Download Why Plates Move… - Mr Vincent Science

Why Plates Move…
The theory of plate tectonics explains how the plates move but not why. What do we know about
the earth’s mantle and crust that might help us determine the mechanisms involved?
Seismic data tells us that the mantle is fluid
The core of the earth is quite hot – heat left over from the earth’s formation and
produced by the decay of radioactive isotopes.
The mantle near the surface is cooler owing to the loss of heat through a thin crust
Hot material rises and cool material sinks
The slab of crust at subduction zones extends a long way into the mantle
Mountains of heavy volcanic rocks exist along MOR’s
As the rocks migrate from MOR’s to subduction zones, they cool and become more dense
Denser material sinks when placed into less dense fluids
Plate movements are at a constant speed, neither accelerating nor decelerating. This
implies the forces are nearly in balance
Plates with large subduction edges relative to their size move more quickly than those
with small subduction edges.
Modelling the Movement of Crustal Plates
Two models of crustal movement are shown in figure 1.8.
1. What is the main driving force in the convection current model?
2. What evidence above supports the convection current model? What contradicts it?
3. What is the main driving force in the push-pull model?
4. What evidence listed above supports the push-pull model? What contradicts it?
5. Compare the convection current and push-pull models.
6. Assess which of the models is more likely. If neither seems reasonable, propose an
alternative model.
Further Questions…
1. Define the term crustal plate.
2. Contrast the chemical properties and modes of formation of mafic and felsic igneous
rocks.
3. Distinguish between convergent and divergent plate boundaries.
4. Outline what happens during subduction.
5. Describes what happens at mid-oceanic ridges.
6. Describe the characteristics of Lithospheric plates.
7. Identify the relationship between the general composition of igneous rocks and plate
boundary type.
8. Outline the motion of crustal plates.
9. Assess current hypotheses used to explain plate motion