Phase transformation of clinopyroxene to majorite in subsolidus pyrolite in the Earth’s mantle transition zone by in situ x-ray diffraction

The mineralogy and phase transitions in the upper mantle have been determined from models that rely on seismic data and high-pressure experiments. However, these experiments have been run at temperatures ~500°C hotter than the ambient mantle. This significantly hinders our understanding of the minerals present and their phase transitions at temperatures along the oceanic geotherm. We propose to conduct high-pressure multi-anvil experiments combined with in-situ XRD at ID06-LVP using a fertile mantle starting material to recreate the subsolidus conditions of the mantle transition zone (16-21 GPa and 1400-1600˚C). The goal is to determine the minerals present across the P-T range of the mantle transition zone and constrain clinopyroxene to majorite transition and verify the occur of two majorites. This will allow us to refine the phase diagram for the upper mantle which has implications for the interpretation of seismological observations of the mantle and thermodynamic models.