Plate Tectonics Theory
Plate Tectonics is a unifying collection of concepts that explains most things geological on Earth, and other planets and moons as well. (Note: Plate Tectonics is the focus of Chapter 4). Plate Tectonics theory explains the structure of the Earth's crust and many associated phenomena as resulting from the interaction of rigid lithospheric plates that move slowly over the underlying mantle.
Plate Tectonics (definition) (Illustrated in Figure 3.25.)
• A theory that states that the earth's solid outer shell (lithosphere) broken into large, rigid pieces called plates that can move relative to each other by sliding atop the non-solid asthenosphere.
• Plates are thought to move due to a combination of convection in the asthenosphere and gravity. These forces are discussed in more detail in Chapter 4.
• Most volcanoes and earthquakes occurs where the solid lithospheric plates meet.
Figure 3.25. General model representing essential concepts presented by Plate Tectonics Theory (discussed in Chapter 4).
Deformation is the action or process of changing in shape or distorting, especially through the application of pressure. In geologic terms, deformation refers to changes in the Earth's crust related to tectonic activity, particularly folding and faulting.
Heat from inside the earth drives mantle convection (hot material rises, cool material sinks, Figure 3.19). The rise and fall of masses of material in the mantle create forces that move the rocks in the cool and brittle lithosphere near the Earth's surface. These motions exert great forces, strong enough to rip continents apart, but the rate of movement is extremely slow on an annual basis (measurable in inches or centimeters per year).
Whereas the fluid-like state of rocks in the asthenosphere move slowly, the solid, brittle material in the lithosphere builds up great pressure (stresses) and the rocks will strain under the pressure until the point that they rupture, causing earthquakes that propagates as a shock waves through the Earth.