Phase relations and formation of chromium-rich phases in the system Mg4Si4O12–Mg3Cr2Si3O12 at 10–24 GPa and 1600°Cстатья
Статья опубликована в высокорейтинговом журнале
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 30 октября 2015 г.
Аннотация:Phase relations in the system Mg4Si4O12–Mg3Cr2Si3O12 were studied at 10–24 GPa and 1,600°C using a high-pressure Kawai-type multianvil apparatus. We investigated the full range of starting compositions for the knorringite-majorite system to derive a P–X phase diagram and synthesize garnets of a wide compositional range. Samples synthesized in the pressure range 10–14 GPa contain knorringite-majorite garnet and Cr-bearing pyroxene. With increasing Cr content in the starting materials, an association of knorringite-majorite garnet and eskolaite is formed. Garnets contain a significant portion of majorite (>10 mol %) even for a pure Mg3Cr2Si3O12 starting composition. Knorringite-majorite garnets were obtained in the pressure range from 10 to 20 GPa. With increasing pressure, the phase assemblages include Cr-bearing MgSiO3-akimotoite and MgSiO3-bridgmanite, as well as MgCr2O4 with calcium-titanate structure, and stishovite. Single crystal X-ray diffraction shows that the incorporation of Cr into the structure of garnet, as well as MgSiO3 akimotoite, and bridgmanite results in an increase of their unit-cell parameters. Results of the experimental high-pressure investigation of the pseudo-binary system Mg4Si4O12–Mg3Cr2Si3O12 (SiO2–MgO–Cr2O3) may be applied to the origin of high-chromium phases (mostly garnet) found as inclusions in peridotitic diamonds and formed in bulk rock compositions with high Cr/Al ratios in relation to the primitive mantle.