Criteria to distinguish between regional and contact zone monazite - A case study from Proterozoic North Delhi Fold Belt (NDFB), India

Abstract

North Delhi Fold Belt (NDFB) is a part of a NNESSW trending Proterozoic mobile belt hosting sulfide mineralization in Khetri Copper Belt (KCB) towards its western margin. It preserves assemblages of amhibolite facies Barrovian metamorphism locally overprinted by a thermal metamorphic event. Monazite (REEPO4) is developed in both the assemblages. Detailed chemistry and chemical geochronology of monazites in regional and contact metamorphic assemblages depict distinct chemical traits and ages. Two stage growth of metamorphic assemblages at ~1100 Ma and ~920Ma is recorded. Contact zone monazite grew at ~650Ma under hydrothermal conditions. It has low thorium and is cerium enriched in comparison to the regional metamorphic monazite. Low Th and high Ce/Th ratio in contact zone monazite is proposed as discriminating criteria between regional and contact metamorphic monazites.