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[Display omitted] • Protoliths of mafic granulites and associated rocks derived from sub-alkaline tholeiitic magma. • Magmatism peaked at 3.1 Ga and occurred in a subduction-related arc setting. • High grade metamorphism at ca. 3.0 associated with collision. • Charnockites and mafic granulites represent the roots of this microblock. The Coorg Block in southern India is an archive of Paleo-Mesoarchean arc magmatism and continental building in the early Earth. Here we investigate a suite of mafic and ultramafic rocks and associated lithologies to characterize the roots of this microcontinent. We present petrologic, geochemical, as well as U-Pb and Lu-Hf data on zircon and U-Pb data on monazite from these rocks which provide insights into the petrogenesis of the rocks as well as the timings of magmatism and subsequent metamorphism. The geochemical features of the mafic granulites indicate that the rock suite was derived from the fractionation of a sub-alkaline tholeiite magma. Most of the rocks correspond to arc setting in a subduction-related tectonic regime. The rocks exhibit relative enrichment in LILE, Pb, and LREE with depletion in HFSE such as Nb and Ta suggesting partial melting of a metasomatized mantle wedge. Their high LILE/HFSE and LREE/HFSE ratios indicate slab dehydration and mantle wedge melting in typical island arc settings. The overall trace element and REE patterns of the rocks indicate that the source magma of the ultramafic and mafic rocks might have been derived from a refractory mantle source followed by the metasomatic enrichment of lithospheric mantle wedge by incompatible elements through the influx of subduction-derived fluids/melts. We present comprehensive zircon U-Pb data and Lu-Hf data on a suite of mafic granulite, garnet-bearing granulite, tremolite actinolite schist, charnockite, and anorthositic gabbro as well as monazite U-Pb data from a charnockite sample. Most zircon grains show cores with magmatic crystallization features and many grains are mantled by metamorphic rims. The age data show a prominent peak at 3.1 Ga for most of the rocks suggesting that the major crustal building in the Coorg Block occurred during the Mesoarchean. Rocks on the margins of the block were affected by the younger (Neoarchean) tectonothermal event in the surrounding blocks. The Lu-Hf isotopic data on zircon grains with ca. 3.1 Ga ages show εHf(t) values ranging from −4.4 to + 3.7 (average + 0.3). In the εHf(t) versus 207Pb/206Pb age diagram, the plots are distributed close to the CHUR line suggesting Paleo-Eoarchean juvenile magma sources. The voluminous mafic lower crust at the root of the Coorg Block is consistent with addition of mafic magmas through slab melting induced by high mantle potential temperatures in the Archean, as well as the interaction of fluids/melts with the mantle wedge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zircon U-Pb data constrain emplacement of mafic–ultramafic suite at ca. 3.2 Ga. • Magmatism within a subduction metasomatised mantle wedge. • Mesoarchean subduction-accretion and amalgamation of ancient continental nuclei. Archean mafic–ultramafic rocks provide important clues on the tectonic and crust building processes in the early Earth. The Western Dharwar Craton (WDC) and the Karwar Block (KB) in southern Peninsular India preserve some of the oldest records of craton building processes in the Archean Earth. The tectonic affinity of the Karwar Block that lies at the western periphery of the WDC remains uncertain. Here we present the results from an integrated study of a mafic–ultramafic rock suite from this block using petrology, whole-rock geochemistry, and zircon U–Pb and Lu-Hf data. These rocks occur as deformed and dismembered units within basement granitic gneiss. The primary igneous minerals such as pyroxene and plagioclase show variable degrees of alteration. The rocks show negative Nb anomalies and prominent Pb enrichment. The uniform enrichment of Th and U over Nb-Ta indicates the influence of metasomatic fluids in the mantle wedge. The geochemical data indicate that these rocks were derived from basaltic magmas generated within a subduction metasomatised mantle wedge in an intra-oceanic arc setting without any significant crustal contamination. U-Pb isotope analysis of zircon grains from the metapyroxenite shows upper intercept ages of 3172 to 3213 Ma and weighted mean ages of 3170 to 3203 Ma. A metagabbro sample yielded upper intercept age of 2792 Ma and the 207Pb/206Pb spot ages in another sample range up to 3202 Ma. Zircon U-Pb data suggest that the mafic–ultramafic suite formed at ca. 3.2 Ga and were overprinted by 2.7 Ga thermal event. The εHf(t) values are all positive and range between 0.73 and 6.02, suggesting that the magma was derived dominantly from Mesoarchean juvenile (depleted mantle) sources. We propose a tectonic model that involves a subduction-accretion stage followed by suturing of the ancient continental nuclei. [ABSTRACT FROM AUTHOR]