| Инд. авторы: | Shatskiy A., Gavryushkin P.N., Sharygin I.S., Litasov K.D., Kupriyanov I.N., Higo Y., Borzdov Y.M., Funakoshi K.-I., Palyanov Y.N., Ohtani E. |
| Заглавие: | Melting and subsolidus phase relations in the system Na2CO 3-MgCO3±H2O at 6 GPa and the stability of Na2Mg(CO3)2 in the upper mantle |
| Библ. ссылка: | Shatskiy A., Gavryushkin P.N., Sharygin I.S., Litasov K.D., Kupriyanov I.N., Higo Y., Borzdov Y.M., Funakoshi K.-I., Palyanov Y.N., Ohtani E. Melting and subsolidus phase relations in the system Na2CO 3-MgCO3±H2O at 6 GPa and the stability of Na2Mg(CO3)2 in the upper mantle // American Mineralogist. - 2013. - Vol.98. - Iss. 11-12. - P.2172-2182. - ISSN 0003-004X. - EISSN 1945-3027. |
| Внешние системы: | DOI: 10.2138/am.2013.4418; SCOPUS: 2-s2.0-84888880938; WoS: 000327049100026; |
| Реферат: | eng: Phase relations in the Na2CO3-MgCO3 system have been studied in high-pressure high-temperature (HPHT) multi-anvil experiments using graphite capsules at 6.0 ± 0.5 GPa pressures and 900-1400 °C temperatures. Sub-solidus assemblages are represented by Na 2CO3+Na2Mg(CO3)2 and Na2CO3+Na2Mg(CO3) 2+MgCO3 with the transition boundary near 50 mol% MgCO3 in the system. The Na2CO3-Na 2CO3+Na2Mg(CO3)2 eutectic is established at 1200 °C and 29 mol% MgCO3. Melting of Na 2CO3 occurs between 1350 and 1400 °C. We propose that Na2CO3+Na2Mg(CO3)2 disappears between 1200 and 1250 °C via congruent melting. Magnesite remains as a liquidus phase above 1300 °C. Measurable amounts of Mg in Na 2CO3 suggest an existence of MgCO3 solid-solutions in Na2CO3 at given experimental conditions. The maximum MgCO3 solubility in Na-carbonate of about 9 mol% was established at 1100 and 1200 °C. The Na2CO3 and Na2CO3+Na2Mg(CO3)2 compounds have been studied using in situ X-ray coupled with a DIA-type multi-anvil apparatus. The studies showed that eitelite is a stable polymorph of Na2CO3+Na2Mg(CO3)2 at least up to 6.6 GPa and 1000 °C. In contrast, natrite, γ-Na 2CO3, is not stable at high pressure and is replaced by β-Na2CO3. The latter was found to be stable at pressures up to 11.7 GPa at 27 °C and up to 15.2 GPa at 1200 °C and temperatures at least up to 800 °C at 2.5 GPa and up to 1000 °C at 6.4 GPa. The X-ray and Raman study of recovered samples showed that, under ambient conditions, β-Na2CO3 transforms back to γ-Na2CO3. Eitelite [Na2CO 3+Na2Mg(CO3)2] would be an important mineral controlling insipient melting in subducting slab and upwelling mantle. At 6 GPa, melting of the Na2CO3+Na2Mg(CO 3)2+MgCO3 assemblage can be initiated, either by heating to 1300 °C under 'dry' conditions or at 900-1100 °C under hydrous conditions. Thus, the Na2CO3+Na 2Mg(CO3)2 could control the solidus temperature of the carbonated mantle under 'dry' conditions and cause formation of the Na- and Mg-rich carbonatite melts similar to those found as inclusions in olivines from kimberlites and the deepest known mantle rock samples-sheared peridotite xenoliths (190-230 km depth).
|
| Ключевые слова: | water; upper mantle; Raman spectroscopy; phase equilibrium; melting; high temperature; high pressure; experimental mineralogy; X-ray diffraction; Raman; Natrite; Na2CO3-MgCO3; In situ X-ray diffraction; High-pressure experiment; Eitelite; Earth's mantle; Alkaline carbonates; carbonate group; |
| Издано: | 2013 |
| Физ. характеристика: | с.2172-2182 |