A new way to make volcanoes

“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 CSI member and senior author Esteban Gazel, Cornell associate professor in the Department of Earth and Atmospheric Sciences. The research published in Nature on May 15. link here to Cornell Chronicle story by Blaine Friedlander

Far below Bermuda’s pink sand beaches and turquoise tides,
Cornell 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.

Volcano core section

Gazel Lab/Provided

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 beneath our planet’s crust – can cause volcanoes to form is new to geologists.

“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, form a now-dormant volcano under the Atlantic Ocean and then
form Bermuda.

Using a 2,600-foot core sample – drilled in 1972, housed at Dalhousie
University, Nova Scotia – co-author Sarah Mazza of the University of
Münster, Germany, assessed the cross-section for signature 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.

The geoscientists developed numerical models with Robert Moucha,
associate professor of Earth sciences at Syracuse University, to
discover a disturbance in the transition zone that likely forced
material from this deep mantle layer to melt and percolate to the

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

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

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

Gazel is a fellow at Cornell’s Atkinson Center for a Sustainable Future and a fellow at Cornell’s Carl Sagan Institute. In addition to Gazel, Mazza, Bizimis and Moucha, co-authors of “Sampling the Volatile-Rich Transition Zone Beneath Bermuda,” are Paul Béguelin, University of South Carolina; Elizabeth A. Johnson, James Madison University; Ryan J. McAleer, United States Geological Survey; and Alexander V. Sobolev, the Russian Academy of Sciences. The National Science Foundation provided funding for this research. written by Blaine Friedlander, Cornell Chronicle

Esteban Gazel, Earth & Atmospheric Sciences

Klarman Hall at sunset

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