DECOMPRESSIONAL P-T HISTORY IN SAPPHIRINE-BEARING GRANULITES FROM KODAIKANAL, SOUTHERN INDIA

The sapphirine-bearing granulites exposed around the Kodaikanal region of the Madurai block, southern India, present a variety of mineral pa rageneses involving garnet, spinel, sillimanite, cordierite, orthopyro xene, phlogopite, potash feldspar and plagioclase. Interpretation of m ultiphase reaction textures in conjunction with mineral chemical data and topology in the (FM)AS system is consistent with the main sapphiri ne-forming reactions: orthopyroxene + sillimanite = sapphirine + cordi erite phlogopite + sillimanite = sapphirine + cordierite + K-feldspar + vapour Mg-tschermak = sapphirine + cordierite The P-T evolution of t hese sapphirine granulites has been constrained through the use of con ventional geothermobarometry, internally consistent TWEEQU programme a nd thermodynamically calibrated MAS equilibria. The P-T estimates defi ne a retrograde trajectory with substantial decompression of c.4 kbar from P-T-max of c.8 kbar at c.800 degrees C. On the basis of the avail able evidence for a Pan-African granulite-facies event in the Madurai and Trivandrum blocks, the emerging concept of East Gondwana assembly is endorsed. Copyright (C) 1996 Elsevier Science Ltd