1. Introduction
Lamproites are rare, hydrous, mafic-ultramafic (Mg# = Mg/Mg+Fe > 60%) to ultrapotassic (K/Na > 3) and peralkaline (Na2O + K2O > Al2O3) igneous rocks, and are characterized by their exceptional enrichment of compatible and incompatible trace elements (Bergman, Reference Bergman1987; Foley et al. Reference Foley, Venturelli, Green and Toscani1987; Kjarsgaard et al. Reference Kjarsgaard, Pearson, Tappe, Nowell and Dowall2009). The lamproites are often derived from the deepest mantle sources, and their unique geochemistry and distinct modes of origin are often utilized to study large-scale geodynamic processes and deep volatile fluxes (Thompson et al. Reference Thompson, Leat, Morrison, Hendry and Gibson1990; Gibson et al. Reference Gibson, Thompson, Dickin and Leonardos1995; Martinotti et al. Reference Martinotti, Andreoli, Giametta, Poli, Bria and Janiri2006; Prelević et al. Reference Prelević, Stracke, Foley, Romer and Conticelli2010; Huang et al. Reference Huang, Niu, Xu, Chen and Yang2010; Yilmaz, Reference Yilmaz2010; Rukhlov, Blinova & Pawlowicz, Reference Rukhlov, Blinova and Pawlowicz2013; Liu et al. Reference Liu, Zhao, Zhu, Niu, DePaolo, Harrison, Mo, Dong, Zhou, Sun, Zhang and Liu2014; Stern, Leybourne & Tsujimori, Reference Stern, Leybourne and Tsujimori2016).
In general, lamproite magmas are derived from the partial melting of heterogeneous mantle sources that include geochemically enriched domains (metasomatized) of the subcontinental lithospheric mantle (Foley, Reference Foley1992; Murphy, Collerson & Kamber, Reference Murphy, Collerson and Kamber2002; Davies et al. Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006), and melts from sub-lithospheric sources further interacts with metasomatized subcontinental lithospheric domains during the melt transit to the surface (Sarkar et al. Reference Sarkar, Giuliani, Phillips, Howarth, Ghosh and Dalton2022). However, the origin of lamproites and the enrichment of incompatible trace elements are debated. Several models for their origin have been proposed, which include (1) ancient subducted continental material in the mantle transition zone (Murphy, Collerson & Kamber, Reference Murphy, Collerson and Kamber2002; Rapp et al. Reference Rapp, Irifune, Shimizu, Nishiyama, Norman and Inoue2008), (2) recycled crustal materials in subcontinental lithospheric mantle (SCLM) (Avanzinelli et al. Reference Avanzinelli, Lustrino, Mattei, Melluso and Conticelli2009; Prelević et al. Reference Prelević, Stracke, Foley, Romer and Conticelli2010; Tommasini, Avanzinelli & Conticelli, Reference Tommasini, Avanzinelli and Conticelli2011), (3) enrichment of a previously depleted SCLM by metasomatic melts originating either from the asthenosphere or subducted crustal slab (McKenzie, Reference McKenzie1989; Foley, Reference Foley1992; Nelson, Reference Nelson1992; Tainton & McKenzie, Reference Tainton and McKenzie1994; Turner et al. Reference Turner, Peate, Hawkesworth, Eggins and Crawford1999; Davies et al. Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006; Tappe et al. Reference Tappe, Foley, Kjarsgaard, Romer, Heaman, Stracke and Jenner2008) and (4) direct formation from a heterogeneous mantle plume (Mirnejad & Bell, Reference Mirnejad and Bell2006; Rukhlov, Blinova & Pawlowicz, Reference Rukhlov, Blinova and Pawlowicz2013; Sushchevskaya et al. Reference Sushchevskaya, Migdisova, Antonov, Krymsky, Belyatsky, Kuzmin and Bychkova2014; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Experimental evidence suggests that the primary melts of Si-rich ultrapotassic rocks require high-degree melting of a phlogopite-bearing mantle source. However, Si-deficient ultrapotassic primary melts may originate in the wehrlitic mantle, facilitated by metasomatic phases that are fluxed by volatiles such as H2O and CO2 (Gülmez et al. Reference Gülmez, Prelević, Förster, Buhre and Günther2023; Förster et al. Reference Förster, Buhre, Xu, Prelević, Mertz-Kraus and Foley2019a; Wang, Foley & Prelevic, Reference Wang, Foley and Prelevic2017). Förster et al. (Reference Förster, Prelević, Buhre, Mertz-Kraus and Foley2019b) investigated the effects of mantle metasomatism through sediment and hydrous mantle melts using a two-layer reaction experiment. The results show that sediment-dunite interactions at low temperatures (<1000°C) form K-enriched phlogopite-pyroxenite, while higher temperature reactions (1200°C) with hydrous basanite led to enrichment in K and K/Na and the generation of lamproite melt. It has also been demonstrated that experimental partial melts of K-richterite-bearing mica pyroxenites produce melts similar to lamproites (Ezad & Foley, Reference Ezad and Foley2022).
The emplacement of lamproites in central India has been correlated with the Paleoproterozoic plume-induced global rifting events (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). The central Indian craton, also known as the Bastar craton, records evidence of distinct lamproite magmatism in the eastern and western domains. The Eastern Bastar Craton (EBC), records lamproite magmatism at Kalmidadar, Amlidadar, Darlimunda, Parkom, Sakri (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) and Khadka (Yellappa, Chalapathi Rao & Chetty, Reference Yellappa, Chalapathi Rao and Chetty2010). However, from the Western Bastar Craton (WBC), only Kawardha lamproites (Lakra & Kujur, Reference Lakra and Kujur2021) have been reported so far. The lamproite magmatism in the EBC is correlated with the widespread 1.1 Ga extensional magmatic flux associated with the Rodinia supercontinent. The EBC lamproites are formed from a metasomatized subcontinental lithospheric mantle source interacting with the upwelling asthenosphere melt (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Similarly, the Kawardha lamproites in WBC are proposed to be derived from the metasomatized SCLM sources. The source of carbonate-rich fluids/melts has been attributed to the subduction recycling of the Archean continental lithosphere (Lakra & Kujur, Reference Lakra and Kujur2021). However, the petrogenetic mechanisms and the tectonic context of lamproite magmatism in the WBC still need to be explored further. Moreover, the detailed geochemical and petrological studies of this rare lamproite occurrence in the Kawardha area of WBC are also significant to understanding the crust-mantle processes in the WBC. In the present study, we used whole-rock geochemistry and mineral chemical analysis to investigate the petrogenetic and tectonic aspects of Kawardha lamproites from WBC. We also evaluated the geochemistry of previously reported lamproites from EBC to delineate regional variations in the source mantle characteristics of lamproite magma generation in Bastar craton and their emplacement mechanisms.
2. Geological framework and study area
The Bastar craton is situated in the central part of the Indian shield (Fig. 1) (Meert et al. Reference Meert, Pandit, Pradhan, Banks, Sirianni, Stroud and Gifford2010). Geographically, the north-eastern periphery of the Bastar craton is bordered by the Mahanadi lineament, which separates it from the Singhbhum craton, while the south-western boundary of the craton is marked by the Godavari lineament, which separates it from Dharwar craton. The southeastern and northern margins of the craton are outlined by the Eastern Ghat Mobile Belt and Central Indian Tectonic Zone, respectively. The craton encompasses crustal components from Mesoarchean to Neoproterozoic (Santosh et al. Reference Santosh, Tsunogae, Yang, Han, Hari, Prasanth and Uthup2020; Manu Prasanth et al. Reference Manu Prasanth, Sharma, Santosh, Yang and Hari2023). This craton is subdivided into two distinct blocks: WBC and EBC, and their boundary is marked by the Kotri-Dongargarh orogeny, also known as Central Bastar Orogen (Santosh et al. Reference Santosh, Tsunogae, Yang, Han, Hari, Prasanth and Uthup2020).
Figure 1. Generalized geological map of the Bastar craton showing the location of Kawardha Lamproites. The inset map illustrates the generalized geology of the Indian subcontinent and the location of the Bastar craton (Modified after Meert et al. Reference Meert, Pandit, Pradhan, Banks, Sirianni, Stroud and Gifford2010).
The Bastar craton consists of five major tectonic belts spanning from Archean to Proterozoic, which are Sausar-Chilpi belt (Mishra & Mohanty, Reference Mishra and Mohanty2021), Bengpal-Sukma belt (Ghosh, Reference Ghosh2004), Sonakhan greenstone belt (Deshmukh et al. Reference Deshmukh, Hari, Diwan and Prasanth2018; Manu Prasanth et al. Reference Manu Prasanth, Hari, Chalapathi Rao, Hou and Pandit2018, Reference Manu Prasanth, Hari, Chalapathi Rao, Santosh, Hou, Tsunogae and Pandit2019), Amgaon belt (Rajesh et al. Reference Rajesh, Mukhopadhyay, Beukes, Gutzmer, Belyanin and Armstrong2009) and Kotri-Dongargarh belt (Manu Prasanth et al. Reference Manu Prasanth, Sharma, Santosh, Yang and Hari2023). The craton also encompasses three supracrustal sequences: Dongargarh, Sakoli and Sausar suites (Mohanty, Reference Mohanty2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Among these, the Bengpal and Sukma groups are the oldest granitic rocks in the craton, with the ages of ca. 3561 Ma (Ghosh, Reference Ghosh2004) and ca. 3582 Ma (Rajesh et al. Reference Rajesh, Mukhopadhyay, Beukes, Gutzmer, Belyanin and Armstrong2009). The Chilpi rock group represents the youngest rock formations of age 1850–2050 Ma (Mohanty, Reference Mohanty2021). Paleoarchean (3.5–3.7 Ga) tonalite trondhjemite gneisses (TTGs) represent the basement ages of the craton (Ghosh, Reference Ghosh2004). The U Pb zircon ages of the TTGs range from 3561 ± 11 Ma (Ghosh, Reference Ghosh2004), 3583 ± 4 Ma (Rajesh et al. Reference Rajesh, Mukhopadhyay, Beukes, Gutzmer, Belyanin and Armstrong2009) to 3726 ± 22 Ma (Ratre et al. Reference Ratre, De Waele, Biswal and Sinha2010). Paleoproterozoic to Mesoproterozoic lamproite magmatism (Yellappa, Chalapathi Rao & Chetty, Reference Yellappa, Chalapathi Rao and Chetty2010; Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) has been reported from Darlimunda (2473 ± 8 Ga, Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018), Khadka (1.88 Ga, Yellappa, Chalapathi Rao & Chetty, Reference Yellappa, Chalapathi Rao and Chetty2010), Sakri (1045 ± 9 Ma, Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) and Nuapada (1055 ± 10 Ma, Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013) areas. Lamproites of the craton are correlated with two distinct magmatic events. The oldest Nuapada lamproites are correlated with the 2.2 Ga rifting event and a Paleoproterozoic large igneous province event (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Other lamproites represent the late Mesoproterozoic magma flux, where it has been correlated with the rifting events associated with the Rodinia supercontinent (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015).
The study area, located in the north-western fringe of the Chhattisgarh basin within the Bastar craton (Fig. 1), comprises the Chilpi group, volcanics of the Nandgaon group and the basaltic lava flows of the Deccan Traps (Lakra & Kujur, Reference Lakra and Kujur2021). The Chilpi group forms a linear north-south trending belt, extending approximately 100 km, and consists predominantly of low-grade metasedimentary sequences (Mishra & Mohanty, Reference Mishra and Mohanty2021). It represents the youngest rock unit in the region, with an estimated age range of 1850–2050 Ma (Mohanty, Reference Mohanty2021). The Pitepani andesites and Bijli rhyolites of the Nandgaon group are the oldest litho-units (∼2663 Ma; Manikyamba et al. Reference Manikyamba, Santosh, Chandan Kumar, Rambabu, Tang, Saha, Khelen, Ganguly, Singh and Subba Rao2016). The entire sequence is further overlain by Chhattisgarh Supergroup.
The Kawardha Lamproites intrude on the Paleoproterozoic meta-andesites of the Nandgaon group (Figs. 2, 3). Two clusters of lamproite occurrences can be noticed in the Piparadhar and Maharajpur areas of the Kawardha district (Fig. 2, insets a and b) (Lakra & Kujur, Reference Lakra and Kujur2021). The studied lamproites dykes are small in dimension (10–40 m length) and occur as isolated exposures within the meta-andesites (Fig. 3). More than ten dykes have been identified as lamproites, of which three are located in the Piparadhar area, and more than seven are confined in the Maharajpur area. The general trend of the studied lamproite dykes is NW-SE. Numerous secondary quartz and carbonate veins traversing the exposed lamproite dykes indicate possible post-magmatic alteration. Field details, which include the trend, dimensions, coordinates and key field observations, are given in Supplementary Table S1.
Figure 2. Generalized geological map of the Kawardha lamproite with the study area indicated within the boxes (modified after Lakra & Kujur, Reference Lakra and Kujur2021). The insets a (Piparadhar cluster) & b (Maharajpur cluster) show the location and trend of the studied lamproite dykes.
Figure 3. Representative field photographs (a, b, c & d) of Kawardha lamproite showing the studied lamproite dykes intruded within the meta-andesite of the Nandgaon group and occur as isolated bodies. The length of the hammer is 13 inches, and the width of the hammerhead is 6.4 inches.
3. Sample preparation and analytical techniques
Whole-rock major and trace element geochemistry of eighteen representative samples were analyzed at the Geochemistry Division, Council of Scientific and Industrial Research-National Geophysical Research Institute (CSIR-NGRI), Hyderabad. X-ray fluorescence (XRF) spectrometer (Phillips MagiX PRO Model 2440) was used for the major element analysis. The pressed pellets of the rock powders were used for the analysis. The details of the analytical methodology, including data gathering, accuracy, detection limits and equipment calibration, are given in Krishna, Khanna & Mohan (Reference Krishna, Khanna and Mohan2016). The trace and rare earth element concentrations were measured using a High-Resolution-Inductively Coupled Plasma Mass Spectrometer (HR-ICP-MS). The techniques used in sample digestion, instrumentation parameters and data acquisition are in Satyanarayanan et al. (Reference Satyanarayanan, Balaram, Sawant, Subramanyam, Krishna and Dasaram2018). The representative major and trace element geochemistry data are presented in Supplementary Table S2. MY-4 (IGEM, Russia) and SARM-39 (MINTEK, RSA) are the internal standards for major oxides and trace element analysis, respectively.
Mineral chemistry and back-scattered electron images of selected silicate and opaque minerals of lamproite dykes were analyzed using CAMECA SX Five electron microprobe analyzer (EPMA) with five wavelength-dispersive spectrometers at EPMA laboratory of Indian Institute of Technology (IIT), Bombay. The 15 keV accelerating voltage and a 20 nA beam current were used by the operating EPMA source. The equipment has a 1μm beam size, and analysis has a dwell period of around three minutes for each point. The representative mineral chemistry data are presented in Supplementary Tables (S3, S4 & S5). The internal standards, precision, accuracy and detection limits of the employed geochemical analysis are provided in Supplementary Table S8.
4. Results
4.a. Petrography and mineral chemistry
The Kawardha lamproites exhibit signs of extensive alteration; however, primary textural features of the major minerals are well-preserved. Olivine phenocrysts are completely pseudomorphosed by calcite and chlorites, potentially indicating secondary alteration processes such as chloritization and carbonatization. Representative photomicrographs of Kawardha lamproite are presented in Fig. 4, showcasing phenocrysts and microphenocrysts of pseudomorphic olivine, phlogopite and spinel set within a chlorite and carbonate-rich groundmass. Overall, a porphyritic texture can be observed with olivine (pseudomorph) as a phenocrystic phase (Fig. 4a). Some of the important petrographic observations of samples from each lamproite dyke have been provided in Table 1.
Figure 4. Representative photomicrographs of Kawardha lamproite, (a) showing the pseudomorphic olivine, (b) phlogopites under plain-polarized-light (PPL), (c) in crossed-nicols (XN), (d) backscattered electron (BSE) photomicrograph of phlogopite grain with TiO2 values of core and rim and (e and f) the BSE images of representative mineral grains of phlogopite, spinel, rutile, apatite, chlorite and carbonate. Ol (Pseud.): pseudomorphic olivine, Phl: phlogopites, Sp: spinel, Rt: rutile, Ap: apatite, Dol: dolomite, Chl: chlorite.
Table 1. Summary of salient petrographic features of Kawardha lamproite samples
Mineral abbreviations: Ol olivine; Phl phlogopite; Sp spinel; Ap apatite; Rt rutile; Il ilmenite; C carbonates; Chl chlorite; Qtz quartz.
* Extremely altered lamproite dykes.
Phenocrysts of phlogopite exhibit straw-yellow with a reddish undertone, which is commonly observed in Ti-rich micas (Fig. 4b) (Mitchell & Bergman, Reference Mitchell and Bergman1991; see also Supplementary Table S3). These grains display extinction parallel to cleavages (Fig. 4c) and exhibit compositional gradients from the core to the rim (Fig. 4d), as well as localized signs of chlorite alteration. The groundmass is rich in carbonate and chlorite, and it may be secondary. It also contains rutile, acicular apatite and euhedral grains of spinel (Fig. 4e, f). The mineral compositions of selected mineral grains are presented in Supplementary Tables S3, S4 and S5, and their geochemical variation has been discussed as follows:
4.a.1. Phlogopite
The Mg# (Mg/Mg + Fe+2 > 65%; Fig. 6a) suggests that phlogopite is a prominent mica phase. The compositional variation of TiO2 and Al2O3 in phlogopites ranges from 1.59 to 5.27 wt% and 9.86 to 13.48%, respectively (Supplementary Table S3). The TiO2 and Al2O3 concentrations of phlogopite are falling close to lamproite field rather than alnoite or minette (Fig. 5). Due to their (Si + Al) composition being less than 8 pfu (Fig. 6b), all of the phlogopites have a considerable amount of tetra-ferric component. Furthermore, octahedral site deficiency and Ti contents of the phlogopite (Fig. 6c) suggest that two significant Ti-accommodating substitution processes were involved, which is also noticeable in micas from the Nuapada lamproite field (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013). When compared to other lamproites from the EBC, micas in the Kawardha lamproites have much lower TiO2 values but show a similar range of Al2O3 concentrations (Fig. 6d).
Figure 6. Compositional variation of micas in Kawardha lamproites and other lamproites from Bastar craton (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) compared with that in Krishna lamproites, southern India (Reddy et al. Reference Reddy, Sridhar, Ravi, Chakravarthi and Neelakantam2003; Chalapathi Rao et al. Reference Chalapathi Rao, Kamde, Kale and Dongre2010) and West Kimberly lamproites (Jaques, Lewis & Smith, Reference Jaques, Lewis and Smith1986; Mitchell & Bergman Reference Mitchell and Bergman1991). (a) Al2O3 vs. 100*Mg/(Mg + Fe+2) plot; (b) Tetrahedral Al vs. Si plot; (c) Ti vs. octahedral site occupancy (OSO) plot and (d) TiO2 vs. Al2O3.
Figure 5. TiO2 (wt%) vs. Al2O3 (wt%) plot showing the compositional variation of phlogopite in the studied Kawardha lamproite. Compositional fields and trends for micas from kimberlite, lamproite, orangeite and minette are taken from Mitchell & Bergman (Reference Mitchell and Bergman1991).
4.a.2. Spinel
The composition of spinels in Kawardha lamproites shows an identical ulvo-spinel trend (Fig. 7a), which is analogous to the spinel trend (T2) of lamproites and orangeites (Mitchell, Reference Mitchell1995). The Ti, Cr and FeT concentrations (see Supplementary Table S4) suggest three different compositions for the spinel grains, which can be grouped as ulvo-spinel (high Ti and high Fe), chrome-spinel (Cr and high Fe) and magnetite (high Fe and low Cr-Ti). Concentrations of Mg and Cr in the chrome-spinel (Fig. 7b) suggest that the Kawardha lamproites are non-diamondiferous. Fe+2/(Fe+2+Mg) ratio for the spinel is nearly equal to 1, which is substantially similar to Sakri lamproites (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015). Whereas, Ti /(Ti+Cr+Al) ratio is highest for ulvo-spinel (> 0.85), moderate for chrome-spinel (0.2–0.6) and lowest for magnetite (nearly zero).
Figure 7. Composition of spinel from the Kawardha lamproites projected onto the front face of the (a) oxidized spinel prisms. Compositional variations of spinels from kimberlite and worldwide lamproites are also shown (adapted from Mitchell & Bergman Reference Mitchell and Bergman1991). (b) MgO vs. Cr2O3 plot for studied Cr-spinel, with diamond inclusion field after Fipke, Gurney & Moore (Reference Fipke, Gurney and Moore1995). The composition of spinel from Sakri lamproites, Bastar craton, is taken from Chalapathi Rao et al. (Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015).
4.a.3. Apatite
CaO content in apatites from Kawardha lamproite ranges from 53.23 wt% to 56.57wt%, and P2O5 is up to 40.83 wt%. Apatites are enriched in fluorine (up to 3.68 wt%; supplementary Table S5b) and are classified as fluorapatites. These fluorine-rich apatites are commonly observed in lamproites and/or lamprophyres (Edgar & Charbonneau, Reference Edgar and Charbonneau1991; Mitchell & Bergman, Reference Mitchell and Bergman1991; Edgar, Pizzolato & Sheen, Reference Edgar, Pizzolato and Sheen1996). The concentration of total FeO (0.1–1.17 wt%), MgO (0–0.9 wt%) and Na2O (0.04–0.4 wt%) is low, possibly suggesting the enrichment of incompatible trace elements like Sr, La and Ce (see Talukdar et al. Reference Talukdar, Pandey, Chalapathi Rao, Kumar, Pandit, Belyatsky and Lehmann2018).
4.a.4. Carbonate
Carbonate is not an essential mineral phase in lamproites (Mitchell & Bergman, Reference Mitchell and Bergman1991), but is sometimes present as accessory phases (Chalapathi Rao et al. Reference Chalapathi Rao, Kamde, Kale and Dongre2010). Our samples show calcite, ankerite and dolomite phases in the groundmass. CaO contents in calcites are high (up to 58.6 wt%) and contain negligible FeO, MgO and MnO. Whereas other carbonate phases are characterized by their high concentrations of FeO, MgO and MnO, which range from 4.14 to 8.4 wt%, 12.62 to 17.8 wt% and 0.3 to 0.95 wt%, respectively (see supplementary Table S5d).
4.a.5. Other groundmass phases
The rutile is mainly iron-bearing and contains FeO up to 1.28 wt%. The chlorites are dominantly pycno-chlorite (Si = 5.4–6.4 apfu) and subsidiary diabantite (Si > 6.4 apfu) in composition.
4.b. Whole-rock major element geochemistry
The bulk rock geochemistry of Kawardha lamproites is presented in Supplementary Table S2. Kawardha lamproites are silica undersaturated (SiO2 = 22.14–39.91 wt%) with MgO ranging from 12.46 to 20.29 wt%. Their Mg# value (34–50%) suggests an evolved nature, while concertation of other major oxides is highly variable such as Fe2O3 (10.6–25.12 wt%), CaO (1.74–22.75 wt%), TiO2 (3.8–7.48 wt%), P2O5 (0.99–3.9 wt%), Al2O3 (2.42–5.64 wt%) and loss on ignition (LOI = 2–17.1 wt%). The K2O concentration in rock samples is very low (<0.71 wt%), which is ascribed to post-magmatic hydrothermal alteration processes (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Low K2O content of the samples can also be attributed to chloritization of phlogopites, which is perceptible in the petrography.
4.c. Whole-rock trace element geochemistry
Kawardha lamproites are enriched in rare earth elements (REE = 406–1596 ppm), compatible trace elements such as Ni (206–824 ppm), Cr (160–1184 ppm) and V (215–503 ppm), and incompatible trace elements like Zr (296–635 ppm), Hf (6–13 ppm), Nb (113–260 ppm) and Ta (5.5–17 ppm). In the chondrite normalized diagram (Fig. 8a), Kawardha lamproites exhibit enrichment in lighter rare earth elements (LREE) relative to heavier rare earth elements (HREE) with (La/Yb)N, and value ranges between 50 and 159. However, it is noticeably depleted in several incompatible trace elements with negative anomalies at Rb, K, Ba, Pb, Sr and Zr in the primitive mantle diagram (Fig. 8b). The negative anomalies may have been somewhat influenced by the fluid-mobile behaviour of some of these elements, especially Rb, K, Ba and Pb (e.g., Mirnejad & Bell, Reference Mirnejad and Bell2006; Davies et al. Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006; Tappe et al. Reference Tappe, Foley, Kjarsgaard, Romer, Heaman, Stracke and Jenner2008).
Figure 8. (a) Chondrite normalized rare earth element, and (b) primitive mantle normalized spider diagrams for Kawardha lamproites. Normalizing values of the Chondrite and primitive mantle are from Sun & McDonough (Reference Sun and McDonough1989). Sakri lamproites (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) and Darlimunda lamproites are shown for comparison (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018).
5. Discussion
5.a. Lamproitic nature of Kawardha dykes
Potassic minerals such as K-feldspar, and/or kalsilite are not preserved in the Kawardha lamproites, resulting in low K nature, which is similar to other lamproite occurrences of Bastar craton (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). However, the presence of pseudomorphic olivine, Ti-rich phlogopite, ulvo-spinel and fluor-apatite with minor ilmenite and rutile indicates their lamproite affinity. Presence of fluor-apatite (F > 3 wt%) in Kawardha dykes is similar to other lamproite occurrences worldwide (see Jaques, Lewis & Smith, Reference Jaques, Lewis and Smith1986; Edgar and Charbonneau, Reference Edgar and Charbonneau1991) and also suggests alkaline nature of the parental melt (Wagner and Velde, Reference Wagner and Velde1986; Matchan et al. Reference Matchan, Hergt, Phillips and Shee2009). The alumina content in mica from our samples provides further evidence of their lamproite affinity, with an average Al2O3 of 11.74 wt%. This value aligns more closely with the global range of lamproites (5–12 wt%) than lamprophyres, which typically exceed 13 wt% (Rock, Reference Rock1991). Different geochemical characteristics, including mica compositional trends, spinel trends and the enrichment of incompatible and compatible trace elements, especially high levels of LREEs (up to 1534 ppm) and TiO2 (up to 6.94 wt%), clearly indicate the lamproitic nature of Kawardha dykes.
5.b. Alteration and crustal contamination
Crustal contamination is a salient process in the modification of the melt chemistry, and it can be estimated by using isotopic and trace element-based geochemical proxies (DePaolo, Reference DePaolo1981; Thompson et al. Reference Thompson, Dickin, Gibson and Morrison1982; Dostal & Dupuy, Reference Dostal and Dupuy1984). The incompatible trace element ratios such as Ce/Pb and Nb/U are important parameters to access the crustal contamination of the mantle-derived mafic-magmas (Xu, Xu & Zeng, Reference Xu, Xu and Zeng2017). The Ce/Pb and Nb/U ratios of the mid-oceanic ridge basalts and oceanic island basalts (Ce/Pb = 25 ± 5 and Nb/U = 47 ± 10; Hofmann et al. Reference Hofmann, Jochum, Seufert and White1986) are significantly higher than the continental crust (average Ce/Pb = 3.9 and Nb/U = 6.2; Rudnick & Gao, Reference Rudnick, Gao and Rudnick2003). The average Ce/Pb and Nb/U ratios of the Kawardha lamproites (46.9 and 61.08, respectively) indicate no significant effect of crustal contamination. In general, crustally contaminated magmas exhibit negative Nb and positive La-Th spikes on the primitive mantle normalized diagrams. Significant enrichments in Rb, Th, K and LREE values (Thompson et al. Reference Thompson, Dickin, Gibson and Morrison1982) can also be observed. The Kawardha lamproite exhibits positive anomalies at Nb-Ta-Ti in the primitive mantle normalized diagram (Fig. 8b), contrary to the lavas that have experienced crustal contamination (Nelson, Reference Nelson1992; Murphy, Collerson & Kamber, Reference Murphy, Collerson and Kamber2002). Highly fractionated REE pattern on chondrite normalized diagram (Fig. 8a) depleted HREE and Y with the absence of positive anomaly at Eu and Pb, which also precludes the significant crustal contamination (see Nelson, Reference Nelson1992; Murphy, Collerson & Kamber, Reference Murphy, Collerson and Kamber2002; Davies et al. Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006; Mirnejad & Bell Reference Mirnejad and Bell2006).
Post-magmatic alterations are more commonly accountable for the compositional modification of potassic-ultrapotassic rocks (Altherr et al. Reference Altherr, Meyer, Holl, Volker, Alibert and McCulloch2004; Mirnejad & Bell, Reference Mirnejad and Bell2006; Davies et al. Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006; Tappe et al. Reference Tappe, Foley, Kjarsgaard, Romer, Heaman, Stracke and Jenner2008). Elevated CaO (up to 22.3 wt%) and LOI values (up to 17.1 wt%; see Supplementary Table S1) in our samples indicate the formation of secondary carbonates and other hydrous minerals (e.g., calcite, dolomites and chlorites) through alteration. The Kawardha lamproites also exhibit low and/or highly variable contents of mobile elements like K (< 0.7wt%), Rb (1.4–51 ppm), Sr (126–577 ppm) and Ba (100–1400 ppm), suggesting alteration of samples. Alteration of olivine can be inferred from the lack of good correlation between MgO and Ni (Fig. 9a). Whereas a good correlation between immobile trace elements such as Hf vs. Zr (Fig. 9b), U vs. Th (Fig. 9c), Nb vs. Ta (Fig. 9d), and Cr vs. V (Fig. 9e) suggests that the concentration of immobile trace elements is appreciably not influenced by alteration processes and can be used to evaluate the petrogenetic processes.
Figure 9. Bivariate plots involving major elements (wt%) and trace elements (ppm) of the Kawardha lamproites: (a) MgO wt% vs. Ni, (b) Zr vs. Hf, (c) U vs. Th, (d) Nb vs. Ta, (e) Cr vs. V.
5.c. Correlations with other lamproites of Bastar craton
The porphyritic texture, liquidus mineralogy (pseudomorphic olivine grains, Ti-phlogopites, prominent ulvospinel trend and abundance of apatite) and distinctive whole-rock chemistry (extremely silica undersaturated, enrichment of incompatible trace elements and REE fractionation patterns) are the chief characteristics of Kawardha lamproites. Regardless of modification in their whole-rock compositions, the mineral chemistry of phlogopite and spinel (Figs. 6, 7) and the overall trace element patterns (chondrite and primitive mantle normalized diagrams; Fig. 8) indicate the Kawardha lamproites are comparable to other lamproite occurrences of Bastar craton such as Sakri and Darlimunda lamproites (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Moreover, similar trace element variations can be observed in Krishna lamproites (Reddy et al. Reference Reddy, Sridhar, Ravi, Chakravarthi and Neelakantam2003; Chalapathi Rao et al. Reference Chalapathi Rao, Kamde, Kale and Dongre2010) of Dharwar craton and West Kimberly lamproites (Jaques, Lewis & Smith, Reference Jaques, Lewis and Smith1986; Mitchell & Bergman, Reference Mitchell and Bergman1991).
Compared with other lamproite occurrences of the Bastar craton, the Kawardha lamproites are broadly similar to the Sakri lamproites (Figs. 6–8). The lamproites in the Darlimunda, Kalmidadar, Amlidadar and Parkom areas of the Nuapada field (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) exhibit relatively higher silica contents. Furthermore, the mica mineral chemistry of Darlimunda, Kalmidadar, Amlidadar and Parkom lamproites (Fig. 6) is closely related to West Kimberly lamproites, whereas the Sakri and Kawardha lamproites have geochemical similarities with the Krishna lamproites from the Eastern Dharwar craton in southern India (Chalapathi Rao et al. Reference Chalapathi Rao, Kamde, Kale and Dongre2010). Micas from the Kawardha lamproites have lower Ti values (0.25–0.5 apfu; supplementary Table S3) than those of other lamproites reported from the Bastar craton (Ti = 0.5–0.9 apfu; Fig. 6b, c). Based on the mica composition and whole-rock elemental variations, Kawardha lamproites exhibit distinct similarities with Sakri lamproites. However, Kawardha lamproite samples have high LREEs (400–1100 times of chondrites) in contrast to Sakri lamproites (LREEs = 400–500 times of chondrites). Whereas, Darlimunda lamproites (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) have appreciably higher HREE (10–40 times of chondrites) contents as compared to Kawardha lamproites (10–20 times of chondrites) and Sakri lamproites (20–30 times of chondrites). The concentrations of LREEs and HREEs in the Bastar lamproites suggest an enriched mantle source. Nevertheless, the LREE contents and (La/Yb) N ratio of the Kawardha lamproites are higher than that of Sakri lamproite but have considerably similar contents of HREEs (Fig. 8). However, Darlimunda lamproites have slightly higher HREEs compared to Kawardha and Sakri lamproites. The initial bulk rock Sr (0.705865–0.709024) and Nd (0.511063–0.511154) isotopic ratios of Sakri lamproites also point out the enriched source (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015).
Previously, Lakra & Kujur (Reference Lakra and Kujur2021) suggested both orogenic and anorogenic origins for the Kawardha lamproites. However, the data of Lakra & Kujur (Reference Lakra and Kujur2021) show low REEs (ƩREE = 59–98 ppm) in the lamproite samples, which are not consistent with other lamproite occurrences. Our new analysis from the Kawardha lamproites shows significantly higher REEs (ƩREE = 406–1596 ppm), which can be correlated with other lamproite occurrences in the Bastar craton. The studied samples (Supplementary Table S9) contain normative olivine (up to 28%), cpx (up to 38%) and leucite (< 1%), which suggests a close affinity towards olivine lamproites rather than leucite lamproites.
In summary, our geochemical comparison of lamproite occurrences in the Bastar craton reveals that Kawardha lamproites share significant geochemical similarities with the Sakri lamproites and other lamproites of the Bastar craton. This suggests, despite the differences in emplacement ages, a common petrogenetic and tectonic process can be inferred for the Precambrian lamproites of Bastar craton.
5.d. Melting conditions of a heterogeneous mantle source and petrogenesis of Kawardha lamproites
The primitive mantle normalized multi-element diagram (Fig. 8a) of Kawardha lamproites exhibits negative anomalies of Rb, Sr and Zr, which indicates the fractionation of various phases. The Rb in multi-element plot signifies residual amphibole or phlogopite (Sato, Katsura & Ito, Reference Sato, Katsura and Ito1997), Sr marks the fractionation of clinopyroxenes (Tappe et al. Reference Tappe, Jenner, Foley, Heaman, Besserer, Kjarsgaard and Ryan2004) and Zr accounts for zirconium silicate in the residuum (Mitchell & Edgar, Reference Mitchell and Edgar2002). The primitive mantle signatures (positive Nb, Ta and Ti anomaly) of the Kawardha lamproite rule out the subduction-related origin.
The high MgO, compatible (Ni, Co, Cr) and incompatible (Ba, Zr, Hf, Nb, LREEs) trace element concentrations and low Al2O3 are comparable to other anorogenic lamproites worldwide (Jaques Lewis & Smith, Reference Jaques, Lewis and Smith1986; Mitchell & Bergman, Reference Mitchell and Bergman1991; Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Kamde, Kale and Dongre2010, Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). Enrichment of LREE over HREE, high La/Yb (50–159) and Dy/Yb (5.1–7.6) ratios, together with a high concentration of compatible trace elements (such as Ni, Cr, Co), suggests the presence of a garnet-bearing source (Mitchell & Bergman, Reference Mitchell and Bergman1991; Mirnejad & Bell, Reference Mirnejad and Bell2006; Davidson et al. Reference Davidson, Turner and Plank2013). The ratios of highly and moderately incompatible trace elements (average La/Nb = 0.93 and average Sm/Yb = 13.34) indicate low-degree partial melting of the mantle peridotite sources within the garnet stability field and mixing of heterogeneous melts. (Stracke & Bourdon, Reference Stracke and Bourdon2009). Kawardha lamproites exhibit high values of Zr/Hf ratio (37.35–55.17) along with enrichment in LREE, which suggests low degree partial melting of the mantle source (Fraser et al. Reference Fraser, Hawkesworth, Erlank, Mitchell and Scott-Smith1985; Foley, Reference Foley1992; Hart & Dunn, Reference Hart and Dunn1993; Tainton & McKenzie, Reference Tainton and McKenzie1994; Weyer et al. Reference Weyer, Münker and Mezger2003). Similar enrichment of incompatible and compatible trace elements in the melt often involves cryptic and/or modal metasomatism and the development of metasomatic veins (Foley, Reference Foley1992). The dehydration reactions or partial melting of the subducted crust also induce metasomatic reactions in the lithospheric mantle. Low-degree partial melting of this heterogeneous mantle source can lead to the formation of lamproite magma (Davies et al. Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006; Prelevic, Foley & Cvetkovic, Reference Prelevic, Foley, Cvetkovic, Beccaluva, Banchini and Wilson2007; Akal Reference Akal2008). The positive anomalies of Nb-Ta on the primitive mantle normalized plot (Fig. 8b) together with Zr/Y, Th/Y and Nb/Y ratios (Fig. 11a, b) suggest that asthenospheric mantle was involved in their genesis (Tainton & McKenzie, Reference Tainton and McKenzie1994; Choukroun et al. Reference Choukroun, O’Reilly, Griffin, Pearson and Dawson2005; Mirnejad & Bell Reference Mirnejad and Bell2006). Earlier researchers (Mitchell & Bergman, Reference Mitchell and Bergman1991; Miller et al. Reference Miller, Schuster, Klötzli, Frank and Purtscheller1999) postulated that the lamproite magma originates from the low degree of partial melting of the phlogopite-bearing metasomatized mantle source. Partial melting of phlogopite-bearing mantle source can be accomplished by peritectic melting under the water-saturated condition (Foley, Reference Foley1993). The non-modal partial melting curves for phlogopite-bearing spinel and garnet lherzolites were generated to estimate the degree of partial melting. The composition of phlogopite-spinel and phlogopite-garnet lherzolite sources is from Miller et al. (Reference Miller, Schuster, Klötzli, Frank and Purtscheller1999). The La vs. La/Yb (Fig. 11a) and La/Yb vs. Yb (Fig. 11b) exhibit that the Kawardha lamproites can be formed by the small degree of partial melting (0.1–2%) of the phlogopite-bearing lherzolite in which melt contribution is from both garnet and spinel stability fields.
Figure 11. Trace element ratios of the Kawardha lamproite samples (a) La vs. La/Yb, and (b) La/Yb vs. Yb. Non-modal batch melting curves for phlogopite-bearing spinel and garnet lherzolites. Phlogopite-spinel and phlogopite-garnet lherzolites are from Miller et al. (Reference Miller, Schuster, Klötzli, Frank and Purtscheller1999). The sources are (i) phlogopite–spinel lherzolite: 0·55 ol, 0·25 opx, 0·11 cpx, 0·03 sp, 0·08 phl; and (ii) phlogopite–garnet lherzolite: 0·55 ol, 0·19 opx, 0·07 cpx, 0·11 gt, 0·08 phl. E-MORB (after Sun & McDonough, Reference Sun and McDonough1989), Darlimunda (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) and Sakri (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) are also plotted for comparison.
5.e. Tectonic setting of Kawardha lamproites
The high field strength elements (HFSEs) such as Zr and Nb are widely used to distinguish between intra-cratonic ultrapotassic alkaline rocks and other arc-related rocks because of their immobile behaviour during various low-grade post-magmatic alterations (Paton et al. Reference Paton, Hergt, Woodhead, Phillips and Shee2009). In the Zr vs. Nb diagram (Fig. 12), the Kawardha lamproites do not show any arc signatures. An anorogenic tectonic setting can also be inferred from the Th-Hf-Zr/2 diagram (Fig. 13).
Figure 12. Zr vs. Nb diagram depicting the arc and non-arc setting. The dotted line represents the field of rocks with very low Nb (< 50 ppm), which are considered to be subduction-related tectonic settings (Sheppard & Taylor, Reference Sheppard and Taylor1992). The field of Krishna lamproites (Paul et al. Reference Paul, Crockett, Reddy and Pant2007; Chalapathi Rao et al. Reference Chalapathi Rao, Kamde, Kale and Dongre2010), West Kimberly province olivine lamproites, West Kimberly province leucite lamproites and Aries kimberlites (Foley et al. Reference Foley, Venturelli, Green and Toscani1987; Altherr et al. Reference Altherr, Meyer, Holl, Volker, Alibert and McCulloch2004) is shown for comparison. Darlimunda (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) and Sakri (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) are also plotted for comparison.
Figure 13. Hf vs. Th vs. Nb/2 ternary tectonic discrimination diagram (after Krmíček et al. Reference Krmíček, Cempírek, Havlín, Príchystal, Houzar, Krmíčeková and Gadas2011) representing anorogenic geodynamic setting for the Kawardha lamproites. Darlimunda and Sakri lamproites are plotted for comparison. Sakri lamproites (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) and Darlimunda lamproites (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) are shown for comparison.
In the Nb/U vs. Nb (Fig. 14a), Ce/Pb vs. Ce (Fig. 14b) and Ta/Yb vs. Nb/Y (Fig. 14c) plots, the lamproite samples from the present study fall very close to oceanic island basalts (OIB) within the mantle array, which implies a deep mantle source for the primary magma (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). However, to evaluate the degree of enrichment or depletion of mantle source, Zr/Y vs. Nb/Y (Fig. 10a; after Fitton et al. Reference Fitton, Saunders, Norry, Hardarson and Taylor1997) and Th/Y vs. Nb/Y (Fig. 10b; after Sun & McDonough, Reference Sun and McDonough1989) ratios were employed in the present study. The high values of Zr/Y (5.8–12.8), Nb/Y (3–5.2), Th/Y (0.2–0.5), Nb/Yb (71–110) and Ta/Yb (3.5–8.3) ratios suggest enriched or fertile mantle domains like OIBs.
Figure 14. (a) Nb/U vs. Nb, (b) Ce/Pb vs. Ce and (c) Ta/Yb vs. Th/Yb plots for the Kawardha lamproites. The mantle array includes constructive plate boundary magmas (normal midocean ridge basalts: N-MORB; enriched midocean ridge basalts; E-MORB) and within-plate alkaline basalts (ocean island basalts; OIB). AUCC: Archean upper continental crust. SCLM: sub-continental lithospheric mantle. Fields for convergent margin basalts include the tholeiitic (TH), calc-alkaline (CA) and shoshonitic (SHO) magma series. The vectors S, C, W and f refer to subduction zone components, crustal contamination, within-plate fractionation and fractional crystallization, respectively (after Pearce, Reference Pearce2008). Fore arc, arc and back-arc fields of recent convergent margins are from Metcalf and Shervais (Reference Metcalf and Shervais2008). Various fields of lamproites are taken from Davies et al. (Reference Davies, Stolz, Mahotkin, Nowell and Pearson2006), Yilmaz (Reference Yilmaz2010), Paul et al. (Reference Paul, Crockett, Reddy and Pant2007) and Chalapathi Rao et al. (Reference Chalapathi Rao, Kamde, Kale and Dongre2010). Plots of Sakri lamproites (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) and Darlimunda lamproites (Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) are also shown for comparison. Data symbols are the same as in Figure 6.
Figure 10. Relative HFSE abundance in the Kawardha lamproite samples, (a) Nb/Y vs. Zr/Y plot (after Fitton et al. Reference Fitton, Saunders, Norry, Hardarson and Taylor1997). (b) Th/Y vs. Nb/Y plot interpreted as evidence for within-plate enrichment. Average N-MORB, E-MORB and OIB compositions from Sun & McDonough (Reference Sun and McDonough1989). Darlimunda (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) and Sakri (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) are also plotted for comparison.
Lamproite and other ultrapotassic magmatism reported from several parts of the Bastar craton have been correlated with intra-continental rifting (Yellappa, Chalapathi Rao & Chetty, Reference Yellappa, Chalapathi Rao and Chetty2010; Lehmann et al. Reference Lehmann, Burgess, Frei, Mainkar, Chalapathi Rao and Heaman2010; Sahu et al. Reference Sahu, Gupta, Patel, Khuntia, Behera, Pande and Das2013; Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015; Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018). We noticed that most of the lamproitic samples of Kawardha, Darlimunda (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) and Sakri (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) from Bastar craton plot in the asthenosphere and lithosphere-asthenosphere interaction array on La/Yb vs. Nb/La diagram (Fig. 15). This further points out that the melting might have initiated at the asthenospheric sources beneath Bastar craton and the melt possibly interacted with the metasomatized lithospheric mantle domains (Fig. 16). In the Bastar craton, active subduction and arc magmatism have been noticed from the Mesoarchean to the Neoarchean (Santosh et al. Reference Santosh, Tsunogae, Yang, Han, Hari, Prasanth and Uthup2020, Manu Prasanth et al. Reference Manu Prasanth, Hari, Chalapathi Rao, Hou and Pandit2018). The Paleoproterozoic granites and layered gabbro-anorthositic complexes in the central part of the craton are proposed to have formed in a post-collisional tectonic regime (Manu Prasanth et al. Reference Manu Prasanth, Sharma, Santosh, Yang and Hari2023). The recycling of early crustal domains might have significantly contributed to the metasomatism of the previously depleted SCLM. Santosh et al. (Reference Santosh, Hari, He, Han and Prasanth2018) postulated that the melt source for the eastern Bastar lamproites (Sakri and Darlimunda) was derived from the asthenospheric mantle, and further interactions with the lithosphere caused variable enrichments in the source. Such enrichment in the deep mantle melts occurs due to assimilating the earlier formed metasomatic veins in the lithospheric mantle source (Pilet, Baker & Stolper, Reference Pilet, Baker and Stolper2008; Pilet et al. Reference Pilet, Baker, Müntener and Stolper2011; Niu, Reference Niu2008). The Kawardha lamproite magmatism is possibly related to the Archean subduction-related metasomatic modification of the SCLM along the eastern margin of the WBC. The interactions with the asthenospheric melts and metasomatized and phlogopite-rich SCLM domains further lead to the formation of the parental melts of Kawardha lamproites. The observed geochemical variations and comparisons with other lamproite occurrences in the EBC further imply that Kawardha lamproites were placed in an intra-cratonic rift setting in the Bastar craton.
Figure 15. La/Yb vs. Nb/La diagram depicts an asthenosphere magma source and interaction of lithospheric and asthenospheric mantle components for the Kawardha lamproites and other lamproites from eastern Baster Craton (modified after Smith et al. Reference Smith, Sanchez, Walker and Wang1999). Darlimunda (Santosh et al. Reference Santosh, Hari, He, Han and Prasanth2018) and Sakri (Chalapathi Rao et al. Reference Chalapathi Rao, Burgess, Nanda, Choudhary, Sahoo, Lehmann and Chahong2015) are also plotted for comparison. The average OIB composition was taken from Fitton, James & Leeman (Reference Fitton, James and Leeman1991).
Figure 16. Schematic diagram showing the emplacement of Kawardha lamproites in the WBC. The possible formation conditions of Pitepani and Bijli volcanic rocks, Dongargarh and Kanker granitic intrusions of WBC are also shown.
6. Conclusions
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1. The ultrabasic lamproite dykes from the Kawardha area are compositionally equivalent to olivine-phlogopite lamproites and are characterized by phenocrysts and microphenocrysts of pseudomorphic olivine, phlogopite, spinel within chlorite – and carbonate-rich groundmass together with rutile and apatite as accessory phases.
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2. The Kawardha lamproite dykes are generated by low degree (up to 2%) partial melting of the mixed phlogopite-spinel and phlogopite-garnet lherzolite source. The melt possibly originated within the asthenospheric mantle; further asthenosphere-lithosphere interaction causes the enrichment of incompatible trace elements.
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3. The subduction-related crustal recycling in the Archean and Paleoproterozoic Bastar craton has led to the metasomatic enrichment of the SCLM domains. The Mesoproterozoic rifting events in the craton caused the asthenospheric mantle melts to interact with the metasomatized domains of SCLM, which created the parental melts of the Kawardha lamproites.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0016756825100186
Acknowledgements
The First author (TH) is thankful to NIT, Raipur, for providing all the necessary facilities and financial assistance (institute fellowship) to carry out the present research work. We are grateful to the XRF & HR-ICP-MS laboratory of NGRI, Hyderabad, and the EPMA laboratory of the Department of Earth Sciences, IIT Bombay, for providing the analytical facilities. Dayanand Tigga, Arth Rawal and Jayant Nayak are also acknowledged for their effortless assistance during fieldwork.
Competing interests
The authors declare no conflict of interest.
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