Granulite Facies Spinel-Cordierite Assemblages from the Kerala Khondalite Belt, Southern India

Granulite facies metapelites at Koliacode in the Kerala Khondalite Belt show compositional bands of cordierite, spinel, sillimanite and biotite alternating with quartz-feldspar rich bands. Reaction textures involving cordierite and garnet show evidence for decompression. Mineral phase equilibria computations provide temperatures of ca. 700-750C and pressures of 4.5-5.0 kbar. Spinel in these rocks is remarkably enriched in Zn (ZnO up to 9.4 wt. %). The metamorphic P-T conditions and mineral reactions indicate that the terrain underwent rapid and near isothermal decompression.