Plate Tectonics

Earth’s Internal Structure Crust Core Mantle

In which layer is most of the mass of the Earth located?

Two Types of Crust

What is one difference between oceanic crust and continental crust? A second difference is that the continental crust is composed of granite while the oceanic crust is composed of basalt. Finally, the density of the continental crust is less than the oceanic crust, thus it floats higher on the mantle.

The mantle increases in temperature depending on how close it is to the core. The rocks in the upper mantle are brittle and break while the rocks in the lower mantle are soft and flow instead of break.

The core is thought to be composed of nickel and iron alloy The core is thought to be composed of nickel and iron alloy. The outer core is liquid while the inner core is solid. Tremendous pressure, produced by the weight of the overlying rocks is believed to crowd the atoms tightly together and prevent the liquid state.

Convergent Boundary Continental/Oceanic Convergent plate boundaries are those moving toward one another. They cause volcanic eruptions, earthquakes, and deform the earth’s crust. As they collide, the less dense continental plate overrides the oceanic plate. As the oceanic plate is forced downward, the temperature increases. At about 100 miles, melting begins. This melting produces magma chambers which begin a slow asscen, melting and fracturing their way upward because they are less dense.

Convergent Boundary Oceanic/Oceanic When two oceanic plates converge the older (most dense) plate will subduct beneath the younger plate. This produces an island chain. With continued development the islands grow larger, merge and an elongate landmass is created.

Continental/Continental Convergent Boundary Continental/Continental The two thick continental plates collide and both of them have a density that is much lower than the mantle, which prevents subduction. The Himalaya Mountain Range is the best active example of this type of plate boundary.

Divergent Boundary Oceanic Divergent plate boundaries are locations where plates are moving away from one another. This occurs above rising convection currents. The rising currents lift the plate as they flow beneath it. This flow causes the plate material above to be dragged along in the direction of flow. At the crest of the uplift, the overlying plate is stretched thin, breaks and pulls apart. When the fissure opens, pressure is reduced on the super-heated mantle and it responds by melting and the new magma flows into the fissure. The magma then solidifies and the process repeats itself.

Divergent Boundary Continental As the two plates pull apart, normal faults develop on both sides of the rift and the central blocks slide downwards. Earthquakes occur as a result of this fracturing and movement. Streams and rivers flow into the rift and form a lake. If this continues and goes deeper, dropping below sea level, ocean water could flow in and form a new ocean basin.

for the animations and blackline drawings Special Thanks to Hobart M. King hobart@geology.com http://geology.com for the animations and blackline drawings As the two plates pull apart, normal faults develop on both sides of the rift and the central blocks slide downwards. Earthquakes occur as a result of this fracturing and movement. Streams and rivers flow into the rift and form a lake. If this continues and goes deeper, dropping below sea level, ocean water could flow in and form a new ocean basin.