Dense hydrous silica could carry water to Earth’s mantle

Current estimates predict about one ocean’s mass of water exists in the mantle, but the amount of water in the earth’s interior is still very much unclear. That water can significantly affect the important physicochemical properties of the mantle material, such as the mineral phase relations, melting temperatures, rheological properties, electrical conductivity, and seismic velocities.

Understanding the water content and storage within the deep water cycle is essential for studying mantle properties and the water on the surface of the earth. To this end, Lin and Mao investigated and summarized how dense hydrous silica (DHS) can transport water to the deep mantle.

“We were curious whether water could be transported into the deepest part of Earth’s mantle because previous studies indicated all of hydrous magnesium silicate phases would break down when they reach the core-mantle boundary along the mantle pressure-temperature condition,” said author Yanhao Lin.

“If we found that a terrestrial mineral can contain water and be stable at extremely high pressure-temperature conditions, this will change the view about the deep water cycle from surface to the core-mantle boundary, which will help us gain a better understanding of the evolution of the Earth’s interior.”

The authors demonstrated that DHS phases may act as a water supplier and catalyst by carrying the liquid along the geothermal gradient. As slabs subduct into the mantle, the silica dehydrates, providing water to the surrounding material and lowering the melting temperature of the mantle rock. This can potentially change the mantle’s physicochemical properties and enhance heterogeneity of the oxygen fugacity, a measure of rock oxidation.

They plan to investigate interactions with other mantle materials and mechanisms at higher temperatures.

Source: “Dense hydrous silica carrying water to the deep Earth and promotion of oxygen fugacity heterogeneity,” by Yanhao Lin and Ho-Kwang Mao, Matter and Radiation at Extremes (2022). The article can be accessed at https://doi.org/10.1063/5.0125744 .

This paper is part of the High Pressure Science 2022 Collection, learn more here .