The system K2CO3–CaCO3 at 3 GPa: link between phase relations and variety of K–Ca double carbonates at ≤ 0.1 and 6 GPa
- 60 Downloads
The K2CO3–CaCO3 system is important both in materials science as a source of new nonlinear optical materials and in the Earth science as a sub-system modeling phase relations in fluxing component of mantle rocks responsible for the generation of deep-seated magmas. Existing data on phase relations in the K2CO3–CaCO3 system at ≤ 0.1 and 6 GPa show significant difference in intermediate compounds and, therefore, do not allow any interpolation between these pressures. Here, we report experimental results on melting and subsolidus phase relations in the system K2CO3–CaCO3 at 3 GPa and 800–1285 °C. At 800 °C, the system has two intermediate compounds: K2Ca(CO3)2, synthetic analog of mineral buetschliite, and K2Ca2(CO3)3. As temperature increases to 850 °C, a third intermediate compound, K2Ca3(CO3)4, appears. The calcite–aragonite transition boundary is located at 962 ± 12 °C. Maximum solid solution of CaCO3 in K2CO3 is 18 mol% at 950 °C. The K carbonate–K2Ca(CO3)2 eutectic is established near 970 °C and 56 mol% K2CO3. The melting point of K2CO3 corresponds to 1275 ± 25 °C. K2Ca(CO3)2 melts incongruently at 988 ± 12 °C to produce K2Ca2(CO3)3 and a liquid containing 53 mol% K2CO3. K2Ca2(CO3)3 melts congruently just above 1100 °C. The K2Ca2(CO3)3–K2Ca3(CO3)4 eutectic is situated near 1085 °C and 29 mol% K2CO3. K2Ca3(CO3)4 melts incongruently at 1100 °C to produce calcite and a liquid containing 28 mol% K2CO3. Considering our present results and previous data on the K2CO3–CaCO3 system, a range of K-Ca double carbonates changes upon pressure and temperature increase in the following sequence: K2Ca(CO3)2 (buetschliite), K2Ca2(CO3)3 (≤ 0.1 GPa; < 547 °C) → K2Ca(CO3)2 (fairchildite), K2Ca2(CO3)3 (≤ 0.1 GPa; 547–835 °C) → K2Ca(CO3)2 (buetschliite), K2Ca2(CO3)3, K2Ca3(CO3)4 (ordered) (3 GPa; 800–1100 °C) → K8Ca3(CO3)7, K2Ca(CO3)2 (buetschliite), K2Ca3(CO3)4 (disordered) (6 GPa; 900–1300 °C).
KeywordsHigh-pressure K–Ca carbonates Buetschliite Fairchildite Raman Phase relations
This work was financially supported by Russian Science Foundation (project No 14-17-00609-П). The SEM and EDS studies of experimental samples were performed in the Analytical Center for multi-elemental and isotope research SB RAS. We are grateful to two anonymous referees for constructive reviews, T. Tsuchiya for editorial handling, and N.S. Karmanov, A.T. Titov, and I.N. Kupriyanov for help in analytical work.
- Arefiev AV, Shatskiy A, Podborodnikov IV, Rashchenko SV, Litasov KD (under review) The system K2CO3-MgCO3 at 3 GPa. High Press ResGoogle Scholar
- Buzgar N, Apopei AI (2009) The Raman study of certain carbonates. Analele Stiintifice de Universitatii AI Cuza din Iasi. Geologie 55(2):97 (Section 2)Google Scholar
- Gavryushkin PN, Behtenova A, Popov ZI, Bakakin VV, Likhacheva AY, Litasov KD, Gavryushkin A (2016b) Toward analysis of structural changes common for alkaline carbonates and binary compounds: prediction of high-pressure structures of Li2CO3, Na2CO3, and K2CO3. Cryst Growth Des 16(10):5612–5617CrossRefGoogle Scholar
- Li Z (2015) Melting and structural transformations of carbonates and hydrous phases in Earth’s mantle. Dissertation, Department of Geology, University of Michigan, USA, pp 126Google Scholar
- McKie D (1990) Subsolidus phase relations in the system K2Ca(CO3)2–Na2Mg(CO3)2 at 1 kbar: the fairchilditess-buetschliite-eitelite eutectoid. Am Miner 75(9–10):1147–1150Google Scholar
- Pabst A (1974) Synthesis, properties, and structure of K2Ca(CO3)2, buetschliite. Am Miner 59(3–4):353–358Google Scholar
- Pertlik F (1981) Structural investigations of synthetic fairchüdite, K2Ca(CO3)2. Zeitschrift Für Kristallogr 157:199–205Google Scholar
- Rashchenko SV, Bakakin VV, Shatskiy AF, Gavryushkin PN, Seryotkin YV, Litasov KD (2017) Noncentrosymmetric Na2Ca4(CO3)5 carbonate of “M13M23XY3Z” structural type and affinity between borate and carbonate structures for design of new optical materials. Cryst Growth Des 17(11):6079–6084CrossRefGoogle Scholar
- Shatskiy A, Gavryushkin PN, Sharygin IS, Litasov KD, Kupriyanov IN, Higo Y, Borzdov YM, Funakoshi K, Palyanov YN, Ohtani E (2013a) Melting and subsolidus phase relations in the system Na2CO3–MgCO3 + -H2O at 6 GPa and the stability of Na2Mg(CO3)2 in the upper mantle. Am Miner 98(11–12):2172–2182CrossRefGoogle Scholar