Plate Tectonics

III. The Theory of Plate III. The Theory of Plate Tectonics.Tectonics.Plate Tectonics:Plate Tectonics: Explains how large Explains how large

pieces of the Earth’s outermost layer, pieces of the Earth’s outermost layer, called tectonic plates, move and called tectonic plates, move and change shape.change shape.

A.A. Tectonic Plate Boundaries:Tectonic Plate Boundaries: A place A place where tectonic plates touchwhere tectonic plates touch1. Convergent boundary1. Convergent boundary2. Divergent boundary2. Divergent boundary3. Transform (Strike-slip) boundary3. Transform (Strike-slip) boundary

NOAA Plate Tectonics Video

Convergent BoundaryConvergent BoundaryConvergent boundaryConvergent boundary : formed by : formed by

the collision of the collision of two lithospheric plates.two lithospheric plates.

3 types:3 types:a) a) Continental-continental collision: :

-Two plates with continental -Two plates with continental crust crust collide buckle and collide buckle and thicken to form thicken to form mountain mountain ranges.ranges.

Convergent BoundaryConvergent Boundary

b) b) Continental-Oceanic:Continental-Oceanic:

-continental and oceanic -continental and oceanic plates collide.plates collide.

-Denser oceanic crust sinks -Denser oceanic crust sinks into into asthenosphere where it is asthenosphere where it is recycled.recycled.Subduction Zone

c) c) Oceanic-Oceanic Collisions:Oceanic-Oceanic Collisions:

-Two oceanic plates collide. -Two oceanic plates collide. One One of the plates is subducted, or of the plates is subducted, or

sinks under the other. sinks under the other.

Subduction Zone

Plate Tectonics: Subduction

Alaska’s Volcanic ArcAlaska’s Volcanic Arc

Subduction ZonesSubduction Zones --Subduction zoneSubduction zone is an area where is an area where

a plate moves under another plate.a plate moves under another plate. The Crust is recycled and causes The Crust is recycled and causes

volcanic activity.volcanic activity. Subduction zones are normally Subduction zones are normally

located at deep ocean trenches.located at deep ocean trenches.

2. 2. Divergent boundary:Divergent boundary: the boundary the boundary between two tectonic plates that are between two tectonic plates that are moving away from each other.moving away from each other.

Ex. Mid-ocean ridges.Ex. Mid-ocean ridges.

3. 3. Transform boundary:Transform boundary: boundary boundary between tectonic plates that are sliding between tectonic plates that are sliding past each other horizontally.past each other horizontally.

-Ex. San Andreas Fault-Ex. San Andreas Fault

Drilling for Core SamplesDrilling for Core Samples Describe how the Describe how the

plates are moving plates are moving relative to one another. relative to one another.

What type of plate What type of plate boundary is this? boundary is this? CheckCheck

What does the sea floor What does the sea floor topography look like in topography look like in this area? this area?

BB. . Possible Causes of Tectonic Possible Causes of Tectonic Plate MotionPlate Motion ConvectionConvection:: Hot rock from deep Hot rock from deep

within the Earth rises, but cooler within the Earth rises, but cooler rock near the surface sinks. rock near the surface sinks.

-Causes lithosphere to move away -Causes lithosphere to move away from mid-ocean ridge.from mid-ocean ridge.