Plates and Plate Plates and Plate MovementMovement

Characteristics of the crustCharacteristics of the crust There are 2 main types of crust There are 2 main types of crust

that lie on plates and each has its that lie on plates and each has its own characteristics:own characteristics:

Oceanic Crust (Sima) Young (under 200 million years), thin, dense and heavy, will sink. Always being created and destroyed. For example, Basalt.

Continental Crust (Sial) Old, light, thick (up to 150km under mountains) permanent, does not sink. For example, Granite.

  Plate marginsPlate margins

Movement of plates is in one of 3 Movement of plates is in one of 3 ways:ways:

1.1. Towards each other:Towards each other: Convergent Convergent (destructive or collision).(destructive or collision).

2.2. Away from each other: Away from each other: Divergent.Divergent.3.3. Alongside each other:Alongside each other: Transform or Transform or

transcurrent.transcurrent.

Convergent plate boundaries Convergent plate boundaries (together)(together)

There is a further There is a further subdivision for subdivision for Convergent plates, Convergent plates, which is dependent on which is dependent on the properties of the the properties of the plates moving towards plates moving towards each other (oceanic each other (oceanic /continental crust)./continental crust).

The two types of The two types of margins that occur margins that occur here are Destructive here are Destructive Margins or Collision Margins or Collision Zones. Zones.

Destructive margins

Oceanic crust moves towards continental crust. Oceanic crust sinks, and slowly destroyed. Results in deep ocean trenches, island arcs and fold mountains. Can be referred to as subduction zones.

Collision Zones Two continental crusts meet, neither sinks, fold mountains result. For example, the Alps.

Divergent plate boundaries Divergent plate boundaries (away)(away)

Also known as a Constructive margin. Also known as a Constructive margin. Plates move away from each other, Plates move away from each other, for example, N.American and for example, N.American and Eurasian plates, cresting mid-ocean Eurasian plates, cresting mid-ocean ridges such as the Mid Atlantic Ridge. ridges such as the Mid Atlantic Ridge. New material appears at the ocean New material appears at the ocean ridge. ridge.

Transform/transcurrent Transform/transcurrent boundariesboundaries

Here plates simply move alongside Here plates simply move alongside each other, land is neither created each other, land is neither created nor destroyed.nor destroyed.

Results of plate movementResults of plate movement Examples of features created and hazards caused Examples of features created and hazards caused

by plate movement are outlined below:by plate movement are outlined below:Destructive plate margins (For example, Nazca and south

American plates)

A Peru – Chile Trench as oceanic crust is subducted.

B Earthquakes, due to the heat created as the Nazca plate is destroyed.

C Fold Mountains such as the Andes.

D Volcanoes if heat from the subduction zone has the opportunity to reach the surface, for example, Cotopaxi.

E Island arcs and volcanic islands, for example, Japan.

Collision zones: Indian Plate and Eurasian Plate created the Himalayas.

Constructive margins: North American plate moving away from the Eurasian plate resulting in the mid Atlantic ridge.

Transform faults: earthquakes such as those linked with the San Andreas Fault.

Hot spotsHot spots

There are examples where volcanic There are examples where volcanic activity is not linked to plate margins activity is not linked to plate margins as in the case of the Hawaiian as in the case of the Hawaiian Islands. This is believed to be due to Islands. This is believed to be due to the presence of ‘the presence of ‘hot spotshot spots’ - places ’ - places of localised heat under the earth’s of localised heat under the earth’s crust that then find their way to the crust that then find their way to the surface.surface.