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Well below the pink sand beaches and turquoise tides of Bermuda, geoscientists have discovered the first direct evidence that materials from the depths of the transition zone of the Earth's mantle – a layer rich in water, crystals and in molten rocks – can seep to the surface to form volcanoes.
Scientists have long known that volcanoes form when tectonic plates (moving above the Earth's mantle) converge or as a result of mantle plumes rising from the core-mantle boundary. to form hot spots at the level of the earth's crust. But to obtain evidence that materials emanating from the mantle transition zone – between 440 and 660 km (400 to 660 km) under the crust of our planet – can cause the formation of volcanoes is a novelty for geologists.
"We have found a new way of making volcanoes – it's the first time we find a clear indication of the deep-seated transition zone in the Earth's mantle that volcanoes can form in this way," he said. lead author Esteban Gazel, associate professor in the Department of the Earth. and atmospheric science at Cornell University. Research published in Nature.
"We were expecting our data to show that the volcano was a mantle plume formation – a deeper mantle water rise – just like in Hawaii," Gazel said. But 30 million years ago, a disturbance in the transition zone caused a rise of magma material on the surface, forming a volcano now dormant under the Atlantic Ocean and then forming Bermuda.
With the aid of a central sample of 2,600 feet (over 700 meters) – drilled in 1972, located at Dalhousie University, Nova Scotia – Sarah Mazza, from the University of Münster, Germany, evaluated the cross section for isotopes, trace elements, proof of moisture content and other volatile matter. The assessment provided a geological and volcanic history of Bermuda.
"I first thought that Bermuda's volcanic past was special because I sampled the core and I noticed the diversity of textures and mineralogy preserved in the various flows. lava, "said Mazza. "We quickly confirmed extreme enrichments in trace element compositions, it was exciting to review our first results … the mysteries of Bermuda began to unfold."
From the cores, the group detected geochemical signatures from the transition zone, which included larger amounts of water trapped in the crystals than in the subduction zones. Water in the subduction zones is recycled to the surface of the Earth. According to Gazel, there is enough water in the transition zone to form at least three oceans, but that is the water that helps cast rocks in the transition zone.
Geoscientists developed numerical models with Robert Moucha, associate professor of Earth Sciences at Syracuse University, to uncover a disturbance in the transition zone that would have likely forced the materials of this deep mantle layer to melt and run off to the surface, said Gazel.
Despite more than 50 years of isotopic measurements in oceanic lavas, the particular and extreme isotopes measured in the Bermuda lava core had never been observed before. Yet, these extreme isotopic compositions have allowed scientists to identify the unique source of lava.
"If we start looking more closely, I think we will find these geochemical signatures in more places," said co-author Michael Bizimis, associate professor at the University of South Carolina. .
Gazel explained that this research provided a new connection between the transition zone layer and the volcanoes on the surface of the Earth. "Through this work, we can demonstrate that the Earth's transition zone is a reservoir of extreme chemicals," Gazel said. "We are just beginning to recognize its importance in terms of global geodynamics and even volcanism."
Gazel said, "Our next step is to examine multiple locations to determine the difference between the geological processes that can lead to intraplate volcanoes and determine the role of the mantle transition zone in the evolution of our planet."
Besides Gazel, Mazza, Bizimis and Moucha, co-authors of "Sampling the Volatile and Rich Transition Area Below Bermuda", are Paul Beguelin, University of South Carolina; Elizabeth A. Johnson, James Madison University; Ryan J. McAleer, United States Geological Survey; and Alexander V. Sobolev, Russian Academy of Sciences.
The National Science Foundation funded this research.
Source of the story:
Material provided by Cornell University. Original written by Blaine Friedlander. Note: Content can be changed for style and length.
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