The role of pyrope garnet in water transport into the topmost lower mantle

The role of oceanic slabs in water transport to the interior of Earth depends on the water-storage capacity of their major minerals. Pyrope garnet is the dominant mineral in basaltic slabs from the crust to the topmost lower mantle, but its water-storage capacity remains controversial owing to the difficulty in growing high-quality single crystals for precise water-content analysis. Here, we systematically investigate the water solubility in pure single crystals of synthetic pyrope garnet at pressures of 5-25 GPa and temperatures of 1100-1900 K by using large-volume presses and Fourier transform infrared spectroscopy. Our results indicate that pyrope garnet can contain up to 2000 wt. ppm H₂O with a strong dependence on pressure and temperature in the transition zone and topmost lower mantle. Therefore, pyrope garnet may serve as a vital water carrier and reservoir in the deep mantle, offering new insights into water cycling up to the topmost lower mantle.