Browsing by Author "Gulab C. Gautam"

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A Ca. 2.25 Ga mafic dyke swarm discovered in the Bastar craton, Central India: Implications for a widespread plume-generated large Igneous Province (LIP) in the Indian shield
(Elsevier B.V., 2021) Rajesh K. Srivastava; Ulf Söderlund; Richard E. Ernst; Gulab C. Gautam
A precise U–Pb baddeleyite age (2251 ± 4 Ma) has been obtained for an ENE-trending dyke exposed near the Chhura region of the Bastar craton, and additional dykes of similar trend are also reported from other parts of the northern Bastar craton such as in the Dongergarh and Pakhanjore areas. We propose a new widespread ENE-trending ca. 2.25 Ga Chhura mafic dyke swarm in the Bastar craton, which represents a continuation of the NE- to ENE-trending ca. 2.26 Ga Kaptipada swarm in the Singhbhum craton. The adjoining Dharwar craton also hosts ca. 2.26–2.25 Ga magmatism, the N- to NNE-trending Ippaguda-Dhiburahalli dyke swarm. A geochemical match between the ca. 2.25 Ga Chhura, the ca. 2.26–2.25 Ga Ippaguda-Dhiburahalli, and most samples of the ca. 2.26 Ga Kaptipada swarms corroborates a genetic link. Together these mafic dykes in Bastar, Singhbhum and Dharwar cratons, define the ca. 2.26–2.25 Ga Ippaguda (-Dhiburahalli-Chhura-Kaptipada) LIP. The relative post-2.25 Ga rotations between the three cratons would allow two alternative locations for the plume centre either at the eastern end of the Kaptipada swarm in the Singhbhum craton or at the south end of the Ippaguda-Dhiburahalli swarm in the Dharwar craton. Alternatively, convergence of the Churra, Kaptipada and Ippaguda-Dhiburahalli sub-swarms could suggest a plume centre location in the Godavari rift, between the Bastar and Dharwar cratons. Magmatic events of approximately this 2.26–2.25 Ga age are known from other parts of the globe including East Antarctica, and Kaapvaal and Zimbabwe cratons. © 2021 Elsevier B.V.
Early Precambrian mafic dyke swarms from the Central Archaean Bastar Craton, India: Geochemistry, petrogenesis and tectonic implications
(2012) Rajesh K. Srivastava; Gulab C. Gautam
The Archaean Bastar craton is known for the presence of different generations of mafic dykes. Less studied many NW-SE trending mafic dykes (intruded into the Archaean supracrustal rocks), encountered from the central part of the Bastar craton, are studied for their petrological and geochemical characteristics. There are many geological evidences which suggest emplacement of these mafic dykes in an intracratonic setting. Two distinct types of mafic dykes are recognized. Petrographically it is difficult to discriminate these two types. Many samples show metamorphic textures and amphibolites facies mineral assemblage but a few samples preserved original igneous texture and mineralogy. Major oxides show sub-alkaline thoeliitic basalt/basaltic andesite nature. High-Fe and high-Mg contents classify them as high-iron and high-magnesium tholeiites. They fall in the gabbronorite field on R1-R2 plot. Geochemical characteristics, particularly high-field strength and rare-earth elements, clearly distinguished them into two types: Group 1 and Group 2 mafic dykes. When compared with well-studied mafic dyke swarms of the Southern Bastar craton, the Group 1 is recognized as Meso-Neoarchaean sub-alkaline mafic dykes (BD1-CBC) and the Group 2 as Neoarchaean-Palaeoproterozoic boninite-norite mafic dykes (BN-CBC). The boninite-norite nature of the second group is also corroborated through immobile trace element ratios. BD1-CBC dykes are characterized by a relatively higher concentration of HFSE and REE in comparison to BN-CBC dykes. Some extent of crustal contamination is observed in BN-CBC dykes but BD1-CBC dykes do not show any indication of crustal contamination. Trace element modelling suggest that BD1-CBC mafic dykes are derived from a melt originated through ~20% melting of a depleted mantle source, whereas BN-CBC mafic dykes are probably derived from a high-Mg magma generated through ~25% melting of a refractory mantle source. Both melts have undergone 30-40% olivine fractionation before the emplacement. Geochemistry also points out involvement of a plume in the genesis of these mafic dykes. © 2011 John Wiley & Sons, Ltd..
Existence of the Dharwar–Bastar–Singhbhum (DHABASI) megacraton since 3.35 Ga: constraints from the Precambrian large igneous province record
(Geological Society of London, 2022) Rajesh K. Srivastava; Richard E. Ernst; Ulf Söderlund; Amiya K. Samal; Om Prakash Pandey; Gulab C. Gautam
We propose a Precambrian megacraton (consisting of two or more ancient cratons), DHABASI in the Indian Shield, which includes the Dharwar, Bastar and Singhbhum cratons. This interpretation is mainly based on seven large igneous provinces (LIPs) that are identified in these three cratons over the age range of c. 3.35–1.77 Ga, a period of at least 1.6 Ga. The absence of any subsequent break-up of DHABASI since 1.77 Ga suggests that this megacraton has existed for the past 3.35 Ga. In addition to their use in recognizing this megacraton, these LIP events may also provide likely targets for Cu–Ni–Cr–Co–platinum group element deposits. We suggest that the megacraton DHABASI was an integral part of supercontinents/supercratons through Earth’s history, and that it should be utilized as a distinct building block for palaeocontinental reconstructions rather than using the individual Dharwar, Bastar and Singhbhum cratons. © 2021 The Author(s).
Geochemical characteristics and petrogenesis of four Palaeoproterozoic mafic dike swarms and associated large igneous provinces from the eastern Dharwar craton, India
(Taylor and Francis Inc., 2015) Rajesh K. Srivastava; Amiya K. Samal; Gulab C. Gautam
Palaeoproterozoic mafic dike swarms of different ages are well exposed in the eastern Dharwar craton of India. Available U-Pb mineral ages on these dikes indicate four discrete episodes, viz. (1) ~2.37 Ga Bangalore swarm, (2) ~2.21 Ga Kunigal swarm, (3) ~2.18 Ga Mahbubnagar swarm, and (4) ~1.89 Ga Bastar-Dharwar swarm. These are mostly sub-alkaline tholeiitic suites, with ~1.89 Ga samples having a slightly higher concentration of high-field strength elements than other swarms with a similar MgO contents. Mg number (Mg#) in the four swarms suggest that the two older swarms were derived from primary mantle melts, whereas the two younger swarms were derived from slightly evolved mantle melt. Trace element petrogenetic models suggest that magmas of the ~2.37 Ga swarm were generated within the spinel stability field by ~15-20% melting of a depleted mantle source, whereas magmas of the other three swarms may have been generated within the garnet stability field with percentage of melting lowering from the ~2.21 Ga swarm (~25%), ~2.18 Ga swarm (~15-20%), to ~1.89 Ga swarm (~10-12%). These observations indicate that the melting depth increased with time for mafic dike magmas. Large igneous province (LIP) records of the eastern Dharwar craton are compared to those of similar mafic events observed from other shield areas. The Dharwar and the North Atlantic cratons were probably together at ~2.37 Ga, although such an episode is not found in any other craton. The ~2.21 Ga mafic magmatic event is reported from the Dharwar, Superior, North Atlantic, and Slave cratons, suggesting the presence of a supercontinent, Superia. It is difficult to find any match for the ~2.18 Ga mafic dikes of the eastern Dharwar craton, except in the Superior Province. The ~1.88-1.90 Ga mafic magmatic event is reported from many different blocks, and therefore may not be very useful for supercontinent reconstructions. © 2014 © 2014 Taylor & Francis.
Geochemical studies and petrogenesis of ~2.21–2.22 Ga Kunigal mafic dyke swarm (trending N-S to NNW-SSE) from eastern Dharwar craton, India: Implications for Paleoproterozoic large igneous provinces and supercraton superia
(Springer-Verlag Wien, 2014) Rajesh K. Srivastava; M. Jayananda; Gulab C. Gautam; Amiya K. Samal
The Archean eastern Dharwar craton is transacted by at least four major Proterozoic mafic dyke swarms. We present geochemical data for the ~2.21–2.22 Ga N-S to NNW-SSE trending Kunigal mafic dyke swarm of the eastern Dharwar craton to address its petrogenesis and formation of large igneous province as well as spatial link to supercontinent history. It has a strike span of about 200 km; one dyke of this swarm runs ~300 km along the western margin of the Closepet granite. Texture and mineral compositions classify them as dolerite and olivine dolerite. They show compositions of high-iron tholeiites, high-magnesian tholeiites or picrites. Geochemical characteristics of the sampled dykes suggest their co-genetic nature and show variation from primitive (Mg#; as high as ~76) to evolved (differentiated) nature. Although geochemical characteristics indicate possibility of minor crustal contamination, they show their derivation from an uncontaminated mantle melt. These mafic dykes are probably evolved from a sub-alkaline basaltic magma generated by ~20 % batch melting of a depleted lherzolite mantle source and about 15–30 % olivine fractionation. Paleoproterozoic (~2.21–2.22 Ga) mafic magmatism is recognized globally as dyke swarms or gabbroic sill complexes in the Superior, Slave, North Atlantic, Fennoscandian and Pilbara cratons. Possible Paleoproterozoic Dharwar–Superior–North-Atlantic–Slave correlations are constrained with implications for the configuration of supercraton Superia. © 2014, Springer-Verlag Wien.
Geochemistry and petrogenesis of Paleo-Mesoproterozoic mafic dyke swarms from northern Bastar craton, central India: Geodynamic implications in reference to Columbia supercontinent
(Elsevier Inc., 2015) Rajesh K. Srivastava; Gulab C. Gautam
Field setting, petrography, geochemistry and available radiometric ages of Proterozoic mafic dykes from the northern Bastar craton have helped to identify four sets of mafic dykes; two Paleoproterozoic [viz. NW-SE North Bastar dykes (NBD) and ENE-WSW Dongargarh-Chhura dykes (DCD)] and two Mesoproterozoic [viz. 1.42 Ga ENE-WSW Bandalimal dykes (BDD) and 1.44 Ga N-S Lakhna dykes (LKD)]. Their petrographic and geochemical characteristics are very distinct and suggest their derivation from different mantle melts. Chemistry of all the four sets suggests different petrogenetic histories and samples of each distinct set are co-genetic nature. The NBD, the DCD and the BDD samples are sub-alkaline tholeiitic in nature, whereas the LKD samples show alkaline nature. Very distinct REE patterns are observed for all the four sets again suggesting their different petrogenetic histories. Geochemical comparison between the studied samples and mafic dyke samples of southern and central parts of the Bastar craton suggests very different picture for the northern Bastar craton. Only one set of northern Bastar dykes, i.e. the NBD, matches with BD1 dykes; no other dyke sets match with any of the dyke swarms identified in southern and central Bastar craton. Geochemically it is not straightforward to confirm crustal contamination, however, on the other hand, possibility of crustal contamination cannot be ruled out completely. A petrogenetic model based on trace element data suggests that all the four sets are derived from different mantle melts. The NBD and the DCD are probably generated within spinel stability field, whereas the BDD and the LKD may be derived from melts generated within garnet stability field. Available geological and geochemical data support the emplacement of studied dykes in a stable continental rift tectonic setting, however earlier intrusions have chemistry similar to N-MORB. The available geological, geochemical and geochronological data on the four indentified sets of mafic dykes from the northern Bastar craton indicate their relation to the assembly and break-up of Columbia supercontinent. © 2014 International Association for Gondwana Research.
Geochemistry of an ENE-WSW to NE-SW trending ~2.37 Ga mafic dyke swarm of the eastern Dharwar craton, India: Does it represent a single magmatic event?
(Elsevier GmbH, 2014) Rajesh K. Srivastava; M. Jayananda; Gulab C. Gautam; V. Gireesh; Amiya K. Samal
A vast tract of ENE-WSW to NE-SW trending mafic dyke swarm transects Archaean basement rocks within the eastern Dharwar craton. Petrographic data reveal their dolerite/olivine dolerite or gabbro/ olivine gabbro composition. Geochemical characteristics, particularly HFSEs, indicate that not all these dykes are co-genetic but are probably derived from more than one magma batch and different crystallization trends. In most samples the LaN/LuN ratio is at ~2, whereas others have a LaN/LuN ratio >2 and show higher concentrations of high-field strength elements (HFSEs) than the former group. As a consequence, we assume that the ENE-WSW to NE-SE trending mafic dykes of the eastern Dharwar craton do not represent one single magmatic event but were emplaced in two different episodes; one of them dated at about 2.37 Ga and another probably at about 1.89 Ga. Trace element modelling also supports this inference: older mafic dykes are derived from a melt generated through ~25% melting of a depleted mantle, whereas the younger set of dykes shows its derivation through a lower degree of melting (~15%) of a comparatively enriched mantle source. © 2013 Elsevier GmbH.
Geochemistry of distinct mafic intrusive rocks from Darba-Kukanar and Kerlapal-Sukma-Mokhpal areas, southern Bastar craton: Further data on the early Precambrian mafic magmatism of Central India
(2007) Rajesh K. Srivastava; Gulab C. Gautam
Geochemistry of mafic igneous rocks of early Precambrian age of the southern Bastar craton in and around Darba-Kukanar and Kerlapal-Sukma-Mokhpal areas are presented. Most of these mafic rocks occur as NW-SE trending dykes intruded into the Archaean granite/ granite-peiss and over metamorphic rocks. Few intrusives also occur as sills or plutonic bodies. On the basis of field relationships between mafic rocks and other exposed rock types and also between the mafic rocks, available geochronological data, petrological and geochemical characteristics, the studied mafic rocks are classified into three main types: (i) Group I (BDI): Mesoarchaean mafic rocks, metamorphosed under mid-amphibolite facies conditions, showing concentration of high-field strength element (HFSE) higher than the Group 3 (boninite-norite) mafic rocks, and lower than the Group 2 (BD2: dolerite-diorite), (ii) Group 2 (BD2): Paleoproterozoic mafic rocks of dolerite-diorite composition, characterized by higher concentration of HFSE than the other two types, and (iii) Group 3 (BN: boninite-norite): Neoarchaean mafic rocks, metamorphosed under greenschist-amphibolite transitional conditions, characteristically showing high-Mg and Si, very low-Ti, and HFSE composition close to boninite. These observations are very similar to the previously studied mafic rocks from the other parts of the southern Bastar craton. It is suggested that the BDI mafic rocks are derived from depleted sub-alkaline basaltic magma, whereas enriched sub-alkaline basaltic magma was responsible for the BD2 mafic rocks. High-Mg boninite-norite (BN) mafic rocks were probably derived from a primary boninitic magma originated from a refractory lherzolitic mantle source. These observations clearly suggest heterogeneous mantle source beneath the Bastar craton during the early Precambrian. © Geol. Soc. India.
Geochronology, whole-rock geochemistry and Sr-Nd isotopes of the Bhanupratappur mafic dyke swarm: Evidence for a common Paleoproterozoic LIP event at 2.37–2.36 Ga in the Bastar and Dharwar cratons
(Elsevier B.V., 2020) Om Prakash Pandey; Klaus Mezger; Ulf Söderlund; Dewashish Upadhyay; Rajesh K. Srivastava; Gulab C. Gautam; Richard E. Ernst
Mafic dykes and dyke swarms in continental settings provide information on the evolution of the subcontinental mantle and can be key elements in the reconstruction of paleo-geographic settings of now separated crustal terranes. This study focuses on the petrogenesis and geochronology of mafic dykes of the WNW (~125°) trending Bhanupratappur swarm in the central Bastar Craton, central India. Dykes of the Bhanupratappur swarm yield an average U-Pb (ID-TIMS) baddeleyite age of 2360 ± 4 Ma, which is interpreted as their emplacement age. The compositions of the dykes range from tholeiitic basalt to basaltic-andesite. Their rare earth element and multi-element patterns indicate the involvement of a crustal component in their petrogenesis. The whole rock initial 87Sr/86Sr2360 Ma ranges from 0.70097 to 0.70506 with most being more radiogenic than the contemporaneous undifferentiated mantle reservoir (i.e. 87Sr/86Sr2360 Ma = 0.70173). The initial εNd 2360 Ma (+0.85 to −2.7) are chondritic to sub-chondritic. The Sr-Nd Isotope composition and major- and trace element chemistry suggest an enriched-heterogeneous mantle source. The closely matching ages and chemistry of the Bhanupratappur swarm (2360 Ma) and the Karimnagar-Bangalore swarms (2363–2369 Ma) of the Dharwar Craton indicate affinities to a common Large Igneous Province, which further implies that the Bastar and Dharwar cratons were already juxtaposed at 2.37–2.36 Ga. The dykes of the Bhanupratappur (WNW-trending) and Bangalore (E-W trending) swarms converge towards the east indicating a plume center in the east. If the Karimnagar swarm was also linked (and was converging) to the same plume, the present-day mismatch in the orientations of the Karimnagar dykes (NE- to ENE-trending) with the Bangalore and Bhanupratappur dykes may indicate a ~55° counterclockwise rotation of the northern block of the Eastern Dharwar Craton with respect to the southern block after 2.37–2.36 Ga. © 2020 Elsevier B.V.
Nd-isotope and geochemistry of an early Palaeoproterozoic high-Si high-Mg boninite–norite suite of rocks in the southern Bastar craton, central India: petrogenesis and tectonic significance
(Taylor and Francis Inc., 2016) Rajesh K. Srivastava; Márcio M. Pimentel; Gulab C. Gautam
Nd-isotope and lithogeochemistry of an early Palaeoproterozoic high-Si high-Mg boninite–norite (BN) suite of rocks from the southern Bastar craton, central India, are presented to understand their nature, origin, and tectonic setting of emplacement. Various types of evidence, such as field relationships, radiometric metamorphic ages, and the global distribution of BN magmatism, suggest emplacement in an intracratonic rift setting, commonly around 2.4–2.5 Ga. On the basis of geochemistry these high-Si high-Mg rocks are classified as high-Ca boninites, high-Mg norites, and high-Mg diorites. Nd-isotope data indicate that the high-Mg norite and the high-Mg diorite samples are similar, whereas the high-Ca boninites have a different isotopic character. The high-Mg norite and the high-Mg diorite samples have younger TDM model ages than the high-Ca boninites. Geochemical and Nd-isotopic characteristics of the studied rocks indicate some prospect of crustal contamination; however, the possibility of mantle metasomatism during ancient subduction event cannot be ignored. Trace-element modelling suggests that the high-Ca boninites may have crystallized from a magma generated by a comparatively greater percentage of melting of a lherzolite mantle source than the source for the other two varieties. Furthermore, the high-Ca boninite rocks are most likely derived from an Archaean subduction process (the Whundo-type), whereas the other two types are the products of the interaction of subduction-modified refractory mantle wedge and a plume, around the Neoarchaean–Palaeoproterozoic boundary. The emplacement of the high-Mg norites and the high-Mg diorites may be linked to crustal thickening and associated cratonization at the end of the Archaean. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
Petrogenesis and Tectonic Significance of An Early Paleoproterozoic High-Mg Boninite-Norite-Diorite Suite of Rocks from the Bastar Craton, Central India
(2016) Rajesh K. Srivastava; Gulab C. Gautam
[No abstract available]
Petrogenesis of Paleoproterozoic Khalari Hornblende-Pyroxenite Intrusion Within the Dongargarh Supergroup, Bastar Craton: Insights From Petrological and Geochemical Studies
(John Wiley and Sons Ltd, 2024) Amiya K. Samal; Gulab C. Gautam; Ankur Ashutosh; Rajesh K. Srivastava
This study investigates Paleoproterozoic hornblende pyroxenite, a lithological unit within the Khalari Ultramafic-Mafic Complex (KUMC), which is intruded into the Neoarchean-Paleoproterozoic Dongargarh Supergroup near Khalari village in the northern Bastar Craton. A comprehensive characterisation has been conducted through petrological analysis, bulk-rock geochemistry, mineral chemistry, and platinum group elements (PGEs)-Au geochemical studies to understand its petrogenesis and geotectonic implications. The presence of primary amphibole, specific pyroxene chemistry (low Ti and Cr), and enriched LILE, LREE and fluid-mobile elements alongside negative Nb–Ta–Ti anomalies suggest these rocks were crystallised from a mantle melt originated from a metasomatized sub-continental lithospheric mantle (SCLM) source. This metasomatization could be due to fluids derived from a subduction event predating the emplacement of the studied rocks. The proposed melt composition is estimated to have formed from 5% to 10% partial melting of a garnet-rich peridotite mantle source. The crystallisation conditions are estimated to have occurred at an average pressure of 7.85 kbar and a temperature of 902°C, indicating moderately shallow depths influenced by fractional crystallisation and slow cooling rates. The emplacement of the KUMC is contemporaneous with several other magmatic activities in the Bastar Craton, around ca. 2.50–2.47 Ga, suggesting that mantle plume might have played a significant role in their formation. Low concentrations of PGEs in the studied samples indicate a PGE-depleted mantle source. © 2024 John Wiley & Sons Ltd.
Petrogenesis of Paleoproterozoic Khalari Hornblende-Pyroxenite Intrusion Within the Dongargarh Supergroup, Bastar Craton: Insights From Petrological and Geochemical Studies
(John Wiley and Sons Ltd, 2025) Amiya K. Samal; Gulab C. Gautam; Ankur Ashutosh; Rajesh Kumar Srivastava
This study investigates Paleoproterozoic hornblende pyroxenite, a lithological unit within the Khalari Ultramafic-Mafic Complex (KUMC), which is intruded into the Neoarchean-Paleoproterozoic Dongargarh Supergroup near Khalari village in the northern Bastar Craton. A comprehensive characterisation has been conducted through petrological analysis, bulk-rock geochemistry, mineral chemistry, and platinum group elements (PGEs)-Au geochemical studies to understand its petrogenesis and geotectonic implications. The presence of primary amphibole, specific pyroxene chemistry (low Ti and Cr), and enriched LILE, LREE and fluid-mobile elements alongside negative Nb–Ta–Ti anomalies suggest these rocks were crystallised from a mantle melt originated from a metasomatized sub-continental lithospheric mantle (SCLM) source. This metasomatization could be due to fluids derived from a subduction event predating the emplacement of the studied rocks. The proposed melt composition is estimated to have formed from 5% to 10% partial melting of a garnet-rich peridotite mantle source. The crystallisation conditions are estimated to have occurred at an average pressure of 7.85 kbar and a temperature of 902°C, indicating moderately shallow depths influenced by fractional crystallisation and slow cooling rates. The emplacement of the KUMC is contemporaneous with several other magmatic activities in the Bastar Craton, around ca. 2.50–2.47 Ga, suggesting that mantle plume might have played a significant role in their formation. Low concentrations of PGEs in the studied samples indicate a PGE-depleted mantle source. © 2024 John Wiley & Sons Ltd.
Petrogenetic and geochemical constraints on ca. 1.89–1.88 Ga Bastanar mafic dyke swarm, Bastar craton, India: Insights into MORB- and OIB-type contributions and interactions with metasomatized subcontinental lithospheric mantle
(Elsevier B.V., 2024) Ankur Ashutosh; Amiya K. Samal; Gulab C. Gautam; Rajesh K. Srivastava
The Bastar craton of the Indian Shield hosts several generations of mafic dyke swarms of various trends, compositions, and ages, which span from ca. 2.7 Ga to 1.42 Ga. This study focuses on geochemical attributes of the ca. 1.89–1.88 Ga NNW-trending Bastanar swarm, aiming to address a perceived discrepancy between its arc-like geochemistry and the influence of a heterogeneous mantle source. To resolve the intra-swarm geochemical variations, we conducted a comprehensive geochemical characterization and petrogenetic interpretation of the ca. 1.89–1.88 Ga Bastanar swarm. The samples from this swarm are categorized into two distinct groups, primarily based on their geochemical composition. The Group 1 samples exhibit higher TiO2 (1.06–1.86 wt%), (La/Yb)N (7.2–8.6), (Gd/Yb)N (2- 2.27), Nb (14.6–16.6 ppm), Th (1.23–3.03 ppm) and Zr (104–118.72 ppm) concentrations than the Group 2 samples. Furthermore, rare-earth element patterns and variations in high-field strength element contents in the Group 1 samples suggest derivation from a deeper, less depleted mantle source resembling an OIB/less MORB-type. This inference is further supported by higher TiO2/Yb, Zr/Nb, and Nb/Y ratios. In contrast, the Group 2 samples indicate derivation from a shallower, more MORB/less OIB-type depleted mantle source, as evidenced by lower TiO2/Yb, Zr/Nb, and Nb/Y ratios. Variations in Dy/Yb and Gd/Yb ratios confirm the involvement of variable mantle sources, implying the derivation of the Group 1 and 2 samples from garnet-rich and spinel-rich lherzolite mantle sources, respectively. The absence of consistent negative Nb-Ta-Ti anomalies in the Group 1 samples suggests an uncontaminated nature, ruling out any role of crustal contamination. On the other hand, the Group 2 samples display negative Nb-Ta-Ti anomalies with enriched LREE and LILE patterns, indicating the involvement of crustal components in their genesis. A trace-element modelling suggests that the ca. 1.89–1.88 Ga mafic dyke swarm exhibits significant intra-swarm variability, with at least two distinct source components contributing to its genesis – a depleted MORB-type and an enriched OIB-type mantle. Notably, the geochemical characteristics of the Group 2 samples suggest interaction with a metasomatized mantle source, possibly enriched by fluids from an earlier subducted slab. Geochemical evidence presented in this work supports Archean subduction-related processes for the crustal growth of the Bastar craton and highlight the enduring influence of a metasomatized sub-continental lithospheric mantle on subsequent magmatism over millions of years. © 2024 The Author(s)
PGE geochemistry of low-Ti high-Mg siliceous mafic rocks within the Archaean Central Indian Bastar Craton: Implications for magma fractionation
(Springer Wien, 2010) Rajesh K. Srivastava; Sisir K. Mondal; V. Balaram; Gulab C. Gautam
Boninite-norite (BN) suites emplaced in an intracratonic setting in Archaean Cratons, are reported from many parts of the world. Such high-Mg low-Ti siliceous rocks are emplaced during Neoarchaean-Paleoproterozoic. The Archaean central Indian Bastar Craton also contains such a boninite-norite suite, which occurs in the form of dykes and volcanics. The spatial and temporal correlation of these high-Mg low-Ti siliceous rocks with similar rocks occurring around the northern Bastar and Dharwar Cratons probably represent a Bastar-Dharwar Large Igneous Province during the Neoarchaean-Paleoproterozoic. Platinum group element (PGE) abundances in these rocks provide constraints on their geochemical evolution during the Neoarchaean-Paleoproterozoic. The PGE geochemistry of the boninite-norite suite from the southern part of the central Indian Bastar Craton is presented to understand their behaviour during magma fractionation. In primitive mantle-normalized plots all samples have similar PGE fractionated patterns that are enriched in Pd, Pt and Rh relative to Ru. The Pd/Ru ratios for eight samples range from 2. 0 to 7. 0 which is higher than primitive mantle (primitive mantle Pd/Ru ≈1. 2). The Pd/Pt ratios range between 0. 2-2. 5 with an average value of 0. 7 which is near chondritic (primitive mantle Pd/Pt ≈0. 5). PGE variations in these rocks together with those of major and other trace elements are consistent with a model involving olivine fractionation along with chromite as a cotectic phase. The Pt fractionation from Pd and Rh is controlled by both olivine and chromite crystallization at an early stage during high temperature crystal fractionation when the Pt was strongly compatible and Pd and Rh were incompatible. Strong negative correlations of the S content with iron and TiO2 plus lithophile element contents of the rock suggest a decrease of the S solubility in the parental high-Mg magma and separation of an immiscible sulfide liquid with decreasing temperature. Palladium plus other available chalcophile elements (e. g., Re, Au, Ag) have been fractionated in this immiscible sulfide liquid after considerable olivine fractionation of the magma. © 2009 Springer-Verlag.
Precambrian mafic magmatism in the Bastar craton, central Indian
(2009) Rajesh K. Srivastava; Gulab C. Gautam
The Bastar craton has experienced many episodes of mafic magmatism during the Precambrian. This is evidenced from a variety of Precambrian mafic rocks exposed in all parts of the Bastar craton in the form of volcanics and dykes. They include (i) three distinct mafic dyke swarms and a variety of mafic volcanic rocks of Precambrian age in the southern Bastar region; two sets of mafic dyke swarms are sub-alkaline tholeiitic in nature, whereas the third dyke swarm is high-Si, low-Ti and high-Mg in nature and documented as boninite-norite mafic rocks, (ii) mafic dykes of varying composition exposed in Bhanupratappur-Keskal area having dominantly high-Mg and high-Fe quartz tholeiitic compositions and rarely olivine and nepheline normative nature, (iii) four suites of Paleoproterozoic mafic dykes are recognized in and around the Chattisgarh basin comprising metadolerite, metagabbro, and metapyroxenite, Neoarchaean amphibolite dykes, Neoproterozoic younger fine-grained dolerite dykes, and Early Precambrian boninite dykes, and (iv) Dongargarh mafic volcanics, which are classified into three groups, viz. early Pitepani mafic volcanic rocks, later Sitagota and Mangikhuta mafic volcanics, and Pitepani siliceous high-magnesium basalts (SHMB). Available petrological and geochemical data on these distinct mafic rocks of the Bastar craton are summarized in this paper. Recently high precision U-Pb dates of 1891. 1±0.9 Ma and 1883.0±1.4 Ma for two SE-trending mafic dykes from the BD2 (subalkaline) dyke swarm, from the southern Bastar craton have been reported. But more precise radiometric age determinations for a number of litho-units are required to establish discrete mafic magmatic episodes experienced by the craton. It is also important to note that very close geochemical similarity exist between boninite-norite suite exposed in the Bastar craton and many parts of the world. Spatial and temporal correlation suggests that such magmatism occurred globally during the Neoarchaean-Paleoproterozoic boundary. Many Archaean terrains were united as a supercontinent as Expanded Ur and Arctica at that time, and its rifting gave rise to numerous mafic dyke swarms, including boninitenorite, world-wide. © Geol. Soc. India.
Sr'Nd isotope geochemistry of the early Precambrian sub-alkaline mafic igneous rocks from the southern Bastar craton, Central India
(Springer Wien, 2009) Rajesh K. Srivastava; Rob M. Ellam; Gulab C. Gautam
Sr-Nd isotope data are reported for the early Precambrian sub-alkaline mafic igneous rocks of the southern Bastar craton, central India. These mafic rocks are mostly dykes but there are a few volcanic exposures. Field relationships together with the petrological and geochemical characteristics of these mafic dykes divide them into two groups; Meso-Neoarchaean sub-alkaline mafic dykes (BD1) and Paleoproterozoic (1.88 Ga) sub-alkaline mafic dykes (BD2). The mafic volcanics are Neoarchaean in age and have very close geochemical relationships with the BD1 type. The two groups have distinctly different concentrations of high-field strength (HFSE) and rare earth elements (REE). The BD2 dykes have higher concentrations of HFSE and REE than the BD1 dykes and associated volcanics and both groups have very distinctive petrogenetic histories. These rocks display a limited range of initial 143Nd/144Nd but a wide range of apparent initial 87Sr/86Sr. Initial 143Nd/ 144Nd values in the BD1 dykes and associated volcanics vary between 0.509149 and 0.509466 and in the BD2 dykes the variation is between 0.510303 and 0.510511. All samples have positive εNd values; the BD1 dykes and associated volcanics have εNd values between +0.3 and +6.5 and the BD2 dykes between +1.9 to +6.0. Trace element and Nd isotope data do not suggest severe crustal contamination during the emplacement of the studied rocks. The positive εNd values suggest their derivation from a depleted mantle source. Overlapping positive εNd values suggest that a similar mantle source tapped by variable melt fractions at different times was responsible for the genesis of BD1 (and associated volcanics) and BD2 mafic dykes. The Rb-Sr system is susceptible to alteration and resetting during post-magmatic alteration and metamorphism. Many of the samples studied have anomalous apparent initial 87Sr/86Sr suggesting post-magmatic changes of the Rb-Sr system which severely restricts the use of Rb-Sr for petrogenetic interpretation. © Springer-Verlag 2009.
U-Pb ID-TIMS baddeleyite age and geochemistry of the newly identified ca. 1.94 Ga magmatic event in the Central-Western Bastar craton
(Elsevier B.V., 2025) Ankur Ashutosh; Ulf Söderlund; Amiya K. Samal; Gulab C. Gautam; Rajesh Kumar Srivastava; Richard E. Ernst; Hafida El Bilali
A NNW-trending mafic dyke from the central-western Bastar craton yields a U[sbnd]Pb ID-TIMS baddeleyite age of 1944 ± 6 Ma. By correlating additional dykes with similar trend and geochemical characteristics, we identify a previously unrecognized dyke swarm, named herein the Pakhanjore swarm. Geochemical evidence suggests that the studied rocks are derived from partial melting of a spinel-rich, shallow lithospheric mantle source, involving 5–15 % partial melting as indicated by the non-modal batch melting model. AFC (Assimilation and fractional crystallization) modelling further reveals that fractional crystallization with moderate crustal assimilation (r = 0.3) contributes to the overall magmatic evolution. The similarity in trend of the ca. 1.94 Ga Pakhanjore swarm with the 1.89–1.88 Ga Bastanar swarm, and the ca. 1.85 Ga Sonakhan swarm of the Bastar craton suggests their emplacement occurred within a shared tectonic regime and/or paleostress field. Although notable geochemical similarities exist between the ca. 1.94 Ga Pakhanjore swarm and the 1.89–1.88 Ga and ca. 1.85 Ga mafic dykes, a direct genetic linkage remains inconclusive. However, based on available geological, geochronological, and geochemical data, the 1.89–1.88 Ga and ca. 1.85 Ga swarms appear to be part of a shared LIP event, whereas the ca. 1.94 Ga event likely represents an independent magmatic episode. The spatial alignment of all three dyke swarms with the NNW-trending Pranhita-Godavari Basin suggests a potential tectonic connection. © 2025 Elsevier B.V.