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Roger Weller, geology instructor
by Shannon Lee Bruce
Types of Tectonic Borders
This picture above shows where the three different types of Tectonic plate borders occur on the earth.
When divergent boundaries occur under the ocean surface, formations like the mid-Atlantic ridge are formed. The two edges of the tectonic plates are pulled apart and hot magma flows to the surface where it meets the water and cools forming new sections of the earth’s crust which is also known as seafloor spreading. When they occur on land you get land like the picture below.
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like the San Andreas Fault in California is a good example of strike- slip
faults. Strike- slip faults occur when two fault blocks move horizontally past
each other in opposite directions along the direction of the strike line. This
is a likely setup for disasters such as earth quakes. An earth quake is a sudden
release of energy underground usually associated with a fault. Another type of
fault that we know of is a thrust fault, which is a low angle reverse fault
where the headwall block moves up and dips over the younger rock. Below is an
illustration showing an example of a thrust fault.
Photo Copyright Roger Weller/Cochise
Convergent boundaries are created when the edge of one tectonic plate is pushed under the other one. There are three different types of convergent boundaries that are possible and these are the oceanic to continental, the continental to continental, and the oceanic to oceanic.
When you have a oceanic to continental convergent boundary the thinner and less denser tectonic plate is pushed under the thicker and denser tectonic plate. With this type of boundary the oceanic crustal slab is pushed beneath the continental crust at about a 30 degree angle. This type of boundary is the cause for the majority of volcanoes such as the ones that are found in the Ring of Fire around the Pacific Ocean. Below is an diagram of oceanic to continental boundary.
Oceanic to continental
When you have a continental to continental divergent boundary which is when two crustal plates at a boundary are moving away from each other, a rift zone will form above the boundary. If it is a convergent boundary, a folded mountain range will be pushed up. An example of this would be the Appalachians or the Ural mountains. The diagram below show how this takes place.
Continental to continental
When an oceanic to oceanic type of boundary occurs, if it is a divergent plate
boundary, an oceanic ridge will form at the boundary. On the other hand, if it
is a convergent boundary, the oceanic plate on one side of the boundary will be
shoved under the other at a steep angle and can cause islands to form in the
ocean. An example of this is the
in Alaska. The diagram below further illustrates this type of boundary.