Plate Tectonics A Key Terms

Plate Tectonics Theory

Lesson 2.1.1 Development of Plate Tectonic Theory

Plate Tectonics Theory

Lesson 2.1.1 Development of Plate Tectonic Theory

States that the lithosphere is a shell of hard, strong rock that floats on the hot, plastic asthenosphere. Additionally, there are 8 large lithospheric plates and several smaller ones that slide slowly over the asthenosphere at rates ranging from less than 1 to about 16 cm per year.

Plate Boundary

Lesson 2.1.1 Development of Plate Tectonic Theory

A fracture that separates one plate from another. There are three types of plate boundaries: Divergent, convergent, and transform.

What can the forces of plate boundaries develop?

Lesson 2.1.1 Development of Plate Tectonic Theory

Mountain ranges, earthquakes, volcanos.

Seismology

Lesson 2.1.1 Development of Plate Tectonic Theory

Study of seismic waves.

Volcanology

Lesson 2.1.1 Development of Plate Tectonic Theory

Study of volcanos.

Topography

Lesson 2.1.1 Development of Plate Tectonic Theory

Study of landforms.

Lithosphere

Lesson 2.1.1 Development of Plate Tectonic Theory

Includes the crust and uppermost mantle. Its average thickness is 100km but ranges from about 75km beneath ocean basins to about 125km under the continents. Temperatures range from 300-500 degrees Celsius.

Gravity Anomaly

Lesson 2.1.1 Development of Plate Tectonic Theory

Ridge Push

Lesson 2.1.1 Development of Plate Tectonic Theory

The downslope sliding of the lithosphere away from a spreading center, which may contribute to the movement of plates.

Spreading Ridges

Lesson 2.1.1 Development of Plate Tectonic Theory

Marks the location of ascending limbs of the convection cells.

Slab Pull

Lesson 2.1.1 Development of Plate Tectonic Theory

When old lithosphere becomes denser than the asthenosphere below and sinks into the mantle in a subduction zone, pulling the trailing plate along with it. May contribute to tectonic plate movement.

Mantle Convection Cells

Lesson 2.1.1 Development of Plate Tectonic Theory

Heat from the core, supplemented by heat produced from radioactive decay, drives the movements of the lithosphere as it cools in direct contact with the lithosphere.

Convection

Lesson 2.1.1 Development of Plate Tectonic Theory

When hotter (less dense because it expands) material rises to the surface, cools (becomes denser because it shrinks), and goes back to the bottom, repeating the process and forming a circular movement.

Why is the bottom of the mantle ductile?

Lesson 2.1.1 Development of Plate Tectonic Theory

If the combined effects of temperature and pressure are close to, but just below, a rock’s melting point, the rock remains solid but loses strength, becoming weak and plastic.

What happens to rock when it melts?

Lesson 2.1.1 Development of Plate Tectonic Theory

Expands by about 10%

Asthenosphere

Lesson 2.1.1 Development of Plate Tectonic Theory

The upper layer of the earth's mantle, plastic and partly molten, in which convection is thought to occur, about 350km thick. Average temperature of 1,800 degrees Celsius.

Continental Drift Theory

Lesson 2.1.1 Development of Plate Tectonic Theory

Wegener’s concept of a single landmass (Pangea) that broke apart to form the modern continents.

Divergence

Lesson 2.1.2 Seafloor Spreading

Also called a spreading center, is when two plates spread apart from one another. The underlying asthenosphere rises upward to fill the gap between the separating plates, creating new crust.

Seafloor Spreading

Lesson 2.1.2 Seafloor Spreading

A general model for the origin of all oceanic crust, supported by the magnetism data preserved along the Mid-Atlantic ridge.

Oceanic Trenches

Lesson 2.1.2 Seafloor Spreading

The surface expression of subduction, where plates descend into Earth’s interior.

Mid-Ocean Ridge

Lesson 2.1.2 Seafloor Spreading

A branch of the larger Mid-Ocean Ridge system.

Continental Rift

Lesson 2.1.2 Seafloor Spreading

When a divergent plate boundary splits apart continental crust as a result of stretching and fracturing.

Subductions

Lesson 2.1.3 Convergent Margins

Where plates descend into Earth’s interior.

Hypocenter/Focus

Lesson 2.1.3 Convergent Margins

The initial rupture point, where abrupt movement creates an earthquake, typically lies below the surface.

Island Arc

Lesson 2.1.3 Convergent Margins

A curving chain of volcanic islands that form as a result of oceanic convergence.

Earthquake

Lesson 2.1.3 Convergent Margins

Vibration of a rock as a result of stress build-up along the plate boundary stored in the rock as energy. When the stress goes over the threshold, it causes the rock to suddenly break, it releases the stored energy causing rock on one side of the break to lurch violently past rock on the other.

Epicenter

Lesson 2.1.3 Convergent Margins

The point on Earth’s surface directly above the focus.

Convergence

Lesson 2.1.3 Convergent Margins

When two llithospheric plates move toward each other and can occur between: oceanic and continental crust, continental and continental crust, and oceanic and ocean

As oceanic crust spreads away from the Mid-Ocean ridge, it becomes:

older, cooler, thicker, and denser.

Oceanic Trench

Lesson 2.1.3 Convergent Margins

Long, narrow depressions on the seafloor in the deepest parts of the ocean.

Orogeny

Lesson 2.1.3 Convergent Margins

A mountain building process that forms at convergent plate boundaries.

Hotspot

Lesson 2.1.4 Hot Spot and Transform Boundaries

When pressure decreases in a rising magma plume, allowing rock melts to form magma. Then, the rising heat and magma produce a hot spot in the upper mantle, which in turn heats the overlying lithosphere, forming a volcanic center.

Strike-and-Slip Fault

Lesson 2.1.4 Hot Spot and Transform Boundaries

The horizontal displacement of land on either side of the fault relative to each other.

Obsidian

Lesson 2.1.4 Hot Spot and Transform Boundaries

Forms at convergent plate boundaries and at hot spots.

Mantle Plume

Lesson 2.1.4 Hot Spot and Transform Boundaries

A relatively small column of plastic mantle rock that is hotter than surrounding rock.

Transform Fault

Lesson 2.1.4 Hot Spot and Transform Boundaries

Where two plates slide horizontally past one another as they move in opposite directions. This can result in frequent earthquakes.