1 Introduction

Fig. 1
figure 1

Map of Deccan Traps showing the location of the study area (after Krishnamurthy et al. 2000).

Full size image

Flood basalt provinces represent important magmatic events which may contribute significantly to the generation of new continental crust. Origin of the continental flood basalt with eruptions of millions of cubic kilometers of basalt in a limited time span is still debatable (Gallagher and Hawkesworth 1992; Coffin and Eldholm 1994; Silver et al. 2006; Ernst and Bleeker 2010; Jowitt and Ernst 2013). The Deccan Large Igneous Province (DLIP) covering \(\sim \)500,000 \(\hbox {km}^{2}\) of Indian shield (figure 1) is mainly composed of nearly flat-lying tholeiitic flows (Bose 1972; Devey and Cox 1987; Hari et al. 2002). The original lava volume has been estimated as (1–3)\(\times 10^{6}\,\hbox {km}^{3}\) (Sen 2001; Jay et al. 2009) with the majority of the eruption in a period less than 1 million year, with catastrophic consequences for life on Earth (Courtillot and Renne 2003; Chenet et al. 2007). Recently, on the basis of Chhattisgarh sub-surface dykes and Mainpur orangeites, Rao et al. (2011) recalculated the areal extent of Deccan lavas as 8.5\(\times \hbox {10}^{4}\,\hbox {km}^{2}\). Deccan volcanic event attributed to the impingement of the Réunion mantle plume and culminated in the final phase of rupture of the Gondwana supercontinent (Mahoney et al. 2002; Collier et al. 2008).

Fig. 2
figure 2

Flow map of the Chhotaudepur region (modified after Hari et al. 2014). PMIC – Phenai Mata Igneous Complex.

Full size image

The DLIP is characterized by both tholeiitic and alkali basalts as well as relatively minor alkaline and carbonatitic intrusions (Basu et al. 1993; Rock et al. 1994; Simonetti et al. 1998; Shrivastava and Pattanayak 2002; Ray et al. 2007; Sen et al. 2009). Alkaline rocks of DLIP is dominated by silica undersaturated rocks such as nephelinites, basanite and tephrites, whereas the alkaline silica-saturated rocks, such as trachytes and syenites, form a minor component (Devey and Cox 1987; Peng et al. 1994; Rock et al. 1994; Greenough et al. 1998; Ray et al. 2007).

During the ascent of a plume-related magma through the continental crust, various magma modification processes such as fractional crystallization and crustal contamination will take place, which eventually changes the composition of the original magma. The concurrent assimilation and fractional crystallization process is regarded as one of the important processes which change the primary nature of the ascending magma (DePaolo 1981; Lightfoot and Hawkesworth 1988; Dessai et al. 2008). In the present paper, we tried to discuss the role of assimilation and fractional crystallization (AFC) on the magma modification process of the flows from the Chhotaudepur area of DLIP.

2 General geology

The Chhotaudepur area, which is located in the northern parts of DLIP (figure 2), comprises mainly of two igneous complexes, the Ambadungar alkaline igneous complex, located in the southeastern corner of DLIP and the Phenai Mata igneous complex, which is located in the western part (Randive et al. 2017). Many workers (e.g., Basu et al. 1993; Rock et al. 1994; Greenough et al. 1998; Hari 1998; Hari et al. 2000, 2014; Shrivastava and Pattanayak 2002; Ravi Kumar and Mohan 2005; Sen et al. 2009; Randive 2015) reported dyke swarms of basalt, dolerite, lamprophyre and tinguite from the Chhotaudepur area. The Ambadungar complex of Chhotaudepur area is dominated by calcite-carbonatites associated with a small portion of red-brown ankeritic-carbonatite. Phenai Mata igneous complex is dominantly composed of tholeiitic basalt, felsic rocks, gabbro and orthopyroxene gabbro (Hari et al. 2000). Hari et al. (2014) reported alkali feldspar syenite with shoshonitic affinity from the Phenai Mata region and proposed a metasomatic genesis for these rocks. Excluding Phenai Mata igneous complex and Ambadungar alkaline complex, the entire area is composed of basalt and basaltic andesite flows. For flow demarcation the methods used by Ganguly et al. (2012, 2014) are taken into consideration and based on field and petrographic studies, nineteen flows (figure 2) were identified in the present area. Most of the flows are characterized by amygdules, spheroidal weathering, red boles and columnar joints. The top flows (mainly second, sixth, tenth and thirteenth flows) are characterized by vesicularity along with the few amygdules. Feeble columnar structures were noticed in the third, fifth and seventh flows. Eighth and ninth, eleventh and twelfth, fourteenth and fifteenth flows can be demarcated by the presence of red boles between them. Further, for more accurate flow demarcation of the entire sequence, petrographic studies were also taken into consideration.

Fig. 3
figure 3

Photomicrographs showing (a) clustered plagioclase phenocrysts, altered olivine and pyroxene forming glomeroporphyritic texture in a ground mass comprised of plagioclase, clinopyroxenes, and opaques. Zoning is observed in plagioclase phenocrysts, (b) altered olivine, pyroxene and plagioclase phenocrysts set in the matrix of plagioclase, clinopyroxenes, and opaques, (c) plagioclase and pyroxene grains in a non-porphyritic flow, and (d) plagioclase phenocrysts in the groundmass of plagioclase, clinopyroxene, and opaques exhibiting intergranular and intersertal texture.

Full size image

3 Petrography

Some of the flows have olivine, pyroxene and plagioclase as phenocrysts and the ground mass is generally comprised of plagioclase, clinopyroxene, glass and opaques (figure 3). Alteration along the boundaries and fracture zones of olivine grains are observed in most of the thin sections (figure 3a). The glomeroporphyritic texture is noticeable in some sections (figure 3b). In few cases, complete alteration of olivine grains either to serpentine or to iddingsite are also perceptible. Clinopyroxenes are identified as augites and the plagioclase grains are identified as labradorites. Few flows have plagioclase and pyroxene phenocrysts set in a matrix mainly composed of plagioclase laths with clinopyroxene, glass, and opaques. In few flows, sporadic plagioclase phenocrysts are noticeable (figure 3c). It is noticeable that all these flows have parallel arrangement of plagioclase laths and exhibiting characteristic flow texture in the groundmass. Higher concentration of opaques with few plagioclase phenocrysts are noticeable in few flows. Some flows exhibit intersertel and intergranular textural patterns also (figure 3c and d).

4 Analytical techniques

Least altered samples of basalts and basaltic andesites were collected from the Chhotaudepur area and analyzed for major, trace and rare earth elemental compositions. Samples were pulverized in an agate mortar and pestle. Major elements were analyzed by XRF-Phillips MAGIX PRO (Model 2440) using pressed powder pellets, with relative standard deviations <3% and totals were all 100±1%. Rare earth elements, HFSEs and other trace elements were determined by ICP-MS (Perkin Elmer SCIEX ELAN DRC II) at the National Geophysical Research Institute (NGRI), Hyderabad. A mixture of double distilled acid (HF + HNO\(_3\) + HCl, 5:3:2 ml) was added to 0.05 g of rock powder in Savillex vessels and kept on a hot plate at \(150^{{\circ }}\hbox {C}\) for 3 days. After 3 days, the entire mixture was evaporated to dryness. The decomposition procedure was repeated by adding 5 ml of the acid mixture (HF + HNO\(_3\) + HCl, 5:3:2 ml) for two days. After that, 20 ml of 1:1 \(\hbox {HNO}_{3}\) was added to the dried samples and heated at \(150^{{\circ }}\hbox {C}\) for 10–15 min. Then 5 ml Rh (1 ppm) was added as the internal standard. After cooling, the volume of the prepared solution is made up to 250 ml. Certified reference materials JB-2 and JGb-1 were run as standard martials along with the samples. Precision and reproducibility obtained for international reference materials are given in table 1. The chondrite normalized and primitive mantle normalized ratios were calculated from the values of Sun and McDonough (1989). The result of the analyses are given in table 2.

Table 1 Major and trace element concentrations of JB-2 and JGb-1 obtained from XRF and HR-ICP-MS.
Full size table

5 Geochemistry

In the total alkali \((\hbox {Na}_{2}\hbox {O}+\hbox {K}_{2}\hbox {O})\) vs. silica \((\hbox {SiO}_{2})\), diagram the samples plot in the fields of basalt and basaltic andesite (figure 4). The \(\hbox {SiO}_{2}\) wt% of the basalts and basaltic andesites ranges from 46.7 to 53.7. The \(\hbox {Al}_{2}\hbox {O}_{3}\) content shows a narrow range between 11.5 and 13.2 wt%. Moderate to high variations in MgO and CaO (6.3–9.9 and 6.5–11.75 wt%, respectively) content were also noticed. The Mg# values range from 0.42 to 0.68. Based on the \(\hbox {TiO}_{2}\) (1.94–3.4 wt%) content, these rocks are classified as high Ti-basalts \((\hbox {TiO}_{2}\ge \)2 wt%). CIPW normative compositions are marked by the presence of quartz (2.1–8.2 wt%), albite (17.0–21.1 wt%) anorthite (19.4–22.2 wt%), diopside (4.5–22.1 wt%) and hypersthene (9.5–16.0 wt%).

All the samples have slightly higher concentrations of large ion lithophile elements (LILE) and light rare earth elements (LREE) (table 2). Low concentration of Ni (4.8–33.4 ppm) and Cr (33.08–143.06 ppm) relative to the primary mantle melts (Mg# \(\sim \)0.7, Ni >400–500 ppm, Cr >1000 ppm) (Wilson 1989) are observed in these rocks. The highly variable Rb (2–74 ppm) and Ba (52.09–1231.2 ppm) concentrations in the studied samples is likely to be caused by post-crystallization alteration processes or crustal contamination. Higher Sr (273.1–745.9 ppm) content and Rb (2–74 ppm) contents compared to OIB (Rb: 31 and Sr: 660 ppm) (Sun and McDonough 1989) are noticeable in these rocks. In comparison with the Nb and Ta concentrations of OIB (Nb: 48 and Ta: 2.7 ppm) (Sun and McDonough 1989; Iwamori and Nakamura 2015), the Nb (10.40–26.3 ppm) and Ta (0.72–1.8 ppm) contents of the studied samples exhibit relatively lower values, except for one sample (F-36). Even though, some of the basaltic flows in the present area exhibit slightly higher Mg# values (0.68), their low Ni and Cr concentrations (table 2) negate their primary magma signature suggesting that magma modification might have taken place.

Table 2 Whole rock geochemical data for the basaltic lava flows from Chhotaudepur area, DLIP.
Full size table

Many researchers suggested the fractional crystallization as an important differentiation process which operated during the evolution of basaltic lava flows of Deccan Traps, particularly in the lava flows of Indore–Khargaon, Mhow–Chikaldara (Chatterjee and Bhattacharji 2001), Jabalpur and Seoni areas (Shrivastava and Pattanayak 2002; Kumar and Shrivastava 2009), Western Ghats section (Mahoney et al. 2002; Melluso et al. 2004, 2006) and Bijasan Ghat section of Satpura Range (Sheth et al. 2004). In order to assess the fractional crystallization process, Ni, Cr, and CaO were plotted against MgO. Positive correlation of Ni and Cr with MgO suggests olivine as well as clinopyroxene fractionation (figure 5), whereas the positive correlation of CaO with MgO suggests plagioclase fractionation. Slight Eu anomaly of some samples in the chondrite-normalized REE diagram (figure 6a) also substantiates plagioclase fractionation.

The  chondrite  normalized   REE   (Sun and McDonough 1989) patterns (figure 6a) exhibit enrichment in LREE relative to the HREE. Minor Eu anomalies and fractionated HREE patterns are also noticeable. The coherent REE chondrite normalized patterns suggest similar genetic relationships among the flows. The primitive mantle normalized (Sun and McDonough 1989) multi-element patterns of the samples also exhibits overall geochemical coherence among the flows from the Chhotaudepur area (figure 6b). Distinct negative Zr anomalies are noticeable in all the samples. Positive Th, Ta, La–Ce, Gd–Tb anomalies and negative U, Ti and Yb anomalies are also noticeable in the primitive mantle normalized multi-element diagram.

Fig. 4
figure 4

Total alkali (\(\hbox {Na}_{2}\hbox {O}+\hbox {K}_{2}\hbox {O}\)) vs. silica \((\hbox {SiO}_{2})\) diagram (after Le Bas et al. 1986) showing the samples from the Chhotaudepur region in the field of basalt and basaltic andesite.

Full size image
Fig. 5
figure 5

Variation diagrams of Cr, Ni, and CaO with MgO of basalt and basaltic andesite flows from the Chhotaudepur region.

Full size image

6 Discussion

6.1 Assimilation and fractional crystallization of Deccan magmas

Assimilation of crustal material in mantle-derived magmas during their ascent to the surface through continental crust has been considered as an important process for the compositional diversity (Hawkesworth et al. 1984; Rudnick et al. 1986; Nicholson et al. 1991; Grunder 1992; Cribb and Barton 1996; Beard et al. 2005; Tegner et al. 2005; Michael and Cheadle 2009; Freund et al. 2013; Genske et al. 2013; Azzone et al. 2016). Ray (1998) on the basis of the Sr isotope systematics, concluded that alkaline silicate rocks of DLIP could be formed due to the crustal contamination of the carbonated silicate parental magma during concurrent fractional crystallization of silicates and exsolution of carbonate melt. Sheth and Ray (2002) developed an AFC model in terms of Sr concentration and Sr isotopic compositions to explain the genesis of the magmatic rocks of Pavagadh area using the western Indian granite as a contaminant. Later on, Sheth and Melluso (2008) discussed the importance of AFC in the genesis of the magmatic rocks of Pavagadh volcanic suite. Hari et al. (2011) proposed that gabbro and orthopyroxene gabbro from Phenaimata igneous complex, part of the Chhotaudepur province were a product of AFC.

Fig. 6
figure 6

(a) Chondrite normalized REE distribution patterns and (b) primitive mantle normalized multi-element spider diagram for basalt and basaltic andesite flows from Chhotaudepur province, of DLIP (normalization values are from Sun and McDonough 1989).

Full size image

In order to evaluate the significance of AFC process in the modification of the magma of Chhotaudepur province, (Nb/Th)\(_{\mathrm{PM}}\) vs. (Th/Yb)\(_{\mathrm{PM}}\) diagram was employed (figure 7a). It is generally accepted that mantle melt compositions have high Nb/Th values and low Th/Yb values, whereas on the other hand, low (Nb/Th)\(_{\mathrm{PM}}\) values and high (Th/Yb)\(_{\mathrm{PM}}\) values are considered to be derived as the result of assimilation of crustal material (Lightfoot and Hawkesworth 1988; Lightfoot et al. 1990; Dessai et al. 2008). The basalts and basaltic andesites of the Chhotaudepur area plot close to a consistent mixing trend between typical mantle composition (i.e., close to 1) and crustal contaminants, indicating that the magmas of the Chhotaudepur region were assimilated with a significant amount of crustal components prior to their emplacement and eruption. The Kalasubai Subgroup data also exhibit a similar trend of Chhotaudepur samples. On the other hand, Wai and Lonavala subgroup magmas have lower assimilation contents (figure 7a). In the Th/Yb vs. Nb/Yb diagram (figure 7b) the field of Reunion basalts represents plume asthenosphere with the variable incorporation of the depleted upper mantle. The basaltic rocks of Chhotaudepur region plot close to the field of Reunion plume and the mantle array. The displacement of the suite is noticeable towards the direction of crustal contamination. Deccan tholeiites and alkaline felsic rocks also exhibit a significant trend of crustal contamination. The marked variations in Rb (2.4–74.11 ppm) values and varying La/Yb (5.5–23.7) ratios in the studied samples also suggest the possibility of crustal contamination. The OIB, continental alkali basalts and kimberlites have La/Yb <1, whereas the continental flood basalts show wider variation in La/Yb ratio (0.5–7) (McDonough and Sun 1995). In the present case, La/Yb values range from 5.5 to 23.7 indicating that basaltic magmas in the Chhotaudepur region have been contaminated by crustal materials during their ascent and emplacement. It is generally considered that positive Th peaks in the primitive mantle normalized multi-element diagram along with variable Th/Ta ratios (1.4–5.06) also point towards crustal contamination of the samples. Further, low and variable Nb/Th ratio basaltic flows of Chhotaudepur region (2.5–7.89) also indicate crustal contamination as Nb/Th ratio of the primitive mantle is 8 and the continental crust is \(\sim \)1.1 (Taylor and McLennan 1985).

Fig. 7
figure 7

(a) (Nb/Th)\(_{\mathrm{PM}}\) vs. (Th/Yb)\(_{\mathrm{PM}}\) plot showing variations in the (Nb/Th)\({_\mathrm{PM}}\) and (Th/Yb)\(_{\mathrm{PM}}\) ratios in samples from the Chhotaudepur region, Wai Subgroup, Kalasubai Subgroup and Lonavala Subgroup. Data for the Wai, Kalasubai and Lonavala Subgroups are from the GEOROCK database (http://georoc.mpch-mainz.gwdg.de/georoc/). The ratios are normalized to primitive mantle values of Sun and McDonough (1989), N-MORB composition is from Hoffman (1988) and average Upper Continental Crust (UCC) composition is from Taylor and McLennan (1985). (b) Th/Yb vs. Nb/Yb diagram of the flows of Chhotaudepur region compared to the Deccan tholeiitic basalts (Lightfoot and Hawkesworth 1988; Chatterjee and Bhattacharji 2001; Sheth et al. 2004), Deccan alkaline felsic rocks (Chatterjee and Bhattacharji 2001), and modern-day Réunion plume basalts (Fisk et al. 1988; Paul et al. 2005). N-MORB, E-MORB, and OIB (Ocean Island Basalt) compositions are from Sun and McDonough (1989). SCLM composition is from McDonough (1990); GLOSS from Plank and Langmuir (1998). Vectors CC and FC approximate the direction of crustal contamination and fractional crystallization, respectively. Dashed lines indicate the mantle array (Pearce 2008).

Full size image
Fig. 8
figure 8

(a) Th/Ta vs. La/Yb plot (Condie 1997) showing plots of Chhotaudepur region, Wai Subgroup, Kalasubai Subgroup, Lonavala Subgroup and the distribution of mantle components. DM: depleted mantle, PM: primitive mantle, PSCL: post-Archean subcontinental lithosphere, LC: lower continental crust, UC: upper continental crust, HIMU: high U/Pb mantle source, EM 1 and EM 2: enriched mantle sources, FOZO: lower mantle plume component (region on the graph beneath and around the word FOZO), AFC: assimilation and fractional crystallization trend. Flows from the Chhotaudepur region of DLIP show an AFC trend towards upper crust. (b) (Th/Yb)\(_{\mathrm{PM}}\) vs. (Nb/Yb)\(_{\mathrm{PM}}\) plot showing variations in the (Th/Yb)\(_{\mathrm{PM}}\) and (Nb/Yb)\(_{\mathrm{PM}}\) ratios of samples from the Chhotaudepur region, Wai Subgroup, Kalasubai Subgroup and Lonavala Subgroup. Ratios are normalized to primitive mantle values of Sun and McDonough (1989). N-MORB composition is from Hofmann (1988), upper continental crust (UCC) composition is from Taylor and McLennan (1985), and enriched mantle (EMI, EMII) and HIMU values are from Condie (1997). Data for the Wai, Kalasubai and Lonavala Subgroups are from the GEOROCK database (http://georoc.mpch-mainz.gwdg.de/georoc/).

Full size image

When the samples of Chhotaudepur region were plotted in the Th/Ta vs. La/Yb diagram (figure 8a), most of the data plot above the mantle component portion. The rise in Th/Ta and La/Yb ratios and the linear trend of the samples indicate the involvement of AFC processes in the genesis of these rocks (Condie 1997). Defant and Nielsen (1990) suggested that AFC processes can elevate Th/Ta and La/Yb ratios by up to a factor of 3 or 4 in the case of upper continental crust and a factor of 2 for the lower continental crust. From figure 8(a), it is evident that the Deccan lavas of Kalasubai, Lonavala, and Chhotaudepur region were dominantly contaminated by the continental crust and the samples of Wai Subgroup, which plot close to the FOZO zone are with less contamination.

The (Th/Yb)\(_\mathrm{PM }\) vs. (Nb/Yb)\(_{\mathrm{PM}}\) diagram (figure 8b) is generally used to elucidate the difference between crustal contamination and variation in the melt sourcing. The (Th/Yb)\(_{\mathrm{PM}}\) and (Nb/Yb)\(_{\mathrm{PM}}\) ratios of enriched mantle sources EMI, EMII, HIMU (Condie 1997) and upper continental crust (Taylor and McLennan 1985) were compared with samples of DLIP. From the (Th/Yb)\(_{\mathrm{PM}}\) vs. (Nb/Yb)\(_{\mathrm{PM}}\) diagram, it can be deciphered that the magma compositions of DLIP are controlled by a mixture of source enrichment and crustal contaminant. Therefore, it can be presumed that AFC was one of the most important processes which were involved in the modification of the magma flows in Chhotaudepur region.

6.2 AFC modelling of the flows

The role of crustal contamination and the depth of magmatic sources are two important parameters required to understand the emplacement mechanisms of a Large Igneous Province (LIP) (Wood 1980; Rudnick et al. 1986; Arndt et al. 1993; Peng et al. 1994; Chesley and Ruiz 1998; Arndt et al. 2000; Xiao et al. 2004; Tegner et al. 2005). Major and trace element concentrations of this study suggest that the Deccan magmas have suffered a significant amount of fractional crystallization coupled with crustal assimilation. Assimilation and fractional crystallization (AFC), which is an important process for the modification of the magma is evaluated by considering 20% olivine, 25% clinopyroxene, 45% plagioclase and 10% titano-magnetite as the fractionating minerals. Mineral/melt partition coefficient values are taken after Claeson and Meurer (2004). The contaminant is taken as the average upper continental crust and the values are taken from Rudnick and Gao (2013). As the primitive magma (picrite) reported by Hari and Swarnkar (2011) from this region exhibit high incompatible elemental concentrations, thus, that rock could not be considered as the primary source of the flows of this region. In order to find out the primary rock, the method of Hofmann and Feigenson (1983) for calculating the parental magma from the differentiated one is adopted. The method involves the addition of minerals that supposedly fractionated from the parental magma. Once the composition of the parental melt was calculated, the calculations for AFC were carried out with the equation by DePaolo (1981) and Powell (1984)

$$\begin{aligned} C_{L }= C^{o}_{L}\cdot f + (r/r-1+D)\cdot C^* \cdot 1-f) \end{aligned}$$
(1)

where \(C^{o}_{L}\) is the concentration of the trace element in original magma, \(C^*\) is concentration of trace element in the contaminant, r is the ratio of rate of assimilation to rate of fractional crystallization, D is the bulk distribution coefficient for the fractionating assemblage, f is \(F^{[(r-1+D)/(r-1)]}\) and F is fraction of magma remaining.

Keeping the rate of assimilation to fractional crystallization (r) as 0.3, the binary plotting was carried out and are presented in figures 9(a–c). It has been found that the samples of the flows, plot within \(r = 0\) (perfect fractional crystallization) and \(r = 0.3\) indicating that these rocks are a product of AFC.

Fig. 9
figure 9

(a) Zr vs. Y, (b) Zr vs. Nb, and (c) Nb vs. Rb plots of the basalts and basaltic andesite flows of Chhotaudepur province. Liquid evolution curves were calculated for both fractional crystallization (FC) and concurrent assimilation and fractional crystallization (AFC). Each tick in the fractionation curve indicates 10% fractionation. The rate of assimilation to fractional crystallization (r) is considered as 0.3. Note that all the plotting of basalt and basaltic andesite fall within FC and AFC lines indicating that these rocks are a product of concurrent assimilation and fractional crystallization.

Full size image

Condie (1997) proposed that the high and low-Ti basalts of DLIP are derived from a mantle plume that interacted with the continental lithosphere. While tracing the source region characteristics of DLIP, Karmalkar et al. (2008) proposed that the magma underplating as a common phenomenon in the Kutch region and the magma chambers beneath the Kutch are connected by a network of interconnected dykes, from which the basaltic magmas periodically erupted. Vijaya Kumar et al. (2010) argued that the parental melts of DLIP have gone through different stages of fractional crystallization and were segregated within the lower crustal magma chamber(s) and underwent first stage fractional crystallization dominated by olivine and clinopyroxene (±spinel), thereby producing Fe- and Al-rich tholeiitic melts. These fractionated melts migrated from the asthenospheric depths to the upper crustal regions and the melt again to get pounded in shallow-level magma chambers where concurrent assimilation and fractional crystallization took place.

7 Conclusions

None of the flow samples from Chhotaudepur province exhibit primary magma signatures as they have low Mg#, Ni (4.8–33.4 ppm) and Cr (33.08–143.06 ppm). 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 (2.4–74.11 ppm) and variable La/Yb (5.5–23.7) ratios suggests that magmas in the Chhotaudepur region were assimilated significantly by the crustal components to their emplacement and eruption. The elevated Th/Ta and La/Yb relation further indicate concurrent assimilation and fractional crystallization process were involved in the genesis of the flows. AFC 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 result reveals that all the flows were modified by assimilation and fractional crystallization process.