Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

B. Basavalinag ¹, A. V. Ganesha ², M. A. Pasha ²

Affiliations
1 Department of Studies in Geology Manasagangotri, University of Mysore, Mysore- 560 006, IN
2 Department of Studies in Geology Manasagangotri, University of Mysore, Mysore - 560 006, IN

Abstract

Experimental studies on the osumilite bearing assemblages relevance to Mg-A1 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°C using bulk representing Al-SI rich portion of KMASH system. The phases obtained in the retrograde runs are low-Corrodorate 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 precurson phase phlogopite did not form, instead high temperature osumilite persists along with corroborates and enstatite at conditions as low as 700°C and 10 Kbar. The osumiliteo bearing etrograde reaction textures observed in run products corroborates well with that of Mg-A1 granulites of Eastern Ghat Mobile Belt.

Keywords

Mg-A1 Granulites, Retrograde Reactions Osumilite KMASH System.

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J. A. K. Tareen ¹, A. V. Ganesha ¹

Affiliations
1 Department of Geology, Manasagangotri, University of Mysore, Mysore-570 006, IN

Abstract

An experimental study in the Mg-Al rich portion of K₂O-MgO-Al₂O,-Si₂O-H₂O (KMASH) system was carried out using bulk composition 2Phl+6Sil+9Qtz. Experiments were done using Internally Heated Pressure Vessel (Gas Bomb) in a P-T range of 3-10 kbar and 900-1250°C with water undersaturated conditions. Three distinct fields were noticed in the given P-T plane: (a) Field-I: Crd+L (up to 1000°C), (b) Field-II: Ind+Sp+L (between 1000 and 1250°Cl up to 6 kbar) and (c) Field-III: Spr+Ind+AI.En±Os±Qtz±L (between 1000 and 1250°C above 6 kbar). The appearance of hexagonal indialite (Ind) instead of orthorhombic cordierite above 1000°C is significant. The analysis of the mineral phases shows that sapphirine is of 2:2:1 type and enstatite is highly aluminous (up to 14 wt% Al₂O₃). The anafyses of indialite lie between 2:2:1 sapphirine and ideal cordierite on the (Al₂O,+K₂O)-MgO-SiO₂, triangular diagram. The analysis of melt is found to depend on the associated restites and the overall composition corresponds to 'granitic'.

Keywords

Mg-Al Granulites, KMASH System, Cordierite, Indialite, Sapphirine, Al-Enstatite, Spinel Stability, UHT Metamorphism.

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