Petrological and geochemical evolution of the Central Gneissic Belt, Rengali Province, eastern India: Implications for the Neoarchean growth and orogenesis

Abstract

This study focuses on the evolution of the Central Gneissic Belt of the Archean Rengali Province which evolved as a craton-margin orogenic belt. The Central Gneissic Belt is constituted of charnockite gneiss, migmatitic hornblende gneiss and granite gneiss often showing gradational contacts. While mafic granulite occurs as enclave within the charnockite gneiss, amphibolite and calc-silicate granofels enclaves are present within the granite gneiss. Mafic granulite shows peak metamorphic assemblage of garnet+clinopyroxene+plagioclase+quartz±orthopyroxene which was stabilized at 10.6±0.5kbar and 860±20°C. Charnockite gneiss with the peak assemblage of orthopyroxene+quartz+plagioclase+K-feldspar was metamorphosed at 792±48°C and 7.6±0.4kbar. Amphibolite and migmatitic hornblende gneiss contain hornblende along with plagioclase and garnet and these rocks were metamorphosed at 800±20°C, 8.5±0.2kbar and 695°C, 8kbar respectively. Later meta-dolerite dikes exhibit relic igneous textures which are slightly modified by greenschist-facies metamorphism. Charnockite gneiss, migmatitic hornblende gneiss and granite gneiss show similar trace and REE characteristics (moderate fractionation in terms of La and Yb, LREE enrichment and flat HREE pattern) implying the same protolith composition for these rock groups. Based on the field, petrographic and geochemical data, we propose that the protoliths for the charnockite gneiss, the migmatitic hornblende gneiss and the granite gneiss crystallized as fractionated magma in within-plate syncollisional setting during the ca. 2860–2780Ma orogeny at the Rengali Province.