15

Chapter II

Geology and Field Relations

2.1 Introduction

The Mobile belts are palaeoconvergent (or suture) zones surrounded by the

stabilized cratonic region of continental crust (Naqvi and Rogers, 1987). The Peninsular

India is mainly composed of Archaean cratons separated by S-shaped prominent mobile

belt (Fig. 2.1). Eastern Ghart mobile belt, Singhbhum mobile belt, Central Indian

Tectonic Zone (CITZ) and Delhi-Aravali mobile belt are the major accreted boundaries

between Northern and Southern Cratonic Provinces. The four main cratons recording the

history of Archaean era are Dharwar Craton in the south, Bastar Craton in the southeast,

Singhbhum Craton in east and Bundelkhand craton in the northern part of India

(Radhakrishna and Naqvi, 1986). These cratons have vast exposure of rocks, and a

number of geosientific issues related to their nucleation growth and stabilization in time

and space has been addressed during the last few decades. However their comparisons

with other mobile belts of Peninsular India and CITZ received less attention because of

complex and sheared nature of lithologies constituting these mobile belts. Mahakoshal

Belt, almost trending ENE-WSW, occupies the northern-most margin of CITZ, which has

also been least studied, and whatever geological and tectonic information exist that are

mostly related to Central India Shear (CIS) Zone of CITZ (Acharyya and Roy, 2000 in

Stein et al., 2004). Although few sparse studies have been carried out and existed on

stratigraphic and structural-based field observations (Pascoe, 1965; Narain, 1962, Yadav

and Tiwari, 1972; Goyal and Jain, 1975; Narain and Thambi, 1979; Roy and

Bandhyopadhyay, 1990 a, b; Nair, 1988, Jain et al., 1991, Bandhyopadhyay, 1995; Nair et

al. 1995; Roy and Devrajan, 2000). There are still lack of establishing the firm and

spectacular field evidences, which could reveal the geology and tectonics of this complex

terrain. Hence, in order to fulfil the existing gap in particular relation to Dudhi and

surrounding regions of Mahakoshal Belt, an attempt has been made to establish the field

relationships between the granitoid plutons and associated lithotypes. Main emphasis has

been given on documenting the field features of genetic significance, classification of

unidentified granitoids and enclosed enclaves and their relationships with associated

lithounits. The Indian Archaean cratons have more-or-less similar tectonothermal and

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amalgamation

histories as recorded from cratonic region of Canada, South America, Africa, Australia,

Russia, and China.

The present work has been carried out in ~200 square km area of Sonbhadra

District in Uttar Pradesh, which is northernmost part of Satpura Mobile Belt or Central

Indian Tectonic Zone (CITZ) known as Mahakoshal Belt. The investigated area covers

number of lithounits forming bulk of Mahakoshal Belt. Geologically significant field

observations have been documented to recognize likely basement lithology and its

relation with associated mafic-felsic magmatism forming the volcano-plutonic igneous

complexes. Field investigations have also been extended linearly towards eastern part of

Mahakoshal Belt so that clear lithological scenario can be built-up. The unnoticeable

Fig. 2.1 Central India Tectonic Zone (CITZ) separates northern cratonic province from southern cratonic

province (after Acharyya and Roy, 2000; Stein et al., 2004). AD-Aravalli Delhi fold belt, B-Bundelkhand

craton, BC-Bastar Craton, CIS-Central Indian Shear Zone, CITZ-Central Indian Tectonic Zone, DC-

Dharwar Craton, EG-Eastern Ghat, KD-Kotri Dongargarh belt, KN-Karnataka nucleus, M-Madras block,

MC-Marwar Craton, MR-Madurai block, N-Nilgiri block, SC-Singhbhum Craton, SK-Sakoli fold belt, SMB-

Sausar mobile belt, SONA-Son Narmada subzone, T-Trivandrum block, TF-Tapti fault, MJ-Malanjkhand,

M-, B-, A-, P-, C Moyar-Bavali, Bhavani, Attur, Palghat and Cauvery shear zones respectively Estelar

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field-based scientific issues that are also addressed here include the basement problem of

Sidhi-Dudhi gneissic complex in the northern part of Mahakoshal Belt, which could be

part of Bundelkhad Craton (Roy and Prasad, 2003; Ramakrishnan and Vaidyanadhan,

2008) or Chotanagpur granitic gneiss (Yadav, 1978, Acharyya, 2001). Contemporaneous

rift-related volcano-sedimentary sequences and synchronous mafic-felsic magmatism

have played important role in the evolution of Mahakoshal Belt, CITZ, whose field

relationships have been discussed below.

2.2 Regional geology and tectonics

The dominant E-W trending more than 700 km long central part of Indian

Continental Crust is known as Central Indian Tectonic Zone (CITZ; Radhakrishna and

Ramakrishna, 1988; Radhakrishna, 1989; Acharyya and Roy, 2000; Stein et al., 2004).

Elsewhere CITZ is also designated as Satpura Mobile belt (SMB), which represents a

continental scale tectonic zone considered as a trans-continental suture (e.g. Harris,

1993). CITZ is a complex orogenic belt separating the Peninsular India into two

provinces and demarcates a prominent tectonic boundary between the northern and

southern cratonic provinces. Son-Narmada North Fault (SNNF) is northernmost and

Central Indian Shear (CIS) zone is southernmost boundaries of CITZ separating the

Bundelkhand Craton in the north, and Bastar, Singhbhum and Dharwar Cratons in the

south (Fig. 2.1). Extension of CITZ continues towards east through Chotanagpur Granite

Gneissic Complex (CGGC) further into Shillong (or Meghalaya) Plateau of northeast

India (Acharyya, 2001). It is mainly comprised of three sub-parallel low-to-medium grade

supracrustal belts associated with granulite belts along the major tectonic divisions.

However, most part of it covered by Deccan trap, Gondwana sediments and Quaternary

alluvium.

The northernmost supracrustal belt i.e Mahakoshal Belt is closely followed by

middle Betul Supracrustal Belt and Sausar Supracrustal Belt, which lie to the southern

part of the CITZ. The granulite belts, sub-parallel with the major supracrustal belts, are

the Makrohar Granulite (MG) Belt in the north, Ramakona-Katangi Granulite (RKG) Belt

in the middle and Balaghat-Bhandara granulite (BBG) Belt in the south (Fig. 2.2). These

supracrustal belts associated with granulites are separated from each other by major

ductile shear zones and faults. The Mahakoshal Belt delineated to the north and south by

two major Moho reaching faults known as Son-Narmada North Fault (SNNF) and Son-

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Narmada South Fault (SNSF) that together constitute SONA fault system. The SONA

fault or lineament is extended further in the northeast India through covered Ganga plain

and Bangal Basin to Brahmaputra lineament (Sen, 1991). To the south of SNSF,

Makrohar Granulite Belt is exposed and it is separated from Betul Supracrustal Belt by

Balrampur Fault. The southern boundary of Betul Supracrustal Belt is demarcated by Tan

Shear Zone, separating it from Ramakona-Katangi Granulite Belt that is followed by

Sausar Group. The Sausar Group is delineated by Bhandara-Balaghat Granulite Belt in

the south. The Bhandara-Balaghat Granulite Belt bounded to the south by Central Indian

Fig. 2.2 Inset map shows mobile belts and cratonic regions of India.Geological map of Central part of

Indian showing Central India Tectonic Zone (CITZ), MGB-Makrohar Granulite Belt RKG-Ramakona-

Katangi Granulite Belt, BBG-Balaghat Bhandara Granulite Belt, CIS-Central India Shear zone (after Roy

and Prasad, 2002). Study area (box) is also shown on the map.

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Shear (CIS) zone which is southernmost boundary of CITZ which separates Bastar

Craton of southern Peninsula (table 1.1). To the south of CIS, the N-S trending ensialic

failed rift system of Neoarchean Sakoli and Dongargarh Mobile Belts is exposed

(Bandyoprdhyay et al., 1995; Roy et al., 1997).

The northern part of CITZ abuts against Vindhayan which demarcates southern

boundary of Bundelkhand Craton. The CITZ having four main tectono-lithounit

components; (i) Aravali Craton in the west, (ii) Chhotanagpur Gneissic Complex in the

east, (iii) Meghalaya plateau further in the northeast, and (iv) Eastern Ghat Mobile Belt

(EGMB) to the northeast. Tectonic connection of CITZ with EGMB constituting Middle

Protrozoic Mobile Belt (MPMB) was suggested by Radhakrishna and Naqvi (1986)

which Leelanandam et al. (2006) considered as Greater Indian Proterozoic Belt (GIPB).

The MPMB or GIPB having a Proterozoic tectono-thermal connection with western

Aravali Mobile Belt (Mewar Craton) passing through CITZ-Chhotanagpur Gneiss-

Meghalaya plateau (Acharyya, 2001) in the zone is referred herein as S-shaped Tectonic

Zone (STZ) or sigmoidal Proterozoic gneissic complex zone (Fermor, 1936). Although,

they might have distinct lithological assemblages as a consequence of differential degrees

of deformational history, they have still recorded a similar pronounced tectono-thermal

event in Proterozoic era that has an extension with unconnected Western Australia

(Harris, 1993), Eastern Australia (Crawford, 1974) and affinity with Columbia

Supercontinent (e.g. Rogers and Santosh, 2002; Rogers and Santosh 2009; Bhowmik et

al., 2010; Bose et al., 2011; Bora, et. al., 2013).

2.2.1 Supracrustal belts

There are three major supracrustal belts contributed in the evolution of continental

crust of CITZ; Mahakoshal Belt in the north, Betul Belt in the middle and Sausar Belt in

the south. The northern most part of CITZ is exposed from Barmanghat to Rihand Dam

covering distance of near about 600 km, referred herein Mahakoshal Belt trending ENE-

WSW. It is mainly comprised of quartzite, phyllite, carbonates, slate, chert, basalt and

tuff formed in a rift basin (Chaudhuri and Basu, 1990; Kumar, 1993; Nair et al., 1995;

Roy and Devarajan, 2000), which commonly rest unconformably over the so called

basement Dudhi granite gneiss. It has been intruded by a number of stock-like, felsic

magmatic plutons such as Barambaba, Jhirgadandi, Tumiya, Harnakachar, Madanmahal

granitoid plutons (named after the localities in and around which most of the granitoid

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bodies are exposed) etc., which have been emplaced into the country-rocks having

features of low-grade contact metamorphism as evident from the presence of cordierite

and andalusite (Roy et al., 2002b). Minor amount of carbonatites, lamprophyre,

ultramafic plug, gabbro and syenite can also be observed. Later magmatic phases as mafic

dykes and dyke swarms have profusely cross-cut the Mahakoshal Belt.

The middle part of CITZ is designated as Betul Belt, sandwiched tectonically

between Mahakoshal and Sausar Supracrustal Belts in the south, extends from Betul in

the west to Chindwara in the east for about 135 km. It is overlain by Gondwana sediments

and Deccan trap and consists of vocano-sedimentary sequences (quartzite, pelite, calc-

silicate, banded iron formation (BIF), garnet-anthophyllite schist and bimodal volcanics)

intruded by mafic-felsic magmatic suites (Srivastava and Chellani, 1995). The arc-type

tectonic setting of bimodal volcanism (basalt-rhyolite) of Betul Belt (Ramachandra and

Pal, 1992; Raut and Mahakud, 2002) makes difference from unimodal volcanism of

Mahakoshal Belt and volcanic-free Sausar Belt. The sedimentary lithounits are dominant

in Sausar Belt in the southernmost part of CITZ, and is separated from Betul Supracrustal

Belt by Tan Shear Zone, intimately associated with RKG and BBG belts in its northern

and southern parts respectively. It extends from Ramakona to Ratanpur for a length of

more than 215 km and is comprised of quartzite-carbonate-pelite-Mn-formation and thin

layers of gritty to pebbly quartzites and polymict conglomerate (Narayanaswami et al.

1963; Devarajan and Hakim, 1992; Pal and Bhowmik, 1998).

2.2.2 Granulite belts

Three main granulite belts running sub-parallel as a part of Supracrustal Belts, viz.

Makrohar Granulite belt, Ramakona-Katangi Granulite belt and Balaghat-Bhandara

Granulite belt associated with Mahakoshal Belt in the north, Betul belt in the middle and

Sausar belt in the south respectively. The Makrohar Granulite Belt has strike continuity

with Betul Belt and consists of more-or-less similar lithological assemblage such as BIF-

marble-calc silicate and intrusive mafic complexes. Its metamorphic event has been dated

ca1.7 Ga (Roy and Prasad, 2003). The Ramakona-Katangi Granulite Belt exposed to the

north of Sausar, is mainly comprised of mafic granulite, migmatite, cordierite bearing

gneiss, garnetiferous metadiorite. These high grade granulite facies have recorded three

stages of collisional (orogenic) related metamorphic events (Bhowmik et al., 1999, 2000)

at ca 1.5 Ga (Roy and Prasad 2003). The Balaghat-Bhandara Granulite Belt is part of

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CITZ exposed discontinuously along Central Indian Shear (CIS) zone (Ramachandra and

Roy, 2001). It is comprised of two pyroxene bearing mafic granulite, charnockite,

cordierite bearing granulite and meta-iron-formation (Ramachandra and Roy, 2001;

Bhowmik 2005), which are enclosed into highly tectonized Amagaon gneissses

(Ramachandra, 1999). Other than this litho-assembly, quartzite-pellite-BIF lithotypes are

associated with the granulites. Granulite facies has undergone two phases of deformation

(Bhowmik and Pal 2000, Ramachandra, 1999), which suggests collisional type orogeny

during suturing of Bundelkhand and Bastar Cratons (Ramachandra and Roy, 2001)

occurred at ca 2.67 Ga (Roy et al., 2006).

2.3 Geology of Mahakoshal belt

The Mahakoshal Belt demarcates the northern most boundary of CITZ lying to the

southern periphery of the Vindhanyan Range that defines southernmost edge of the

Bhundelkhand Craton. It is an arc-shaped supracrustal belt, which extends from Jabalpur

District of Madhya Pradesh through Sonbhadra District of Uttar Pradesh to Palamau

District in Jharkhand. Its northern most boundary marks the Son-Narmada North Fault

(SNNF) whereas Son-Narmada South Fault (SNSF) demarcates the southern boundary,

together constituting SONA faults system. It is unconformably overlain the Sidhi and

Dudhi gneissic complexes exposed to the south of Mahakoshal Belt, which are considered

equivalent to the rocks of Bundelkhand Craton (Ramakrishnan and Vaidyanadhan, 2008).

Most parts of the Mahakoshal Belt are covered under Gondwana sediments, Deccan trap,

and Quaternary alluvium. The main lithological compositions of Mahakoshal Belt are

quartzite, phyllite, chert, carbonate, BIF, greywacky-argillite and mafic volcanics. Some

have considered that metavolcanics of Mahakoshal represent integral part of greenstone

belt; however it is not valid because of fact that sedimentary lithounits dominate over the

mafic volcanics. Erstwhile, it has also been compared with Bijawar Group of rocks that

unconformably rest over the Bundelkhand Craton (Medlicott, 1859). Since rocks of the

Mahakoshal Belt are relatively more deformed and metamorphosed as compared to those

of Bijawar Group, and hence they are referred as “Transition Series” (Oldham, 1893).

Auden (1993) redefined it as the “Bijawar of Narmada”. Later, it has been separately

recognized as Mahakoshal Group by Narian and Thambi (1979). Further Nair et al.,

(1995) and Jain et al. (1995) have brought out a stratigraphy sequence of Mahakoshal

Belt which consists of three Formations that rest unconformably over the Dudhi

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Table 2.1: Lithostratigraphy of the Mahakoshal Belt (after Nair, et. al., 1995 and Jain et. al.,1995)

Intrusives

lithounits:

Dunite, harzburgite, gabbro, diorite, quartz porphyry, quartz veins, syenite and

associated alkaline dykes, carbonatite, barite veins, lamprophye/trachyte and

associated intrusive. Barambaba granite and equivalents.

Formation (Fm.) Lithology

Vindhyan Supergroup and Jungel Group

---Unconformable and at places Son-Narmada North Fault (SNNF)---

Parsoi Fm. Tuffaceous and carbonaceous phyllite, feldspathic quartzite and conglomerate,

tuffaceous phyllite and metabasalt intercalations

Agori Fm. Banded hemaetite/magnetite quartzite and jasper with associated tuff and ash beds.

Impure marble, dolomite and interbedded calc-chlorite schist with occasional

metabasalt lenses and conglomerate

Chitrangi Fm. Mafic and Ultramafic plugs and dykes including peridotites and serpentine

agglomerates, metabasalt and peridotite pillow lava

-------------Son-Narmada South Fault (SNSF)-------------

Dudhi Gneissic

Complex

Granite Gneisses and Migmatites

Table 2.2 Comparison of lithostratigraphy of the Mahakoshal Belt (after Nair, et. al., 199; Jain et. al.,

1995) with those given after Roy and Devarajan (2000).

Intrusive

lithounits

Quartz porphyry, albite granite, syenite, lamprophye, dolerite,

dunite/peridotite with granitoids; Barambaba Jhirgadandi,

Madanmahal, Tamakhan (after Roy and Devarajan, 2000)

after Nair, et.

al., 1995 and

Jain et.

al.,1995

Formation (Fm.) Lithology Formation

Dudhmaniya Fm. Alternating sequence of BIF and phyllite

Parsoi Fm.

---------Gradational Contact------------

Parsoi Fm. Greywacke-argillite, carbonaceous phyllite, feldspathic quartzite

and basal polymict conglomerate

Parsoi Fm.

-----------Faulted Contact/Unconformity-----------

Sleemanabad Fm. Pillowed basalt, maganiferous chert, BIF and ultramafic plugs

Quartz arenite, stromatolitic carbonate, BIF and phyllite

Chitrangi Fm

Agori Fm.

-------------Unconformity-------------

Sidhi and Dudhi

Gneissic Complex

Sidhi gneiss and Dudhi granitoids with enclaves of supracrustal

rocks.

Dudhi

Complex

gneissic complex (table 2.1). The stratigraphy of Mahakoshal Belt was again revised by

Roy and Devarajan (2000) in which volcano-sedimentary sequences were deposited in a

continental-rift tectonic setting (table 2.2). These lithounit assemblages are clubbed with

Agori Formation and Chitrangi Formation, which together constitute Sleemnabad

Formation. It is overlain by sedimentary sequences made up of greywacke-argillite,

carbonaceous phyllite, feldspathic quartzite and basal polymict conglomerate of Parsoi

Formation and followed gradationally by alternate sequence of BIF and phyllite of

Dudhmaniya Formation.

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Initially the Mahakoshal Belt was considered pericratonic shallow level marine

basin along the southern margin of the Bundelkhand Craton in which sedimentary

successions were deposited (Roy and Devarajan, 2000). Afterward basin had experienced

explosive nature of volcano-thermal event in the rift environment as suggested by the

abundance of pyroclastic flows. The mafic volcanism was generated by high degree

melting of shallow level mantle (Chaudhuri and Basu, 1990; Kumar, 1993; Nair et al.,

1995). Finally, rocks of the Mahakoshal Belt were intruded by ultramafic-mafics, alkaline

rocks and granitoid plutons during a time span of 2.045 Ga to 1.75 Ga (Sarkar, et al.,

1988; Roy and Deverajan, 2000).

2.4 Field observation

Intrusive granitoid plutons have played significant role in the crustal evolution of

Mahakoshal Belt. These granitoid plutons are emplaced either as diapiric or non-diapiric

forms. Granitoid plutons intrude the volcano-sedimentary lithounits of Mahakoshal

Group. These include an elongated Jhirgadandi granitoid pluton, laccolith-like Tumiya

granitoid pluton, stock-like Nerueadamar granitoid pluton, Raspahari granitoid pluton,

Harnakachar granitoid pluton, and Katoli granitoid pluton. Apart from these plutons

porphyritic to massive felsic to mafic volcanics having distinct mode of emplacement

within the belt can also be observed. Jhirgadandi pluton intrudes the siliceous chert and

meta-pelitic country rocks. Nerueadamar and Tumiya plutons intrude the phyllite whereas

Harnakachar pluton is intrusive into quartzite. Raspahari pluton is emplaced into

metavolcano-sedimentary rocks of Mahakoshal Group (Fig. 2.3). Enclaves as xenoliths of

mica-schist, quartzite, phyllite, and metavolcanics can be observed hosted in Katoli

granitoid pluton and in Dudhi granite gneiss, which suggest intrusive relation with deep

burial lithounits. Microgranular enclaves of mafic to hybrid nature similar to as described

elsewhere (e.g. Didier, 1973, Didier and Barbarin, 1991, Kumar et al., 2004a; Kumar

2010a; Bora et al., 2013) are ubiquitous in the plutons except in Tumiya and

Neureadamer plutons. Moving from northern to southern parts of Mahakoshal Belt, first

cherty lithounit is exposed that laterally graded into phyllite towards quartzite. Further

south of these sedimentary lithounits, volcanic sequences are well exposed, which have

almost E-W trend broadly correlating with the major shear zone of CITZ. The sequences

of porphyritic to massive volcanics alternating with sedimentary lithounits extend from

Sidhi-Singrauli (M.P.) to Dudhi regions of Sonbhadra (U.P). The exposed volcano-

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sedimentary sequences were deposited penecontemporaneously similar to as commonly

observed in marginal rift environment. The volcano-sedimentary sequences and some

granitoid plutons have undergone varying degrees of deformation due to regional-scale

shearing forces operated during the formation of CITZ. Based on subtle field observation,

chert appeares to represent deeper lithological sediments deposited in marine

environment. Phyllite has been formed by metamorphism of shale protolith that might

have also deposited in a shallow-level environment and graded southward into terrestrial

quartzite. In these volcano-sedimentary sequences later intrusion of bimodal magmatism

took place.

The so called Neoarchean basement rock Dudhi granite gneiss (DG), well exposed

near Dudhi locality, is moderately to strongly deformed, foliated, and even migmatized as

exhibited in folded layers of melanosome, mesosome and leucosome mostly prevalent in

the central part. However, at periphery, it is relatively less deformed and contains coarse

crystal (megacryst) of K-feldspar giving rise to porphyritic granite gneiss appearance. The

Fig. 2.3 Geological map of the eastern most part (Dudhi region) of Mahakoshal Belt showing

locations of granitoid plutons and associated lithounits (after Raju and Rastogi, 2001).

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DG contains few elongated (stretched) enclaves and the stretching of enclave and K-

feldspar megacrysts correlated well with the E-W strike of CITZ. It is mostly exposed in

and around Dudhi area and cross-cut by numerous dykes parallel to the foliation plane.

Lensoidal boundins of leucosome can be distinctly noticed. Exactly at the southeastern

fringe of so called basement DG, coarse to medium grained leucocratic granitoids are

exposed referred herein as Raspahri granitoid (RG) pluton, which is mainly comprised of

biotite, feldspars and quartz. It contains elongated abundant country-rock fragments of

metamorphosed volcano-sedimentary lithounits and a few mafic to hybrid microgranular

enclaves showing typical magmatic flowage textures in relation to host granitoids.

To the west of the basement DG in and around Katoli locality, a differentiated

felsic magmatic lithounits can be encountered, which varies texturally from melanocratic

porphyritic granitoid through medium to coarse grained granitoid to leucogranitoid

collectively constitute Katoli granitoid (KG) pluton. Medium to coarse grained variety of

Katoli pluton consists dominantly of mafic to hybrid microgranular enclaves having

diffused boundaries with host granitoids. The Katoli granitoids appear highly

differentiated as evident from melanocratic to leucocratic, medium to coarse grained,

equigranular to porphyritic nature, and varying amounts of modal minerals. Later these

granitoids are cross-cut by mafic dykes as well as feldspathic veins. At few places Katoli

granitoid pluton is highly affected by potash-rich hydrothermal fluid flush giving rise to

pinkish stain of the rocks. The hydrothermal fluids appear injected along parallel to sub-

parallel foliation planes formed during crustal scale shearing of CITZ, which has indeed

developed a sigmoidal shaped geometry as discussed earlier.

Further, to the north of Katoli granitoid pluton, a small body of leucocratic

equigranular granitoids frequently hosting clots of mica-rich enclaves can be observed

referred herein Nerueadamar granitoid pluton. Leucocratic two-mica (bt-ms) granitoids

forming the Nereuadamar (NG) pluton intrude the phyllite country-rocks. A leucocratic

granitoid almost identical to that of Nerueadamar granitoids are exposed in and around

Tumiya region, referred herein as Tumiya granitoid pluton, which intrudes the slate of

Parsoi Formation of Mahakoshal Belt. Andalusite crystals were developed into the

phyllitic country-rock as a consequence of contact (thermal) metamorphism.

Nerueadamar granitoids consist of xenoliths of country-rock and surmicaceous mica-rich

enclaves which most likely represent restite (residue) from source region. Tumiya

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granitoid (TG) pluton appears emplaced as laccolith (dome) mass having very passive and

winty nature of intrusion with the slate country-rock. It has been cross-cut by coarse

grained leucocratic quartzo-feldspathic pegmatite enriched in mica flakes and tourmaline

crystals. Post-plutonic dolerite dykes have intruded the TG pluton.

In between TG pluton and Dudhi granite gneiss, a small stock-like melanocratic

equigranular garnet-bearing granitoid body is exposed in and around Harnakachar

locality, referred herein as Harnakachar granitioid (HG) pluton. It is free from any

country-rock xenoliths but bears rounded to subrounded mafic to hybrid microgranular

enclaves. An elongated elliptical-shaped granitoid body is exposed in the northern most

part of the Mahakoshal Belt in and around Jhirgadandi locality, referred herein as

Jhirgadandi granitoid (JG) pluton. It consists of various shape and size of mafic to hybrid

microgranular enclaves and country-rock xenoliths. Microgranular enclaves and host

granitoid magmas were coeval and recorded an important Columbian Supercontinent

event at ~ 1750 Ma (Bora et al., 2013). To the east of these plutons, vast exposures of

volcano-sedimentary sequences extend upto Sidhi District (M.P), which is eastward

extension of Mahakoshal Belt. Detailed field observations have been documented for

these granitoid plutons and associated volcano-sedimentary lithountits of Mahakoshal

Belt which are explained and discussed in the forth coming paragraphs.

2.4.1 Harnakachar granitoid (HG) pluton

Equigranular to porphyritic, coarse grained granitoids are well exposed to the east

of Dudhi granite gneiss i.e. in and around Harnakachar locality, which constitute small

stock-like body referred herein as Harnakachar pluton. The granitoids are mainly

composed of biotite-feldspars-quartz±garnet assemblage (Fig. 2.4a). Some crystals of

garnet and sub-rounded garnetiferous microgranular enclaves are hosted in granitoids

(Fig. 2.4b, c). The enclaves have diffused margins (Fig. 2.4c). Country-rock xenoliths

were not observed in the Harnakachar pluton. However, diffused contacts between fine

grained arkosic quartzite and granitoids can be observed (Fig. 2.4d). Pink K-feldspar

crystals are ubiquitous in the country-rock quartzite (Fig. 2.4e). These K-feldspar crystals

are gradually diminished towards the granitoid pluton suggesting nucleation and growth

of K-feldspars in the country rock during melt percolation and potash diffusion within

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quartzite country rock. Later the granitoids were cross-cut by mafic dykes and aplitic

veins. Both mafic dykes and aplitic veins appear composite in nature as they are parallel

to each other. The presence of garnets in both microgranular enclaves and host granitoids

might have been developed during syn-to-post deformational events. Small dismembered

non-garnetiferous angular xenoliths of hornblende diorite hosted in Harnakachar granitoid

pluton can be noticed which are cross-cuts by feldspathic veins (Fig. 2.4f).

Fig. 2.4 (a) Fresh and closer view of Harnakachar granitoid which also contain reddish brownish garnet in

it, b) large elongated microgranular enclaves hosted in coarse grained equigranular Harnakachar

granitoids, (c) Rounded to subrounded garnet bearing enclave having diffused contact with host coarse

grained Harnakachar granitoids, (d) contact between granitoids and sedimentary arkosic quartzite, (e)

Development of K-feldspar crystals in the country rock (sedimentary) lithounits due to thermal

metamorphism by the intruding granitoids, (f) Harnakachar granitoids contain xenolith of hbl-diorite which

later cross-cut by veins formed by potassic fluids.

(a) (b)

(c) (d)

(e) (f)

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2.4.2 Jhirgadandi granitoid (JG) pluton

The northern most felsic magmatism in Mahakoshal Belt is referred as

Jhirgadandi granitoids (JG) forming an ellipsoidal stock-like pluton which consists of

diverse nature of enclaves viz. microgranular enclaves and country-rock xenoliths. The

JG pluton exposed in a wide region from Asnadhor to Pipraha localities and contain mafic

to hybrid microgranular enclaves and country-rock xenoliths. The JG pluton exhibits

Fig. 2.5 a) Coarse-grained equigranular biotite monzogranite of Jhirgadandi pluton b) Partly dissolved

(disequilibrated) xenocrysts of K-feldspar and quartz in diorite, c) Dismembered xenolith in granitoid, (d)

An elongated (ca 60 cm in length) microgranular enclave hosted in medium-grained granitoid, e) Hybrid

microgranular enclave and felsic phenocrysts hosted in granitoids, (h) Feldspathic vein cuts the

porphyritic granitoid and microgranular enclave. Diameter of coin is 2.2 cm. Diameter of camera lens

cap is 5 cm. Length of marker pen is 13.5 cm. Length of hammer is 26.1 cm (after Bora et al., 2013)

(a) (b)

(c) (d)

(e) (f)

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textural and mineralogical variations from rim to core forming more-or-less a zoned

pluton. Marginal part of the JG pluton is porphyritic, coarse grained, K-feldspar and

biotite rich, and contains ubiquitous country-rock xenoliths of meta-pellite and siliceous

chert (Fig. 2.5a-c). The K-feldspar phenocrysts, microgranular enclaves and country rock

xenoliths are aligned almost in E-W direction correlating well with the long axis of the JG

pluton and broadly with the strike direction of CITZ. However, core part of the JG pluton

is medium to coarse grained with lesser amount of biotite and can be characterized by the

absence of country rock xenoliths and presence of few but relatively large elongated

mafic to hybrid microgranular enclaves (Fig. 2.5d). Megascopically, the enclaves of JG

can be classified into (1) angular country rock fragments known as xenoliths (2) mafic

(equigranular) to hybrid (xenocryst-bearing) microgranular enclaves (3) early crystallized

mafic biotite clots or segregation forming autolith or cognate and (4) mafic schelierens

showing magmatic flowage. Microgranular enclaves are spheroidal, elongated, and at few

places ameboidal in shape having crenulated (irregular) margins with occasional diffused

boundaries with host granitoids (Fig. 2.5d-f). Mafic (biotites) scheliers and K-feldspar

megacrysts exhibit magmatic flowage patterns in host granitoids. The K-feldspar

megacrysts show greyish (fresh) to pale pink-coloured (stained) rim affected by

hydrothermal fluids. Since Jhirgadandi granitoids have vast exposure as compared to the

rest of the granitoid plutons of Mahakoshal Belt and hence detailed field features have

been documented along Asnadhor-Salaidih-Jhirgadandi-Pipraha localities described

below.

2.4.2.1 Asnadhor locality

The western margin of JG near Asnadhor locality is porphyritic in nature with K-

feldspar phenocrysts and biotite enriched. It contains rounded, elliptical shaped

porphyritic to phenocryst-free microgranular enclaves and angular country-rock xenoliths

which got dismembered due to the thermal effect of the intruding host granitoid magma.

Porphyritic microgranular enclaves contain K-feldspar xenocrysts identical to those found

in host granitoids. Fine grained microgranular enclaves are xenocryst-free and more

melanocratic in nature. It is worth mentioning that K-feldspar megacrysts of granitoids

and microgranular enclaves follow a similar magmatic alignment. Few cms thick veins of

aplite, at places, cross-cut both the granitoids and enclaves, which strongly point to later

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evolution of silica-rich melt that closely followed the solidification of coeval granitoid-

enclave magma system.

2.4.2.2 Saliadih locality

Medium to coarse grained, melanocratic, equigranular diorite is associated with

coarse grained equigranular granitoids in and around Saliadih locality. About a meter

long elongated microgranular enclave can be found hosted in the granitoids depleted in

mafic (biotites) content. Country-rock xenoliths have not been observed in it. Beyond this

5m wide pink-coloured aplitic vein intruding the granitoids can be noticed. About half a

km ahead from the exposure of aplitic vein, K-feldspar megacryst (phenocryst) bearing

hybrid diorite (Fig. 2.5b) mass has diffused contacts with granitoids which most likely

suggest coeval nature of diorite and granitoid magmas. However, at places gradational

contact between them can also observed that probably indicate partial (local) mixing

phenomena between diorite and granitoid melts. K-feldspar phenocrysts in diorite appear

partially dissolved or resorbed (melted) over which felsic (silicic) rims are also grown

giving rise to rounded to sub-rounded, rapakivi-like texture formed in hybrid magma

environment. Hence, K-feldspar phenocrysts in diorite are xenocrysts. Small sized

lenticular microgranular enclaves are also hosted in granitoids. K-feldspar xenocrysts

bearing diorite has much resemblance to those of hybrid microgranular enclaves, which

are commonly observed in the granitoids of Asnadhor, Pipraha and Jhirgadandi localities.

2.4.2.3 Jhirgadandi locality

Porphyritic (K-feldspar phenocryst) biotite-rich granitoids are exposed in and

around Jhirgadandi locality ~3 km ahead of Salaidih towards east i.e. the centre of the

plutonic body. K-feldspars are randomly oriented within the host granitoids. Rounded to

elongated mafic to hybrid microgranular enclaves are ubiquitous and are moderately

aligned E-W direction whereas angular to sub-angular pelitic country-rock are absent or

meagre. Microgranular enclaves are porphyritic (xenocryst bearing) and equigranular

(massive) in nature having sharp and diffuse margins with host granitoids. The K-feldspar

xenocrysts in enclaves are identical to those found in the host granitoids except to the

partly dissolved crystal outlines. Mafic schelierens and biotite aggregates (autolith) are

also observed. The hybrid enclaves are coarser than the fine grained microgranular

enclave suggesting that they might have mingled at various stages of interactions between

mafic and felsic magmas.

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2.4.2.4 Pipraha locality

At the eastern fringe of the pluton granitoids have more-or-less similar

characteristic features as commonly observed in the granitoids of Jhirgadandi locality.

However, country-rock xenoliths are abundant at this locality because of intrusive

margin. The K-feldspar phenocrysts at this place are larger in size with dark greyish core

than those seen elsewhere. Some K-feldspars are aligned along the contact outline

between the hybrid enclave and granitoids.

2.4.3 Katoli granitoid (KG) pluton

Katoli granitoid pluton is of relatively larger dimension at exposed level covering

an area extending from west of the Dudhi granite gneiss towards east in and around

Katoli to the Majholi localities. It contains fine to coarse grained porphyritic to

equigranular, leucocratic to mesocratic granitoids which are either enclave-bearing or

enclave-free. During the field sessions there were many dug-wells excavated under

‘MNREGA’ scheme of Government of India (Fig. 2.6a), where the contact and intrusive

relationships between country-rocks (mica-schist) and granitoids can be very well

established. It has been observed that Katoli granitoids intrude the quartz mica-schist and

carbonates as country rocks, the xenolith of which can be seen hosted in granitoids, along

with amphibolite xenolith, cognate and frequent microgranular enclaves. Xenoliths are

recognized based on their original sedimentary or metamorphic fabrics, which commonly

have close resemblance with the country-rocks. Mica-schist xenoliths retain the schistose

fabric (Fig. 2.6b) whereas metavolcanics (amphibolite) xenolith exhibits some reaction

signatures with host granitoid melt forming some siliceous rims around the xenolith (Fig.

2.6c). The microgranular enclaves are fine grained equigranular to porphyritic in nature,

giving an impression of partial (mingling) to complete (mixing) hybridization (Fig. 2.6d,

e). However, some remnants of mafic end-member which participated in mingling to

mixing events at outcrop scale can still be recognized (Fig. 2.6e). Mafic (small) and large

porphyritic (hybrid) microgranular enclaves having rounded to sub-rounded, crenulate

and sharp to slightly diffuse boundaries with host granitoids can be observed.

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Interestingly, hybrid enclave contains large rounded mafic and small anhedral felsic

phenocrysts (xenocrysts) similar to as noted in granitoids. Granitoids display features of

heterogeneity with respect to mafic and felsic components which are randomly dispersed

and diffused. These features are commonly achieved when crystal-charged mafic and

felsic magmas partially mixed and frozen prior to complete homogenization because of

much rheological contrast and differences in mass fractions of interacting magmas. At

some places mafic bodies (dyke-like) have been dislodged and dismembered by the

intruding leucocratic granitoid melt (Fig. 2.6f). These mafic blocks appear to have moved

Fig. 2.6 (a) Rock exposures in the wells dugged under the MNREGA scheme of Govt. of India, in and

around Katoli locality of Sonbhadra in Uttar pradesh, (b) Medium grained euigranular leucocratic

granitoids contain xenolith of quartz-mica-schist in Katoli granitoid, Note the metamorphic fabric in the

xenolith, (c) Xenolith of metavolcanics of Mahakoshal Group armoured by felsic melt, (d) Porphyritic

melanocratic coarse grained Katoli granitoids contain rounded to subrounded microgranular enclaves,

(e) Xenocrysts bearing microgranular enclave having irregular boundaries hosted in coarse grained

leucocratic KG granitoids, (f) Dismembered mafic dyke by intruding leucocratic felsic melt.

(a) (b)

(c) (d)

(e) (f)

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to a certain distance leaving behind the trail of their small undigested pieces, which

indeed followed the direction of magmatic flowage at a limited scale. The characteristic

feature of each lithounit from melanocratic to leucocratic felsic magmatism forming the

KG pluton has gradational relationship, which suggests gradual evolution of felsic

magma. At few places extreme evolved leucocratic quartz-rich melt phase of KG is cross-

cutting the melanocratic KG forming boudinage-like structural features, which suggest

melt generation and emplacement during extensional tectonic setting. Later it is cross-cut

by mafic dykes and feldspathic veins, and the latter were formed by hydrothermal fluids.

At few outcrops these feldspathic veins have been dislocated during their injection in E-

W direction which most likely suggests that fluids were generated during syn-tectonic

shearing regimes related to CITZ. The peripheral part of the granitoid pluton is

mesocratic to melanocratic whereas core part is leucocratic. Near fault zone, the marginal

part of KG pluton is moderately to strongly foliate whereas rest part of the pluton is not

affected by deformation, and preserved primary magmatic features. It is interesting to

observe that KG has a gradational relation with the Dudhi granite gneiss rather than

intrusive relation.

2.4.4 Dudhi granite gneiss

Dudhi granite gneiss is well exposed in and around Dudhi locality. It is

moderately to intensively deform forming folded structure of leucosome and melanosome

(Fig. 2.7a-f). The SNF system is passing through the granite gneiss which is also locally

known as Dudhi fault (Nair et al., 1995). Because of intense shearing operated in the fault

zone, granite gneiss has locally melted to produce leucocratic melt. Away from the fault,

it is deformed and coarse grained porphyritic, and contains K-feldspar phenocrysts and a

few elongated microgranular enclaves (Fig. 2.7a). At few exposures, it is relatively fresh

(grey) coarse grained slightly deformed resulted in crudely aligned of early-crystallized

K-feldspar and biotites (Fig. 2.7b). Later it is intruded by mafic dyke and commonly

emplaced parallel to the foliation direction of the migmatized granite gneiss. Gradational

contacts between Katoli granitoid and Dudhi granite gneiss have been observed in

western and southern parts of granite gneiss exposures.

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2.4.5 Sidhi granitic gneiss

Erstwhile Sidhi and Dudhi granite gneisses are considered equivalent and

basement of Mahakoshal Group. Field observation was therefore extended in and around

Sidhi region just to compare field features of both gneissic rocks. The Sidhi granite gneiss

exposed in and around Sidhi area bears exactly the similar feature as observed for Katoli

granitoid pluton and Dudhi granite gneiss. For instance, Sidhi granitoid is fine to coarse

grained mesocratic to melanocratic through leucocratic in nature and consists of

Fig. 2.7 Moderately to intensively deformed Dudhi granite gneiss, which has gradational contact with

Katoli granitoid pluton, (a) Coarse grained granitoids contain elliptical microgranular enclave without

any deformational feature exposed near Dudhi locality, (b) Moderately foliated mesocratic K-feldspar

phenocryst bearing Dudhi granite gneiss, (c) & (d) Strongly deformed Dudhi granite gneiss forming the

migmatite, e) Gradational relationship of the Dudhi granite gneiss with the equigranular coarse grained

granitoids of Katoli pluton, and f) Peripheral part of migmatite/Dudhi granite gneiss which grades into

less deformed coarse grained grey granitoids.

(a) (b)

(c) (d)

(e) (f)

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ubiquitous microgranular enclaves, xenoliths of quartz mica-schist, carbonates and

phyllites. At few exposures, it has undergone intense deformation and strong foliation

forming migmatite-like appearance (Nair et al., 1995). The overall component of the

Sidhi granite ranges from granodiorite to granite and mainly composed of hornblende,

biotite, plagioclase, K-feldspar and quartz. Based on identical field features, textural and

mineralogical components, Katoli granitoids, Dudhi and Sidhi granite gneisses can be

considered equivalent, and hence Sidhi granite gneiss is considered simply an eastward

extension of Dudhi granite gneiss. Dudhi and Sidhi Group of rocks are also considered as

equivalent to Chotanagpur granite gneisses (Yadav, 1978).

2.4.6 Raspahari granitoid (RG) pluton

Granitoids forming Raspahari pluton are exposed only in and around Raspahari

area. They are coarse grained, mesocratic and frequently contain metavolcano-

sedimentary enclaves and scarce hybrid microgranular enclaves (Fig. 2.8a-d).

Metavolcano-sedimentary enclaves are indeed agents of volcano-sedimentary lithounits

Fig. 2.8 a) Xenolith swarms of metavolcanics which are floating during the magmatic flowage of Raspahari

granitoids, (b) Elongated hybrid microgranular enclave hosted in coarse grained equigranular Raspahari

granitoids. (c) Angular contact relationship of the metavolcanics without any remelting effect on its margin

during thermal intrusion of Raspahari granitoid, (d) Sigmodal magmatic wrapping of felsic melt along partially

assimilated metavolcanic xenolith trailing at opposite ends.

(a) (b)

(c) (d)

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belonging to Mahakoshal Belt, which are synchronous with epidiorite and epidiorite

porphyry. The xenoliths of metavolcanic and meta-peletic rocks are aligned parallel (Fig.

2.8a) along with a few hybrid enclaves (Fig. 2.8b) which appear to have undergone

syndeformational magmatic flowage. However, equigranular granitoids do not exhibit

any magmatic flowage pattern. Occurrence of country-rock xenoliths in granitoids

suggests intrusive nature of RG pluton (Fig. 2.8c). These xenoliths are partially

assimilated by the intruding magmas, which along with unmelted fragments have formed

interfingering or intervening structures (Fig. 2.8d). This suggests that the melt was having

enough temperature to rejuvenate thermally the country-rocks, and has therefore

assimilated partially the solid fragments giving rise to melt flowage structures define by

engulfed xenoliths into it. This is somewhat analogous to the features formed by rivers

which have not enough energy condition to bring and to carry cobbles during flowage,

and thus leave its sediment in its own channel and forming transverse bars in braided

channel system. Because of flowage and high temperature of the melt sigmoidal-shape

structure is developed with xenoliths, where relict part have circular shape with partially

melted or assimilated tails at both opposite ends. This structural flowage pattern has been

formed due to differential velocities of the interfingered melt branches like braided bar

channel system. Microgranular enclaves are rimmed by plagioclase crystals, and cross-cut

by mm to cm sized leucogranite and quartz veins. Xenoliths of meta-volcanic can be

clearly observed hosted in Raspahari pluton.

2.4.7 Nerueadamar (NG) and Tumiya (TG) granitoids

Although granitoid bodies are exposed apart in and around Nerueadamar and

Tumiya regions are separate, their textural and compositional features are identical (Fig.

2.9a-d). Hence, they have been described under a common heading. Both the granitoids

are leucocratic, equigranular, two-mica bearing granitoids. Muscovite dominates over

biotite and forms aggregates or books at places giving rise to appearance like

surmicaceous enclaves in Nerueadamar granitoids (Fig. 2.9a). Nerueadamar granitoids

also contain abundant angular fragments and blocks of country-rock xenoliths (Fig. 2.9b).

Their intrusive relationships can be observed near Harnakachar village, where cylindrical

needles of andalusite are formed in phyllitic country rocks due to thermal effect (Fig.

2.9c). Since phyllites are Al-rich, and hence thermally metamorphosed to form andalusite

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and bluish quartz emplaced as needles and veins respectively. Very few angular xenoliths

can also be observed in the Tumiya granitoids (Fig. 2.9d). Leucocratic nature of two-mica

granitoids is also exposed in the southeastern part of the Nerueadamar pluton, and in and

around Windamganj and Tumiya localities where they are emplaced as laccolith and as a

result country-rock (slate) has become folded because of winty intrusive effects (Fig.

2.9e). This inference holds truth because of fact that country-rock xenoliths are not

present in granitoids. Abundant tourmaline-rich pegmatites contain bunch of muscovite,

Fig. 2.9 (a) Mica-rich (surmicaceous) restitic-type of enclave hosted in Neureadamar granitoids (NG), (b)

Angular county-rock xenolith in the euigranular leucocratic two-mica granitoids of NG pluton., (c)

Andalusite crystals in phyllite developed near the contact between NG pluton, (d) Angular pelitic-country

rock xenolith in leucocratic, equiganular, coarse grained two-mica granitoids of Tumiya pluton. (e) Folding

in slaty county rock as a consequence of winty intrusion of Tumiya granitoids (TG), which cut by pegmatite,

and (f) Closer view of tourmaline-bearing pegmatite intruding the Tumiya granitoid pluton.

(a) (b)

(c) (d)

(e) (f)

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K-feldspar and quartz cross-cut the granitoids (Fig. 2.9f) and also the mafic dykes. The

presence of country-rock xenoliths and surmicaceous enclaves in the granitoids of

Nerueadamar makes it different from granitoids of Tumiya. Both the granitoid bodies

(Nerueadamar and Tumiya) are however devoid of microgranular enclaves.

Fig. 2.10 (a) Megascopic feature of porphyritic and non-porphyritic mafic volcanics of Mahakoshal

belt exposed in same quarry near Rihand Dam, (b) Greenish color mafic sill emplaced parallel to the

volcanics trending E-W direction, (c) Porphyiritic diorite exposed in and around Rihand Dam in a

quarry section, which has gradational relationships with fine grained mafic volcanics, (d) Similar

porphyritic diorite but slightly foliated exposed in Sidhi area consists of phenocrysts of plagioclase

poikilitically enclosing biotite inclusions which are suggestive of magmatic origin, (e) Larger outcrop

(xenolith) of Bundelkhand granite hosted in pyroxenite of Mahakoshal Belt in and around Sidhi

region,and (f) Closer view of Bundelkhand granite embbeded as xenolith in pyroxenite.

(a) (b)

(c) (d)

(e) (f)

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2.4.8 Volcanics of Mahakoshal Belt

The volcanic rocks of Mahakoshal Group are well exposed in and around Rihand

Dam, Sonbhadra District. Volcanics are fine grained melanocratic and have emplaced as

sills and flows. They have gradational relationships with porphyritic volcanics (Fig.

2.10a-d). Porphyritic volcanics have occupied the middle part of the volcanic flows. At

the base plagioclase phenocrysts are aligned parallel showing magmatic texture (Fig.

2.10c, d). However, these phenocrysts are randomly distributed while moving towards

upper volcanic sequences. Biotites are poikilitically enclosed in plagioclase which

suggests their magmatic origin. They are deposited parallel (E-W) recording some

imprints of shearing. Absence of having remarkable and distinct boundaries between the

lithounits such as volcano-sediments epidiorite, dolerite sill/dyke, and porphyritic

volcanics (Fig. 2.10b-d) suggests that they were penecontemporaneous or closely

deposited one after another in space and time.

The lateral E-W extension of the fine grained and porphyritic volcanics and

sedimentary sequences are also exposed in and around Sidhi and upto Singrauli (M.P.).

Field observations are confined to eastward exposures of volcano-sedimentary lithounits

of Mahakoshal Belt. There are, at some places, associated with Banded Iron Formation

(BIF), Banded Hametite Jasper (BHJ) with alternate sequence of carbonaceous shale,

phyllite and quartzite. Most frequent lithological associations are mm to cm thick

alternate sequence of quartzite-basalt and shale-basalt. The vast exposure of foliated and

non-foliated porphyritic basalts can also be observed. The foliated porphyritic diorite

contains poikilitic plagioclase with inclusion of biotite, which is similar to those observed

near Rihand Dam in Sonbhadra District. Other than these lithounits, ultramafic to mafic

(pyroxenite, dunite and gabbroic) bodies are also well exposed in and around Devsar

locality of Sidhi District (M.P.). At this place a rare and controversial outcrop of

(Bundelkhand) granite has been encountered, which occurs as large xenolith block (~ 10

m) hosted into the pyroxenite lithounit. The pyroxenite and gabbro contain 10-15 cm long

angular fragments (or xenoliths) of Bundelkhand granite. However, if this would have not

been the case then volcanic sequence must have contained xenoliths of Dudhi and Sidhi

granite gneiss instead of xenoliths of Bundelkhand granite (Fig. 2.10e-f).

It is most likely that Neoarchaean (Bundelkhand) granite could be the basement of

Mahakoshal belt rather than Dudhi and Sidhi granite gneisses which have intrusive

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relation with the volcano-sedimentary sequences. Because of the E-W trending major

shear zone some of the granitoid plutons in Mahakoshal Belt are highly deformed and

formed the migmatite. Based on field evidences, the lithostratigraphic sequence of

Mahakoshal Belt is revised, where Bundelkhand granitoids serve as basement followed

by volcano-sedimentary sequences which were intruded by vast granite magmatism, and

finally intrusion of mafic and pegmatite dyke system.

2.5 Magnetic susceptibility of granitoids and volcanic lithounits

Magnetic property has been measured from rocks of Dudhi gneissic complex,

Mahakoshal belt (table 2.3-2.5) in order to classify the granitoid plutons into ilmenite and

magnetite series granitoids (Ishihara, 1977) that correspond to I-type and S-type

(White and Chappel, 1974) granitoids respectively. The northern most elongated JG

pluton exhibits higher values of magnetic susceptibility (60.58-15.25x10-3

SI unit; n = 14)

as compared to the other granitoid plutons, whereas the aplitic lithounit measures low MS

value ranging from 0.04 (n=8) to 0.74 (n =20) x10-3

SI unit. The dioritic lithounit occurs

in the middle part of the pluton and because of its mafic nature MS value ranges between

80.27 and 31.63x10-3

SI unit. It is interesting to observed that both the opposite marginal

part of the JG pluton measure comparatively low MS values (20.35 x 10-3

SI unit, n = 22

and 18.52 x 10-3

SI unit, n = 42; Fig. 2.11) because of presence of abundant country rock

xenoliths at the margin of the pluton. However, further granitoids in the inner part of the

JG pluton regains its original and high MS values (20.51-23.60 x 10-3 SI unit) since it

does not contain country rock xenoliths and hence there is no reaction leading to

reduction of granitoids. Core part of the pluton except the diorite measures low MS value

due to decrease in modal content of mafic minerals and more evolved nature of

granitoids. JG bears relatively lower MS value from middle (19.76 X 10-3

SI unit, n= 11)

Fig. 2.11 (a) and (b) Graphical and bar diagrams are representing magnetic susceptibility values from

granitoids of Jhirgadandi plutons.

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Table 2.3 Samples location and their magnetic susceptibility values measured for plutons and volcanic lithounits of Dudhi gneissic complex Mahakoshal Belt.

S. No.

Pluton Sample

No./rocktype

/locality

Latitude and

longitude

Magnetic susceptibility (MS) of rock at

exposure

Corrected MS value

(10-3 SI unit)

Average Min-max

1. J

G p

luto

n

JG Porphy coarse grained granitoid

(AE, AX, AG-2,

AG-5 )

N24026’27.7”

E 83015’4.8” 21, 16.2, 18.2, 16.6, 19.7, 15.8, 17.8, 17.7, 16, 13, 18, 14.3, 15.1, 12.9, 10.6, 23.1, 23.1, 22.8,

20.8, 19.3, 20.6, 16.7

24.15, 18.63, 20.93, 19.09, 22.65, 18.17, 20.47,20.35, 18.4, 14.95, 20.7, 16.44, 17.36, 4.83, 12.19, 26.56,

26.56, 26.22, 23.92, 22.195, 23.69, 19.21

Av (n=22) 20.35

12.19-26.56

2. SLD-1 quartz diorite

N24026’27.4” E 83013’57.2”

53.8, 61.8, 27.5, 61.4, 62.3, 45.9, 54, 53.8, 69.8, 49.6, 63.9, 63.5, 37.6, 32.6

61.87,71.07,31.625,70.61,71.64,52.78,62.1 61.87,80.27,57.04,73.48,73.02,43.24,37.49

(n=14) 60.58 31.63-80.27

3. SLD-3 N24026’27.4”

E 83013’57.2” 17.1, 18.2, 20, 18.3, 19.8, 14.3, 16, 17.5, 25.1, 17.1, 17.8, 13.3, 14.9, 20.3

19.66, 20.93, 23, 21.04, 22.77, 16.44, 18.4, 20.12, 28.86, 19.66, 20.47, 15.29, 17.135

23.34

20.51 (n=)

15.30-28.87

4. Aplite of JG N24026’30.6”

E 83014’8.7”

0.24, 0.19, 0.03, 0.12, 0.2, 0.67, 0.18, 0.2 0.26, 0.20, 0.03, 0.13, 0.21, 0.72, 0.19, 0.21 (n=8) 0.24 0.03-0.72

5. leucocratic JG at

core

N24026’29.7”

E 83014’10.5”

16, 11.6, 9.06, 12.7, 14.4, 16.6, 10.5, 12.7, 17,

12.7, 12.6

18.40, 13.34, 10.42, 14.61, 16.56, 19.09, 12.08,

14.61, 19.55, 14.61, 14.49

15.25 (n=11) 10.42-19.55

6. Berahwa BG N24027’34.3” E83011’56.7”

18.8, 20.2, 19.6, 17.9, 17.3, 10.2, 18.4, 19.2, 17.1, 14.4, 15.9

21.62, 23.23, 22.54, 20.58, 19.89, 11.73, 21.16, 22.08, 19.66, 16.56, 18.28

19.76, (n= 11) 11.73-23.23

7. Pipraha P-6, PX-7 N24026’52.4”

E 8309’51.9”

15.6, 16.9, 21, 19.4, 25.1, 20.9, 13.9, 14.5, 20.6,

16.6, 13.1, 12.6, 16.8, 15.7, 14, 12.8, 12.9, 12.8,

15.8, 16.2, 17.2, 16, 14.8, 14.1, 12.1, 13.6, 11.7, 14, 20.9, 15.4, 13.5, 16.2, 14.8, 15.2, 16.3, 18.7,

16, 17.9, 20.6, 16.2, 14.4, 19.7

17.94, 19.44, 24.15, 22.31, 28.87, 24.04, 15.99,

16.68, 23.69, 19.09, 15.07, 14.49, 19.32, 18.06,

16.10, 14.72, 14.84, 14.72 18.17, 18.63, 19.78, 18.40, 17.02, 16.22, 13.92,

15.64, 13.46, 16.10, 24.04, 17.71, 15.53, 18.63,

17.02, 17.48, 18.75, 21.51, 18.40, 20.59, 23.69, 18.63, 16.56, 22.66

n=42, 18.52 13.46-28.87

8. Jhirga JG, JX N24026’49.6”

E 83010’51.2”

23.4, 23.8, 20, 18.6, 23, 16.2, 25.8, 16.8, 17.1 26.91, 27.37, 23, 21.39, 26.45, 18.63, 29.67, 19.32,

19.665

23.60 n=09) 18.63-29.67

9.

NG

plu

ton

NG N24016’54.3” E 83022’25.2”

0.81, 0.91, 0.9, 0.84, 0.102, 0.09, 0.092, 0.81, 0.76, 0.47, 0.71, 0.77, 0.75, 0.55, 0.78, 0.89,

0.98, 0.1, 0.7, 0.78

0.93, 1.05, 1.04, 0.97, 0.12, 0.10, 0.11, 0.93, 0.87, 0.54, 0.82, 0.89, 0.86, 0.63, 0.90, 1.02, 1.13, 0.12,

0.81, 0.90

0.74 (n=20) 0.10-1.13

10. Xenolith in NG N24016’54.3” E 83022’25.2”

0.161 ,0.188, 1.61, 1.62, 0.269, 0.216, 0.329, 0.303

0.19, 0.22, 1.85, 1.86, 0.31, 0.25, 0.38, 0.35 0.68 (n=8) 0.19-1.86

11. Surmicaceous

enclave of NG

N24016’54.3”

E 83022’25.2”

0.269, 0.334, 0.244, 0.258, 0.321, .325 0.31, 0.38, 0.28, 0.30, 0.37, 0.37 0.34 (n=6) 0.28-0.38

12. TG WT-2 N24016’45.2” E 83023’23.8”

0.126, 0.043, 0.059, 0.086, 0.046, .041 0.145, 0.049, 0.068, 0.099, 0.053, 0.047 0.077 (n=6) 0.047-0.145

Continued…………

Estelar

42

Table 2.4 Samples location and their magnetic susceptibility values measured for plutons and volcanic lithounits of Dudhi gneissic complex Mahakoshal Belt.

S. No.

Pluton/

lithounit

Sample No./ rock

type

Latitude and longitude Magnetic susceptibility (MS) of rock at

exposure

Corrected MS value

(10-3 SI unit)

Average Min-Max

13. D

G g

ran

ite g

neis

s D-1 N24013’15.7”

E 83013’36.3”

0.38, 0.4, 0.36, 0.4, 0.28, 0.34, 0.42 0.44, 0.46, 0.41, 0.46, 0.32, 0.39, 0.48 0.42 (n=7) 0.32-0.48

14. DGGn N24013’50” E 83014’29.7”

0.23, 0.19, 0.185, 0.145, 0.204, 0.236, 0.227, 0.251, 0.141, 0.147

0.265, 0.213, 0.213, 0.167, 0.235, 0.271, 0.261, 0.289, 0.162, 0.169

0.224 (n=10) 0.162-0.289

15. Migmatite N24013’50”

E 83014’29.7”

0.427, 0.201, 0.413, 0.204, 0.409, 0.792, 0.589,

0.789, 0.647, 0.706, 0.643, 0.997, 0.749, 0.1, 0.158, 0.31, 0.277, 0.25, 0.267, 0.287, 0.193, 0.248

0.491, 0.231, 0.475, 0.235, 0.470, 0.911, 0.677,

0.907, 0.744, 0.812, 0.739, 1.147, 0.861, 0.115, 0.182, 0.357, 0.319, 0.288, 0.307, 0.330, 0.222,

0.285

0.505 (n=22) 0.115-1.147

16. DH-8 N24013’44.8”

E 83014’29.0”

0.329, 0.224, 0.088, 0.158, 0.067, 0.147, 0.257,

0.219, 0.089

0.378, 0.258, 0.101, 0.182, 0.077, 0.169, 0.296,

0.252, 0.102

0.202 (n=09) 0.077-0.378

17.

HG

plu

ton

HK-6 N24016’0.45”

E 83022’19.8”

1.13, 0.466, 0.589, 0.541, 0.754, 0.844, 0.644,

0.681, 0.561, 0.462, 0.263, 0.267, 0.328

1.30, 0.54, 0.68, 0.62, 0.87, 0.97, 0.74, 0.78,

0.65, 0.53, 0.30, 0.31, 0.38

0.67 (n=13) 0.30-1.30

18. HKG N24016’0.45” E 83022’19.8”

2.4, 2.94, 1.89, 1.15, 2.42, 2.45, 2.91, 2.56, 1.97, 2.64, 2.6

2.76, 3.38, 2.17, 1.32, 2.78, 2.82, 3.35, 2.94, 2.27, 3.04, 2.99

2.71 (n=11) 1.32-3.38

19. RG

pluton

RP-1, RP-2, RP-3 RP-4, RPE

N2409’20.7” E 8203’47.5”

0.229, 0.65, 0.195, 0.225, 0.666, 0.165, 0.21, 0.218, 0.105, 0.082, 0.112, 0.132, 0.129, 0.114,

0.072, 0.073, 0.071, 0.048, 0.032, 0.055

0.26, 0.74, 0.22, 0.25, 0.76, 0.19, 0.24, 0.25, 0.12, 0.09, 0.13, 0.15, 0.15, 0.13, 0.08, 0.08,

0.08, 0.05, 0.04, 0.06

0.21 (n=20) 0.04-0.76

20.

KG

plu

ton

K-1 N24011’50.3” E 83008’35.1”

7.83, 8.68, 7.78, 8.93, 8.09, 8.08 9.00, 9.98, 8.94, 10.26, 9.30, 9.292 9.46 8.94-10.26

21. K2A leuco N24012’6”

E 83008’19.7”

0.36, 0.046, 0.024, 0.06, 0.069, 0.029, 0.065, 0.064 0.414, 0.053, 0.028, 0.069, 0.079, 0.033, 0.076,

0.074

0.103 (n=8) 0.027-0.414

22. MPG N24012’6”

E 83008’19.7”

0.088, 0.241, 0.071, 0.061, 0.062, 0.068, 0.058,

0.06, 0.168, 0.165, 0.416, 0.341, 0.134, 0.366

0.101, 0.277, 0.082, 0.070, 0.071, 0.078, 0.067,

0.069, 0.193, 0.190, 0.478, 0.392, 0.154, 0.421

0.189 (n=14) 0.067-0.478

23. K-5 N24012’14.1” E 83008’2.6”

0.1, 0.11, 0.112, 0.149, 0.116, 0.1 0.115, 0.127, 0.129, 0.171, 0.133, .115 0.132 (n=06) 0.115-0.171

24. K13 A N24011’53.3”

E 83008’44”

3.55, 5.96, 4.87, 5.01, 4.49, 3.73 4.08, 6.85, 5.60, 5.76, 5.16, 4.29 5.29 (n=06) 4.08-6.85

25. K14 N24012’24.3” E 83009’16.4”

0.859, 0.854, 0.855, 0.841 0.988, 0.982, 0.983, 0.967 0.980 (n=04) 0.967-0.988

26. K15H N24012’22.7”

E 83009’11.4”

3.79, 4.05, 3.59, 4.59 4.36, 4.66, 4.13, 5.28 4.61 (n=04) 4.13-5.28

27. K15E N24012’22.7”

E 83009’11.4”

17.3, 12.3, 3.94, 11.9, 10.6, 5.9, 8.44, 11.2, 14.2 19.89, 14.14, 4.53, 13.68, 12.19, 6.78, 9.706,

12.88, 16.33

12.24 (n=09) 4.53-19.90

Continued…………

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43

Table 2.5 Samples location and their magnetic susceptibility values measured for plutons and volcanic lithounits of Dudhi gneissic complex Mahakoshal Belt.

S. No.

Pluton/

lithounit

Sample

No./ rock

type

Latitude and longitude Magnetic susceptibility (MS) of rock at

exposure

Corrected MS value

(10-3 SI unit)

Average Min-max

28. K

G p

luto

n

Hybrid enclave

N24011’41.9” E 83009’13.1”

1.13, 0.937, 1.09, 1.25, 1.19, 1.26 1.300, 1.078, 1.254, 1.438, 1.369, 1.449 1.314 (n=6) 1.078-1.449

29. K-16 N24013’49.1”

E 83014’28.1”

4.23, 5.2, 4.12, 3.14, 3.96, 3.68, 4.51, 4.15, 5.18,

2.96, 5.49

4.86, 5.98, 4.74, 3.61, 4.55, 4.23, 5.19, 4.77,

5.96, 3.40, 6.31

4.87 (n=11) 3.40-6.31

30. K17 H N24012’22.8”

E 83009’03.1”

1.14, 1.00, 1.03, 0.99, 0.916, 1.35 1.31, 1.15, 1.18, 1.14, 1.05, 1.55 1.23 (n=6) 1.05-1.55

31. K-17E N24012’22.8” E 83009’03.1”

5.92, 6.12, 4.77, 5.91, 3.19, 2.38, 4.69, 6.25, 5.16 6.808, 7.038, 5.485, 6.79, 3.66, 2.74, 5.39, 7.19, 5.93

5.67 (n=9) 2.74-7.19

32. K-21E N24012’24.4” E 83009’02.6”

1.9, 2.72, 1.91, 2.16, 2.66, 3.01, 2.48 2.19, 3.13, 2.20, 2.48, 3.06, 3.46, 2.85 2.77 (n=7) 2.19-3.46

33. K-22 N24012’22.6” E 83009’03.7”

1.79, 2.44, 1.42, 3.48, 2.88, 2.79, 3.42 2.06, 2.81, 1.63, 4.00, 3.31, 3.21, 3.93 2.99 (n=7) 1.63-4.00

34. K35/36

Diorite

N24010’47.7”

E 83010’11.4”

.530, .492, .505, .526 .861, 1.24, .744, .852, .502 0.61, 0.57, 0.58, 0.60, 0.99, 1.43, 0.86, 0.98,

0.58

0.80 (n=9) 0.57-1.43

35. K38 E N24010’44.5”

E 8308’21.5”

5.14, 6.71, 5.14, 4.45, 6.7 5.91, 7.72, 5.91, 5.12, 7.71 6.47 (n=5) 5.12-7.72

36. K 38 H N24010’44.5”

E 8308’21.5”

3.70, 3.59, 4.95, 5.94, 5.97, 5.78 4.26, 4.13, 5.69, 6.83, 6.87, 6.65 5.74 (n=6) 4.13-6.87

37. K41 N24012’20.9”

E 8305’33.6”

0.698, 0.628, 0.619, 0.568, 0.563, 0.586, 0.637,

0.573

0.803, 0.722, 0.712, 0.653, 0.647, 0.674, 0.733

0.659

0.700 (n=8) 0.647-0.803

38. K45 N24009’2.3” E 83003’38.2”

3.16, 2.64, 2.42, 2.7, 2.56, 3.05, 2.66, 2.41 3.63, 3.04, 2.78, 3.11, 2.94, 3.51, 3.06, 2.77 3.11 (n=8) 2.77-3.63

39.

Vo

lca

nic

lith

ou

nit

s

R1, R2, R3, R4, R5

N24012’34.7” E 82050’21.6”

0.441,0 .731, 0.297, 0.358, 0 .336, 0.393, 0.368, 0.358, 0.473

.441, .731, .297, .358, .336, .393, .368, .358,

.473 (MS measurement of volcanics is on

smooth surface thus MS value without any

correction)

0.417 (n=9) 0.297-0.731

40. R7A , R8, R9, R10,

R7B, R11,

R12, R13

N24012’29.6” E 82057’55.3”

0.159, 0.044, 0.78,0 .196, 0.109, 0 .117, 0.124, 0.190, 0.186, 0.186,.066, 0.257, 0.217, 0.162,

0.134, 0.195, 0.249, 0.157.56, 0.354, 0.793

0.159, .044, 0.78, 0.196, 0.109, 0.117, 0.124, 0.190, 0.186, 0.186, 0.066, 0.257, 0.217,

0.162, 0.134, 0.195, 0.249,0 .157, 0.56, 0.354,

0.793

0.249 (n=21) 0.044-0.793

Estelar

44

to the core (15.25 X 10-3

SI unit, n = 11) part of JG. Overall, the granitoids of JG belong

to magnetite series (I-type), except the aplititic vein which belongs to ilmenite series

granitoids.

The two-mica bearing NG, TG and RG plutons exhibit lowest MS values (NG:

0.74 x 10-3

SI unit, n =20; TG: 0.077 x 10-3

SI unit, n = 6 and RG: 0.21 x 10-3

SI unit, n=

20; table 2.3). It is inferred that these plutons represent purely ilmenite series (S-type) of

granitoids of Dudhi gneissic complex, Mahakoshal Belt. Both, the highly deformed

(0.505 x 10-3

SI unit, n =22; 0.224 x 10-3

SI unit, n = 10) to moderately deformed DG

(0.202 x 10-3

SI unit, n =09; 0.47 x 10-3

SI unit, n= 0.47) also belong to ilmenite series

granitoids. The low MS value of DG might have occurred because of deformational

activity (table 2.4). In the eastern part, a small stock-like Harnakachar granitoid (HG)

pluton (table 2.4) exhibits magnetite (1.32-3.28 x 10-3

SI unit) to ilmentite (0.30-1.30x10-3

SI unit) series nature of granitoids. It is due to the fact that these are very close to the

country rock and therefore measure low MS value whereas higher MS value is observed

in enclave bearing middle part of the HG.

The MS value for KG pluton varies according to colour index from melanocratic

(K-1: 9.46 x 10-3

SI unit, n = 07; K-13A: 5.29 x 10-3

SI unit, n = 06; K15H: 4.60 x 10-3

SI

unit n = 04, K16: 4.87 x 10-3

SI unit, n = 11; K38H: 5.74 x 10-3

SI unit, n = 06, K45: 3.11

x 10-3

SI unit, n = 08) to leucocratic (K1:0.103 x 10-3

SI unit, n =08; K2A: 0.189 x 10-3

SI

unit, n = 14; MPG: 0.132 x 10-3

SI unit, n = 06; K14: 0.980 x 10-3

SI unit, n = 04K17H:

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

HKG(n=27)

JG(n=109)

KG(n=90)

DG(n=32)

RG(n=20)

NG(n=27)

TG(n=57)

MS

(10 S

I unit

) -3

Fig. 2.12 Summarized range of magnetic susceptibility (MS) shown by bar diagram for various

granitoids plutons of Dudhi gneissic complex from Mahakoshal Belt.

Estelar

45

1.23 x 10-3

SI unit, n = 06; K22: 2.99 x 10-3

SI unit, n =07; K 41: 0.700 x 10-3

SI unit, n=

08) types that correspond to magnetite to ilmenite series of granitoids respectively (tables

2.4-2.5), except to the diorite of KG which exhibits low MS value (0.57-1.43 x 10-3

SI

unit) because of absence of magnetic minerals such as magneitite, sphene in the early

phase of the melt or Fe-Mg elements were leached out during chemical weathering

(consistent with petrography). It is interesting to note further that MS measurement of

enclaves exhibits higher MS value than their respective host granitoids (K15E: 12.24 x

10-3

SI unit, n =09; K15H: 4.61 x 10-3

SI unit, n = 04; K17E: 5.67 x 10-3

SI unit, n = 09;

K17H:1.23 x 10-3

SI unit, n = 0.06 and K38E: 6.47 x 10-3

SI unit, n = 05; K38H: 5.74 x

10-3

SI unit, n = 06) which suggest more mafic nature of enclave magmas than the host

granitoids. Hybrid enclaves exhibit more or less similar MS values as noted for host

granitoids (K 21E: 2.77 x 10-3

SI unit, n= 07; K22: 2.99 x 10-3

SI unit, n = 07) as a result

of mixing between mafic felsic end-members noted at a few outcrops.

The volcanic lithounits exhibit low MS value (0.417 x 10-3

SI unit, n = 09; 0.249 x

10-3

SI unit, n = 21; table 2.5) as it is associated with synchronous sedimentary lithounits,

which might have reduced the magnetic property of the rocks during partial assimilation.

Thus, JG exhibits higher MS value, and all the metaluminous granitoid plutons

(HG, JG, KG) correspond to magnetite series granitoids whereas rest of the plutons (RG,

NG, TG) belong to ilmenite series granitoids. However, the DG granite gneiss measures

low MS values, which might have reduced because of deformation (Fig. 2.12).

Estelar