Plate tectonics is the splitting and movement of plates.

Main Ideas of the Theory

1. According to this theory, the earth’s crust is made up of rigid blocks called plates.
2. These plates are in constant slow movement.

Plate Movement

The movement of plates is caused by conventional currents from heat in the earth’s interior. Plates move at a rate of about 1-2cm per year. Some are moving away from each other (divergent plates), some plates move towards each other (convergent plates) while some by-pass each other. Where the plates meet, separate or by-pass each other are called Plate margins. Major landforms, earthquakes and volcanoes of the world occur at plate margins.

Types of Plates

There are two types of plates. These are:

• Continental plates made up of SIAL and SIMA.
• Oceanic plates made up of only the oceanic crust.

Some plates are large while others are small.

Major Plates

• The African plate
• The North American plate
• The South American plate
• Indo-Australian plate
• Pacific plate
• Antarctic plate
• Eurasian plate

Except for the pacific plate all major plates carry continents.

Types of Plate Margins

The movement of plates has produced plate margins. Tectonic forces occur at this plate margins which create some major landforms or features. There are three types of plate margins. These are:

• Divergent or Constructive plate margins,
• Convergent or Destructive plate margins and
• Conservative or Transform plate margins

1. Divergent or Constructive plate margins

These are plate boundaries where two plates separate and move away from each plate. Eg:

• South American
• African plate
• Atlantic ocean

Features produced include:

5. Major plateau and mountain ranges
5. Rift valleys and block mountains
5. Earth quakes

2. Convergent or Destructive plate margins

These are plate boundaries where plates move towards each other. Eg:

• Eurasian plate and

• African plate

Features produced at this margin:

5. Fold mountains
5. Deep sea trenches
5. Volcanic mountains and volcanic islands
5. Earth quakes.

3. Convergent or Destructive plate margins

These are zones where two plates by-pass each other without collision. Eg:

• The North American plate and
• The Pacific plate in California.

The main processes here are:

5. Tear faulting and
5. Earthquakes.