Plate TectonicsPlate Tectonics

Tectonic plates move or float on top of Tectonic plates move or float on top of the upper mantle.the upper mantle.

However they do not float freely. However they do not float freely.

The plates are forced in specific The plates are forced in specific directions by the flow of magma directions by the flow of magma beneath. beneath.

Plate Tectonics – cont’dPlate Tectonics – cont’d Plates move with the flow of magma. Plates move with the flow of magma.

The magma The magma closer to the corecloser to the core heats and then heats and then risesrises towards the surface as its density decreases.towards the surface as its density decreases.

Once the rising magma reaches the lithosphere it Once the rising magma reaches the lithosphere it moves in opposite directions. moves in opposite directions.

The magma forms The magma forms convectional currentsconvectional currents. .

Plate Tectonics – Convection CurrentsPlate Tectonics – Convection Currents

Divergent BoundariesDivergent Boundaries

Tensional ForcesTensional Forces occur where two tectonic occur where two tectonic plates are pulled plates are pulled apartapart. The tension is created . The tension is created as the plates move away from each other. as the plates move away from each other.

Ridge ZonesRidge Zones sometimes occur where two sometimes occur where two plates move apart. The plates move apart. The magma risesmagma rises between between the plates and forms a the plates and forms a ridge.ridge.

Again caused byAgain caused by convectional currents in convectional currents in the magmathe magma

Tensional Forces – Ridge ZonesTensional Forces – Ridge Zones

This diagram above shows “Sea Floor Spreading”

Where’s the TENSION?Where’s the TENSION?

ConvergentConvergent Boundaries Boundaries

Compressional ForcesCompressional Forces occur where two occur where two tectonic plates come together. They tectonic plates come together. They compress against each other.compress against each other.

Subduction ZonesSubduction Zones sometimes occur where sometimes occur where compressional forces result from two plates compressional forces result from two plates colliding and one plate colliding and one plate slips underslips under the the other.other.

Again caused byAgain caused by convectional currents in convectional currents in the magmathe magma

Compressional Forces – Compressional Forces – SubductionSubduction

Where’s the Subduction / Where’s the Subduction / Compression?Compression?

More about Plate More about Plate TectonicsTectonics

our text p. 10 - 12our text p. 10 - 12

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