| Инд. авторы: | Podborodnikov I.V., Shatskiy A., Arefiev A.V., Rashchenko S.V., Chanyshev A.D., Litasov K.D. |
| Заглавие: | The system Na2CO3-CaCO3 at 3GPa |
| Библ. ссылка: | Podborodnikov I.V., Shatskiy A., Arefiev A.V., Rashchenko S.V., Chanyshev A.D., Litasov K.D. The system Na2CO3-CaCO3 at 3GPa // Physics and Chemistry of Minerals. - 2018. - Vol.45. - Iss. 8. - P.773-787. - ISSN 0342-1791. - EISSN 1432-2021. |
| Внешние системы: | DOI: 10.1007/s00269-018-0961-2; SCOPUS: 2-s2.0-85045047211; WoS: 000443572900006; |
| Реферат: | eng: It was suggested that alkali-alkaline earth carbonates may have a substantial role in petrological processes relevant to metasomatism and melting of the Earth's mantle. Because natrite, Na2CO3, Na-Ca carbonate (shortite and/or nyerereite), and calcite, CaCO3, have been recently reported from xenoliths of shallow mantle (110-115km) origin, we performed experiments on phase relations in the system Na2CO3-CaCO3 at 3GPa and 800-1300 degrees C. We found that the system has one intermediate compound, Na2Ca3(CO3)(4), at 800 degrees C, and two intermediate compounds, Na2Ca(CO3)(2) and Na2Ca3(CO3)(4), at 850 degrees C. CaCO3 crystals recovered from experiments at 950 and 1000 degrees C are aragonite and calcite, respectively. Maximum solid solution of CaCO3 in Na2CO3 is 20mol% at 850 degrees C. The Na-carbonate-Na2Ca(CO3)(2) eutectic locates near 860 degrees C and 56mol% Na2CO3. Na2Ca(CO3)(2) melts incongruently near 880 degrees C to produce Na2Ca3(CO3)(4) and a liquid containing about 51mol% Na2CO3. Na2Ca3(CO3)(4) disappears above 1000 degrees C via incongruent melting to calcite and a liquid containing about 43mol% Na2CO3. At 1050 degrees C, the liquid, coexisting with Na-carbonate, contains 87mol% Na2CO3. Na-carbonate remains solid up to 1150 degrees C and melts at 1200 degrees C. The Na2CO3 content in the liquid coexisting with calcite decreases to 15mol% as temperature increases to 1300 degrees C. Considering the present and previous data, a range of the intermediate compounds on the liquidus of the Na2CO3-CaCO3 join changes as pressure increases in the following sequence: Na2Ca(CO3)(2) (0.1GPa)Na2Ca(CO3)(2), Na2Ca3(CO3)(4) (3GPa)Na4Ca(CO3)(3), Na2Ca3(CO3)(4) (6GPa). Thus, the Na2Ca(CO3)(2) nyerereite stability field extends to the shallow mantle pressures. Consequently, findings of nyerereite among daughter phases in the melt inclusions in olivine from the sheared garnet peridotites are consistent with their mantle origin.
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| Ключевые слова: | Nyerereite; Shortite; Raman; Carbonatite; ALKALI-CARBONATE MELTS; 900-1400 DEGREES-C; PHASE-RELATIONS; LITHOSPHERIC MANTLE; DEEP MANTLE; OPTICAL-MATERIALS; CRYSTAL-STRUCTURE; RICH MELTS; PETROGENESIS; Na-Ca carbonates; 6 GPA; High-pressure experiment; |
| Издано: | 2018 |
| Физ. характеристика: | с.773-787 |