Earth’s Tectonic Plates Are Weaker Than Once Thought

David Goldsby, teaming with Christopher A. Thom, a doctoral student at Penn, as well as researchers from Stanford University, the University of Oxford, and the University of Delaware, has resolved a long-standing question in the area of plate tectonics. While previous laboratory experiments resulted in widely disparate estimates of the strength of olivine in the lithospheric mantle, the relatively cold and therefore strong part of Earth’s uppermost mantle, the new work, published in the journal Science Advances, resolves the previous disparities by finding that, the smaller the grain size of the olivine being tested, the stronger it is.

“We are interested in large-scale geophysical processes, like how plate tectonics initiates and how plates move underneath one another in subduction zones,” says Goldsby, Associate Professor of Earth and Environmental Science. “To do that, we need to understand the mechanical behavior of olivine, which is the most abundant mineral in the upper mantle of the earth.”

Because olivine in Earth’s mantle has a larger grain size than most olivine samples tested in labs, the results suggest that the mantle, which comprises up to 95 percent of the planet’s tectonic plates, is in fact weaker than once believed. This more realistic picture of the interior may help researchers understand how tectonic plates form, how they deform when loaded with the weight of, for example, a volcanic island such as Hawaii, or even how earthquakes begin and propagate.

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