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The Nagercoil block, which is situated at the southernmost part of the Southern Granulite Terrane of south India, is dominantly comprised of garnet-bearing I-type massive charnockites. These charnockites preserve imprints of two major thermal events timed at Palaeoproterozoic (∼2.0–1.9 Ga) and Neoproterozoic (∼550 Ma). However, there is a lack of understanding on correlating the growth and stabilization of garnets within these charnockites, corresponding to these events. In the present study, rare earth element-based partition modeling between garnet and age-constrained accessory phases such as zircon and monazite is carried out to identify the exact timing of garnet formation in a representative sample from the area. U-Pb dating of zircon cores constrains the timing of protolith emplacement at ∼2.0 Ga and metamorphism at ∼550 Ma from zircon rims and monazites. REE modeling of zircon and monazite from these age domains suggests an equilibrium relation between the Neoproterozoic zircon rims and monazites, while the Palaeoproterozoic zircon cores are not in equilibrium with garnet. These results suggest that the formation of garnets in the Nagercoil charnockites is in response to the Neoproterozoic metamorphism recorded in the terrane associated with the final stage of the Gondwana supercontinent assembly. [ABSTRACT FROM AUTHOR]

This study presents the results of petrology, SHRIMP zircon U–Pb analysis, conventional Fe–Mg geothermobarometry, REE (rare earth element)‐based geothermobarometry, and phase equilibrium modelling, for newly discovered ultramafic‐mafic granulites (garnet pyroxenite with minor plagioclase and garnet‐bearing granulite) in the Namakkal Block of the southern granulite terrain (SGT), India. Results from this study shed light on the growth, evolution, and thermal state of lower continental crust during the Neoarchean, as a cross‐section of the Archean lower continental crust is well‐exposed in the SGT. SHRIMP zircon U–Pb dating of a garnet pyroxenite sample (18ID‐41) yielded a weighted mean 207Pb/206Pb age of 2531 ± 6 Ma, which is the same within uncertainty as one weighted mean SHRIMP metamorphic zircon 207Pb/206Pb age of 2519 ± 9 Ma from mafic granulite sample (18ID‐43). In addition, zircon U–Pb analyses also yielded an apparent 207Pb/206Pb age of 2474 ± 3 Ma (1σ) for the garnet pyroxenite, and a weighted mean 207Pb/206Pb age of 2489 ± 8 Ma for the mafic granulite. Thus, the timing of metamorphism of the ultramafic‐mafic granulites was constrained to be ca. 2530–2470 Ma. The peak metamorphic phase assemblage of the garnet pyroxenite is grt–cpx–pl–ilm–liq, which was modelled to be stable at 1058–1172°C/7.8–11.6 kbar, whereas the retrograde mineral assemblage of grt–cpx–hbl–pl–qz–ilm–liq occurred at 877–888°C/9.9–11 kbar. The mafic granulite was demonstrated to record similar peak and retrograde metamorphic P–T conditions to those of the garnet pyroxenite but have a relatively small P–T range of the peak mineral assemblage. The ultrahigh temperature metamorphism of these ultramafic‐mafic granulites was further confirmed by the temperature results (1057–1087°C) from the REE‐in‐two‐pyroxene thermometer. As a result, a retrograde metamorphic P–T path characterized by near‐isobaric cooling from ~1080°C at ~10 kbar to ~900°C at ~10 kbar was constructed for these rocks, which is consistent with an extremely high thermal state that persisted for ca. 60 Ma in the lower crust. [ABSTRACT FROM AUTHOR]

• The Sandmata Complex preserves Neoarchaean protolith ages of 2.68–2.42 Ga. • Zircon-monazite ages indicate peak granulite facies metamorphism at 1.90–1.78 Ga. • Sandmata quartzofeldspathic gneisses record an isobaric cooling P–T path. • The complex was tectonically active up to the Neoproterozoic (∼0.90–0.78 Ga). The Sandmata Complex in the Aravalli Craton of northwestern India experienced syn- to post-collisional high-grade metamorphism and migmatization related to the 1.9–1.7 Ga Aravalli orogeny. Garnet-bearing quartzofeldspathic gneisses are an important rock type in the Sandmata Complex. Their prograde assemblage is represented by garnet cores and inclusion minerals Bt + Pl + Qz, whereas the assemblage Pl + Kfs + Qz + Bt matrix + Sil + Ilm, along with chemically homogeneous garnet porphyroblasts, represents peak metamorphism. Post-peak retrograde metamorphism is reflected in the growth of muscovite, chlorite and biotite, and diffusion adjustments in garnet rims. Mineral paragenesis, mineral chemistry, conventional thermobarometry, and phase equilibrium modelling indicate P–T conditions of 6.7–10.2 kbar at 725–830 °C for peak metamorphism, and 4.8–6.9 kbar at 450–610 °C for post-peak retrogression. The P–T conditions determined from the quartzofeldspathic gneisses define a near-isobaric cooling P–T path. In contrast, previously studied high-grade pelitic gneisses and metagranitoids from the Sandmata Complex define an isothermal decompression P–T path. U–Pb dating of magmatic zircon cores in the quartzofeldspathic gneisses provides the crystallization age of their felsic protoliths as ∼ 2.52 Ga. Zircon and monazite geochronology show that peak metamorphism occurred at ∼ 1.90–1.78 Ga and thus shortly preceded the emplacement of the Gyangarh-Asind igneous suite and Anjana granite, previously dated at ∼ 1.72–1.64 Ga. A model of oceanic crust subduction followed by continent–continent collision during the Aravalli orogeny can explain granulite facies metamorphism in the Sandmata Complex. The combined results of this and previous studies support the operation of modern-style plate tectonic processes involving subduction and continental collision during Palaeoproterozoic time. We also identify a younger (∼0.90–0.78 Ga) metamorphic episode, preserved mostly in recrystallized monazite grains elongated parallel to the final deformation fabric, likely related to the South Delhi orogeny. [ABSTRACT FROM AUTHOR]

• The metamafic volcanics and metasediments from the Sargur Greenstone Belt recorded the 2.50–2.44 Ga regional metamorphism. • The garnet-bearing amphibolite and garnet-staurolite-kyanite mica schist yield an amphibolite-facies metamorphism with peak P–T conditions of 681–769 °C and 7.5–9.3 kbar. • The ca. 2.50–2.44 Ga regional metamorphism was possibly resulted from accretion-collision of different Archean blocks in the WDC. 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. [ABSTRACT FROM AUTHOR]