Model Answer
0 min readIntroduction
Cratons are stable continental blocks, typically forming the cores of continents, characterized by ancient, highly deformed crystalline basement rocks. They represent the oldest and most stable parts of the continental lithosphere, having survived multiple orogenic (mountain-building) events. These regions have experienced minimal tectonic activity in recent geological times. Understanding cratons is fundamental to deciphering the geological evolution of continents, including India. India comprises two major cratons – the Bundelkhand and the Deccan Craton – along with several smaller blocks. This answer will focus on the evolution and stratigraphy of the Singhbhum Craton.
The Singhbhum Craton: An Overview
The Singhbhum Craton, located in eastern India (Jharkhand and Odisha states), is one of the oldest cratons in the Indian shield. It’s a Proterozoic craton, meaning its core rocks formed during the Proterozoic Eon (2.5 billion to 541 million years ago). The craton is bounded by mobile belts representing zones of past tectonic activity. It’s significant for its iron ore deposits and provides valuable insights into the early Earth’s geological processes.
Stratigraphy of the Singhbhum Craton
The stratigraphy of the Singhbhum Craton can be broadly divided into the following sequences, presented in chronological order (oldest to youngest):
1. Archaean Basement (Older than 2.5 billion years)
The basement comprises granitic-gneissic complexes, representing the oldest rocks of the craton. These rocks are highly metamorphosed and deformed, indicating their involvement in ancient tectonic events. They are primarily composed of tonalite-trondhjemite-granodiorite (TTG) suites, indicative of early crustal formation. The Singhbhum Granite is a prominent feature of this basement.
2. Proterozoic Sedimentary and Volcanic Sequences (2.1 – 1.8 billion years)
This phase is characterized by the formation of the Iron Ore Series. This series is crucial for understanding the evolution of banded iron formations (BIFs) and the early atmosphere. Key formations include:
- Noamundi Iron Ore Series: Predominantly composed of BIFs, shale, and dolomite. These BIFs are among the world’s richest iron ore deposits.
- Badampahar Formation: Characterized by volcanic rocks (rhyolites, basalts) interbedded with sedimentary rocks.
- Gurrumahisani Formation: Contains manganese ores along with iron formations.
3. Middle Proterozoic Sedimentary Sequences (1.8 – 1.0 billion years)
This period witnessed the deposition of platform-type sedimentary rocks, indicating a period of relative tectonic stability. The main formations include:
- Paila Formation: Consists of shale, sandstone, and conglomerate.
- Chaibasa Formation: Dominated by shale and sandstone, representing a shallow marine environment.
4. Younger Proterozoic Sequences (1.0 billion years – Present)
This phase is marked by the deposition of the Kolhan Group, which includes:
- Porahat Group: Characterized by quartzites, shales, and conglomerates.
- Gangpur Group: Contains ironstones, shales, and sandstones.
These younger sequences are often associated with rift-related sedimentation and volcanic activity.
Evolution of the Singhbhum Craton
The evolution of the Singhbhum Craton can be summarized as follows:
- Archaean Crust Formation (Older than 2.5 billion years): Formation of the granitic-gneissic basement through partial melting of the mantle and early crustal differentiation.
- Early Proterozoic Orogeny (2.1 – 1.8 billion years): Tectonic activity leading to the formation of the Iron Ore Series, associated with the evolution of an oxygen-rich atmosphere and the precipitation of iron from seawater.
- Middle Proterozoic Stabilization (1.8 – 1.0 billion years): A period of relative tectonic quiescence, marked by the deposition of platform-type sedimentary rocks.
- Late Proterozoic Rifting (1.0 billion years – Present): Rift-related sedimentation and volcanic activity, leading to the formation of the Kolhan Group.
The craton has undergone several episodes of deformation, metamorphism, and magmatism throughout its history, resulting in its complex geological structure. The presence of extensive iron ore deposits makes it a significant geological province.
Conclusion
The Singhbhum Craton stands as a testament to the Earth’s early geological processes, offering a window into the Proterozoic Eon. Its stratigraphy reveals a complex history of crustal formation, tectonic activity, and sedimentary deposition. Understanding the evolution of such cratons is crucial for reconstructing the geological history of the Indian subcontinent and for resource exploration. Further research, including precise geochronological studies, is vital to refine our understanding of the craton’s evolution and its place in the global tectonic framework.
Answer Length
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