The orange colored area enclosed by a dashed line denotes a magma layer that scientists believe is facilitating the motion of the Cocos plate off Nicaragua. The blue areas represent the Cocos plate sliding across the mantle and eventually diving beneath the Central American continent, while the black dots signify earthquake locations. The discovery was made by analyzing data collected by an array of seafloor electromagnetic instruments, shown as inverted triangles. (Photo : Scripps Institution of Oceanography / University of California, San Diego)

Researchers have found a layer of molten rock in the Earth's mantle that acts like a lubricant and facilitates the movement of tectonic plates.

The discovery was made by researchers at the Scripps Institution of Oceanography at UC San Diego, who found the layer of lubricant at the Middle America trench offshore Nicaragua.

For years, researchers weren't sure what helps the tectonic plates slide. One theory was that water with dissolved minerals beneath the crust could act as a lubricant for the tectonic plates. However, there wasn't any evidence supporting or disproving this theory.

Now, researchers have gotten images of a 15.5 mile (about 25 kilometer) thick layer of semi-molten rock below the edge of the Cocos plate which moves beneath Central America, according to a news release.

"This was completely unexpected. We went out looking to get an idea of how fluids are interacting with plate subduction, but we discovered a melt layer we weren't expecting to find at all-it was pretty surprising," said Kerry Key, an associate research geophysicist from the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps.

Researchers captured the images of the magma during an expedition onboard the Melville - a research vessel owned by the U.S. Navy.

"Our data tell us that water can't accommodate the features we are seeing. The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle and that's really what's creating this ductile behavior for plates to slide," Samer Naif, a Scripps graduate student and lead author of the paper.

Researchers said that the study will help geologists better understand the movement of tectonic plates, and how that affects earthquakes and volcanoes.

"One of the longer-term implications of our results is that we are going to understand more about the plate boundary, which could lead to a better understanding of earthquakes," added Key.

The study is published in the journal Nature.