Aravalli Range

The Aravalli Range (also spelled Aravali) is a mountain range in north-western India, running approximately 670 km (420 mi) 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 1,722 m (5,650 ft). Aravalli range is the oldest fold-mountain belt in India, dating back to the Paleoproterozoic era.

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

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 (of the Phanerozoic) 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.

It consists of two main sequences formed in the Proterozoic eon, metasedimentary rock (sedimentary rocks metamorphosed under pressure and heat without melting) and metavolcanic rock (metamorphosed volcanic rocks) sequences of the Aravalli Supergroup and Delhi Supergroup. These two supergroups rest over the Archean Bhilwara Gneissic Complex basement, which is a gneissic (high-grade metamorphism of sedimentary or igneous rocks) 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 (Rishabhdev) 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 (a type of archipelago composed of an arc-shaped chain of volcanoes closely situated parallel to a convergent boundary between two converging tectonic plates) from the west around 1.5 Ga. This tectonic plates collision event involved early thrusting with partial obduction (overthrusting of oceanic lithosphere onto continental lithosphere at a convergent plate boundary) of the oceanic crust along the Rakhabdev lineament, flattening and eventual wrenching (also called strike-slip plate fault, sideways horizontal movement of colliding plates with no vertical motion) parallel to the collision zone. Associated mafic igneous rocks show both continental and oceanic tholeiitic geochemistry (magnesium and iron-rich igneous rocks) from phanerozoic eon (541–0 million) 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 (crust and uppermost mantle, such as Aravalli and Himalayas fold mountains) 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.

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 (sedimentary unmetamorphosed rock), felsic (volcanic rock), and plutons (crystallised solidified magma). 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 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 c. 4000 BCE. Ancient Kalibangan and Kunal, Haryana settlements obtained copper here.

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 (Marwar-Mewar Craton or Western Indian 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.