Physical Geology 101
What force drives plate motion?
Wegener motivation model?
Problems with this model?
Hess motivation for seafloor spreading:
Convection is the transfer of heat due to circulating material.
Heat from Core is transferred Mantle.
Mantle becomes hot and rises due to lower density.
Mantle cools as heat transfers to crust. Sinks back down toward core.
Two Tier Convection
Convection in Lower Mantle, driven by heat from Outer Core.
Lower Mantle rises, transfers heat to Upper Mantle
Upper Mantle rises and transfers heat to crust.
Mantle spreads out, drags crust with it.
What is the driving force?
Mantle material is injected into MOR under pressure, forcing plates apart.
Mid-ocean ridges are elevated areas.
Plates on either side of MOR slide down hill under influence of gravity.
As plate descends into trench, it sinks faster than plate behind it.
Sinking plate pulls remaining plate with it.
Convection - Problems
Plate Push - Problems
Plate Slide - Problems
Plate Pull - Problems
Four Models - Which One?
Most geologist will agree that Convection plays a part in plate motivation.
Plate Pull and Plate Slide are often confused by geologists.
Many geologists will say plate pull is one of the main driving forces behind plate motivation.
But when asked to explain the mechanism - they describe what is occurring in plate slide - "gravity is pulling the plate into the trench"