Far under Bermuda’s sandy beaches, Earth’s deep mantle hosts a transition zone, which is a mineral-rich layer consisting of water, crystals and melted rock that contributes to how volcanoes form. A new study sheds light on how volcanoes come into existence, as a result of chemical processes going on in Earth’s deep mantle.
The common knowledge of volcano formation is that they form as a result of tectonic plates movement, as well as mantle plumes that can rise from the core-mantle boundary making hot spots on Earth’s crust. However, a group of geoscientists found evidence that material located in Earth’s deep mantle that emanates from the transition zone, which is between the upper and lower mantle, from 250 to 400 miles below Earth’s crust, can cause volcanoes to form. This discovery of how volcanoes can form is new to scientists. The results were reported in the journal Nature.
“We found a new way to make volcanoes. 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,” senior author Esteban Gazel, associate professor in the Department of Earth and Atmospheric Sciences at Cornell University said in a statement.
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The team determined the results using a 2,600-foot core sample which was drilled in 1972. The sample was sitting at Dalhousie University, Nova Scotia. With the help of Sarah Mazza, co-author of the study at the University of Münster, Germany, the team was able to process cross-sections for isotopes, as well as find the composition of the sample. The analysis revealed evidence of water, as well as other material which is often associated with how volcanoes form. More importantly, the analysis provided more geological history of Bermuda.
“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,” Mazza said. “We quickly confirmed extreme enrichments in trace element compositions. It was exciting going over our first results … the mysteries of Bermuda started to unfold.”
The analysis of the core samples also provided geochemical evidence of the transition zone, where larger amounts of water surrounded the crystals from subduction zones. The water found in subduction zones often finds its way up to Earth’s surface, with enough water in this area to fill up three more oceans, Gazel said. However, the water in the zones has an important role, it helps rock melt in the transition zone.
To have a better understanding on how volcanoes form, the researchers developed several computer models which would reveal any disturbances in the transition zone that forced material to melt and break through the surface.
Even though there is a 50-year-long record of isotopic measurements in the ocean lava, researchers haven’t looked deep into Bermuda yet. However, detailed isotopic compositions revealed the direct source of the lava.
“If we start to look more carefully, I believe we’re going to find these geochemical signatures in more places,” said co-author Michael Bizimis, associate professor at the University of South Carolina.
According to Gazel, Earth’s deep mantle revealed a lot about how volcanoes form. Future plans include testing new locations and marking differences between geological processes in those areas respectively. Also, further knowledge about the transition zone could shed light on Earth’s evolution.