A study by Carnegie’s Yanhao Lin and Michael Walter demonstrates that a key mineral called stishovite is capable of storing and transporting large amounts of water even under the extreme conditions found in Earth’s lower mantle.
This is significant because it shows that substantial amounts of water could be present farther into the mantle than previously thought, indicating that a whole-mantle water cycle could exist.
“To get down into the mantle, water must be incorporated into minerals on the surface and then be stably maintained in those structures under conditions found deep inside the planet,” said lead author Lin.
We already know that substantial amounts of water can be stored in silicate minerals in the Earth’s upper mantle but the team examined stishovite and water under simulated conditions like those found deep in the lower mantle.
“Stishovite is a silica based mineral and major component of oceanic crust.” explained Mao, one of Lin’s colleagues. “In plate tectonics, there are areas called subduction zones where an oceanic plate slides beneath a continental plate, sinking from the Earth’s surface into its depths. When this happens, stishovite is transported into the mantle.”
The study subjected samples of stishovite with water to extreme pressures and heat and found that the mineral can accommodate large amounts of water under these conditions.
“If water can be stored in minerals at lower mantle pressures and temperatures, it could indicate that there is a global water cycle occurring on very long geologic time scales,” said Walter. “This could alter our understanding of how deep planetary interiors may influence or control the water content at the surface.”
https://phys.org/news/2019-12-deep-earth-planetary-evolution.html