The correct option is Block Faulting.
Explanation
The Peninsular Block of India is primarily a stable, rigid landmass composed of ancient gneisses and granites. However, it has undergone significant geological changes due to vertical movements and fracturing, leading to the formation of specific structural features such as rift valleys and block mountains.
Detailed Analysis:
- Block Faulting: The rift valleys of the Narmada, the Tapi, and the Mahanadi are the result of block faulting. This geological process occurs when the Earth's crust cracks (faults) due to tension or compression, causing a block of land to subside between two parallel faults. The subsided block forms a rift valley (or graben), while the uplifted blocks form block mountains (or horsts).
- Narmada and Tapi: These rivers flow through distinct rift valleys. The Narmada flows between the Satpura and Vindhya ranges, while the Tapi flows south of the Satpura range. These valleys were formed by the subsidence of the crust along fault lines.
- Mahanadi: The Mahanadi basin is also associated with linear faulting, which preserved the Gondwana coal deposits within the trough-like depressions.
- Comparison with other options:
- Folding: This process creates fold mountains (e.g., the Himalayas) through compressional forces, not rift valleys.
- Volcanic Eruption: While the Deccan Trap is a result of volcanic activity, the specific linear depressions (rift valleys) are structural features caused by faulting, not the eruption itself.
- Glacial Erosion: This is a geomorphic agent dominant in high-altitude or high-latitude regions (e.g., the Himalayas) and is not responsible for the formation of these peninsular valleys.
Key Takeaway:
The linear rift valleys of the Narmada, Tapi, and Mahanadi in the Indian Peninsular Block are structural depressions formed specifically by Block Faulting.