Far below Bermuda’s pink sand beaches and turquoise tides, geoscientists have discovered the first direct evidence that material from deep within Earth’s mantle transition zone — a layer rich in water, crystals and melted rock — can percolate to the surface to form volcanoes.
Scientists have long known that volcanoes form when tectonic plates (traveling on top of the Earth’s mantle) converge, or as the result of mantle plumes that rise from the core-mantle boundary to make hotspots at Earth’s crust. But obtaining evidence that material emanating from the mantle’s transition zone — between 250 to 400 miles (440-660 km) beneath our planet’s crust — can cause volcanoes to form is new to geologists.
«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,» said senior author Esteban Gazel, associate professor in the Department of Earth and Atmospheric Sciences at Cornell University. The research published in Nature.
«We were expecting our data to show the volcano was a mantle plume formation — an upwelling from the deeper mantle — just like it is in Hawaii,» Gazel said. But 30 million years ago, a disturbance in the transition zone caused an upwelling of magma material to rise to the surface, forming a now-dormant volcano under the Atlantic Ocean and then forming Bermuda.
Using a 2,600-foot (over 700-meter) core sample — drilled in 1972, housed at Dalhousie University, Nova Scotia — co-author Sarah Mazza of the University of Munster, in Germany, assessed the cross-section for isotopes, trace elements, evidence of water content and other volatile material. The assessment provided a geologic, volcanic 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.»
From the core samples, the group detected geochemical signatures from the transition zone, which included larger amounts of water encased in the crystals than were found in subduction zones. Water in subduction zones recycles back to Earth’s surface. There is enough water in the transition zone to form at least three oceans, according to Gazel, but it is the water that helps rock to melt in the transition zone.
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Materials provided by Cornell University. Original written by Blaine Friedlander. Note: Content may be edited for style and length.