Geochronology and geochemistry of meso-to neoarchean magmatic epidote-bearing potassic granites, western dharwar craton (Bellur–nagamangala–pandavpura corridor), southern india: Implications for the successive stages of crustal reworking and cratonization

Abstract

We present field and petrographical characteristics, zircon U–Pb ages, Nd isotopes, and major and trace element data for the magmatic epidote-bearing granitic plutons in the Bellur–Nagamangala–Pandavpura corridor, and address successive reworking and cratonization events in the western Dharwar Craton (WDC). U–Pb zircon ages reveal three stages of plutonism including: (i) sparse 3.2 Ga granodiorite plutons intruding the TTG (tonalite–trondhjemite–granodiorite) basement away from the western boundary of the Nagamangala greenstone belt; (ii) 3.0 Ga monzogranite to quartz monzonite plutons adjoining the Nagamangala greenstone belt; and (iii) 2.6 Ga monzogranite plutons in the Pandavpura region. Elemental data of the 3.2 Ga granodiorite indicate their origin through the melting of mafic protoliths without any significant residual garnet. Moderate to poorly fractionated REE patterns of 3.0 Ga plutons with negative Eu anomalies and Nd isotope data with εNd(T) = 3.0 Ga ranging from −1.7 to +0.5 indicate the involvement of a major crustal source with minor mantle input. Melts derived from those two components interacted through mixing and mingling processes. Poorly fractionated REE patterns with negative Eu anomalies of 2.6 Ga plutons suggest plagioclase in residue. The presence of magmatic epidote in all of the plutons points to their rapid emplacement and crystallization at about 5 kbars. The 3.2 Ga intrusions could correspond to reworking associated with a major juvenile crust-forming episode, whilst 3.0 Ga potassic granites correspond to cratonization linked to melting of the deep crust. The 2.6 Ga Pandavpura granite could represent lower-crustal melting and final cratonization, as 2.5 Ga plutons are absent in the WDC.