|
Do carbonate liquids become denser than silicate liquids at pressure? Constraints from the fusion curve of K2CO3 to 3.2 GPa.
Авторы: Liu Q., Tenner T., Lange R.
2007 г.
Contrib.Miner.Petrol.
Brackets on the melting temperature of K2 CO3 were experimentally determined at 1.86 ± 0.02 GPa (1,163–1,167C), 2.79 ± 0.03 GPa (1,187–1,195C), and 3.16 ± 0.04 GPa (1,183–1,189C) in a piston-cylinder apparatus. These new data, in combination with published experiments at low pressure (<0.5 GPa), establish the K2CO3 fusion curve to 3.2 GPa. On the basis of these experiments and published thermodynamic data for crystalline and liquid K2CO3, the high-pressure density and compressibility of K2CO3 liquid were derived from the fusion curve. The pressure dependence of the liquid compressibility (K¢0 = dK0/dP, where K0 = 1/b0) is between 16.2 and 11.6, with a best estimate of 13.7, in a third-order Birch–Murnaghan equation of state (EOS). This liquid K¢0 leads to a density of 2,175 ± 36 kg/m3 at 4 GPa and 1,500C, which is ~30% lower than that reported in the literature on the basis of the falling-sphere method at the same conditions. The uncertainty in the liquid K¢0 leads to an error in melt density of ± 2% at 4 GPa; the error decreases with decreasing pressure. With a K¢0 of 13.7, the compressibility of K2CO3 at 1,500C and 1 bar (K0 = 3.8 GPa) drops rapidly with increasing pressure ( K4 GPa ¼ 33 GPa), which prevents a density crossover with silicate melts, such as CaAlSi2O8 and CaMgSi2O6, at upper mantle depths.
Файл: 494.pdf
|
