Инд. авторы:	Shatskiy A., Podborodnikov I.V., Arefiev A.V., Litasov K.D., Chanyshev A.D., Sharygin I.S., Karmanov N.S., Ohtani E.
Заглавие:	Effect of alkalis on the reaction of clinopyroxene with Mg-carbonate at 6 GPa: Implications for partial melting of carbonated lherzolite
Библ. ссылка:	Shatskiy A., Podborodnikov I.V., Arefiev A.V., Litasov K.D., Chanyshev A.D., Sharygin I.S., Karmanov N.S., Ohtani E. Effect of alkalis on the reaction of clinopyroxene with Mg-carbonate at 6 GPa: Implications for partial melting of carbonated lherzolite // American Mineralogist. - 2017. - Vol.102. - Iss. 9. - P.1934-1946. - ISSN 0003-004X. - EISSN 1945-3027.
Внешние системы:	DOI: 10.2138/am-2017-6048; РИНЦ: 31045663; SCOPUS: 2-s2.0-85029355592; WoS: 000410608000015;
Реферат:	eng: The reaction between clinopyroxene and Mg-carbonate is supposed to define the solidus of carbonated lherzolite at pressures exceeding 5 GPa. To investigate the effect of alkalis on this reaction, subsolidus and melting phase relations in the following systems have been examined at 6 GPa: CaMgSi2O6+2MgCO3 (Di+2Mgs); CaMgSi2O6+NaAlSi2O6+2MgCO3 (Di+Jd+2Mgs); CaMgSi2O6+Na2Mg(CO3)2 (Di+Na2Mg); and CaMgSi2O6+K2Mg(CO3)2 (Di+K2Mg). The Di+2Mgs system begins to melt at 1400 °C via the approximate reaction CaMgSi2O6 (clinopyroxene) + 2MgCO3 (magnesite) = CaMg(CO3)2 (liquid) + Mg2Si2O6 (orthopyroxene), which leads to an essentially carbonate liquid (L) with composition Ca0.56Mg0.44CO3 + 3.5 mol% SiO2. The initial melting of the Di+Jd+2Mgs system occurs at 1350 °C via the reaction 2CaMgSi2O6 (clinopyroxene) + 2NaAlSi2O6 (clinopyroxene) + 8MgCO3 (magnesite) = Mg3Al2Si3O12 (garnet) + 5MgSiO3 (clinopyroxene) + 2CaMg(CO3)2 (liquid) + Na2CO3 (liquid) + 3CO2 (liquid and/or fluid), which yields the carbonate liquid with approximate composition of 10Na2CO3 ·90Ca0.5Mg0.5CO3 + 2 mol% SiO2. The systems Di+Na2Mg and Di+K2Mg start to melt at 1100 and 1050 °C, respectively, via the reaction CaMgSi2O6 (clinopyroxene) + 2(Na or K)2Mg(CO3)2 (solid) = Mg2Si2O6 (orthopyroxene) + (Na or K)4CaMg(CO3)4 (liquid). The resulting melts have the alkali-rich carbonate compositions Na2Ca0.4Mg0.6(CO3)2 + 0.4 mol% SiO2 and 43 K2CO3 ·57Ca0.4Mg0.6CO3 + 0.6 mol% SiO2. These melts do not undergo significant changes as temperature rises to 1400 °C, retaining their calcium number and a high Na2O, K2O, and low SiO2. We suggest that the clinopyroxene-Mg-carbonate reaction controlling the solidus of carbonated lherzolite is very sensitive to the carbonate composition and shifts from 1400 to 1050 °C at 6 GPa, which yields K-rich carbonate melt if the subsolidus assemblage contains the K2Mg(CO3)2 compound. Such a decrease in solidus temperature has been previously observed in the K-rich carbonated lherzolite system. Although a presence of eitelite, Na2Mg(CO3)2, has a similar effect, this mineral cannot be considered as a potential host of Na in carbonated lherzolite, because the whole Na added into the system dissolves as jadeite component in clinopyroxene if bulk Al/Na ≥ 1. The presence of jadeite component in clinopyroxene has little impact on the temperature of the solidus reaction decreasing it to 1350 °C at 6 GPa. © 2017 by Walter de Gruyter Berlin/Boston.
Ключевые слова:	partial melting; mantle structure; lherzolite; high temperature; high pressure; clinopyroxene; carbonatite; carbonate; partial melting; K2Mg(CO3)2; high-pressure experiment; eitelite; Earth's mantle; Carbonatite; carbonated peridotite; peridotite;
Издано:	2017
Физ. характеристика:	с.1934-1946