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Plate Tectonics and Interior Heat — The Connection
4.1 Theory of Plate Tectonics
Wegener's Continental Drift (1912)
Alfred Wegener (1880–1930) proposed Continental Drift Theory based on four lines of evidence:
- Jigsaw-fit of continents (especially South America and Africa)
- Identical fossils (Glossopteris flora, Mesosaurus) on separate continents
- Matching geological formations across oceans
- Evidence of ancient climates (coal in Antarctica, glacial scars in India)
Hess's Sea-Floor Spreading (1960)
Harry Hess (1906–1969) proposed that new oceanic crust forms at mid-ocean ridges where magma wells up from the mantle. The ocean floor moves like a conveyor belt, with old crust subducted at trenches. Evidence includes paleomagnetism (symmetric magnetic stripes on ocean floor) and age of ocean floor rocks.
Plate Boundaries
| Boundary Type | Movement | Example | Geological Feature |
|---|---|---|---|
| Divergent | Moving apart | Mid-Atlantic Ridge | Rift valleys, new oceanic crust, basaltic volcanism |
| Convergent (ocean-ocean) | Colliding | Mariana Trench (Pacific) | Island arc, deep ocean trench, explosive volcanism |
| Convergent (ocean-continent) | Colliding | Andes + Nazca Plate | Coastal mountain range, deep trench, andesite volcanism |
| Convergent (continent-continent) | Colliding | Himalayas (India + Eurasia) | Fold mountains, no trench, no volcanism |
| Transform | Sliding sideways | San Andreas Fault (California) | Earthquakes, no volcanism, no mountain building |
4.2 India's Geological Journey (Gondwana to Himalayas)
India's geological history is the best-studied example of plate tectonics for RPSC candidates. The key stages are:
- Carboniferous–Permian (~300 Ma): India part of Gondwana supercontinent; Glossopteris flora; Gondwana coal deposits (Jharkhand, Odisha, Chhattisgarh, Rajasthan — Palana coalfield is Paleocene age)
- Jurassic (~150 Ma): Gondwana breaks up; India separates
- Cretaceous (~90 Ma): India a large island, drifting northward; Deccan Traps volcanism (~67 Ma)
- Early Eocene (~50 Ma): India collides with Asia → Himalayan orogeny begins; Tethys Sea disappears; Indo-Gangetic Plain forms as foreland basin
- Neogene–Present: Himalayas still rising (India continues to push north at ~4–5 cm/year); Indo-Australian Plate; periodic great earthquakes along this collision zone