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 (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. of
plate margins 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 the
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.
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 (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 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 , in Rajasthan. 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.
Tectonic-stratigraphic evolution Tectonic-stratigraphic evolution of the Aravalli Range: •
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 ==Human history==