Model Answer
0 min readIntroduction
The Dharwar Craton, located in southern India, is one of the oldest and most important cratonic blocks in the Indian Shield. It represents a significant portion of the Archean crust and holds crucial information about the early Earth processes. Subdividing this craton is essential for understanding its complex geological evolution and mineral potential. Based on various geological parameters, the Dharwar Craton is broadly divided into two subcratons: the Western Dharwar Craton (WDC) and the Eastern Dharwar Craton (EDC). This division is based on differences in age, lithological associations, structural patterns, and geochemical characteristics.
Geological Parameters for Subdividing the Dharwar Craton
The subdivision of the Dharwar Craton into WDC and EDC is based on a combination of geological observations and analyses. Key parameters include:
1. Age and Stratigraphy
- Western Dharwar Craton (WDC): Predominantly characterized by older rocks (3.6-3.3 Ga) belonging to the Sargur Group, comprising high-grade metamorphic rocks like khondalites, charnockites, and granites. It exhibits a relatively simpler stratigraphic sequence.
- Eastern Dharwar Craton (EDC): Dominated by younger rocks (3.0-2.5 Ga) of the Dharwar Supergroup, including sedimentary and volcanic sequences (greywackes, shales, banded iron formations) and granitic intrusions. It displays a more complex and extensive stratigraphic record.
2. Lithological Associations
- WDC: High-grade metamorphic terrains with extensive granitic intrusions and limited sedimentary sequences. The presence of TTG (Tonalite-Trondhjemite-Granodiorite) suites is prominent.
- EDC: A wider range of lithologies, including greenstone belts (volcanic and sedimentary rocks), granite-greenstone terrains, and extensive sedimentary basins. Banded Iron Formations (BIFs) are particularly abundant.
3. Structural Features
- WDC: Characterized by relatively less deformation and simpler structural patterns. Major shear zones are less prominent compared to the EDC.
- EDC: Exhibits complex structural features, including multiple phases of deformation, faulting, and folding. The Chitradurga Shear Zone, a major crustal-scale shear zone, defines the boundary between the EDC and the WDC and has significantly influenced the EDC’s structural evolution.
4. Geochemical Signatures
- WDC: Displays relatively primitive geochemical signatures, indicating a less evolved crustal source. Nd isotopic ratios suggest an older crustal component.
- EDC: Shows more evolved geochemical signatures, reflecting a more mature crustal source and extensive crustal recycling. The presence of continental crust-derived signatures is more pronounced.
The following table summarizes the key differences:
| Parameter | Western Dharwar Craton (WDC) | Eastern Dharwar Craton (EDC) |
|---|---|---|
| Age | 3.6-3.3 Ga (Older) | 3.0-2.5 Ga (Younger) |
| Lithology | High-grade Metamorphic, Granites | Greenstone Belts, Sedimentary Rocks, BIFs |
| Structure | Less Deformation, Simpler Patterns | Complex Deformation, Major Shear Zones |
| Geochemistry | Primitive Signatures, Older Crust | Evolved Signatures, Mature Crust |
The Chitradurga Shear Zone
The Chitradurga Shear Zone is a critical feature in understanding the subdivision. It represents a major boundary between the WDC and EDC, marking a significant change in geological characteristics. This shear zone acted as a long-lived tectonic boundary, influencing the evolution of both subcratons.
Conclusion
In conclusion, the Dharwar Craton’s subdivision into the WDC and EDC is based on a robust set of geological parameters, including age, lithology, structural features, and geochemical signatures. These differences reflect distinct evolutionary histories and provide valuable insights into the Archean crustal development of southern India. Further research, particularly focusing on high-resolution geochronology and detailed geochemical studies, will continue to refine our understanding of this ancient and geologically significant region.
Answer Length
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