The system K_2CO_3-CaCO_3 at 3 GPa: link between phase relations and variety of K-Ca double carbonates at 0.1 and 6 GPa

Publication

Reference: Arefiev Anton V., Shatskiy Anton, Podborodnikov Ivan V., Rashchenko Sergey V., Chanyshev Artem D., Litasov Konstantin D. (2019). The system K $_2$ CO $_3$ -CaCO $_3$ at 3 GPa: link between phase relations and variety of K-Ca double carbonates at $\łeq$ 0.1 and 6 GPa. Phys. Chem. Miner., 46, 229 - 244.

Authors

Names

Anton V. Arefiev
Anton Shatskiy
Ivan V. Podborodnikov
Sergey V. Rashchenko
Artem D. Chanyshev
Konstantin D. Litasov

Article and keywords

Title: The system K $_2$ CO $_3$ -CaCO $_3$ at 3 GPa: link between phase relations and variety of K-Ca double carbonates at $\łeq$ 0.1 and 6 GPa
Abstract: The K $_2$ CO $_3$ -CaCO $_3$ 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 K $_2$ CO $_3$ -CaCO $_3$ system at $\łeq$ 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 K $_2$ CO $_3$ -CaCO $_3$ at 3 GPa and 800-1285 °C. At 800 °C, the system has two intermediate compounds: K $_2$ Ca(CO $_3$ ) $_2$ , synthetic analog of mineral buetschliite, and K $_2$ Ca $_2$ (CO $_3$ ) $_3$ . As temperature increases to 850 °C, a third intermediate compound, K $_2$ Ca $_3$ (CO $_3$ ) $_4$ , appears. The calcite-aragonite transition boundary is located at 962 $\pm$ 12 °C. Maximum solid solution of CaCO $_3$ in K $_2$ CO $_3$ is 18 mol% at 950 °C. The K carbonate-K $_2$ Ca(CO $_3$ ) $_2$ eutectic is established near 970 °C and 56 mol% K $_2$ CO $_3$ . The melting point of K $_2$ CO $_3$ corresponds to 1275 $\pm$ 25 °C. K $_2$ Ca(CO $_3$ ) $_2$ melts incongruently at 988 $\pm$ 12 °C to produce K $_2$ Ca $_2$ (CO $_3$ ) $_3$ and a liquid containing 53 mol% K $_2$ CO $_3$ . K $_2$ Ca $_2$ (CO $_3$ ) $_3$ melts congruently just above 1100 °C. The K $_2$ Ca $_2$ (CO $_3$ ) $_3$ -K $_2$ Ca $_3$ (CO $_3$ ) $_4$ eutectic is situated near 1085 °C and 29 mol% K $_2$ CO $_3$ . K $_2$ Ca $_3$ (CO $_3$ ) $_4$ melts incongruently at 1100 °C to produce calcite and a liquid containing 28 mol% K $_2$ CO $_3$ . Considering our present results and previous data on the K $_2$ CO $_3$ -CaCO $_3$ system, a range of K-Ca double carbonates changes upon pressure and temperature increase in the following sequence: K $_2$ Ca(CO $_3$ ) $_2$ (buetschliite), K $_2$ Ca $_2$ (CO $_3$ ) $_3$ ( $\łeq$ 0.1 GPa; < 547 °C) -> K $_2$ Ca(CO $_3$ ) $_2$ (fairchildite), K $_2$ Ca $_2$ (CO $_3$ ) $_3$ ( $\łeq$ 0.1 GPa; 547-835 °C) -> K $_2$ Ca(CO $_3$ ) $_2$ (buetschliite), K $_2$ Ca $_2$ (CO $_3$ ) $_3$ , K $_2$ Ca $_3$ (CO $_3$ ) $_4$ (ordered) (3 GPa; 800-1100 °C) -> K $_8$ Ca $_3$ (CO $_3$ ) $_7$ , K $_2$ Ca(CO $_3$ ) $_2$ (buetschliite), K $_2$ Ca $_3$ (CO $_3$ ) $_4$ (disordered) (6 GPa; 900-1300 °C).
Keywords: Raman spectroscopy, MIR, FIR, high pressure, high temperature, Phase relations, band position, minerals, K-Ca carbonates, alpha-K2Ca(CO3)2, K2Ca2(CO3)3, K8Ca3(CO3)7, K2Ca3(CO3)4, butschliite, buetschliite, fairchildite
Content: band list data, spectral data, experimental physics, earth sciences

Journal

Year: 2019
Journal: Physics and Chemistry of Minerals
Volume: 46
Number: 3
Pages: 229 - 244

Type and state

Document type: article
Publication state: published

Links

Doi

10.1007/s00269-018-1000-z

Identifiers

bibcode: 2019PCM....46..229A