Origin of Rajasthan

 Pangaea

• This name was given by Alfred Wegener during the discovery of continental theory. 

Alfred Wegener (1880-1930)

• According to him, Pangaea is called the combined form of the super continents which is divided into 2 parts:
• Angara Land (Laurentia)- it is the northern part of  Pangaea.
• Gondwana Land- is the southern part of  Pangaea.

  

  Pangaea

Panthalassa

• Alfred named the combined form of the oceans as Panthalassa and its main ocean is considered as the Pacific Ocean. It was the vast water body around Pangaea.

Panthalassa

Tethys Sea

• It is the form of an oceanic geosyncline which was situated between the Angara Land, and the Gondwana Land.
• From the Gondwana Land, the Hadauti Plateau & the Aravalli Mountain range of Rajasthan have been formed, while the western desert & plains have been formed from the Tethys Sea.
• The Aravalli range & the plateau of Hadauti are considered to be part of the peninsular plateau, while the western desert & the plains are considered to be the part of the Great Northern Plain of India.
• Origin of Rajasthan is not from Angara Land but from the Gondwana Land & Tethys Sea.

Western & Eastern Rajasthan

Geological structure of Rajasthan

    1. Protozoic Era/Archean Era (4,250 to 45,000 million years ago)

• Pre-Aravalli 
• This rock group is one of the oldest mountain groups in the world which exists today as residual ranges.
• The rocks of this era extend from the north of Delhi in North-East & till the Gulf of Khambhat in the South-West in form of Aravalli Mountain Ranges.
• The Aravalli range was uplifted in the Pre-Cambrian Period.
• These mountain ranges are found between Chittor & Bhilwara in Bundelkhand gneiss, Bedach Valley, also known as Bhilwara Super Group.
• In this group rocks like granite, hornblende, amphibolite, schist, sigmatite, pegmatite, etc. are found.
• There is a huge syncline (a fold in rock layers that curved downwards with the youngest rock layers in the center of the fold) in the middle of the Aravalli Range which is parallel to the Great Boundary Fault located in the East. The rocks of Delhi & Aravalli group are found in this huge syncline. 

Syncline

• Pre-Cambrian
• Aravalli Supergroup
• In this subgroup mainly phyllites & greywax rocks and quartzites, dolomites, conglomerate rocks are classified.
• Phyllite rock is a carbon-rich & strips of dolomite and quartzites are found in it.
• Stromatolites are found in dolomite rock group which are important deposits of phosphorite.
• The upper part of the Aravalli supergroup is made up of phyllites & quartzites which form a very thick fold.
• Aravalli group is divided into Jhadol group & Udaipur Group.
• Delhi Supergroup
• The rock of this group is spread over the widest part in Rajasthan. It extends from Delhi in North-East to Gujarat in the South-West.
• In Ajmer & Western Mewar, the rocks of this supergroup form many mountains.

• Delhi supergroup includes Raialo, Alwar & Aligarh rock group.
• Mainly limestone, marble, quartzites & conglomerate rock group are classified in Raialo group.
• Alwar group of rocks form the mountain ranges around Alwar. In this sequence, arcozoic schist, quartzites, meta conglomerate rocks are found.
• The basal rock of the Ajabgarh group is mainly biotite cyst in which pegmatite and apelite igneous rocks are intruded.

    2. Paleozoic Era

• Vindhya Supergroup
• In Rajasthan the rocks of this supergroup are mainly spread from Karauli, Dholpur in the North-East to Nimbahera & Suket in South-West in the basin of  eastern Rajasthan.
• In western Rajasthan, the contemporary rocks of the Vindhya Supergroup have been cut into two separate basins:
  
• Nagaur Basin- starting from Jodhpur till Pokharan in the west & extending upto Bikaner-Ganganagar in the North. The rock groups of this basin are incised on the Malani-igneous rocks.

Rajasthan

• Birmania Basin-There is a small basin to the South of Jaisalmer. It is affected by symmetrical folding.
• Permian Carboniferous
• Bap Boulder Beds- In the Bap region of Jodhpur, extensive circular beds are ice-carrying which are contemporary with the Talcher Boulder band.
• Bhadura Sandstone- These are fossilized sandstones which have been formed in marine condition. It is mainly spread from North-West of Bhadura to Harbans in different colors & sizes.

    3. New Age Hahakalpa/Cenozoic Era

    This era has been divided into 2 eras:

• Tertiary Era- The rock groups of  Tertiary Era are mainly present in Nagaur, Bikaner, Jaisalmer, and Barmer districts in form of soft sandstone, fossilized limestone, bentonite soils, multani soil, lignite, etc.
• Quaternary Era- The rock groups developed under this rock mainly form rivers, drains, snow-carried conglomerate, alluvial & sand on the land areas.

The geo-structure of Rajasthan is very complex, as a result various rock-groups have expanded as follows:

• Bhilwara Super Group-
• Under this Bundelkhand gneiss, Petite gneiss combination is included. It is dominated by granite which is available in various colors.
• Gneiss is a metamorphic rock belonging to the ancient Archaean age. Its expansion is in Southern Rajasthan apart from Udaipur, Chittorgarh districts.
• This rock is not found in pure form but in a mixed group.
• Aravalli System-
• Rocks consisting of metamorphosed ancient rocks are found in which igneous rocks predominate.
• Under this quartzites, grits, phyllites, limestone & mixed gneiss are important.
• Mixed gneiss found in Alwar, Ajmer, Udaipur, Sawai Madhopur are belonged to this system.
• Delhi Super Group-
• Under this, mainly calcite, quartzites, grit, schist rocks are found in Raialo group, Alwar group, Ajabgarh group.
• Vindhya Range-
• Under this, there is a dominance of sandstone, limestone rock. The expansion of this style is more in western Rajasthan.
• Lava erupted granite is found in Jalore, Siwana, Mokalsar, Jodhpur.
• The rocks are found in Karauli, Dholpur, Nimbahera, Suket, Bundi, Sawai Madhopur areas are of this range.
• Malani Range-
• Its rocks are made of rhyolitic lava group, which rests on the Aravalli bedrock. 
• Jalore, Granite, Siwana & Erinpura granite belong to this.
• Naphline Syenite-
• This rock group is found in areas around Kishangarh, Madanganj.
• They form intrusive rocks in pre-Aravalli rock groups. Pegmatite rocks are found along with these rocks.
• Deccan Trap-
• Volcanic eruptions in the late Cretaceous period resulted in horizontal lava flows in peninsular India. 
• This has led to the formation of plateau basin or Deccan trap. These rocks are found in Hadoti region & some parts of Mewar.