly four millimeters per year. This matches the movement of the tectonic plate. However, as a result of 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," Kaban explained.
This study suggests that there are more mechanical, chemical, and thermal interactions between cratons and the Earth's upper mantle than previously thought.
Their study can be found in the online publication Nature Geoscience.
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