TY - JOUR

T1 - The system Na2CO3–CaCO3 at 3 GPa

AU - Podborodnikov, Ivan V.

AU - Shatskiy, Anton

AU - Arefiev, Anton V.

AU - Rashchenko, Sergey V.

AU - Chanyshev, Artem D.

AU - Litasov, Konstantin D.

N1 - Publisher Copyright: © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.

PY - 2018/9/1

Y1 - 2018/9/1

N2 - 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 (110–115 km) origin, we performed experiments on phase relations in the system Na2CO3–CaCO3 at 3 GPa and 800–1300 °C. We found that the system has one intermediate compound, Na2Ca3(CO3)4, at 800 °C, and two intermediate compounds, Na2Ca(CO3)2 and Na2Ca3(CO3)4, at 850 °C. CaCO3 crystals recovered from experiments at 950 and 1000 °C are aragonite and calcite, respectively. Maximum solid solution of CaCO3 in Na2CO3 is 20 mol% at 850 °C. The Na-carbonate–Na2Ca(CO3)2 eutectic locates near 860 °C and 56 mol% Na2CO3. Na2Ca(CO3)2 melts incongruently near 880 °C to produce Na2Ca3(CO3)4 and a liquid containing about 51 mol% Na2CO3. Na2Ca3(CO3)4 disappears above 1000 °C via incongruent melting to calcite and a liquid containing about 43 mol% Na2CO3. At 1050 °C, the liquid, coexisting with Na-carbonate, contains 87 mol% Na2CO3. Na-carbonate remains solid up to 1150 °C and melts at 1200 °C. The Na2CO3 content in the liquid coexisting with calcite decreases to 15 mol% as temperature increases to 1300 °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 (0.1 GPa) → Na2Ca(CO3)2, Na2Ca3(CO3)4 (3 GPa) → Na4Ca(CO3)3, Na2Ca3(CO3)4 (6 GPa). 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.

AB - 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 (110–115 km) origin, we performed experiments on phase relations in the system Na2CO3–CaCO3 at 3 GPa and 800–1300 °C. We found that the system has one intermediate compound, Na2Ca3(CO3)4, at 800 °C, and two intermediate compounds, Na2Ca(CO3)2 and Na2Ca3(CO3)4, at 850 °C. CaCO3 crystals recovered from experiments at 950 and 1000 °C are aragonite and calcite, respectively. Maximum solid solution of CaCO3 in Na2CO3 is 20 mol% at 850 °C. The Na-carbonate–Na2Ca(CO3)2 eutectic locates near 860 °C and 56 mol% Na2CO3. Na2Ca(CO3)2 melts incongruently near 880 °C to produce Na2Ca3(CO3)4 and a liquid containing about 51 mol% Na2CO3. Na2Ca3(CO3)4 disappears above 1000 °C via incongruent melting to calcite and a liquid containing about 43 mol% Na2CO3. At 1050 °C, the liquid, coexisting with Na-carbonate, contains 87 mol% Na2CO3. Na-carbonate remains solid up to 1150 °C and melts at 1200 °C. The Na2CO3 content in the liquid coexisting with calcite decreases to 15 mol% as temperature increases to 1300 °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 (0.1 GPa) → Na2Ca(CO3)2, Na2Ca3(CO3)4 (3 GPa) → Na4Ca(CO3)3, Na2Ca3(CO3)4 (6 GPa). 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.

KW - Carbonatite

KW - High-pressure experiment

KW - Na–Ca carbonates

KW - Nyerereite

KW - Raman

KW - Shortite

KW - PETROGENESIS

KW - CARBONATED ECLOGITE

KW - 6 GPA

KW - CRYSTAL-STRUCTURE

KW - NYEREREITE

KW - SOLIDUS

KW - DEGREES-C

KW - Na-Ca carbonates

KW - PHASE-RELATIONS

KW - RICH MELTS

KW - MANTLE METASOMATISM

UR - http://www.scopus.com/inward/record.url?scp=85045047211&partnerID=8YFLogxK

U2 - 10.1007/s00269-018-0961-2

DO - 10.1007/s00269-018-0961-2

M3 - Article

AN - SCOPUS:85045047211

VL - 45

SP - 773

EP - 787

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

SN - 0342-1791

IS - 8

ER -