GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
ARTICLE
Geochemistry and petrogenesis of Proterozoic granitoids from Central Indian Tectonic Zone (CITZ): elemental and isotopic constraints
Meraj Alam , Mukesh-Kumar Mishra, Tatiana-Vladimirovna Kaulina, Talat Ahmad, Ashwini-Kumar Choudhary
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Keywords: granitoids, Nd-Sr isotope, protoliths, lithosphere, Proterozoic crustal evolution, Central Indian Tectonic Zone (CITZ)
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2022 Volume 56 Issue 5 Pages 160-176

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Abstract

The Central Indian Tectonic Zone (CITZ) is major E-W trending suture zone between Northern and Southern Indian crustal blocks. The southern portion of the CITZ comprises three litho-tectonic units: Tirodi Gneissic Complex (TGC), Sausar Mobile Belt (SMB) and Bhandara-Balaghat Granulite Belt (BBGB). Elemental and isotopic data are used to constrain the genesis of granitoids and their protoliths, which may help us to understand the Proterozoic crustal evolution in CITZ. Geochemical and isotopic results are consistent with previous studies that these granitoid plutons are linked to the felsic magmatism of the Columbian crustal assembly in India, North America and North China. Granitoids varies from tonalite to granite, alkalic to calcic, metaluminous to peraluminous composition. Normalized elemental ratios of La/Sm, La/Yb, La/Lu, and Gd/Yb depict variable LREE enrichments and varying degrees of partial melting of heterogeneous crustal/lithospheric sources. The studied rocks are characterized by positive anomalies for Pb and negative anomalies for Nb, Sr, P, Ti, which indicate the influence of subduction-zone fluids in the source regions. Negative anomalies for K, Sr, and Ti for SMB and BBGB granitoids may also be attributed to K-feldspar, plagioclase, and Fe-Ti oxide fractionation. However, TGC porphyritic leucogranites display K, Ba and Eu positive anomalies, probably related to the accumulation of K-feldspar phenocrysts. Nd-Sr data presents initial ratios of 143Nd/144Nd t = 1.6 Ga ranges between 0.509961 and 0.510300; εNd t = 1.6 Ga ranges from –5.3 to –11.9 with TDM ages ranging from 2.20 to 2.78 Ga for TGC granitoid. The ratios of 143Nd/144Nd t = 1.6 Ga ranges between 0.510232 and 0.510985; εNd t = 1.6 Ga ranges from +0.2 to +8.2 and TDM ages varies from 1.5 to 3.0 Ga. The initial 87Sr/86Sr t = 1.6 Ga ratios ranges between 0.699834 and 0.797151 for SMB granitoid. However, BBGB granitoids show the ratios of 143Nd/144Nd t = 1.6 Ga ranges between 0.509752 and 0.510910; εNd t = 1.6 Ga ranges from +6.7 to –16, and TDM ages range from 1.51 to 3.29 Ga. The initial 87Sr/86Sr (t = 1.6 Ga) ratios varies between 0.705096 and 0.717440. These ranges of εNd (t) and TDM values possibly indicate their derivation from enriched and heterogeneous crustal/lithospheric sources, and minor components from depleted lithospheric sources.

Introduction

During the Archaean-Proterozoic period, the generation of granitic magma and their emplacement represent significant events such as the growth and recycling of continental crust (Choukroune et al., 1997; Martin et al., 2005; Brown and Rushmer, 2006; Kemp et al., 2007; Vigneresse, 2007; Hacker et al., 2011; Sawyer et al., 2011; Cawood et al., 2013; Hawkesworth et al., 2019, 2020). Granitoids are generated by partial melting of diverse crustal/lithospheric, sources along with subsequent differentiation of primary magmas, followed by extensive tectonic processes for their emplacement (Martin et al., 2005; Moyen, 2020).

Indian Shield is characterized by widespread granitic magmatism, as evidenced from the Aravalli, Bundelkhand, Dharwar, and Bastar cratons during the Archean-Proterozoic boundary. The rocks from Dharwar craton have been studied in detail for their field relationships, geochemical and isotopic characterization, petrogenesis, and geochronology (Jayananda et al., 2020). The Indian subcontinent evolved through the amalgamation of Northern and Southern Indian cratonic blocks (NIB and SIB) along the Central Indian Tectonic Zone (CITZ), trending east-west for ~1600 km (Naqvi and Rogers, 1987; Rogers and Gird, 1997; Stein et al., 2004; Bhowmik et al., 2012, Fig. 1). Although, this amalgamation is still debated regarding the direction of subduction of NIB and SIB units. Few models have supported the southerly subduction of the NIB beneath the SIB (Yedekar et al., 1990; Jain et al., 1991; Eriksson et al., 1999; Acharyya, 2003). However, northerly subduction of the SIB beneath the NIB is suggested by Roy and Prasad (2003) and Chattopadhyay et al. (2017). This cratonic amalgamation produced the Greater Indian Landmass (GIL) during the late Grenville time (1100–900 Ma) (Naganjaneyulu and Santosh, 2010; Bhowmik et al., 2012).

Fig. 1.

(a) Outline map of India showing locations of different mobile belts including important blocks NIB and SIB with respect to the study area. (b) Geological map of the CITZ showing study area including TGC, SMB and BBGB along with the major lineaments and Supergroups from north to south. (c) Simplified geological map showing TGC & SMB (after Bhowmik, 2019). (d) Geological map of BBGB showing study area and lithotectonic unit (modified after Bhandari et al., 2011). Abbreviations: NIB - North Indian Block; SIB - South Indian Block; CITZ - Central Indian Tectonic Zone; TGC - Tirodi Gneissic Complex; SMB - Sausar Mobile Belt; BBGB - Bhandara-Balaghat Granulite Belt.

Present study deals with three lithotectonic units, namely Tirodi Gneissic complex (TGC), Sausar Mobile belt (SMB) and Bhandara-Balaghat Granulite Belt (BBGB), situated in the southern part of the CITZ (Fig. 1). These units are associated with granulite-gneiss domains and intrusive granitoids (Acharyya and Roy, 2000). Mohanty et al. (2000) has proposed five stages in the form of age groups (1850 ± 50 Ma, 1600 ± 50 Ma, 1300 ± 50 Ma, 1100 ± 50 Ma, and 900 ± 100 Ma) for CITZ granitoids related to different tectonothermal events of the region. Bhowmik (2019) has suggested three stages of development of GIL. The first stage represents accretionary orogenesis (c.a 1.6–1.5 Ga), the second stage represents Proterozoic extension leading to the fragmentation of Proto-Greater India and the third stage represents a continental collision (Himalayan-type), recorded during 1.06–0.93 Ga.

U-Pb zircon age of 1618 ± 8 Ma for granite gneiss is reported from the northern part of the SMB (Bhowmik et al., 2011). U-Pb zircon and monazite ages for granite gneiss range from 1603 ± 23 Ma to 1584 ± 17 Ma from the southern domain of the SMB (Bhowmik et al., 2011). These authors have reported magmatic and metamorphic events ranging from 1.62 to 1.42 Ga, which may correspond to the generation of an early Mesoproterozoic accretionary orogen in the CITZ. The Isotopic data indicate contrasting sources for the anatectic granite in the BBGB and Tirodi biotite gneiss in the TGC at 1.62 Ga. These are derived from the mature crustal source of Paleoarchean age and Early Paleoproterozoic source, respectively (Bhowmik et al., 2011; Bhowmik, 2019).

Rocks from CITZ have not been subjected to much detailed geochemical studies to understand their geochemical characteristics, petrogenesis, and nature of their protolith. We aim to address these issues by using new elemental and isotopic (Nd-Sr) data on Proterozoic granitoids from TGC, SMB and BBGB terrains of the CITZ. We also compare the studied granitoids with those from the consanguineous regions to understand the formation and disintegration of the Columbia Supercontinent. The development of the Columbia Supercontinent (ca. 1.7–1.6 Ga) was recorded globally (Rogers and Santosh, 2002; Zhao et al., 2004; Nance et al., 2014). The fragmentation of Columbia started at ca. 1.6 Ga in India, North America and north China rifting continued in most parts of the supercontinent until ~1.4 Ga (Rogers and Santosh, 2002, 2009).

Geological Setting

The CITZ came into being by the amalgamation of NIB (comprised of Archean Bundelkhand and Aravalli cratons) and SIB (comprised of Archean Bastar, Singhbhum, and Dharwar cratons) (Eriksson et al., 1999) (Fig. 1a). The CITZ runs more than 1600 km in length and 200 km in width extends into Chotanagpur Granite Gneiss Complex (CGGC) to the east, further to northeastern India into the Shillong plateau (Acharyya, 2001; Bhandari et al., 2011). These belts have recorded multiphase tectonomagmatic history throughout Paleoproterozoic to Neoarchean time (Acharyya and Roy, 2000). Further, ultra-high-temperature and high-pressure metamorphic rocks and K-rich granites are developed by the influence of post-collisional activity (Acharyya, 2003; Bhowmik et al., 2005; Bhandari et al., 2011). Moreover, CITZ is also comprised of lineaments locally referred to as Son-Narmada North Fault (SNNF) situated in the North and Central Indian Shear Zone in the south (Yedekar et al., 1990, Fig. 1b). This E-W trending Central Indian Shear Zone incorporates numerous structural features such as shears and faults, mainly at the southernmost boundary. The zone can be separated into two distinct regions along with different lithologies: (a) high-grade metamorphic terrain in the north and (b) low-grade volcanic and volcano-clastic terrain in the south (Radhakrishna and Naqvi, 1986).

The lithotectonic units from the study area are TGC and SMB situated in the northern portion of Central Indian Shear Zone, while BBGB occurs along the Central Indian Shear Zone towards the south (Fig. 1c). TGC comprises distinct suites with variable composition from trondhjemitic to granitic composition, metabasalt, amphibolites, rare granulite, quartzite, banded iron formation (BIF), kyanite-sillimanite schist and garnet-staurolite schists. SMB comprises volcano-sedimentary sequences (calc-silicate, quartzite, pelite, BIF, garnet-anthophyllite schist, and bimodal volcanic), sandstone, shale, and phyllites intruded by the felsic-mafic magmatic bodies (Roy et al., 2006; Mohanty, 2010; Chattopadhyay et al., 2015) (Fig. 1c). BBGB is an allochthonous block that has experienced multiphase tectono-thermal and tectono-magmatic events (Bhowmik, 2019) (Fig. 1d). BBGB is characterized by two-pyroxene granulite (mafic granulite) in the form of gabbroic magmatic emplacement in the Bhandara region (Alam et al., 2017).

Petrographic Observations

TGC rocks are recognized as leucocratic biotite-bearing porphyritic granitoids, comprising quartz, K-feldspar, sodic plagioclase and biotite in decreasing abundance; these rocks exhibit inequigranular porphyritic texture (Fig. 2a). The approximate percentage proportion of the mineral abundances occurring in these rocks are quartz = 38–45%, K-feldspar = 23–32%, plagioclase = 10–17% and mafic mineral abundances vary from 2–7%.

Fig. 2.

Field Photo and photomicrographs of granitoid for TGC, SMB, and BBGB from CITZ. (a) TGC leucocratic biotite bearing porphyritic granitoids, comprising of quartz, K-feldspar, sodic plagioclase and biotite with inequigranular to the porphyritic texture. (b) SMB granitoids showing well developed sphene bounded by hornblende and quartz. (c) SMB granitoids showing megacryst of K-feldspar showing inclusions of biotite and quartz showing porphyritic texture pointing towards magmatic origin. (d) Sequentially packed crystals of biotite, K-feldspar and quartz showing magmatic fabric in BBGC granitoids.

SMB rocks are characterized by massive porphyritic granitoids that overlie the TGC and are associated with meta-sediments. These rocks comprise quartz, K-feldspar, sodic plagioclase and biotite with some accessory phases viz. hornblende, muscovite, sericite, apatite, sphene, zircon, and opaque (Fig. 2b, c). The approximate percentage proportion of the mineral abundances occurring in these rocks are quartz = 38–45%, K-feldspar = 23–32%, plagioclase = 10–17% and mafic mineral abundances vary from 2–7%.

BBGB rocks occur along the southern margin of CITZ, relatively finer grained, which contains an assemblage of quartz, feldspar (alkali and plagioclase feldspar), and biotite (Fig. 2d). The approximate percentage proportion of the mineral abundances in these rocks are quartz = 40–44%, K-feldspar = 25–30%, plagioclase = 10–16% and mafic mineral abundances vary from 2–8%.

Megacrysts of K-feldspar show inclusions of biotite and quartz and all these crystals show magmatic fabric (Fig. 2d).

Analytical Methods

Nineteen samples of granitoids were collected from the study area (GPS coordinates of selected samples from TGC, SMB and BBG belts are given in Table 1 and Fig. 1), were analysed for major, trace and Rare Earth Elements (REEs). The studied samples were analyzed by X-ray fluorescence spectrometry (XRF) (Panalytical Model Philips Magix Pro Model 2440) at the University of Delhi, Delhi, India, precision limit for the major elements is better than 1% for SiO2 and 2% for other major elements, 2–5% for minor elements and better than 10% for trace elements (Longjam and Ahmad, 2012). Analysis of other important trace elements and REEs was carried out using ICP-MS (Perkin Elmer, Sciex Elan DRC II) at IIT, Roorkee, India. Several international rock standards (JG-2, G-3, JR-2, JR-3, and DGH) were used in calibrating the instrument. The precision limit was ±4.1% RSD for the ICP-MS data (Bhattacharya et al., 2012).

Table 1. Sample description of selected samples, GPS coordinates of location and their rock composition and ages from TGC, SMB and BBG belts, CITZ.
Sample Rock type GPS-Coordinates Rock composition TDM age (Ga)
B8 granodiorite N 22° 05' 12.9''
E 77° 51' 54.4''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap 2.36
B6 granite N 22° 05' 10.0''
E 77° 51' 54.2''		 Qtz + Kfs + Pl + Bt ± Ms ± Ap —
BT3a granodiorite N 22° 01' 39.8''
E 77°41' 32.2''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap 2.66
BT3b granite N 22° 01' 39.8''
E 77° 41' 32.2''		 Qtz + Kfs + Pl + Bt ± Ms ± Ap 2.56
BT4 granodiorite N 22° 41' 41.9''
E 77° 45' 32.5''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap 2.78
MA32 granite N 21° 47' 39.1''
E 80° 5' 43.5''		 Qtz + Kfs + Pl + Bt ± Spn ± Hbl ± Ms ± Ap —
MA34 granodiorite N 21° 47' 33.8''
E 80° 5' 41.4''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap 2.20
MA31 granite N 21° 47' 39.1''
E 80° 5' 43.5''		 Qtz + Kfs + Pl + Bt ± Spn ± Hbl ± Ms ± Ap 3.00
MA35 tonalite N 21° 47' 33.6''
E 80° 5' 1.6''		 Pl + Qtz + Bt + Fe-Ti oxides ± Kfs ± Spn ± Hbl ± Ms ± Ap —
MA36 granite N 21° 47' 33.7''
E 80° 5' 1.6''		 Qtz + Kfs + Pl + Bt ± Spn ± Hbl ± Ms ± Ap —
MA90 granodiorite N 21° 40' 16.6''
E 80° 06' 44.6''		 Pl + Kfs + Qtz + Bt ± Fe-To oxide ± Ms ± Ap 1.49
MA92 granodiorite N 22° 07' 16.2''
E 80° 09' 30.6''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap 2.32
MA93 granodiorite N 22° 07' 24.7''
E 80° 09' 32.8''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap —
MA96 granodiorite N 22° 07' 12.2''
E 80° 09' 1.5''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap —
MA48 granite N 21° 42' 34.8''
E 80° 5' 55.4''		 Qtz + Kfs + Pl-fs + Bt ± Ms ± Ap 2.18
MA62 granodiorite N 21° 33' 17.9''
E 79° 55' 57.7''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap —
MA66 granite N 21° 40' 18.8''
E 80° 06' 24.5''		 Qtz + Kfs + Pl-fs + Bt ± Ms ± Ap 3.29
MA68 granite N 21° 40' 18.8''
E 80° 06' 24.5''		 Qtz + Kfs + Pl-fs + Bt ± Ms ± Ap 2.00
MA79 granodiorite N 21° 40' 16.6''
E 80° 06' 44.6''		 Pl + Kfs + Qtz + Bt ± Ms ± Ap 1.51

Nd-Sr isotopic analyses for SMB and BBGB were carried out at the National Facility laboratory for Isotope Geology and Geochronology, IIT Roorkee using a Thermo Fisher TRITON multi-collector thermal ionization mass spectrometer (TIMS) and the method followed double isotope dilution analysis described by Boelrijk (1968). The ratios of 143Nd/144Nd were standardized to 146Nd/144Nd = 0.7219 and the mean values for the Japanese Nd standard JNdi-1 was 0.512105 ± 10 (1 SE; quoted value 0.512106, Tanaka et al., 2000) during analysis. The 87Sr/86Sr ratios were normalized to 88Sr/86Sr = 0.1194. Mean value for NIST Sr standard SRM-987 was 87Sr/86Sr = 0.710248 ± 10 (1 SE; quoted value 0.710245, Ravikant, 2006) during the period of analysis.

Four samples of TGC were analyzed for Sm-Nd isotopic ratios at the Russian Academy of Sciences, Apatity, Russia. The ratios of 143Nd/144Nd were normalized by146Nd/144Nd = 0.7219. During analysis, the mean value for the 143Nd/144Nd was obtained from the La Jolla standard (0.511833 ± 6 (2σ, n = 11)). The minimum error of 0.003% have been observed based on the reproducibility of the La Jolla standard.

Results

Whole-rock geochemistry

The chemical analysis of representative granitoids from TGC, SMB, and BBGB are presented in Table 2 and illustrated in Fig. 3. TGC have higher silica contents (68 to 72 wt%), very low TiO2 contents (0.13 to 0.31 wt%), low Fe2O3 (3.56 to 3.98 wt%), very low MgO content <1 wt%. SMB have moderate silica contents (57 to 68 wt%), lower TiO2 (0.64 to 0.90 wt%), Fe2O3 (6.61 to 8.58 wt%), variable K2O (1 to 5 wt%) and higher Al2O3 (14 to 17 wt%). However, BBGB show moderate silica contents (61 to 68 wt%), lower TiO2 (0.8 to 1.12 wt%), higher Al2O3 (13 to 15 wt%), Fe2O3 (8.45 to 10.00 wt%), lower MgO contents (1 to 2 wt%), moderate K2O contents (2 to 4 wt%) and lower content of P2O5 <0.5 wt%.

Table 2. Major oxide (wt%) and trace elements (ppm) data of representative samples of granitoids from TGC, SMB and BBGB, CITZ. Normalization values are after Sun and McDonough (1989).
Sample Tirodi Gneiss Complex (TGC) Sausar Mobile Belt (SMB) Bhandara-Balaghat Granulite Belt (BBGB)
B8 B6 BT3a BT3b BT4 MA32 MA34 MA31 MA35 MA36 MA90 MA92 MA93 MA96 MA48 MA62 MA66 MA68 MA79
SiO2 67.24 71.66 68.04 72.12 70.7 68.07 66.15 67.7 63.29 68.4 56.64 56.76 58.44 59.91 68.28 62.86 63.88 64.15 60.29
TiO2 0.24 0.13 0.35 0.22 0.31 0.77 0.91 0.83 0.71 0.82 0.64 0.69 0.64 0.68 0.8 1.1 0.79 0.93 1.12
Al2O3 16.45 16.11 14.99 14.51 13.87 14.72 14.66 14.71 17.58 14.05 15.17 15.4 14.24 13.92 14.46 13.51 14.44 14.6 14.21
Fe2O3 3.56 2.04 5.2 3.33 3.98 7.56 8.04 8.58 6.86 6.86 7.99 7.21 7.65 8.08 6.61 10 8.45 8.65 8.9
MnO 0.03 0.03 0.1 0.04 0.06 0.08 0.09 0.07 0.05 0.07 0.29 0.21 0.22 0.18 0.08 0.1 0.09 0.08 0.12
MgO 0.53 0.34 0.74 0.35 0.6 1.71 1.85 1.61 1.51 1.51 2.66 2.38 2.62 2.58 1.7 2 1.45 1.18 2.04
CaO 1.9 1.09 2.74 2.28 2.01 0.48 1.58 0.48 0.1 0.24 12.26 13.16 11.96 8.37 0.5 5.18 5.02 4.49 5
Na2O 5.17 4.26 3.54 4.01 2.78 1.52 1.74 1.49 0.79 1.52 1.36 1.14 0.9 1.89 1.21 3.35 3.56 3.84 4.88
K2O 2.84 3.64 3.08 2.44 3.82 3.61 3.22 3.58 5.1 2.45 1.29 0.68 2.08 3.62 3.71 1.87 3.01 2.61 2.12
P2O5 0.06 0.05 0.09 0.05 0.06 0.1 0.14 0.11 0.12 0.08 0.15 0.15 0.15 0.12 0.1 0.35 0.26 0.35 0.47
LOI 0.95 1.23 0.82 0.54 0.67 0.5 1.9 0.5 3 2.3 0.78 0.9 0.94 1.2 2.1 0.8 0.1 0.4 0.22
SUM 98.97 100.58 99.69 99.87 98.86 99.1 100.28 99.66 99.11 98.3 99.23 98.68 99.84 100.55 99.55 101.12 101.05 101.28 99.37
Rb 29 258 83 85 87 175 162 175 115 57 93 46 125 228 180 21 40 35 43
Ba 1189 1236 1632 1563 1534 165 171 168 74 43 2653 1553 1835 2079 179 341 410 419 913
Th 15 15 2 4 2 29 31 34 9 8 23 22 23 20 29 2 2 2 4
U 4 6 0 2 2 6 6 7 2 2 3 2 2 2 6 2 2 2 2
Nb 6 11 3 2 6 20 20 22 5 5 16 16 15 17 20 24 18 27 31
Pb 30 44 35 18 19 35 36 35 8 6 16 12 5 22 22 30 34 34 4
Sr 138 375 322 220 169 38 29 63 34 250 251 243 211 223 55 235 239 260 312
Zr 170 216 273 246 252 235 267 281 164 301 173 180 176 196 300 95 157 221 140
Y 6 11 15 10 10 46 46 52 22 19 50 41 51 69 40 28 25 27 21
Ni 29 11 136 12 18 44 49 41 19 19 62 41 47 53 35 44 56 38 30
Cr 237 636 883 430 404 290 303 38 68 94 295 240 232 139 219 151 133 184 247
V 29 29 30 10 21 72 59 22 39 217 130 120 112 128 251 19 270 92 114
Co 20 4 25 20 21 17 19 16 17 8 36 28 27 29 17 27 28 22 20
Sc 3 3 11 8 9 5 6 7 11 72 20 18 19 20 6 10 15 2 14
Cu 5 7 13 9 10 12 8 25 11 57 17 52 32 29 15 55 39 28 54
La 21.24 24.58 37.63 39.92 23.74 19.8 31.65 52.38 23.41 59.24 50.01 46.68 49.05 53.06 37.73 39.75 57.28 58.52 53.21
Ce 33.98 44.09 60.1 61.5 36.05 115.43 47.7 38.81 30.08 119.32 106.27 105.28 94.17 86.11 39.92 39.98 46.73 42.37 41.58
Pr 3.37 4.67 6.02 5.92 3.55 12 13.23 14.63 6.87 5.21 10.79 9.79 11.24 10.02 10.95 7.55 7.2 10.31 10.76
Nd 12.06 17.65 21.78 20.8 12.72 16.78 25.72 47.22 19.99 49.8 41.56 38.03 39.59 41.34 32.16 28.87 41.12 44.2 43.45
Sm 2.33 2.89 3.23 3.25 2.68 2.86 4.64 9.23 3.43 9.14 8.02 7.78 7.82 7.53 5.76 4.95 6.84 8.64 8.193
Eu 1.4 1.3 2.03 2.25 2.81 1.7 1.9 1.94 0.78 0.58 1.91 1.69 1.8 1.82 1.61 2.38 2.19 2.58 2.12
Gd 3.34 4.8 5.06 4.83 2.95 9.47 10.96 11.19 4.28 3.25 7.58 7.36 7.4 7.09 8.47 6.25 5.52 7.26 6.56
Tb 0.26 0.42 0.47 0.39 0.27 1.57 1.8 1.82 0.65 0.5 0.96 0.93 1.06 0.88 1.42 0.94 0.76 1 0.78
Dy 1.19 2.04 2.54 1.87 1.51 9.8 11.09 11.07 3.76 3.03 6.34 6.28 5.96 5.77 9.17 5.4 4.41 5.41 3.94
Ho 0.21 0.35 0.46 0.33 0.29 1.47 1.66 1.68 0.54 0.44 1.26 1.23 1.03 1.13 1.38 0.8 0.66 0.81 0.62
Er 0.53 0.89 1.21 0.84 0.84 5.09 5.7 5.77 1.77 1.55 3.65 3.62 3.69 3.2 4.74 2.65 2.16 2.67 2.04
Tm 0.07 0.11 0.17 0.11 0.13 0.7 0.75 0.78 0.23 0.2 0.42 0.42 0.58 0.38 0.65 0.34 0.28 0.34 0.28
Yb 0.47 0.78 1.2 0.73 1 5.69 6.15 6.37 1.89 1.67 2.63 2.64 3.66 2.29 5.46 2.82 2.39 2.83 1.64
Lu 0.07 0.12 0.19 0.12 0.19 0.88 0.96 0.98 0.28 0.25 0.58 0.58 0.56 0.51 0.88 0.47 0.42 0.48 0.27
DF 5.19 3.26 2.3 2.4 1.1 –3.5 –2.7 –3.7 –2.6 –3.9 2.8 3.2 2.2 2.1 –3.6 0.8 2.5 2.5 4
DF1 1.96 –0.11 2 1.8 –1.1 –1.7 –0.5 –0.8 –2.5 –1.1 7.8 8.8 5.6 2.1 –2.8 4.4 3.8 4.5 4.3
DF2 5.63 5.36 3 3.4 3 –1.7 –1.7 –1.9 –0.3 –3.1 –1.3 –1.6 –1 1.1 –1.8 –0.4 2.5 2.4 2.5

Note: LOI: Loss On Ignition

Fig. 3.

(a–i) Harker variation plot of selected major elements for TGC, SMB, and BBGB granitoids from CITZ.

In the Harker diagram, most of the sample shows negative correlation of MgO, CaO, MnO, P2O5, TiO2 and Fe2O3 against SiO2 (Fig. 3a–g); however, Na2O and K2O show positive correlation (Fig. 3h, i). The elemental variation in Fig. 3 indicate that most of the elemental ratios have maintained nearly pristine characteristics, although some effects of post crystallization perturbation and limited mobility for some of the elements can not be ruled out.

The studied samples are classified as granodiorite, monzogranite, syenogranite, and tonalite in the QAP normative classification plot (Le Maitre et al., 2002, Fig. 4a); further, in normative An–Ab–Or (after Barker, 1979) diagram, studied samples plot in granite, trondhjemite, granodiorite and tonalite fields (Fig. 4b). Moreover, these are metaluminous to peraluminous (A/CNK = 0.47 to 2.51, avg. 1.16, A/NK = 1.38 to 5.89, avg. 2.43) in composition (Fig. 4c, d).

Fig. 4.

Major element plots for TGC, SMB, and BBGB granitoids from CITZ. (a) QAP normative classification diagram (Le Maitre et al., 2002). (b) An–Ab–Or normative classification (Barker, 1979). (c) SiO2 vs. A/CNK diagram discriminating granitoid rocks into the field of I and S-type (after Chappell and White, 1974). (d) Alumina Saturation Index: A/CNK = molar Al/(Ca + Na + K) vs. Alkalinity Index: A/NK = molar Al/(Na + K) diagram (Maniar and Piccoli, 1989).Symbols are the same as in Fig. 3.

Trace elements including REEs

TGC granitoids

In terms of trace elements, TGC samples show large variation in rubidium contents (29 to 258 ppm), barium content varies from 1189 to 1632 ppm, uranium content varies from 1 to 6 ppm, thorium content varies from 2 to 15 ppm, niobium content varies from 2 to 11 ppm. Strontium content varies from 138 to 375 ppm and the average ratio of K/Rb is 366.

REE patterns depicts moderate LREE enrichment (~100 to 200 times chondrite and average ∑LREE/HREE ratios: 5.73) with an average value of (La/Lu)N = 24.55, (La/Yb)N = 26.68, (La/Sm)N = 6.51 and (Gd/Yb)N = 4.23 (Table 3, Fig. 5a). Primitive Mantle (PM) normalized patterns show enrichment of incompatible trace elements; however, these patterns show depletion of high field strength elements (HFSE: Nb, P, and Ti), and strong positive Pb anomaly (Fig. 5b).

Table 3. Trace and Rare Earth elements (ppm) ratios value of representative samples of granitoids from TGC, SMB and BBGB, CITZ.
Sample B8 B6 BT3a BT3b BT4 MA32 MA34 MA31 MA35 MA36 MA90 MA92 MA93 MA96 MA48 MA62 MA66 MA68 MA79
(Gd/Yb)N 5.53 4.81 3.33 5.19 2.31 1.38 1.48 1.45 1.87 1.61 1.89 1.79 1.67 1.97 1.28 1.83 1.91 2.12 3.07
(La/Lu)N 30.75 22.52 21.01 34.78 13.68 6.39 6.2 6.88 12.2 10.12 10.32 9.24 8.9 11.26 5.68 8.55 10.24 12.92 19.8
(La/Sm)N 5.89 5.49 7.53 7.92 5.71 3.39 3.18 3.41 3.9 3.74 4.25 4.02 3.87 4.55 3.32 2.9 3.37 3.65 4.66
(La/Yb)N 32.13 22.49 22.59 39.17 16.99 6.6 6.49 7.07 11.99 10.06 12.13 10.55 9.15 12.79 6.12 9.59 11.94 14.52 19.86
(La/Nb)N 3.47 2.3 11.36 17.44 3.85 1.84 2.19 2.23 0.79 1.21 11.6 10.29 8.98 10.79 1.6 2.56 1.68 2.79 5.17
(Y/Nb)N 0.15 0.15 0.7 0.67 0.25 0.08 0.09 0.1 0.03 0.05 0.46 0.47 0.36 0.4 0.07 0.1 0.05 0.07 0.11
Sr/Y 23 35 21 22 17 1 1 1 2 13 5 6 4 3 6 9 11 12 10
K/Rb 803 117 307 238 365 172 165 169 368 359 115 124 138 132 171 727 631 628 165
Fig. 5.

(a, c, e) Rock/Chondrite normalized REE patterns and, (b, d, f) Rock/Primitive mantle normalized multi-element patterns for TGC, SMB, and BBGB granitoids from CITZ. Normalization values of chondrite and primitive mantle use after Sun and McDonough (1989).

SMB granitoids

SMB granitoids show rubidium content range from 46 to 228 ppm, uranium contents varies from 2 to 7 ppm, thorium content varies from 8 to 34 ppm, and niobium content varies (5 to 22 ppm). They have strontium content varies from 29 to 251 ppm, the average value of K/Rb is 194 ppm, and barium contents are highly variable from 43 to 2653 ppm.

SMB granitoids have moderate LREE enrichment (~100 to 280 times Chondrite and average ∑LREE/HREE ratios: 4.55, Fig. 5c) with an average value of (La/Lu)N = 9.06, (La/Yb)N = 9.65, (La/Sm)N = 3.81 and (Gd/Yb)N = 1.68 (Table 3). Multi-element plots show enrichment of the incompatible trace elements. However, some of the LILE (K, Rb, Ba, Sr, Eu) show depletion, while Pb shows a strong positive anomaly. The HFSE (Nb, P, Zr, Ti) show negative anomalies (Fig. 5d).

BBGB granitoids

BBGB granitoids show rubidium content varies from 21 to 180 ppm, barium content varies from 179–913 ppm, uranium content varies from 2 to 6 ppm, thorium content varies from 2 to 29 ppm, and niobium content varies from 18 to 31 ppm. Whereas, strontium content varies from 55 to 312 ppm and the average value of K/Rb ratios is 464.

The REE pattern shows moderate LREE enrichment (~150 to 250 times chondrite, average ∑LREE/HREE ratios: 4.86, Fig. 5e) with fractionated patterns, reflected by (La/Lu)N = 11.44, (La/Yb)N = 12.41, (La/Sm)N = 3.58 and (Gd/Yb)N = 2.04 (Table 3). The multi-element plot shows moderate LILE enrichment with wide variations (Fig. 5e). The LILEs like K, Rb, Ba, Sr, Th, and U show depletion. HFS elements like P and Ti show prominent negative anomalies, while Pb shows positive anomaly (Fig. 5f).

Isotope geochemistry

Nd-Sr characterization

The whole rock Nd-Sr isotopic data of Sm-Nd (12 samples), and Rb-Sr (7 samples) are tabulated in Table 4. The fractionation of Sm/Nd ratios ranges from 0.14 to 0.16 and fSm/Nd (–0.51 to –0.56) for TGC, and Sm/Nd ratios ranges from 0.19 to 0.20, fSm/Nd (–0.26 to 0.40) for SMB and the ratio of Sm/Nd ranges from 0.16 to 0.19 with fSm/Nd (–0.41 to –0.43) for BBGB granitoids (whereas, fSm/Nd = [(147Sm/144Nd (sample)/147Sm/144Nd CHUR) – 1] (CHUR = 0.196700, Rollinson, 1993). We consider U-Pb zircon age of 1.6 Ga for the TGC granitoids after Ahmad et al. (2009) and Bhowmik et al. (2011), to calculate initial ratios 143Nd/144Nd (t = 1.6 Ga) and εNd (t = 1.6 Ga) for the present set of data (Table 4). The initial 143Nd/144Nd (t = 1.6 Ga) ratios varies from 0.509961 to 0.510300, εNd (t = 1.6 Ga) ranges from –5.3 to –11.9 with depleted mantle model (TDM) ages (2.20 to 2.78 Ga) for TGC granitoid. The SMB granitoids shows that the initial 143Nd/144Nd (t = 1.6 Ga) ratios are relatively elevated and varies from 0.510232 to 0.510985, εNd (t = 1.6 Ga) ranges from +0.2 to +8.2 for two samples; whereas, εNd (t = 1.6 Ga) values for three samples are –1.8, –4.1 and –6.6, respectively, and Nd model ages (TDM) from 1.5 to 3.0 Ga. However, BBGB granitoids show the initial ratios of 143Nd/144Nd (t = 1.6 Ga) varies from 0.509752–0.510910 and εNd (t = 1.6 Ga) values are +1.1, +6.7 and –16.0 with model (TDM) ages (1.51–3.29 Ga). The Nd isotopic diagrams show the evolution curve of 143Nd/144Nd and εNd against time (whereas, the reference lines for depleted mantle (DM) (Goldstein et al., 1984) and the Chondritic Uniform Reservoir (CHUR, Fig. 6). The observed initial 143Nd/144Nd (t) ratios and a wide range of εNd (t) indicate that the TGC granitoids were derived dominantly from isotopically enriched sources. However, the SMB and BBGB granitoid depicts their derivation from diverse sources, varying from isotopically depleted to enriched sources, although all the studied samples indicate longer crustal residence periods (Fig. 6). Furthermore, the ratios of 147Sm/144Nd (<0.14) show a wide range from 0.08700 (sample B3b) to 0.145400 (sample MA31), typically have depleted mantle model ages ranging from 1.49 to 3.00 Ga. The wide range of 147Sm/144Nd ratios amongst studied samples is very unusual amongst the granitoids that may indicate that the protolith of these granitoids were from heterogeneous crustal/lithospheric sources. However, the uncertainty in calculated depleted mantle model ages may sometime increases due the wide range of ratios 147Sm/144Nd (Arndt and Goldstein, 1987).

Table 4. Nd-Sr isotopic data of TGC, SMB and BBGB granitoid rocks from CITZ.
Sample Sm (ppm) Nd (ppm) Sm/Nd 143Nd/144Nd 147Sm/144Nd fSm (143Nd/144Nd)(t) εNd (t) Age (Ga) TDM (Ga)
B8 1.64 10.40 0.1577 0.511302 0.095270 –0.520 0.510300 –5.2 1.6 2.36
BT3a 2.33 14.48 0.1609 0.511104 0.097241 –0.510 0.510081 –9.5 1.6 2.66
BT3b 2.30 15.95 0.1442 0.511011 0.087013 –0.560 0.510096 –9.2 1.6 2.56
BT4 1.46 9.38 0.1557 0.510952 0.094210 –0.520 0.509961 –11.9 1.6 2.78
MA34 10.94 53.53 0.2044 0.511768 0.122800 –0.376 0.510476 –1.8 1.6 2.20
MA31 11.10 56.82 0.1954 0.511761 0.145400 –0.261 0.510232 –6.6 1.6 3.00
MA90 8.51 44.75 0.1902 0.511954 0.092100 –0.532 0.510985 8.1 1.6 1.49
MA92 8.02 41.56 0.1930 0.511589 0.116642 –0.407 0.510362 –4.0 1.6 2.32
MA48 6.03 31.40 0.1920 0.511802 0.116093 –0.410 0.510581 0.2 1.6 2.18
MA66 4.45 24.16 0.1842 0.510924 0.111420 –0.434 0.509752 –16.0 1.6 3.29
MA68 6.84 41.12 0.1663 0.511793 0.111100 –0.435 0.510624 1.0 1.6 2.00
MA79 6.77 37.14 0.1823 0.512070 0.110285 –0.439 0.510910 6.6 1.6 1.51
Sample Rb (ppm) Sr (ppm) Rb/Sr 87Sr/86Sr 87Rb/86Sr fRb (87Sr/86Sr)i(1.6) εSr (t) Age
MA68 21.20 126.73 0.167 0.723379 0.258400 –0.63 0.717440 –82.0 1.6
MA79 33.51 311.86 0.107 0.720364 0.664400 –0.06 0.705096 –211.7 1.6
MA34 117.11 83.23 1.407 0.805950 1.322200 0.88 0.775565 –376.6 1.6
MA31 127.00 58.98 2.153 0.831941 1.513900 1.15 0.797151 –417.7 1.6
MA90 111.84 285.02 0.392 0.725980 1.137728 0.61 0.699834 –359.7 1.6
MA92 51.79 251.09 0.206 0.720310 0.597705 –0.15 0.706574 –190.5 1.6
MA95 31.02 211.41 0.147 0.699660 0.424392 –0.40 0.689907 –139.2 1.6

Note: The total procedure blank in the laboratory is less than 8 ng of Sr and less than 1 ng for Nd at present. The reported 87Sr/86Sr and 143Nd/144Nd ratios for the samples are the means of about 350 ratios, and the errors are standard errors on the mean. 143Nd/144Nd CHUR = 0.512636, 147Sm/144Nd CHUR = 0.196700 (Rollinson, 1993). The ‘Age’ column refers to the value used in the calculation of initial isotopic compositions. The 1.6 Ga age for the Tirodi gneissic complex is based upon the U–Pb results after Ahmad et al. (2009); Bhowmik et al. (2011). The value of λ = 6.54 × 10–12 yr–1 (Lugmair and Marti, 1978) and λ = 1.42 × 10–11 yr–1 (Steiger and Jager, 1977) for decay constant for Nd and Sr, respectively.

Fig. 6.

(a) Plot143Nd/144Nd vs. Time (Ga) and, (b) Plot εNd vs. Time (Ga) is showing evolution curves for TGC, SMB, and BBGB granitoids from CITZ. The reference lines for depleted mantle (DM) (Goldstein et al., 1984) and the Chondritic Uniform Reservoir (CHUR).

Rb-Sr (whole-rock) for SMB and BBGB granitoids are presented in Table 4. The Rb/Sr ratios ranges from 0.10 to 0.16, and fRb/Sr ranges from –0.15 to +1.5 for SMB. The Rb/Sr ratios ranges from 0.14 to 2.1, and fRb/Sr ranges from –0.06 to +0.88 for BBGB granitoids (whereas, fRb/Sr = [(87Rb/86Sr (sample)/87Sr/86Sr (CHUR) – 1] (CHUR = 0.745), DePaolo, 1988). These analysis has lesser reliability to calculate the model ages because the Rb/Sr ratios can change because of elemental mobility during the alteration and crustal processes such as magmatic differentiation and metamorphism (Möller et al., 1998). SMB and BBGB granitoids show that their initial 87Sr/86Sr (t = 1.6 Ga) ratio varies from 0.699834 to 0.797151 and 0.705096–0.717440, respectively. These initial values of 87Sr/86Sr (t = 1.6 Ga) are greater than the value of 0.706 except for two samples (MA79 = 0.705096 and MA92 = 0.706574); the more elevated values may correspond to the alterations (sample MA31).

Discussion

Nature of the protolith

The precise geochemical results are vitally important to constrain the nature of protolith and understand the crustal evolution of the CITZ. The geochemical characteristics depict that the TGC has higher silica content than the SMB and BBGB granitoids (Table 2). These granitoids are metaluminous to peraluminous with higher concentrations of (A/CNK = 0.47 to 2.51). Total alkalis (K2O + Na2O) in TGC vary from 6.4 to 8.01 wt%, lower in SMB (1.82 to 5.89 wt%) and towards higher side in BBGB (5.22 to 7 wt%) (Fig. 4c, d). Experimental petrology postulates that the partial melting of meta-igneous rocks (I-type) or meta-sedimentary rocks (S-type) (Patiño-Douce, 1999; Clemens and Stevens, 2012) could generate per-aluminous granites. They can also be derived by fractional crystallization from mafic and meta-aluminous magmas and thus belong to I-type (Lee and Morton, 2015). Negative relationships between major oxides (MgO, CaO, Al2O3, MnO, TiO2, Fe2O3) versus SiO2; positive trend of K2O and Na2O against SiO2 (Fig. 3), could indicate primary magmatic characteristics. The negative correlation between P2O5 and SiO2 in the I-type granites may differentiate the meta-igneous rocks-derived melt and restite containing apatite crystals (Chappell, 1999).

It is interesting to ascertain the nature of the protolith of studied granitoids, whether these are related to igneous or sedimentary origin. Discriminant Function (DF) equation derived by Shaw (1972), the equation is only admissible for quartzo-feldspathic rocks with MgO <6% and SiO2 <90%. The calculated positive value of DF indicate igneous origin; whereas a negative value of DF can mark the sedimentary parentage. These values are sometimes subject to debate over elemental mobility; this mobility might change the nature of the original parentage. The present study indicates that BBGB and TGC granitoids depict positive values that suggest their igneous parentage. However, the samples (MA32, 34, 31, 35, and MA36) from SMB granitoids show a negative value; whereas samples (MA90, 92, 93, and MA96) show a positive value that indicates both sedimentary and igneous parentage, respectively for the SMB granitoids. Similarly, the relationship between A/CNK and SiO2 also indicate I-type granite affinity for TGC and BBGB, respectively; however, both (I and S-type) granite affinities for SMB (Fig. 4). Thus, the geochemical evidence discussed above indicates dominantly igneous protoliths for the granitoid of the CITZ.

Partial melting and fractional crystallization

The trace elements show variable enrichments of incompatible trace elements, because of variations in the degrees of partial melting and variably enriched sources. Commonly, the observed large variation in trace elements can not be explained independently through fractional crystallization of various phases from a uniform parental melt (Ahmad and Tarney, 1991). Lower degree partial melting is reflected in the higher concentration of LREE (ƩLREE = 692 ppm, sample MA32), while the higher degrees of partial melting is reflected by the lower abundances pattern (ƩLREE = 221 ppm, sample B8). Thus, the REE and trace elements data indicate that the studied granitoids are derived by varying degrees of partial melting of enriched sources, as indicated by the observed variations in the REE and multi-element patterns with the depletion in HFSE and positive Pb anomalies. Hence, these geochemical signatures suggests the studied granitoids are probably derived from crustal/lithospheric sources. Moreover, the normalized REE patterns for TGC and BBGB samples show somewhat concave upward patterns from MREE to HREE, which could be due to fractional crystallization of amphiboles or it may reflect the presence of amphibole in the residual source (Ahmad and Rajamani, 1988). REE and multi-element plots are used to understand the geochemical characteristics of different groups of granitoids, most of the samples show enrichment of LILEs. However, elements like K, Sr show negative anomalies in granitoids of SMB and BBGB, which suggest K-feldspar fractionation. On the other hand, in some cases e.g. TGC granitoids, elements like K, Sr, and Eu show positive anomalies, which may indicate accumulation of feldspars (orthoclase and plagioclase) in the melt. HFSE such as Zr, Nb, P, Ti, and Th are incompatible elements and are strongly partitioned into magmas, and hence their abundance increases systematically during magmatic evolution. Nevertheless, negative anomalies of Nb, P, and Ti in the case of TGC, may indicate lithospheric/crustal sources and to some extent the fractionation of Ti-magnetite. The wide variation of Ba and Sr may be attributed to a variable degree of partial melting and high content in barium (>2000 ppm) may also suggest the influence of fluid activity (Motoki et al., 2010). In a collisional tectonic environment, magma interacts with the lithospheric/crustal segment and then undergoes crystallization of Ti-rich phases such as rutile, ilmenite, and sphene (Foley et al., 2002).

Partial melting and fractional crystallization are two leading processes to understand the variation in incompatible elements Sr, Rb, and Ba and compatible elements Co, V, Cr, and Ni (Pearce, 1975; Luais and Hawkesworth, 1994). Luais and Hawkesworth (1994) used bi-variate diagrams (Sr, Y, Ba, and Nb against Rb) for granitic rocks. Thus, the trends illustrated on Sr vs. Ba, Sr vs. Rb, and Sr vs. Ba/Sr (Fig. 7a, b, d) indicate that K-feldspar, biotite, plagioclase, and hornblende fractionated out of the parental melts. The trend in Ba against Sr (Fig. 7a) indicates hornblende fractionation or it being the residual phase in the protoliths. However, accessory minerals like ilmenite, Ti-magnetite, apatite, allanite, and monzonite are fractionated during the processes of differentiation which is reflected in La vs. (La/Yb)N (Fig. 7c). The elevated content of Ba (1189–1632) and Sr (138–375) occurring in TGC granitoids may reflect their derivation from the enriched source, probably related to subduction processes. Singh et al. (2019) have reported high contents of Ba (400–2517 ppm) and Sr (184–693) in sanukitoids from Bundelkhand craton, which could suggest their derivation from enriched sources of the subducting slab (Lobach-Zhuchenko et al., 2008).

Fig. 7.

Plots (a) Sr vs. Ba, (b) Sr vs. Rb, (c) Sr vs. Ba/Sr, (d) Sr vs. Ba/Sr for the TGC, SMB and BBGB from CITZ. Vectors showing crystal fractionation of different minerals in figures (a), (b), (c), and (d).

Implication of Nd model ages and time constraints on protoliths

Sm-Nd isotopic studies are often used to evaluate the event related to crustal growth and crust formation age, which define the differentiation of crust from the mantle (Arndt and Goldstein, 1987). Although, the use and misuse of Nd model ages is something that can lead to fictitious information over the development of the crustal growth and reworking (Arndt and Goldstein, 1987). DePaolo (1988) has suggested that fractionation between Sm and Nd occurs during the melt extraction from the mantle source. The partial melting and high-grade metamorphism can slightly affect the Sm/Nd systematic, however, Sm-Nd system is ideal for getting the model mantle extraction age (DePaolo, 1988). On account of granite generated by partial melting of diverse crustal/lithospheric and subsequent differentiation of primary magmas, model age gives the time of mantle fractionation of the more basaltic precursor of the granite. It is a fact that ratios of Sm/Nd do not get disturbed by the process of intra-crustal fractionation (Arndt and Goldstein, 1987). Therefore, the granitoids derived by melting the older continental crust will give model ages, which may indicate the age of the extraction of the protolith from the mantle source. High whole-rock ratios of Sm/Nd (>0.15), usually indicate the excessive fractionation of Sm compare to Nd and bulk mafic composition, possibly occurred under the particular metamorphic or other tectonothermal conditions (e.g., Arndt and Goldstein, 1987; Burton and O’Nions, 1990; Nambaje et al., 2021). The samples of the studied granitoids show (>0.15, except one sample BT3b, Table 4) and Nd model ages (TDM) ranging from 1.49 to 3.29 Ga, the lower model ages overlap the U-Pb zircon ages (1534–1618 Ma; Ahmad et al., 2009; Bhowmik et al., 2011). These results indicate the protoliths in the form of the mafic components extracted from the mantle during the crust forming events during or before 1600 Ma. A wide range of εNd (t = 1.6 Ga) indicate that the studied granitoids are derived from variable mantle/lithospheric sources with a longer crustal residence period (Fig. 6). Furthermore, the initial 87Sr/86Sr (t = 1.6 Ga) ratios vary from 0.699834 to 0.797151 of SMB, and 0.705096 to 0.717440 of BBGB granitoids. The lower 87Sr/86Sr (t = 1.6 Ga) group (<0.706) (sample MA79, 90, and 92) are considered to represent mantle-derived magma generated by varying degrees of partial melting. On the other hand higher 87Sr/86Sr (t = 1.6 Ga) group (>0.706) (Sample MA68, 34, and 31) are indicative of being generated within the crust. Also, the elevated initial 87Sr/86Sr (t = 1.6 Ga) ratios may correspond to the alterations (sample MA31).

The enrichment characteristic of fSm/Nd and fRb/Sr provide the measured deviation in the ratios of Sm/Nd and Rb/Sr of a rock from a model primitive undifferentiated bulk earth source composition (Bielski-Zyskind, et al., 1984). The fractionated ratios of fSm/Nd (–0.26 to –0.56) and fRb/Sr (–0.15 to +1.15) corresponding to the studied granitoids are derived from variable mantle/lithospheric sources. The bi-variate plot between f(Sm/Nd) and εNd(t = 0) (Fig. 8) has been used to evaluate the processes of crustal evolution within the Indian sub-continent. All the studied granitoids show positive trend and plot within the field of “Archaean granitoids and mafic rocks” including the “closepet granite, India” except for one sample from BBGB which plot closer to the “adakites/younger granitoids” field (Fig. 8). The geochemical and isotopic characteristics summarized above may provide enough evidence to establish the relationship amongst the studied granitoids and their protoliths, belonging to the different parts of the Indian shield spanning from Archaean to recent ages. Ahmad et al. (2008) have observed that the same lithospheric sources were involved in many parts of the Precambrian Gondwanaland, presently parts of Asia, South Africa and South America. Moreover, Zhao et al. (2003) also highlighted a direct connection of Columbia between India and North China Craton (NCC) based on the correlation between the Trans North China Orogen (TNCO) along which eastern and western blocks were sutured at both NCC and CITZ. Further, Zhao et al. (2002) have also attempted to highlight a correlation and amalgamation between NIB and SIB along the CITZ.

Fig. 8.

Variation of εNd with ƒ(Sm/Nd) diagram for studied rocks which are plotted in the field of Archean granitoids and mafic rocks, clospet granitoids from south India and adakites and/or younger granitoids. The data have been used after Ahmad et al. (2000, 2008), Clemens et al. (2006), Jahn et al. (1998), Jayananda et al. (2000), Saha et al. (2004), Stern and Hanson (1991), Whalen et al. (2002), Wang et al. (2007), Xiao and Clemens (2007) and Zang et al. (2007).

Conclusions

(1) The TGC, SMB, and BBGB granitoids from CITZ are characterized by granite, trondhjemite-granodiorite, and tonalite. These granitic magmas were generated by diverse sources with significant crustal/lithospheric/crustal components.

(2) Trace element geochemistry indicates the generation of granitic magmas from variably enriched crustal/lithospheric sources followed by dominantly K-feldspar, biotite, and plagioclase and hornblende fractionation from the parental magmas. However, the partitioning of accessory minerals viz. ilmenite, titanomagnetite, apatite, allanite, and monzonite also occurred during differentiation processes.

(3) The wide range of εNd (t) indicate isotopically variable sources dominantly enriched lithospheric/crustal sources and minor components of depleted lithospheric sources, both with longer crustal residence period. Large variation in initial 87Sr/86Sr (t) ratios is considered to comprise mantle-derived magma with varying degrees of partial melting of the enriched but diverse source.

(4) The Nd (TDM) model ages of TGC, SMB, and BBGB granitoids are (2.36 to 2.78 Ga), (1.49 to 3.00 Ga), and (1.51 to 3.29 Ga), respectively. The lower model ages overlap U-Pb zircon ages (1534–1618 Ma; Ahmad et al., 2009; Bhowmik et al., 2011), and may indicate that these rocks formed from the material extracted from the crustal/lithosphere during the crust forming events during or before 1600 Ma (Fig. 9a–e).

Fig. 9.

A tectonic cartoon model for the CITZ evolution modified after Roy and Prasad (2003) (a–e) showing evolution of the terrain at different phases and emphasized on the continent-continent collision related granitic magmatism. Abbreviations: BKC - Bundelkhand craton; BC - Bastar craton; BBGB - Bhandara-Balaghat Granulite Belt; SNNF - Son-Narmada North Fault; SNSF - Son-Narmada South Fault; MGB - Makrohar Granulite Belt; RKG - Ramakona-Kattangi Granulite.

(5) Geochemical and isotopic results may suggest that the studied granitoids plutons had links with the felsic magmatism during Columbian crustal assembly. They were also influenced by the evolution of the larger Indian landmass (Indian Peninsula) and the disintegration of the Columbia supercontinent.

Acknowledgments

Constructive reviews by the Editor and two anonymous Reviewers gratefully acknowledged. TA thanks the Department of Science and Technology (DST), Government of India for financial assistance for project No. SR/S4/ES-402/2009. TA also thanks the SERB support through J.C Bose Fellowship during the compilation of this work. We thank the Head, Department of Geology, University of Delhi and Director, IIT Roorkee for providing the analytical facilities at the Department of Geology and National Facility for Isotope Geology and Geochronology at Institute Instrumentation Center, IIT Roorkee. We are also thankful to Shri Kamal Singh for keeping the TRITON healthy and to Ms. Poornima Saini for maintaining the cleanliness of the chemistry laboratory. We thank all the members of Isotope Geology Laboratory, Russian Academy of Sciences, Apatity, Russia.

References
 
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