Scientists Recreate Extreme Conditions Involved in Melting the Oceanic Tectonic Plates

Learning more about what happens below Earth's crust is crucial for understanding the processes that shape our planet. Now, scientists have recreated the extreme conditions 600 to 2,900 km below Earth's surface to better understand the extreme melting of basalt in the oceanic tectonic plates.

Earth is a very active planet. The heat it contains is capable of inducing the mantle convention that's responsible for plate tectonics, which helps shape the very continents. This energy comes from the heat that accumulated during the formation of our planet, the latent heat of crystallization of the inner core, and radioactive decay. Yet the temperatures inside are planet are not well known.

Convection causes hot material to rise to the surface of Earth and cold material to sink down toward the core. This means that when the ascending mantle begins to melt at the base of oceanic ridges, then basalt flows along the surface to form the oceanic crust. Over the course of millennia, the crust then undergoes subduction; its greater density causes it to sink into the mantle, constantly recycling itself as new crust is formed.

It's thought that the temperature at the core-mantle boundary increases by more than 1,000 degrees over a few hundred kilometers. This could potentially cause the partial melting of the mantle; yet this idea has left other geophysical observations unexplained. That's why the scientists decided to investigate a bit further.

The researchers exposed microscopic pieces of rock to extreme pressures and temperatures while simultaneously studying their structure with a powerful X-ray beam. This revealed that basalt produced on the ocean floor has a melting temperature lower than peridotite, which forms Earth's mantle. Near the core-mantle boundary, the melting basalt produces liquid rich in silica, which react rapidly with the mantle and indicate a speedy dissolution of the basalt rock back into the depths of Earth. This, in particular, provides a new explanation for seismic abnormalities at the base of the mantle.

"It could solve a long time controversy about the peculiar role of the core-mantle boundary in the dynamical properties of the Earth mantle," said Denis Andrault, one of the researchers, in a news release. "We know now that the cycle of crust formation at the mid-ocean ridges and crust dissolution in the lowermost mantle may have occurred since plate tectonics were active on our planet."

The findings are published in the journal Science.