The oxidation state of the Earth's deep mantle

During crystallisation, a small proportion of diamonds (no more than 2%), captures tiny inclusions of other minerals. These mineral inclusions sometimes derive from great depths and are our only window into the Earth’s transition zone (410-660 km) and the lower mantle (660-2900 km), regions of our planet, impossible to sample directly.
Here we propose to implement the Synchrotron Mössbauer Source (beamline ID14) in order to measure Fe3+/Fe2+ in the mineral inclusions (ferropericlase, Ca-perovskite, majoritic garnet) within two large diamonds and also in separate 10 majoritic garnets, all from Juina, Brazil. The second aim of this proposal is to use these data for devising an oxygen barometer for the deep mantle, that currently does not exist.
This will have important implications to the mantle rheology and transport properties as well as to mantle convection and material circulation between the upper and lower mantle.