Phase relations on the diopside-hedenbergite-jadeite join up to 24 GPa and stability of Na-bearing majoritic garnet

Bobrov, A.V.; Kojitani, H.; Akaogi, M.; Litvin, Y.A.

Авторы: Bobrov A.V., Kojitani H., Akaogi M., Litvin Yu A.
Журнал: Geochimica et Cosmochimica Acta
Том: 72
Год издания: 2008
Издательство: Pergamon Press Ltd.
Местоположение издательства: United Kingdom
Первая страница: 2392
Последняя страница: 2408
DOI: 10.1016/j.gca.2008.03.003
Аннотация: Phase relations on the diopside (Di) – hedenbergite (Hd) – jadeite (Jd) system modeling mineral associations of natural eclogites were studied for the compositions (mol.%) Di70Jd30, Di50Jd50, Di30Jd70, Di20Hd80 и Di40Hd10Jd50 using toroidal anvil-with-hole (7 GPa) and a Kawai-type 6—8 multi-anvil apparatus (12—24 GPa). We established that Di, Hd, and Jd form complete series of solid solutions at 7 GPa, and melting temperatures of pure Di (1980°C) and Jd (1870°C) for that pressure were estimated experimentally. Melting temperature for the Di50Jd50 composition at 15.5 GPa is 2270ºС. The appearance of garnet is clearly dependent on initial clinopyroxene composition: at 1600°C first garnet crystals are observed at 13.5 GPa in jadeite-rich part of the system (Di30Jd70), whereas diopside-rich starting material (Di70Jd30) produces garnet only above 17 GPa. The proportion of garnet increases rapidly above 18 GPa as pyroxene dissolves in the garnet structure and pyroxene-free garnetites are produced from diopside-rich starting materials. Garnet in all experiments coexists with stishovite (St). At a pressure above 18 GPa pyroxene is completely replaced by an assemblage of majorite (Maj) + St + CaSiO3-perovskite (Ca-Pv) in Ca-rich systems, whereas Maj is associated with almost pure Jd up to a pressure of 21.5 GPa. Above ~22 GPa, Maj and St are associated with NaAlSiO4 with calcium ferrite structure (Cf). We established that Hd component also spreads the field of pyroxene stability up to 20 GPa. In the Di70Jd30 system at 24 GPa an assemblage of Maj+Ca-Pv+MgSiO3 with ilmenite structure (Mg-Il) was obtained. Correlation between Na, Si, and Al contents in Maj with pressure, established experimentally in Grt(Maj)–pyroxene assemblages, may be the base for “majorite” geobarometer. Results of our experiments are applicable to the upper mantle and transition zone of the Earth (400—670 km) demonstrating a wide range of transformation from eclogite to perovskite-bearing garnetite. In addition, mineral associations obtained allowed us to simulate parageneses of inclusions in diamonds formed under the conditions of transition zone and lower mantle.
Добавил в систему: Бобров Андрей Викторович

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Phase relations on the diopside-hedenbergite-jadeite join up to 24 GPa and stability of Na-bearing majoritic garnetстатья