DESTRUCTIVE PLATE MARGIN
Plates move towards eachother at desctructive margin, rock is destroyed. Oceanic crust pushes into continental curst there is a collision. Because the continental crust is less dense, the more dense oceanic crust forces its way underneath it. This is called SUBDUCTION and happens at a SUBDUCTION ZONE. As the oceanic crust is subducted down into the mantle is starts to melt. Also, it rubs against the continental crust, friction is created which also creates heat and causes the rock to melt.
CONSTRUCTIVE PLATE MARGIN
Plates move apart and rock is created. Constructive margins occure between 2 pieces of continental crust which is pulled apart by the convection currents in the mantle. As the crusts seperate , a gap is left in the middle which allows magma to fill it from the mantle. The magma cools and solidifies and creates new igneous rock which overtime can cause the creation of ocean ridges such as the mid atlantic ridge. Iceland is on a constructive plate boundary.
CONSERVATIVE PLATE MARGINS
The plates slide past eachother in the opposite directions or at different speeds in the same direction. The sliding motion causes the plates to get stuck due to the rough edges of the rock which builds up pressure and when released, can cause powerful earthquakes. An example is Andreas Fault in California.