Geochemists Measure New Composition of Earth’s Mantle

What is the chemical composition of the Earth’s interior? Because it is impossible to drill more than about ten kilometres deep into the Earth, volcanic rocks formed by melting Earth’s deep interior often provide such information. Geochemists at the Universities of Münster (Germany) and Amsterdam (Netherlands) have investigated the volcanic rocks that build up the Portuguese island group of the Azores. Their goal: gather new information about the compositional evolution of the Earth’s mantle, which is the layer roughly between 30 and 2,900 kilometres deep inside the Earth. Using sophisticated analytical techniques, they discovered that the composition of the mantle below the Azores is different than previously thought –suggesting that large parts of it contain surprisingly few so-called incompatible elements. These are chemical elements which, as a result of the constant melting of the Earth’s mantle, accumulate in the Earth’s crust, which is Earth’s outermost solid layer.

The researchers conclude that, over Earth’s history, a larger amount of Earth’s mantle has melted – and ultimately formed the Earth’s crust – than previously thought. “To sustain the material budget between Earth’s mantle and crust, mass fluxes between the surface and Earth’s interior must have operated at a higher rate,” says Münster University’s Prof. Andreas Stracke, who is heading the study.

As the material below the Azores rises from very deep within Earth’s mantle – and is unexpectedly similar to most of its upper part – the composition of Earth’s entire mantle may differ from current thinking. “Our results have opened up a new perspective,” says Andreas Stracke, “because we will now have to reassess the composition of the largest part of the Earth – after all, Earth’s mantle accounts for over 80 percent of Earth’s volume.” The study has been published in the journal “Nature Geoscience”.

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