The system K2CO3-MgCO3 at 6 GPa and 900-1450  C Academic Article uri icon

abstract

  • Phase relations in the K2CO3-MgCO3 system have been studied in high-pressure high-temperature (HPHT) multi-anvil experiments using graphite capsules at 6.0 ± 0.5 GPa pressures and 900-1450 °C temperatures. Subsolidus assemblies comprise the fields K 2CO3+K2Mg(CO3)2 and K2Mg(CO3)2+MgCO3 with the transition boundary near 50 mol% MgCO3 in the system. The K2CO 3-K2Mg(CO3)2 eutectic is established at 1200 °C and 25 mol% MgCO3. Melting of K2CO 3 occurs between 1400 and 1450 °C. We propose that K 2Mg(CO3)2 disappears between 1200 and 1300 °C via congruent melting. Magnesite is observed as a subliquidus phase to temperatures in excess of 1300 °C. At 6 GPa, melting of the K 2Mg(CO3)2+MgCO3 assemblage can be initiated either by heating to 1300 °C under "dry" conditions or by adding a certain amount of water at 900-1000 °C. Thus, the K 2Mg(CO3)2 could control the solidus temperature of the carbonated mantle under "dry" conditions and cause formation of the K- and Mg-rich carbonatite melts similar to those found as microinclusions in "fibrous" diamonds. The K2Mg(CO 3)2 compound was studied using in situ X ray coupled with a DIA-type multi-anvil apparatus. At 6.5 GPa and 1000 °C, the structure of K2Mg(CO3)2 was found to be orthorhombic with lattice parameters a = 8.8898(7), b = 7.8673(7), and c = 5.0528(5), V = 353.39(4). No structure change was observed during pressure decrease down to 1 GPa. However, recovered K2Mg(CO3)2 exhibited a trigonal R3m structure previously established at ambient conditions.

published proceedings

  • American Mineralogist

author list (cited authors)

  • Shatskiy, A., Sharygin, I. S., Gavryushkin, P. N., Litasov, K. D., Borzdov, Y. M., Shcherbakova, A. V., ... Ohtani, E

citation count

  • 53

complete list of authors

  • Shatskiy, A||Sharygin, IS||Gavryushkin, PN||Litasov, KD||Borzdov, YM||Shcherbakova, AV||Higo, Y||Funakoshi, K-I||Palyanov, YN||Ohtani, E

publication date

  • August 2013