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Cratons of Indian Shield
University of Allahabad
Precambrian basement of India
• The earliest phase of earth’s history representing Archean is preserved in
rock sequence of Precambrian basement.
• The Archean rocks have undergone repeated phase of orogenic
deformation, plutonism and high grade metamorphism.
• The stratigraphic correlation of Archean rocks is based on data obtained
from petrographical, geochemical, structural and chronological
investigations.
• Archean succession of the Indian shield has extremely complex geological
history.
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• The Dharwar province has relatively continuous geological history for
most part of Archean.
• The central India has preserved rock sequence of only Late Archean.
• Singhbhum province has preserved rock sequence of Early and
Middle Archean periods only.
• The Middle Archean rocks are missing from Aravalli Bundelkhand
province.
• Stabilization of various province in Indian peninsula is marked by
emplacement of igneous plutons.
• The provinces attained their stability in different times, either during
Archean or during beginning of Proterozoic.
• Singhbhum Province, Bundelkhand Aravalli Province were stabilized
during Archean era.
• The Dharwar and Central India province stabilized only at the
beginning of Proterozoic era.
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Introduction
• The Indian shield is made up of a mosaic of Precambrian metamorphic
terrains that exhibit low to high‐grade crystalline rocks in the age range of
3.6–2.6 Ga.
• The Archaean—Proterozoic crust of many Precambrian terrains consists of
two contrasting tectonic units:
• Archaean cratonic blocks made up of granite—greenstone terrains and
• Archaean—Proterozoic mobile zones, fold belts and orogens which separate and
tend to surround and flow around the cratons.
• These terrains, constituting the continental crust, attained tectonic
stability for prolonged period (since Precambrian time) and are designated
cratons.
• The cratons or microplates collided and developed the fold belts that
occur peripheral to the cratonic areas of the Indian shield.
• The rocks making up the fold belts were the sediments derived from
crustal rocks and volcanic material all deformed and metamorphosed
during subsequent orogeny.
• The cratons are relatively rigid blocks, but have a history of ductile and
brittle deformations.
• The surrounding mobile belts are either high‐strain, high‐grade
metamorphic belts or folded basins.
• Thus, the relatively rigid cratons are surrounded by more ductile zones
of mobility.
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Cratons in the Indian shield
• Five Archean province have been identified in the Indian Peninsula/Shield:
• Dharwar craton
• Baster craton (Central India or Bhandara craton)
• Singhbhum craton
• Aravalli Bundelkhend craton
• Southern Granulite Province
• The southern granulite province also contains Archaean‐age crustal elements
that are dissected by younger orogenic belts.
• Each of these five cratons shows different geological structural characteristics.
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• Each of the cratonic elements contains Precambrian‐ Early Paleozoic
sedimentary (or metasedimentary) sequences that form the basinal
infrastructure of Peninsular India.
• The best‐preserved sedimentary sequences are the called “Purana”
or ancient basin.
• These include the large Cuddapah, Chhattisgarh and Vindhyan basins
along with several smaller regional basins known as the Indravati,
Khariar, Prahnita‐Godavari, Kaladgi, Bhima, Kunigal, Kurnool and
Marwar.
• Purana‐I basins began development in the Paleoproterozoic (2.5‐1.6
Ga); Purana‐II basins formed during the Mesoproterozoic (1.6‐1.0
Ga); and the development of Purana‐III basins is confined to the
Ediacaran‐Cambrian interval.
541my
Ediacaran
Neoproterozoic
635my
• Basinal development and closure may be temporally related to the
formation/breakup of the supercontinents Columbia (Purana‐I),
Rodinia (Purana‐II) and Gondwana (Purana‐III).
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Eparchean unconformity
• The stratigraphic boundary demarcating the Archean rocks and Closepet
granite from Cuddapah supergroup is one of the best defined geological
boundary.
• It is a major discontinuity of stratigraphic significance that represents a
period of remarkable geological history of the earth.
• It is seen at the steep natural slopes in the Triputi‐Tirumala ghat road,
Chittoor district, AP.
• This feature forms the boundary between Proterozoic rocks and Archean
rocks.
• The time gap between the formation is at least 500 MPa
• The boundary is between sedimentary rocks of Cuddapah supergroup
(~1600 my) and Archean rocks comprising granites, gneisses and dolerite
dykes (~2100 my).
Eparchaean Unconformity
(Tirupati hills)
The boundary is between sedimentary rocks of
the Cudappah Supergroup, 1600 million years in
age, and Archaean rocks comprising granites,
gneisses and dolerite dykes that are more than
2100 million years old, a 500 million year gap of
deposition
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Dharwar craton
• It is made up of granite‐gneiss‐
greenstone (GGG trinity) belts.
• It is limited in the south by the
Neoproterozoic Southern Granulite Belt
(SGT) or Pandyan Mobile belt;
• in the north by the Deccan Trap (late
Cretaceous);
• in the northeast by the Karimnagar
Granulite belt (2.6 Ga old) which
occupies the southern flank of the
Godavari graben; and
• In the east by the Eastern Ghats Mobile
Belt (EGMB) of Proterozoic age.
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• The boundary between the Dharwar Craton and the SGT is arbitrarily taken as
Moyar‐Bhavani Shear (M‐Bh) Zone while the boundary between the Dharwar
Craton and the EGMB is demarcated by the Cuddapah Boundary Shear Zone.
• There are many sub‐parallel NNW to N‐S trending shear zones within the main
Dharwar Craton, mostly at the eastern boundaries of major schist belts.
• The Archean gneisses and schist are the oldest rocks of the Indian shield
constituting a large part of Peninsular India.
• The Dharwar schists in western part of the craton is divided into two Groups, the
older Sargur Group (3.1–3.3 Ga) and the younger Dharwar Supergroup (2.6–2.8
Ga) because the Sargur and Dharwar successions are separated by angular
unconformities at several localities in western Dharwar craton.
• Trondhjemite is a leucocratic
(light‐colored) intrusive igneous
rock.
• It is a variety of tonalite in which
the plagioclase is mostly in the
form of oligoclase.
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• Dharwar craton, consists of tonalite‐trondhjemite‐granodiorite (TTG) gneisses. A
major part of Indian craton exposes vast areas of these rocks which are collectively
known as Peninsular gneisses.
• The TTG suite is believed to be the product of hydrous melting of mafic crust.
• The second category of rocks in the Dharwar craton is greenstones or schist belts
with sedimentary associations.
• Greenstone belts are zones of metamorphosed mafic/ultramafic volcanic rocks
with associated sedimentary rocks that occur in narrow basins within the
Precambrian granite and gneiss bodies.
• The greenstones are mainly basalts with fine clastics and in certain areas with
basal conglomerate and shallow water clastics (e.g. ripple‐bedded quartzites) and
shelf sediments (limestone and dolomite).
• Both volcanics and sediments as supracrustal rocks were laid upon the basement
of Peninsular gneiss.
• During Dharwar Orogeny (2500 Ma) the volcanics have been
metamorphosed into greenschist (chlorite schist) and amphibolite and
even higher grade basic granulites while the associated sediments have
recrystallized into quartzite, crystalline marbles.
• Dharwar Craton is divided into two blocks—the Western Dharwar and the
Eastern Dharwar craton, separated by the Chitradurga Shear Zone (ChSz).
• The shear zone occurs all along the western margin of the 2.5 Ga old
Closepet Granite.
• It is interesting to note that the schist belts in both cratonic blocks show
the same N‐S trend with almost constancy of strike and dip of the foliation
(regional foliation).
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• The greenstone belts of the Western Block are characterized by mature,
sediment‐dominated supracrustals with subordinate volcanism and are
recrystallized in intermediate pressure (kyanite‐sillimanite type)
Barrovian metamorphism.
• Greenstone belts of the Eastern block are often gold bearing and show
low‐pressure (andalusite‐sillimanite type) metamorphism.
• Geophysical work revealed that the Western Block has a thicker crust of
40–45 km while the Eastern Block has a thinner crust of 35–37 km.
Eastern Dharwar Craton
• The craton is composed of the Dharwar Batholith (dominantly granitic),
greenstone belts, intrusive volcanics, and Middle Proterozoic to more recent
sedimentary basins.
• The basins in EDC are: Cuddapah, Pranhita‐Godavari, Bhima basin.
• The majority of intrusive events of the Eastern Dharwar Craton (EDC) are
represented by mafic dykes, kimberlites and lamproites (Ultra Potassic igne. rock).
• Intrusives cluster around the Cuddapah Basin and have three main trends: NW–
SE, E–W, and NE–SW.
• Most of the dykes disappear beneath the Cuddapah Basin, indicating that
intrusion of the host granitic gneiss took place before the basin developed.
• Kimberlites and lamproites are found in relative abundance in four areas within
the EDC. They are characteristically potassic volcanic rocks that sometimes bear
diamonds.
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Greenstone belt & schist belts
• Greenstone and schist belts of the EDC are concentrated in the western half of the craton and
are stretched into linear arrays.
• The belts continue to the east where they are covered by the Proterozoic Cuddapah Basin.
• The greenstone belts together with the metasediments designated as the Dharwar Schist Belts
have N‐S trend and show a gradual increase of metamorphic grade from N to S.
• Metamorphism is limited to greenschist/amphibolite facies.
• Age trends in the belts generally infer a younging trend from west to east.
• Age constraints on the greenstone belts in the Eastern Dharwar Craton are known from only a
few locations and all appear to be Neo‐Archaean.
Sandur schist belt
• The Sandur schist belt is
characterized by dominant green
schist facies metamorphism with
higher amphibolite grade rocks
occurring at the margins.
• It is located at the northern end
of the Closepet Granite and
differs from most of the belts in
that it is not a thin N–S trending
belt.
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Kolar–Kadiri ‐ Jonnagiri–Hutti belt
• The KKJH superbelt is stretched from the southern portion of the EDC and
can be found till north and is a discontinuous band of linear belts.
• The southern portion of the superbelt grades into a characteristic
charnockitic terrain, while the north end (Kadiri belt) disappears beneath
the Cuddapah Basin.
• The Kolar region contains mostly amphibolite grade metamorphic rocks.
• As with the other greenstone belts in the region, the KKJH are intruded by
various felsic dykes.
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Dharwar Batholith
• The Dharwar Batholith is a term to describe a series of parallel plutonic belts.
• Previous works consistently used the term ‘Peninsular Gneisses’ to describe the
majority of the EDC; however, it is compositionally different than the WDC
gneisses, more granitic than gneissic, and hence the new terminology is more
appropriate.
• The plutonic belts are approximately 15–25 km wide, hundreds of km long and
separated by greenstone belts.
• Age constraints from the WDC Peninsular gneisses suggest an early Archaean age,
whereas the granitic gneisses of the Dharwar Batholith are of Late Archaean age.
• Ages for granitic units appear to decrease from west to east; however, gneissic
protolith ages of >2900 Ma.
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Closepet Granite
• The Closepet Granite is located on the western margin of the EDC and is a
linear batholith that trends ~North‐South.
• The granite is 400 km long and approximately 20‐30 km wide with shear
zones on both sides.
• The exposed rock is divided into northern and southern components by a
part of the Sandur Schist Belt; however, both sections appear to be
lithologically similar at the outcrop level.
• The Closepet Granite is dated to 2513 Ma and appears to be part of a
widespread Neo‐Archaean phase of plutonism in both the Eastern and
Western Dharwar Cratons that is considered to mark the stabilization age
for the WDC and EDC.
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Western Dharwar Craton
• The Western Dharwar Craton
(WDC) is located in southwest
India.
• The division between the WDC
and EDC is based on the nature
and abundance of greenstones,
age of surrounding basement
and regional metamorphism.
• The WDC shows an increase in
regional metamorphic grade
from greenschist and
amphibolite facies in the north
and granulite facies in the south.
WDC
• The Archaean Tonalitic–Trondhjemitic–Granodioritic (TTG) Gneisses are found
throughout the Western Dharwar Craton, dated at 3.3 to 3.4 Ga.
• Three generations of volcanic‐sedimentary greenstone granite sequences are
present in the WDC:
• the 3.1–3.3 Ga Sargur Group,
• the 2.6–2.9 Ga Dharwar Supergroup and
• The 2.5–2.6 Ga calc‐alkaline to high potassic granitoids, the largest of which is the
Closepet Granite.
• The Dharwar supracrustal rocks uncomformably overlie widespread gneiss‐
migmatite of the Peninsular Gneissic Complex (3.0–3.3 Ga) that encloses the Sargur
schist belts.
• The main Dharwar Schist Belts of the Western Block are: (1) Shimoga‐Western
Ghat‐Babubudan, and (2) Chitradurga
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The Sargur Group
• They are mainly exposed as schistose inclusion in peninsular gneisses.
• These comprise of ultramafic to mafic volcanic rocks, quartzites,
carbonates and argillaceous sediments.
• The Sargur Group greenstone belts display well‐preserved volcano‐
sedimentary sequences.
• The rocks have undergone high degree of metamorphism ranging from
amphibolite to granulite facies.
• The Sargur Group developed from several distinct geodynamic processes
across a span of millions of years.
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• Different elements report various ages and the age of the Sargur Group
is taken around 3.1 Ga.
• The older ages present in these analyses are likely inherited from the
basement material, and may represent the older limit of the group.
• The Sargur unit appears to have formed in a subduction setting, likely
derived from the melting of oceanic slab materials.
• The extensive ultramafic to basaltic flows present in the WDC may
represent accreted oceanic plate crust.
• Abundant pillow lava textures are evidence of the oceanic character of
the crust seen in the ultra‐mafic units, indicative of submarine flows.
The Dharwar Supergroup
• The sediments of Dharwar supergroup were laid over a basement of Sargur schist
and Peninsular gneissic complex.
• The sedimentation was marked by intense magmatic activity in the early phase.
• The supergroup can be divided into two fold division: the lower horblendic
division and upper Chloritic division based on the difference in chemical
characters.
• The lower unit comprises mafic and ultramafic rocks of volcanic origin whereas
upper unit is composed of geosynclinal sediments.
• The lower unit is named as Bababudan group and the upper unit is named
Chitradurga group and the Dharwar Supergroup is exposed in these two large
schist belts .
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• The Bababudan Group is spread over a 300 km long and 100 – 150 km
wide area, and is made up of the Babadudan schist belt, Western
Ghats belt, and the Shimoga schist belt.
• The Bababudan schist belt covers an area of approximately 2500 km2.
• The base of this unit is represented by the Kartikere conglomerate
that discontinuously extends along the southern margin of the belt
for ~ 40 km.
• This unit grades into a quartzite.
• The Western Ghats Belt is a large schist belt about 2200 km2 in
extent, and about 150 km by 15 km in dimension.
• The stratigraphy closely resembles the Babaudan belt; however, a major
group of basalts, felsic volcanics, and pyroclastic units is also seen in the
upper levels.
• The Shimoga schist belt is a large (25,000 km2) NW trending belt separated
from the previous two by outcropping TTG basement gneiss.
• Mn bearing formation are found along the western margin of Shimoga,
Chitradurga and Sandur schist belts.
• Mn bearing formations mark the boundary between Chitradurga and
Bababudan groups.
• The contact between these basement gneisses and the schist belt is
observed as a zone of high grade metamorphism, often with kyanite and
garnet phases present.
• Granitioid intrusions are also present in the north of the belt.
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Proterozoic dyke swarms and Basin: WDC
• Mafic dyke swarms varying in orientation and composition, intrude many
areas of the WDC.
• There are three main dyke swarms of Proterozoic age in the Western
Dharwar Craton known as the (1) Hassan‐Tiptur dykes; (2) Mysore dykes
and (3) “Dharwar” dykes.
• The E–W trending Kaladgi–Badami Basin is the only significant Proterozoic
intracratonic basin of the Western Darwar Craton located along the
northern edge of the craton.
• This basin formed on TTG gneisses and greenstones of Archaean age.
• The Kaladgi Supergroup preserves the record of sedimentation in the basin,
and consists of sandstones, mudstones and carbonates.
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