Solid-state NMR of high-pressure silicates in the earth's mantle

Abstract

The Earth's mantle is primarily composed of solid silicates, which undergo a number of phase transitions with increasing pressure and temperature. A detailed knowledge of these phases is integral to our understanding of the physical and chemical properties of the inner Earth. In particular, the Earth's mantle is believed to contain a large amount of water that is at least equivalent to that present in the oceans and atmosphere; however, the way in which this water is stored within the mantle is not well understood. Nuclear magnetic resonance (NMR) spectroscopy can offer an unparalleled insight into the structure, disorder and dynamics on the atomic scale, making it an ideal probe for such systems. In this review, we explore applications of NMR spectroscopy for the study of high-pressure silicates in the Earth's mantle. We first highlight some of the experimental techniques used and discuss the properties of NMR-active nuclei that are relevant to the study of high-pressure silicates. After summarising the chemical nature of the Earth's mantle and discussing synthetic methods for the preparation of the silicate phases present at different depths, we then review applications of NMR spectroscopy for the study of mantle silicates with a particular focus on the hydration of nominally anhydrous minerals.