Researchers suspect greater dynamics than previously assumed between the Earth's surface and its mantle.
What is the chemical composition of the Earth's interior? Because it is impossible to drill more than ten. kilometers deep in the Earth, volcanic craters formed by the melting depths of the Earth often provide such information. Geochemis ts at the University of Münster (Germany) and Amsterdam (Netherlands) are investigating volcanic eruptions that form the Portuguese island group of the Azores. Their goal: to gather new information on the compositional evolution of the Earth's mantle, which is the layer approximately between 30 and 2,900 kilometers inside the Earth. Using sophisticated analytical methods, they discovered that the composition of the mantle beneath the Azores was different than previously thought – that it was higher that large portions contained surprisingly few so-called incompatible elements. These are chemical elements that, as a result of the continuous melting of the Earth's mantle, accumulate in the Earth's crust, which is the widest solid layer of Earth.
Researchers have concluded that, in the history of the Earth, a larger amount of Earth's mantle has dissolved – and eventually formed the Earth's crust – than previously thought. "In order to maintain the material budget between the Earth's mantle and crust, mass flakes between the Earth's surface and interior must operate at a higher rate," said Prof. Andreas Stracke of Münster University, who is leading the study.
As the material below. the Azores rise from the very depths of the Earth's mantle – and not unexpectedly like most of the upper part of it – the composition of the Earth's entire mantle may be different from what is currently thought. "Our results open a new perspective," says Andreas Stracke, "because we will need to re-evaluate the composition of the largest part of the Earth – after all, Earth's mantles account for more than 80 percent of the volume of the Earth. " The studying. published in the journal Nature Geoscience .
Background and methods:
In their study, geochemists examined the olivine mineral and its melting constituents, that is, magma was incorporated during the period study. crystallization of olivine before lavas burst. Researchers isolated these soluble compounds, only a few micrometer sizes, cleared them of the chemical and separated some chemical elements. These elements have been modified by radioactive decay during their lifetime and ascent from the interior of the Earth – traveling thousands of kilometers for hundreds or even thousands of millions of years.
Researchers have investigated the isotopic composition of solvents with an extremely sensitive mass spectrometer. Such methods allow measuring the relative abundance of different atoms in one element – the so-called isotopes. "Due to the high efficiency of our measurements, we were able to evaluate the isotopic composition of one billionth of a gram of the element," says co-author Dr. Felix Genske from the University of Münster's Institute of Mineralogy, who does most of the analytical work. In this way, researchers have not directly obtained information on the composition of the Earth's mantle: isotope analysis has shown that it contains less rare Earth elements such as samarium and neodymium, but also similar ones. chemical elements such as thorium and uranium.
"On the basis of similar geochemical data on volcanic rocks from different regions, e.g. Hawaii, other parts of Earth's Earth may also contain a higher proportion of material strongly to the sequence elements, "says Andreas Stracke. Researchers hypothesize that this global deficiency may be compensated by a higher rate of incompatible crust-rich crust elements back to Earth's mantle. In their ongoing study the researchers wanted to confirm their working hypothesis by examining samples from other volcanic islands around the world.
The study received financial support from the German Research Foundation and from the international research network "Europlanet 2020 RI", funded through the European Union's "Horizon 2020" program.
"Ubiquitous ultra-depleted domain on Earth's mantle" by Andreas Stracke, Felix Genske, Jasper Berndt and Janne M. Koornneef, 16 September 2019, Nature Geoscience
DOI: 10.1038 / s41561-019-0446-z