The Theory of Plate Tectonics

What is the theory of Plate Tectonics?

Earth’s lithosphere is broken up into tectonic plates that move

around on top of the asthenosphere

What makes the tectonic plates move?

Convection Currents in

the mantle move the

plates as the core

heats the slowly-

flowing asthenosphere

(the elastic/plastic-like

part of the mantle).

These plates interact at

plate boundaries

Some key vocabulary …

Plate Boundary

location where edges of Earth’s tectonic plates meet

Stress

how the tectonic plates move past each other

Fault

break in Earth’s crust where

rocks move past each other

Divergent Boundary

•2 Types

Oceanic-OceanicContinental-Continental

•How are the plates moving?

Plates are moving apart from each other and separating

How are the rocks pulled? (Stress)

Rocks get thin in the middle

as the plates pull apart

This stress is called

“Tension”

What happens when the rock snaps from the stress of tension? (Fault)

a Normal Fault

Rock drops down

as it breaks

“Real World” Examples of Divergent Boundaries

Rift Valleys

(i.e. the Red Sea)

Mid-Ocean Ridges(i.e. the Mid-Atlantic Ridge)

Convergent Boundary

•3 Types

Oceanic-OceanicContinental-Continental

Continental-Oceanic

•How are the plates moving?

Plates are moving towards each other

Continental-ContinentalConvergent Boundary

•How are the plates moving?

Plates are moving towards each other to collide and bucklewhich causes the crust to thicken and push upwards

Continental-OceanicConvergent Boundary

•How are the plates moving?

Plates are moving towards each other and the Oceanic plate, which is colder & denser, subducts andmoves under the continental plate

Oceanic-OceanicConvergent Boundary

•How are the plates moving?

Plates are moving towards each other and one plate subducts under the other into the interior of the Earth

How are the rocks pulled? (Stress)

Rocks move towards one

another and collide

This stress is called

“Compression”

What happens when the rock snaps from the stress of tension? (Fault)

a Reverse Fault

Rock is forced upward

as it is squeezed

“Real World” Examples of Convergent Boundaries

Mountains(i.e. the Himalayan Mts.)

Trenches(i.e. the Mariana Trench)

Volcanoes(i.e. Mount St. Helens)

Transform Boundary

•How are the plates moving?

Plates are sliding past each other horizontally

How are the rocks pulled? (Stress)

Rocks are pushed in two

opposite directions

(pushed sideways – no

rock is lost)

This stress is called

“Shearing”

What happens when the rock snaps from the stress of tension? (Fault)

a Strike-Slip Fault

Rocks on each side

slip past each other

as they break

“Real World” Examples of Transform Boundaries

Dead Sea BasinFaults(i.e. the San Andreas Fault in

California)