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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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16
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
17
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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19
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…………
Estelar
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