Aravalli Range


The Aravalli Range is a mountain range in north-western India. running approximately in a south-west direction, starting near Delhi, passing through southern Haryana and Rajasthan, and ending in Ahmedabad, Gujarat. The highest peak is Guru Shikhar in Mount Abu, Rajasthan at. The Aravalli Range is the oldest fold-mountain belt in India, dating back to the Paleoproterozoic era.

Etymology

Aravalli, a composite Sanskrit word from the roots "ara" and "vali", literally means the "line of peaks".

Natural history

Geology

The Aravalli Range, an eroded stub of ancient mountains, is believed to be the oldest range of fold mountains in India. The natural history of the Aravalli Range dates back to times when the Indian Plate was separated from the Eurasian Plate by an ocean. The Proterozoic Aravalli-Delhi orogenic belt in northwest India is similar to the younger Himalayan-type orogenic belts of the Mesozoic-Cenozoic era in terms of component parts and appears to have passed through a near-orderly Wilson supercontinental cycle of events. The range rose in a Precambrian event called the Aravalli-Delhi Orogen. The Aravalli Range is a northeast–southwest trending orogenic belt located in the northwestern part of Indian Peninsula. It is part of the Indian Shield that formed from a series of cratonic collisions. In ancient times, Aravalli were extremely high but since have worn down almost completely from millions of years of weathering, whereas the Himalayas, young fold mountains, are still continuously rising. Aravalli have stopped growing higher due to the cessation of upward thrust caused by the tectonic plates in the Earth's crust below them. The Aravalli Range joins two of the ancient Earth's crust segments that make up the greater Indian craton, the Aravalli Craton which is the Marwar segment of Earth's crust to the northwest of the Aravalli Range, and the Bundelkand Craton segment of the Earth's crust to the southeast of the Aravalli Range. Cratons, generally found in the interiors of tectonic plates, are old and stable parts of the continental lithosphere that have remained relatively undeformed during the cycles of merging and rifting of continents.
File:ConMarRJS.jpg|thumb|upright=1.5|Global convergent boundary of plate margins
It consists of two main sequences formed in the Proterozoic eon, metasedimentary rock and metavolcanic rock sequences of the Aravalli Supergroup and Delhi Supergroup. These two supergroups rest over the Archean Bhilwara Gneissic Complex basement, which is a gneissic basement formed during the archean eon 4 Ga ago. It started as an inverted basin, that rifted and pulled apart into granitoid basement, initially during Aravalli passive rifting around 2.5 to 2.0 Ga years ago and then during Delhi active rifting around 1.9 to 1.6 Ga years ago. It started with rifting of a rigid Archaean continent banded gneissic complex around 2.2 Ga with the coexisting formation of the Bhilwara aulacogen in its eastern part and eventual rupturing and separation of the continent along a line parallel to the Rakhabdev lineament to the west, simultaneous development of a passive continental margin with the undersea shelf rise sediments of the Aravalli-Jharol belts depositing on the attenuated crust on the eastern flank of the separated continent, subsequent destruction of the continental margin by accretion of the Delhi island arc from the west around 1.5 Ga. This tectonic plates collision event involved early thrusting with partial obduction of the oceanic crust along the Rakhabdev lineament, flattening and eventual wrenching parallel to the collision zone. Associated mafic igneous rocks show both continental and oceanic tholeiitic geochemistry from the Phanerozoic eon with rift-related magmatic rock formations.
The Aravalli-Delhi Orogen is an orogen event that led to a large structural deformation of the Earth's lithosphere due to the interaction between tectonic plates when a continental plate is crumpled and is pushed upwards to form mountain ranges, and involve a great range of geological processes collectively called orogenesis.

Minerals

The archean basement had served as a rigid indentor which controlled the overall wedge shaped geometry of the orogen. Lithology of area shows that the base rocks of Aravalli are of Mewar Gneiss formed by high-grade regional metamorphic processes from preexisting formations that were originally sedimentary rock with earliest life form that were formed during the archean eon, these contain fossils of unicellular organism such as green algae and cyanobacteria in stromatolitic carbonate ocean reefs formed during the paleoproterozoic era. Sedimentary exhalative deposits of base metal sulfide ores formed extensively along several, long, linear zones in the Bhilwara aulacogen or produced local concentration in the rifted Aravalli continental margin, where rich stromatolitic phosphorites also formed. Tectonic evolution of the Aravalli Mountains shows Mewar Gneiss rocks are overlain by Delhi Supergroup type of rocks that also have post-Aravalli intrusions. Metal sulfide ores were formed in two different epochs, lead and zinc sulfide ores were formed in the sedimentary rocks around 1.8 Ga years ago during Paleoproterozoic phase. The tectonic setting of zinc-lead-copper sulfides mineralisation in the Delhi supergroup rocks in Haryana-Delhi were formed by mantle plume volcanic action around one billion years ago covering Haryana and Rajasthan during the mesoproterozoic. In the southern part of the Aravalli supergroup arc base metal sulfides were generated near the subduction zone on the western fringe and in zones of back-arc extension to the south-east. Continued subduction produced tungsten-tin mineralisation in S-type, felsic, and plutons. This includes commercially viable quantities of minerals, such as rock phosphate, lead-zinc-silver mineral deposits at Zawar, Rikahbdev serpentinite, talc, pyrophyllite, asbestos, apatite, kyanite and beryl.

Mining

Mining of copper and other metals in the Aravalli Range dates back to at least the 5th century BCE, based on carbon dating. Recent research indicates that copper was already mined here during the Sothi-Siswal period going back to. Ancient Kalibangan and Kunal, Haryana settlements obtained copper here.

Geographical features

The Indian Craton includes five major cratons. Cratons are part of continental crust made up of upper layer called platforms and older bottom layer called basement rocks. shields are part of a craton where basement rock crops out at the surface and it is the relatively oldest and most stable part that are undeformed by the plate tectonics. The Aravalli Craton covers Rajasthan as well as western and southern Haryana. It includes the Mewar Craton in the east and Marwar Craton in the west. It is limited by the Great Boundary Fault in the east, the Thar Desert in the west, Indo-gangetic alluvium in the north, and the Son River-Narmada River-Tapti River basins in the south. It mainly has quartzite, marble, pelite, greywacke and extinct volcanos exposed in the Aravalli-Delhi Orogen. Malani Igneous Suite is the largest in India and third largest igneous suit in the world. The uniqueness of the geological feature of Malani Igneous Suite at Jodhpur prompted the Geological Survey of India to declare the site as a National Geological Monument.

Tectonic-stratigraphic evolution

Tectonic-stratigraphic evolution of the Aravalli Range:
  • Neoproterozoic: Marwar Group
  • 500–550 Ma: Malani Igneous Suite
  • 720–750 Ma: Sindhrath/Punagarh Group
  • 800–850 Ma: Sirohi Group
  • 900 Ma: Erinpura granite
  • Mesoproterozoic: Delhi Supergroup
  • 1100–900 Ma: South Delhi fold belt
  • 1600–1450 Ma: North Delhi fold belt
  • Paleoproterozoic: Hindoli Group
  • 1800–1700 Ma: Sandmata Complex
  • 2200–1800 Ma: Aravalli Supergroup and mineralised basin at Rajpura-Dariba
  • Neoarchean : Mangalwar Complex with Bhilwara Group
  • Mesoarchean : Mewar gneiss with ''Jagat Supergroup''

    Stratigraphic classification

The stratigraphic classification of the Aravalli Range can be divided into the following parts :
  • The Archean basement is a banded gneissic complex with schists, gneisses, composite gneiss and quartzites. It forms the basement rock for both the Delhi Supergroup and the Aravalli Supergroup.
  • Aravalli Supergroup: The Aravalli supergroup passes through Rajasthan state, dividing it into two halves, with three-fifths of Rajasthan on the western side towards the Thar Desert and two-thirds on the eastern side consisting of the catchment area of Banas and Chambal rivers bordering the state of Madhya Pradesh. Guru Shikhar, the highest peak in the Aravalli Range at in Mount Abu of Rajasthan, lies near the south-western extremity of the Central Aravalli range, close to the border with Gujarat state. The southern Aravalli Supergroup enters the northeast of Gujarat near Modasa where it lends its name to the Aravalli district, and ends at the centre of the state at Palanpur near Ahmedabad.
  • * Champaner Group is a rectangular outcrop composed of subgreywacke, siliceous phyllite, pelitic schist, quartzite and pertomict conglomerate.
  • * Lunavada Group is a polygon area in the south of the Aravali Orogen composed of greywacke-phyllite
  • * Jharol Group is spread over 200 km2 area with average width of 40 km carbonate-free phyllite and arenite with turbidite facies and argillaceous rocks.
  • * Udaipur Group is a thick accumulation of greywacke-phyllite basement overlain by dolomite.
  • * Debari Group consists of Carbonates, Quartzite, and rocks which are overlain by the Delwara group.
  • * Delwara Group is spread over a 500 km2 area with average thickness of 500 m and includes basement orthoquartzite overlain by volcanic conglomerate.
  • * Unconformities
  • ** Mangalwar/Sandmata Complex and Mewar Gneiss with enclaves of the Jagat group
  • Delhi Supergroup
  • * Alwar Group with arenaceous and mafic volcanic rocks
  • ** Delhi Ridge, in the north
  • ** Haryana Aravalli ranges, in the west
  • *** Tosham Hill range basement rocks include quartzite with chiastolite, the upper layers of quartz porphyry ring dyke, felsite, welded tuff and muscovite biotite granite rocks which have commercially nonviable tin, tungsten and copper. The Tosham Hill range, west of Bhiwani in Haryana, is the northernmost end of the Aravalli range. A northeastern extension of the Aravalli extends to the national capital of India also. Locally known as a ridge it diagonally traverses to the South Delhi, where at the hills of Bandhwari, it meets the HaryanaAravalli range consisting of various isolated hills and rocky ridges passing along the southern border of Haryana.
  • *** Madhogarh hill
  • *** Satnali hill
  • *** Nuh-Ferozepur Jhirka hill range, runs along Haryana-Rajasthan border from Nuh to the south of Ferozepur Jhirka.
  • ** Rajasthan Alwar range, in the east
  • * Ajabgarh Group – Kumbhalgarh Group with carbonate, mafic volcanic and argillaceous rocks
  • * Raialo Group with mafic volcanic and calcareous rocks