Precambrian of India | Geology Optional for UPSC PDF Download

 Dharwar Craton

Greenstone belts, known as Dharwar Schist Belts, trend NNW-SSE, showing a metamorphic grade increase from north to south, transitioning to granulites (charnockites and khondalites) in the south. The oldest rocks, dated 3.5–3.4 Ga, include zircons from Holenarsipur greenstone belts and the Banded Gneissic Complex of Rajasthan.

 Stratigraphic Classification

Introduced in 1978 by the Geological Survey of India, the Dharwar Craton includes the Dharwar Supergroup and Sargur Schist Complex. Early classifications by W.F. Smeeth (1915–16), B. Ramarao (1936), Radhakrishan (1967), and S.V.P. Iyergar (1976) evolved with geochemical and geochronological data. Swami Nath et al. (1976) divided the craton into Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC), separated by the Chitradurga Shear Zone.

 Western Dharwar Craton (WDC)

WDC, or Karnataka Nucleus, comprises two orogenic cycles: the older Sargur Group (3100–3300 Ma) and the younger Dharwar Supergroup (2600–2800 Ma). The Peninsular Gneiss (TTG, >3000 Ma) forms the basement, marked by a regional unconformity with quartz-pebble conglomerate (QPC). Key superbelts include:

• Bababudan–Western Ghats–Shimoga
• Chitradurga–Gadag

Gorur Gneiss: The oldest (3300–3400 Ma) TTG gneiss in WDC.

Sargur Group: Enclaves of ultramafic-mafic complexes, komatiites, BIF, quartzites, and marbles within Gorur Gneiss.

Dharwar Supergroup: Divided into Bababudan and Chitradurga Groups. Bababudan Group includes basaltic volcanics, quartz arenites, and BIF (e.g., Mulaingiri Formation). Chitradurga Group, spanning 450 km, features bimodal volcanics, pillow basalts, greywacke, and BIF (e.g., Hiriyur, Ingaldhal, Vanivilas Formations).

 Eastern Dharwar Craton (EDC)

EDC hosts volcanic-dominated, gold-rich greenstone belts, engulfed by younger granitoids (2500–2600 Ma). Key superbelts include:

• Ramgiri–Penakacherla–Hungund
• Kolar–Kadiri–Hutti
• Velligallu–Raichur–Gadwal

The Kolar Group, correlated with Chitradurga Group, features amphibolites (~2700 Ma) and Champion Gneiss (felsic volcanics).

Mineral Potential: WDC hosts copper, iron, manganese, and minor gold (e.g., Gadag, Kudremukh). EDC is known for gold (Kolar, Hutti), iron, and manganese.

 Cuddapah Supergroup

The Cuddapah Basin, a crescent-shaped Proterozoic basin (44,500 km²) in Andhra Pradesh and Telangana, trends N-S along the eastern margin of the Dharwar Craton. It comprises the Cuddapah Supergroup (orthoquartzite-carbonate, volcanics) and the unconformably overlying Kurnool Group (carbonates, fine clastics).

Stratigraphic Classification

King (1872) proposed a fourfold classification, later revised by Narayanaswami (1976) and Nagaraja Rao et al. (1987) into three groups:

• Papaghni
• Chitravati
• Nallamalai

Lithology

Papaghni Group: Includes Gulcheru Quartzite (conglomerates, arkoses, quartzites) and Vempalle Formation (stromatolitic dolomites, shales, sandstones, ~1800 Ma volcanics).

Chitravati Group: Comprises Pulivendla Quartzite, Tadpatri Formation (argillaceous, felsic pyroclastics), and Gandikota Quartzite (shales, quartzites).

Nallamalai Group: Includes Bairenkonda Quartzite (quartzite-pelitic cycle) and Cumbum Formation (shaly, dolomites, quartzites).

Srisailam Quartzite: Red quartzites with glauconite, deposited in shallow marine environments.

Igneous Activity: Dolerite, picrite, gabbro sills, basaltic flows, and kimberlite dykes (~1225 Ma) in Vempalle, Tadpatri, and Cumbum Formations.

Life: Columnar stromatolites (Conophyton, Kussiella, Colomnella) in Vempalle and Tadpatri Formations indicate Riphean age.

Mineral Potential: Hosts diamonds (Koh-i-noor), asbestos, baryte, base metals, uranium, steatite, and high-grade limestones.

 Vindhyan Supergroup

The Vindhyan Basin, a sickle-shaped Proterozoic basin (100,000 km²) on the Bundelkhand Craton, spans Rajasthan, Madhya Pradesh, Uttar Pradesh, and Bihar. It is divided into Rajasthan, Bundelkhand, and Son Valley sub-basins, with ~4500 m of sandstone, shale, and carbonates.

Stratigraphic Classification

Divided into four groups (Auden, 1933):

• Semri
• Kaimur
• Rewa
• Bhander

Lithology

Semri Group: Basal conglomerates, sandstones, shales, and stromatolitic limestones (Kajrahat, ~1720 Ma). Includes Chopan Porcellanite (felsic volcanics, ~1632 Ma).

Kaimur Group: Argillo-arenaceous succession with Sasaram Sandstone, Ghurma Shale, and Dhandraul Quartzite, deposited in tidal flat environments.

Rewa Group: Panna Shale, Asan Sandstone, and Govindgarh Sandstone, indicating lagoonal to near-shore environments.

Bhander Group: Ganurgarh Shale, Lakheri Limestone, and Maihar Sandstone, with evaporitic and tidal flat settings.

Age: Sedimentation from ~1720 Ma (Semri) to 700 Ma (Bhander).

Life: Stromatolites (Collenia clappii, Conophyton garganicus), microfossils, and trace fossils in Semri and Bhander Groups.

Mineral Potential: Diamonds, limestones, base metals, and building stones.

Delhi Supergroup

The Delhi Supergroup, part of the Aravalli Craton, spans ~700 km in Rajasthan, Haryana, Delhi, Gujarat, and Madhya Pradesh. It overlies the Archaean Banded Gneissic Complex and Aravalli Supergroup.

Stratigraphic Classification

Divided into three groups:

• Raialo
• Alwar
• Ajabgarh

Raialo Group: Basal conglomerates, quartzites, and basic volcanics (Dogeta, Serrate, Tehla Formations).

Alwar Group: Conglomerates, quartzites, arkoses (Rajgarh, Kankwarhi, Pratapgarh Formations).

Ajabgarh Group: Carbonaceous shales, phyllites, quartzites (Kushalgarh, Sariska, Thanagazi, Bhakrol, Arauli Formations).

Life: Trace fossils and bioturbation in quartzites.

Mineral Potential: Copper (Khetri belt), asbestos, baryte, marble, and building stones.

 Summary