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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.
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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).
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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
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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.
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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).
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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
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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.
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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).
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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).
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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
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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).
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