Understanding Rajmahal Highlands and Bundelkhand Gneiss

This question asks us to evaluate two geological statements about India: one concerning the Rajmahal highlands and the other about the Bundelkhand gneiss.

Analyzing Statement 1: Rajmahal Highlands and Lava Flow Deposits

The first statement says that the Rajmahal highlands consist of lava flow deposits. Let's look into the geological formation of this region.

• The Rajmahal Traps are a large igneous province located in eastern India, covering parts of Jharkhand, West Bengal, and Odisha.
• They were formed during the Jurassic period, around 117-118 million years ago, through significant volcanic activity.
• This volcanic activity resulted in massive outpourings of basaltic lava, which accumulated in layers, forming extensive lava flow deposits.
• These accumulated lava flows cooled and solidified over time, creating the plateau-like structure that characterizes the Rajmahal highlands.

Therefore, statement 1 is correct. The Rajmahal highlands are indeed composed of lava flow deposits, specifically the Rajmahal Traps.

Analyzing Statement 2: Bundelkhand Gneiss and Oldest Achaean Rocks

The second statement claims that Bundelkhand gneiss belongs to the oldest Achaean rocks of India. Let's examine the geological age of the Bundelkhand region.

• The Bundelkhand craton is one of the stable continental blocks or cratons in the Indian Shield, located in central India.
• Its core is largely composed of granite and gneissic rocks.
• Geological studies have shown that the Bundelkhand gneiss is extremely old, dating back to the Achaean Eon, approximately 2.5 to 3.5 billion years ago.
• These Achaean rocks are considered among the oldest exposed rock formations in the Indian subcontinent.
• Other very old Achaean rocks are found in regions like the Dharwar craton in South India, but the Bundelkhand gneiss is certainly among the prominent examples of the oldest Achaean rocks in India.

Thus, statement 2 is also correct. The Bundelkhand gneiss represents some of the oldest Achaean rocks found in India.

Conclusion

Based on the analysis of both statements, we find that both statements are geologically accurate.

• Statement 1 correctly identifies the Rajmahal highlands as being formed from lava flow deposits.
• Statement 2 correctly identifies the Bundelkhand gneiss as belonging to the oldest Achaean rocks of India.

Therefore, both statements are correct.

Revision Table: Rajmahal and Bundelkhand Geology

Additional Information: Geological Time Scale and Indian Rocks

Understanding the geological time scale is crucial when discussing the age of rocks.

• The Achaean Eon is one of the earliest periods in Earth's history, following the Hadean Eon and preceding the Proterozoic Eon.
• Rocks from the Achaean period are extremely old, often representing the core of continents (cratons).
• India has several cratons (like Dharwar, Singhbhum, Bundelkhand, Aravalli), which contain some of the oldest rocks on Earth.
• The Rajmahal Traps, while extensive, are much younger than the Achaean rocks, belonging to the Mesozoic Era (Jurassic period).
• Different geological processes like volcanic eruptions, sedimentation, and metamorphism have shaped India's diverse landscape over billions of years.