Paleo-Mesoarchean crustal evolution in the Coorg Block, southern India: Insights from magmatic and metamorphic records in mafic granulites

Abstract

Lower crust mafic granulites are key components in understanding the formation and growth of the continental crust. Here we investigate the mafic granulites and associated rocks from the Paleo-Mesoarchean Coorg Block in southern India with a view to gain insights into the crust-mantle dynamics and the subduction–accretion‐collision history. We present petrology, mineral chemistry, conventional thermobarometry and computed pseudosections, whole‐rock geochemistry including major, trace element, and rare earth element (REE), and zircon U–Pb and Lu-Hf isotopes to trace the magmatic evolution and metamorphism of these rocks. The petrological features, mineral chemistry data and phase equilibria modelling suggest that the rocks underwent HP metamorphism at peak temperatures up to 900 °C and pressures up to 9.5–10 kbar along a clockwise P–T path followed by near isobaric cooling. Zircon U–Pb data from the mafic granulites place the peak emplacement time of the protolith at 3.1 Ga with a minor group of younger zircons indicating a post-collision thermal event at 2.7 Ga. Zircon REE patterns suggest the involvement of continental crust components in the magma source. Zircon Lu-Hf analysis yield positive εHf(t) values from 0.5 to 4.1 with model ages (TDM) of 3.3 Ga for rocks from the northern margin of the block and the bordering Mercara suture zone while samples from the southern margin display slightly older (3.4 Ga) ages. Our data indicate that the parent magmas were derived from both juvenile and reworked Paleoarchean sources. The mafic granulites record Mesoarchean subduction-related magmatism and crust building in the Coorg block. Our study contributes to the understanding of geodynamic processes and continent formation in the Early Earth.