From The University of Twente [ynivɛrsiˈtɛit ˈtʋɛntə] (NL) : “Mapping the chemistry of the Earth’s mantle”

From The University of Twente [ynivɛrsiˈtɛit ˈtʋɛntə] (NL)

K.W. Wesselink – Schram MSc (Kees)
Science Communication Officer (available Mon-Fri)
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Credit: Unsplash/CC0 Public Domain.

The Earth’s mantle makes up about 85% of the Earth’s volume and is made of solid rock. But what rock types is the mantle exactly made of, and how are they distributed throughout the mantle? An international team of researchers – including UT researcher Dr Juan Carlos Afonso (Faculty of ITC) – have been able to reveal the existence of pockets of rocks with abnormal properties that suggest that they were once created at the surface, transported to vast depths along subduction zones, and accumulated at specific depths inside the Earth’s mantle.

There is no direct access to the deep Earth. Insights into the composition of the mantle-necessary to understand planetary evolution-rely on indirect observations. For example, seismologists look at specific features of seismic waves to unravel the type of material the waves passed through. In a recent study published in the prestigious journal PNAS [below], Dr Juan Carlos Afonso – a geophysicist – and collaborators used computer simulations and a vast amount of seismic data to reveal the fate of oceanic crust when it is subducted deep into the mantle.

Anomalous accumulation of basaltic pockets

The study discovered an anomalous accumulation of a rock type called ‘basalt’ (a rock making up the oceanic crust) near the base of the so-called “mantle transition zone”, a region located at around 500 km beneath our feet that separates the upper and the lower mantle. The geographical distribution of these materials suggests that the main delivery mechanism is the subduction of oceanic plates (a tectonic plate sliding beneath another), and the detachment of large basalt chunks from the subducted oceanic plate. The preferential accumulation of this basaltic component in the transition zone reveals a new recycling process inside the planet and indicates that this region of the mantle acts as a gatekeeper for heat and mass transport through the mantle.

700 million years

Having measured the volume of basalt in the transition zone, the researchers combined that knowledge with the speed at which basalt is delivered (in direct relation to the drifting speed of plates on the surface). They estimated a 700 million-year timescale to replenish the basalt reservoir in the transition zone. This is roughly seven times longer than the time necessary for subducted plates to reach the core-mantle boundary from the surface. This means that present-day mantle composition near the transition zone is the result of multiple cycles of subduction, segregation, and accumulation.

The scientists hope to generalize their approach to a variety of seismic waves so that in the future, they will better understand the mixing and segregation mechanisms of the various rock types inside the Earth.

Science paper:

See the full article here.

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The University of Twente (NL) [ynivɛrsiˈtɛit ˈtʋɛntə] is a public technical university located in Enschede, the Netherlands.

The University of Twente collaborates with The Delft University of Technology [Technische Universiteit Delft](NL), Eindhoven University of Technology [Technische Universiteit Eindhoven](NL) and the Wageningen University & Research [Wageningen Universiteit & Onderzoek](NL) under the umbrella of 4TU and is also a partner in the European Consortium of Innovative Universities.

The University has been placed in the top 400 universities in the world by three major ranking tables. The UT was ranked 65th in the Reuters’s 2017 European Most Innovative Universities, and, 184th worldwide in 2019 according to the Times Higher Education magazine.
The university was founded in 1961 as Technische Hogeschool Twente or (THT). After Delft University of Technology and Eindhoven University of Technology, it became the third polytechnic institute in the Netherlands to become a University. The institution was later renamed to Universiteit Twente (University of Twente) in 1986, as the result of the changes in the Dutch Academic Education Act in 1984.

The Dutch government’s decision to locate the country’s third technical university in Enschede, the main city of Twente, had much to do with the north-eastern province’s rich manufacturing industry (textiles, metal, electrical engineering, chemicals). Another important consideration was the fact that the local economy needed a boost to compensate for the dwindling textile industry. Just as the fact that the municipality of Enschede made the Drienerlo estate available for the first campus University of the Netherlands.