Researchers suspect more dynamics than previously thought between the Earth's surface and its mantle.
What is the chemical composition of the Earth's interior? Because it is not possible to drill more than about ten kilometers deep into the Earth, volcanic rocks formed by the melting of the deep interior of the Earth often provide such information at the Universities of Münster (Germany) and Amsterdam (The Netherlands) have studied volcanic rocks, who form the Portuguese island group of the Azores. Their goal: to gather new information about the compositional evolution of the Earth's mantle, which is a layer between 30 and 2900 kilometers deep inside the Earth. Using sophisticated analytical techniques, they discovered that the composition of the mantle beneath the Azores is different than previously thought ̵
Researchers conclude that over the course of Earth's history, more Earth mantle has melted down – and eventually formed the Earth's crust – than previously thought. "In order to maintain the material budget between the mantle and the Earth's crust, the mass flows between the surface and the interior of the Earth must work at a faster rate," says Professor Andreas Strek of the University of Munster, who directs the study.
As material below, the Azores rise very deep into the earth's mantle – and unexpectedly resemble most of its upper part – the composition of the entire mantle on Earth may be different from current thinking. "Our results have opened a new perspective," says Andreas Strak, "because now we will have to re-evaluate the composition of the largest part of the Earth – after all, the Earth's mantle represents over 80 percent of Earth's volume." The study was published in the journal Nature Geoscience .
General Information and Method:
In their study, geochemists studied the olivine mineral and its inclusions, i. magma encapsulated during the crystallization of olivine before eruption of lava. Researchers isolate these melt inclusions, measuring just a few micrometers, dissolving them chemically and separating certain chemical elements. These elements change through radioactive decay during their lifetime and ascent from the interior of the Earth – traveling over thousands of miles for hundreds or even thousands of millions of years.
Researchers analyzed the isotopic composition of the melt with highly sensitive mass spectrometers. Such methods allow the measurement of the relative abundance of different atoms in an element, the so-called isotopes. "Thanks to the high efficiency of our measurements, we were able to analyze the isotopic composition of one billion grams of the element," says co-author Dr. Felix Genske of the Institute of Mineralogy at the University of Münster, who did most of the analytical work. Thus, the researchers indirectly obtained information about the composition of the material in the earth's mantle: isotopic analyzes show that it contains far less rare earth elements such as samarium and neodymium, but also chemically similar elements such as thorium and uranium.
"Based on similar geochemical data in volcanic rocks from different regions, such as Hawaii, other parts of the Earth's mantle may also contain a higher proportion of material that is highly depleted in incompatible elements," says Andreas Strake. Researchers suggest that this global deficit may be offset by a higher degree of recycling of Earth's crust-incompatible crust back into the Earth's mantle. With ongoing research, researchers want to confirm their working hypothesis by examining samples from other volcanic islands around the world.
The study has received financial support from the German Research Foundation and the Europlanet 2020 RI International Research Network, which is funded through the European Union's Horizon 2020 program.
"Omnipresent ultra-depleted domains in the earth's mantle" by Andreas Stracke, Felix Genske, Jasper Berndt, and Janne M. Koornneef, September 16, 2019, Nature 1959 ].
DOI: 10.1038 / s41561-019-0446-z