AN EXPERIMENTALLY CONSTRAINED PETROGENETIC GRID IN THE SILICA-SATURATED PORTION OF THE SYSTEM KFMASH AT HIGH TEMPERATURES AND PRESSURES

Abstract

Experiments in the quartz-saturated part of the system KFMASH under fO2 conditions of the haematite–magnetite buffer and using bulk compositions with XMg of 0·81, 0·72, 0·53 define the stability limits of several mineral assemblages within the P–T field 9–12?kbar, 850–1100°C. The stability limits of the mineral assemblages orthopyroxene + spinel + cordierite ± sapphirine, orthopyroxene + garnet + sapphirine, sapphirine + cordierite + orthopyroxene and garnet + orthopyroxene + spinel have been delineated on the basis of P–T and T–X pseudosections. Sapphirine did not appear in the bulk composition of XMg = 0·53. A partial petrogenetic grid applicable to high Mg–Al granulites metamorphosed at high fO2, developed in our earlier work, was extended to higher pressures. The experimental results were successfully applied to several high-grade terranes to estimate P–T conditions and retrograde P–T trajectories.