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Conditions of magmatic crystallization of Na-bearing majoritic garnets in the Earth mantle: evidence from experimental and natural dataстатья
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: 18 июля 2013 г.
- Авторы: Bobrov A.V., Dymshits A.M., Litvin Yu A.
- Журнал: Geochemistry International
- Том: 47
- Номер: 10
- Год издания: 2009
- Издательство: Maik Nauka/Interperiodica Publishing
- Местоположение издательства: Russian Federation
- Первая страница: 1011
- Последняя страница: 1026
- DOI: 10.1134/S0016702909100012
- Аннотация: Results of experimental study at 7.0-8.5 GPa and 1300-1900 C of the systems pyrope Mg3Al2Si3O12 (Prp)-Na2MgSi5O12 (NaGrt) modeling solid solutions of Na-bearing garnets, Prp-jadeite NaAlSi2O6 (Jd) in a simplified mode demonstrating melting relations of Na-rich eclogite, and Prp-Na2CO3 are presented. Prp-Na2MgSi5O12 join is pseudobinary that results from decomposition of Na@Grt on to coesite and Na-pyroxene. Synthesized garnets are characterized by Na admixture (> 0.32 wt % Na2O). Maximal Na2O concentrations (1.5 wt % Na2O) are reached on the solidus of the system at 8.5 GPa. Clear correlation between Na and Si was established in synthesized garnets; this provides evidence for heterovalent isomorphism of Mg + Al - Na + Si type with the appearance of Na2MgSi5O12 component as mechanism of such garnet formation. The Prp-@Jd join is also pseudobinary that results from the formation of two series of solid solutions: (1) garnet (Prp-NaGrt-majorite) and (2) pyroxene (Jd-clinoenstatite-Eskola molecule), and the appearance of kyanite at the solidus of the system, where garnets with the highest Na2O contents (>0.8 wt %) are formed. In spite of quite wide field of garnet crystallization (20-100 mol % Prp), garnets with significant sodium concentration (>0.3 wt % Na2O) are formed in Jd-rich part of the system (20-50 mol % Prp). In the Prp-Na2CO3 system at 8.5 GPa garnet crystallizes in a wide range of starting compositions as a liquidus mineral containing up to 0.9 wt % Na2O. Our experiments demonstrate that melt alkalinity, as well as PT-parameters control crystallization of Na-bearing majoritic garnets. The results obtained provide evidence for the fact that the majority of natural diamonds with inclusions of Na-bearing majoritic garnets containing <0.4 wt % Na2O were formed in alkaline silicate (carbonate-silicate) melts at a pressure of <7 GPa. Only a small portion of garnets with higher sodium concentrations (>1 wt % Na2O) could be formed at a pressure of >8.5 GPa.
- Добавил в систему: Бобров Андрей Викторович