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The Role of Gravity

Mantle Convection

Another force that has long been thought to be one of the most significant driving mehcanisms behind plate motion is mantle convection. It has long been known that throughout the mantle there are convection currents circulating, caused by the difference in temperature at the earth's interior and surface. Hot material from the earth's outer core rises very slowly (over millions of years) throughout the mantle. This hot material eventually cools enough to sink back down towards the core. It has been proposed that these convection currents act as a sort of converyor belt, carrying the lithospheric plates along above it. Ziegler in particular holds this view from studies of plate motion throughout the Phanerozoic (Wilson, 1993). However, mantle convection is not held to be as significant as it once was as a driving force.

Fig.3.6. Illustration showing the relationship between mantle convection currents and plate tectonics. It is proposed that the convection currents carry the plates around like a converyor belt.

Overview of Forces

All the forces listed above can be summarised in the diagram below.

Mechanisms
Fig.3.7. Driving mechanism of plate tectonics
  • Slab pull, slab (trench) suction and ridge push forces drive plate motion
  • Slab resistance, continental reistance, transform fault resistance and basal drag oppose plate motion

When resisting forces become greater than the driving forces, collision between the plates will eventually cease.
The Role of Gravity...
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