Calorimetric and phase equilibrium data were used to establish an internally consistent thermodynamic database for the Si-undersaturated part of the system Na2O-FeOnCaO-MgO-Al2O3-SiO2. This database has been used to calculate the stability fields of assemblages involving olivine, orthopyroxene, clinopyroxene, spinel, plagioclase, and garnet at high P and T. In the six-component system CaO-MgO-Al2O3-SiO2 the stable assemblages are ol-opx-cpx-plag at P < 8 kbar at 1300ºC and <6 kbar at 900ºC. Above these P, spinel replaces plagioclase until P of 16 kbar at 1300ºC and 14 kbar at 900ºC are reached. At higher P, garnet lherzolite (ol + opx + cpx + gt) is stable. Stable phase assemblages have also been calculated for Na- and Fe-bearing compositions postulated as possible martian mantles. The McGetchin-Smyth composition would not contain orthopyroxene and a low-pressure assemblage of plag+ol+cpx+sp would be replaced by gt+ol+cpx+sp at pressures above 13 kb. In contrast, the Morgan-Anders composition has stability fields of plagioclase Iherzolite (P < 8 kb) and garnet lherzolite (P > 8 kb) and a small field of spinel Iherzolite at about 6 kb at temperatures below 900°C.
|Number of pages||12|
|Journal||Journal of Geophysical Research|
|Issue number||Suppl. 1|
|Publication status||Published - 1982|
|Event||Lunar and Planetary Science Conference (13th : 1982) - Houston, United States|
Duration: 15 Mar 1982 → 19 Mar 1982