Geology of India
The geology of India is diverse. Different regions of the Indian subcontinent contain rocks belonging to different geologic periods, dating as far back as the Eoarchean Era. Some of the rocks are very deformed and altered. Other deposits include recently deposited alluvium that has yet to undergo diagenesis. Mineral deposits of great variety are found in the subcontinent in huge quantities. Even India's fossil record is impressive in which stromatolites, invertebrates, vertebrates and plant fossils are included.
India's geographical land area can be classified into the Deccan Traps, Gondwana and Vindhyan.
The Deccan Traps covers almost all of Maharashtra, a part of Gujarat, Karnataka, Madhya Pradesh and Andhra Pradesh marginally. During its journey northward after breaking off from the rest of Gondwana, the Indian Plate passed over a geologic hotspot, the Réunion hotspot, which caused extensive melting underneath the Indian Craton. The melting broke through the surface of the craton in a massive flood basalt event, creating the Deccan Traps. It is also thought that the Reunion hotspot caused the separation of Madagascar and India.
The Gondwana and Vindhyan include within its fold parts of Madhya Pradesh, Chhattisgarh, Odisha, Bihar, Jharkhand, West Bengal, Andhra Pradesh, Maharashtra, Jammu and Kashmir, Punjab, Himachal Pradesh, Rajasthan and Uttarakhand. The Gondwana sediments form a unique sequence of fluviatile rocks deposited in Permo-Carboniferous time. The Damodar and Sone river valleys and Rajmahal hills in eastern India contain a record of the Gondwana rocks.
The Geological Survey of India has published the List of National Geological Monuments in India.
Plate tectonics
The Indian Craton was once part of the supercontinent of Pangaea. At that time, what is now India's southwest coast was attached to Madagascar and southern Africa, and what is now its east coast was attached to Australia. During the Jurassic Period about 160 Ma, rifting caused Pangaea to break apart into two supercontinents, namely Gondwana and Laurasia. The Indian Craton remained attached to Gondwana, until the supercontinent began to rift apart about in the early Cretaceous, about 125 million years ago. The Indian Plate then drifted northward toward the Eurasian Plate, at a pace that is the fastest known movement of any plate. It is generally believed that the Indian Plate separated from Madagascar about 90 Million years ago, however some biogeographical and geological evidence suggests that the connection between Madagascar and Africa was retained at the time when the Indian Plate collided with the Eurasian Plate about 50 Million years ago. This orogeny, which is continuing today, is related to closure of the Tethys Ocean. The closure of this ocean which created the Alps in Europe, and the Caucasus range in western Asia, created the Himalaya Mountains and the Tibetan Plateau in South Asia. The current orogenic event is causing parts of the Asian continent to deform westward and eastward on either side of the orogen. Concurrently with this collision, the Indian Plate sutured on to the adjacent Australian Plate, forming a new larger plate, the Indo-Australian Plate.Tectonic evolution
The earliest phase of tectonic evolution was marked by the cooling and solidification of the upper crust of the earth's surface in the Archaean Era which is represented by the exposure of gneisses and granites especially on the Peninsula. These form the core of the Indian Craton. The Aravalli Range is the remnant of an early Proterozoic orogen called the Aravali-Delhi Orogen that joined the two older segments that make up the Indian Craton. It extends approximately from its northern end to isolated hills and rocky ridges into Haryana, ending near Delhi.Minor igneous intrusions, deformation and subsequent metamorphism of the Aravalli Mountains represent the main phase of orogenesis. The erosion of the mountains, and further deformation of the sediments of the Dharwarian group marks the second phase. The volcanic activities and intrusions, associated with this second phase are recorded in the composition of these sediments.
Early to Late Proterozoic calcareous and arenaceous deposits, which correspond to humid and semi-arid climatic regimes, were deposited the Cuddapah and Vindhyan basins. These basins which border or lie within the existing crystalline basement, were uplifted during the Cambrian. The sediments are generally undeformed and have in many places preserved their original horizontal stratification. The Vindhyans consist of a lower Supergroup that was deposited sometime between ~1800–1600 Ma. The lower Vindhyan rocks were slightly deformed and the Upper Vindhyan sequence lies unconformably over the Lower Vindhyan. The age of Upper Vindhyan sedimentation is contentious. Kaimur rocks were intruded by the 1073 Ma Majhgawan kimberlite and are therefore older than 1073 Ma. The Rewa contains diamondiferous conglomerates suggesting that they formed after the Kaimur. The Rewa is conformably overlain by the Bhander Group. Indirect evidence for the age of the Upper Vindhyan was discussed by Meert and Pandit who noted the similarity in paleomagnetic directions from the 1073 Ma Majhgawan kimberlite, the 1.1 Ga Mahoba dyke and sediments of the Bhander and Rewa Groups. In addition, multiple detrital zircon studies failed to isolate any ages younger than ~1000 Ma from Upper Vindhyan rocks. A recent claim of the iconic Ediacaran fossil "Dickinsonia" located in the Upper Bhander required an Ediacaran age for that Group; however, Meert et al. demonstrated that the fossil was misidentified and therefore the age of the Upper Vindhyan is still debated.
Early Paleozoic rocks are found in the Himalayas and consist of southerly derived sediments eroded from the crystalline craton and deposited on the Indian platform.
In the Late Paleozoic, Permo-Carboniferous glaciations left extensive glacio-fluvial deposits across central India, in new basins created by sag/normal faulting. These tillites and glacially derived sediments are designated the Gondwanas series. The sediments are overlain by rocks resulting from a Permian marine transgression.
The late Paleozoic coincided with the deformation and drift of the Gondwana supercontinent. To this drift, the uplift of the Vindhyan sediments and the deposition of northern peripheral sediments in the Himalayan Sea, can be attributed.
During the Jurassic, as Pangea began to rift apart, large grabens formed in central India filling with Upper Jurassic and Lower Cretaceous sandstones and conglomerates.
By the Late Cretaceous India had separated from Australia and Africa and was moving northward towards Asia. At this time, prior to the Deccan eruptions, uplift in southern India resulted in sedimentation in the adjacent nascent Indian Ocean. Exposures of these rocks occur along the south Indian coast at Pondicherry and in Tamil Nadu.
At the close of the Mesozoic one of the greatest volcanic eruptions in earth's history occurred, the Deccan lava flows. Covering more than area, these mark the final break from Gondwana.
In the early Tertiary, the first phase of the Himalayan orogeny, the Karakoram phase occurred. The Himalayan orogeny has continued to the present day.
Greater India
Greater India or the Greater India Basin means the Indian Plate plus a postulated northern extension which either subducted under Eurasia or pressed against Eurasia's ancient volcanic mountains farther north. As a result, the crust of this formerly coastal region shortened under compression and thickened to become what is today the Tibetan Plateau. The term was used before plate tectonic theory, but the term has seen increased usage since the 1970s.The Indian Plate and the Eurasian Plate have converged up to ±. The upper crustal shortening is documented from the geological record of Asia and the Himalaya as up to approximately less. Much of the lost area was pushed under Asia to form the Tibetan highland.
Major rock groups
Precambrian super-eon
A considerable area of peninsular India, the Indian Shield, consists of Archean gneisses and schists which are the oldest rocks found in India. The Precambrian rocks of India have been classified into two systems, namely the Dharwar system and the Archaean system.Image:SouthIndiaGeology.svg|thumb|upright=1.25|The Dharwar System
The rocks of the Dharwar system are mainly sedimentary in origin, and occur in narrow elongated synclines resting on the gneisses found in Bellary district, Mysore and the Aravalis of Rajputana. These rocks are enriched in manganese and iron ore which represents a significant resource of these metals. They are also extensively mineralised with gold most notably the Kolar gold mines located in Kolar. In the north and west of India, the Vaikrita system, which occurs in Hundar, Kumaon and Spiti areas, the Dailing series in Sikkim and the Shillong series in Assam are believed to be of the same age as the Dharwar system.
The metamorphic basement consists of gneisses which are further classified into the Bengal gneiss, the Bundelkhand gneiss and the Nilgiri gneiss. The Nilgiri system comprises charnockites ranging from granites to gabbros.