The ancient, now-dormant volcano on which the island of Bermuda sits formed in a completely unique way, scientists have discovered. The finding not only solves a long-standing mystery about the island’s volcanic origins, but it also describes a new way volcanoes form.
In studying a rock core sample taken from Bermuda, drilled from 1972, 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.
Researchers have long known that volcanoes form when tectonic plates converge, or as a result of mantle plumes that rise from the core-mantle boundary to make hotspots at Earth’s crust.
Illustration of how the volcano underneath Bermuda formed. (Photo Credit: Wendy Kenigsberg / Clive Howard, Cornell University)
But finding that material from the mantle’s transition zone — some 250 to 400 miles beneath our planet’s crust — can cause volcanoes to form is new to geologists, according to the National Science Foundation.
“We found a new way to make volcanoes,” said geologist Esteban Gazel, associate professor at Cornell University and senior author of the paper published in Nature. “This is the first time we’ve found a clear indication from the transition zone deep in the Earth’s mantle that volcanoes can form this way.”
According to Gazel, researchers were expecting the data to show that the volcano was a mantle plume formation — an upwelling from the deeper mantle — like Hawaii. This was not what they found.
“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,” said the paper’s co-author Sarah Mazza of the University of Münster, Germany. “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 researchers 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 and discovered a disturbance in the transition zone that likely forced material from this deep mantle layer to melt and percolate to the surface. This is thought to have taken place about 30 million years ago and provided the foundation that Bermuda sits on today.
Despite more than 50 years of isotopic measurements in oceanic lavas, the peculiar and extreme isotopes measured in the Bermuda lava core was something scientists had never seen before.
With knowledge of this new model for volcano-making, Bermuda may not be alone: Other volcanoes could exist in the Atlantic Ocean that formed by the same or similar processes, said Mazza. “We just haven’t found them yet,” she says.
Gazel said that the 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 volcanism.”
Read the full study here.
More on Geek.com:
- Watch: Mexico’s Popocatépetl Volcano Explodes in One of Largest Eruptions in Years
- 35 Incredible Images of Earth’s Mountains and Volcanoes From Space
- Man Injured After Falling From Cliff Into Volcano Caldera in Hawaii
Scientists Discover a New Way Volcanoes Form, Sheds Light on Bermuda"s Origins - Geek
0 Comments: