Bermuda has a unique volcanic past. About 30 million years ago, a fault in the transitional zone of the mantle supplied the magma with the volcanic foundation on which the island is now resting. Photo credits: Wendy Kenigsberg / Clive Howard – Cornell University, modified by Mazza et al. (2019)
Deep beneath Bermuda's pink sandy beaches and turquoise tides, geoscientists have found the first direct evidence that material from the mantle transition zone – a layer rich in water, crystals, and molten rock – can seep to the surface to form volcanoes.
Scientists have long known that volcanoes form when tectonic plates (moving on the Earth's mantle) converge or as a result of clouds of earth rising from the core-mantle boundary and forming trouble spots on the Earth's crust. Evidence that material from the mantle transition zone – between 250 and 400 miles (440-660 km) below the Earth's crust – can form volcanoes is new to geologists.
"We have found a new way to make volcanoes" This is the first time that we have found a clear indication from the deep-mound transition zone that volcanoes can form in this way, "said lead author Esteban Gazel , Associate Professor, Department of Earth and Atmospheric Sciences, Cornell University, study published in Nature .
"We had expected our data to show that the volcano is a cloud formation – an upswing the deeper mantle – just like in Hawaii, "said Gazel, adding that 30 million years ago, disruption in the transitional zone caused magma material to rise to the surface, forming a dormant volcano under the Atlantic, which then formed Bermuda.
– Drilled in 1972, housed at Dalhousie University in Nova Scotia – Co-authored Sarah Mazza of the University of Münster in Germany Check the cross-section for isotopes, trace elements, water content and other volatile material. The investigation revealed a geological, volcanic history of Bermuda.
"I suspected for the first time that Bermuda's volcanic past was special when I examined the core and noticed the various textures and mineralogies that were preserved in the various lava flows," Mazza said. "We quickly confirmed extreme accumulations of trace elements and it was exciting to go beyond our first results … the secrets of Bermuda began to decode."
From the core samples, the group identified geochemical signatures from the transition zone that contained larger amounts of water trapped in the crystals than in subduction zones. Water in subduction zones is returned to the earth's surface. There is enough water in the transition zone to create at least three oceans, according to the Gazel, but it is the water that promotes melting of the rocks in the transition zone.
Earth scientists collaborated with Robert Moucha, Associate Professor of Earth's numerical models, to develop scientists at Syracuse University to discover a disruption in the transition zone that was likely to cause material to melt from this deep cladding layer and seep to the surface, said Gazel.
Despite more than 50 years of isotopic measurements in oceanic lavas, which are peculiar, and extreme isotopes measured in Bermuda lava core, had not previously been observed. These extreme isotopic compositions, however, allowed the scientists to identify the unique source of lava.
"If we look closely, I think we will find these geochemical signatures in more places," said co-author Michael Bizimis, adjunct professor at the University of South Carolina.
Gazel explained that this research establishes a new link between the transition zone layer and volcanoes on the Earth's surface. "With this work, we can show that the Earth's transition zone is an extreme chemical reservoir," Gazel said. "We have just begun to realize its importance for global geodynamics and even for volcanism."
Gazel said, "Our next step is to study more sites to determine the difference between geological processes that can lead to intraplated volcanoes and determine the role of the transition zone of the mantle in the evolution of our planet."
Diamond inclusions indicate free-flowing water at the boundary between the upper and lower mantle
Sarah E. Mazza et al., Sampling of the Transient Transition Zone under Bermuda, Nature (2019). DOI: 10.1038 / s41586-019-1183-6
Scientists discover a new way out of the mantle how volcanoes form (2019, 15 May)
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