Scottish researchers have cast new light on long-held assumptions about the deep Earth.

An international team of scientists led by researchers from SUERC and the University of Glasgow’s School of Geographical & Earth Sciences have uncovered ‘surprising’ results in a new study of volcanic lavas which erupted in the read sea from the Afar mantle plume.

Analysis of tiny bubbles of ancient gas trapped in the volcanic rocks combined with new modelling has allowed them to offer new insights into it.

Mantle plumes are columns of unusually hot rock which rise to the Earth’s surface from 2,900 kilometres below ground between the core and the mantle. They fuel volcanic activity wherever they force their way to the surface, often with enough energy to split the continents apart.

Current consensus among scientists is that plumes transport ‘primordial’ material created when the earth formed from the deep mantle to the surface and if that is the case, volcanic rocks formed when the magma erupted should contain significant traces of it.

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That consensus could change now that researched found that volcanic rocks cleared from the floor of the red sea contained very low concentrations of helium, a primordial gas, than is required by the prevailing models of the Earth.

In a new paper published in the Nature Communications Earth & Environment journal, the researchers and scientists concluded that the Afar plume in in fact dominated by material that has previously been at the Earth’s surface.

Their findings are based on analysis of samples of glass collected from the Red Sea and the Gulf of Tadjoura and suggests that mantle plumes complex mixture of primitive deep mantle and rocks that have been recycled back into Earth’s interior through ‘subduction’.

Ugur Balci, a postgraduate research student at SUERC and the paper’s lead author, said: “The Afar mantle plume is situated beneath thin crust at the junction of three tectonic plates making it a remarkable natural laboratory to study deep Earth.

“The surprising result of our work is that the plume is largely made up of rock that was at the Earth surface no more than 100 million years ago, which challenges the prevailing understanding of how mantle plumes are formed.”

The team also analysed seismic tomography models, which is a technique similar to MRI that uses earthquakes to enable scientists to ‘look’ inside the interior of the earth..

Using this information they could get an idea of the location, orientation and surface source of the subducted sea floor and estimate the speed at which it sank to meet the Afar plume.

Dr Antoniette Greta Grima, from the University of Glasgow’s School of Geographical & Earth Sciences, is a co-author of the paper. She said: “The isotopic fingerprints from the rocks give us one part of the picture of the processes which formed the Afar mantle plume, and seismic tomography models provides us with another important lens through which we could understand the interaction of the mantle and the subducted ancient sea floor, which we cannot access directly.

“The geochemical data suggests the upward moving plume is interacting with younger subducted sea floor material at 660 km below the surface instead of the very ancient subducted material at the boundary between the core and the mantle as previously assumed. Using a combination of seismic tomography models, slab sinking calculations and plate reconstruction models we have identified the subducted sea floor and linked it to a present-day active subduction zone underneath the Zagros mountains.“

Professor Fin Stuart from the Scottish Universities Environmental Research Centre (SUERC) led the project. He said: “Mantle plumes were first recognised in the early 1960s. They are fundamental to the planet; they drive plate tectonics, cool the Earth, bring elements that are essential to life to the surface and are our best window into the deep Earth.

“This study questions the prevailing paradigm that all plumes transport deep Earth to the surface. The key to unlocking this new insight was linking SUERC’s expertise in isotope geochemistry with geodynamic modelling capability in the School of Geographical & Earth Sciences.”