Tectonic Plate Boundaries - Quick Notes

Divergent Plate Boundary

  • Definition: Two tectonic plates move apart; mainly at mid-ocean ridges; also called constructive boundaries.
  • Key features: magma rises from the mantle; formation of mid-ocean ridges or rift valleys.
  • Formation Process (brief):
    • Continental crust stretches and thins as tectonic forces pull apart.
    • Magma rises from the mantle, causing cracks and fractures.
    • Continued stretching creates a rift valley with possible volcanic activity.
    • Rift valley deepens and is flooded by seawater, forming a narrow sea or young ocean basin.
    • Continued divergence creates new oceanic crust along a mid-ocean ridge; basin expands.
  • Examples:
    • Mid-Atlantic Ridge: separates North American and Eurasian plates; linked to seafloor spreading and continental drift theory.
    • East African Rift: continental divergent boundary; extends from Afar Triangle to Mozambique; volcanic activity and potential new ocean basin.
    • Red Sea Rift: continental divergent boundary between Arabian and African plates.

Convergent Plate Boundary

  • Definition: plates move toward each other and collide; often involves subduction where one plate sinks beneath another.
  • Three Types of Convergent Boundaries: 33 types:
    • Ocean-Ocean: oceanic plates collide; subduction of one beneath another (e.g., Pacific Plate under others) → Aleutian Islands, Marianas Trench.
    • Oceanic-Continental: oceanic plate subducts under continental plate; Andes Mountains and Peru Trench (Nazca Plate under South America).
    • Continental-Continental: continental plates collide and crumple; Himalayas formed by Indian plate colliding with Eurasian plate.

Transform Boundary

  • Definition: plates slide past one another horizontally; a conservative boundary.

  • Key features: transform faults connect offsets in mid-ocean ridges; many occur in ocean basins.

  • Types (by crust type):

    • Continental Transform Boundaries
    • Oceanic Transform Boundaries

  • Types (by the boundaries they connect):

    • Ridge-Ridge
    • Ridge-Trench
    • Trench-Trench

  • Notable examples:

    • San Andreas Fault (continental transform in California).
    • Romanche Fracture Zone (oceanic transform in the Atlantic).
    • Blanco Transform Fault (oceanic transform).
    • Dead Sea Transform Fault (regional transform).
    • Alpine Fault (New Zealand).

  • Additional notes:

    • Transform boundaries often link segments of mid-ocean ridges and accommodate lateral motion between plates.
    • Related features include trenches, island arcs, and mountain ranges associated with other boundary interactions.