Plate Tectonics Definitions

Plate Tectonics

A theory explaining 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.

Geology

Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them.

Rodinia

In geology, Rodinia (from the Russian "Родина", ródina, meaning "The Motherland") is the name of a hypothesized supercontinent, a continent which contained most or all of Earth's landmass.

Convergent Boundary

In plate tectonics, a convergent boundary, also known as a destructive plate boundary (because of subduction), is an actively deforming region where two (or more) tectonic plates or fragments of the lithosphere move toward one another and collide.

Divergent Boundary

In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other.

Magma

Molten rock material that occurs below Earth's surface. When it erupts onto the surface, it is known as "lava."

Transform Boundary

A strike-slip fault that connects offsets in a mid-ocean ridge, or links sections of two other faults.

Continental Drift

The gradual movement of the continents across the earth's surface through geological time.

Craton

The name given to the stable (usually interior) portions of continental lithospheric plates that have not been deformed or metamorphosed for at least one billion years. Cratons are usually underlain by crystalline basement rock that is sometimes overlain by younger sedimentary rocks.

Sea-Floor Spreading

The process that occurs at mid-ocean ridges in which convection currents below pull the plates apart and create new sea floor.

Continental Crust

The relatively thick part of the earth's crust that forms the large landmasses. It is generally older and more complex than the oceanic crust.

Oceanic Crust

The relatively thin part of the earth's crust that underlies the ocean basins. It is geologically young compared with the continental crust and consists of basaltic rock overlain by sediments.

Lithosphere

The rigid outer shell of the earth which includes the crust and a portion of the upper mantle.

Subduction

The sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate.

Magnetic Field

A region around a magnetic material or a moving electric charge within which the force of magnetism acts.

Asthenosphere

A portion of the upper mantle that is directly below the lithosphere. A zone of low strength in the upper mantle defines the top of the asthenosphere. This weak zone allows the plates of the lithosphere to slide across the top of the asthenosphere.

Convection Current

A current in a fluid that results from convection.

Terrane

A fault-bounded area or region with a distinctive stratigraphy, structure, and geological history.

Seismic Waves

A generic term for the numerous types of waves that are produced by an earthquake and travel through the earth.

Pangaea

A large continental landmass that existed from about 300 million years ago through about 200 million years ago. It included most of the continental lithosphere present at that time. It has since broken up and the fragments have drifted to become the configuration of Earth's present day continents.

Rift Valley

A large elongated depression with steep walls formed by the downward displacement of a block of the earth's surface between nearly parallel faults or fault systems.

Trench

A long, narrow, deep depression in the ocean floor that parallels a convergent plate boundary involving at least one oceanic plate.

Mid-Ocean Ridge

A long, seismically active submarine ridge system situated in the middle of an ocean basin and marking the site of the upwelling of magma associated with seafloor spreading. An example is the Mid-Atlantic Ridge.

Tectonic Plates

The dozen or so plates that make up the surface of the Earth. Their motion is studied in the field of plate tectonics.