Tectonic Framework of India | Geology Optional Notes for UPSC PDF Download

Introduction 

The term "peninsula" refers to a landmass that is surrounded by water on three sides. Peninsular India is bordered by the Bay of Bengal to the east, the Indian Ocean to the south, and the Arabian Sea to the west. This geographical feature is why it is called Peninsular India. 
Due to its large size, India is considered a subcontinent, and its vast area contributes to its geological complexity. The geological history of India spans nearly the entire history of our planet, from the early Archaean eon to the Holocene epoch, which is about 3.7 billion years ago to the present time. 

Physiographically, India is divided into three major contrasting regions: 

• Peninsular India
• Indo-Gangetic Plain
• Extra-Peninsular India or the Himalayas

These regions exhibit distinct differences in their geological, tectonic, and physical characteristics. Additionally, there are minor units such as the Thar Desert, coastal plains, and islands. 
Peninsular India and the Himalayan mountain belt are particularly significant from a geotectonic perspective. The Indian landmass is made up of several crustal blocks, each of which is a large area with its own unique geological, tectonic, structural, and stratigraphic characteristics and history, which differ from those of nearby blocks. 

Geology of Peninsular India

•  Peninsular India is a triangular region surrounded by low mountain ranges. 
•  To the north, it is bordered by the Vindhyan hills, and to the northeast, by the Satpura range. 
•  Geologically, Peninsular India is a stable and ancient part of the Earth's crust, known as the Indian Shield. 
•  This shield is made up of very old rocks, primarily crystalline igneous and metamorphic rocks from the Precambrian era. 
•  The region is characterized by Archaean cratons and Proterozoic mobile belts, which may form the foundation for younger rocks. 
•  The oldest rocks in this area, over 500 million years old, are called the basement rocks, and they consist of igneous and metamorphic materials. 
• Cratons are stable parts of the continent that haven’t undergone significant deformation for a long time, usually since the Precambrian or early Paleozoic era. 
•  These cratons are regions of the shield that have been stabilized after several episodes of mountain building, volcanic activity, and metamorphism, and they are typically of Archaean or early Proterozoic age. 
• Orogenic Belts, also known as mobile belts, are areas that have experienced folding and other deformations during mountain building. 
•  These belts are tectonically active and unstable, located between cratons, and have undergone fracturing, faulting, and shearing along their margins with the cratons. 
•  A tectonic suture zone is a narrow, complex region where two tectonic plates are fused together, resulting in the formation of a continuous landmass. 
•  Crustal blocks with different geological structures and settings are often welded together along these suture zones. 
•  The Peninsular Indian region is notable for its well-preserved geological features from the Precambrian era, including cratons and mobile belts. 
•  The main Archaean cratons in this region include the Dharwar, Bastar, Singhbhum, Bundelkhand, and Aravalli cratons, while the Meghalaya craton is of Proterozoic age. 
•  The primary Proterozoic sedimentary basins in Peninsular India include the Vindhyan, Cuddapah, Chhattisgarh, and Delhi supergroups. 

Major Tectonic Features of Indian Shield

• Cratons are stable parts of the continent that have not experienced significant deformation for a long period, typically since the Precambrian or early Paleozoic era. 
•  These areas have been stabilized after undergoing several cycles of mountain building, igneous activity, and metamorphism. 
•  Cratons are usually of Archaean or early Proterozoic age. 
•  In Peninsular India, the main cratons include the Dharwar, Bastar, Singhbhum, Bundelkhand, and Aravalli cratons, with the Meghalaya craton being of Proterozoic age. 
•  The Eastern Ghat, Pandyan, Satpura, Aravalli, and Chhotanagpur-Singhbhum mobile belts are significant tectonic features in Peninsular India. 
•  These mobile belts are linear regions that have experienced folding and other deformations during mountain building episodes. 
•  They are tectonically active or unstable zones situated between cratons and have witnessed fracturing, faulting, and shearing along their margins with the cratons. 
•  The Precambrian cratons and mobile belts are prominent features of Peninsular India, consisting of well-preserved stratigraphic units. 
•  The cratons are regions of Archaean or early Proterozoic age, while the mobile belts are Proterozoic in age. 
•  These mobile belts are also known as orogenic belts and are characterized by their linear shape and tectonic activity. 
•  Intra-cratonic rifts and basins are important geological features in Peninsular India that developed during the Proterozoic era and were re-activated during the early stages of the break-up of Pangaea, possibly in the Late Paleozoic era. 
•  The expansion of these rifts led to the formation of valleys or basins, which were subsequently filled with sediments. 
•  These filled rift valleys are known as the Gondwana Supergroup, which is famous for its coal deposits. 
•  The Gondwana Supergroup is of Permian to Lower Cretaceous age and is well-developed in the Godavari, Son, Mahanadi, Narmada, and Damuda rift valleys. 
•  After separating from Antarctica and Madagascar during the Cretaceous period, the Indian plate crossed over the Kerguelen and Reunion hotspots. 
•  Volcanic eruptions from these hotspots on the surface of the Indian plate resulted in the formation of the Rajmahal and Deccan traps in Peninsular India. 
•  During the Upper Cretaceous period, with the advancing sea, sedimentation occurred along the Son-Narmada lineament in Central India, leading to the formation of the Bagh and Lameta formations. 

Archaean Cratons

The Archaean region of Peninsular India, dating from 3.8 to 2.5 billion years ago, comprises rigid and tectonically stable cratons. The main cratons of the Indian shield include the Dharwar, Bastar, Singhbhum, Bundelkhand, and Aravalli cratons, located in southern, central, eastern, northern, and western Peninsular India, respectively.
These cratons are primarily composed of:

• Tonalite-trondhjemite-granodiorite suites
• Greenstone belts
• Granitoid rocks

Dharwar Craton

• The Dharwar Craton, also known as the Karnataka Craton, is one of the largest cratonic areas in the Indian shield. It is located in Karnataka, with parts extending into Andhra Pradesh and Tamil Nadu.
• This craton is bordered by the Pandyan Mobile Belt to the south, covered by the Deccan Traps to the north, and bounded by the Eastern Ghats Mobile Belt to the east, with the Arabian Sea to the west.
• The Dharwar Craton is divided into two main terrains: Eastern Dharwar Craton (EDC) and Western Dharwar Craton (WDC).
• The boundary between these two terrains is marked by the Chitradurga Shear Zone, which is a transition zone.
• The Western Dharwar Craton (WDC) is characterized by older gneissic rocks, aged between 3.3 to 2.7 billion years, and has a thicker crust.
• The dominant rock type in the WDC is tonalite-trondhjemite-granodiorite gneisses, previously referred to as Peninsular gneisses.
• The Eastern Dharwar Craton (EDC) features a thinner crust with younger granitoids, approximately 2.52 billion years old.
• The EDC also contains gold-bearing greenstone belts aged between 2.7 to 2.5 billion years.

Bastar Craton

• The Bastar Craton, also known as the Bhandara Craton, is situated northeast of the Dharwar Craton and spans a large area in Central India.
• It is bordered by the Pranhita-Godavari rift to the south, the Mahanadi Rift to the northeast, and the Satpura Mobile Belt to the north. The Eastern Ghats Mobile Belt lies to the east, and the Deccan Traps are to the west of the craton.
• The Bastar Craton is primarily composed of granites and granitic gneisses, collectively known as the Gneissic Complex. This craton has a complex geological history, having undergone several orogenic cycles, and is rich in mineral resources.
• It contains significant deposits of copper and iron ores, particularly derived from Banded Iron Formations.

Singhbhum Craton

• The Singhbhum Craton, also referred to as the Singhbhum-Odisha Craton, is located in Eastern India and encompasses parts of Jharkhand, Odisha, and West Bengal.
• This craton contains some of the oldest rocks in the Indian subcontinent and is bordered by the Chhotanagpur Granite-Gneiss Complex (often called the Chhotanagpur Craton) to the north, and by the Eastern Ghats Mobile Belt to the southeast.
• The Bastar Craton lies to the southwest, while alluvium covers the eastern part of the craton. The Singhbhum Craton has a triangular shape, with its core consisting of granite known as the Singhbhum Granite. All of the rocks in this craton have undergone regional metamorphism, specifically of the amphibolite facies.
• The craton is rich in minerals and is the source of India’s largest deposits of iron ore and chromite.

Bundelkhand Craton

• The Bundelkhand Craton is the northernmost craton of the Indian Shield, located in Madhya Pradesh and parts of Uttar Pradesh. It has a semicircular shape and is one of the smallest cratons in the Indian Shield.
• The craton is bordered by the Satpura Mobile Belt to the south and the Aravalli Mobile Belt to the east. The northern and northeastern margins are partially concealed under Indo-Gangetic alluvium.
• The Bundelkhand Craton primarily consists of granite with gneissic bands, as well as mafic to ultramafic rocks and Banded Iron Formation. The granites are commonly referred to as the Bundelkhand Granite Massif.

Aravalli Craton

• The Aravalli Craton, also known as the Rajasthan Craton, is located to the north of the Bundelkhand Craton, separated by the Vindhyan basin. It spans the state of Rajasthan and parts of Gujarat, Madhya Pradesh, Haryana, and Delhi.
• The craton is bordered by the Narmada-Son Lineament to the south and the Great Boundary Fault to the east. The southern margin is adjacent to the Deccan Traps. The Aravalli Craton is also divided into two parts: the Mewar Craton in the east and the Marwar Craton in the west.
• The craton is primarily composed of gneisses, migmatites, meta-volcanic, and meta-sedimentary rocks, with several granitic intrusions. In some classifications, the Aravalli and Bundelkhand cratons are combined into a single unit known as the Aravalli-Bundelkhand Craton or the Rajasthan Craton.

Proterozoic Basins

In a specific (stratigraphical) sense, a basin refers to the place where sediments are deposited. The Proterozoic sedimentary basins in Peninsular India that are less disturbed and unmetamorphosed are known as the Purana Basins. These basins rest on deformed and metamorphosed Archaean. Palaeoproterozoic basement rocks and were formed within a narrow time frame, between the Late Palaeoproterozoic and Early Mesoproterozoic, approximately 1900 to 1600 billion years ago. The main Proterozoic basins in Peninsular India include the Vindhyan, Chhattisgarh, Cuddapah, Marwar, and Pranhita-Godavari basins. These basins have distinct characteristics and geological significance. Let’s discuss them one by one.

1. Vindhyan Basin:

• The Vindhyan basin is the largest among the Purana Basins and the second largest Proterozoic basin globally.
• It spans from the Palaeoproterozoic to Neoproterozoic era and is known for its diverse depositional environments ranging from shallow marine to nonmarine or continental settings.
• The Vindhyan sediments, with a maximum thickness of 6.2 km, are primarily exposed on the eastern and western sides of the Bundelkhand Massif within the Bundelkhand Granite Complex.
• This succession overlies Early Proterozoic metasediments of the Bijawar and Mahakoshal Groups and underlies the Gondwana Supergroup.

2. Chhattisgarh Basin:

• The Chhattisgarh basin features a succession of mixed siliciclastic-carbonate lithology, approximately 2.7 km thick, lying unconformably over the Bastar craton.
• It exhibits a shrinking, bowl-shaped structure with a concentric outcrop pattern and contains alternating evaporites and carbonates, indicative of a desiccated-basin setting in an intra-cratonic depositional mode.
• The basin is proposed to have formed during the Mesoproterozoic era.

3. Cuddapah Basin:

• The Cuddapah basin, crescent-shaped and covering about 44,500 km2 on the eastern part of the Dharwar craton, hosts a sedimentary and volcanic rock package ranging from 6 to 12 km in thickness.
• The basin’s sediments non-conformably overlie Archaean gneisses, granites, and greenstone belts and are categorized into the Cuddapah Supergroup and the Kurnool Group.
• While the western Cuddapah sediments are largely unmetamorphosed and undeformed, the eastern sediments exhibit deformation, manifesting as a fold-thrust belt.
• These sediments are thought to have originated from various environments, including alluvial, complex beach, sub-tidal, intertidal, offshore, and carbonate shelf settings.

4. Marwar Basin

•  The Marwar basin is prominently visible in western Rajasthan. 
•  It comprises rocks that are undisturbed and unaltered, lying to the west of the Delhi-Aravalli mountain range. 
•  The basin is mainly made up of evaporites and is situated on top of Malani volcanic rocks. 
•  This supergroup is divided into three groups: Jodhpur, Bilara, and Nagaur. 
•  During the time of deposition, the climate was warmer. 
•  The Marwar basin spans from the Neoproterozoic to the Lower Cambrian boundary. 

5. Kaladgi-Badami Basin

•  The Kaladgi-Badami basin is situated in the northern parts of the Dharwar craton. 
•  It contains approximately 4 km of thick shallow marine platform sediments. 
•  The basin rests on an Archaean crystalline basement and features conglomerate beds at its base. 
•  A significant portion of the basin is covered by the Upper Cretaceous Deccan Traps. 
•  This basin is unique as a Purana basin, exhibiting axial zone deformation and low-grade metamorphism. 
•  It is recognized as an intra-cratonic rift basin. 
•  The Kaladgi-Badami basin is divided into two units: Badami Group and Kaladgi Supergroup. 
•  The Badami Group, which lies above the Kaladgi Supergroup, is known for its diverse microfossils. 

6. Pranhita-Godavari Basin

• The Pranhita-Godavari rift system has been intermittently active since the Mesoproterozoic era or even earlier.
• It contains sedimentary fills of over 6 km thickness, known as the Godavari Supergroup.
• These Proterozoic rocks are exposed in two linear belts, eastern and western, surrounding the Gondwana rocks.
• The Pakhal and Penganga groups are located in the western belt, while the Somanpalli Group is found in the eastern belt.

Proterozoic Mobile Belts and Faults

The Archaean cratons, including the Dharwar, Bastar, Singhbhum, Bundelkhand, and Aravalli cratons, are separated by mobile or fold belts. These mobile belts were formed during Proterozoic times, which span from 2.5 billion years to 541 million years ago. The boundaries of these mobile or fold belts are marked by shear or fault zones.

A shear zone is a planar rock mass that exhibits significantly higher strain than the surrounding rocks. The width of shear zones can range from a few millimeters to several tens of kilometers. While a shear zone behaves similarly to a fault system, the fault plane is not visible. The mobile belts are composed of metamorphosed Proterozoic rocks, with schists, gneiss, amphibolite, and migmatites being the dominant rock types.

Let us discuss the main Proterozoic mobile belts of the Peninsular India.

(a) Eastern Ghat Mobile Belt

The Eastern Ghat Mobile Belt is located along the east coast of India, separating the Dharwar and Bastar cratons to the east from the Singhbhum craton to the south. This belt spans approximately 1000 km in a northwest to southwest direction, running parallel to the east coast of the Indian plate and bordered by the Bay of Bengal. It has a tectonic contact with the Cuddapah Supergroup to the west. The Eastern Ghat Mobile Belt is characterized by high-grade metamorphic rocks such as charnockites, granulites, migmatites, khondalites, and granite gneisses. This mobile belt was formed during the Mesoproterozoic era, approximately 1.6 to 1.0 billion years ago.

(b) Pandyan Mobile Belt

The Pandyan Mobile Belt, also known as the Southern Granulite Terrain or Madurai block, is the southernmost mobile belt in Peninsular India. It is situated to the south of the Dharwar craton and the Eastern Ghat Mobile Belt. This belt is composed of high-grade metamorphic rocks such as charnockites, khondalites, and granulites, along with granitic intrusions of various ages. The southern boundary of the Pandyan Mobile Belt is defined by a system of shear zones, including the Moyar Bhavani and Palghat Cauvery Shear Zones. The Moyar Bhavani shear zone is located south of the Dharwar craton, while the Palghat Cauvery shear zone is found north of the Pandyan Mobile Belt. The Chitradurga shear zone further divides the Dharwar craton into Eastern and Western regions. These shear zones enclose relatively undeformed blocks and lenses of granulites, anorthosite, gabbro, and ultramafic complexes.

(c) Satpura Mobile Belt

The Satpura Mobile Belt, named after the Satpura Mountain range, is an east-west trending mobile belt that separates the Indian shield into northern and southern parts. The southern part includes the Dharwar, Bastar, and Singhbhum cratons, as well as the Deccan Traps, while the northern part encompasses the Bundelkhand craton. The central portion of the Satpura mobile belt is referred to as the Central Indian Tectonic Zone.

(d) Aravalli Mobile Belt

The Aravalli Mobile Belt is a northeast to southwest trending belt, approximately 700 km long, situated north of the Central Indian Suture Zone. This belt lies to the west of the Bundelkhand craton and separates the Bundelkhand craton from the Aravalli craton. During the Aravalli orogeny, the belt experienced lower crust rifting and subduction-related processes.

(e) Chhotanagpur-Singhbhum Mobile Belt

The Chhotanagpur-Singhbhum Mobile Belt is an east to west trending mobile belt located between the northern margin of the Singhbhum craton and the southern margin of the Chhotanagpur Granite-Gneiss Complex. This belt is composed of low to medium grade metamorphic rocks and volcanic igneous rocks. Intra-continental rift basins developed in this mobile belt during Palaeoproterozoic to Mesoproterozoic times, approximately 2.5 to 1.2 billion years ago.

Proterozoic Suture Zones

• Definition. Suture zones are areas where two continental plates have come together through subduction and collision. These zones are characterized by the presence of oceanic relics like ophiolites, which indicate former ocean basins. 
• Geological Activity. Suture zones are sites of intense geological activity, including deformation, high magmatic activity, and complex mountain-building processes known as collisional orogeny. 
• Rock Mixture. At suture zones, a mixture of rock fragments from one plate or the other is found, which have been accreted, sutured, or welded together. 
• Location. Suture zones also develop along the margins of cratons and mobile belts. 
•  Cratons. Stable portions of the continental crust that have survived the cycles of plate tectonics. 
• Mobile Belts. Regions of the crust that have been subjected to significant tectonic activity, leading to the formation of mountains and other geological features. 

1. Cauvery Suture Zone 

• Location. Southernmost suture zone in Peninsular India, oriented east-west, approximately 400 km long and 70 km wide. 
• Geological Features. Separates the Dharwar craton to the north from the granulites of the Pandyan mobile belt to the south. 

Boundary Shear Zones. 

•  Northern Boundary: Moyar Bhavani shear zone 
•  Southern Boundary: Palghat Cauvery shear zone 
• Rock Types. 
  •  High-grade metamorphic rocks: Granulites, Charnockites, Migmatites 
  •  Igneous rocks: Dunites, Peridotites, Anorthosites 

 2. Central India Suture Zone 

• Other Name. Central India Tectonic Zone 
• Location and Orientation. Runs east-northeast to west-southwest for over 800 km, separating North Indian and South Indian crustal blocks. 
• Width. Up to 400 km. 
• Northern Block. Contains the Archaean Bundelkhand craton. 
• Southern Block. Composed of Dharwar, Bastar, and Singhbhum cratons. 
• Major Rivers. Narmada and Tapti rivers flow within the suture zone. 
• Structural Features. Narmada and Tapti faults are prominent features. 

Geological Units. 

•  Metamorphosed supra-crustal belts 
•  Metamorphosed mafic and ultramafic bodies 
•  Metacarbonates 
•  Iron and manganese formations 
•  Tonalite-trondhjemite-granodiorite gneisses 
•  Charnockites 
•  Arc magmatic suites 
• Northern Lineament. Son-Narmada-Tapti Lineament located north of the suture zone. 

 3. Phulad Suture Zone 

• Location. Northwestern margin of the Indian shield, demarcating the western margin of the Proterozoic Delhi-Aravalli Fold Belt. 
• Physiographic Feature. Part of the Delhi-Aravalli Mountains range, with the eastern boundary marked by the Great Boundary Fault. 
• Geological Significance. A long and narrow zone of extreme deformation, exposing ophiolites along the western margin of the South Delhi Fold Belt. 

Rock Assemblages. 

• North Eastern Assemblage. Pelites, amphibolites, and calc-silicates. 
• South Western Assemblage. Primarily granitic rocks. 

 4. Singhbhum Shear Zone 

• Location. Eastern India, between the Chhotanagpur plateau and the Singhbhum craton. 
• Size. Over 200 km long and 2 to 10 km wide. 
• Characteristics. Tectonic mélange region with multiple metasomatism events, extensive ductile shearing, and migmatisation. 
• Rock Types. Quartz-mica phyllonite, quartz-tourmaline rock, granitic mylonite, and volcanoclastic rocks. 
• Mineral Deposits. Rich in copper, uranium, tungsten, and phosphate, leading to its alternative name, Singhbhum Copper-Uranium Belt. 

 5. Great Boundary Fault 

• Location. Southeastern Rajasthan. 
• Geological Features. Separates weakly deformed and unmetamorphosed Vindhyan sediments from the older and deformed Aravalli Supergroup. 

Structural Characteristics. 

•  Folding of Archaean basement and Proterozoic Vindhyan sediments into large-scale low plunging folds. 
•  Development of folds, oriented fabric, and re-crystallisation in a brittle-ductile regime. 
•  Moderate to steep dip of the fault towards the basement. 
•  Juxtaposition of basement rocks in the hanging wall with younger sediments in the footwall. 
• Origin. Fault originated as a thrust. 

Gondwana Rift Valleys

• After the deposition of the Proterozoic Vindhyan Supergroup, sedimentation in Peninsular India ceased for most of the Palaeozoic Era. However, significant sedimentation occurred from the Upper Carboniferous to Lower Cretaceous periods in the intracratonic rift valley basins of Peninsular India.
• These basins, formed by normal faulting, are known as Gondwana basins and constitute the Gondwana Supergroup stratigraphically.
• The rocks of the Gondwana Supergroup are mainly found in four isolated patches represented by linear tracts: Pranhita-Godavari Rift Basin, Son-Narmada Rift Basin, Mahanadi Rift Basin, and Damodar Rift Basin.
• The rift valleys are characterized by fault systems consisting of grabens, half-grabens, and horsts.
• The Pranhita-Godavari Rift Valley is approximately 470 km long and features northwest-southeast trending faults. It is located between the eastern Dharwar and Bastar cratons in the states of Telangana and Andhra Pradesh, passing through the Eastern Ghat mobile belt. The Proterozoic sedimentary rocks in this rift valley are known as the Pakhal Supergroup, Penganga Group, and Albaka Group.
• The Son-Narmada Rift Valley is oriented in an east-northeast to west-southwest direction and delineates the boundary between the Bundelkhand craton and the Bastar-Singhbhum cratons in Central India.
• The Mahanadi Rift, located in the states of Chhattisgarh and Madhya Pradesh, separates the Singhbhum craton from the Bastar craton.
• The Damodar Basin is an east-west trending rift zone situated in West Bengal and Jharkhand, known for its extensive deposits of high-quality Permian age coal.

Neotectonic Activities in India

The Earth is an active planet constantly undergoing deformational processes since its formation, though these processes are currently more pronounced in some regions than others. To describe what is happening tectonically today or in the recent geological past, the term neotectonics was introduced by V. Obruchev in 1948. 
Neotectonics focuses on the study of young tectonic events, specifically the deformation of the Earth's upper crust, which have occurred or are still occurring in a region after its orogeny or significant tectonic setup. It broadly includes the investigation of post-Miocene structures and the structural history of the Earth's crust. 

Scales of Neotectonics

• Macro-scale: Involves Neogene movements of tectonic plates. 
• Meso-scale: Includes vertical and lateral movements of mountain chains like the Himalayas and vertical isostatic movements. 
• Micro-scale: Deals with movements on individual faults and folds with dimensions as small as a few kilometers. 

Indicators of Neotectonic Activities
Various geomorphological features serve as indicators of neotectonic activities in an area, including: 

• Waterfalls 
• Entrenched meanders 
• River terraces 
• Steeply sloping valleys 
• Sudden changes in river flow direction 
• Hot water springs 
• Narrow gorges 
• Uplifted caves and beaches 
• Active volcanoes 
• Long straight river valleys 

The entire Indian subcontinent is currently experiencing neotectonic activity manifested through morphological changes in rivers, alterations in drainage patterns, tilting of river terraces, soft sediment deformation, and the development of angular unconformities in recent sediments.