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Chapter 2 Geology of the Study Area Geology of the Study Area CHAPTER 2 GEOLOGY OF THE STUDY AREA 2.1. Overview of Indian Peninsular Shield Cratons are broad central areas of continents that have remains tectonically stable for prolonged periods. They are affected only by younger epeirogenic movements. Whereas the mobile belts are the curvilinear, high-grade, gneiss-granulite belts that surround the cratons (Ramakrishnan and Vaidyanadhan (2010). The Indian Peninsular shield is a mosaic of such cratons and mobile belts. It consists of mainly four Archean cratons: Bundelkhand Craton in the north, Singhbhum craton in the east, Bastar craton in the center and Dharwar craton in the south. These cratons are surrounded by Proterozoic mobile belts viz. Eastern Ghat Mobile belt (EGMB), Delhi-Aravalli Mobile belt, Singhbhum mobile belt and Central Indian Tectonic Zone (CITZ) and Kotri-Dongargarh mobile belt (Fig 2.1) (Radhakrishna, 1989; Yedekar, 1990; Roy and Prasad, 2003). The Precambrian tectonics of India is mainly confined in Peninsular & Central part of India. Studying Central India gives the clue regarding the early formation of Archean crust with subsequent rifting and subduction in Precambrian Indian continent. Precambrian crust of Central India in the states of Madhya Pradesh and Maharashtra is a combination of several tectono-metamorphic domains, each characterized by distinct litho-associations (Roy Abhinaba et al 2000). These domains are distributed in two crustal provinces, namely the Northern Crustal Province (NCP) and Southern crustal province (SCP), separated by a prominent ENS-WSW shear zone (Ramachandra and Roy 1998; Roy et al 2000). The supra-crustal belts and other tectono-metamorphic provinces are distributed in the Southern Crustal Province including the Bastar Craton and the Sakoli Fold Belt, and in the Northern Crustal Province comprising of Bundelkhand Craton and the CITZ. 4 Geology of the Study Area Fig. 2.1: Outline map of India showing different cratons and mobile belts of the Indian Shield (modified after Radhakrishna, B. P. 1989; Longjam, K.C. and Ahmad, T., 2012) 2.2. Regional Geology of Central India The Central Indian Tectonic Zone (CITZ) is a significant continental scale tectonic zone of Proterozoic age. It divides the Indian shield into two tectono-magmatic provinces, the northern crustal province comprising Bundelkhand craton and the southern peninsular crustal province comprising Bastar, Dharwar and eastern Singhbhum craton (Stein et al., 2004; Acharya and Roy 2000). 5 Geology of the Study Area Table 2.1: Generalized tectonostratigraphy of Central India (Roy et al., 2000) Generalised Tectonostratigraphy of the Precambrians of Central India Age Meso- to Neoproterozoic Supergroup/Group SCP NCP Cover sequences of the Chattisgarh Supergroup and Indravati, Khariar, Albaka, Pakhal, Sullavai Groups Cover sequences of the Vindhyan Supergroup Sausar Mobile Belt Palaeo- To Mesoproterozoic Sausar Group (Younger Supracrustals) Sausar granulites (Younger granulites) Betul-Chhindwara and Bilaspur- Raigarh and surguja belts Sakoli Group (younger Supracrustals) Cover sequences of the Khairagarh Cover sequences of the Bijawar and Gwalior Groups Group and Abhujhmar Group Palaeoproterozoic Donagargarh Malanjkhand granitoids Neoarchaean to Plaeoproterozoic Younger supracrustals of the Chilpi Group, Nandagaon Group, Sonakhan Group, Bengpal belt, Bailadila Group and equivalents, older intrusive granitoids Neoarchaean Bhopalpatnam granulites, Kondagon granulites (older granulite belts) Palaeo and Mesoarchaean Older supracrustals of the Sukma Group and equivalents, Amagaon Group, including unclassified gneissic complexes relic TTG enclaves 6 Younger intrusive components of Bundelkhand granitoids, younger supracrustals of the Mahakoshal group Older supracrustals of Bundelkhand and Sidhi gneiss-supracrustal association Geology of the Study Area CITZ is over 1600 km long with a width upto 200 km (Stein et al., 2004), and is bounded by lineaments namely, Son-Narmada North Fault (SNNF) in the north and Central Indian Suture (CIS) in the south (Fig. 2.1). In between these extreme boundaries two more lineaments have been identified as Son-Narmada South fault (SNSF) and Gavilgarh-Tan Shear Zone (GTSZ), (Yedekar, 1990; Jain 1991). The Central Indian Suture zone (Yedekar et al., 2003, 1990) is a major ENE-WSW trending ductile mylonite zone separating the Bundelkhand and Bastar cratons. It is almost 500 km in length and the width ranges from 0.02 to 4 km . On surface CIS is marked by a thick zone of mylonites and phyllonites indicating ductile deformation (Jain et al., 1989). The presence of high grade (amphibolite) Sausar metasediments and granulites on the northern part of CIS and presence of low grade (greenschist) metasedimentary rocks and volcanics such as those of Sakoli, Nandgaon and Kotri- Dongargarh Groups in the south has been interpreted as an Island arc setting with probable subduction from the north to south (Fig. 2.2) (Yedekar et al., 1990, 2003) The north to south subduction direction proposed by Yedekar et al., (1990, 2003), is however contested by Bandyopadhyay et al., (1995) based on the absence of the oceanic crust or ophiolites, deep sea sediments, tectonic mélange and blue schist facies metamorphism. Roy and Prasad (2003), state that the origin of these rocks proposed by Yedekar et al., (1990, 2003), if seen in light of geochemical data, does not stand upto the scrutiny. They proposed the subduction direction from south to north on the basis of their observation of the gradual younging of sediments in the Sausar basin in the same direction. According they comprehended that Sausar basin received its sediments from Bastar craton on the south and not from the Bundelkhand craton in north. Bhowmik et al., (2005) showed that the pressure-temperature-time (P-T-t) assemblage of Ramakona-Katangi granulite belt bordering the northern margin of Sausar basin are of higher grade than those of Bhandara-Balaghat granulites in southern margin of Sausar belt, thus invoking the northward direction of subduction. 7 Geology of the Study Area Fig. 2.2: Geological map of part of the Central Indian Shield (modified after Chattopadhaya et al., 2001; Ahmad et al., 2009; Chattopadhaya and Khasdeo, 2011) Felsic magmatism was dominant in Archean followed by the predominance of bimodal felsic-mafic volcanism in the Proterozoic Bastar Craton, Central India (Mondal et al., 2006). Within the Bastar Craton, the Dongargarh Supergroup lies within the Kotri– Dongargarh Belt. This is a predominantly low‐grade volcano‐sedimentary succession (Deshpande et al., 1990) trending NNE–SSW and extending along strike for about 250 km (Acharya, 2001; Roy et al., 2000; Naganjaneyulu and Santosh, 2010; Chattopadhyay and Khasdeo, 2011). 8 Geology of the Study Area 2.3. Lithology and Stratigraphical Succession of Study Area 2.3.1. Sausar Group The Sausar Group (SSG), also known in literature as the Sausar mobile belt (SMB) constitutes the southern boundary of CITZ and is bounded by CIS on its south. It is 300 km long and 70 km wide, curvilinear (convex towards south) in shape, ESE - WNW to E–W to ENE–WSW trending orogenic belt bounded by two cratonic blocks, the Bundelkhand craton in the north and Bastar cratons in the south (Roy et al., 2006). The southern most unit of SSG is the Bhandara- Balaghat granulite (BBG) domain, which is bounded by CIS. It consists of a suite of high grade metamorphic rocks that include mafic granulite, charnokite, enderbite, gneisses, meta-ultrabasites, iron formation granulite, cordierite granulite and kyanite quartzite. Table 2.2: Stratigraphy of the study area. Modified after Deshpande et al. (1990) Chattisgarh Supergroup (<900 Ma) Unconformity Khairagarh Orogenic Phase (c. 900 Ma) Kotima volcanics Ghogra formation- Sandstone Shale Mangikhuta volcanics Khairagarh Karutola Formation-Sandstone KotriGroup Sitagota volcanics Dongargarh (Intertrappean Shale) Supergroup Bortalao Formation-Sandstone Basal shale (1534 Ma?) ^^^^^^^^^^Unconformity^^^^^^^^^^^^^^ Dongargarh granite (c. 2200 Ma) Nandgaon Pitepani volcanics Group Bijli Rhyolite (c. 2200 Ma) ^^^^^^^^^^^^^^^^^^^^^^^^Unconformity^^^^^^^^^^^^^ Sakoli orogeny, metamorphism and granitization (2200 Ma?) Phyllites with minor Fe quartzite Epidote amphibolite Carbonaceous- and Muscovite-biotite phyllite Sakoli Group Heamatite-qaurtzite with impersistent feldspathic quartzite Muscovite biotite phyllite, quartz schist and amphibolites Muscovite-quartz schist Amgaon Orogeny Metamorphism and granitization (c. 2300 Ma) Psammatic metamorphites alternating with metabasic lava Amgaon Feldspathic and impure quartzite, quartz-sericite schist, hornblendeGroup biotite-feldspar-qaurtz schist, garnet-epidote quartzite, ortho- and metahornblende schists Basement gray and migmatitic gneisses 9 Geology of the Study Area The central portion comprises of a stable platform sequence of manganese bearing pelite-arenite-carbonate rocks along with Tirodi biotite gneiss and intrusive granitoids. They also show Barrovian type of regional metamorphism with metamorphic grade consistently increasing from south to north (Bhowmik and Roy, 2003, Stein et al., 2004, Roy et al., 2006). The northern part of the SSG consists of Ramakona-Katangi granulite belt (RKG), consisting mainly of cordierite gneiss, mafic granulite, felsic migmatitic gneiss and foliated gneisses (Roy et al., 2006). These three domains in the Sausar Group, indicate towards an early continental subduction in the southern CITZ followed by a later continent-continent collision from south towards north around Grenvillian time (Bhowmik and Roy 2003) accompanied by tectonic interweaving of older units into the younger units (Stein et al., 2004). 2.3.2. Sakoli Group The Sakoli Group of rocks cover an area of 3500 km2 and lies between N20°30' - 21°30' / E79°15' - 80°15' in eastern Maharashtra and is one of the main Proterozoic supracrustal suites present in the northern part of the Bastar craton (Ahmad et al., 2007). Stratigraphically, it occupies a position, at the convergence of the Kotri Dongargarh mobile belt, that runs N-S and falls parallel to the eastern margin of the Sakoli triangle, towards its north it has the ENE-WSW trending Central Indian Suture zone (CISZ) and to its south it has the Godavari graben which trends NW-SE (Bandyopadhyay et al., 1995). Major lithology of the Sakoli Fold Belt comprises of quartz-chlorite muscovite schist (+ magnetite, + andalusite, + chloritoid, + garnet, + staurolite), phyllites, tuffs, metapelites, minor quartzite, arkose, conglomerate, BIF, and the bimodal volcanics that include rhyolite, tuffs, epiclastic rocks, metabasalts and meta-ultramafic rocks (Saha et al., 2004). This sequence is intruded by pre to early tectonic dykes or sills of weakly metamorphosed dolerite gabbro and syntectonic granitoids especially along its margin and central parts. Pegmatites, quartz veins and reefs locally occur as intrusives. 10 Geology of the Study Area The volcano-sedimentary sequences of Sakoli Group are divided into four formations (Bandyopadhyay et al., 1995). They are listed from base to up by Stein et al. (2004) as follows: 1. Conglomerate and arkose with carbonaceous phyllite, ferruginous, quartzite and BIF; 2. Metabasalts with minor metapelite, chert bands and meta-ultramafic rocks; 3. Meta-pelitic schists with interbanded bimodal volcanics dominated by rhyoliterhyodacite, tuffs, breccia, epiclastic rocks and minor basalts of Bhivapur formation; 4. Slate phyllite, debris flow deposits, meta-arkose and quartzite The Sakoli Group also hosts quartz veins, quartz reefs, silicified shear zones, granitoids, pegmatites, tourmaline granite and gabbro/dolerites. The Gondwana Supergroup and Deccan basalts overlies the Sakoli Group. The Bhiwapur Formation hosts the Au-Cu deposits of Pula-Parsori-Thutanbori belt. The gold occurs either structurally bound in sulfides associated with quartz-carbonate veins or occurs as native Au in quartz veins localized along shear zones (Mishra et al., 2001). 2.3.3. Kotri-Dongargarh Supergroup The Kotri-Dongargarh Supergroup extends upto 400 km and constitutes a significant Neoproterozoic stratigraphic unit in the Central Indian craton (Naqvi, 2005). This group is younger to the Sakoli Group of rocks and directly overlies the basement. This Supergroup comprises of the older Nandgaon group, consisting a bimodal suite of basalts and rhyolites along with epiclastic rocks (Bandyopadhyay et al., 1995). This bimodal tholeiitic basalt-rhyolite association was earlier interpreted as of continental non-orogenic origin by Krishnamurthy et al. (1990) but subsequent studies showed them to be arc volcanic rocks (Naqvi, 2005). The Dongargarh granite batholith contains numerous enclaves of rhyolite, basalts (Nandgaon) and metasediments, as it intrudes rocks of Nandgaon Group, Amgaon basement and its equivalents like Bangpal and Bailadila Groups (Bandyopadhyay et al., 1995). 11 Geology of the Study Area Khairagarh Group overlies the Nandgaon Group and is made up of alternating bands of volcanic sequences and metasediments. Volcanics belong to Sitagota, Mangikhuta and Kotima Formations while the meta-sedimentary rocks are of Boratlao, Karutola and Ghogra Formations (Deshpande et al., 1990). The Kotri volcanic belt, an equivalent of Dongargarh Group, lies in Bastar district towards south. It is N-S trending, ~250 km long linear belt with width of ~50 km. It consists of bimodal volcanic suite, arkoses and conglomerates, and is intruded by Madanbara granite, which is an equivalent of Dongargarh granite. 2.3.4. Amgaon Gneissic Complex Sarkar, (1957) proposed a new system of rocks named as Dongargarh Supergroup, which included the rocks of “Amgaon Formation” and “Sakoli Group”, but later stratigraphic and tectonic work supported by age data suggested Amgaon as basement of the Sakoli Group, so Sarkar et al., (1981) renamed “Amgaon Formation” as “Amgaon Group”. The term Central Indian Gneissic Complex was coined to define the basement gneisses of both Bundelkhand and Bastar craton collectively. It included Amgaon gneisses, Bangpal gneisses, Tirodi gneisses and Sakoli gneisses (Bandyopadhyay et al., 1995). The Tirodi gneisses constitute the basement for the supracrustals of the Bundelkhand craton, which is in the north of CIS and occur intimately with Sausar group of rocks, (Subba Rao et al., 2000; Yedekar et al., 2003). However, Amgaon gneisses are reported south of CIS and considered basement for supracrustals of Kotri-Dongargarh Supergroup and Sakoli Group. Sakoli gneiss, is the term used rarely for the gneisses in the Sakoli inlier, whereas the Bangpal gneisses are located in southern Bastar. Amgaon Group consistently occupies the basement position in stratigraphic successions proposed by Sarkar, (1981); Naqvi and Rogers, (1987); Deshpande et al., (1990); Sarkar et al., (1994), Bandyopadhyay et al., (1995); Divakara Rao et al., (2000); Yedekar et al., (2003). 12 Geology of the Study Area The Amgaon group or Amgaon Gneissic Complex (AGC) lithologically consists of granite-gneiss-migmatite assemblages, with vestiges of TTG suite ranging from trondhjemitic to granitic composition, the minor components include the amphibolite, metabasalts, quartzites, BIF, kyanite-sillimanite and garnet-staurolite schists (Ramchandra and Roy, 1999; Roy et al., 2000; Yedekar et al., 2003). 2.4. Geotectonic Implications of Study Area The Dongargarh Supergroup rocks unconformably overlie the Archean Amgaon Gneissic Complex (Wanjari and Ahmad, 2007) and comprise a basal bimodal volcanic sequence (Nandgaon Group) and a younger volcano‐sedimentary assemblage (Khairagarh Group), the two sequences being separated by an unconformity (Sarkar et al., 1994; Krishnamurthy et al., 1990; Table 2.2). Volcanic rocks of the Dongargarh Supergroup belong to five different Formations viz. Bijli rhyolite, Pitepani mafic volcanics, Sitagota mafic volcanics, Mangikhuta mafic volcanics and Kotima mafic volcanics (Rao, 1981; Sarkar et al., 1981; Deshpande et al., 1990). The Bijli rhyolite and Pitepani volcanics belong to the lower Nandgaon Group whereas the upper three belong to the Khairagarh Group (Table 1; modified after Sarkar et al., 1981; Rao, 1981; Deshpande et al., 1990). The Khairagarh Group occurs in a doubly‐plunging syncline with axes trending NNE–SSW to the west of Dongargarh (Ramakrishnan and Vaidyanadhan, 2010). The generalized stratigraphic succession of the Khairagarh Group is presented in Table 2.2. The Khairagarh Group is one of the Proterozoic volcano-sedimentary sequences exposed in the northwestern part of the Bastar Craton. It comprises of a volcano‐sedimentary succession including the Sitagota and Mangikhuta volcanics that overlie the metasediments of the Bortalao Formation. These volcanics are interlayered with the Karutola sedimentary sequences. The Kotima volcanics is separated from the Mangikhuta volcanics by sandstone and shale of the Ghogra Formation (Rao, 1981; Deshpande et al., 1990). The samples collected are very fine grained, glassy and greenish in colour; some samples show vesicles with inclusions of quartz. Well preserved pillow basalt are found in the Pandripat Syncline. The age of the Khairagarh Group rocks varies from 1686 to >900Ma (Sarkar et al., 1981). According 13 Geology of the Study Area to Asthana et al. (1996) the Khairagarh Group has close chemical affinity with island‐arc magmas and Andean‐type rift tectonic setting. The adjoining Sakoli Group in the Bastar Craton is dated at ca. 1675 ± 180 Ma (Ahmad et al., 2009). The eruption age of the Dongargarh lavas of the Bastar Craton varies from ca. 2462 to 1367 Ma (e.g. the Nandgaon Group), followed by an arc‐related volcano‐sedimentary sequence of the Khairagarh Group (Neogi et al., 1996; Pophare et al., 2005). The collisional orogeny and suturing zone of the southern Bastar Craton and the northern Bundelkhand Craton along the Central Indian Tectonic Zone is dated ca. 1.5 Ga (Roy and Prasad, 2003). All the above ages indicate that mafic magmatism in this part of the Central Indian Shield may be related to the supercontinents − Ur and Columbia (Rogers and Santosh, 2004, 2009; Yakubchuk, 2010; Mohanty, 2011). 14