Zircon U-Pb dating of the rhyolitic Panjal Traps yielded Early Permian 206Pb/238U crystallization ages (287.2 ± 2.5 Ma; 287.1 ± 2.8 Ma; 290.5 ± 3.3 Ma; 287.5 ± 3.3 Ma; 287.0 ± 3.7 Ma). A minor amount of Carboniferous xenocrystic zircons (309.2 ± 2.8 Ma) were identified and are likely representative of the earliest rift-related volcaniclastic rocks of the Panjal Traps (i.e., Agglomeratic slate). The zircons from all rhyolites have enriched εHf(t) isotopic values (εHf(t) = -10.4 to −4.2) indicating that they were derived by partial melting of continental crust. The lone dacite of the study did not yield a definitive crystallization age, but contains abundant xenocrystic zircons with Neoarchean (2.6 − 2.5 Ga), Paleoproterozoic (2.4 − 1.8 Ga), Mesoproterozoic (1.4 − 1.0 Ga), Neoproterozoic (0.9 − 0.6 Ga), and Early Paleozoic (0.58 − 0.43 Ga) groups. The xenocryst groupings match the detrital zircon age populations from the Indus River system, Indus Group sedimentary rocks, and major tectonomagmatic periods within the Archean-Paleoproterozoic Aravalli-Bundelkhand Craton. Furthermore, the xenocrystic zircons show secular variability in their Hf isotopic values (εHf(t) = -18.9 to + 10.2). The isotopic variability indicates that isotopically juvenile magmas were injected into the Aravalli-Bundelkhand Craton during the Paleoproterozoic (1900 − 1700 Ma) suggesting that there was an isotopic re-fertilization event.

Charnockite is one of the conspicuous lithologies in Precambrian granulite terranes, and isotope studies on them can help better understand regional tectonics. Here, we present new petrological, geochemical, and zircon U-Pb and Lu-Hf isotopic data for charnockite and associated felsic/mafic orthogneisses from the Northern Marginal Zone (NMZ) of the Limpopo Complex, a Neoarchean orogen regarded to have been formed by the collision of the Zimbabwe and the Kaapvaal Cratons in southern Africa. The REE and trace element patterns reveal volcanic arc affinity for the charnockites. Oscillatory-zoned and near-concordant zircons from the charnockites yielded weighted-mean Pb-207/Pb-206 and concordia intercept ages of 2691 +/- 6 to 2640 +/- 16 and 2607 +/- 55 Ma, respectively. The age of felsic orthogneiss (2628 +/- 16 Ma) is nearly consistent with those of the charnockites. Zircons from the mafic granulite, which occurs as a layer parallel to the foliation of the 2607 Ma charnockite and shows arc-magmatic geochemical signatures such as Nb, P, and Zr depletion, yielded a weighted-mean age of 2607 +/- 16 Ma. As both charnockite and the protolith of the mafic granulite from the same locality show consistent magmatic crystallisation ages, bimodal magmatism under a magmatic-arc setting is inferred. Zircons from a Chilimanzi Suite Granite (Zimbabwe Granite) of the Zimbabwe Craton adjacent to the NMZ show a weighted-mean Pb-207/Pb-206 age of 2607 +/- 35 Ma and a concordia-intercept age of 2627 +/- 36 Ma, which is comparable with the age range of charnockite. Therefore, the charnockite probably corresponds to the lower-crustal equivalent of the Chilimanzi Suite Granite. The syn- to post-tectonic Razi Granite from the NMZ-Zimbabwe Craton boundary yielded a weighted-mean age of 2542 +/- 16 Ma, which marks the youngest intrusion event in this region. Lu-Hf isotopic data of magmatic zircon cores from the Neoarchean charnockite, felsic orthogneiss, Zimbabwe Granite, and Razi Granite samples all show negative epsilon Hf(t) values (-11.18 to -2.20) with T-DM (c) ages of 3699-3158 Ma, suggesting their protolith formation by crustal recycling in an arc setting through partial melting of Eo- to Paleoarchean crustal components such as the Tokwe Segment of the Zimbabwe Craton. Our new data thus support northward subduction of the oceanic plate underneath the proto-Zimbabwe Craton, and the southern margin of the proto-Zimbabwe Craton corresponds to a continental arc.

We report new petrology, mineral chemistry, P-T conditions, and fluid inclusion data on mafic granulites from the Mettupalayam region along the Bhavani Suture Zone, Southern Granulite Terrane, India. Phase equilibria modelling of mafic granulites yielded peak P-T conditions of 780-860 degrees C and 7.6-10.1 kbar followed by a near isothermal decompression along a clockwise P-T path. The trapped fluid inclusions in the peak metamorphic minerals display a melting temperature range from -57.4 degrees C to -56.6 degrees C, close to the triple-point temperature of pure CO2. The primary inclusions homogenized at -18.9 degrees C to +0.2 degrees C, corresponding to density values of 0.93-1.03 g/cm(3). Homogenization of the secondary inclusions occurred within the range from -6.3 to +18.1 degrees C, corresponding to low CO2 densities of 0.79-0.96 g/cm(3). From the textural characteristics of the high-density primary carbonic fluid inclusions, we interpret these inclusions as the CO2-rich syn-metamorphic fluid present during the high-grade metamorphism. The secondary fluids characterised by lower densities have undergone re-equilibration during the exhumation stage (decompression) from the peak granulite-facies metamorphism along a clockwise P-T trajectory. This interpretation is consistent with the occurrence of hornblende + plagioclase symplectite around the porphyroblastic garnet, suggesting decompression. We infer that the high-density CO2 was the dominant syn-metamorphic fluid components present during the granulite-facies metamorphism in the Mettupalayam region. Such carbonic fluids, possibly derived by degassing from carbonates or mantle sources, probably played a significant role in stabilizing high-grade mineral assemblages along this collisional suture zone.

The Early Permian (c. 290 Ma) Panjal Traps is the most extensive sequence of flood basalts within the Tethyan domains of the Himalaya. The Panjal Traps erupted during a period of tensional plate stress related to the rifting of Cimmerian terranes from the Tethyan margin of Gondwana. The majority of the mafic Panjal Traps were affected by postemplacement low-temperature deuteric alteration and/or regional deformation. Consequently, constraining the magmatic conditions of the rocks is difficult. The least altered Panjal Traps are located within the Guryal Ravine section of the western Zanskar Range and the southern Pir Panjal Range. The rock and mineral textures are preserved and they have a primary mineralogy of clinopyroxene (Wo(30.3-42.5)En(29.4-49.7 )Fs(13.8-34.2)) and plagioclase (An(61.0-43.5)) phenocrysts within an aphanitic matrix. Secondary minerals include chlorite, epidote, actinolite, quartz, albite, orthoclase, rutile, and titanite and indicate that some of the rocks underwent greenschist to sub-greenschist facies metamorphism. Clinopyroxene-liquid geothermobarometers were used to assess the equilibrium crystallization temperature and pressure of the least altered Panjal Traps. The clinopyroxene-liquid saturation conditions yielded temperatures of 1104-1184 degrees C and pressures of 1.8-7.0 kbar which are within the uncertainty of the jadeite-diopside-hedenbergite exchange thermometer (1064-1167 degrees C) and the Al exchange barometer (1.1-6.8 kbar). The equilibrium temperatures are not anomalously high and similar to lavas that erupt at a passive rift setting rather than from a mantle plume. The whole rock V/Sc and V/Ga ratios suggest that the oxygen fugacity of the lavas was likely at or below the fayalite-magnetite-quartz buffer (triangle FMQ triangle FMQ = 0 to-1). Rhyolite-MELTS modeling (triangle FMQ triangle FMQ = -1; P = 2 kbar) indicates the water content within the basalts was variable and probably did not exceed 2.25 wt% prior to eruption. The post-emplacement metamorphic conditions are constrained using Perple_X modeling and demonstrate that the rocks from both Guryal Ravine and southern Pir Panjal Range (P = < 3.0 kbar and T = 390 - 415 degrees C) underwent greenschist facies metamorphism at similar temperature. However, the pressure is not well constrained. We attribute the metamorphism to regional deformation associated with terrane accretion to the Indian plate during the Mesozoic and Cenozoic that occurred after the deposition of the Late Permian to Early Triassic Pangea megasequence but before the Oligocene.

The circum-Gondwana subduction initiated by the early Cambrian has been suggested to reflect the establishment of the modern plate tectonics. The metamorphic rocks with low thermobaric (T/P) ratios indicative of cold subduction in the present tectonic regime have not been well investigated. To better understand the circum-Gondwana subduction and to test its possible link with the emergence of the modern plate tectonics, this study focused on blueschist-facies metamorphic rocks in the Altyn Tagh of the southeastern Tarim craton. Mineral assemblage and chemistry, phase equilibrium modelling, and quartz-in-garnet Raman elastic geobarometry reveal that the zoisite blueschist and glaucophane (Gln)bearing quartz schist in northern Altyn Tagh were metamorphosed to lawsonite to epidote blueschistfacies at 520-545 degrees C and 16-19 kbar. It reflects high-pressure (HP)/low temperature (LT) metamorphism with low T/P ratios of <300 degrees C/GPa and thermal gradients of <10 degrees C/km. These blueschist-facies metamorphic rocks underwent rapid decompression starting at P-T conditions of <495 degrees C and <9.6 kbar during exhumation. Ar-Ar geochronology records paragonite Ar-Ar plateau ages of 520-506 Ma for the zoisite blueschist samples and phengite Ar-Ar plateau ages of 522-516 Ma for the Gln-bearing quartz schist samples, suggesting that the peak HP/LT metamorphism occurred prior to ca. 522 Ma. Based on new results and available data from the major Gondwana blocks, cold subduction was suggested to profoundly operate along circum-Gondwana in the early Cambrian after the amalgamation of Gondwana. The extensive circum-Gondwana subduction represents the earliest global cold subduction in Earth's history associated with the establishment of the modern plate tectonics, as directly recorded by the studied early Cambrian blueschist-facies metamorphic rocks and a dramatic drop in the mean T/P of metamorphism since the early Paleozoic.(c) 2023 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Fluid inclusions trapped in high-grade metamorphic minerals offer direct evidence for the nature and role of fluids involved in lower crustal processes. Here, we report extremely high-density (-1.155 g/cm3) carbonic fluid inclusions preserved within garnet grains in metagabbros from the central segment of the Palghat-Cauvery Su -ture Zone (PCSZ) in southern India. The metagabbros are composed of coarse-grained garnet, clinopyroxene, orthopyroxene, plagioclase, quartz, and retrograde calcic amphibole. Garnet occurs either as porphyroblastic grains formed during prograde to peak stage, or as fine-grained aggregates around plagioclase possibly formed by post-peak decompressional (near-isobaric) cooling. The peak and retrograde P-T conditions have been estimated as-940 ?/-11.5 kbar and -840-850?/-9.3-10.2 kbar, respectively, based on phase equilibria modelling using pseudosection computation. Fluid inclusions occur as primary and secondary phases within the por-phyroblastic garnet and matrix plagioclase. The melting temperatures of these fluid inclusions are in the range of-57.4 to-56.6 ?, indicating nearly pure CO2 composition. The lowest homogenization temperature from the primary inclusions in garnet (-50.1 ?) translates to extremely high density of 1.155 g/cm3. The calculated isochores for the inclusions (-11.3 kbar at 950 ?) are broadly consistent with the peak P-T conditions, sug-gesting that the fluids are trapped near the peak metamorphic stage under a dry condition. The preservation of ultrahigh-density carbonic inclusions is probably due to isochore-parallel decompressional cooling after the peak metamorphism. The secondary inclusions show slightly lower densities of 1.014-1.053 g/cm3 (in garnet) and 0.955-0.976 g/cm3 (in plagioclase), the isochores of which suggest a lower-pressure range of 4.8-5.8 kbar at 800 ?. The high-density pure CO2 fluids reported in this study as well as in previous studies from the PCSZ, and the isochoric evolution provide robust evidence for the presence of supercritical carbonic fluids in the lower continental crust.

The Magondi Belt has been regarded as a Paleoproterozoic orogen formed by the collision of the Zimbabwe Craton and an unknown continental block. The Dete-Kamativi Inlier (DKI) located approximately 200 km westsouthwest of the main Magondi Belt has been regarded as an extension of the belt. Here, we report new geochmnological data for pelitic schists and a felsic orthogneiss from the DKI using monazites (CHIME method) and zircons (LA-ICP-MS analysis), and discuss the tectonic evolution of the region. Zircons from a felsic orthogneiss in the Kamativi area yielded magmatic and metamorphic ages of 2279 +/- 25 Ma and 2020 +/- 28 Ma, respectively. Similar Paleoproterozoic ages of ca. 2.1-1.8 Ga were also obtained from subhedral and rounded monazite grains in the pelitic schists. In contrast, irregular-shaped monazite intergrown with biotite in a different pelitic schist gave three latest Mesoprotemzoic isochron ages of 1196 +/- 37 Ma, 1143 +/- 32 Ma, and 1070 +/- 25 Ma, suggesting a long-lived (>120 million years) thermal event with several monazite-growing stages. Consistent isochron ages of 1062 +/- 41 Ma and 1061 +/- 26 Ma were obtained from monazites in the felsic orthogneiss and metapelite samples from an adjacent region. The application of phase equilibrium modeling for the peak mineral assemblage in the garnet-andalusite-biotite-cordierite-bearing pelitic schist with 1196-1070 Ma metamorphic ages indicated a peak P-T condition of 520-600 degrees C and 1.5-2.5 kbar, suggesting low-pressure amphibolite-facies metamorphism. The condition is lower than that obtained from the hornblende-plagioclase geothermometry of amphibolites (>700 degrees C) from the southwest part of the DKI, which probably corresponds to an earlier (ca. 2.0 Ga) high-grade metamorphic condition. The youngest thermal event, 994-982 Ma, from monazite rim in a mylonitic orthogneiss might correspond to the timing of later deformation. The latest Mesoproterozoic (1.2-1.1 Ga) amphibolite-facies metamorphism was likely associated with an intracratonic orogeny related to the activity of broadly coeval orogenic events, such as the Namaqua-Natal omgenic belt related to the amalgamation of the Rodinia supercontinent. Regional magmatic activity of the Umkondo large igneous province at 1112-1108 Ma could have also been an additional heat source.

We have uncovered evidence of Neoarchean ultrahigh-temperature (UHT) metamorphism in the Karimnagar Granulite Terrane (KGT), southern India, based on new petrological and mineralogical data of sapphirine-bearing and related granulites. We investigated their petrogenesis and implications of a hot orogen along the north-eastern margin of the Eastern Dharwar Craton (EDC). We found various reaction textures, such as spinel mantled by sapphirine and hydration of orthopyroxene, indicating a peak mineral assemblage of cordierite + sapphirine + spinel + orthopyroxene + biotite + rutile + K-feldspar. Phase-equilibria modelling in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 system indicates peak metamorphic conditions of 905 degrees C-910 degrees C and 4.5-4.6 kbar. The peak stage was followed by a retrograde metamorphic stage represented by increasing modal abundance of biotite and consumption of rutile and spinel at similar to 730 degrees C and similar to 4 kbar, suggesting near-isobaric cooling. Using the chemical Th-U-Pbtotal isochron method, we dated monazites in textural asso-ciation with sapphirines and cordierites in a sapphirine-spinel-orthopyroxene-cordierite granulite. The resulting Neoarchean age (2638 +/- 44 Ma) probably represents the timing of peak UHT metamorphism. We infer that Neoarchean UHT metamorphism and post-peak near-isobaric cooling took place in the terrane during the ter-minal stage of complex accretion-collision tectonic processes related to amalgamation of microcontinents and/or magmatic arcs that occurred during 2.70-2.62 Ga, one of the major episodic crust-forming events in the EDC. Our findings and regional distribution of lithologies overturn the existing tectonic model of the KGT as a collisional suture zone between the EDC and the Bastar Craton. Moreover, we propose that the KGT is a discrete tectonic block composed of similar to 2.7-2.6-Ga granulites and younger granite representing the mid-crustal segment of the EDC, which was uplifted as a tilted tectonic block along the southern flank of the Kadam outlier.

The southern part of the Malawi Basement Complex is regarded as being part of the Mozambique Belt, which was formed by a series of collisions between Archean cratons and/or Proterozoic magmatic arcs during Neoproterozoic to Cambrian time. The region is particularly important because of its location near the junction between the East-African (ca. 600-550 Ma) and Kuunga (ca. 560-530 Ma) orogens, which means that complex magmatic or metamorphic episodes may have been recorded in high-grade metamorphic rocks in the region. Here we report on new petrological, geochemical, and zircon U-Pb age data on felsic to mafic orthogneisses as well as on a syn-tectonic syenite from the Lilongwe-Zomba-Blantyre area in southern Malawi, with a view to evaluating the timing and pressure-temperature (P-T) conditions of the collision events as well as the protolith formation. The geochemical data on the felsic orthogneisses suggested magmatic-arc signatures, whereas the mafic orthogneisses had both magmatic-arc and non-arc signatures. Metamorphic P-T estimates for the orthogneisses based on conventional geothermometry and phase-equilibria modeling indicated high-pressure granulite-facies conditions of 9.1-11.6 kbar and 840 degrees C-930 degrees C. Zircons obtained from charnockite, biotite gneiss, and garnet-bearing mafic granulite yielded magmatic ages of 1011-808 Ma, 1013 Ma, and 1076 Ma, respectively, suggesting the presence of Stenian-Tonian crustal growth related to arc magmatism. Ediacaran (573 Ma) intrusion of granitic rock was also inferred from magmatic zircons found within a granitoid gneiss. The timing of the high-grade metamorphism was constrained by the ages of the zircon rims and found to be 569-557 Ma, thus coinciding with the intrusion of syn-tectonic syenite at 562 Ma. The results of this study suggest that the southern part of Malawi is composed of remnants of the Stenian-Tonian magmatic arc, which were metamorphosed together with surrounding metasediments around 560 Ma. The Ediacaran high-grade metamorphism is consistent with the age of the Zambezi Belt located immediately southwest of the Malawi Basement Complex. Both the Lilongwe-Zomba-Blantyre area and the Zambezi Belt may correspond to a single suture zone formed by the latest Neoproterozoic collision between the Kalahari and Congo Cratons.

The Bastar craton in central India, surrounded by cratonic blocks and Paleoproterozoic to Neoproterozoic orogenic belts, is a window to investigate the Archean-Paleoproterozoic crustal evolution and tectonic processes. Here we propose a new tectonic classification of the craton into the Western Bastar Craton (WBC), Eastern Bastar Craton (EBC), and the intervening Central Bastar Orogen (CBO). We present petrologic, geochemical and zircon U-Pb, REE and Lu-Hf data from a suite of rocks from the CBO and along the eastern margin of the WBC Including: (1) volcanic successions comprising meta-andesite and fine-grained amphibolite, representing arc-related volcanics along a convergent margin; (2) ferruginous sandstone, in association with rhyolite, representing a volcano-sedimentary succession, deposited in an active trench; and (3) metamorphosed mafic-ultramafic suite including gabbro, pyroxenite and dunite invaded by trondhjemite representing the section of sub-arc mantle and arc root adjacent to a long-lasting subduction system. Petrologic studies indicate that the mafic-ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment. The chondrite-normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from MORB magma. The mixed characters from N-MORB to E-MORB of the studied samples are consistent with subduction modification of a MORB related magma, involving partial melting of the metasomatized mantle wedge. Our zircon U-Pb age data suggest that the cratonic nuclei was constructed as early as Paleoarchean. We present evidence for active subduction and arc magmatism through Mesoarchean to Neoarchean and early Paleoproterozoic, with the trench remaining open until at least 2.3 Ga. Two major crust building events are recognized in the Bastar craton: during Mesoarchean (recycled Paleoarchean subduction-related as well as juvenile/depleted mantle components) and Neoarchean (accretion of juvenile oceanic crust, arc magmatism including granite batholiths and related porphyry mineralization). The final cratonization occurred during latest Paleoproterozoic, followed by collisional assembly of the craton and its incorporation within the Peninsular Indian mosaic during Mesoproterozoic. In the global supercontinent context, the craton preserves the history of Ur, the earliest supercontinent, followed by the Paleo-Mesoproterozoic Columbia, as well as minor thermal imprints of the Neoproterozoic Rodinia and associated Grenvillian orogeny. (c) 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The Bhavani Suture Zone in the Southern Granulite Terrane marks the zone of amalgamation of the Neoarchean Nilgiri Block and the northwestern Madurai Block in southern India. Here, we report detailed petrological, geochemical, and geochronological data on the Mettupalayam mafic–ultramafic complex within this suture zone with a view to evaluate the tectonothermal history of the Bhavani Suture Zone and adjoining crustal blocks. The metamorphosed complex includes charnockite, hornblende‐biotite gneiss, mafic granulite, amphibolite, garnet‐bearing mafic granulite, and dioritic gneiss along with metamorphosed banded iron formation. The mafic granulite and the dioritic gneiss occur as concordant layers of varying thickness within the hornblende‐biotite gneiss. The salient geochemical features of the mafic granulite and the dioritic gneiss including the enrichment of large‐ion lithophile elements and depletion of high‐field‐strength elements suggest a subduction‐related arc magmatic setting. However, the amphibolites show MORB‐related affinity, suggesting its formation from a N‐MORB‐related source and their accretion together with the overlying banded iron formation. The peak metamorphic conditions of the garnet‐bearing mafic granulite were estimated using conventional geothermobarometers as 800–820 °C/8.5–9.2 kbar, which we further confirm through phase equilibrium modelling in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO) system. Magmatic zircons with high Th/U ratio from the amphibolite display a well‐defined discordia with an upper intercept age of 2,600 ± 38 Ma. Zircon grains from the dioritic gneiss show weighted mean 206Pb/207Pb age of 2,524 ± 6 Ma from concordant zircon spots and a comparable upper intercept age of 2,562 ± 34 Ma from discordant zircon spots, indicating protolith emplacement related to Neoarchean arc magmatism as inferred from our geochemical data. The thin overgrowth rims around the magmatic zircon grains in the amphibolite yielded an upper intercept age of 2,520 ± 20 Ma, which is comparable with the protolith crystallization age of the dioritic gneiss. Slightly younger weighted mean 207Pb/208Pb ages of 2,463 ± 27 Ma (from dioritic gneiss) and 2,422 ± 30 Ma (from amphibolite) are also obtained from the metamorphic zircon rims. These ages are correlated to the timing of high‐grade metamorphism associated with final collision of the Nilgiri Block and the northwestern Madurai Block. Similar Neoarchean–Paleoproterozoic magmatism and high‐grade metamorphism were reported from many localities south of the Dharwar Craton. Our study further confirms the previous tectonic model that envisages multiple subduction and collision of magmatic arcs and continental fragments towards the Dharwar Craton during the Archean–Paleoproterozoic transition.