Ocean- Continental Convergent Boundary

This type of convergent boundary also features a subduction zone (one plate descending beneath another plate). This boundary features an ocean trench and a continental volcanic arc.
As the ocean crust sinks/ subducts beneath the continental crusts, this ocean crust is destroyed. As the ocean crust is melted, forms magma, this magma can rise to the surface because the density of the magma is less than that of the rocks it was made from.

Continental-Continental Convergent Boundary

The best example of this type of boundary is what happened when the Indian landmass slammed into the southern edge of the Eurasian plate. The result of this collision formed the world's most famous mountain range - the Himalayans. These mountains are not volcanic as neither plate descends therefore very little magma is produced.

Transform Faults

This is a picture of the San Andreas Fault in California (photo credit:Wikipedia). A transform fault is a plate boundary where two plates grind past one another without destroying or producing new lithosphere. The lithosphere is the crust and upper part of the mantle.

Ocean-Ocean Convergent Boundary

A convergent boundary occurs when one plate descends (subduction) beneath another boundary due to a difference in density. The major features of this type of boundary is the ocean trench and a volcanic island arc. As the subduction plate descends earthquake foci increase in depth.
This ocean-ocean convergent boundary has produced many of the islands in the western Pacific Ocean.

Divergent Boundries

Let's look at divergent plate boundaries:

• mid-ocean ridges (pictures on left )- this is also known as seafloor spreading. At these boundaries new ocean crust is formed at an average rate rate of 5 cm per year. As one moves away from these ridges the crust cools, becomes denser and is older. As the seafloor spreads the age of the sediments that are on the ocean floor also increases. The top picture on left is a diagram of magnetic reversals. As the seafloor spreads and cools the magnetic rock particles align themselves with the magnetic poles of the earth. These reversals provide evidence for seafloor spreading.
  
• continental divergent boundaries (picture on right)- the Red Sea is an example of continental divergent boundaries. This is when a land mass splits apart.
• In both these examples magma pushes up through the lithosphere, volcanoes and volcanic activity is a product of these types of boundaries.
  

Wegener- The Continental Drift Man

Alfred Wegener proposed the theory of continental drift, (that all continents at one time were joined together as one) based on several pieces of evidence:

• the fit of the continents
• same type of rocks/ mountain chains on different continents
• fossils of the same organisms have been found on different continents
• the climates of the continents were different in the past than they are now.

These tectonics plates which consists of the upper mantle and crust move an average of 5 centimeters per year. The movement of these plates has been attributed to the convection currentsin the mantle.

Earth's Crust

The Earth's core is made of an alloy of iron and nickel. The mantle is most of the volume of the Earth and is a "plastic" like material. The thin, rocky outer layer of the the Earth is the crust. The ocean floor crust is basalt while the continental crust is mostly granite. The lithoshere is the crust and the upper mantle.