Chromium-bearing phases in the Earth's mantle: Evidence from experiments in the Mg2SiO4–MgCr2O4 system at 10–24 GPa and 1600°Cстатья
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Дата последнего поиска статьи во внешних источниках: 4 сентября 2019 г.
Аннотация:Phase relations in the system Mg2SiO4–MgCr2O4 were studied at 10–24 GPa and 1600°C using a high-pressure Kawai-type multianvil apparatus. We investigated the full range of starting compositions for the forsterite-magnesiochromite system to derive a P–X phase diagram and synthesize chromium-bearing phases such as garnet, wadsleyite (Wad), ringwoodite (Rgw), and bridgmanite of a wide compositional range Samples synthesized at 10 GPa contain olivine with small chromium content and magnesiochromite. Mg2SiO4 wadsleyite is characterized by the pressure-dependent higher chromium solubility (up to 7.4 wt % Cr2O3). The maximal solubility of chromium in Rgw in the Fo–MChr system (~18.5 wt% Cr2O3) was detected at P = 23 GPa, which is close to the upper boundary of the Rgw stability. Addition of Cr to the system moves the boundaries of Ol/Wad and Wad/Rgw phase transformations to lower pressures. Increase in the Cr concentration results in an expansion of the area of Ol/Wad and Wad/Rgw phase transitions at the expense of the appearance of divariant fields. Our experiments simulate Cr-rich phase assemblages found as inclusions in diamonds, mantle xenoliths, and UHP podiform chromitites.