Zircon-monazite geochronology and P-T evolution of the Sargur Greenstone Belt: Implications for the end-Archean tectonics of the Dharwar Craton in southern India

Abstract

We report petrological and geochronological data for metamafic volcanics and metasediments from the Sargur Greenstone Belt, Western Dharwar Craton (WDC), southern India and discuss the end-Archean metamorphic P–T conditions of the Sargur Greenstone Belt, as well as geotectonic implications of the end-Archean metamorphism in the WDC. The LA-ICP MS zircon U-Pb dating yields a metamorphic age of 2500 ± 20 Ma for the garnet-bearing amphibolite. The garnet-staurolite-kyanite mica schist sample has metamorphic zircon and monazite U-Pb ages of 2443 ± 7 Ma and 2468 ± 10 Ma, respectively, consistent with metamorphic zircon U-Pb ages of 2459 ± 17 Ma and 2455 ± 18 Ma yield by the amphibole-garnet schist samples. The peak mineral assemblage of the garnet-bearing amphibolite is garnet + clinopyroxene + amphibole + plagioclase + quartz + rutile + ilmenite, and that of the metapelitic schist is garnet + staurolite + kyanite + biotite + muscovite + quartz + plagioclase. Phase equilibrium modelling, together with geothermobarometers yield P–T conditions of 7.9–8.9 kbar/681–769 °C and 7.5–9.3 kbar/683–694 °C for the garnet-bearing amphibolite and garnet-staurolite-kyanite mica schist, respectively, corresponding to a medium geothermal gradient of 20–25 °C/km. These data indicate that the Sargur Greenstone Belt has experienced a typical Barrovian-type (amphibolite-facies) metamorphism at ca. 2.50–2.44 Ga. Combined with the previous studies, it is suggested that the Sargur Greenstone Belt was most likely to be formed during 3.35–3.12 Ga and was reworked through four episodes of magmatic-metamorphic events occurred at ca. 3.1 Ga, ca. 3.0 Ga, ca. 2.8–2.6 Ga and ca. 2.5–2.4 Ga. The prominent ca. 2.5–2.4 Ga regional metamorphism is the last stage of the Neoarchean tectono-thermal event in the WDC and thus most possibly indicate accretion-collision of different Archean blocks at ca. 2.5–2.4 Ga and lead to the final cratonization (stabilization) of the whole Dharwar Craton.