"On the Water Content of the Lower Mantle"

Oliver Tschauner, University of Nevada

We present the first study on the solubility of water in lower mantle minerals conducted at a water activity of one. Our study bases on a combination of forward and reversed diffusion and addresses the effect of iron- and aluminum-content on the water solubility in silicate perovskite. The water content of the recovered samples was determined from micro-IR transmission spectra. We find that even under conditions of maximal water activity, the partition coefficient for water, silicate-perovskite, and ferropericlase range around 10³ and 20-50, respectively. We estimate the water content of the lower mantle to be less than 3 ppm.