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Münster (upm/kk).
A collage of three images. The images show a man standing on the research ship, a close-up of the dredge being pulled into the sea and a close-up of the dredge.<address>© Alessio Sanfilippo</address>
After a topographic map was made, the team dredged rocks (peridotites) from the upwelling Iceland plume from the ocean floor, and analyzed their chemical and isotopic composition.
© Alessio Sanfilippo

Driving force of the Iceland plume reconsidered

The chemical composition triggers upwelling of mantle currents from Earth’s interior / Findings published in “Nature Geoscience” journal

Researchers around the world investigate the dynamic processes in Earth’s deep interior, hundreds to thousands of kilometers below the surface. These processes drive plate movements and volcanism but still keep many secrets. As part of an international team, researchers from the University of Münster were the first to investigate rocks rising from the deep Earth– the so-called Iceland plume – and measure its chemical composition. The studied rocks are exposed at the Mid-Atlantic Ridge – which is part of the globe-encircling mid-ocean ridge system – more than thousand kilometers south of Iceland. The researchers discovered that the buoyancy force of the upwelling mantle current under Iceland is not, as previously assumed, caused only its high temperature, but also by its chemical composition. The findings have been published in “Nature Geoscience”.

The thin sections of the rocks examined (peridotites) are translucent and enable the researchers to specify individual minerals. In this process, the minerals (clinopyroxenes) – marked dark green in the small schematic images – are separated from the rocks, and the isotope ratios for the elements hafnium (Hf) and neodymium (Nd) are measured. These provide information on how the chemical composition of the peridotites has developed over hundreds of millions – or even billions – of years in the Earth’s mantle before being sampled on the ocean floor today.<address>© Sanfilippo, et al.</address>
The thin sections of the rocks examined (peridotites) are translucent and enable the researchers to specify individual minerals. In this process, the minerals (clinopyroxenes) – marked dark green in the small schematic images – are separated from the rocks, and the isotope ratios for the elements hafnium (Hf) and neodymium (Nd) are measured. These provide information on how the chemical composition of the peridotites has developed over hundreds of millions – or even billions – of years in the Earth’s mantle before being sampled on the ocean floor today.
© Sanfilippo, et al.
The Iceland plume is an upwelling of hot rock from Earth’s deep mantle. “The material rises under Iceland, where the crust is 15 kilometres thick, but continues its path below the adjacent Mid Atlantic Ridge to more than thousand kilometers south of Iceland,” explains Prof. Andreas Stracke from the Institute of Mineralogy. “On board a research vessel, Italian and Russian colleagues sampled rocks from the Iceland plume at a so-called transform fault south of Iceland– at which the Earth’s crust is displaced laterally, but parts of the underlying mantle are exposed on the ocean floor.” The researchers determined the chemical composition of these rocks – so-called peridotites – which form most of the Iceland plume. The team members in Münster also measured the isotope ratios of the elements hafnium (Hf) and neodymium (Nd).

These analyses show that the investigated peridotites have melted more than one billion years ago, which made them lighter, and thus more buoyant than the ambient mantle. Hence the composition, and not only the temperature, is a major factor for the low density of the Iceland plume, and triggers its upwelling from Earth’s deep interior. When they reach the shallow mantle (less than ca. 100 km depth), the rocks of the Iceland plume partially melt again and produce enormous volumes of magma, which triggers volcanic eruptions, on Iceland and along the Mid-Atlantic Ridge south of Iceland. These massive amounts of lava have built up a topographical swell in the entire North Atlantic, with Iceland on its top emerging above sea level. In contrast, the rest of the Mid-Atlantic Ridge lies several thousand metres below sea level. “Our findings also suggest that compositional variations may be responsible for periodic changes in the upwelling velocity of the rising plume. These led to variations in magma production and have produced the characteristic morphology of the ocean floor over a length of several hundred kilometers south of Iceland. Changes in seafloor topography may have also influenced the deep-water flow in the North Atlantic,” says Andreas Stracke. The researchers expect that their new findings will change the current view of the buoyancy forces of deep mantle plumes – which trigger the largest volcanic eruptions on Earth – and the interior forces that sustain Earth as a dynamic planet in general.

The researchers’ work received financial support from the German Research Foundation (DFG), from the Italian Programma di Rilevante Interesse Nazionale and from the Russian Foundation for Basic Research.

Original publication

Sanfilippo A., Stracke A., Genske F., Scarani S., Cuffaro M., Basch V., Borghini G., Brunelli D., Ferrando C., Peyve A. A., Ligi M. (2024). Upwelling of melt-depleted mantle under Iceland. Nature Geoscience. DOI: 10.1038/s41561-024-01532-z

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