The Aravalli Mountain Range is a northeast-southwest trending

orogenic belt An orogenic belt, or orogen, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collecti ...

in the northwest part of

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

and is part of the

Indian Shield The Indian Shield is part of the Indian Craton and occupies two-thirds of the southern Indian peninsula. The shield has remained relatively stable since its formation, over 3500 million years ago. It is delimited on the west, south and east by the ...

that was formed from a series of

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

ic collisions.Mishra, D.C.; Kumar, M. Ravi. Proterozoic orogenic belts and rifting of Indian cratons: Geophysical constraints. Geoscience Frontiers. 2013 March. 5: 25–41. The Aravalli Mountains consist of the Aravalli and Delhi fold belts, and are collectively known as the Aravalli-Delhi orogenic belt. The whole mountain range is about 700 km long.Mckenzie, N. Ryan; Hughes, Nigel C.; Myrow, Paul M.; Banerjee, Dhiraj M.; Deb, Mihir; Planavsky, Noah J. New age constraints for the Proterozoic Aravalli–Delhi successions of India and their implications. Precambrian Research. 2013 November. 238: 120–128. Unlike the much younger Himalayan section nearby, the Aravalli Mountains are believed much older and can be traced back to the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

Eon. They are arguably the oldest geological feature on Earth. The collision between the Bundelkhand craton and the Marwar craton is believed to be the primary mechanism for the development of the mountain range. The precise evolutionary processes responsible for the Aravalli Mountain Range remains controversial today, and there are diverse theories put forward for the tectonic history.

Geology of the Aravalli Mountains

The Aravalli Mountain Range features a horst-like structure and consists of a series of Proterozoic rocks that are intensely deformed and metamorphosed.Verma, P.K.; Greiling, R.O.. Tectonic evolution of the Aravalli Orogen (NW India): an inverted Proterozoic rift basin?. Geol Rundsch. 1995 August. 84: 683–696.

General formation

Three main subdivisions of rocks constitute the stratigraphy of the mountain range, with the Archean Bhilwara

Gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

ic Complex basement being the lowest strata, followed by the overlying lower Aravalli Supergroup and the upper Delhi Supergroup. The northern part of the mountain range only consists of the Delhi Supergroup, and this has given to its name of ‘North Delhi Belt. On the southern side, however, both the Aravalli and Delhi supergroups are present. The mountain range is bounded by the Eastern and Western marginal faults, where the former is also termed as the Great Boundary Fault.

Archean Bhilwara Gneissic Complex basement

The Bhilwara Gneissic Complex basement is about 2.5 Ga old. It is made up of a group of metamorphic and

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

rocks that are mainly

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...

to granulite grade, tonalitic to granodioritic gneisses and intrusive

granitoid A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz ...

s with a minor amount of metasedimentary and metavolcanic rocks.Kaur, Parampreet; Zeh, Armin; Chaudhri, Naveen; Gerdes, Axel; Okrusch, Martin. Archaean to Paleoproterozoic crustal evolution of the Aravalli mountain range, NW India, and its hinterland: The U-Pb and Hf isotope record of detrital zircon. Precambrian Research. 2011 March. 187: 155–164.Lente, B. Van; Ashwal, L.D.; Pandit, M.K.; Bowring, S.A.; Torsvik, T.H.. Neoproterozoic hydrothermally altered basaltic rocks from Rajasthan, northwest India: Implications for late Precambrian tectonic evolution of the Aravalli Craton. Precambrian Research. 2009 January; 170: 202–222. The basement is categorized into two subdivisions: the Sandmata Complex and the Mangalwar Complex.Rao, V. Vijaya; Prasad, B. Rajendra; Reddy, P.R.; Tewari, H.C.. Evolution of Proterozoic Aravalli Delhi Fold Belt in the northwestern Indian Shield from seismic studies. Tectonophysics. 2000 June. 327 (1–2): 109–130.Sinha-Roy, S.; Malhotra, G.; Guha, D.B.. A transect across Rajasthan Precambrian terrain in relation to geology, tectonics and crustal evolution of south-central Rajasthan. In: Sinha-Roy, S., Gupta, K.R. (Eds.), Continental Crust of NW and Central India. Geological Society, India. 1995. 31: 63–89. The Sandmata Complex refers to gneisses and granitoids while the Mangalwar Complex refers to the metasedimentary and metavolcanic series which are considered to be metamorphosed older granite-greenstone belt.

Aravalli Supergroup

On top of the Archean basement, the Aravalli Supergroup overlies with clear

unconformities An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

separating the two strata. The Aravalli Supergroup is divided into three groups: lower Delwara Group, middle Debari Group, and Upper Jharol Group.Meert, Joseph G.; Pandit, Manoj K.. The Archean and Proterozoic history of Peninsular India: tectonic framework or Precambiran edimentary basins in India. In: Mazumder, R. & Eriksson, P. G. (eds), Precambrian Basins of India: Stratigraphic and Tectonic Context. Geological Society, London. 2015 March. 43: 29–54 The lower and middle groups shared similar lithology, where both groups are dominated by carbonates,

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

, and

pelitic A pelite (Greek: ''pelos'', "clay") or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, ...

rocks, thus suggesting a

shelf Shelf ( : shelves) may refer to: * Shelf (storage), a flat horizontal surface used for display and storage Geology * Continental shelf, the extended perimeter of a continent, usually covered by shallow seas * Ice shelf, a thick platform of ice f ...

depositional environment.

Turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...

facies and argillaceous rocks are prominent in the upper Jharol group, thus suggesting a deep marine depositional environment. The depositional age of these sequences ranges approximately from 2.1 to 1.9 Ga. Three major episodes of deformation and metamorphism were involved in the Aravalli Supergroup, including foldings,

shearing Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a '' shearer''. Typically each adult sheep is shorn once each year (a sheep may be said to have been "shorn" or ...

, kink bands and crenulations etc. Metamorphic grades of the rocks generally range from greenschist facies to amphibolite facies.

Delhi Supergroup

The upper Delhi Supergroup overlies on the Aravalli Supergroup with a clear unconformity. This supergroup hosts two main types of rocks: a thick sequence of volcanic rocks that is of continental affinity; and sedimentary rocks that represent

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

and shallow marine environments and deep marine depositional environment. The depositional age of these sequences is approximately from 1.7 to 1.5 Ga. In the ‘North Delhi belt’, the Delhi Supergroup is classified into three groups: lower Raialo Group, middle Alwar Group, and upper Ajabgarh Group. The Raialo Group consists predominantly of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

and calcareous rocks. The Alwar Group mainly consists of arenaceous and mafic volcanic rocks. The Ajabgarh Group is dominated by carbonate, mafic volcanic and argillaceous rocks. In the southern part, similar rock types, despite different names, are identified, where they are Gogunda Group (equivalent to Alwar group) and the Kumbhalgarh Group (equivalent to Ajabgarh Group).

Four phases of tectonic evolution

The tectonic evolution of the Aravalli-Delhi orogenic belt can be divided into four phases: # Bhilwara Gneissic Complex (~ 2,500 Ma) # Aravalli Orogeny (~ 1,800 Ma) # Delhi Orogeny (~ 1,100 Ma) # Post-orogenic evolution (~ 850 – 750 Ma) Two phases of

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

ing,

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

, collision and

suturing A surgical suture, also known as a stitch or stitches, is a medical device used to hold body tissues together and approximate wound edges after an injury or surgery. Application generally involves using a needle with an attached length of threa ...

were documented in the tectonic evolution of the Aravalli-Delhi orogenic belt. During Proterozoic Eon, N-S convergence between the Bundelkhand and Bhandara cratons at the Satpura Mobile Belt, and E-W convergence between the Bundelkhand and Marwar cratons at the Aravalli-Delhi orogenic belt have synchronously occurred in India. This resulted in an overall resultant force of NE-SW convergence of the Aravalli-Delhi orogenic belt, and also led to the arcuate shape of its convergent zone.

Evolution of the Archean basement

The Aravalli Mountains basement started with an older sialic crust evolving into extensive granitic

batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such ...

s by the emplacement of granitic bodies during the period ca. 3.0 to 2.5 Ga. This subsequently led to rapid

cratonization A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging an ...

and rapid thickening of crust to about 20–25 km. The main crustal source is believed to be old crustal components of the area. The region subsequently experienced a large scale metamorphic event that granite is partly metamorphosed into

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

ic rocks, forming the Archean Basement. These cratonization processes continued together signifying the end of amalgamation of cratonic nuclei that constitutes the development of an early continental crust.

Aravalli Orogeny

During the

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

Era, the opening of Aravalli oceanic basin separated the eastern Bundelkhand craton and the western Marwar craton. Sedimentation of the Aravalli Supergroup took place simultaneously with basic magmatism and followed by a gradual subsidence of the Aravalli Basin floor. Soon after the rifting phase ended, the compressional phase took place where the eastern Bundelkhand craton

subducted Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

under the western Marwar craton. As collision continued, the subduction zone steepened, leading to the development of an island arc between the two cratons. After collision had proceeded for a certain period of time, the uplift of the Aravalli Supergroup was induced at around 1800 Ma. In the last stage of convergence, the

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

further steepened and the colliding blocks eventually become sutured. The suture zone is marked by the Great Boundary Fault.

Delhi Orogeny

During the Mesoproterozoic Era, another rifting phase began. At that time, the Bundelkhand-Aravalli-BGC and the Marwar craton lie on the eastern side and western side respectively as the rifting phase separated the Bhilwara Gneissic Complex (BGC) from the Marwar craton. The oceanic basin created in the course of rifting received the Delhi Supergroup sediments. The compressional phase that followed led to eastward subduction of the western Marwar craton. Continuous subduction of the western block might have created another island arc, and similar to the Aravalli orogeny, further collision between the two blocks with island arc in between gave rise to the development of the Delhi orogeny around 1100 Ma. The suture zone between the two cratons is marked by the Western Marginal Fault and the emplacement of the Phulad

Ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found i ...

Suite in the region.

Post-orogenic evolution

Acid magmatic events

The epilogue of the tectonic evolution was marked by granitic and

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

tic events, namely the emplacement of the Erinpura granite and the Malani Volcanics on the western side of Aravalli-Delhi orogenic belt. This event is ranked third among the largest igneous province in the globe, with a total area of about 52,000 km² in India. Malani Igneous Suite is a collective term for bimodal volcanic and plutonic rocks aged 873–800 Ma in the area. The lithologies of the rock suite are predominantly rhyolitic and rhyodacitic volcanic rocks with granitoid intrusions overlying unconformably or intruding through the Delhi Supergroup.

Purana basins formation

Apart from the vigorous post-orogenic magmatic event, a large number of so-called ‘Purana’ basins was actively developing near the orogenic belts. The word ‘Purana’ means ‘ancient’ and was used to depict the group of isolated sedimentary basins with thick Proterozoic sedimentary strata that are relatively undeformed on the Indian Shield. The Vindhyan Basin and the Marwar Basin are part of the Purana basins that sit near the Aravalli Mountain Range. * Vindhyan Basin The Vindhyan Basin is located on the southeastern side of the Aravalli Mountain Range where its formation is believed to be associated to the large downwarp of the crust after Delhi Orogeny. It spans an area of about 104,000 km² in the northwestern part of India overlying on the Archean Bhilwara Gneissic Basement.Turner, Candler C.; Meert, Joseph G.; Pandit, Manoj K.; Kamenov, George D.. A detrital zircon U-PB and HF isotopic transect across the Son Valley sector of the Vindhyan Basin India: Implications for basin evolution and paleogeography. Gondawa Research. 2013 June. https://dx.doi.org/10.1016/j.gr.2013.07.009 The Vindhyan Supergroup is classified into two fundamental strata, lower and upper Vindhyan, with a large unconformity representing 500 million years interval between the strata. Within each stratum, it is further categorized into major groups. The lower Vinhydan comprises the Semri Group while the upper Vinhyan consists of the Kaimur Group, Rewa Group, and Bhander Group. The earliest sedimentation forming the lower Vindhyan can be traced back to Paleoproterozoic and stopped somewhere around early Mesoproterozoic (~1,721 Ma to 1,600 Ma). Sedimentation forming the upper Vindhyan resumed again in the Mesoproterozoic and ceased in Neoproterozoic.Azmi, R.J.; Joshi, D.; Tewari, B.N.. 2008. A synoptic view on the current discordant geo- and biochronological ages of the Vindhyan Supergroup, central India. Journal of Himalayan Geology. 29: 177–191. Vindhyan Supergroup portrayed transitional to shallow marine depositional environment, such as alluvial fan,

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

tidal flat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...

, carbonate ramp etc. * Marwar basin To the west of the Aravalli Mountain Range and far beyond the Vindhyan Basin lies the Neoproterozoic-to-

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

-aged Marwar Basin. The Marwar Basin sits on the Malani Igneous Suite and contains a sedimentary section of 2 km in thickness. Similar to other Purana basins, the Marwar Supergroup is less deformed and unmetamorphosed. The Marwar Supergroup is classified into three major groups: the lower Jodhpur Group, the middle Bilara Group, and the upper Nagaur Group. Arenaceous rocks,

calcareous rock Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

s and evaporites are the dominant rock type in the Marwar Basin.

Association with supercontinent cycles

The tectonic events and basin developmental phases are thought to be correlated to the amalgamation and breakup of plates during

supercontinent cycle The supercontinent cycle is the quasi-periodic aggregation and dispersal of Earth's continental crust. There are varying opinions as to whether the amount of continental crust is increasing, decreasing, or staying about the same, but it is agreed ...

s of Columbia,

Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago and broke up 750–633 million years ago. were probably ...

, and

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

. The Aravalli orogeny (~1,800 Ma) began with the development of oceanic basin. The rifting process is believed to be associated with the formation of the Columbia supercontinent, which happened from 2.5 Ga to 1.8 Ga and was coeval with the onset of Aravalli orogeny's rifting basin. The opening of another sedimentary basin during the Delhi orogeny (~-1,100 Ma) coincided with the time where the supercontinent Columbia broke up, and the cessation of basin development followed by a compressional phase was concurrent with the assembly of

. The deposition of the upper Vindhyan Supergroup may also denote the final episode of Rodinia formation. Several geochemical analyses show that detrital

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

samples obtained from the Marwar basin are highly linked to the breakup phase of Rodinia and the assembly phase of

Map gallery

File:Paleoglobe NO 1590 mya-vector-colors.svg, Reconstruction of Columbia supercontinent File:Rodinia reconstruction.jpg, Reconstruction of Rodinia supercontinent File:Laurasia-Gondwana.png, Godwana supercontinent

References

{{Reflist Geology of India Aravalli Range