Experimental Simulation of Prograde and Retrograde Reactions of Osumilite-Bearing Assemblages: Relevance to Mg-Al Granulites

Experimental studies on the osumilite bearing assemblages relevance to Mg-Al granulites were carried out and simulated certain retrograde reaction textures. Piston - cylinder runs were conducted in the P-T range of 5-10 Kbars and 700 - 1100 degrees C using bulk representing At-Si rich portion of KMASH system. The phases obtained in the retrograde runs are low-cordierite, osumilite, low Al-enstatite and melt. These phases distinctly differ from the high P-T minerals of prograde runs. It is interesting to note that in retrograde runs the precursor phase phlogopite did not form, instead, high temperature osumilite persists along with cordierite and enstatite at conditions as low as 700 degrees C and 10 Kbar. The osumilite hearing retrograde reaction textures observed in run products corroborates well with that of Mg-Al granulites of Eastern Ghat Mobile Belt.