Geochemical constraints on the multistage metamorphic evolution of mafic granulites from the South Delhi Terrane, Northwestern India

Abstract

Mafic granulites from the Balaram area, South Delhi Terrane, Aravalli–Delhi Mobile Belt (ADMB), provide important insights into the petrogenesis and tectonometamorphic evolution of the lower continental crust. These rocks are characterized by the mineral assemblage orthopyroxene + clinopyroxene + plagioclase ± garnet ± hornblende ± biotite, with accessory ilmenite, magnetite, and rutile. Petrographic features such as granoblastic texture, coronae, and symplectites indicate granulite-facies metamorphism followed by retrograde rehydration under amphibolite-facies conditions. Whole-rock geochemical data show enrichment of LREE over HREE, negative Eu anomalies, and elevated total REE contents (86.26–314.90 ppm), suggesting crustal involvement, plagioclase fractionation, and enrichment inherited from the protolith. Major- and trace-element systematics indicate that the protolith was derived from partial melting of older, clay-poor crustal sources with minor mantle input, producing a hybrid precursor composition. Tectonic discrimination based on Ti/Zr and Zr/Y–Y relationships suggests magma generation in a transitional setting influenced by both volcanic arc basalt and mid-ocean ridge basalt affinities. These results constrain a multistage evolution involving extensional magmatism, high-grade metamorphism, and later compressional reworking during the evolution of the ADMB.