Introduction

The geological evolution of magmatic rocks and their high-precision U-Th-Pb geochronology provides a significant stimulus for reconstructions of ancient supercontinents, namely the Paleoproterozoic Columbia (Rogers and Santosh 2005; Rogers 2009; Zhao et al. 2011; Meert and Santosh 2017), the Mesoproterozoic Rodinia (Hoffman 1991; Dalziel et al. 2000) and Neoproterozoic/Cambrian Gondwalanand (Collins and Pisarevsky 2005; Meert et al. 2013, 2017).

There is a general agreement that the Indian continent was an integral part of a Palaeo-Mesoproterozoic supercontinent, Columbia, that existed between 1900 and 1800. The Paleoproterozoic collisional orogenesis that framed the architecture of Columbia supercontinent for the Indian peninsula has been studied from the Satpura orogeny in Central India (Bhandari et al. 2011; Bhowmik et al. 2012; Bhowmik 2019), Aravalli-Delhi Orogeny in north-western India (Saha et al. 2008; Bhowmik et al. 2009; Kaur et al. 2013a), and the trans-north china orogen in China (Zhao and Zhai 2013). Also, the Paleo-Mesoproterozoic tectono-thermal activities related to Columbia assembly has been studied from the 1900–2000 Ma Capricorn orogen in western Australia (Van Kranendonk and Collins 1998), Nimrod Orogeny in Antarctica (Goodge et al. 2001; Goodge and Fanning 2016), the Kimbam Strangways orogeny in central Australia (Payne et al. 2009) and the Trans-Hudson Orogen in northern America (Hoffman 1988; St-Onge et al. 2007).

In the Indian peninsula, the high-grade rocks and granite magmatism in the Central Indian Suture (CIS) and its extension towards the east, and the Aravalli-Delhi Fold-Belt in north-western India, and the tectonic domains at the southern and eastern margin of Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC) respectively, record evidence of Paleoproterozoic metamorphism that constitutes the framework of supercontinent Columbia in Indian perspective (Fig. 2, Chatterjee and Bhattacharji 2001; Kaur et al. 2007; Saha et al. 2008; Chatterjee and Ghose 2011; Kaur et al. 2011b, 2013a, 2015; Bhowmik et al. 2012; Sanyal and Sengupta 2012; Harley and Nandakumar 2016; Liu et al. 2017; Prakash et al. 2018; Bhowmik 2019). Also, researchers, as Upreti (1999); Miller et al. (2000); Richards et al. (2006); Chambers et al. (2009); Singh et al. (2009); Kohn et al. (2010); Phukon et al. (2018); Sen et al. (2019); and Singh (2020) document 2100–1800 Ma magmatic activity and granite emplacement from various stratigraphic levels from of Lesser Himalayan (LH) sequences. The geochemistry of LH granites and U-Pb zircon ages in the Himalaya are variably interpreted either as A-type granites that were emplaced during Columbia disintegration (Singh et al. 2009; Larson et al. 2019; Singh 2020) or mostly S-type granites that were emplaced at lower crustal levels during the final amalgamation of Columbia in a subduction zone settings (Chambers et al. 2008; Kohn et al. 2010; Kaur et al. 2013b; Sen et al. 2013; Phukon et al. 2018). Miller et al. (2000); Chambers et al. (2008); Kohn et al. (2010); Phukon et al. (2018); Pathak and Kumar (2019); Sen et al. (2019); and Mukherjee et al. (2019) provide geochemical and geochronological evidence supporting subduction zone tectonics and related magmatism in the LH sequences. Also, Kaur et al. (2009, 2011b) correlated the granites from the Aravalli craton with the LH granites and suggested LH granites were emplaced in a volcanic arc along North Indian Cratonic Block (NICB). However, Larson et al. (2019); Singh (2020) reported contradictory geochemical evidence supporting a rift-related passive margin.

The Aravalli craton and the Bundelkhand craton as part of NICB, the Dharwar, the Bastar, and the Singhbhum craton, as a part of South Indian Cratonic Block (SICB), amalgamated along the Central Indian Tectonic Zone (CITZ) to constitute the tectonic framework for traditional Columbia in Indian perspective. In the absence of reliable paleomagnetic data, the traditional Columbia reconstruction after Rogers and Santosh (2002) and Zhao et al. (2002) are principally based on chronologically correctable tectonic activities from the SICB as precise geochronological and metamorphic data from the NICB are meager. For example, the Mahanadi-Lambert rift in India-Antarctica landmass and rift basins in the western margins of present-day (North America Belt and Unita Trough) are temporarily correctable (Fig. 7.8 of Rogers and Santosh 2002). Accordingly, Rogers and Santosh (2002) placed eastern India adjacent to the western margin of North-America. Zhao et al. (2002) correlate 2100–1800 Ma geological data across major landmasses, supporting the traditional Columbia hypothesis.

Even after two decades of extensive research and its role in supercontinent assembly and destruction processes, the tectonic evolution of the CITZ is debatable. The critical metamorphic ages from CITZ fall at 2500 Ma, 1600 Ma, and 1000 Ma. Stein et al. (2004) suggested NICB and SICB suturing occurred at 2500 Ma, followed by reworking at 1600 Ma and 1000 Ma. Basu Sarbadhikari and Bhowmik (2008); Bhandari et al. (2011); Mandal et al. (2013) contradict Stein et al. (2004) model and favor a 1600 Ma orogenesis involving SICB and NICB.

Hou et al. (2008) correlate the occurrences of 1800 Ma dyke swarms from North China Craton, SICB, and North America and suggest that these three cratons were united to form a landmass before its breakup at 1400–1300 Ma. In support of the growth of 1850 Ma Columbia supercontinent, Hou et al. (2008) suggest the occurrences of a subduction zone along the northern margin of NICB that was probably continuous with subduction zones along the south-eastern margin of North America, Greenland, Baltica to North-China craton - eastern Antarctica (Fig. 7 of Hou et al. 2008).

Meert and Santosh (2017) utilized the palaeomagnetic data to validate the traditional Columbia configuration. The paleomagnetic data imply Siberia, Laurentia, and Baltica constitute the coherent long-lived core (1900–1300 Ma) for the Columbia supercontinent (Evans and Mitchell 2011). However, in the absence of 1800–1600 Ma paleomagnetic data from the Indian subcontinent, the position of Indian in the Columbia framework remains problematic. Meert and Santosh (2017) placed India at a considerable distance from present-day Laurentian and close to Baltica based on ~1465 Ma Lakhna pole from SICB.

The absence of reliable geochronological and geochemical data from the northern extremity of the Indian shield leads to three possible scenarios: (i) India-Madagascar-Kalahari-Zimbabwe-Australia, and parts of Antarctica formed a single continental block that occurred along the eastern margin of North America (Rogers and Santosh 2002; Fig. 1a), (ii) India and North China craton occurred close to each other along the western margin of East Antarctica and that the Trans-North China Orogeny was linked to Central Indian Tectonic Zone (Zhao et al. 2002), Fig. 1b), (iii) closely associated North China Craton and India occurred along the western margin of North America (Hou et al. 2008; Fig. 1c). However, none of the models address the nature of the tectonic boundary at the northern margin of NICB due to a lack of well-constrained P-T-t conditions of tectonic events related to supercontinent assembly.

Fig. 1
figure 1

a-c Different configurations of Paleoproterozoic supercontinent Columbia after Roger and Santosh (2002), Zhao et al. (2002), and Hou et al. (2008), respectively

Full size image

The present study is based on a comprehensive set of geochemical data from Paleoproterozoic granites and SHRIMP geochronology: It aims at establishing P-T conditions of granite emplacement and probable P-T conditions for magma generation from the Wangtu Gneissic Complex, Sutlej Valley. These data will augment the Paleoproterozoic tectonic evolution of the north-Indian continental margin.

Geological setting

General geology of Himalaya

The Himalaya in India’s north-east is one of the world’s active and youngest orogenic mountain belts (Fig. 2). A spectacular assemblage of metasedimentary and meta-igneous/volcanic rock exposed in the Himalayan range preserves the Precambrian to recent P-T-t evolutionary history lower-middle crustal rocks during the repeated continental collision (Fig. 2). Gansser (1964); Windley (1985); and Valdiya (2016) suggested a threefold lithodemic classification of the Himalayas from south to north, namely the Lesser Himalayas (LH), the Higher Himalayan (HH) crystallines, and the Tethyan Zone (TZ). The LH rocks are separated from the sub-Himalayan Miocene-Pliocene molasse deposits by the Main Boundary Thrust (MBT). The Main Central Thrust (MCT and its equivalents) separate the LH and HH rocks. The HH rocks are bound to the north by the Tibetan Detachment system, north of which lies the Tethyan series (TS) marine sediments. The higher and lower Himalayan sequences are distinct lithodemic units in the Himalayan orogens, and the high-grade HH rocks are sandwiched between the low-grade LH and TS rocks in the south and north, respectively (Chakrabarti 2016; Valdiya 2016).

Fig. 2
figure 2

Generalized geological map of Himalaya showing the distribution of Proterozoic granitoids represented by a star (modified after Yin, 2006; French et al. 2008; Singh et al. 2009; Kohn et al. 2010). The corresponding radiometric emplacement ages are given in Table 1

Full size image

Ahmad et al. (2000) identified an intra-formational thrust in the LH rocks from the western Himalaya that separate the fossiliferous rocks of inner lesser Himalaya (1900–1600 Ma) from the Cambrian fossiliferous rocks of the outer Lesser Himalaya (~ 500 Ma, summarized in Richards et al. 2005). Le Fort (1975); Brookfield (1993); Upreti (1999); Gehrels et al. (2006); Saha (2013), and Larson et al. (2019) suggested that the protoliths of LH metasedimentary rocks represent a basinal sequence that was deposited on the passive margin of the northern extremity of the Indian peninsula. The HH rocks represent an ensemble of high-grade metamorphic rocks and granites that were emplaced between 680 and 480 Ma (Singh 2020). Valdiya (2016) suggested an intra-basinal marginal thrust (MCT) separates the lower grade HH rocks from the higher grade HH rocks. Jain and Manickavasagam (1993; Harrison et al. (1997) interpreted MCT as several hundreds of kilometer-wide high-strain zones that developed a wide range of P-T conditions during the Himalayan orogeny.

Basic volcanic and granites intruded the LH rocks at various stratigraphic levels (Kohn et al. 2010). The mafic-volcanic bodies are similar in compositions to basalts generated in a plume setting (Bhat et al. 1998; Ahmad et al. 1999; Ahmad 2008). Bhat and Le Fort (1992) reported Sm-Nd whole rock isochron, 2509 ± 94 Ma from basic volcanics exposed in the Kulu-Rampur area, western Lesser Himalaya. Bhat and Le Fort (1992) Bhat et al. (1998); Ahmad et al. (1999), and recently Larson et al. (2019) correlated mafic volcanism with rifting in the North Indian continental crust during Archean-Proterozoic transitions. Singh and Jain (2003) and Singh et al. (2003, 2009) identified the 2000–1800 Ma granites from the western Lesser Himalaya as within plate A-type granites that were emplaced during the rise of a Proterozoic mantle plume in a rift-related tectonic setting. In a contrasting view, Miller et al. (2000); Richards et al. (2005, 2006); Kohn et al. (2010); Phukon et al. (2018), and Pathak and Kumar (2019) suggested the existence of an extensive Paleoproterozoic arc based on the geochemical data from granites and geochronology of zircons from granites and adjoining metasedimentary rocks from Bhutan-Arunachal, Nepal and western Lesser Himalaya.

Wangtu Gneissic Complex

The present study area lies along the Sutlej valley, Himachal Pradesh, where granitic rocks are exposed in and around Chaura, Taranda, Wangtu, and Karcham towards the north-eastern direction of amphibolite-grade meta-sediments known as the Jutogh group (Fig. 3a; Miller et al. 2000; Richards et al. 2005). Jutogh group is bounded by the Munsiari and Vaikrita thrusts. It has been variously assigned either to the Lesser Himalayan Sequences (Ahmad et al. 2000) or to the Greater Himalayan Sequence based on the metamorphic grades (Jain and Manickavasagam 1993; Singh et al. 2009). The WGC has been subject to several structural, geochemical, and geochronological studies. Jain and Manickavasagam (1993); Singh (1993); Singh et al. (2009); and Sen et al. (2013) documented two-stage folding and deformation in WGC. The first folds are mostly upright with NW-SE vergent fold closures and probably formed simultaneously with the significant Himalayan thrust forming events. The D2 folds have a nearly orthogonal axis with the D1 folds and formed during late- Cenozoic events.

Fig. 3
figure 3

a Generalized lithological map of Wangtu Gneissic Complex (WGC, after Vannay and Grasemann 1998) with modification from authors own field observation. The red and black filled circles mark the sample locations. Black circles represent samples used for the SHRIMP study; b Field photograph showing clasts of plagioclase feldspar and quartz, which impart the rock’s leucocratic appearance; c Hand specimen of porphyroclastic granitic gneiss near Karcham area where the biotite flanks the undeformed clasts; d paleosol (schist) and quartzite horizon within the WGC; e Mafic enclaves within the WGC. HHCS = Higher Himalayan Crystalline Sequence; LHCS = Lesser Himalayan Crystalline Sequence; LHS = Lesser Himalayan Sequence; STDS = South Tibetan Detachment System; MCT = Main Central Thrust; MT = Munsiari Thrust; CT = Chail Thrust

Full size image

Initially, the WGC rocks have been classified to be with peraluminous-meta aluminous chemical signature (Rao et al. 1991, 1995; Singh et al. 2009). Sen et al. (2013) documented the variation in the chemical composition in WGC. They suggested that the chemical composition of WGC locally resembles I-type granite, although a significant portion of the same resembles S-type granite of Chappell and White et al. (2001). Singh et al. (2009) reported U-Pb zircon ages of 1866 ± 64 Ma with a single point U-Pb analysis that yield an older age of ~3000 Ma from the WGC. Miller et al. (2000) obtained a Pb-Pb evaporation age of 1840 ± 16 Ma and 1800 ± 13 Ma from meta-rhyodacites and metabasalts, respectively, from the Kullu-Rampur Window. A much younger Ar-Ar age of 9.3 ± 0.3 Ma from biotite probably marked the doming of WGC during the Himalayan orogeny (Tripathi et al. 2012; Sen et al. 2013). Pant et al. (2006) reported a Paleoproterozoic metamorphic field gradient preserved in the Jutogh metasediments in the Jeori-Rampur-Wangtu section. The Paleoproterozoic contact metamorphism is correlated with the emplacement of 1800 Ma granites adjacent to the Jutogh metasediments.

Samples and analysis

Sample description

The studied samples were collected from the Wangtu Dam, Sutlej Valley. They consist of medium- to coarse-grained, porphyroclastic granitic gneiss (Fig. 3a). K-feldspar, plagioclase feldspar, and quartz are the major porphyroclast that impart a leucocratic appearance to the rock (Fig. 3 b, c). Locally biotite and hornblende are present as accessory minerals. Biotite flakes warp around the undeformed feldspar porphyroclasts (Fig. 3c). The WGC contains numerous xenoliths of highly foliated rocks and paleosol horizons (Fig. 3d). Several mafic dikes intruded into the WGC (Fig. 3e).

Sample preparation

Powdered whole rock from each sample was used for major, trace, and rare earth analysis. The samples were cleaned by 0.01 N HCl, dried, and subsequently crushed by using a jaw breaker. After coning and quartering the crushed samples, the reduced sample was pulverized in a planetary ball mill.

The observed samples do not exhibit any distinct lineation; petrological thin sections were prepared using rock-chips cut in orthogonal directions to foliations. The rock chips were polished using silicon-carbide powder. The polished rock-chips were mounted in glass slides using Epoxies. Subsequently, the mounted chips were cut using a Buhler make Petrothin machine to achieve the desired thickness. The rough petrological thin sections were polished using micro-diamond suspension liquid.

Zircon grains were separated from sieved whole-rock powder using hydraulic, magnetic, and heavy liquid techniques and were finally handpicked under a binocular microscope. Selected grains were mounted in epoxy together with FC1 (Duluth gabbroic anorthosite, 1099 Ma; Paces and Miller 1993) and SL13 (Sri Lankan gem zircon; U = 238 ppm) reference zircon samples, and ground and polished to expose internal textures. Before analysis, the grains were inspected under an optical microscope and photographed.

Analytical details

Major element oxides were analysed using a Phillips MagiX PRO Model 2440 X-ray fluorescence (XRF) spectrometer. Pressed pellets were prepared by weighing 2 g of finely powdered samples and standards in collapsible aluminum cups filled at the bottom with 2.5 g of boric acid. The cup and the powdered samples/standards were pressed under a hydraulic pressure of 25 t to obtain the pellet. International rock reference materials from the United States Geological Survey (USGS) and the Geological Survey of Japan were used to construct major elements’ calibration curves. Simultaneously, the pressed pellets of samples and geochemical reference materials were loaded and analysed to control the analysis’s accuracy (Krishna et al. 2007). The precision and accuracy of the analysis were 2% relative standard variation (RSD) for almost all the major oxides.

Trace-element concentrations were determined using inductively coupled plasma-mass spectrometry (ICP-MS) analysis, following the protocol of Satyanarayanan et al. (2018). For trace and rare earth elements (REE), solutions from the homogenized powder were dissolved in reagent grade HF: HNO3 acid mixture in Savillex screw-top vessels. 25 ml Savillex Teflon pressure decomposition vessels were weighed with an aliquot (0.05 g) of the homogenized powdered sample. 10 ml of an acid mixture (containing 7:3 HF:HNO3) was added to each sample. 103Rh solution (0.5 ml of 10 mg/mL) was added to each sample as an internal standard. The vessels were tightly closed and kept on a hot plate at ~140 °C for 48 h after complete swirling. The solution was evaporated to incipient dryness after adding 1 mL of HClO4 to ensure complete HF removal from the mixture. The residue was dissolved by adding ultra-distilled water in 20 ml of 1:1 HNO3 and brought to a final volume of 250 ml. The sample batch was prepared with the geochemical certified reference material JG-1A along with a couple of blanks. Solutions were analyzed using a Nu Instruments Attom high resolution inductively coupled mass spectrometry (HR-ICP-MS) system opaerated in jump-wrapping mode at a moderate resolution of 300, which allowed us to measure precisely all analytes of interest. A solid-state 1.6 KW radio frequency (RF) generator running at 27.12 MHz was used by the ICP source. A software program is used for RF matching and tuning of the torch box. Mass flow controllers were used to getting a stable plasma gas control. The operating parameters include 4313 V for focus lens voltage, 2990 V extraction lens voltage, Ar flow rates of 1.076 L/min for samples and 0.9 L/min for Auxiliary flow, and 1300 W forward and reflected power (1300 W. Parameters were optimized carefully for maximum sensitivity and accuracy. The instrument tuning was performed using one ng/mL multi-element (Li, Be, Mg, Sc, Co, Y, In, Cs, Tb, Tm, Pb, U). The precision and accuracy are better than 3% RSD for most of the measured elements.

Back-scattered electron (BSE) images were obtained by means of a ZEISS Gemini scanning electron microscope (SEM) operated at 20 kV and 478 pA. Silicate minerals of WGC samples were analyzed using a CAMECA SX-100 electron probe micro-analyser (EPMA). The following analytical conditions were applied: accelerating voltage 15 kV, beam current 15 nA, and beam diameter 1–5 μm. A LaB6 cathode was used. The following reference materials were used for calibration: MgO for Mg, apatite for Ca, haematite for Fe, rhodonite for Mn, orthoclase for K, rutile for Ti, albite for Na and Si, and almandine for Al.

BSE and cathodoluminescence (CL) images of zircon grains were acquired using a JEOL (JSM 6610) SEM. The accelerating voltage is set to 15 kV and the beam size to 60 μm. For the SHRIMP analysis, a 2.5–2.8 nA mass filtered O2− primary beam was focused to a spot of approximately 25 μm diameter on the polished surface of the target zircon grain. Each spot was rastered with the primary beam for about 2 min before the analysis and then analyzed five cycles with a single electron multiplier. During one cycle, the magnet was stepped through nine peaks of 90Zr216O (counting time = 2 s), 204Pb (10 s), 206Pb (10 s), 207Pb (20 s), 208Pb (5 s), 238U (5 s), 232Th16O (2 s) and 238U16O (2 s) and 204.1 (10 s; background-position). Data processing was conducted using SQUID 2.50 (Ludwig 2009) and the Concordia plots produced using Isoplot 3.75 (Ludwig 2012) programs, running under Excel 2003. Weighted mean ages of zircon were calculated using 207Pb-corrected 206Pb/238U ratios after excluding outliers under statistical t-test and reported at 95% confidence. Correction for common Pb was done using the 207Pb (for dates <1000 Ma) or 204Pb (for dates >1000 Ma) methods, respectively, based on the model by Stacy and Kramers (1975).

Data generation

Since garnet is notably absent in the studied samples, frequently cited net-transfer and exchange reactions could not be utilized to determine the P-T conditions for granite emplacement. Nevertheless, the peak temperature is estimated using empirical expressions involving zircon saturation in silicate melt (Gervasoni et al. 2016) and compared temperature calculated using thermodynamic expressions involving Ti incorporation in biotite (Henry et al. 2005; Wu and Hongxu 2014).

P-T pseudosection is also constructed using PERPLEX (Connolly 2009) to constrain the magmatic assemblages’ P-T conditions in granites. Thermodynamic data of mineral phases are adapted from Holland and Powell (2011) and its subsequent modifications (hp633ver.dat). The activity-composition relationships for plagioclase, melt, biotite, white mica are adopted from Newton et al. (1980); Holland and Powell (2001); Coggon and Holland (2002); and Tajčmanová et al. (2007), respectively, for calculating the phase-relationship in granite. As biotite and K-feldspar are present in the studied samples, the amount of H2O is adjusted from biotite’s modal abundances in the studied samples. In the first step, ten petrological thin sections of granites were scanned in a SEM to estimate the relative proportion of biotite compared to K-feldspar. Since biotite and K-feldspar are only minerals to contain K2O as a major component, and plagioclase feldspar is likely to contain K2O < 1 wt%, the total K2O content in the studied sample is adjusted based on the relative modal abundances of biotite and K-feldspar. As the maximum amount of volatiles (OH, F) present is twice to cations (K, Na, and Ca) present in the I site of ideal biotite stoichiometry (Deer et al. 2013), the reallocated molar K2O for biotite is doubled to estimate the minimum amount of H2O, required to stabilize biotite with predicted abundances similar to the amount of biotite present in the studied samples. The molar albite fraction of plagioclase [(Na/Na + Ca + K)  Χ100] and Fe# of biotite [(Fe/Fe + Mg)  Χ100] was calculated to constrain the P-T conditions of granites.

Generally, the magma generated from the partial melting of lower crust and mantle ascent upward to cool down and crystallize magmatic phases. Thus, the emplacement P-T conditions may not be similar to the P-T conditions at which magma was generated. Since S-type granites are mostly derived from sedimentary sources (Chappell and White 2001), the adjoining Jutogh metasediments’ chemical composition is approximated for the source materials for the present study (Chambers et al. 2008). The thermodynamic data and minerals solution models for garnet, staurolite, biotite, mica, cordierite, plagioclase, and melt are adapted from the activity-composition relationship defined specifically for metapelite by White et al. (2007) to model phase relations in Jutogh metasediments. Quartz is assumed to be excess. As mica and biotite are the abundant hydrous minerals in metapelites, the H2O is adjusted for just-saturation for mica and biotite stabilization. The modal abundances of silicate phases, and weight fractions of SiO2, Na2O + K2O, and Al2O3/(Na2O + K2O), were modeled to constrain the P-T conditions for magma generation. In all the calculations, all Fe is assumed to be Fe2+ that may lead to a pseudo-stabilization of garnet in the computed phase diagrams (White et al. 2000; Tinkham et al. 2003).

Results

Geochemistry

A summary of the geochemical analysis of ten representative samples from WGC is given in Table 1. Results of geochemical analysis of individual samples are provided in Table S1 in electronic supplementary material (ESM). The studied granites are calc-alkaline in composition (Fig. 4a; Irvine and Baragar 1971). The SiO2 and Al2O3 content of the studied sample varies between 69 and 72 wt% and 13–15 wt%, respectively. The Fe2O3t content of the same samples varies between 2 and 6 wt%. In contrast to higher Fe2O3 content, the granites are poor in MgO content (0.5–2.5 wt%). Regarding the alkali element content, the Na2O and K2O vary between 2.16–3.11 wt% and 4.13–6.21 wt%, respectively, with K2O/Na2O ratio between 1.5–3.3. The CaO content is variable between 1.0–2.5 wt%. The TiO2 and P2O5 content are <1 wt%.

Table 1 Available geochronological information for Paleoproterozoic magmatism across the Himalayas
Full size table
Fig. 4
figure 4

Geochemical classification diagram for WGC samples. a A (Na2O + K2O) – F (FeOt) – M (MgO) triangular diagram (after Irvine and Baragar 1971); b A/CNK – A/NK bivariant plot after Shand (1943), discriminating metaluminous, peraluminous, and peralkaline compositions; c-d Primitive mantle normalized trace elements variation diagram, and chondrite normalized rare- earth element plots for WGC samples, respectively. Normalization factors are from Sun and McDonough (1995). Shaded symbols represent samples used for geochronological studies

Full size image

In the total alkali versus silica diagram (Middlemost 1994), data obtained from the samples studied herein plot between the quartz-monzonite and granite fields (Fig. S1a in ESM). The A/CNK of the studied samples is scattered between 0.94–1.54, with an average value of 1.20. Accordingly, in an A/CNK versus SiO2 plot, a majority of the samples with A/CNK > 1.0 concentrate in the peraluminous field resembling S-type granites, although a small set of samples with A/CNK < 1.0 concentrate in the meta-aluminous area resembling I-type granite (Fig. 4b). In a K2O versus SiO2 plot, the studied samples are classified as shoshonite (Fig. S1b in the ESM). The scattered A/CNK values of the studied samples probably indicate variable sources for the origin of WGC.

In a primitive mantle normalized trace element plot (McDonough and Sun 1995), the WGC is characterized by a positive K anomaly and a negative Nb-Ti-Ta- anomaly (Fig. 4c). The total REE content (ƩREEs) of studied samples varies between 157.48–491.36. In an REE normalized spider diagram (McDonough and Sun 1995), the (La/Lu) N and LaN/SmN vary in the ranges 7.72–21.63 and 2.63–5.02, respectively, with pronounced negative Eu anomaly (Table S1 in the ESM, Fig. 4d) (Table 2).

Table 2 Major oxides, trace and rare-earth-elements content, of representative WGC samples (number of samples =10)
Full size table

Petrography and mineral chemistry

In-situ mineral chemical analysis of representative samples is given in Tables 3, 4 and 5. K-feldspar, plagioclase, and biotite are the major minerals in the studied samples. Zircon, apatite, and iron-oxides (hematite) occur as accessory phases. The central part of WGC is mostly undeformed, although the intensity of deformation increases towards HH-WGC contact in the north near Karcham. In the relatively undeformed variety, plagioclase (ab mol% = 70–78), K-feldspar (Or mol% = 85–90) occur porphyroclast in a moderately fine-grained groundmass of K-feldspar and quartz. Plagioclase grains are mostly tabular (average grain size ~50–75 μm), undeformed, and exhibit lamellar twins. Spindle-shaped deformation band and twin-lamellae are notably absent in plagioclase. Quartz grains are relatively coarser (average diameter ~ 200 mm) and exhibit wavy grain boundaries, chessboard twinning, and undulose extinction. Discontinuous biotite flakes (Mg# = 28–30) wrap the porphyroblasts. In the plagioclase rich domains, the biotite flakes are mostly parallel to the lamellar twin lamellae. The Fe# and TiO2 of biotite vary between 70 and 73 and 2.89–3.83 wt%, respectively. Myrmekite occurs at the plagioclase and K-feldspar grain boundary. White-mica is mostly muscovite with Si between 3.01–3.02 apfu (based on 11 O atoms per formula unit).

Table 3 Chemical compositions (EPMA results), calculated mineral formulae and calculated end-member fractions for plagioclase and K-feldspar from representative WGC samples
Full size table
Table 4 Chemical compositions (EPMA results), calculated mineral formulae and calculated end-member fractions for biotite from representative WGC samples
Full size table
Table 5 Chemical compositions (EPMA results), calculated mineral formulae and calculated end-member fractions for muscovite and ilmenite from representative WGC samples
Full size table

P-T conditions for magma emplacement

Single element thermometers

The Ti saturation in magmatic zircon yields crystallization temperature ~ 650–750 °C (Fig. 5a). The TiO2, FeO, and MgO content of biotite from the studied sample point towards the magmatic origin (Fig. 5b, Nachit et al. 2005). The TiO2 content and Mg# of biotite yield temperature 680 °C ± 50 °C, between a pressure range of 0.4–0.6 GPa (Henry et al. 2005). Empirical formulations after Wu and Hongxu (2014) estimate temperature ~ 700 ± 50 °C and 850 °C ± 50 °C at pressure 0.5 GPa and 1.2 GPa, respectively (Fig. S2 in the ESM).

Fig. 5
figure 5

a Zr abundance in WGC rocks compared with Zr saturations contours computed for temperature 550–750 °C from empirical formulations (Grevasoni et al. 2016). The Zr content and G values of studied samples reflect Zr saturation of WGC between temperature 550–750 °C. b TiO2-MgO-FeO tripartite plot for WGC biotites (Nachit et al. 2008)

Full size image

P-T pseudosection analysis

The phase topology constructed for the WGC sample (WG-49B) between temperature 600–900 °C and pressure 0.5–1.4 GPa is shown Fig. 6a. In the P-T pseudosection, the assemblage plagioclase+biotite+mica+san + melt is stable at temperature < 700 °C for pressure 0.5–1.4 GPa. An increase in temperature > 800 °C leads to the destabilization of biotite by stabilizing garnets and sillimanite. Since the studied sample does not contain garnet or sillimanite, the “garnet-in” and “sillimanite-in” marked the maximum pressure and temperature the rock has experienced. Figure 6b shows the modeled chemical parameters for plagioclase and biotite. The modeled ab mol% isopleths have a relatively shallow slope with an increasing value towards higher pressure. The modeled Fe# of biotite has a steep slope with an increasing Fe# towards higher temperatures. The intersection of modeled compositional isopleths corresponding to the measured composition intersects at temperature ~ 700 °C and pressure ~ 1.0–1.1 GPa. Thus, the P-T conditions obtained from isopleth thermobarometry correspond to a geothermal gradient of 750 °C/GPa (Brown 2008).

Fig. 6
figure 6

a The results of P-T pseudosection analysis using whole-rock bulk composition (molar Na2O: 2.75, CaO: 1.40, K2O: 3.68, FeO: 3.51, MgO: 0.94, Al2O3: 10.09, H2O: 5.80, SiO2 saturated) for sample WG-49; b The modeled composition of plagioclase and biotite. A grey filled box marks the P-T condition obtained from the intersection of feldspar and biotite compositional isopleths

Full size image

Magma parental to the S-type granite originate due to the partial melting of the supracrustal rocks that have been developed through one or more cycles of weathering of the parental rocks (Chappell and White 2001). Chambers et al. (2008) document a Paleoproteorozoic (1810 Ma) crustal anatexis in the Jutogh metasediments. On a similar approach, several researchers, e.g., Chambers et al. (2008); Kohn et al. (2010), suggested the melting of metapelites to explain the origin of Paleoproterozoic S-type granites in the LH. However, none of the authors address the degree of partial melting of metapelites and the P-T conditions of magma generation. Thus, to address the physical conditions of magma generation, the melting of the averaged whole-rock chemical compositions of Jutogh metapelite (Chambers et al. 2008) is modeled using PERPLEX (Connolly 2009).

The phase topology for the Jutogh metasediments in the temperature range of 600–1000 °C and pressure 0.5–1.4 GPa is shown in Fig. 7a. The P-T pseudosection is divided into three distinct domains, i.e., HP-LT kyanite bearing domains, HT-HP sillimanite bearing domains, and HT-LP cordierite bearing domains. In the sillimanite bearing domains, the assemblage mica-biotite-plagioclase-sillimanite-staurolite (Pant et al. 2006) is stable in a narrow field at temperature < 650 °C, pressure 0.6–0.7 GPa. Staurolite is unstable with a change in P-T conditions, and mica-biotite-plagioclase-sillimanite (without staurolite) becomes stable at temperature > 650 °C, between pressure 0.5–0.7 GPa. Similarly, an increase in pressure > 0.7 GPa at temperature < 650 °C leads to the stabilization of mica-biotite-plagioclase-kyanite-garnet (without melt and staurolite).

Fig. 7
figure 7

a The results of P-T pseudosection analysis using average Jutogh metapelite chemical composition (molar TiO2: 0.60, Na2O: 1.21, CaO: 1.08, K2O: 2.80, FeO: 4.73, MgO: 3.40, Al2O3: 10.06, H2O: 1.86, SiO2 saturated) for sample WG-49; b-d The modal abundances of biotite-mica, melt-garnet, and plagioclase, respectively; e-f The modeled chemical parameters for silicate melts. A grey-filled box in e marks the suggested P-T condition for melting

Full size image

Silicate melt appears as a stable phase at temperature 700 °C, pressure 0.5 GPa to temperature 750 °C, pressure 1.4 GPa. The subsequent increase in temperature lead to the subsequent destabilization of mica and biotite between temperature 750–850 °C. Finally, garnet, sillimanite, and rutile-ilmenite coexist with silicate melt at temperature > 900 °C between pressure 0.5–1.4 GPa.

The modal abundances of the minerals are shown in Fig. 7 b-d. The muscovite modal abundance increases with an increase in pressure in the kyanite domain and decreases with an increase in temperature in the sillimanite domain. The biotite and feldspar abundances decrease with an increase in pressure. The modal abundances for melt and garnet increase with an increase in temperature. The opposite trends for muscovite, biotite, plagioclase and melt, garnet imply melting of hydrous phases (biotite, muscovite) and plagioclase leading to silicate melt and garnet formation with an increase in temperature.

The P-T conditions of melt generation are further constrained by constraining the chemical composition of silicate melt (Fig. 7 e-f). The SiO2 (wt%) of silicate melt increases with an increase in temperature. Similarly, the Na2O + K2O (wt%) of the melt increases with an increase in temperature. The intersection of modelled isopleths having values similar to the WGC, i.e., SiO2 = 68–70 wt%, (Na2O + K2O) ~ 10–8 wt% intersect at temperature 850–900 °C, and pressure 1.1–1.2 GPa. The modeled A/NK values in the predicted P-T window are between 1.6–1.9 and are consistent with observed A/NK values of the WGC rocks.

U-Pb zircon geochronology

Generalities

Two representative samples (WG 49B and WG-86A) that exhibit the least deformed pristine igneous assemblages are selected for U-Pb geochronological studies. The representative CL images from both the samples are shown in Fig. 8. The geochronological data are presented in Tables 6 and 7, respectively. The 207Pb/206Pb ratio is considered for age calculation. More than >70% of data falls near Concordia for the studied samples. The age distribution of zircon varies between 2487 ± 20 Ma to 1867 ± 7 Ma of all the analyses taken together.

Fig. 8
figure 8

a-b CL images of representative zircon grains from WG-49 WG-86. c CL images of representative zircon grains from WG-49B and WG-86A. The Pb-Pb spot ages are shown for each grain.

Full size image
Table 6 Zircon U-Pb data (SHRIMP results) for granite (WG-49B) from Wangtu Gneissic Complex
Full size table
Table 7 Zircon U-Pb data (SHRIMP results) for granite (WG-86A) from Wangtu Gneissic Complex
Full size table

Sample WG-49B

A total of 21 spots, including seven core and 14 rims, are analyzed from 16 zircons separated from sample WG 49B. The size of the zircon crystals ranges between 150 and 210 μm, and the aspect ratio varies from 2:1 to 4:1. The zircons are euhedral-subhedral and preserve multifaceted prismatic crystals. In the CL images, most of the zircon grains exhibit a distinct core, overgrown by rims of variable thickness exhibiting magmatic oscillatory zonation (Fig. 8 a-b). Some zircon cores are homogeneous (Fig. 8a; grain 3,6,10,12) while others show convolute zonation (Fig. 8a; grain 2,5,7–8). Xenocrystic cores are preserved in some zircons grains that exhibit complex zonation and are characterized by resorbed grain boundaries (Fig. 8b, grain 13–16). Most of the zircons lack any metamorphic growth; however, the effects of recrystallization and metamictization are observed in some grains (Fig. 8a, grain 7,8). The U and Th concentrations range from 219 to 1901 ppm and 50 ppm - 462 ppm, respectively, with an average Th/U ratio of 0.3.

The probability density function plot shows two peak ages obtained from the U-Pb ages from the core and rim of the analyzed zircon grains (Fig. 9a). The weighted average ages calculated using Isoplot 4.1 (Ludwig 2012) are (a) 2418 ± 140 Ma (MSWD = 0.061, n = 7), and (b) 1846 ± 88 Ma (MSWD = 0.094, n = 16). The older peak is at 2418 ± 140 Ma and retrieved from the xenocrystic cores that are possibly derived from an old crustal component. The younger peak is obtained at 1846 ± 88 Ma and retrieved from zircon rims showing magmatic zonation. In a U-Pb Concordia diagram, out of seven spots, a combination of four spots analysis obtained from the zircon cores yield s an upper intercept age of 2487 ± 20 Ma (MSWD = 2.0; concordance percentage > 70%, Fig. 9c). The ages obtained from zircon rims provide an upper intercept age of 1873 ± 15 Ma (MSWD = 2.1; concordance percentage > 70%, Fig. 9d).

Fig. 9
figure 9

a-b Probability density function plots for sample WG-49B and WG-86A. The weighted average ages for statistically separable groups are also given. c-e U-Pb Concordia plots for samples WG-49 and WG-86, respectively. Ellipses indicate 1σ uncertainty, which is smaller than the symbols used in the main plot. MSWD – mean square weighted deviation

Full size image

Sample WG-86A

A total of 18 spots were analyzed from 15 zircon grains separated from sample WG-86A. The grains are euhedral to subhedral in shape. The size varies between 110 to 220 μm, and the aspect ratio ranges from 2:1 (stubby grains) to 4:1 (elongated grains). The CL imaging reveals that most of the grains display oscillatory zoned rims around distinct cores, reflecting the varying amount of Th and U incorporated during magmatic growth (Fig. 8c). Some zircon cores are homogeneous (Fig. 8c; grain 7,8,9), while others show convolute zonation (Fig. 8c; grain 3,6,11–14). A few zircon grains contain fluid or mineral inclusions (Fig. 8c; grain1,2,8), suggesting preservation of the primary magmatic character. Some of the grains exhibit a relatively young core compared to the zircon rim in WG-86A (Fig. 8c; grain 2). The apparent discrepancy probably reflects the U-Pb system’s resetting due to fractures that extend throughout the grain.

The Th and U concentrations in the analyzed grains vary from 37 to 267 ppm and 138–944 ppm, respectively. The average Th/U ratio obtained from all zircon grains is 0.30. The probability density function plot shows a single peak age at 1862 ± 80 Ma obtained from the core and rim of the zircon grains (Fig. 9b), suggesting that all the zircon grains have been formed during a single magmatic event. In the U-Pb Concordia diagram, a cluster of 18 spot analyses yields an upper intercept age of 1868 ± 6 Ma (MSWD = 1.3; Fig. 9e).

Discussion

General remarks

Geochemistry and geochronology of magmatic rocks from the LH sequences bear global importance as they can provide vital information regarding the thermal and tectonic evolution of the north Indian continental margins during the Paleoproterozoic Columbia supercontinent assembly. Researchers have reported the occurrence of Paleoproterozoic granites from LH sequences that were variably interpreted either as A-type anorogenic granite (Singh 2020) or calc-alkaline- silica saturated S, and I type granites that were formed in a volcanic arc and subduction zones setting at the northern margin of the Indian peninsula (Kohn et al. 2010; Mandal et al. 2016). Kaur et al. (2007, 2011a, 2013b) correlate the Paleoproterozoic granitic rocks of Aravalli craton with the LH rocks. They suggest that the ~1700 Ma A-type granites are derived from partial melting of older 1900–1800 Ma granites in such a volcanic arc present in LH. However, the extent and geometry of the arc, the source rock, and its depth of melting to generate magma parental to WGC remain speculative due to contrasting geochemical interpretation and the absence of thermodynamic modeling of appropriate source rocks.

Magma source and possible tectonic settings

The following geochemical evidence implies crustal sources and collisional tectonic settings for the origin of the WGC: The major element chemistry of WGC plot in metasediments source field in an Al2O3/(FeO + MgO) – 3 × CaO – 5 × (K2O/Na2O) ternary plot after (Laurent et al. 2014), (Fig. 10a). The higher Pb content in the studied sample points towards magma mixing with crustal sources for WGC rocks. Muscovite is a common mineral in metasedimentary rocks and can host a significant Pb in its crystal structure. Finger and Schiller (2012) suggest that muscovite is a significant carrier for Pb that can be liberated and contribute to the magma during muscovite dehydration breakdown. Compared to other incompatible elements, Nb and Ta′s relative depletion in the WGC rocks is a critical geochemical feature of the subduction-related arc-magmatism since rutile and titanite residual phases retain Nb, Ta, and Ti (Briqueu et al. 1984). Accordingly, studied samples are classified as syn-collisional peraluminous granite fields in Rb – (Ta + Yb) and Rb – (Y + Nb) plots (Fig. 10b, c) after Pearce et al. (1984). Also, the TiO2-Al2O3 and Y-Zr content of studied samples imply an arc-related origin (Müller et al. 1992, Fig. 10d, e). In addition to the geochemical signatures, the Ti saturation in magmatic zircon (Gervasoni et al. 2016) yields a temperature ~ 600 °C for crystallization temperature for WGC rocks. The temperature estimates from WGC are consistent with the magmatic temperature of S-type granites reported from other parts of the Himalayas (Kohn et al. 2010).

Fig. 10
figure 10

a Al2O3/(FeO + MgO) – 3 × CaO – 5 × (K2O/Na2O) ternary plot for studied samples. In the triangular plot, the different source fields are after Laurent et al. (2014). b Rb – (Yb + Ta) and c Rb – (Y + Nb) plot for the studied samples. The different tectonic settings are adapted from Pearce et al. (1984). Abbreviations: syn-COLG – syn-collisional granite, WPG – within plate granite, ORG – ocean ridge granite, VAG – volcanic arc granites. d-e TiO2 – Al2O3 and Y – Zr plots of the studied samples to discriminate between “within plate” and “arc-related” related tectonic settings (Muller et al. 2010)

Full size image

Zircon geochronology

Morphological features, internal zonations, as observed in the CL images, and Th-U content of the analyzed zircon grains imply magmatic origin (Corfu et al. 2003). Also, the presence of fluid and mineral inclusions suggests the perseverance of pristine magmatic character. The upper intercept ages, 1873 ± 15 Ma obtained from the zircon margins of WG-49B, and 1867.7 ± 6.2 Ma obtained from zircons of WG 86A, respectively, is similar and overlap with the U-Pb ages obtained from Kumaon Himalaya (Phukon et al. 2018); Uttarakhand Himalaya (Mukherjee et al. 2019); Nepal Himalaya (Kohn et al. 2010); Bhutan and Arunachal Himalaya (Pathak and Kumar 2019). The older ages obtained from the zircon core with an upper intercept of 2487 ± 20 Ma in WG 49B reveal the contribution of ~2500 Ma crustal materials either from the adjacent Bundelkhand craton (Saha et al. 2016; Nasipuri et al. 2019 and references therein) and Aravalli craton (Kaur et al. 2013). The convolute zonation is preserved as ~2500 Ma core in zircon grains (Fig. 9a), imply high-temperature metamorphism in the adjoining Archean cratons (c.f. Harley et al. 2007). The results of geochemistry and geochronology from the present study, when compared with the geochemistry of ~1800 Ma LH granites along the Himalayas, point towards the existence of a volcanic arc, temporally similar to those suggested from different segments of LH.

Possible P-T conditions

In the last three decades, several researchers, e.g., Le Breton and Thompson (1988); Conrad et al. (1988); Vielzeuf and Holloway (1988); Patiño Douce and Johnston (1991); Vielzeuf and Montel (1994); Carrington and Harley (1995); Gardien et al. (1995); Montel and Vielzeuf (1997); Patiño Douce and Harris (1998); Anenburg and Katzir (2013); and Dyck et al. (2020) have studied the significance of muscovite and biotite melting in metapelites and other mica-rich rocks for the origin of magma parental to S-type granites.

A compilation of available experimental data implies that muscovite reacts with quartz to produce sillimanite, K-feldspar, and silicate melt in dry rocks (Patiño Douce and Harris 1998; Pickering and Johnston 1998). The H2O present muscovite melting produces melt and sillimanite (without K-feldspar) as a peritectic phase (Patiño Douce and Harris 1998). Similarly, the fluid absent, biotite melting in metapelites, produces K-feldspar-garnet-cordierite along with silicate melt (Le Breton and Thompson 1988; Patiño Douce and Harris 1998). The phase stability information from melting experiments indicates that muscovite stability in metapelite depends on the amount of free H2O present in the rock, as dehydration melting of mica begins at 750–800 °C, in contrast to the H2O saturated melting that beings at relatively lower temperature ~ < 730 °C–750 °C (Patiño Douce and Harris 1998; Pickering and Johnston 1998). Biotite is relatively stable at a higher temperature compared to muscovite and begins melting at temperature > 812 °C to produce silicate melt and restite garnet (Pickering and Johnston 1998; Gardien et al. 2000).

Several researchers, e.g., White et al. (2001, 2014); Brown (2007a); Holland and Powell (2011); Korhonen et al. (2013b, 2015) have modeled mica and biotite melting in TiNCKFMASH chemical systems to understand the interplay between subsolidus stability of hydrous minerals, its dehydration melting mechanisms and volume of magma production. The modeled phase relations for the Jutogh metasediments (Fig. 7a) are comparable with the P-T pseudosection constructed from average metapelite composition (Harris et al. 2000; Tinkham et al. 2001; Brown 2007b; White et al. 2007; Korhonen et al. 2013a, 2015; Fumes et al. 2019). Among several similar phase relations between the Jutogh metasediments and ideal metapelite phase topology, the most significant is the appearance of silicate melt at ~750–800 °C, and finally complete exhaustion of hydrous minerals and stability of garnet, sillimanite, rutile along with silicate melt at temperature > 850 °C. The modeled abundances of muscovite reveal that muscovite begin melting at temperature ~ 700 °C under H2O saturated condition and is completely exhausted at temperature 800 °C, between pressure 0.5–1.4 GPa. Biotite is relatively stable at a higher temperature and is completely destabilized at a temperature ~ 850 °C—the modeled abundances of melt and garnet increase with an increase in temperature in the P-T pseudosection. The steep positive slope of the ‘melt-in’ line also implies that magma production is principally due to mica and biotite melting due to an increase in temperature and pressure along a prograde segment of a P-T path.

The SiO2 and Na2O + K2O contents of silicate melts increase with temperature. The compositional isopleths for melt and the modal abundances of biotite and muscovite when compared together also imply destabilization of muscovite and biotite, leading to SiO2 and Na2O + K2O enrichment in the modeled silicate melt composition with an increase in temperature. The intersection of modelled isopleths having values similar to the averaged WGC, i.e., SiO2 68–70 wt% and (Na2O + K2O) ~8.5 wt% intersect at 850–900 °C and 1.2–1.3 GPa. The modeled P-T conditions correspond to a crustal depth of ~45 km with a geothermal gradient >750 °C/GPa (Brown 2014).

The P−T modeling also predicts 60–70 vol% melt, 5–6 vol% garnet, and 3–4 vol% rutile in the P-T window defined intersection of modeled chemical parameters as the anticipated melt volume is higher than the limits of the melt percolation threshold for granitic magma (~20–25% of melt, Vigneresse et al. 1996), the melt thus generated by melting of biotite and muscovite can leave the system and ascent upwards by leaving the garnet and rutile residue in the lower crustal levels.

Tectonic model

A correlation of the geochemistry and emplacement ages of LH granites with the paleogeographical maps of Columbia implies two possible tectonic settings of the northern margin of the Indian peninsula. First of all, the anorogenic A-type granite emplacement in parts of Rajasthan (Pandit and Khatatneh 1998; Kaur et al. 2011b, 2017) and lesser Himalaya (Singh and Jain 2003; Saha 2013; Larson et al. 2019; Singh 2020) in 2100–1800 Ma suggested, the northern margin of Indian Peninsula is probably a passive margin, as indicated in the Columbia models after Rogers and Santosh (2002) and Zhao et al. (2011). On the contrary, recent reports of 2100–1800 Ma S-type granites from the LH rocks (Kohn et al. 2010; Phukon et al. 2018; Pathak and Kumar 2019) imply the existence of a volcanic arc and subduction zone beneath the NICB, in agreement with the paleogeographic models after Hou et al. (2008). In the following sections, P-T conditions for granite emplacement and melt generations m and projected geothermal gradients are combined with geochronological data that provide valuable insights for the tectonic characterization of the northern margin of the Indian plates.

Based on the geochemical, geochronological results, and P-T pseudosection modeling, we suggest a tectonic scenario where sediments similar in composition with Jutogh metasediments were deposited in a paleo-ocean basin at the northern boundary of the NICB. The ~2500 Ma zircon cores in WGC suggest that sediments were probably derived from weathering of ~2500 Ma K-feldspar granites from the adjoining NICB, comprising the Archean Aravalli and Bundelkhand craton (Fig. 11a). The initiation of extensional tectonics in the NICB is marked by emplacement of mafic dykes at 1978 ± 8 Ma in Mahoba, Bundelkkahnd craton (Pradhan et al. 2012). French et al. (2008), Söderlund et al. (2019) reported 2370–1790 Ma extensional tectonics and mafic dyke emplacement from the Bastar and the Dharwar craton. We suggest that the rifting and mafic dyke emplacement in the NICB and SICB should have provided the necessary horizontal force for the north-ward movement by initiating a subduction zone trench-volcanic arc system at the northern margin of NICB (Fig. 11b). As the subduction process continues, the melting of the subducting slab leads to I type magma formation and its emplacement at the base of NICB (Fig. 11c). The geochemistry and modeled P-T conditions for magma generation, i.e., temperature ~ 900 °C, pressure 1.1–1.2 GPa, correspond to a geothermal gradient of 1000 °C/GPa indicative of a magma ponding and melting of crustal materials. The ongoing subduction and melting of the oceanic crust will lead to slab breakoff and asthenosphere upwelling that can provide additional heat for the melting of the Jutogh metasediments for the genesis of the WGC (Fig. 11d). Pant et al. (2006) document high-temperature contact metamorphism from Jutogh metasediments, probably due to the emplacement of 1800 Ma granites. Therefore, this article’s suggested tectonic model also explains Paleoproterozoic contact metamorphism in the metasedimentary rocks adjacent to the WGC. Subsequently, extensive asthenosphere melting in the back-arc region may cause rifting and emplacement of A-type granite (Singh et al. 2009).

Fig. 11
figure 11

Cartoon showing the possible tectonic scenario on NICB (not to scale). a Configuration of the North Indian Continental Block (NICB) syn-post 2500 Myr ago. Chemical weathering of NICB and its subsequent deposition led to the formation of Jutogh metasedimentary sequences; b At 1978 Myr ago rifting and mafic dyke emplacement in the Bundelkhand craton. The rifting can provide additional horizontal force for the northward movement of parts of NICB; c Initiation of subduction below NICB at ~1900 Myr ago; d Slab breakoff and asthenosphere upwelling at the base of NICB to initiate mica and biotite melting and formation of S-type granite between 1900 and 1860 Myr ago

Full size image

Conclusions

The results of this study imply that a majority of the WGC rocks resemble peraluminous S-type granite. The results of Ti in Zircon thermometry and P-T pseudosection analysis constrain temperature ~ 600 °C and pressure 0.9–1.1 GPa as magmatic crystallization conditions. The predominant U-Pb zircon ages from WGC imply magmatism during 1867–1873, Ma. Accordingly, the ~2500 Ma zircon cores reveal the contribution of older crustal materials in the protoliths parental to WGC magma. Finally, the phase-equilibria modeling implies that 60–70% melting of the metasediments similar in composition to the present-day Jutogh metasedimentary sequences at temperature ~ 850 °C and pressure 1.1–1.2 GPa can produce magma similar in composition to WGC. The tectonic setting and magmatic events in the LH rocks from Himachal Himalaya can be correlated with the 1900–1800 Ma subduction driven global magmatism related to the Columbia assembly.