Water may not control the flow of rocks in Earth’s interior as much as researchers had thought.
Convection in the Earth’s mantle (orange ring around the yellow outer core) may not depend on water’s presence for a lubricating effect, contrary to what geophysicists have assumed.
For decades, scientists have believed that the presence of water in deep-Earth rock makes it less viscous and allows it to flow. That movement underpins all sorts of geophysical phenomena, from the jostling of tectonic plates to giant convection patterns that transfer heat within Earth’s mantle. It also helps control the planet’s cycling of carbon and other life-critical elements from the deep interior toward the surface and back.
But high-pressure experiments on crystals of olivine, a common mineral in the mantle, hint that the textbook explanation may be at least partly wrong. Hongzhan Fei, a geochemist at the University of Bayreuth in Germany, and his colleagues describe the findings today in Nature.
Many laboratory experiments have demonstrated water’s weakening effect on minerals. But most of those studies looked at multiple crystals that were oversaturated with water, says Fei. When the crystals were squeezed, water between the grains could have allowed them to slide along their boundaries rather than causing deformation inside the crystals, as would be expected with true rock flow. Read more
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