The rocks we are interested in are igneous – the frozen remains of magma formed at depths of 100 km or more from the mantle and then spewed out of volcanoes
- John Maclennan
If it was possible for us to drill to the centre of the Earth, about 6,500 km below the thin crust on which we live, the largest part to traverse would be the mantle. Although solid, this complex mix of minerals is capable of flowing, albeit over long timescales, as a consequence of the massive variations in pressure and temperature to which it is subjected.
But even the deepest drill cores have so far failed to penetrate the dynamic, flowing parts of the Earth’s mantle. Studying these deep layers is crucial to understanding the inner workings of our planet and the driving force behind movement of tectonic plates. Magma produced in the mantle feeds volcanic eruptions and supplies the cocktail of chemical elements required for the maintenance of a habitable planet.
Now a new study funded by the Natural Environment Research Council in the University’s Department of Earth Sciences has turned to a unique rock collection, amassed since at least the early 1800s and held within its Sedgwick Museum, to provide fresh understanding of the composition of the mantle.
The collection contains around 160,000 specimens of rock and about 250,000 slide-mounted rock slices that, at half the width of a human hair, are thin enough to let light through. “The rocks we are interested in are igneous – the frozen remains of magma formed at depths of 100 km or more from the mantle and then spewed out of volcanoes,” explained project leader Dr John Maclennan, who is working with Dr Arwen Deuss and Dr Tim Holland. “They carry a message about the composition of the deep Earth that we can decrypt using rock chemistry.”
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Image: Thin section of igneous rock photographed under a polarising microscope
Credit: Sedgwick Museum of Earth Sciences
Reproduced courtesy of the University of Cambridge
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