From the deep mantle of the Earth, scientists find a new way in which volcanoes form.


From the deep mantle of the Earth, scientists find a new way in which volcanoes form.

Bermuda has a unique volcanic past. About 30 million years ago, a disturbance in the transition zone of the mantle supplied the magma to form the now inactive volcanic base on which the island is located. Credit: Wendy Kenigsberg / Clive Howard – Cornell University, modified by Mazza et al. (2019)

Far below Bermuda's pink sand beaches and turquoise tides, geoscientists have discovered the first direct evidence that the material found deep in the transition zone of the Earth's mantle, a rich layer in water, crystals and melted rock, it can leach to the surface to form volcanoes.

Scientists have known for a long time that volcanoes form when tectonic plates (traveling on the Earth's mantle) converge, or as a result of mantle plumes that rise from the core mantle boundary to make access points in the earth's crust. But to obtain evidence that the material that emanates from the transition zone of the mantle, between 250 and 400 miles (440-660 km) below the crust of our planet, can cause volcanoes to form is something new for geologists.

"We found a new way to make volcanoes, this is the first time we have found a clear indication of the transition zone in the Earth's mantle that volcanoes can be formed in this way," said lead author Esteban Gazel, an badociate professor at the Department of the Earth. and Atmospheric Sciences at Cornell University. The research published in Nature.

"We expected our data to show that the volcano was a mantle plume formation, an emergence of the deeper mantle, just as it is in Hawaii," Gazel said. But 30 million years ago, a disturbance in the transition zone caused a magma material to surface, forming a volcano now dormant beneath the Atlantic Ocean and then forming Bermuda.

Using a central sample of 2,600 feet (more than 700 meters), drilled in 1972, located at the University of Dalhousie, Nova Scotia, co-author Sarah Mazza of the University of Münster, Germany, evaluated the isotopes and trace elements section. , evidence of water content and other volatile materials. The evaluation provided a geological, volcanic history of Bermuda.

"I first suspected that Bermuda's volcanic past was special when I tested the nucleus and noticed the various textures and mineralogy preserved in the different lava flows," said Mazza. "We quickly confirmed the extreme enrichments in the trace element compositions, it was exciting to review our first results … the mysteries of Bermuda began to develop."

From the deep mantle of the Earth, scientists find a new way in which volcanoes form.

In a cross polarized microscopic section of a core sample, the blue and yellow crystal is titanium-augite, surrounded by a mbad of minerals from the soil, which include feldspars, phlogopite, spinel, perovskite and apatite. This set suggests that the source of the mantle, rich in water, produced this lava. Credit: Gazel Lab / Provisto

From the core samples, the group detected geochemical signatures from the transition zone, which included larger amounts of water encased in the crystals than those found in the subduction zones. The water in the subduction zones is recycled back to the surface of the Earth. There is enough water in the transition zone to form at least three oceans, according to Gazel, but it is the water that helps the rock melt in the transition zone.

Geoscientists developed numerical models with Robert Moucha, badociate professor of Earth sciences at Syracuse University, to discover a disturbance in the transition zone that probably forced the material from this deep layer to melt and seep to the surface said Gazel.

Despite more than 50 years of isotopic measurements in oceanic lavas, the peculiar and extreme isotopes measured in the lava core of Bermuda had not been observed before. However, these extreme isotopic compositions allowed scientists to identify the unique source of the lava.

"If we start looking more closely, I think we're going to find these geochemical signatures in more places," said co-author Michael Bizimis, an badociate professor at the University of South Carolina.

Gazel explained that this research provides a new connection between the layer of the transition zone and the volcanoes on the surface of the Earth. "With this work we can show that the transition zone of the Earth is an extreme chemical reservoir," said Gazel. "We are now beginning to recognize its importance in terms of global geodynamics and even volcanism."

Gazel said: "Our next step is to examine more locations to determine the difference between the geological processes that can result in intraplate volcanoes and determine the role of the mantle transition zone in the evolution of our planet."

The diamond inclusions suggest water that flows freely in the boundary between the upper and lower mantle

More information:
Sarah E. Mazza et al, Sampling the volatile rich transition zone below Bermuda, Nature (2019). DOI: 10.1038 / s41586-019-1183-6

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From the deep mantle of the Earth, scientists find a new way in which volcanoes form (2019, May 15)
recovered on May 15, 2019

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