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Plate tectonics go to the core

Posted February 1, 2017

This image, taken by an astronaut in early 2003, shows the land-sea interactions along a section of Mexico’s west coast just south of Mazatlan and the Isla Marias archipelago. The islands are a manifestation of intersecting plate boundaries — the spreading center of the East Pacific Rise, which traces south from the Gulf of California, and the subduction zone that consumes the Cocos plate beneath southern Mexico.

The heat from Earth’s core has a significant effect on tectonic plate movement.

The new research challenges the previous school of thought that movement of Earth’s tectonic plates is driven largely by negative buoyancy created as they cool.

The team, including Lawrence Livermore National Laboratory scientist Nathan Simmons and university collaborators, combined observations of the East Pacific Rise (the Earth’s dominant mid-ocean ridge) with insights from modeling of the mantle flow beneath the Pacific Ocean.

“It’s likely that heat from the deep Earth plays a significant role in global plate tectonics,” Simmons said. “The cooling and sinking of plates is not the only significant plate-driving force.”

The new findings also challenge the theory that underwater mountain ranges known as mid-ocean ridges are passive boundaries between moving plates. The findings show the East Pacific Rise is dynamic as heat is transferred from the deep Earth.

“We see strong support for significant deep mantle contributions of heat-to-plate dynamics in the Pacific hemisphere,” said University of Chicago (link is external) professor David Rowley, lead author of the paper. “Heat from the base of the mantle contributes significantly to the strength of the flow of heat in the mantle and to the resulting plate tectonics.”

Earth’s tectonic plates are generally considered to be driven largely by negative buoyancy associated with subduction of the ocean’s rocky upper mantle. Most mid-ocean ridges (MORs) are likely more passive plate boundaries whose flow is driven by subduction of oceanic slabs at trenches.

“Through modeling and observations, we found that over the past 80 million years, plate separation along the East Pacific Rise is driven significantly by heat drawn from Earth’s core, which is uncharacteristic relative to other MORs,” Simmons said.

Simmons helped develop the global-scale tomographic models of Earth’s mantle that were used to simulate mantle convection forward and backward in time to demonstrate the persistence of large-scale mantle upwelling beneath the East Pacific Rise region.

The East Pacific Rise is a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from (north to south) the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate and the Antarctic Plate. It runs south from the Gulf of California in the Salton Sea basin in Southern California to a point where it joins the Pacific-Antarctic Ridge

It has not significantly moved east-west for 50 to 80 million years, even as parts of it have been spreading asymmetrically. The researchers said these dynamics cannot be explained solely by subduction — the process in which one plate moves under another and sinks. The team attributes the phenomena to buoyancy created by heat arising from deep in the Earth’s interior.

Source: LLNL

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