GLOSSARY  
   
Accretion
indicates a mass of sediment and oceanic crust has been transferred from the subducting plate to the less dense, overriding plate as a result of a collision.
 
Active Plate Boundary
The margin of a lithospheric plate undergoing tectonic processes of subduction, collision, accretion, or spreading. The west coast boundary of North America is active; the Atlantic edge of the continent is passive.
Biostratigraphy
A dating technique which uses index fossils to correlate the ages of rocks in different locations.
Composite Terranes
Terranes which are made up of two or more distinct terranes that were joined together before beginning their travels.
Conodonts
Conodonts are a group of extinct microscopic marine, worm-like animals that lived from 570 to 200 mya. Their fossil remains are used to date rocks.
Continental Drift
A theory presented by German scientist, Alfred Wegener in 1912. Using corresponding floral and faunal fossils, corresponding shapes of the east continental shelf of South America and the west continental shelf of Africa, and distinct geological features that crossed continental boundaries, Wegener proposed the continents had once been assembled in a huge land mass (Pangaea) and then broke apart, drifting into present positions.
Convergent Zones
Convergent Zones are areas where two lithospheric plates come together. If one or both of the plates is oceanic (denser), subduction will occur. If both plates are continental, mountain forming will occur.
Cordillera
The name given to the mountainous region of the western North American continent. It includes the Rockies, the Cascades, and the Sierra Nevada Mountains.
Cratons
Cratons are parts of the Earth's continents which have remained relatively stable and earthquake-free for long periods of time. They are usually thought of as the continental shield and the surrounding platform.

Disrupted Terranes
As their name implies, disrupted terranes contain rocks from different backgrounds and ages - oceanic crust, shallow-water limestone, deep-water chert, and greywacke - usually found in a matrix of shale or serpentinite.
Divergent Zones
Areas where two lithospheric plates are rifting or moving away from one another while soft mantle rock rises between them, forming new oceanic lithosphere.
Exotic Terranes
Crustal blocks displaying properties identified as having originated elsewhere than their present location through discontinuities in lithography, floral and faunal fossil evidence, paleomagnetic readings, and geochemical markers.
Fusulinids
Marine microfossils dating back to the Permian period (250 - 290 million years ago). They are used as index fossils during biostratigraphic dating of rocks.
Metamorphic Terranes
These terranes show signs of terrane-wide geologic changes, before or after collision, which has been sufficiently powerful to obscure original rock formation.
Microplates
(also called terranes) are fragments of crustal plates broken off from a larger, distant plate during rifting.
Microplate Tectonics
A term used to indicate the movement of small fragments of crustal plates; formation, drifting, collision, displacement and accretion.
Miogeocline
A geosyncline in which volcanism is not associated with sedimentation; the non-volcanic aspect of an orthogeosyncline, located near the craton.
Orogeny
The geological term for mountain building, and it is usually associated with a specific historic event such as the Antler orogeny, or the Taconian orogeny.
Paleomagentic signatures
are read from rocks to help determine the latitude of the rock at the time of its formation. The fixed orientation of the rock's magnetized fraction does not change even if the magnetic field of the Earth reverses.
Potassium-Argon Techniques
Forms of isotope dating tests used on rocks between 100,000 and 4 billion years old. It relies on the extremely long half-life of radioactive isotopes of potassium which decay into argon.

Radiolarians
Single-celled organisms that lived in the oceans from 500 - 160 mya. Their fossils are used to date rocks representing deep ocean origins.
Rifting
A process of spreading and thinning of the crustal plate. This forms a depression in the crust and often results in the separation of the crust into two or more smaller plates.
Stratified Terranes
These terranes have layers of rock which indicate the order of deposition. These terranes can be a.) fragments of continents, characterized by Precambrian basement rock under shallow-water sediments from the Paleozoic and Mesozoic ages; b.) ocean crust, with typical extruded molten rock under layers of siliceous chert; c.) fragments of volcanic arcs, with deep igneous roots under sedimentary volcanic debris.
Subducting
The sinking of the ocean crust edge as a result of convergence with lesser density. This process often causes earthquakes and can result in chains of volcanoes.
Tethys Sea
A seaway that existed between Gondwanaland and Laurasia from the Permian through the Eocene. Very diverse and distinctive tropical fauna distinguishes it.
Alfred Wegener
Wegener is credited with the theory of continental drift (1912) from which the discipline of plate tectonics grows. Trained as an astronomer, he was also an explorer of Greenland and the Arctic, and had an interest in meteorology.
Glossary List