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This review discusses in detail the process of hot forging and the types of machines involved and explains the die materials used for hot forging of the respective types of machines, such as vertical forging presses (friction presses), drop hammer forging presses and horizontal forging machines. Forging requires forging the metal using compressive forces. It investigates the chemical properties of die materials used in hot forging. The article covers the materials, the properties of the forging die inserts and the master die inserts. The hardness of the materials has been defined on the basis of the chemical composition and the heat treatment process, the heat treatment is widely used for tungsten-based and chromium-based hot work tool steel to achieve microstructure. This article ends with the required die content and uses it on the basis of the hardness of the billet utilized.

Traditional drilling is still not appropriate for working with Inconel625 and Inconel718 alloys, since such metals become hard to remove substances. The aim of this article is really to evaluate the two separate metals from empirical data of the micro electrochemical machining (μ-ECM) process on overcut. The overcut was most much a concern when alloys were extracted during machining. Unconventional scientific data is derived from studies unless the authors are using the same instruments for testing the same process variables. Those process variables are chosen for evaluation, such as the volts, the chloride concentration as well as the feed rate of stainless-steel electrodes. Apart from the material removal rate and surface roughness, the overcut is one of the important response variables of μ-ECM. The best possible outcome of an overcut value of 0.021 mm has achieved by Inconel718 alloy. The effects of the overcut on Inconel alloys are compared.

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.

The NNW trending tholeiitic Sonakhan mafic dyke swarm of the Northern Bastar Craton is comprised of basalt to basaltic andesite (SiO2 = 46.3 wt% to 55.3 wt%; Mg# = 37 to 70) dykes. A single basaltic dyke yielded a weighted-mean 207Pb/206Pb baddeleyite age of 1851.1 ± 2.6 Ma. The Sr and Nd isotopes (87Sr/86Sri = 0.70396 to 0.70855; eNd(t) = −5.7 to +2.0) are variable which is a consequence of crustal contamination. Trace element modeling suggests the dykes were likely derived by partial melting of a spinel-bearing mantle source. The Sonakhan dykes are 30 million years younger than the 1.88 Ga Bastar-Cuddapah dykes (Bastanar-Hampi swarm) of the southern and central Bastar Craton indicating they represent a distinct period of magmatism. However, much like the 1.88 Ga dykes, the Sonakhan dykes appear to be correlative with dykes from the Yilgarn Craton (Yalgoo dyke = 1854 ± 5 Ma) of Western Australia. The temporal and compositional similarity of the Sonakhan dykes with the Yalgoo dyke is evidence that they are petrologically related and may represent different branches of the same dyke swarm. The existence of two distinct Paleoproterozoic dyke swarms in the Bastar Craton that each have a correlative unit in the Yilgarn Craton is supportive of a link between India and Australia before 1.9 Ga. Moreover, it suggests that the break-up of India and Western Australia was protracted and lasted for at least 30 million years.

The Indian Shield is cross-cut by a number of distinct Paleoproterozoic mafic dyke swarms. The density of dykes in the Dharwar and Bastar Cratons is amongst the highest on Earth. Globally, boninitic dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the Southern Indian Shield. Geochronology and geochemistry are used to constrain the petrogenesis and relationship of the boninitic dykes (SiO2 = 51.5 to 55.7 wt%, MgO = 5.8 to 18.7 wt%, and TiO2 = 0.30 wt% to 0.77 wt%) from the central Bastar Craton (Bhanupratappur) and the NE Dharwar Craton (Karimnagar). A single U-Pb baddeleyite age from a boninitic dyke near Bhanupratappur yielded a weighted-mean 207Pb/206Pb age of 2365.6 ± 0.9 Ma that is within error of boninitic dykes from the Dharwar Craton near Karimnagar (2368.5 ± 2.6 Ma) and farther south near Bangalore (2365.4 ± 1.0 Ma to 2368.6 ± 1.3 Ma). Rhyolite-MELTS modeling indicates that fractional crystallization is the likely cause of major element variability of the boninitic dykes from Bhanupratappur whereas trace element modeling indicates that the primary melt may be derived from a pyroxenite mantle source near the spinel-garnet transition zone. The Nd isotopes (eNd(t) = −6.4 to +4.5) of the Bhanupratappur dykes are more variable than the Karimnagar dykes (eNd(t) = −0.7 to +0.6) but they overlap. The variability of Sr-Nd isotopes may be related to crustal contamination during emplacement or is indicative of an isotopically heterogeneous mantle source. The chemical and temporal similarities of the Bhanupratappur dykes with the dykes of the Dharwar Craton (Karimnagar, Penukonda, Chennekottapalle) indicate they are members of the same giant radiating dyke swarm. Moreover, our results suggest that the Bastar and Dharwar Cratons were adjacent but likely had a different configuration at 2.37 Ga than the present day. It is possible that the 2.37Ga dyke swarm was related to a mantle plume that assisted in the break-up of an unknown or poorly constrained supercontinent.

Archean-Proterozoic boundary represents a significant transitional phase in the Earth's history. Bastar Craton is one of the major Archean cratons in the Indian subcontinent with voluminous granites, supracrustal rocks, and tectonic belts. Malanjkhand, Dongargarh, and Kanker are the three major granitic plutons emplaced during the Archean-Proterozoic transition in the Bastar Craton, and this study is confined to the granites of Kanker pluton. Based on geochemical systematics, the Kanker granites are classified into sanukitoids, biotite and two-mica granites, and hybrid granites. The compositional diversity of the Kanker granites is attributed to two end-member sources, i.e., the enriched mantle and an older felsic crust, and the interactions between them. The sanukitoids were derived from an enriched mantle source that was metasomatized by the subducted sediments. Heat supplied by the sanukitoid magmas induced the crustal melting to form the biotite and two-mica granites. The interaction between these two mutually end-member sources, i.e., the enriched mantle and an older felsic crust, resulted in the formation of hybrid granites. The evolution of the Kanker granites can be accounted for a transitional geodynamic environment, involving subduction, and collisional tectonics during the Archean-Proterozoic transition.

We report contrasting magmatic conditions in the generation of anorogenic (A-type) felsic rocks from the Phenai Mata hill of Deccan Large Igneous Province. The felsic units in the present study area can be classified as granite, monzonite, quartz monzonite and granodiorite. The field as well as the geochemical evidences collectively indicate the mixing and mingling of contrasting magma compositions which were widely involved in the genesis of these anorogenic intrusions. Based on the anorogenic granite classification diagrams, it has been observed that the granite shows A1 type character whereas the monzonite, quartz monzonite and granodiorite exhibit A2 type characters. Both A1 and A2 type intrusions were compared with the associated basaltic andesites in the variation diagrams and found that the A1 type rocks exhibit a well-defined trend pointing towards a fractional crystallization process. The A2 type rocks do not exhibit any particular geochemical relation with the mafic rocks. Moreover, the A2 type rocks are characterized by negative Nb and Ta anomalies in the normalized diagrams indicating the involvement of crustal components. From the field and geochemical evidence, it can be presumed that the A1 type rocks represent the fractional crystallization sequence from a basaltic magma, whereas the A2 rocks might have been produced by the melting of the pre-existing crust or by the assimilation of crustal components into the mafic magma during ascent. These contrasting magmas along with the mafic magma variably interacted in the shallow crustal levels to form present-day field features in the Phenai Mata Igneous complex.

Baddeleyite from a mafic dyke near Bhanupratappur of the central Bastar Craton (India) yielded a weighted-mean 207Pb/206Pb age of 1882.4 ± 1.5 Ma. The dykes are tholeiitic and have variable Mg# (41–60), TiO2 (0.83–1.74 wt%) and low CaO (

Potassic and ultrapotassic magmatism from deep lithospheric sources in intra-cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of Large Igneous Provinces (LIPs) triggered by mantle plumes. Here we report for the first time, precise zircon U–Pb age data from a suite of lamproites in the Bastar Craton of central India that mark the onset of Paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major LIP events during the Precambrian evolution of the Indian shield. The lamproites from the Nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile, apatite and zircon. The rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite. Geochemical features of the lamproites correlate with their counterparts in Peninsular India and other similar suites elsewhere in the world related to rift settings, and also indicate OIB-like magma source. The associated syenite shows subduction-related features, possibly generated in a post-collisional setting. Magmatic zircon grains with high Th/U ratios in the syenite from the Nuapada lamproite form a coherent group with an upper intercept age of 2473 ± 8 Ma representing the timing of emplacement of the magma. Zircon grains in three lamproite samples yield four distinct age groups at ca. 2.4 Ga, 2.2 Ga, 2.0 Ga and 0.8 Ga. The 2.4 Ga group corresponds to xenocrysts entrained from the syenite whereas the 2.2 Ga group is considered to represent the timing of emplacement of the lamproites. The ca. 2.0 Ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern Bastar and the adjacent Dharwar Cratons. A few young zircon grains in the syenite and lamproites show a range of early to middle Neoproterozoic ages from 879 to 651 Ma corresponding to younger thermal event(s) as also represented by granitic veins cutting across these rocks and extensive silicification. Zircon Lu–Hf isotope data suggest magma derivation from a refertilized Paleo-Mesoarchean sub-continental lithospheric mantle, or OIB-type sources. The differences in Hf-isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale. A combination of the features from geochemical and zircon Hf isotope data is consistent with asthenosphere-lithosphere interaction during the lamproite magma evolution. The timing of lamproite emplacement in central India correlates with the global 2.2 Ga record of LIPs. We link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction-accretion history prior to the Neoarchean cratonization, as well as the thermal blanket effect of the Earth's oldest supercontinent. Pulsating plumes and continued rifting generated voluminous dyke swarms across the Bastar and Dharwar Cratons, forming part of a major global rifting and LIP event.

Tectonic fractures are otherwise known as joints or fissures. The density of tectonic fractures is governed by the lithology, layer thickness and structures. The distribution and density of tectonic fractures in the Kuqa Depression in the northern Tarim Basin of Northwest China are dominantly controlled by the regional faulted fold belt. Our purpose of this paper is to analyze how folding and faulting control the development of tectonic fractures, based on outcrop and logs of drill data. In the folded tight sandstone reservoirs in the Kuqa Depression, the extensional area, transition area and shortening area have been separated by two neutral lines, which control the distribution and density of tectonic fractures in the buckle folds. From the twelve sites of field measurements, six logs of drill core data and analysis of the micro-texture of tectonic fractures, it can be deduced that the fracture development in the sub-salt faulted fold belt is related to the neutral lines and related faults. The high-density tensile fractures in the vicinity of fold hinges are more developed than in the limbs of the fold. Folding is thus the first level of control over the general pattern of fracture distribution. The fractures in the hanging wall of the thrust faults are more developed than those in the footwall. Further more, the fractures in the hinge zone and steeply tilted limbs of folds close to thrust faults are more developed than the gently tilted limbs which are far from faulting. This suggests that faulting is a secondary control over the development of local fractures within the faulted fold belt. The development of fractures related to faulted folds in the Kuqa Depression can be also divided into three episodes: pre-folding, syn-folding and post-folding, which are identified by field observation.

The Neo-Archean Sonakhan Greenstone Belt (SGB) located in the north-eastern fringes of Bastar craton, Central India, is dominated by Basalts, Andesites, Dacites and Rhyolites association. Partial melting modeling on the SGB metabasalts indicates that these rocks were derived by 20% melting of spinel peridotite. Fractional crystallisation modeling with REE reveal that the most evolved samples represent the product of fractional crystallization of least evolved magma with 35% plagioclase, 35% clinopyroxene, 20% olivine, 5% magnetite and 5% ilmenite as fractionating minerals with 40% remaining magma. Depletion of HFSE with reference to the LILE and LREE/HFSE ratios and Nb, Zr anomalies in the multi-element diagram of the mafic rocks of SGB indicate Island arc magmatic setting. The enriched Th/Yb values further substantiate that the mantle arrays were modified by subduction-related fluids or melts. The general conclusions drawn indicate that the metabasalts from the SGB were formed as a result of subduction of an intraoceanic lithosphere in a fore-arc suprasubduction zone environment.

The Neoarchean Sonakhan Greenstone Belt, located in the northeastern fringes of Bastar Craton, Central India, is dominated by basalts, andesites, dacites, and rhyolites and also contains some basic rocks with very high MgO (up to 33.4 wt%). Chromite mineralization is present in these rocks along with the cumulates of olivine and clinopyoxenes. The rocks are classified as siliceous high-magnesium basalts (SHMB) exhibiting enriched large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements. Elevated Th/Yb ratios and negative Nb-Ta-Ti anomalies in the primitive mantle normalized multielement diagram indicates a significant role of subduction-related melts/fluids in their genesis. The chromites in SHMB have high Cr# (0.67–0.75) and moderate Mg# (0.11–0.5) values. Parental melt calculations in the chromites indicate that they are crystallized from an SHMB magma in an island-arc setting. A plausible model for the genesis of the rocks of Sonakhan Greenstone Belt includes initial subduction of an intraoceanic lithosphere followed by eruption of lava in an oceanic environment. Continued subduction of the slab followed by slab rollback followed by the generation of SHMB parental magma, which was introduced into the basal portions of the lithosphere in which cumulates of olivine and clinopyroxene have been developed and the chromite mineralization occurred in the inter cumulus space. Final emplacement of the magma took place in a forearc suprasubduction-zone environment with SHMB signature carrying the cumulates, which were located in the lower part of the lithosphere.

The Paleo-Mesoproterozoic Zhongtiao aulacogen in the North China Craton and Cuddapah basin in the Indian Craton, have both been interpreted as intra-continental rift formed by a mantle plume that led to the breakup of Columbia supercontinent, but the mechanism has not been completely deciphered. In this paper, the mechanism of the Zhongtiao aulacogen and Cuddapah basin related to initial breakup of Columbia has been evaluated with 2D elastic finite element models of the North China Craton and the Indian Craton. The trajectories of the horizontal maximum principal compressive stress of the best-fit model fit well with the trends of dyke swarms in the North China Craton and the Indian Craton. When the other three models generated were compared with the best-fit model, it can be found that a mantle plume beneath the Zhongtiao and Cuddapah areas played the most vital role in developing the Zhongtiao aulacogen, Cuddapah basin and initial breakup of Columbia supercontinent. The boundary subduction forces, including the northern margin of the NCC, the northwest and southwest margins of the Indian Craton are indispensable factors for the rifting and breakup, whereas the mechanical properties have little influence on these modeling results. The initial breakup of Columbia supercontinent might have been resulted from the coupling between a mantle plume upwelling and some plate tectonic forces.

The importance of the Ordos Block, which is surrounded by different Chinese continental blocks, is well documented, but the development of the structural fractures and the stress fields within the Late Mesozoic and Cenozoic eras in this stable block (dips of the Mesozoic and Cenozoic strata are less than 3°) have been poorly studied. In this paper, two dominant groups of structural fractures with NW to EW and NNE to ENE trends are identified through field measurements and imaging log observations. The maximum principal compressive stress magnitudes and stress trajectories are calculated employing 2D finite element models (2D-FEM). Based on the displacement fields, the rotation of the Ordos Block and comparisons between the measured and the calculated stresses, it can be deduced that there are two episodes of fracture formation in the Ordos Block. The calculated orientations of maximum compressive stress in the Late Mesozoic and the Cenozoic eras are found to be WNW and NE respectively, which imply that the NW to EW trending structural fractures were developed in a Late Mesozoic stress field whereas the NNE to ENE ones were developed in a Cenozoic stress field in the block. The change in stress fields may have resulted in the change in tectonic setting from the northwestward subduction of the Izanagi Plate in the Late Mesozoic to the collision between the Indian Plate and the Eurasian Plate in the Cenozoic. The change in the Mesozoic and Cenozoic stress fields is of great significance to the further fracture prediction in fractured reservoirs, basin analyses in the Ordos Basin and research on the geodynamics of the North China Craton.

Basaltic and basaltic andesitic flows have been identified from the Chhotaudepur area in the Deccan Large Igneous Province. The $$\hbox {SiO}_{2}$$ content of these flows varies from 46.7 to 53.7 wt%. None of the samples have primary magma signatures as they exhibit low Mg# (0.42–0.68), Ni (4.8–33.4 ppm) and Cr (33.08–143.06 ppm). Highly variable concentrations of the LILE [Rb (2–74 ppm), Ba (52–351 ppm), Cs (0.1–1 ppm) and Sr (273–745 ppm)] and relatively enriched LREE are also noticed. The coherent chondrite normalized REE diagram and primitive mantle normalized multi-element diagram suggests a consanguinity among the flows. Low (Nb/Th) $$_{\mathrm{PM}}$$ (0.30–1.09), high (Th/Yb) $$_{\mathrm{PM}}$$ (3.09–16.58) ratios and marked variations in Rb concentration (2.4–74.11 ppm) with variable La/Yb (5.5–23.7) ratios suggests that magmas in the Chhotaudepur region were assimilated by the crustal components. The elevated Th/Ta and La/Yb relation further indicate concurrent assimilation and fractional crystallization process was involved in the genesis of the flows. Assimilation and fractional crystallization modelling of the flows was carried out with 20% olivine, 25% clinopyroxene, 45% plagioclase and 10% titano-magnetite as fractionating minerals and upper continental crust as the assimilant. The results reveal that all the flows were modified by AFC process.

Field and petrographic studies are carried out to characterize the interactions of mafic and felsic magmas from Pithora region of the northeastern part of the Bastar Craton. The MMEs, syn-plutonic mafic dykes, cuspate contacts, magmatic flow textures, mingling and hybridization suggest the coeval emplacement of end member magmas. Petrographic evidences such as disequilibrium assemblages, resorption textures, quartz ocelli, rapakivi and poikilitic textures suggest magma mingling and mixing phenomena. Such features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of mafic magmas into the felsic magmas before initiation of crystallization of the latter, results in hybrid magmas under the influence of thermal and chemical exchange. The mechanical exchange occurs between the coexisting magmas due to viscosity contrast, if the mafic magma enters slightly later into the magma chamber, then the felsic magma starts to crystallize. Blobs of mafic magma form as MMEs in the felsic magma and they scatter throughout the pluton due to convection. At a later stage, if mafic magma enters the system after partial crystallization of felsic phase, mechanical interaction between the magmas leads to the formation of fragmented dyke or syn-plutonic mafic dyke. All these features are well-documented in the study area. Field and petrographic evidences suggest that the textural variations from Pithora region of Bastar Craton are the outcome of magma mingling, mixing and hybridization processes.

The Bohai Sea is a Late Mesozoic-Cenozoic feature of the basin-mountain system located in eastern North China Craton (NCC). The Late Mesozoic thinning of the lithosphere signals the early destruction of the NCC. The onset of the destruction was due to the delamination of thick lithosphere of the craton, represented by the NW-trending grabens in an en-echelon arrangement west to Tanlu Fault, and by the NNE-trending grabens within the Tanlu Fault Zone. The Late Mesozoic NW-trending grabens are overprinted by structures related to the Cenozoic NE-trending pull-apart basin with very thick Mesozoic-Cenozoic sediments in the eastern NCC. C-frequency diagrams of growth faults and the extension factor (β) of four sections across the basin suggest that the extension migrated from the margin to the center of Bohai Sea, and that the Mesozoic and Cenozoic extension factors for Bohai Sea are higher than that of the margin. These evidences suggest that the greatest extension occurred in the center of Bohai Sea, which is consistent with the thinnest crust being found in the center of the sea. The extension ratios and tectonic evolution of the Bohai Sea suggest that it is the key region for the destruction of the NCC, as evidenced by the topography. However, the NCC experienced two stages of destruction with the late stage related to the tectonic regime of Northeast Asia.

Two petrologically distinct alkali feldspar syenite bodies (AFS-1 and AFS-2) from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidiomorphic texture and consists of feldspar (Or55Ab43 to Or25Ab71), ferro-pargasite/ferro-pargasite hornblende, hastingsite, pyroxene (Wo47, En5, Fs46), magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene (Wo47-50, En22-39, Fs12–31) set in a groundmass matrix of alkali feldspar (Or99Ab0.77 to Or1.33Ab98), titanite and magnetite. In comparison to AFS-1, higher elemental concentrations of Ba, Sr and ∑REE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is ∼1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.

Indravati “The lifeline of Bastar” is changing its course, in style and degree in a very short span of time which has invited attention of geo-scientists and policy makers to avoid any expected unpleasant circumstances .Here we have investigated the drainage rearrangement of Indravati river water, where , earlier, Jaura Nala( which used to flow northwards) connecting Kolab river and Indravati river acting as a feeder for Indravati, now flowing southward and draining the water of Indravati, has become a matter of serious concern for the sediment budgets and biotic distributions in the surroundings. Due to the stated changes, the likely hydro morphological impacts have also been discussed along with the possible measures to be adopted to avoid any disparity in future. A serious multidisciplinary probe into the possible causes ,the natural factors and human intervention, is warranted, taking in to account the considerations of changing surface topography including evidences derived from satellite and topographic data, understanding of geomorphological and sedimentological observations and impact due to man made structures like dams on the upstream side in Odisha.

A numerical model – “rifts – plume or hot spot – drift model” – is proposed for the first time in this paper for the generation of the three regional-scale dyke swarms (the Narmada–Tapi dyke swarm, the Nasik–Pune dyke swarm and the West Coast dyke swarm) within the Deccan Large Igneous Province (LIP) on the basis of the geological evolution of Deccan LIP and the orientations of dyke swarms. The dyke swarms have been modelled with finite element method (FEM) in three stages (stages I–III) considering that there was about 20° counterclockwise rotation of the Indian subcontinent since 65 Ma. During stage I, the orientation of the horizontal maximum principal compressive stress (σ1) is ∼ENE–WSW, generating the ENE–WSW-trending Narmada–Tapi dyke swarm. In stage II, the σ1 orientations are weakly preferred in NW–SE and E–W which are in agreement with the orientations of Nasik–Pune dyke swarm. In stage III, the σ1 orientation is ∼N–S generating the nearly N–S-trending West Coast dyke swarm. The rifts, plume or hot spot and the northward counterclockwise motion of Indian subcontinent altogether contributed to the generation of Deccan LIP and its associated dyke swarms.

Bhopalpatnam Granulite Belt which occur along SW margin of Bastar Craton and NE shoulder of Pranhita-Godavari Rift comprise of charnockite (enderbitic variety), garnet-sillimanite-biotite gneiss, quartzo-feldspathic gneiss and corundum bearing aluminous gneiss. High La/Yb ratio, low Eu anomaly (Eu/Eu*=1.0), high LREE/HREE ratio with uniform REE pattern, high La/Sc ratio (0.53–6.43), high Th/Sc ratio (0.03–2.56), low Ni (5.52–20.95), low Cr (31.05–117.05) and uniform Zr/Hf distribution pattern indicate a Proterozoic character. Distribution pattern of K2O, Na2O and CaO in ternary diagram show quartz-monzonite-granodiorite trend for the bulk rocks indicating that the bulk rock composition is close to TTG of early Archaean, which might have supplied the sediments for the rocks of Bhopalpatnam Granulite Belt. Geochemical and mineralogical evidence indicate an argillaceous protolith for garnet — sillimanite — biotite gneiss and corundum bearing aluminous gneiss, whereas an arkosic protolith for quartzo-feldspathic gneiss. The geochemical signatures also suggest an active continental margin setting for the rocks of Bhopalpatnam Granulite Belt with prominent Nb and Ta anomaly favouring a subduction environment between Bastar Craton and East Dharwar Craton. This is in conformity with the finding of the earlier workers suggesting a clockwise P-T path based on the combined fluid inclusion and mineral phase equilibria. The LILE geochemistry of charnockite suggests a bi-phase evolution. High LREE/HREE ratio portrays a highly evolved nature of the charnockitic melt generated through partial melting of the continental crust at the final stage of the granulite facies metamorphism during collision between Bastar and East Dharwar Cratons.

We report the occurrence of orthopyroxene gabbro from the Phenai Mata Igneous Complex (containing thoeliitic and alkaline rocks) that occur within Deccan Traps. The P-T calculations based on two pyroxene thermometry vary from 8.5±1.0 kbar and 963±39 °C. These gabbroic rocks exhibit high Mg# (0.67 to 0.71). But their primary magma signature can be negated due to their high SiO2 (> 50 wt %), low Ni (32–35 ppm) and Cr (105–182 ppm) contents. Further, simple fractional crystallization was not responsible for the modification of the magma. Modeling carried out using trace element concentrations revealed that concurrent assimilation and fractional crystallization (AFC) was responsible for the genesis of these rocks. Small pods of magma could have accumulated in the crustal portions and concurrent assimilation and fractional crystallization have taken place in the generation of gabbro and orthopyroxene gabbro in the present study area.

We present 40Ar/39Ar whole-rock ages of 63.7 ± 2.7 Ma (2σ, 92% Ar release) and 66.6 ± 2.2 Ma (2σ, 96% Ar release) for two samples of sub-surface mafic dykes intrusive into the sedimentary rocks of the Mesoproterozoic Chhattisgarh basin, Bastar craton, Central India. The obtained ages are synchronous with those of the Deccan Traps whose nearest exposures are at a distance of ~ 200 km to the west, and the recently dated diamondiferous orangeites (Group-II kimberlites) of the Mainpur area (located ~ 100 km SE within the Bastar craton). The chemical composition of the Chhattisgarh mafic dykes is indistinguishable from the chemostratigraphic horizons of the upper Deccan lavas of the Wai Subgroup (Ambenali and Poladpur Formations) and confirms them to be a part of the Deccan Large Igneous Province (LIP). The geological setting of the Deccan-age mafic dykes in the Chhattisgarh basin is analogous to that observed in other LIPs of the world such as (i) Pasco Basin of NW U.S.A, (ii) Ellisras sub-basin of southern Africa, (iii) Rift basins of New England in the NE U.S.A and (iv) the West Siberian Basin of Russia where LIP-related basalts and sills have been emplaced in distant domains from the main province. The Deccan-age of the Chhattisgarh dykes and the Mainpur orangeites permits a substantial increase of at least 8.5 × 104 km2 in the spatial extent of the Deccan LIP. The temporal link at ~ 65 Ma between the Deccan Traps and (i) sub-surface mafic dykes within the Chhattisgarh basin and orangeites in the Bastar craton, (ii) Ambadongar carbonatite in western India, (iii) Salma mafic dyke in the Eastern Indian craton, (iv) Rajahmundry Traps off the eastern coast of southern India and (v) tholeiitic dykes and basalts from the Seychelles, suggests a common tectonomagmatic control, via a vast mantle plume-head of the order of 2000–2500 km. Our study has relevance to the (i) origin (plume vs non-plume) of the Deccan LIP, (ii) plumbing system for Deccan dykes and lavas in domains far away from the presently exposed Trap regions, (iii) palaeo-environmental issues at the K–T boundary and (iv) metallogeny (diamond, Ni–Cu–PGE) in the Bastar craton.

The Central Indian collage incorporates the following major granulite belts: (1) the Balaghat–Bhandara Granulite Belt (BBG), (2) the Ramakona–Katangi Granulite Belt (RKG), (3) the Chhatuabhavna Granulite (CBG) of Bilaspur–Raigarh Belt, (4) the Makrohar Granulite Belt (MGB) of Mahakoshal supracrustals, (5) the Kondagaon Granulite Belt (KGGB), (6) the Bhopalpatnam Granulite Belt (BGB), (7) the Konta Granulite Belt (KTGB) and (8) the Karimnagar Granulite Belt (KNGB) of the East Dharwar Craton (EDC). We briefly synthesize the general geologic, petrologic and geochronologic features of these belts and explain the Precambrian crustal evolution in Central India. On the basis of the available data, a collisional relationship between Bastar craton and the EDC during the Paleo-Mesoproterozoic is reiterated as proposed by the earlier workers. The tectonic evolution of only few of the orogenic belts (BGB in particular) of Central India is related to Columbia.

Thisisthesecondpartofatwo-volumespecialis- sue of Open Geoscience (formerly Central European Jour- nal of Geosciences) that aims to be instrumental in pro- viding an update of Mac-Ultramac Rocks and Alkaline

The Bhopalpatnam granulite belt (BGB) flanks the Pranhita–Godavari (PG) rift basin with ages ranging from 1.6 to 1.9 Ga, representing a major Mesoproterozoic thermal regime in central India. We present here new results on the metamorphic P–T conditions from garnet-bearing enderbitic charnockite and pelitic gneisses, and document the fluid regimes from detailed fluid inclusions studies in corundum and quartz in corundum-bearing gneiss and garnet–sillimanite–rutile gneiss, respectively, from this granulite belt. A peak pressure–temperature window of 8–9.5 kbar and 720–800 °C is defined by phase equilibrium considerations on garnet–clinopyroxene–plagioclase–quartz assemblages in garnet–bearing charnockite. The garnet–plagioclase–sillimanite–quartz assemblages in pelitic gneiss yield slightly lower P–T estimates of 660–720 °C at 4.7–6.5 kbar. Primary fluid inclusions in corundum comprise monophase carbonic inclusions with melting temperatures varying from −56.6 to −57.4 °C, indicating that the dominant part of the trapped fluid is pure CO 2 . The inclusions homogenize into the liquid phase at temperatures in the range of −18.5 to −5.9 °C (1.024–0.961 g/cm 3 ). Fluid inclusions in quartz from garnet–sillimanite–rutile gneiss correspond to two categories; Group I (primary) and Group II (pseudosecondary). Both the groups show melting temperatures in the range of −55.9 to −62.9 °C, suggesting the presence of traces of other volatiles (CH 4 /N 2 ) in addition to CO 2 . The homogenization temperature of Group I inclusions ranges from −46.3 to −0.1 °C, the extreme low homogenizations indicating very high-density (up to 1.140 g/cm 3 ) for the carbonic fluid. Group II inclusions show higher homogenization temperatures of up to 16.2 °C. The estimated CO 2 isochore for primary inclusions in corundum and quartz intersects the peak P–T condition of the BGB derived from mineral phase equilibria. We therefore, infer that CO 2 was the dominant fluid species that was trapped at or near the peak metamorphic conditions in BGB. The metamorphic and fluid regimes, as well as the exhumation history of this granulite belt are thus constrained from a combination of petrologic and fluid inclusion studies.

The ‘Three Phenocryst Basalts’ (TPB) from Pavagadh hill constitute one of the most primitive basalts in Deccan traps. Electron microprobe analyses of phenocryst minerals from the TPB reveal that the Fo % of olivine varies from 89 to 68, the clinopyroxene grains are diopside/salite or augite and the Cr# [Cr/(Cr+Al)] in spinel is about 0.65. The An content of feldspar varies from 63 to 67. The mineral chemical data allow us to infer that olivine and spinel crystallized early, and when olivine attained Fo76–73%, the crystallization of clinopyroxene was initiated. Plagioclase crystallization occurred at the late stage. It is indicated that the source region of the TPB may possibly be undepleted mantle (lherzolite zone) at about 85 km depth and 27 kbar pressure, where Cr# of spinel is about 0.47.

Melt inclusions in olivine and pyroxene phenocrysts in kersantite and camptonite at Chhaktalao in Madhya Pradesh, India are mainly of the evolved type forming daughter minerals of olivine, pyroxene, plagioclase, spinel, mica, titanomagnetite and sulphides. Heating studies exhibit a temperature range from 1215° to 1245°C for the melt inclusions in olivine in camptonite and 1220–1245°C for olivine in kersantite. The temperature for melt inclusions in pyroxene ranged from 1000° to 1150°C in camptonite and 850–1100°C for pyroxene in kersantite. The bubble inside these melt inclusions is mainly CO 2 . The T h °C of CO 2 into liquid phase occurred between 26° and 31°C in olivine and 25–30°C in pyroxene from kersantite and camptonite. The maximum density estimated is 0.72 g/cm 3 and the minimum is 0.45 g/cm 3 . The depth of entrapment of the melt inclusion is estimated between 10–15 km. The pressure of entrapment of melt inclusion in olvine is 4.6 kbar where as that in pyroxene is 3.7 kbar. The lamprophyres in the Chhaktalao area are considered to be derived from low depth and low pressure region, possibly within spinel lherzolite zone.

Of twelve flows at Pavagadh Hill, the two three-phenocryst-basalt flows with Mg#∼0.70 and Ni/MgO∼33 are the most primitive and perhaps as primitive as any basalts in the Deccan province. Scatter on variation diagrams and the occurrence of primitive flows at two different levels in the volcanic sequence implies that most rocks are probably not, strictly speaking, comagmatic. Nevertheless, mass balance calculations indicate a generalized differentiation scheme from primitive basalt to hawaiite that involved removal of olivine, augite, plagioclase and Fe-Ti oxides in the proportions 40:33:22:5 with ∼ 50% of the magma remaining. Crustal assimilation had a minimal effect on evolution of the basalts but rhyolites at the top of the volcanic sequence may have been produced by crustal melting following prolonged heat release from alkali basalt pooled along fault zones in the continental crust. Major element based calculations indicate that the most primitive basalts were generated by 7 to 10% melting of mantle peridotite. These low percentages of melting, typical of alkali basalts, are consistent with the steep slopes on chondrite-normalized REE diagrams. Low heavy REE concentrations point to residual garnet in the source region. Incompatible element concentrations (e.g. Rb, Ba, Zr, La) in Pavagadh basalts exceed those in Deccan tholeiitic basalts but are substantially lower than those reported for some other Deccan alkali basalts. Obviously Pavagadh basalts do not reflect the lowest percentages of melting and greatest amount of source region metasomatic enrichment attained in the Deccan province. Deccan tholeiitic and alkali basalts are largely characterized by low La/Nb ratios and high La/Ba ratios similar to those in oceanic island basalts. This indicates minimal involvement of the subcontinental lithospheric mantle in their petrogenesis. Comparison with continental mafic magma provinces where a subcontinental lithospheric mantle imprint is common indicates long periods of extension and/or melting of mantle lithosphere still hot from pre-extension subduction are more likely to produce magmas bearing the lithospheric imprint.

Geochemistry of five basaltic and three doleritic dykes traversing through Deccan Traps in Kawant with similar trace element characteristics revealed a genetic relation among them. Various discrimination diagrams clearly indicate that all these basalts and dolerites are tholeiitic in nature. Of these, one picrite dyke (12–13 wt% MgO, 47–48 wt% SiO2 and 2.06–2.19 wt% total alkali) has high Mg# value (0.64–0.66), Ni (395–486 ppm), Cr (997–1155 ppm) and Ni/MgO (32–40) exhibiting a primitive magma signature. The mineral chemistry of this dyke reveals that Fo% of olivine varies from 79 to 85. The high CaO content than “mantle olivine” and slightly lower NiO content than “mantle peridotite” of the olivine grains in picrite indicate that they are not xenocrysts from mantle peridotite, but are crystallized from a relatively undifferentiated magma. Pyroxene grains in picrite are either diopside or augite and no major chemical variations are noticeable within these grains. Considerable variations are noticeable in the feldspar grains. Some grains represent alkali feldspars in the mesostasis, whereas the other phenocrystal grains are plagioclase with varying An contents (An 26–An 69). Higher HREE concentrations of picrite point to residual spinel in the source region. The major element modelling revealed that picrite has been derived by 8–13% partial melting of the mantle. Trace element ratios and OIB normalized spider diagram suggest that crustal contamination did not play any vital role in the evolution of these rocks. The results of mass balance calculations suggest a generalized differentiation scheme from picrite to the most evolved rock that involved removal of olivine, pyroxene and Fe-Ti oxides in the proportion 44:50:6 with ~ 64% of the magma remaining.