Experimental study of phase equilibria in the pyrope-grossular join at a pressure of 30 kbar

The phase diagram of the pyrope-grossulor join at P = 30 kbar is revised on the basis of new experimental data. The experimental study was carried out in a piston-cylinder apparatus. Phases were identified optically in thin s ections and by X-ray diffraction. The composition of phases was analyzed on an electron microprobe. At a pressure of 30 kbar and temperatures below 10 75-1100 degrees C the Mg3Al2Si3O12-Ca3Al2Si3O12 join includes stable, compl ete series of pyrope-grossular garnet solid solutions is stable. Above 1100 degrees C, clinopyroxene appears, and a gap in the continuous garnet solid solution series occurs. The pyrope-rich portion of the join at temperature s from 1100 degrees C to 1350-1400 degrees C is occupied by the Cpx + Grt Crn field. At higher temperatures the assemblage Grt + Cpx is stable. Melt ing takes place at about T = 1543 degrees C by the reaction Grt + Cpx = Spl + L. In the grossular-rich portion of the join at temperatures 1100-1200 d egrees C, the Cpx + Grt + Crn assemblage is stable and gives way to the Grt + Cpx assemblage at higher temperatures. The melting of the Grt + Cpx asse mblage is found to begin between 1550 and 1600 degrees C. The compositions of the solid solutions an in good agreement with the data of previous studi es. The obtained results differ in that the Crt + Cpx + Crn assemblage is s table within the pyrope-rich portion of the join only at temperatures below 1400 degrees C, and corundum is absent at the liquidus.