Plate Tectonics

Summary

Plate tectonics describes the movement of rigid lithospheric plates over the ductile asthenosphere.

Core idea

Understand the system

Plate tectonics describes the movement of rigid lithospheric plates over the ductile asthenosphere.

Why and how it happens

Causes and context

Plate motion is driven by the thermal and gravitational energy of the Earth system: mantle convection contributes, elevated ridges encourage gravitational sliding, and dense subducting slabs pull attached lithosphere downward. These forces create relative motion between rigid plates.

How it works

At divergent boundaries, mantle material rises and cools into new crust. At convergent boundaries, dense oceanic lithosphere may subduct or continents may collide and thicken crust. At transform boundaries, plates slide laterally and accumulated strain is released as earthquakes.

Key facts

• Oceanic lithosphere is generally denser than continental lithosphere.
• Subduction produces trenches, volcanic arcs and deep earthquakes.
• The Himalaya formed through collision of the Indian and Eurasian plates.

Important terms

• lithosphere
• asthenosphere
• subduction
• seafloor spreading
• transform fault

Examples and case studies

• The Himalaya and the Pacific Ring of Fire show contrasting collision and subduction settings.

Causes and components

• Mantle heat drives convection and contributes to lithospheric motion.
• Slab pull occurs as dense cold oceanic lithosphere sinks at subduction zones.
• Ridge push results from gravitational sliding away from elevated mid-ocean ridges.

Effects and significance

• Divergence creates new oceanic crust through seafloor spreading.
• Convergence produces subduction, trenches, volcanic arcs or collision mountains.
• Transform motion generates earthquakes while conserving crustal area.

Geography connection

The Himalaya and the Pacific Ring of Fire show contrasting collision and subduction settings. This illustrates how plate tectonics varies by location, scale or environmental context.

Bangladesh connection

Bangladesh lies on the Indian Plate near the boundary systems of the Himalaya, Indo-Burma ranges and the Bengal Basin.

BCS preliminary facts

• Oceanic lithosphere is generally denser than continental lithosphere.
• Subduction produces trenches, volcanic arcs and deep earthquakes.
• The Himalaya formed through collision of the Indian and Eurasian plates.

BCS written analysis

Build an analytical answer

• Compare divergent, convergent and transform boundaries by motion, landform and hazard.
• Explain how slab pull and ridge push help, but do not mechanically reduce, plate motion to one cause.
• Relate the Indian Plate's northward motion to Himalayan collision and seismic stress around Bangladesh and the Indo-Burma arc.

Common misconceptions

• Continental collision does not normally create a mid-ocean ridge.
• Transform boundaries mainly conserve crust rather than create it.

Quick revision

• Plate Tectonics
• Oceanic lithosphere is generally denser than continental lithosphere.
• Subduction produces trenches, volcanic arcs and deep earthquakes.
• lithosphere / asthenosphere
• Definition → process → spatial example