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Large-scale helium accumulations are rarely reported in tectonically active continental subduction zones. This study shows geochemical variations in helium and other volatiles (N 2 , CO 2 , Ne and Ar) in hot springs from the India–Asia continental convergent margin (Indus–Yarlung suture, IYS) to the intracontinental extensional region in southern Tibet and identifies a 1200-km-long helium enrichment zone (He > 5000 ppm) within 50 km north of the IYS. In total, 144 gas samples were categorized into four groups: Group A, with dominant N 2 species and He concentrations (0.07–2.31 vol%) 1.4–23 times higher than industrial-grade He resources (0.05–0.1 vol%); Group B, with dominant CO 2 species and high He concentrations (0.05–1.57 vol%); and Groups C and D, depleted in He (<0.05 vol%) and dominated by CO 2 and N 2 , respectively. The gas mixtures exhibit systematic variations from the extensional zone to the continental convergent margin, changing from deep-origin, He-depleted, CO 2 -dominated fluids (Group C) to relatively shallow crust-derived, He-rich, N 2 -dominated gases (Group A). The former exhibits small but detectable amounts of mantle-derived He (2.3 ± 2.6%) and CO 2 (<3.2%), primarily atmosphere-derived N 2 (δ15N = 0.0 ± 0.6‰) and Ar (40Ar/36Ar = 307 ± 25), and crustal CO 2 (82 ± 9% from carbonate and 17 ± 9% from sediments/metasediments) from the subducted Indian slab-carbonate and Tibetan crust. The low He flux of Group C matches the steady release of He from the 70-km-thick crust into the geothermal waters during 0.02–43.5 ka. Shallow calcite precipitation and dissolution reactions cause CO 2 loss and slight He enrichment in the extensional zone. Group A samples at the convergent margin show pure crustal He, more radiogenic 40Ar (40Ar/36Ar = 330 ± 67), and higher sedimentary contributions of 28 ± 23% for N 2 and 37 ± 11% for CO 2. A high He flux near the IYS requires an external source with high 4He/N 2 (∼0.05) and 4He/20Ne (103–105) to provide >62% of the total He flux. This finding is best explained by He production in the south-dipping Gangdese granitic belt and deep crust, accumulation below the accretionary wedge, and episodic liberation along Great Counter thrust structures since 0.7 Ma by Tibetan Plateau uplifts and intense hydrothermal activity. The He-rich fluids mix with the sedimentary and atmosphere-derived N 2 from the accretionary wedge, forming He-rich N 2 -type gases. This study systematically reports large-scale He enrichment along the continental convergent margin for the first time and demonstrates that complex crustal-scale structures in the convergent margin significantly controlling gas geochemistry. These results have profound implications for potential helium resource exploration and He-CO 2 -N 2 recycling in continental subduction zones. [ABSTRACT FROM AUTHOR]

Much of the geological record of the northern Indian passive continental margin has been lost due to erosion or obscured due to tectonic burial associated with the India-Eurasia collision. Consequently, tectonic models of India's breakup from East Gondwana incorporate limited data from the northern margin of Greater India. We present evidence of the Late Jurassic clastic dykes crosscutting contemporaneous sedimentary sequences in the Tethys Himalaya. We propose that the original orientation of the clastic dykes provides kinematic information about Greater India's breakup from East Gondwana. The clastic dykes are meters to hundreds of meters long and centimeters to meters wide. They taper downwards and crosscut country rocks at high angles. The clastic dykes and their host strata are quartzose sandstones and share similar textures and detrital zircon age populations (dominantly 600–500 Ma and 1000–800 Ma zircon grains). These similarities indicate the clastic dykes and their host rocks share a common source as well as comparable transport and deposition dynamics. Notably, the clastic dykes lack distinct signs of ptygmatic folds, shale/mudrock clasts, surface orientated structures, or bifurcations on dyke margins. Decompaction and structural restoration of the sequences show that the sandstone dykes/fractures and en échelon dyke arrays can be classified into three distinct orientation groups NW (349° − 295°), SW (∼210°) and NE (∼40°). There is no apparent difference in the age or provenance of the clastic material within the different orientation groups. We propose that the clastic dykes signify passively infilled tensile fractures formed within a NW-SE dextral strike-slip megashear system during the Late Jurassic. This system likely developed in a transform zone within Greater India prior to the separation of the Indian Plate from East Gondwana. [Display omitted] • Quartz clastic dykes found in Late Jurassic sequences of Tethys Himalaya. • Restored dyke orientations indicate main NE and SE palaeostress orientations. • Passive infilling clastic dykes formed within a strike-slip megashear system. • A transform zone developed in Greater India during East Gondwana breakup. [ABSTRACT FROM AUTHOR]

We examined the microstructures of three ductile shear bands of granitic composition that deformed under mid-to-upper greenschist facies. These shear bands, from the Bundelkhand Craton, India, are 0.8–4.4 mm thick with 20–30 μm median grain sizes and share sharp contacts with the host granite. Comminution of the rheologically stronger feldspars increased permeability, promoted fluid influx, and allowed strain localisation in the incipient shear bands. The major components, quartz and feldspars, deformed via phase-specific crystal plastic deformation mechanisms. Quartz in the monomineralic bands deformed predominantly via dislocation creep, while the feldspars deformed via diffusion creep. Finer quartz grains, which occur at plagioclase triple junctions, resulted from myrmekitisation – also evident from the anti-clustered distribution of quartz-plagioclase phase boundaries and CPO inheritance. The weak CPOs and high mean misorientation angles of the fine plagioclase and K-feldspar grains and yet a high shear strain (γ = 16–37) suggest a significant contribution of grain boundary sliding (GBS) in strain localisation inside the ductile shear bands. Since intracrystalline slip alone cannot explain the high ductile strain in the shear bands, we suggest that GBS controlled the deformation and maturation of the shear bands and promoted superplasticity to accommodate further shearing. • Thin granitic shear bands show large shear strain accommodation. • Feldspar and quartz dynamic recrystallisation reduced the grain sizes. • Myrmekitisation caused phase mixing of plagioclase and quartz grains. • Fine quartz and feldspar grains show weak CPOs and high mean misorientation. • The enormous shear strain is mostly accommodated by GBS. [ABSTRACT FROM AUTHOR]

• Calc-alkaline shoshonitic lamprophyre at Dharwar craton-Southern Granulite terrane boundary. • U-Pb titanite SHRIMP-II dating yielded a Tonian age of 820 ± 15 Ma. • Sr and Nd isotopes suggest the derivation from an enriched lithospheric mantle source. • Involvement of large-scale rifting, associated with the break-up of Rodinia, • Implications for India-South China Block paleoposition during Neoproterozoic. We present petrology, U-Pb titanite geochronology, bulk-rock and Sr-Nd geochemistry of an undeformed and unmetamorphosed shoshonitic lamprophyre (spessartite) from the Mysuru area (Halaguru- Harohalli alkaline province) located approximately 80 km north of the tectonic contact between the Western Dharwar Craton and the Southern Granulite Terrane, southern India, to understand its origin and to evaluate its geodynamic significance. The lamprophyre shows a typical porphyritic-panidiomorphic texture with amphibole phenocrysts. Clinopyroxene occurs only as xenocrysts with feldspar, apatite, titanite and titano-magnetite confined to the groundmass. Amphibole mineral composition classifies them as pargasite and tremolite, and the groundmass is essentially constituted of alkali feldspar. High whole-rock Mg# (56–65), Ni + Cr (245 to 730 ppm), a lack of correlation between SiO 2 and Rb/Sr as well as ɛNd (i) indicates that crustal contamination experienced by the lamprophyre magma is limited. U-Pb titanite (n = 18) SHRIMP-II dating yielded a Neoproterozoic Tera-Wasserburg concordia age of 820 ± 15 Ma (MSWD = 5.9). Whole-rock derived 87Sr/86Sr (i) (0.70425–0.70530) and ɛNd (i) (-6.3 to −4.3) suggest origin of the lamprophyre from an enriched lithospheric mantle source. Paleoproterozoic depleted-mantle model ages of ca. 1.8 Ga suggest the existence of a long-lived enriched mantle which correspond to the timing (ca.1.9–1.7 Ga) of widespread mafic dyke swarms' emplacement in the Dharmapuri-Agali-Tiruvannamalai domain in the Salem block at the northernmost portion of the Southern Granulite Terrane. The Tonian emplacement age of the studied lamprophyre is synchronous with several co-spatial Neoproterozoic (i) alkaline complexes ± carbonatite ± lamprophyre from the northern part of the Southern Granulite Terrane, and (ii) other mafic alkaline dykes of the Halaguru-Harohalli alkaline province from the southern part of the Eastern Dharwar Craton. Our results highlight the importance of this lamprophyre dyke, present close to the'Fermor Line' as well as near the boundary between Eastern and Western Dharwar Cratons, which provides a rare opportunity to understand its spatio-temporal link with alkaline dykes of the Southern Granulite Terrain. Our findings also help understand the role of repeated large-scale rifting, associated with the Rodinia break-up, leading to the generation of a wide spectrum of Tonian-Cryogenian alkaline magmas in southern Indian Shield. The new age data also have implications for the configuration of India's paleoposition during the Neoproterozoic and support the idea that South China Block-India were located on the periphery of Rodinia or were already detached from the supercontinent. [ABSTRACT FROM AUTHOR]

The Saurashtra peninsula in the northwestern Deccan Traps continental flood basalt province, India, contains notable concentrations of rhyolitic rocks. The Chhapariyali rhyolite dyke, part of the compositionally diverse Southeastern Saurashtra dyke swarm, intrudes basaltic lava flows. It shows vitrophyric portions, basaltic magma enclaves, gabbroic mineral assemblages (plagioclase + clinopyroxene ± Fe-Ti oxide aggregates), spectacular quench textures, and intense spherulitisation. Thermobarometric calculations on equilibrium mineral–whole-rock (or glass) pairs indicate clinopyroxene crystallisation at 1120–890 °C overlapping with plagioclase crystallisation at 948–932 °C, and a pressure range of 3.6–0.1 kbar, indicating crystallisation during magma storage or ascent in the upper crust. Petrographic, mineral chemical, and whole-rock geochemical (including Sr-Nd isotopic) data suggest advanced fractional crystallisation of a mafic magma with considerable assimilation of ancient granitic crust, or anatexis of such crust, due to heating by a basaltic magma chamber. In either scenario, abundant gabbroic cumulates were left by the crystallising basaltic magmas. A new basalt magma recharging the chamber entrained the gabbroic crystal mush and formed enclaves by mingling with the rhyolite magma stored above. Continued basaltic recharge pushed the enclave-bearing, gabbroic cargo-laden rhyolite magma out of the chamber and into the basaltic lava flows via a dyke. Strong supercooling within cold basaltic rock, possibly aided by meteoric water ingress, led to the development of spectacular quench textures in the crystallising rhyolite, whereas extensive low-temperature alteration produced intense spherulitisation. This case study of the Chhapariyali dyke underscores significant thermal and material inputs from basalt in rhyolite petrogenesis. [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]

[Display omitted] • Juvenile crust in Singhbhum Craton formed at ∼3.51, ∼3.45, 3.38–3.25, 3.15–3.05 and ∼2.80–2.75 Ga. • Reworking of older crust in the craton occurred at ∼3.46, ∼3.3, ∼3.1 and ∼2.8 Ga. • Maximum crustal thickness was attained at ∼3.3 Ga followed by a possible reduction over ∼3.1–2.8 Ga. • Paleo-Meso–Archean continental growth occurred through episodic intraplate juvenile magmatism and resultant crustal reworking. The composition of continental crust and its temporal variation, the mechanism of crust-mantle interaction, and the degree of mantle depletion during the early Archean have been widely debated. To address these issues related to the Singhbhum Craton, we present whole-rock sediment geochemistry, detrital zircon U-Pb date, trace element and Hf isotope data from four Archean clastic sedimentary successions. The rocks have high whole-rock K 2 O/Na 2 O, relatively high La and Th compared to Ni and Sc, distinct negative Eu anomaly and flat HREE patterns, and high detrital zircon U/Yb ratios. These features suggest attainment of early crustal stability with the sediments derived from a strongly weathered basement dominated by granitoids formed through shallow intracrustal melting. Detrital zircon U-Pb and Hf isotope data indicate episodic crust formation at ∼3.51, ∼3.46, 3.38–3.25, 3.15–3.05 and ∼2.80–2.75 Ga. Each major crust formation event is marked by addition of depleted mantle-derived juvenile crust and its quick reworking. Besides, episodic tapping of older crust, as indicated by a wide range (both positive and negative) of zircon εHf t values, are evident at ∼ 3.46, ∼3.3, ∼3.1 and ∼2.8 Ga. Pressure-sensitive zircon trace element ratios suggest that the crust attained the maximum thickness at ∼3.3 Ga followed by a possible reduction in thickness over ∼3.1–2.8 Ga. In the absence of strong evidence of subduction, the rock association and their temporal distribution (coeval granitoid and mafic-ultramafic magmatism) suggest that the Paleoarchean-Mesoarchean crustal growth in the Singhbhum Craton was a result of episodic, depleted mantle-derived, intraplate magmatic injection and attendant crustal reworking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sources of Cenozoic sediments in the Kuqa Depression were changed for four times. • The South Tianshan Range experienced the Cenozoic intra-continental uplift initiated at 50–46 Ma. • The entire Tianshan Range was rapidly uplifted during the Middle Miocene (13–10 Ma). • The Kuqa fold-thrust belts were mainly formed in the Early Pliocene (∼6.5 Ma). Influenced by the far-field effect of the India–Eurasia collision during the Cenozoic, both the Tianshan Range and Kuqa Depression underwent multi-phases of intracontinental tectonic activation. The extremely thick Cenozoic sediments in the Kuqa Depression recorded the basin-mountain coupling process of the South Tianshan and Kuqa Depression. In this study, detailed structural investigations, stratigraphic analysis, and detrital zircon U–Pb dating of the Cenozoic sediments were conducted in the Kuqa Depression to reconstruct the Cenozoic uplift history of the South Tianshan Range. U–Pb ages of detrital zircon from sandstones show four age peaks that correspond to four significant provenance changes in the Kuqa Depression. These four periods of changes occurred at the Cretaceous–Early Cenozoic, Late Eocene–Oligocene, Early Miocene–Middle Miocene, and Early Pliocene–Early Pleistocene. These changes in provenance reflect variations in tectonic activation and paleogeographic settings in the Kuqa Depression–Tianshan Range. Combined with the syn -tectonic growth strata and previously published magnetostratigraphy and low-temperature thermochronology data, we therefore argue that significant Cenozoic deformation and uplift of the Tianshan Range was initiated at the Early Eocene (50–46 Ma), strengthening in the Late Eocene(∼36 Ma), becoming more evident and extending to the entire Tianshan and Basin–Range boundary during the Middle Miocene (13–10 Ma), and culminating and extending to the southern Kuqa Depression since the Early Pliocene (∼6.5 Ma), thus suggesting the continuous convergence of the on-going India–Eurasia collision in the Cenozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Duolong ore district experienced two periods of exhumation and two periods of burial. • The periods of burial are attributed to northeast-southwest striking fault and thrust nappe structure related to the Lhasa-Qiangtang collision. • The India-Asia collision is the main reason for the exhumation and uplift of the Duolong ore district since Paleocene. The Early Cretaceous Duolong porphyry-epithermal copper ore district is one of the largest copper ore districts in the central Tibetan Plateau. In order to investigate the preservation mechanism of Early Cretaceous porphyry-epithermal mineralization, new apatite and zircon fission track dating and (U-Th)/He dating of pre-ore sandstone, ore-related and barren intrusive rocks, and post-ore igneous rock, thermal modeling together with previous thermochronological data of the Duolong ore district were combined to study the burial and exhumation processes. Apatite fission track ages range from 68 ± 4 to 40 ± 4 Ma, with mean track lengths varying from 12.1 ± 2.0 to 12.8 ± 2.4 μm. Zircon fission track ages range from 106 ± 4 to 86 ± 4 Ma. In addition, apatite (U-Th)/He yields average age ranging from 62.7 ± 4.2 to 22.6 ± 1.2 Ma, and zircon (U-Th)/He yields average age of 112.3 ± 5.1 Ma. The thermal modeling shows that the Duolong ore district experienced two periods of exhumation and two stages of burial. The first period of exhumation with rate of 0.14 km/m.y. took place immediately after the ore formation which caused the erosion of orebody. Two periods of burial are thought to be related to northeast-southwest striking fault and thrust nappe structure induced by Lhasa-Qiangtang collision between 110 and 65 Ma when the overlying rocks of orebodies were thickened to 4 km. The last period of exhumation with rate of 0.062 km/m.y. (since 65 Ma) is attributed to lithospheric delamination related to India-Asia collision. The preservation of the Duolong ore district mainly benefited from the burial related to the Lhasa-Qiangtang collision. The exhumation and uplift of Duolong ore district was mainly attributed to the India-Asia collision since Paleocene. [ABSTRACT FROM AUTHOR]

• Two-stage clock wise P-T evolution of UHT sapphirine granulites in Madurai block. • U-Pb zircon-monazite-rutile-apatite geochronology record heating/cooling episodes. • Evidence for long-lived Neoproterozoic UHT orogeny and subsequent slow cooling. • Identification of Kambam UHT belt as an important tectonic boundary within SGT. The Precambrian granulite terrane of south India is known for the preservation of regional-scale high to ultrahigh-temperature (HT-UHT) metamorphic rocks. In the Madurai block, the largest crustal block in the terrane, a significant proportion of these HT-UHT rocks occur along a narrow belt referred to as the Kambam ultrahigh-temperature belt. Understanding the P-T-t evolution of these HT-UHT granulites is vital in decoding the spatial and temporal evolution of the Madurai block in relation to other crustal blocks. Here we present the petrology, mineral chemistry, phase equilibrium modelling, and accessory mineral (zircon, monazite, rutile and apatite) geochronological and geochemical data for a hitherto unreported sapphirine granulite from the Kambam ultrahigh-temperature belt. Combined mineral reaction and phase equilibrium modelling indicate extreme P-T conditions up to 1130 °C at 11 kbar. The geometry of the P-T path is clockwise with initial isothermal decompression followed by near isobaric cooling. LA-ICPMS U-Pb geochronological studies on accessory phases report two distinct thermal events: (i) Paleoproterozoic high-T event and associated crustal anatexis at ∼2.5 Ga from zircons and (ii) Neoproterozoic UHT event at ∼550 Ma from monazites. The monazite ages suggest a 50–60 Ma prolonged thermal event, attributed to Ediacaran-Cambrian collisional orogenesis. Additional metamorphic pulses are also identified, demonstrating the polydeformed crustal evolution history of the terrane. U-Pb age dating of rutile and apatite in the sample provide ages of ∼458 Ma and ∼392 Ma and cooling rates of ∼6 °C/Ma and ∼0.3–2 °C/Ma respectively. This suggests a complex history of slow cooling followed by ultraslow cooling. The results bring forth the significance of the Kambam ultrahigh-temperature belt in understanding the tectonothermal evolution of Madurai block and provide additional evidence for long-lived Neoproterozoic UHT orogenesis in south India. [ABSTRACT FROM AUTHOR]

Palaeomagnetic analysis of the Lakhna Dykes (Bastar Craton, India) yields a palaeopole at 36.6°N, 132.8°E, dp=12.4°, dm=15.9°, and the U Pb zircon age obtained from one of the rhyolitic dykes is 1466.4±2.6Ma (MSWD=0.21, concordia age based on two analyses with identical Pb/U ages), similar to previously published U Pb ages. Major and trace element analyses of the Lakhna Dykes show shoshonitic and high-K calc-alkaline affinities consistent with a subduction related characteristics suggesting an active continental margin setting. This is in keeping with the Palaeo- to Mesoproterozoic tectonic environments in the eastern Indian margin. The new 1460Ma Indian palaeopole was used to test possible palaeopositions of India within the Mesoproterozoic supercontinent Columbia. Of the four palaeomagnetically permissible reconstructions, juxtaposing western India against south-west Baltica is geologically the most reliably constrained and best fitting model. Our preferred reconstruction implies a long Palaeo- to Mesoproterozoic accretionary orogen stretching from south-eastern Laurentia through south-western Baltica to south-eastern India. Breakup of India and Baltica probably occurred in the Late Mesoproterozoic, but additional constraints are needed. [ABSTRACT FROM AUTHOR]

Abstract: The Himalayan orogeny, a result of the collision of India and Eurasia, provides direct evidence of strain accommodation and large-scale rheological behavior of the continental lithosphere. Knowledge of the timing of the India–Eurasia collision is essential to understand the physical processes involved in collisional systems. Here we present a geochronological and multi-isotopic study on rocks from the upper crust of the Kohistan Paleo-Island Arc that formed in the equatorial part of the Neo-Tethys Ocean. In situ U–Pb geochronology and Hf isotopes in zircon, and whole-rock Nd and Sr isotopic data of plutonic rocks from the Kohistan-Ladakh Batholith, are used to construct a continuous record of the isotopic evolution of the source region of these granitoids that are related to both the subduction of the oceanic lithosphere and subsequent arc–continent collisions. We demonstrate that profound changes in the source region of these rocks correspond to collisional events. Our dataset constrains that the Kohistan–Ladakh Island Arc initially collided along the Indus suture zone with India at 50.2±1.5Ma, an age generally attributed to the final India–Eurasia collision for the entire Himalayan belt. In the western Himalaya, the final collision between the assembled India/Arc and Eurasia however, occurred ∼10Ma later at 40.4±1.3Ma along the so-called Shyok suture zone. We present evidence indicating that a similar dual collision scenario can be extended to the east and conclude that a final India/Arc–Eurasia collision at ∼40Ma integrates crucial aspects of the magmatic, tectonic, and sedimentary record of the whole Himalayan mountain belt. [Copyright &y& Elsevier]

Abstract: Mafic dykes in the central Indian Bundelkhand and eastern Indian Bastar cratons are potential sources for tracing the location of the Indian shield within Palaeoproterozoic supercontinent reconstructions. A total of 610 oriented core samples were collected from 27 mafic dykes (342 samples) in Bundelkhand craton and 20 dykes (268 samples) in Bastar craton. The characteristic magnetisations identify distinct groups of directions. The derived palaeopoles are integrated with recently reported U–Pb isotopic ages from the Bundelkhand and Bastar cratons and correlated with palaeopoles from the mafic dykes in the Dharwar craton, South India. Characteristic remanence (ChRM) identified in these dykes are classified into (i) steep upward/downward components further sub-grouped as ca. 2.37Ga steep 1 (λ =10.2°S; Ф =75.0°E; A 95 =18.1° in Bundelkhand and λ =22.3°N; Ф =71.4°E; A 95 =21.6° in Bastar), component comparable with ca. 2.4–2.45Ga steep 2 group from one dyke in Bundelkhand (λ =14°S; Ф =101°E; A 95 =26.1°) and one dyke in Bastar (λ =6°N; Ф =113°E; A 95 =26.5°). A steep component (λ =60.4°N; Ф =45.3°E; A 95 =9.7° in Bundelkhand and a comparable component λ =49°N; Ф =129°E; A 95 =15.1° from one dyke in Bastar) is not assigned an age at present. (ii) ca. 2.18Ga shallow easterly and antipodal shallow westerly components (λ =0.4°S; Ф =347°E; A 95 =21.6° in Bundelkhand and λ =18.0°N; Ф =344.0°E; A 95 =8.1° in Bastar) and (iii) 1.99Ga shallow northwest and antipodal shallow southeast (λ =57.5°N; Ф =309.0°E; A 95 =4.7° in Bundelkhand and λ =39°N; Ф =321°E; A 95 =28° in Bastar). A group (iv) of ∼2.2Ga northeast shallow components (λ =36.0°S; Ф =357.0°E; A 95 =9.4°) is found only in the Bundelkhand craton. The distinct groups of palaeomagnetic pole determinations from dykes of the Bundelkhand and Bastar craton exhibit a remarkable match with palaeomagnetic poles determined from Precambrian mafic dykes in the Dharwar craton. The close comparison of mafic dyke magnetisations between the cratons suggests close proximity since 2.45–2.5Ga. Models suggesting amalgamation of crustal blocks along the Central Indian Tectonic Zone at 1.8Ga or a 1.0Ga collision along this zone to form Rodinia are untenable. Testing of proposed NeoArchaean-Palaeoproterozoic supercontinent reconstructions showing a north China–India linkage or India''s close proximity to Slave craton to form a supercraton ‘Sclavia’ are not supported. Instead, the data are compatible placing India in close proximity to the Yilgarn block of Western Australia. [Copyright &y& Elsevier]

Abstract: U–Pb and Hf isotopes in zircon from the highly metamorphosed core of the Himalaya in the Garhwal region of India indicate that the ortho- and paragneiss units of the Greater Himalayan Sequence (oGHS and pGHS, respectively) are geochemical distinct from the older Lesser Himalayan Crystalline Sequence (LHCS). Zircon grains from Paleoproterozoic metasediment of the LHCS yield U–Pb crystallization ages from 1614±14Ma to 2679±14Ma with a single distinct peak in the age spectra at 1870Ma. εHf values from zircon in the LHCS range from 1 to −8. In contrast, zircon grains from the Neoproterozoic pGHS yield U–Pb crystallization ages from 481±10Ma to 2560±8Ma with a single distinct peak at 860Ma. εHf values from these zircons range from 13 to −21. The oGHS yields zircon grains with U–Pb crystallization ages from 416±2Ma to 2740±2Ma with a single distinct peak at 472Ma. These grains often exhibit older inherited cores ranging from ~800Ma to ~2740Ma with Ordovician rims (416Ma to 510Ma). The εHf values of zircon grains in the oGHS have two distinct modes: the ~860Ma inherited zircon cores have a similar range to the ~860Ma zircons from the pGHS (13 to −21), whereas the ~480Ma rims range from −7 to −11. The detrital zircon U–Pb age spectra from the pGHS in the Garhwal region differs significantly from the U–Pb age spectra in other parts of the range (Nepal and Bhutan). These differences indicate wide lateral variations in provenance for the various source regions of the pGHS. Comparisons of the U–Pb and Hf data from the Garhwal region with potential ~1800Ma source regions show overlap with metasediments of the Aravalli shield of India. In the pGHS the most juvenile εHf values overlap with those of the northern Arabian Nubian Shield in Israel. However, these rocks show little crustal contamination at ~800Ma, whereas the pGHS has significant crustal contamination at ~860Ma. The Ordovician oGHS has εHf values that match the average εHf values of the paragneiss implying that it was sourced from the paragneiss. Although the nature of this Ordovician igneous event is still poorly understood, it is clear that the Hf isotopes can provide further insight into the petrogenesis of the magmatic rocks associated with it. [Copyright &y& Elsevier]

Abstract: Mesozoic post-collisional andesites occur in the Gerze area within the Qiangtang Terrane of northern Tibet, China. Geochronological, geochemical, and whole-rock Sr–Nd isotopic analyses were performed on this suite of volcanic rocks to characterize their petrogenesis. Laser ablation-inductively coupled plasma-mass spectrometry U–Pb zircon analyses yielded consistent ages ranging from 122.4±0.4Ma to 124.4±0.4Ma for two andesite samples (JC01 and GZ01). The andesites belong to the alkaline and sub-alkaline magma series in terms of K2O+Na2O contents (4.7–10wt.%), and belong to the high-K calc-alkaline and calc-alkaline series on the basis of their high K2O contents (1.0–3.3 wt.%). The volcanic rocks are further characterized by the enrichment of light rare earth elements [(La/Yb)N =7.4–11.5] and large-ion lithophile elements (e.g., Rb), slightly negative Eu anomalies (Eu/Eu* =0.79–0.94), and negative anomalies in high field strength elements (e.g., Nb, Ta, and Ti) relative to primitive mantle. The samples show slightly elevated (87Sr/86Sr)i values that range from 0.7049 to 0.7057, and low ε Nd(t) values of −3.4 to 0.7. These results suggest that the rocks were derived from a compositionally heterogeneous mantle source and that their parent magmas are basalt magma. The parent mafic magmas may have undergone fractional crystallization of olivine, pyroxene, hornblende, and to a lesser extent, plagioclase during ascent through the thickened crustal pile, with minor or no crustal contamination, before the finally erupting as andesites. [Copyright &y& Elsevier]

Abstract: High-pressure (HP)/low-temperature (LT) metamorphic rocks, such as eclogite and blueschist, are generally regarded as an indicator of subduction-zone metamorphism. Eclogites have recently been discovered in the central Qiangtang Block. Their occurrence is highly significant to the understanding of the closure of the Paleo-Tethys and tectonic evolution of northern Tibet. We report the results of petrological, mineralogical and geochronological investigations of these rocks, and discuss their tectonic implications. The Qiangtang eclogite occurs as blocks and lenses in Grt–Phn schist and marble, and is composed of garnet, omphacite, phengite and rutile. Eclogitic garnet contains numerous inclusions, such as glaucophane and phengite in the core, and omphacite in the mantle or inner rim. In strongly retrograded eclogite, the omphacite is replaced by glaucophane, barroisite and albite. Four stages of metamorphic evolution can be determined: (1) prograde blueschist facies; (2) peak eclogite facies; (3) decompression blueschist facies and (4) retrograde greenschist facies. Using the Grt–Omp–Phn geothermobarometer, a peak eclogite facies metamorphic condition of 410–460°C and 2.0–2.5GPa was determined. Zircon U–Pb dating gave ages of 230±3Ma and 237±4Ma for two eclogite samples. The ages are interpreted as the time of eclogite facies metamorphism. Moreover, 40Ar/39Ar dating of phengite from the eclogite and Grt–Phn schist yielded ages about 220Ma, which are probably indicative of the time of exhumation to the middle crust. We conclude that the HP/LT metamorphic rocks were formed by northward subduction of the Paleo-Tethys Ocean and they marked a Triassic suture zone between the Gondwana-derived block and Laurasia. [Copyright &y& Elsevier]

Abstract: The Subhimalaya of NW India exposes a well developed marine to continental foreland sequence preserving sediments shed from the tectonically evolving Cenozoic Himalayan orogen. Detrital zircon U–Pb ages and their Hf isotopic compositions, of seven samples, were analyzed from the Subathu sub-basin foreland formations to constrain sediment provenance. The detrital zircon U–Pb age spectra yielded a similar pattern, for all foreland formations, with major peaks clustered at ~500–650Ma, 900–1000Ma and ~2500Ma, corresponding to (indistinguishable) Tethyan Himalaya and Higher Himalayan Crystalline sources and those at ~1800–1900Ma corresponding to lower a Lesser Himalayan arc source. Comparison of the foreland detrital zircon U–Pb age spectra with Himalayan lithotectonic source units, in conjunction with their Hf isotopes and previously determined sediment petrography and age constraints, suggest that the sediments to the flysch marine Subathu Formation (~65 to >41Ma) were sourced from a positive-relief area of the Tethyan Himalaya mixed with detritus from lower Lesser Himalaya and additional cratonic northern Indian Precambrian rocks. No Cretaceous to Eocene-aged detrital zircons, contributed by eroding Ladakh batholith north of the Indus Tsangpo suture zone, were recorded in the Palaeogene-aged foreland samples. The younger synorogenic continental Dagshai Formation (<30 to <22Ma) sediments were sourced from the very low-grade Tethyan Himalaya, whereas the alluvial-facies Kasauli Formation (<22 to 13Ma) began to receive sediments additionally from erosion of the medium-grade metamorphic rocks of the Higher Himalayan Crystalline and the lower Lesser Himalaya. The Lower Siwalik Formation sediments (~13–11.5Ma) were derived from the low-grade rocks of the Tethyan Himalaya, both the upper and lower Lesser Himalaya and additionally from the eroding high-grade migmatitic gneisses of the Higher Himalayan Crystalline. Thus, from the similar detrital zircon age spectra of the foreland formations, we infer that differences in the continental sediment detritus into the foreland basin reflect a straightforward sediment mixture of variable proportions from fixed Himalayan lithotectonic sources which progressively shifted towards the foreland with development of the orogen. [Copyright &y& Elsevier]

Abstract: Multiple subduction events occurred preceding the collision of Greater India with the Karakoram terrane that consumed the Neotethyan Ocean between Early Cretaceous and Eocene time. Zircon U–Pb dating and Hf isotope analyses of granitic rocks collected from the Karakoram terrane and Ladakh batholith have been conducted to constrain these geological processes. Undeformed Ladakh batholith granodiorite yielded zircon U–Pb ages of 68 and 64 Ma with ε Hf(t) values of +6.4 and +10.3, and three diorites near Leh and Darbuk, gave zircon U–Pb ages of 50.4–51.0 Ma and ε Hf(t) values of +7.4 to +8.9, indicating that the Paleocene–Eocene was the most important period of granitic magmatism that derived from a juvenile source. Three tonalite–granodiorite enclaves at Skyangpoche within the Karakoram batholith have zircon U–Pb ages of 101–103 Ma with ε Hf(t) values of −2.3 to −3.7, indicating generation of granitic rocks by partial melting of the Karakoram basement. Three samples of the Miocene Karakoram batholith, from around Darbuk, yielded ages of 16.6–19.1 Ma with ε Hf(t) values of −8.5 and −10.5, that indicate an input of ancient crust from the Indian plate. Granodiorite within the Karakoram metasedimentary sequence (zircon U–Pb age ∼74 Ma, ε Hf(t) of +5.4 from the Tangtse gorge) and granite around Muglib (zircon U–Pb age of 63 and 56 Ma, ε Hf(t) of +6.8 and +6.0) indicate similar geochronological and isotopic characteristics to those of the Ladakh batholith. Thus the time resolved Hf isotopic compositions of magmatic zircons from the granites in the Karakoram and Ladakh batholith show a large variation that indicate their derivation from both ancient and juvenile continental crusts, in active continental margin since at least the Mid Cretaceous. [Copyright &y& Elsevier]

• 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]

The aim of this paper is to determine the composition and age of high-temperature (HT) hydrothermal fluids in Closepet granites (Dharwar craton, India). The magmatic origin of the Neoarchaean Closepet batholith has been recognized and dated many times, whereas a HT fluid system, strong evidence for which has been partly investigated, has never been dated. Titanite was chosen for a geochemical study on its pristine and altered domains to illustrate the fluid composition; the domains were dated to recognize the timing of fluid activity. Titanite presents distinct trace element enrichments in non-altered domains and strong depletions in trace elements in marginal, irregular, patchy zones. The high total rare earth element (REE) concentrations and the marked negative Eu anomalies suggest crystallization from a residual melt. The negative Eu anomalies diminish progressively in the REE patterns of altered parts and become positive. Trace element ratios (Nb/Ta, Y/Ho, and U/Th) indicate fluid-crystal interactions. Strong U/Th fractionation might be linked to the presence of CO 2 and Cl−. Zr-in-titanite thermometry yields a crystallization/recrystallization temperature of ~700 °C for both magmatic and altered domains. The titanite factor Ti+4/(Al+3 + Fe+3) reveals an affinity with significant mantle input to the fluid system. Pristine and altered titanite domains have been successfully dated by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Reversely discordant apparent ages suggest interaction with fluids, which modified the Pb composition of the magmatic titanite. The oldest semi-concordant analyses of titanite cores indicate an age of approximately 2500 Ma, which we interpret as the minimum age of magmatic titanite crystallization. Narrow dark rims of titanite with considerably lower Th/U ratios form a more coherent group of analyses defining an upper concordia intercept age of 2345 ± 0.016 Ma, interpreted as the best estimate for the time of complete titanite resetting associated with the metasomatic event. The HT fluid system appears to have remained active into the Palaeoproterozoic. Confirmation by dating that the tested fluids belonged to the Archaean hydrothermal system gives us information about this system at the time, but the information that it worked at least until the Palaeoproterozoic provides additional valuable information about the hydrothermal systems during the Neoarchaean-Palaeoproterozoic transition. [Display omitted] • Sustained HT fluid of mantle-crust origin operating in the Neoarchaean granite • First Neoarchaean fluids system dating using pristine/altered titanite domains • Indication of the extension of the fluids activity timing to the Palaeoproterozoic • Unique and relevant processes in the Neoarchaean - Palaeoproterozoic transition [ABSTRACT FROM AUTHOR]

• SIMS U-Pb zircon age of 2522 ± 12 Ma for anorthosite from the Sittampundi Complex. • Plagioclase 87Sr/86Sr ratios and chromite γ Os values argue for depleted mantle source. • Parental magma of anorthosite was contaminated by ancient mafic lower crust. • Anorthositic-gabbroic intrusions likely represent the lowermost crust of the Dharwar Craton. • Magmas underplating facilitated the Dharwar cratonization. Mantle-derived magmas at the base of the lower crust exerted a key control on late Archean cratonization in many continents. Since well-preserved, complete lower crustal section is rarely exposed, direct studies on the genetic link between mantle-derived magmas and cratonic lower crustal stabilization are inadequate. Cratonic lower crustal section is well-preserved in the southern margin of the Dharwar Craton (southern India), with a number of late Archean anorthositic-gabbroic complexes. Among these complexes, the Sittampundi anorthosite complex (SAC) consists of white- and dark-anorthosite (>60 vol%), gabbros, and ultramafic rocks. In this study, SIMS zircon U-Pb dating of the anorthosite revealed a minimum emplacement age of 2522 ± 12 Ma, similar to the chromite Os model ages (2528–2563 Ma) of the anorthosite-hosted chromitite. In-situ plagioclase (87Sr/86Sr) i ratios (0.70079–0.70100) of the dark anorthosite and the chromite γ Os (T) values (−0.2 to −0.4) of the chromitite suggest that the SAC was derived from a depleted mantle source. From the dark to white anorthosite, the (87Sr/86Sr) i ratios increase while the An contents decrease, suggesting crustal assimilation occurred during fractionation. Similarly, the mantle-like zircon δ18O values and relatively-wide ε Hf (T) (−2.1 to +8.4) range of the SAC anorthosite suggest that the parental magma had assimilated the ancient mafic lower crust. Emplacement ages of the SAC and published ages of the mafic/felsic granulites and charnockites altogether indicate that the anorthosites were formed during the Dharwar cratonization, and that the mantle-derived magma underplating may have led to extensive lower crustal melting. We argued that during underplating, high-density olivine-pyroxene cumulates (from fractionation of the mantle-derived magma) and partial-melting residues (in the overlying lower crust) mostly sank back to the underlying mantle. In contrast, the lower-density plagioclase and minor amphibole remained in the lower crust to form anorthositic-gabbroic sills. The magmas underplating and subsequent lower-crustal melting have likely made the cratonic lower crust more refractory and buoyant, which facilitated cratonization. [ABSTRACT FROM AUTHOR]

• Hercynite-quartz-bearing granulites occur on the southern tip of the South Delhi Terrane, India. • Preserved metamorphic reaction microstructures are indicative of a decompression event. • New SHRIMP data provide evidence for a Neoproterozoic age as a time of metamorphic overprint. • South Delhi basin would have been a remnant of the proto-Mozambique Ocean in NW India. Diwani Hill granulites occurring on the southern tip of the South Delhi Terrane (SDT) of Aravalli Mobile Belt (AMB), comprises rocks of granulite facies and represent the deeper level of the crust. The SDT represents an admixture of charnockites, granites, calc-granulites and hercynite-quartz-bearing pelitic granulites. The symplectite and corona textures recorded in the hercynite-quartz-bearing granulites from a part of SDT provides a wide spectrum of P-T sensors in support of the petrological evolution. P-T evolution of these hercynite-quartz-bearing granulites has been constrained through the use of THERMOCALC program, conventional thermobarometry, and pseudosection modelling in the NCKFMASHTO model system using Perple_X software. The unification of these three calculations, demonstrates that the hercynite-quartz-bearing granulites experienced peak pressure and temperature at 6.7 kbar and 750 °C, respectively. The textural imprints, multistage reaction textures, P-T pseudosections as well as the application of multi-equilibrium calculation give evidence for decompressive history related to their exhumation. SHRIMP U-Pb chronological results yield ages between 780 and 680 Ma as a time of metamorphic overprint, and the ages between 1591 and 1216 Ma corresponding with detritus derived from magmatic source for hercynite-quartz-bearing granulites. Zircon ages reflect that continental crust in the SDT resulted from the Mesoproterozoic protolith of an igneous origin whereas sedimentary succession was deposited between 1216 and 780 Ma. The present study envisages that the South Delhi basin would have been a remnant of the proto-Mozambique Ocean in NW India which was closed due to subduction. This subduction metamorphosed the sediments of the basin to granulite facies and the rocks were subsequently, uplifted because of the thrust sheet tectonics during the Neoproterozoic times. [ABSTRACT FROM AUTHOR]

• Two diamictites units are recognized on the western margin of Cathaysia Block, and correlate with the global Sturtian and Marinoan glaciations. • Late Tonian, middle Cryogenian and early Ediacaran siliciclastic rocks overlying the Cathaysia Block were derived from sources external to South China. • The Cathaysia Block was linked to North India before 720 Ma. Neoproterozoic paleogeography of the Cathaysia Block of South China is directly linked to the formation of Rodinia, its break-up, and the subsequent amalgamation of Gondwana. Two diamictite units occur in the Neoproterozoic sedimentary successions on the western margin of Cathaysia Block. In combination with our detrital zircon U-Pb dating results and corrected chemical weathering index data (CIA corr), these units coincide with the global Sturtian and Marinoan glaciations. Late Tonian to early Ediacaran sedimentary rocks from western Cathaysia contain abundant late Mesoproterozoic to early Neoproterozoic (1150–870 Ma) and some mid-Neoproterozoic (800–720) detrital zircons. Paleocurrent data indicate sediment transport to the northwest. The timing and character of the ages of detrital zircons match the records of North India and East Antarctica, indicating that the Cathaysia Block received detritus from Gondwana. Thus, South China lay adjacent to northern Gondwana since at least 720 Ma, and possibly considerably earlier. [ABSTRACT FROM AUTHOR]