Researchers have discovered the first direct evidence that material from the mantle transition zone can percolate and form a volcano.
The team, which included geologists from Cornell University, made the discovery while analyzing a core sample extracted from a dormant volcano underneath the Atlantic Ocean back in 1972.
"We found a new way to make volcanoes," stated Esteban Gazel, an associate professor at Cornell University's Department of Earth and Atmospheric Sciences. "This is the first time we found a clear indication from the transition zone deep in the Earth's mantle that volcanoes can form this way."
Volcanic History Of Bermuda
Prior to the discovery, there were two events in which a volcano is formed: when tectonic plates converge or when mantle plumes rise from the core-mantle boundary to make hotspots at the crust.
Gazel and team were expecting to find evidence that the volcano was formed after an upswelling from deeper into the mantle, just like what happened in Hawaii. Instead, they found that 30 million years ago, a disturbance in the transition zone caused magma material to rise to the surface. The event formed a volcano in the Atlantic Ocean and, eventually, gave birth to the beautiful island of Bermuda.
Sarah Mazza of the University of Münster in Germany and a co-author of the study, analyzed the 2,600-foot core sample. She assessed the cross-section for isotopes, water content, trace elements, and other volcanic materials.
They found that the samples contained geochemical signatures from the transition zone, including a larger amount of water encased in crystal compared to those found in the subduction zone. The transition zone contains three times more water than in all the oceans around the world combined.
"I first suspected that Bermuda's volcanic past was special as I sampled the core and noticed the diverse textures and mineralogy preserved in the different lava flows," said Mazza. "We quickly confirmed extreme enrichments in trace element compositions."
A New Way For Volcanoes To Form
Gazel added that the findings, which were published in the journal Nature, provide a new connection between the transition zone and the volcanoes at the surface of the Earth.
The team also believes that there will be other examples of volcanoes being formed in a similar fashion.
Their next goal is to examine more locations and determine the role that the mantle's transition zone might have played in the evolution of the planet.