TY - JOUR

T1 - Pyroxene-carbonate reactions in the CaMgSi2O6 ± NaAlSi2O6 + MgCO3 ± Na2CO3 ± K2CO3 system at 3–6 GPa

T2 - Implications for partial melting of carbonated peridotite

AU - Shatskiy, Anton

AU - Podborodnikov, Ivan V.

AU - Arefiev, Anton V.

AU - Bekhtenova, Altyna

AU - Vinogradova, Yulia G.

AU - Stepanov, Konstantin M.

AU - Litasov, Konstantin D.

N1 - Funding Information: We thank the associate editor (D. Canil) for useful suggestions and comments and two anonymous reviewers for constructive reviews. This study was done on the state assignment of IGM SB RAS and supported by RFBR No. 21-55-14001. KDL was supported by the state assignment of IHPP RAS. The SEM and EDX studies of experimental samples were performed in the Analytical Center for multi-elemental and isotope research SB RAS. We are grateful to N.S. Karmanov and A.T. Titov for their help in the analytical works. Publisher Copyright: © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/5

Y1 - 2021/5

N2 - The reactions between pyroxenes and carbonates have been studied in the CaMgSi2O6 + MgCO3 (Di + 2Mgs), CaMgSi2O6 + NaAlSi2O6 + 2MgCO3 (Di + Jd + 2Mgs), CaMgSi2O6 + Na2Mg(CO3)2 (Di + Eit), and CaMgSi2O6 + K2Mg(CO3)2 (Di + K2Mg) systems at pressures of 3.0 and 4.5 GPa in the temperature range 850–1300 °C and compared with those established previously at 6.0 GPa. The Di + 2Mgs solidus locates at 1220 °C / 3 GPa and 1400 °C / 6 GPa. Near-solidus melt is carbonatitic with SiO2 < 4 wt% and Ca# 56. The Di + Jd + 2Mgs solidus locates near 1050 °C at 3 GPa, rises to 1200 °C at 4.5 GPa, and 1350 °C at 6 GPa. The solidus is controlled by the reaction: 4NaAlSi2O6·2CaMgSi2O6 (clinopyroxene) + 12MgCO3 (magnesite) = 2MgAl2SiO6·5Mg2Si2O6 (clinopyroxene) + 2[Na2CO3·CaCO3·MgCO3] (liquid) + 6CO2. As pressure increases, the composition of solidus melt evolves from 26Na2CO3∙74Ca0.58Mg0.42CO3 at 3 GPa to 10Na2CO3∙90Ca0.50Mg0.50CO3 at 6 GPa. Melting in the Di + Eit and Di + K2Mg systems is controlled by the reactions: CaMgSi2O6 (clinopyroxene) + 2(Na or K)2 Mg(CO3)2 (eitelite) = Mg2Si2O6 (orthopyroxene) + 2[(Na or K)2CO3∙Ca0.5Mg0.5CO3] (liquid). The Di + Eit solidus locates at 925 °C / 3 GPa and 1100 °C / 6 GPa, whereas the Di + K2Mg solidus is located at 50 °C lower. The resulting melts have alkali-rich carbonate compositions, (Na or K)2CO3∙Ca0.4Mg0.6CO3. The obtained results suggest that most carbonates belong to the ultramafic suite would survive during subduction into the deep mantle and experience partial melting involving alkaline carbonates, eitelite or K2Mg(CO3)2, under geothermal conditions of the subcontinental lithospheric mantle (35–40 mW/m2). On the other hand, the jadeite component in clinopyroxene would be an important fluxing agent responsible for the partial melting of carbonated rocks under the rift margin geotherm (60 mW/m2) at a depth of about 100 km, yielding the formation of Na-carbonatite melt.

AB - The reactions between pyroxenes and carbonates have been studied in the CaMgSi2O6 + MgCO3 (Di + 2Mgs), CaMgSi2O6 + NaAlSi2O6 + 2MgCO3 (Di + Jd + 2Mgs), CaMgSi2O6 + Na2Mg(CO3)2 (Di + Eit), and CaMgSi2O6 + K2Mg(CO3)2 (Di + K2Mg) systems at pressures of 3.0 and 4.5 GPa in the temperature range 850–1300 °C and compared with those established previously at 6.0 GPa. The Di + 2Mgs solidus locates at 1220 °C / 3 GPa and 1400 °C / 6 GPa. Near-solidus melt is carbonatitic with SiO2 < 4 wt% and Ca# 56. The Di + Jd + 2Mgs solidus locates near 1050 °C at 3 GPa, rises to 1200 °C at 4.5 GPa, and 1350 °C at 6 GPa. The solidus is controlled by the reaction: 4NaAlSi2O6·2CaMgSi2O6 (clinopyroxene) + 12MgCO3 (magnesite) = 2MgAl2SiO6·5Mg2Si2O6 (clinopyroxene) + 2[Na2CO3·CaCO3·MgCO3] (liquid) + 6CO2. As pressure increases, the composition of solidus melt evolves from 26Na2CO3∙74Ca0.58Mg0.42CO3 at 3 GPa to 10Na2CO3∙90Ca0.50Mg0.50CO3 at 6 GPa. Melting in the Di + Eit and Di + K2Mg systems is controlled by the reactions: CaMgSi2O6 (clinopyroxene) + 2(Na or K)2 Mg(CO3)2 (eitelite) = Mg2Si2O6 (orthopyroxene) + 2[(Na or K)2CO3∙Ca0.5Mg0.5CO3] (liquid). The Di + Eit solidus locates at 925 °C / 3 GPa and 1100 °C / 6 GPa, whereas the Di + K2Mg solidus is located at 50 °C lower. The resulting melts have alkali-rich carbonate compositions, (Na or K)2CO3∙Ca0.4Mg0.6CO3. The obtained results suggest that most carbonates belong to the ultramafic suite would survive during subduction into the deep mantle and experience partial melting involving alkaline carbonates, eitelite or K2Mg(CO3)2, under geothermal conditions of the subcontinental lithospheric mantle (35–40 mW/m2). On the other hand, the jadeite component in clinopyroxene would be an important fluxing agent responsible for the partial melting of carbonated rocks under the rift margin geotherm (60 mW/m2) at a depth of about 100 km, yielding the formation of Na-carbonatite melt.

KW - Alkalis

KW - Carbonate

KW - Carbonatite melt

KW - Clinopyroxene

KW - Earth’s mantle

KW - High-pressure experiment

UR - http://www.scopus.com/inward/record.url?scp=85104349194&partnerID=8YFLogxK

U2 - 10.1007/s00410-021-01790-9

DO - 10.1007/s00410-021-01790-9

M3 - Article

AN - SCOPUS:85104349194

VL - 176

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 5

M1 - 34

ER -