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Plate tectonics and plate boundaries

Short answer

Plate tectonics is the theory that Earth's lithosphere is divided into moving plates, causing earthquakes and volcanoes at their boundaries. Divergent boundaries create new crust as plates move apart; convergent boundaries destroy crust through subduction or collision, forming trenches and mountains; transform boundaries involve horizontal sliding, causing strike-slip faults.

What is plate tectonics? Describe the different types of plate boundaries (margins).

Plate tectonics is the theory that the Earth's rigid outer shell, the lithosphere, is broken into a number of large and small plates that float on the plastic asthenosphere and move relative to each other at a few centimetres per year. Most earthquakes, volcanoes and mountain building occur along plate edges.

Types of plate boundaries

1. Divergent (constructive) boundary

  • Plates move apart; magma rises and forms new crust.
  • Examples: Mid-Atlantic Ridge, East African Rift.
  • Features: mid-ocean ridges, rift valleys, shallow earthquakes, basaltic volcanism.

2. Convergent (destructive) boundary

  • Plates move towards each other; one may sink (subduct) under the other.
  • Types:
    • Ocean-ocean: island arcs and trenches (Japan, Mariana).
    • Ocean-continent: trench and volcanic mountain chain (Andes).
    • Continent-continent: collision and folded mountains (Himalaya, Alps).
  • Features: shallow to deep earthquakes, volcanoes (not at continent-continent collisions), trenches, fold mountains.

3. Transform (conservative) boundary

  • Plates slide horizontally past each other; crust is neither created nor destroyed.
  • Example: San Andreas Fault.
  • Features: strike-slip faults, shallow strong earthquakes.
 Divergent      Convergent       Transform
 <-- | -->      --> | <--       ^  |
   ridge          trench         | v

✓ Answer checked by Claude Opus 5.5 (high effort)

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