| Term | Definition |
|---|
| accreted terrane | An individual, geologically coherent fragment of an amalgamation of odd pieces of crust - island arcs, seamounts; remnants of thickened oceanic plateaus; old mountain ranges; and other slivers of continental crust - that were plastered onto the leading edge of a continent as it moved across Earth's surface. |
| accretion | A process of continental growth in which buoyant fragments of crust are attached (accreted) to continents during plate motions. |
| craton | A stable nucleus composed of the eroded remnants of ancient deformed rocks that comprises the continental shields and platforms. |
| cratonic keel | A part of the lithosphere that extends into the convecting asthenosphere at 100 to 200 km beneath the cratons like the hull of a boat into water. |
| epeirogeny | The gradual downward and upward movements of broad regions of crust without significant folding or faulting. |
| granite-greenstone terrains | Areas of massive granite intrusions in Archean cratons that surround smaller pockets of deformed, metamorphosed volcanic rocks (greenstones), primarily of mafic composition. |
| high-grade metamorphic terrains | Areas of high-grade (granulite facies) metamorphic rocks in Archean cratons, derived primarily from the compression, burial, and subsequent erosion of ancient granitic crust. |
| orogen | An elocated mountain belt arrayed around a continental craton and formed by a later episode of compressive deformation. |
| rejuvenation | Renewed uplift ina mountain chain on the site of earlier uplifts, returning the area to a more youthfaul stage. |
| shield | A large region of stable, ancient crystalline basement rocks within a continent. |
| tectonic age | The age of a rock that corresponds to the last major episode of crustal deformation. |
| Wilson cycle | A general plate tectonic cycle that comprises 1) rifting during the breakup of a supercontinent, 2) passive-margin cooling and sediment accumulation during seafloor spreading and ocean opening, 3) active-margin volcanism and terrane accretion during subduction and ocean closure, and 4) orogeny during the continent-continent collision that forms the next supercontinent. |
| andesitic lava | A lava of intermediate composition that has a higher silica content than basalt, erupts at lower temperatures, and is more viscous. Extrusive equivalent of diorite. |
| ash-flow deposit | An extensive sheet of hard volcanic tuff. |
| basaltic lava | A lava of mafic composition that has a low silica content, erupts at high temperatures, and flows readily. Extrusive equivalent of gabbro. |
| caldera | A large, steep-walled, basin-shaped depression formed after a violent eruption in which large volumes of magma are discharged, when the overlying volcanic structure collapses catastrophically through the roof of the emptied magma chamber. |
| crater | 1) a bowl-shaped pit found at the summit of most volcanoes, centered on the vent. 2) A depression caused by the impact of a meteorite. |
| diatreme | A volcanic vent formed by the explosive escape of gases and often filled with breccia. |
| fissure eruption | A volcanic eruption emanating from an elongate fissure rather than a central vent. |
| flood basalt | An immense basaltic lava plateau extending many km in flat, layered flows originating from fissure eruptions. |
| hot spot | A volcanic center found at the beginning of progressively older aseismic ridges or within a continent far from a plate boundary. Hypothesized to be the surface expression of a mantle plume. |
| hydrothermal activity | The circulationof water through hot volcanic rocks and magmas, producing hot springs and geysers on the surface. |
| lahar | A torrential mudflow of wet volcanic debris prodcued when pyroclastic or lava deposits mix with rain or the water of a like, river, or melting glacier. |
| large igneous province | A voluminous emlacement of predominantly mafic extrusive and intrusive igneous rock whose origins lie in processes other than normal seafloor spreading. Include continental flood basalts, ocean basin flood basalts, and aseismic ridges. |
| mantle plume | A narrow, cylindrical jet of hot, solid material rising from deep within the mantle and thought to be responsible for intraplate volcanism. |
| pyroclast | A volcanic rock fragment ejected into the air during an eruption. |
| rhyolitic lava | The lava that is richest in silica, making it the stickiest and least fluid kind of lava. It erupts at temperatures of only 600 to 800 C. |
| shield volcano | A broad, shield-shaped volcano many tens of km thick in circumference and more than 2 km high built by successive flows of fluid basaltic lava from a central vent. |
| stratovolcano | A concave-shaped volcano containing alternating layers of lava flows and beds of pyroclasts. |
| volcanic geosystem | The total system of rocks, magmas, and interactions needed to describe the entire sequence of events from melting to eruption. |
| volcano | A hill or mountain constructed from the accumulation of lava and other erupted materials. |
| chemical stability | A measure of a substance's tendency to remain in a given chemical form rather than reacting sontaneously to become a different chemical substance. |
| chemical weathering | The weathering that occurs when the minerals in a rock are chemically altered or dissolved. |
| erosion | The set of processes that loosen soil and rock and move them downhill or downstream, where they are deposited as layers of sediment. |
| exfoliation | A physical weathering process in which large flat or curved sheets of rocks fracture and are detached from an outcrop. |
| frost wedging | A physical weathering process in which the expansion of freezing water in a crack breaks a rock. |
| hematite | The principal iron ore; the most abundant iron oxide at Earth's surface. |
| humus | The remains and waste products of hte many plants, animals, and bacteria living in a soil. |
| kaolinite | The white to cream-colored clay produced by the weathering of feldspar. |
| mass wasting | All the processes by which masses of rock and soil move downhill under the influence of gravity. |
| soil | A weathering product composed of fragments of bedrock, clay minerals, and organic matter. |
Combine with other sets
Share on Facebook
Share on MySpace