Reaction textures and metamorphic evolution of spinel-bearing metapelites of Kerala Khondalite Belt, Southern Granulite Terrain, India

Kerala Khondalite Belt is the southern part of the Southern Granulite Terrain consisting of khondalites, garnet biotite gneiss and cordierite gneiss. This study briefly describes the petrography and reaction textures of spinel-bearing metapelites of KKB. The metapelites with the assemblage of cordierite + garnet + sillimanite + spinel + biotite + quartz + plagioclase + K -feldspar are very well exposed in Kulappara (KLP), Koliakode (KKD) and Ayiravalli (AYV) quarries and garnet + cordierite + orthopyroxene + spinels + plagioclase + k-feldspar assemblage in Koodal Mavanad (KDM), Koodal Dharshan (KDD), Koodal Palakkattu (KDP) and Koodal Ambadiyil (KDA) quarries. This study was carried out to understand the reaction textures of spinel and associated minerals in KKB. Several reaction textures described in this study help to unravel the polyphase metamorphism and evolution of spinel-bearing granulites. The KKB has a clockwise P–T path is indicated by the presence of prograde mineral relics and later retrograde textural reactions. The spinel-forming reactions from biotite-sillimanite assemblages correspond to biotite ”dehydration” or ”dehydration-melting” reactions. The reaction texture related to spinel-cordierite mineral phase, involving the subsequent decompression reaction in which spinel reacted to produce cordierite, such textures observed in the study area thus mark a series of decompression reactions following peak metamorphism. After the isothermal decompression in the KKB experience, an isobaric cooling path was observed from the growth of biotite. Thus, our present results show three types of reaction textures on spinel-bearing metapelites of KKB, which have already been proposed by different authors based on P-T estimation and petrography as high temperature–moderate pressure peak metamorphism followed by decompression and cooling.