J. Earth Syst. Sci. (2021) 130:118 Ó Indian Academy of Sciences

https://doi.org/10.1007/s12040-021-01607-0 (0123456789().,-volV)(0123456789().,-volV)

Geology of granitoids of – Belt from Mesoproterozoic Supergroup: Tectonic implications

1, 1 1 2 RIYA DUTTA * ,HARSH BHU ,RITESH PUROHIT and KAMAL KANT SHARMA 1Department of Geology, M. L. S. University, Udaipur, 313 001, . 2Department of Geology, Government College, , Rajasthan 307 001, India. *Corresponding author. e-mail: [email protected] MS received 11 May 2020; revised 3 February 2021; accepted 15 February 2021

Granitoids from Pindwara–Abu Road Belt (PARB) are studied to characterize their tectonostratigraphic status in relation to the associated metasediments. The PARB lies along the southern swathes of the Mesoproterozoic Delhi Supergroup (DSG) in the Aravalli Delhi Mobile Belt (ADMB) of the northwestern Indian Shield. The outcrop scale granitoids of the study area are categorized into massive and gneissic variants. The former variety is being prominently exposed as leucocratic variant intrusive into the melanocratic gneisses as well as associated metasediments. Massive intrusive granitoids have been dated previously representing three major regional thermal events of 1000, 850, and 750 Ma. These multiple tectono-thermal events have led to diminished preservation of pristine gneissic character in the granitoids outcropping as dismembered bodies in the PARB. Consequently, the Beld relationship between the granitoids and associated metasediments is extremely obliterated. The present study, with the help of regional and detailed mapping on different scales and petrography, has attempted to establish basement–cover relationship between the gneissic granitoids and the associated metasediments. Quartzite outcrops are delineated as marker horizons characterizing the contact lithounit between the two. The cover rocks have sheared contact with the gneissic basement, which has a limited patchy outcrop pattern as ‘Remnants’. These ‘Remnant’ outcrops, conceivably behaved as primitive relicts, perhaps acted as a cradle for the proximal metasediments. Earlier studies, based on heavy carbon isotope character, have given an age span of *1200–1300 Ma for the associated calcareous metasediments of the PARB. The gneissic granitoid, basement to these metasediments, is hence considered to be pre-1300 Ma, older than the massive granitoids (1000–750 Ma). The span of events reveals that the southern terrane of the DSG of rocks, especially the PARB has a younger geological history as compared to the northern terrane of the Delhi Supergroup which has records of 1700–1400 Ma. The events recorded from the PARB of the DSG are younger in age and indicate Meso-Neoproterozoic transition (*1300–750 Ma). Globally, these are correlatable with the Grenvillian orogeny followed by Rodinia Supercontinent, amalgamation, and splitting tectonism in the northwestern Indian Shield. Keywords. Granitoids; remnants; pristine character; Pindwara–Abu Road Belt (PARB); Delhi Supergroup (DSG); Meso-Neoproterozoic transition. 118 Page 2 of 17 J. Earth Syst. Sci. (2021) 130:118

1. Introduction SDT. Similarly, Maheshwari et al.(2009), Purohit (2005), and Purohit et al.(2012), also interpreted Geological mapping in complexly deformed Pre- younger span of calcareous metasediments based cambrian terrane is exigent. Multiple cycles of on stable carbon isotope studies of the study area. tectono-thermal reconstitution defy the nature of The 13C values of these carbonates of PARB vary contact between litho-units. Competent and between 0 and +4 per mil PDB which are different incompetent rocks behave differently to the stres- from zero per mil values of the carbonates of the ses developed during deformation accompanied by Ambaji area in the east from the Kumbhalgarh metamorphism. The outcrops in such terranes are Group (of the DSG) marking interval in time of differentiated into separate inliers and outliers deposition (Purohit 2005; Maheshwari et al. 2009; because of the development of synclines and Purohit et al. 2012). Wang et al.(2017) also opined respective anticlines. Basement remnant rocks similarly that the diverse age signatures from bearing pristine character show tectonized contact northeastern and southwestern segments of the with the younger supracrustals exhibited as ductile DSG indicate a distinct depositional environment shear zones and mylonites. Parts of such a poly- and represent discrete sub-basins. Amidst, the cyclic gneissic basement can be older than the concepts of the diachronous litho-tectonic evolu- supracrustals (Ghosh 1990 and references therein). tion of the region, the granitoids of the PARB are Such, features are commonly observed in the Pre- studied to differentiate older and younger compo- cambrian rocks of the Aravalli Delhi Mobile Belt nents. There are several deformed plutons of (ADMB) (Roy and Jakhar 2002; Sinha-Roy et al. granite, granitic gneisses, and migmatites collec- 2013) resulting in the advancement of different tively described as granitoids which outcrop in the theories of crustal evolution. Crustal evolution is study area around Moras, Malera, Waloriya, interpreted based on litho-tectonic studies. Similar Wasa, Sanwara, Bhula, Dovtra, Bori-Bhuj, Paba, studies have been made by several authors to and Mandwa villages. Zhao et al.(2018) have unravel the crustal evolution of the ADMB (Gupta recently dated the Moras granitoids as 976 ± 12 Ma. et al. 1981, 1997; Sinha-Roy 1984; Sengupta 1984; These granitoids were variably described by pre- Biswal et al. 1998a, b; Deb et al. 2001; Roy and vious workers either as part of Erinpura Granite Jakhar 2002; Singh et al. 2010; Just et al. 2011; Roy (Coulson 1933; Pandit et al. 2003), Sendra-Ambaji and Purohit 2015, 2018; Tiwari et al. 2019, 2020). Granite-Gneiss (Deb et al. 2001; Pandit et al. 2011) Granitoid plutons of different ages have been and part of Todgarh Formation, Kumbhalgarh reported from the Delhi Supergroup (DSG) of rocks Group of the Delhi Supergroup (Gupta et al. 1997). which range in age between 1700 and 750 Ma These granitoids are aAected by later events that (Pandit et al. 2003, 2011; Singh et al. 2010; Dharma include polyphase deformation, granitic intrusions, Rao et al. 2012; Zhao et al. 2018; Jaideep et al. anorogenic thermal perturbations, and further by 2020). Younger intrusive granitoids of *850 and younger lead loss events of *540 Ma correlatable *750 Ma have been also reported from Pind- with the Pan-African orogeny. The relationship of wara–Abu Road Belt (PARB) (Dharma Rao et al. granitoid bodies with the adjoining metasediments 2012; Chatterjee et al. 2017, 2020; Zhao et al. and metavolcanics is obliterated. The granitoids 2018). Chaudhary et al. (1984) gave a diachronous show strong development of mylonitic fabrics at evolution of the Delhi Supergroup (DSG) rocks, Canks. The present study is conducted to under- which has been also supported by Singh et al. stand the ambiguity in features related to the (2020). According to the authors, the Delhi Fold partial reconstitution of these granitoids and their belt was evolved in two phases in which North relationships with the associated cover rocks. Delhi Belt is supposed to be older and South Delhi Belt is supposed to be younger. Singh et al.(2010) have also opined the younger phase of crustal 2. Geological setting evolution in the South Delhi Terrane (SDT) based on the detrital zircons in pelitic granulites derived The distributions of granitoids of PARB of the from magmatic sources which span in age from SDT are shown in Bgure 1(a). The eastern bound- 1620 to 1240 Ma. Besides this, in a recent study by ary is marked by a prominent thrust zone, i.e., Kaur et al. (2020) gave the minimum age for Kaliguman Dislocation Zone which separates the magma emplacement (1581+24 Ma), and corre- DSG rocks from the Sandmata Terrane rocks of the sponding younger sedimentation (1.2–1.1 Ga) in Banded Gneissic Complex in the north; and the J. Earth Syst. Sci. (2021) 130:118 Page 3 of 17 118

Aravalli Supergroup rocks in the south. The rocks of the DSG are exposed extensively, covering southwestern, central, and northeastern regions of the ADMB. The outcrops are along a linear belt striking NE–SW and popularly named as Delhi Fold Belt. The DSG rocks are dominant of cal- careous–arenaceous metasediments, later intruded by different generations of granitoid plutons along with maBcs and ultramaBcs. The SDT is charac- terized by a prominent shear zone trending NE–SW, named as Phulad Shear Zone (Gupta et al. 1981). It almost bounds the SDT towards the west and is also named Western Margin Fault by Pandit et al.(2011). This separates Sirohi Group rocks to the west from the DSG rocks. The study area is lying along the Western Margin Fault and east of marked in Bgure 1(a). There are evidences of polyphase folding from tight, isoclinal, recumbent/reclined folds (DF1) to upright/steeply inclined, moderately plunging folds (DF2) to upright kink folds (DF3). Meta- morphism varies in grade from greenschist to upper amphibolite facies (Roy et al. 1985) with some patchy occurrences of granulites at Balarampur near Ambaji (Roy et al. 2004; Biswal 1988; Biswal et al. 1998a, b; Srikarni et al. 2004). The metasediments of the SDT are named as Gogunda Group and Kumbhalgarh Group which are con- sidered equivalent to Alwar Group and Ajabgarh Group of the North Delhi Terrane (NDT) by Gupta et al.(1981). The lithoassemblages of the study area were assigned the status of Todgarh Formation of the Kumbhalgarh Group. The gran- itoids of the PARB have been designated strati- graphic status equivalent to Sendra-Ambaji granitic-gneisses by Gupta et al.(1997). Separation of granitoids of the PARB into various generations is a herculean task due to masking by multiple tectono-thermal events like Erinpura Granite intrusion and Malani Magmatism (Roy et al. 2004; Rao et al. 2013).

3. Methodology

The following methods were implemented to comprehend the problem of the study area: (A) LANDSAT-ETM, Digital Elevation Model- Figure 1. (a) Location of the study area (PARB) in Delhi SRTM imageries were (downloaded from Earth Supergroup in Precambrian Geological Map of Rajasthan (modiBed after Roy and Jakhar 2002). (b) Regional map of the Explorer of USGS) processed in Arc GIS 10.3 study area showing the distribution pattern of various software by overlapping Google Earth imageries, lithologies, prepared with the help of imageries on a scale of Survey of India Toposheets (45D/13, 45D/14, 1:50,000. 45D/15, 45H/1, 45H/2, 45H/5, 45H/6, 45H/9) and 118 Page 4 of 17 J. Earth Syst. Sci. (2021) 130:118

Geological map (Coulson 1933 and GSI et al. 1995). bodies. The ridges of quartzite layout in two sub- The regional distribution pattern of different litho- parallel linear belts are striking NNE–SSW units has been marked (Bgure 1b) in 1:50000 scale, (Bgure 2a). Both the bands of quartzite show a covering an area of *1000 km2 (Coordinate: northeasterly enechelon^ pattern. Both quartzites 24°45025.9200N/73°02011.5400E–24°45051.3400N/73°110 and granitoids are dissected by E–W disjoins, which 18.5900E–24°25057.6500N/72°57014.3900E–24°28027.2400/ signify later displacements. The outcrop pattern N72°48014.3500E). Facts were later veriBed by Beld also reveals that the eastern and western boundaries survey. Regional Beld veriBcation, detailed Beld of the quartzite are trails of the two regional linea- data collection has been conducted in the PARB. ments. The western boundary is the continuation of All the collected Beld data were processed and the Pisanganj–Vadnagar Lineament, whereas the plotted by Arc GIS 10.3 software followed by eastern boundary is the continuation of the Kis- drawing lithological boundaries. Distribution pat- hangarh–Chipri Lineament both trending NE–SW terns of quartzites and granitoids were analyzed on (Dasgupta et al. 2000). a regional scale (Bgure 2a and b). (B) During Beld veriBcations of outcrops, litho- 4.2 Lithology logical sampling was carried out and simultaneously petrographic characterization of the lithoassemblages 4.2.1 Granitoids was done by the conventional method of thin section studies in polarized light and Cross-Nicol. Geological mapping of the PARB has revealed two (C) Detailed mapping was done along major types of granitoids which can be broadly Bhula–Swaroopgunj transect in the PARB to categorized into gneissic and massive variants. understand the nature of contact and metasedi- mentary successions on a scale of 1:12,500 (Bgure 3). 4.2.1.1 Gneissic granitoids Further structural analyses of the study area were performed by dividing the area into three sectors These granitoids are banded granitic-gneisses with (northwestern, middle, southeastern sector) and noticeable separation between leucocratic and S-pole diagrams were plotted and interpreted melanocratic components (Bgure 5b). The abun- (Bgure 4a, scale 1:25,000). Microstructural studies dance of biotite has given rise to melanocratic bands were also performed along with petrological studies. alternating with leucocratic bands having a fair amount of muscovite, quartz, and feldspar. These 4. Result granitoids are shelved by mylonitic zones which show an intricate folded pattern. Fracture foliation 4.1 Regional mapping seems to be secondary foliation that gives evidence of profuse reconstitution. Not only that, the discrete Outcrop patterns are studied through regional-scale and pronounced occurrence of maBc micro-granular mapping to decipher the occurrences of granitoids enclaves of varying dimensions within gneiss also and other lithoassemblages, that dominantly gives evidence of reconstitution. Textural variations include quartzites which are juxtaposed to granitoid noticed in hand specimens include sheared, myloni- bodies on the outcrop scale (Bgure 5a). The tized granite-gneiss, and coarse-grained non- notable presence of matured and resistant extensive sheared, massive granite. The granitoids range in ridges of quartzites along with the contact of the composition from granite to granodiorite essentially granitic-gneisses is a striking feature. The quartzites composed of quartz, feldspar, muscovite, biotite, of the PARB are associated with metasediments of amphibole, and other accessories. diverse nature in the west and with granitoids in the Under the microscope, gneissic granitoids show east. The quartzites are easily recognized and partially or completely recrystallized fabrics with delineated on the imageries by razor-edge sharp bimodal grain size distribution. Large plagioclase boundaries with the Cat low-lying granitoid terrane. crystals are randomly oriented and are anhedral to The outcrops of the other associated metasediments subhedral in shape with irregular to sutured grain display broad slopes and escarpments. One of the boundaries. Almost all of these plagioclase feld- most characteristic features revealed is that the spars are twinned. Both growth twins and defor- quartzite ridges, as well as granitoids bodies, show mation twins are present. In some cases, an enechelon^ distribution pattern (Bgure 2a and b). deformation twins show bending of twin planes, The granitoids and quartzites occur as dismembered intergranular displacement across twinned planes, J. Earth Syst. Sci. (2021) 130:118 Page 5 of 17 118

Figure 2. (a) NNE–SSW striking sub-parallel linear eastern and western bands of quartzite ridges. (b) NNE–SSW striking sub- parallel Cattened bodies of granitoids in PARB. 118 Page 6 of 17 J. Earth Syst. Sci. (2021) 130:118 and strain-induced grain boundary migration are of the study area. Such massive and leucocratic evident. In gneissic granitoids of Bhula, Sanwara, granites are medium to coarse-grained equigranular, Wasa areas, plagioclase feldspars are generally Ceshy pink to light grey, less deformed, and devoid of crowded with several types of inclusions and are shearing and metamorphism. Although most of this highly altered along grain boundary as well as variety are massive, some of them rarely show poor along fractures and cleavage planes. Plagioclase foliation, marked by mica Cakes. In the thin section, compositions are more calcic and vary from An42 to they show typical igneous interlocking texture with An88 (Andesine to Anorthite). Quartz grains are completely or partially unaltered and less deformed highly irregular in shape and size showing inter- coarse granular aggregates and without preferred lobate to seriate grain boundary. These grains are dimensional orientations of minerals (Bgure 5f). highly strained, fragmented, deformed and the They are essentially composed of quartz, alkali majority of these grains show undulose extinction feldspar, mica, little or no plagioclase feldspar, and and development of deformation bands. Polycrys- other accessory maBc minerals. talline quartz aggregates, sub-grain formation In several outcrops (near Paba, Bori-Bhuj, (Bgure 5c), and grain boundary migration indicate Waloriya), reddish to pinkish, massive, Bne- dynamic recrystallization in gneissic granitoid bod- grained aplitic leucocratic granitoid variety is ies. Light to dark brown laths of biotite occur in a present, whereas granitoids of Bhula, Sanwara, and parallel orientation, giving rise to gneissic foliation Wasa are melanocratic and dominantly contain in this rock. Muscovite occurs as irregular Cakes or plagioclase, biotite, and maBcs. The massive blebs of varied dimensions. Biotite shows retrograde granitoids near Paba, Waloriya, Mandwa, Moras, alteration to chlorite along the grain boundary. and Malera areas are containing albitic plagioclase Zircon is also common in these granitoids. (An4–An40). Alkali feldspars are mainly microcline Epidote, sericite, chlorite, zoisite occur as alter- with few orthoclase feldspars. They enclose sub- ation products in granitoid. The eAects of sericiti- rounded grains of quartz and plagioclase feldspar zation and sausaritization are commonly observed and are commonly less deformed and strain-free. in feldspars of these granitoids. The feldspars are Microcline in few cases is surrounded by the Bnely also accompanied by aggregates of sphene, zoisite, granulated matrix that may be formed due to poly- zircon, calcite, amphibole, pyroxene, and staurolite. crystallization. Myrmekitic texture is very com- The presence of Bne needles of fresh feldspar grains mon in these granites (Bgure 5g). Plagioclase feld- within large grains indicates an exsolution texture. spars are generally free of inclusions. In some parts Microclines occur less with respect to plagioclase in of thin sections, epidote with secondary growth of such granitoids and are relatively fresh and mostly mica and chlorite on the central core gives rise to devoid of inclusions. They are irregular in shape corona texture. No preferred dimensional orienta- and generally show tartan twinning. In some parts, tion, mylonitic foliation, the eAect of recrystal- orthoclase is also present in a small amount showing lizations, etc., are observed in such granitoids. simple twinning. Asymmetric myrmekites are Feldspar grains are mostly unaltered and do not commonly observed which may be formed by pla- show any type of sericitization and kaolinization. gioclase recrystallization, altered by hydrothermal solutions after cataclastic deformation. The por- phyroblasts of feldspar with asymmetric pressure 4.2.2 Metavolcanics with serpentinites shadow, boudinage quartz grains, and mylonitic foliations (Bgure 5d) are indicating the shearing Metavolcanics surrounds the granitoid outcrops eAect on gneissic components. (Bgure 3). The litho-assemblages include mainly amphibolites with plugs of serpentinite pockets. Amphibolites in few outcrops grade to biotite- 4.2.1.2 Massive granitoids chlorite schists showing wide textural variations from massive granular to schistose. Dark green- These granitoids are homogenous, massive, and coloured amphibolites characterized with light- leucocratic in nature, having cross-cutting features pistachio green scattered patches indicate compo- with metasediments on the outcrop scale (Bgure 5e). sitional variation. The amphibolite bodies are These granitoids occur as discrete intrusive bodies in highly jointed, sheared, and variably foliated the gneiss and other adjoining metasediments, (Bgure 5h). These rocks are essentially composed of especially towards the southeast and northern parts hornblende with small aggregates of tremolite, J. Earth Syst. Sci. (2021) 130:118 Page 7 of 17 118

Figure 3. Lithological map along Bhula–Swaroopgunj transect on 1:12500 scale. actinolite, opaques, and serpentine group minerals. (grading into biotite schist), garnet-bearing quartz- Serpentinites are distinct near the Basant- chlorite schist, etc. Quartzites are dirty cream, garh–Ajari belt, in the western part of the Bhula foliated, and occur as the most prominent arena- granite body, and around Pipela. Serpentinite ceous metasediment litho unit. At places, the pockets are pale greenish with a soapy feel showing quartzites are brecciated and chertiBed (Bgure 5j). alterations to talc and carbonates. Serpentinites They show bimodal grain size distribution with are transforming gradually into talc-schist and highly strained elongated (in NE–SW direction) chlorite schist. Relicts of parent magma repre- grains. Bulging, interlobate grain boundaries, sub- sented by disoriented and elongated prismatic oli- grains, grain reBnements of such rocks infer the vine and pyroxene are present within serpentinites. eAect of dynamic recrystallization in the peripheral The contact between serpentinite and other part of quartzite ridges, whereas, in the central country rock is mostly sheared (Bgure 5i). part of each enechelon^ ridge, the mineral grains are more or less polygonal with straight to smoothly 4.2.3 Arenaceous and calcareous curved grain boundaries having triple junction metasediments with no subgrain formation. Such grains are strain- free, but strongly deformed and show the eAect of Arenaceous metasediments include quartzite, static recrystallization. Both sigma type and delta quartz-muscovite schist, quartz-chlorite schist type of deformed porphyroblasts of feldspar are 118 Page 8 of 17 J. Earth Syst. Sci. (2021) 130:118 present in mylonitized and sheared quartzites. 4.3 Structural analyses Relic porphyroblasts show the strong shape-pre- ferred orientation of mineral grains, brittle frac- 4.3.1 Folding tures, bending of twinned lamellae in feldspar, Detailed mapping was done to understand the kinking of mica, asymmetric tailing of porphyrob- impact of deformation on granitoids and associated lasts, elongated Bsh-shaped polycrystalline quartz litho-assemblages (Bgure 4a). Different phases of and calcite aggregates, asymmetric intrafolial deformation are identiBed mainly in terms of folds, deformed elongated quartz ribbons, boudi- folding and superposition. Two generations of folds naged polycrystalline quartz aggregates (Bgure 5k) are prominently present in the study area, which is in thin section. Mylonitic foliation in schistose in conjunction with the deformation displayed in metasediments shows incipient development of C the rocks of the Delhi orogeny. The Brst-generation and S fabrics, where C is demarcated by the pre- fold corresponds with the characteristic Brst ferred orientation of biotite, muscovite, chlorite deformation of the Delhi orogeny designated as Cakes, and S is marked by Cattened polycrystalline DF1 (Bgure 5o). It is identiBed as a tight isoclinal quartz, feldspar, garnet, etc. The angle between C fold with NE–SW trending axial traces and this and S fabric in schistose mylonite (Bgure 5l) asso- phase represents penetrative bedding parallel ciated with individual quartzite ridges decreases schistosity (S0 —— S1). This S1 is coaxially refolded from center to periphery (*22° to 0°). to form a steeply inclined/reclined to upright and Calcareous metasediments include calc-silicate, moderately plunging fold corresponding to the DF2 calc schist, and marble. Large, linear bands of fold of Delhi orogeny that has tight geometry in the marble occur within calc-silicate and are mostly proBle section (Bgure 5p) and the orientation of the dark grey coloured, medium to coarse-grained. axial plane is also NE–SW. The fold axes of DF2 They show variation in composition in the form of vary considerably from sub-horizontal to gently several impurities. Calc-silicates crop out as grey- plunging. At places, the third generation of fold ish green to greenish-white to buA outcrops having (DF3) occurs as small-scale upright sharp-hinged prominent banding in few places. Some quartzo- fold with NW–SE trending axial plane (Bgure 5q). feldspathic veins of varying dimensions cross-cut S0 —— S1 is a very prominent schistosity in this area. the outcrops. Most of the exposures of calc-silicate In some areas, schistosity planes have been puck- preserve asymmetric folds (Bgure 5m), several ered due to DF3 fold and thus form crenulation intrafolial folds, and evidence of shearing in the cleavages (S2) within the schistose rock. In this outcrop scale. study area, two sets of lineation are deBned by the occasional presence of intersection lineation (DL1) 4.2.4 Dykes, veins, and enclaves which are at an acute angle with pucker axis lin- eation (DL2) related to folding. The multiple The gneissic foliations are cut across by tourma- phases of folding have produced three types of line-bearing pegmatite veins and metamorphosed superposition that are identiBed locally by dome- foliated amphibolite dykes. Amphibolite dykes are basin, mushroom, and hooked patterns (Bgure 5r). composed of hornblende, chlorite, few biotite, and The structural databases of the study area like showing crude foliation. Some maBc, microgranular attitudes of bedding planes, schistosity, and folia- enclaves with varying dimensions occur within tions are plotted in different stereo-pole diagrams. granite gneiss. Most of these are rounded to ellip- In the stereo-pole diagram (Bgure 4b), the contours tical, some of these are lens-shaped and some of of bedding parallel schistosity (S0 —— S1) of schistose these are polygonal. Compositionally these metasediments are plotted and they show the mean enclaves are amphibolitic and biotitic (Bgure 5n). great circle girdle having a vertical attitude with In the thin section, they are Bne-grained with a corresponding sub-horizontal b axis (fold axis) preferred dimensional orientation giving rise to plunges 003°?209°. For gneissic foliation planes, schistosity. Some of these are exotic in nature. Few plotted contours in the stereo-pole diagram felsic enclaves occur as boudins within gneisses and (Bgure 4c) are showing mean great circle girdle they are composed of coarse crystals of feldspar and few biotite Cakes. Gneissic granitoids are cross-cut having attitude 79°?N33° E and calculated b axis by felsic veins. Calcareous vein-lets are also present plunges 11°?213°. The contour diagrams in the in gneisses which are in proximity with the stereographic plot for both bedding parallel schis- calcareous metasediments. tosity and foliation regionally show upright, gently J. Earth Syst. Sci. (2021) 130:118 Page 9 of 17 118

Figure 4. (a) Structural trend map along Bhula–Swaroopgunj transect with sector-wise S-pole diagrams on 1:25000 scale. (b) Stereo-pole contour diagram of bedding parallel schistosity (S0 —— S1) for metasediments and metavolcanics of the study area. (c) Stereo-pole contour diagram of gneissic foliation of granitoids of the study area. (d) Stereo-pole contour diagram of mylonitic foliation for sheared mylonites of the study area. plunging fold geometry with NE–SW axial trace. upright anticline with metasediments dipping on Plotted data of bedding and schistosity of these the eastern and western sides and the granitoids litho units also show that schistosity is developed are in the core. Three generations of folds had almost parallel to the bedding plane and this S0 —— developed among which the Brst two were co-axial S1 is dominant in this area. The structural trend folds with NE–SW trending axial trace almost map of the study area also depicts a regionally parallel to the shear zone. The fold hinge of earlier 118 Page 10 of 17 J. Earth Syst. Sci. (2021) 130:118

(a) (b) (c)

(d) (e) (f) E

Massive Calc- Granite metasedime

(g) 100 μm (h) (i)

(j) (k) (l)

S

C

Figure 5. (a) High rising quartzite ridge juxtaposed to peneplain basement granitoids in the study area (snap is taken from southeast). (b) Gneissic bands of granitoids in the west of Bhula from PARB (snap is taken from south). (c) Photomicrograph of sub-grains of quartz in recrystallized granitoids of Wasa. (d) Photomicrograph of mylonitic foliation in schistose mylonite along the granitoids Canks at the western contact of Bhula granite with Deldar quartzite. (e) Discrete occurrence of massive granitoid with adjoining metasediment near Paba (snap is taken from south). (f) Photomicrograph of undeformed coarse granular aggregates without preferred dimensional orientation of mineral grains in massive granitoid from Malera. (g) Photomicrograph of asymmetric myrmekitic texture of granitoids from Pindwara. (h) Foliated and sheared amphibolite outcrops from Sanwara (snap taken from southeast). (i) Sheared contact of serpentinite bearing metavolcanics with metasediments near Bor Umri (snap taken from East). (j)ChertiBed brecciated quartzite rocks of Petari Padar (in plan view). (k) Photomicrograph of boudinaged polycrystalline quartz aggregates along with Bne calcite grains in calc- silicate mylonite at the west of Jaba. (l) Photomicrograph of S-C fabric in garnet in biotite–chlorite schist of Pipela. J. Earth Syst. Sci. (2021) 130:118 Page 11 of 17 118

(m) (n) (o)

(p) (q) (r)

(s) (t) (u)

(v) (w)

Figure 5. (m) Minor Asymmetric folds of calc-silicates at the west of Bhula (in plan view). (n) Elliptical enclave/xenolith of chlorite-biotite schist within granitoids from Sanwara (in plan view). (o) 1st generation fold (DF1) identiBed as tight isoclinal fold with NE-SW trending axial trace (axial plane is marked by red dotted line). (p) 2nd generation fold (DF2) identiBed as steeply inclined/ reclined to upright fold (axial plane is marked by red dotted line). (q) 3rd generation fold (DF3) identiBed as small scale upright sharp-hinged fold/ Kink fold (axial plane is marked by red dotted line). (r) Type 3 superposition (hook pattern) in the planar view shown in calc-silicate of Malera (F1 axial plane is marked by red dotted line and F2 axial plane is marked by yellow dotted line). (s) Elongated deformed porphyroblasts with mylonitic foliation in granite mylonite from Bhula granite (snap taken from West). (t) Rotation of domino boudin shown in the sheared calc-silicate rock near Malera (snap taken from SE). (u) Dextral rotation of tension gashes in quartz-mica schist along NE-SW shear direction near Pipela (Snap has taken in plan view. (v) Sigma-type deformed porphyroblast in sheared calc-silicate near Malera. (w) Less deformed massive granitoids intermingling with gneissic granitoid (plan view). 118 Page 12 of 17 J. Earth Syst. Sci. (2021) 130:118 is almost rotated parallel to the stretching 5. Discussions lineation. The deformed lineations become strongly curved and appear asymmetric U-pattern. The fold 5.1 Regional map was initially reclined and the hinge was rotated to become sub-horizontal along stretching direction The enechelon^ alignment pattern of quartzite and develop planar sheath folds with an apical bands (Bgure 2a) and granitoid bodies (Bgure 2b) direction parallel to stretching lineation. observed in the regional map is possibly due to zone-parallel shearing or alternatively due to zone- normal shortening or both acting together, which characterizes transpressional deformation or 4.3.2 Shearing shearing (Fossen and Tikkof 1993, 1998). Strike- Apart from the evidence of multi-phases defor- slip movement had occurred parallel to the strike of mation in terms of folding, the most intense the regional lineaments. Perhaps trans-tension had shearing occurred along a narrow zone from west also developed later with these bodies and simul- of Bhula granitoid body through Pipela, Basant- taneously shortening has also taken place trans- garh, Ajari, Malera to the west of Moras granitoid verse to the direction of strike-slip movement. In body (Bgure 4a) and is manifested as mylonitic such a tectonic environment, the granitoids and foliation in intercalated calcareous and quartzo- quartzites promulgated the enechelon^ pattern feldspathic masses. The stereo-pole diagram (Bgure 2a and b). This outcrop pattern can also be (Bgure 4d) for mylonitic foliation shows that they explained alternatively as a result of asymmetric are mostly NE–SW trending (38°–218°) and dip- folding or parasitic folding in the limbs of a large ping 63° southeasterly and in outcrop scale, they fold, in which individual folded parts got detached show prominent stretching lineation along the due to layer parallel stretching and disrupted by downdip direction (Bgure 5s), which is deBned by boudinage (Ramsay 1967). elongated deformed porphyroblasts of varying It is very unlikely that a rock body is deformed dimension. The partly concordant pegmatite only due to shearing or only by pure shortening. It venation within western Bhula and Wasa grani- is presumed that the rocks of the study area were toids shows continuous fabric with shear foliation deformed by the combined eAect of shearing and suggesting syn-tectonic emplacement. As the shortening, resulting in oblique deformation, giving shear fabric is continuous to all the rock types rise to the enechelon^ pattern. As a result of oblique from gneissic granitoids to metavolcanics to deformation, there is non-coaxiality of the shear metasediments, it is also related to pegmatite zones leading to complexity in deformation. Stret- venation. Some other mesoscopic evidence like ched and elongated enechelon^ bands of quartzite pinch and swell structure, asymmetric intrafolial show a dextral sense of shearing that represents the folds, rotation of boudins (Bgure 5t), eneche-^ left limb of the regional antiformal fold. This is lon veinlets (Bgure 5u), deformed sigma porphyro- conceivably the result of simultaneous transpres- blasts (Bgure 5v) are very prominent along the sional and transtensional tectonic forces that western part of this study area. The shear zone in worked in the region. The regional dextral pattern the study area displays both brittle and ductile is observed on the outcrop scale where the calc- characters, which implies that the shear zone pas- silicates associated with the quartzite show clock- ses through the rocks of contrasting rheological wise rotation (dextral) of boudins relative to the properties. The shear zone contains boudins, rock enclosing banding materials in the outcrop. These fragments, and porphyroblasts of more brittle are the small-scale manifestations of regional dex- rocks, similarly contain tectonized fabrics like tral shearing also observed in the younger Sirohi mylonitic foliation, lineation, etc., in incompetent Orogeny (de Wall et al. 2012). rocks of lithologically diverse sequence. Not only It is suggested that the regional enechelon^ pat- have that, the tectonized fabrics which resemble a tern of quartzite and granitoid outcrops are prob- mylonitic fabric on the outcrop scale, had many ably the results of alternating transpressional and brittle aspects in microscopic scales, like micro- trans-tensional tectonic forces which were active faults, grain-scale fractures, micro-breccia, etc. during the last phase of the orogenic cycle in this Taken together these features indicate the shear region (de Wall et al. 2012; Arora et al. 2017; zone in the study area is developed in the brittle- Chatterjee et al. 2020). This transpressional kine- ductile regime. matic in our study area may cause the domal uplift J. Earth Syst. Sci. (2021) 130:118 Page 13 of 17 118 of quartzite ridges in the central part with gradual Deformation is penetrative and overlapping in subsidence as narrow basins in the peripheral part. gneissic granitoids, whereas massive granitoids are least deformed, though closely intermingled with the former (Bgure 5w). The gneissic granitoids 5.2 Petrographic studies behaved competently for the subsequent deforma- tion cycle. In all probability, the diapiric rise of The occurrences of recrystallized and variably massive granitoids within highly deformed, meta- metamorphosed gneissic granitoids show granite morphosed gneissic granitoids and adjacent coun- and granodiorite composition along with maBc try rocks led to the development of structural microgranular enclaves, dykes, veinlets whereas complexity of the SDT. However, the structural massive granitoids appear rather as fresh outcrops complexity could be attributed to multiple remo- which are least deformed and unaltered with a true bilization events to which the rocks of PARB granitic composition. The presence of myrmekitic underwent and during which the competent and intergrowth with vermicular texture has developed incompetent rocks behaved in a ductile manner (cf. due to plagioclase recrystallization and alteration Naha and Mohanty 1988). by granitic melt. Associated quartz grains are The shear zone structure like regional enechelon^ highly strained deformed as most of these are ridge distribution pattern, rotation of mylonitic showing undulose extinction and the development foliation along with stretching lineation, enechelon^ of deformation bands. Interlobate grain bound- veinlets, rotation of boudins, development of pla- aries, polycrystalline quartz aggregates, sub-grain nar sheath folds along the shear foliation, etc., formation, grain boundary migration are indicative present in our study area are possibly deciphering of the recrystallization of gneissic granitoids. regional transpressional deformation for the tec- Development of mylonitic foliation, sigmoidal tonic evolution of this terrane. The Cattened rotation of deformed porphyroblast, development elliptical, dismembered outcrops of granitoids, of S-C fabrics, and intergranular faults mimic the narrow high rising ridges of quartzite along the regional shearing eAects. shear direction, planar sheath folds along shear The bimodal grain size distribution in micro- foliation infer Cattening type bulk deformation scopic scale with changes of degree of recrystal- along the transpressional shear zone. These fea- lizations from dynamic in the periphery to static in tures are also found in other parts of SDT like the central part of each enechelon^ quartzite ridges Phulad area (Sengupta and Ghosh 2004; Choud- and changes in the angle between C and S fabrics hary et al. 2016; Chatterjee et al. 2020) and Ambaji (nearly parallel in peripheral part to around 22° in area (cf. Tiwari and Biswal 2019). the central part) in the associated schistose rocks mimic to the regional scale rock deformation pat- tern. Deformed porphyroblasts with asymmetric 5.4 Implication of tectonics on granitoids pressure shadow, elongated polycrystalline quartz aggregates, mica Bsh, calcite Bsh, deformed elon- Tectono-thermal reconstitution of the DSG rocks gated quartz ribbons, boudinaged polycrystalline led to widespread overprinting implying feeble quartz aggregates, etc., in schistose mylonitic rocks chances of preservation of remnants. Henceforth, are also indicating Cattening type bulk deformation there are frail chances that these older components along with dextral shearing. These microstructural have distinct outcrops. Reconstitution is well- features suggest that these granitoids are marked by discrete and pronounced occurrences of aAected by regional stress, tectonic squeezing, and maBc microgranular enclaves of varying dimen- shearing. sions, as observed in Bhula, Sanwara, Wasa gran- itoid outcrops. The late kinematic intrusion of Erinpura Granite and Sendra–Ambaji Granite 5.3 Structural analyses along with anorogenic Malani Magmatism is con- sidered to be responsible for reheating and recon- The rocks of PARB display the structural geome- stitution of the Delhi Supergroup (DSG) rocks try pertain to the Delhi orogenic cycle. The Brst (Roy et al. 2004). two generations of folds and their NE–SW axial Discrete ages of 1015, 966, and 808 Ma are trace are the most prominent structural features reported from Peshuwa, Devala, and Sai by both on macro and microscopic scales. Dharma Rao et al. (2013). Moras Granite has also 118 Page 14 of 17 J. Earth Syst. Sci. (2021) 130:118 been dated as 976+12 Ma by Zhao et al.(2018). Ma aged Seoli Granitoids (Choudhary et al. 1984) These studies indicate the impact of two thermal of the North Delhi Terrane. The magmatic zircon events through granite emplacements, one is the age of 1581±24 Ma orthogneiss of Beawar (Kaur older and more prominent event which was et al. 2020) can be compared to the gneissic gran- around 1000 Ma and the other one is the younger itoids of PARB. This is in conBrmation with the and feeble event of around *810 Ma. The older ages of zircons from pelitic granulites indicating Moras Granites were the outcome of the melting the granitic source of 1620–1240 Ma (cf. Singh et al. of the juvenile maBc crust (Zhao et al. 2018). So 2010). massive granitoids in the study area around The lithoassemblages of the study area indicate Moras, Malera, Paba, Waloriya, Mandwa, etc., that they were aAected by Meso-Neoproterozoic represent the younger phase of granitic intrusion. thermal overprinting and are suggested to be The massive granitoid of the Moras area plausibly related to the period of late Grenvillian orogeny, represents the southern extension of Sendra perhaps during the formation of the Rodinia granite in PARB. Younger age granitoids of *750 Supercontinent. Ma are also reported from southern parts of the study area by Roy et al.(2004) showing the 6. Conclusions impact of Malani Magmatism thermal event in this area. The study has revealed that granitoids of different Gneissic granitoids which are presumed to be the nature and character in PARB have different tec- older components within the granitoid masses also tonic implications. The outcomes are concluded as portray incompatibly with the associated meta- follows: sediments. The incompatibility is evident by the development of ductile shear zones along the con- • The granitoids are separately identiBed as mas- tacts of the two. This nature of contact is not siveandgneissicvariantsontheoutcropscaleas deciphered in case of massive granitoids not well as on the microscopic scale. The gneissic showing deformation and on the other hand, the variants have patchy occurrences with obliterated gneissic granitoids are deformed and characterize pristine characters outcropping as melanocratic the basement in the region. These are having tec- grey gneisses. These are characterized by the tonized contact with the cover rock. Polyphase presence of mylonitic foliation with intricate deformation accompanied by multiple thermal folding. These granitoids show tectonized shear remobilizations led to the diminishing of pristine contact with metasediments and lack intrusive characters of these basal rocks. Only relicts of characters. On the microscopic scale, these are pristine lithoassemblages remain preserved, while partially or completely deformed and the rest of others got variably transformed. The recrystallized. pristine basement granitoids occurring as remnants • Massive granitoids are intrusive and domi- are constrained to few pockets and represent a nantly leucocratic in nature, characterized by mass scale protolith. The gneissic granitoid out- fresh, unaltered, discrete isolated bodies. They crops actually represent these ‘Remnant base- are coarse-grained, massive, and show faint ments’ and certainly indicate basement cover traces of foliation on the outcrop scale and relationship with the associated metasediments. typical igneous interlocking texture on the Based on heavy carbon isotope studies, it has microscopic scale. These granitoids show intru- been opined that the overlying calcareous sive contact with gneissic granitoids and metasediments spanned between 1200 and 1300 Ma metasediments. (cf. Purohit 2005; Maheshwari et al. 2009; Purohit • The Beld relationship studies have revealed that et al. 2012). Hence, it can be presumed that the the quartzite bands are marker horizons between remnant basements are possibly pre-1300 Ma in the basement and metasediments. The base- age. A study by Singh et al.(2010) constrained that ment–cover relationship is characterized by the the sedimentation in the south Delhi Terrane tectonized contact of gneissic granitoids with (SDT) spanned between 1240 and 966 Ma. Both metasediments and pene-contemporaneous these studies suggest that the crustal evolutionary deformational features. The intrusive massive history of PARB is quite younger than the North variety led to the thermal remobilization of Delhi Terrane. Pre-1300 Ma status of the basement gneissic granitoids leading to a diminished granitoids is, however, comparable with the *1500 pristine character. The dismembered gneissic J. Earth Syst. Sci. (2021) 130:118 Page 15 of 17 118

granitoids or the ‘Remnant’ granitoids represent under the scheme of WOS-A for RD project (Pro- the ‘domal inliers’ generated from multiple ject Reference No: SR/WOS-A/EA-1017-B/2015) deformations (cf. Ghosh 1990). and conducted at the Department of Geology, M L • The region witnessed deformation related to S University, Udaipur, Rajasthan and Department Delhi orogenic cycle represented by DF1 features of Geology, Government College, Sirohi, Rajas- and superposed by later deformation represented than. The authors are thankful to the Heads of the by DF2. DF3 deformational features are related Departments for providing necessary working to shear deformations which are common to both facilities. The authors are also thankful to the the Mesoproterozoic Delhi Supergroup rocks as anonymous reviewers, whose suggestions have well as the Neoproterozoic Sirohi Group rocks improved the manuscript. (Arora et al. 2017; Chatterjee et al. 2020). This shear-related deformation criss-cross all the for- mations and so possibly is the youngest event and Author statement post-Delhi Orogenic also (de Wall et al. 2012). This shear deformation has a transpressional Ritesh Purohit and Harsh Bhu: Conceptualization, tectonic character, leading to regional enechelon^ supervision, validation; Kamal Kant Sharma: pattern distribution of quartzite metasediments visualization, mentoring, reviewing and editing; as well as granitoids (Bgure 2aandb).Besides and Riya Dutta: Methodology, investigation, data this, mylonitic foliation with oblique stretching collection, analysis, preparation of Bgures, writing lineation, NE–SW apical direction of sheath folds, and validation. continuous spatial variation of stretching lin- eation, contemporaneous folding of shear folia- References tion, rotation of relict clasts infers that there was wall-parallel shearing along with shortening Arora D, Pant N C, Sharma S and Sadiq M 2017 Inferring a across the shear zone wall. These observations Neoproterozoic orogeny receding the Rodinia break-up in suggest regional transpressional deformation. the Sirohi Group, NW India; Geol. Soc. London, Spec. Publ. • The realization of the basement–cover relation- 457(1) 319–338. ship between the gneissic granitoids and metased- Biswal T K 1988 Polyphase deformation in Delhi rocks, SE of Amirgad, Banas Kantha dist. of Gujarat; In: Precambrian iments conBrms that the granitoids are pre-dated of the Aravalli Mountain, Rajasthan, India (ed.) Roy A B, to metasediments. The calcareous metasediments Mem. Geol. Soc. India 7 267–278. of PARB span *1200–1300 Ma (Maheshwari Biswal T K, Gyani K C, Parthasarathy R and Pant D R 1998a et al. 2009; Purohit 2005;Purohitet al. 2012)so Implication of the geochemistry of the pelitic granulites of the gneissic granitoids, which acted as cradle the Delhi Supergroup, Aravalli Mountain, Rajasthan, India; Precamb. Res. 87 75–85. must be pre-1300 Ma or even older. Biswal T K, Gyani K C, Parthasarathy R and Pant D R 1998b • Taking into consideration of age span of massive Tectonic Implication of Geochemistry of Gabbro-Norite- granitoids (*1000 to 750 Ma) and the estimated Basic Granulite Suite in the Proterozoic Delhi Supergroup, age of the gneissic granitoids (pre-1300 Ma), it can Rajasthan India; J. Geol. Soc. India 52 721–732. be assumed that the lithoassemblages of the study Chatterjee S M, Roy Choudhury M, Das S and Roy A 2017 area display Meso-Neoproterozoic transition cor- Significance and dynamics of the Neoproterozoic (810 Ma) Phulad Shear Zone, Rajasthan, NW India; Tectonics 36(8) responding to Grenvillian Orogeny (*1.5–0.8 Ga) 1432–1454. on the global scale (Hahn et al. 2020). Globally Chatterjee S M, Sarkar A K and Manna A 2020 Mid- speaking, the mobile belt underwent disintegration Neoproterozoic tectonics of northwestern India: Evidence during Rodinia splitting and later coalesced with of stitching pluton along 810 Ma Phulad Shear Zone; othercontinentsofeasternGondwanaduring Tectonics, American Geophysical Union, pp. 1–23. Choudhary M R, Das S, Chatterjee S M and Sengupta S 2016 Neoproterozoic and later Pan-African Orogeny Deformation of footwall rock of Phulad Shear Zone, around 540 Ma (Mahadani et al. 2013). Rajasthan: Evidence of transpressional shear zone; J. Earth Syst. Sci. 125(5) 1033–1040. Choudhary A K, Gopalan K and Sastry A C 1984 Present status of the geochemistry of the Precambrian rocks of Acknowledgements Rajasthan; Tectonophys. 105 131–140. Coulson A L 1933 The geology of Sirohi state, Rajputana; Geol. Surv. India 63(I) 166. The work has been funded by the Department of De Wall H, Pandit M K, Dotzler R and Just J 2012 Science and Technology, Government of India Cryogenian transpression and granite intrusion along the 118 Page 16 of 17 J. Earth Syst. Sci. (2021) 130:118

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Corresponding editor: RAJNEESH BHUTANI