Plate Tectonics: Causes of Plate Movements

Overview

• Key Forces: Slab pull, ridge push, convection current
• Learning Objectives:
  1. Describe convection current, slab pull, and ridge push
  2. Explain the causes of plate tectonics

Convection Current

• Analogy: Works like a conveyor belt
• Definition: Continuous loop of sinking hot, soft rocks caused by energy transfer in the asthenosphere
  • Convection Cell: Circular pattern of sinking and rising materials in the mantle
• Process:
  • Heat causes materials to expand and become less dense
  • Buoyant hot materials rise, cooler materials sink
  • Cycles create seafloor spreading and subduction
• Theory Origin: Proposed by Arthur Holmes
  • Heated mantle rises and spreads, cooled material sinks
  • Driven by pressure-heated magma breaking continents apart and bringing them together again

Slab Pull Theory

• Definition: Gravity and plates themselves drive tectonics through subduction
• Demonstration: Paper clip chain mimics subducting tectonic plates
  • Denser slabs sink faster due to gravitational pull
  • Subducting slab drags the rest of the plate with it
• Theory: Mantle convection is a product of subduction, not the cause

Ridge Push

• Definition: Driving force for plate motion occurring at mid-ocean ridges
• Process:
  • Rigid lithosphere slides down hot, raised asthenosphere below mid-ocean ridges
  • Gravity-driven due to differences in gravitational potential energy
• Theory Origin: Proposed by Bot, a geologist
  • Plates slide down asthenosphere slope due to weight differences
  • Ridge push force increases towards subduction zones as plates get thicker and denser

Conclusion

• Understanding these forces helps explain the movement and interaction of tectonic plates
• Theories complement each other in illustrating the mechanisms behind plate tectonics