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Topic 10
The Dynamic Crust
| Question | Answer |
|---|---|
| Asthenosphere (plastic mantle) | The partially fluid portion of the upper mantle; the region of the mantle directly below the lithosphere; the portion of the mantle located between approximately 100 km and 250 to 300 km. |
| Atmosphere | The mixture of gases that surround the Earth, consisting primarily of nitrogen, oxygen, argon, carbon dioxide, and water vapor. |
| Basalt | An extrusive igneous rock having a fine-grained texture and mafic composition (plagioclase feldspar, pyroxene, olivine, and amphibole). |
| Bedrock | The solid rock that is found beneath sediments or soil. |
| Contact metamorphism | A form of thermal metamorphism that occurs as a result of igneous intrusion. Heat and hydrothermal solutions from the igneous material causes the alteration of the pre-existing rocks. |
| Continental crust | The upper portion of a lithospheric plate that makes up one of the large land masses of the Earth. Continental crust is composed mainly of the felsic igneous rock granite. |
| Convection | A method of heat transfer through fluids such as air or water. The circulatory motion that occurs when different areas of a fluid are at different temperatures. The motion results from the variation of density of the fluid and the action of gravity. |
| Convection currents | A method of heat transfer in liquids and gases (fluids) that involves density differences and produces a circulation pattern within the fluid |
| Converging plate boundary | A region where two lithospheric plates move towards each other. Subduction zones form where oceanic plates converge with each other, or continental plates. |
| Cross-cutting relationships | A principle of geology that indicates that any rock layer or structure, such as a fault or and intrusion, is younger than the rock layers or structures it intersects (cuts across). |
| Crust | The outermost zone of the Earth. The solid surface of the planet separated from the solid upper mantle by the Mohorovicic Discontinuity (Moho). The crust and solid upper mantle make up the lithosphere. |
| Crustal movement | The shifting of sections of the Earth’s outer most section that results from dynamic processes. |
| Delta | A feature that forms where a river enters into a large body of water and deposits sediments. Some deltas, such as the Nile Delta, look like the Greek letter (Δ). Other deltas, such as the Mississippi Delta, look like a bird’s foot. |
| Diverging plate boundary | Any lithospheric plate boundary at which one plate is moving apart from another plate. Diverging plate boundaries in the marine environment form oceanic ridges. Rift valleys form when plates carrying continents separate under the land mass. |
| Down-warping | The downward movement of large sections of Earth’s crust. |
| Earthquake | The sudden motion or vibration of a section of the crust or lithosphere that are the result the release of stresses that have built up over time. Most earthquakes occur at lithospheric plate boundaries. |
| Earthquake focus | The location on or within the Earth from which earthquake waves originate. Foci are classified on the basis of depth into three categories: shallow focus, intermediate focus, and deep focus. |
| Epicenter | The point on the surface directly above the focus of an earthquake. The geographic location above an earthquake. |
| Felsic | Any igneous rock containing an abundance of potassium feldspar, quartz, and muscovite mica. The mineral composition gives the resulting rock a light color and low density. |
| Folding | The plastic deformation of rocks that results in the formation of monoclines, anticlines, and synclines. |
| Granite | An intrusive igneous rock having a coarse-grained texture and a felsic composition (potassium feldspar, quartz, muscovite mica biotite mica, and hornblende)., |
| Hot spots | Also called mantle plumes; regions at which magma rises from the core-mantle boundary and moves by convection towards the surface. Regions of localized volcanic activity, for example, Hawaii, Iceland, and Yellowstone National Park. |
| Igneous intrusion | The movement of magma (molten rock) into pre-existing rock. The igneous rock formed from the solidification of magma below the surface. |
| Index fossil | A fossil that is used to determine the relative age of the rock layer in which it is found. To be useful, an index fossil should have existed for some limited time and should have been distributed over a wide geographic distance. |
| Inner core | The inner-most zone of the Earth. The solid interior part of the Earth that is believed to be composed primarily out of crystalline iron. |
| Isostacy | A theory that states that various sections of the Earth’s lithosphere are in balance. It further indicates that continents, which are composed of granitic rock, will tend to “float” higher than the more dense rocks that make up the oceanic crust |
| Lag time | The difference between the P-wave arrival time and the S-wave arrival time that is used to calculate the distance between an earthquake and a seismic station. |
| Limestone | Any sedimentary rock that is composed primarily of calcium carbonate (lime). Limestones can form by deposition of lime muds, precipitation of crystals, or by the secretions of living organisms. |
| Lithosphere | The solid surface of the Earth. The portion of the Earth consisting of crust and solid upper mantle. |
| Longitude | The angular distance, measured in degrees, east and west of the Prime Meridian |
| Mafic | Any igneous rock containing an abundance of ferromagnesian minerals. The mineral composition gives the resulting rock a dark color and high density. |
| Magma | Molten rock found beneath the Earth’s surface. A silicate melt that can intrude into existing rock or extrude onto the surface forming lava. |
| Magnetic Reversals | Periodic changes in a magnetic field in which the north pole becomes a south pole while the south pole becomes a north pole Changes in Earth’s magnetic field are recorded by magnetic minerals such as magnetite as lavas solidify. |
| Mantle | The zone of the Earth located below the crust and above the core. The mantle is subdivided into a upper portion and a lower portion. The Mohovoricic Discontinuity (Moho) separates the mantle from the crust. |
| Mantle plume | Long, narrow columns or bodies of magma rising through the mantle. Many mantle plumes originate at the mantle-core boundary. Some rise to the surface and underlie hotspots. |
| Mass movement/mass wasting | The down slope movement of rock or soil caused by gravity. |
| Metamorphism | The processes resulting from heat and pressure that change one form of rock to another form of rock. |
| Mid-Atlantic Ridge | The portion of the mid-oceanic ridge system located on the bottom of the Atlantic Ocean; a diverging plate boundary found between the North American Plate and the Eurasian Plate, and between the South American Plate and the African Plate. |
| Mid-ocean ridge | A system of volcanic mountains that form at diverging plate boundaries in all of the oceans. Activities at mid-ocean ridges include: active vulcanism, seafloor spreading, high heat flow, and the separation of lithospheric plates. |
| Oceanic crust | The upper portion of a lithospheric plate that makes up the ocean bottoms. Oceanic crust is composed of mafic igneous rocks |
| Original horizontality | The principle that indicates that sedimentary rocks form in horizontal layers. Sedimentary rocks that are not horizontal generally indicate that crustal movement has occurred after deposition. |
| Outcrop | Any portion of a geologic formation or structure that is exposed at the surface. |
| Outer core | The zone of the Earth’s interior located between mantle and the inner core. The outer core extends from a depth of approximately 2,883 km to a depth of 5,200 km. The outer core is believed to be fluid |
| Plate boundary | Interface between two or more sections of the Earth’s lithosphere. Areas of frequent crustal activity, including earthquakes, volcanoes, and trenches. Plate boundaries can be classified as being: diverging, converging, or transform. |
| Plate Tectonics | A theory that states that the Earth’s surface is composed of several sections of crust and solid upper mantle. Forces within theEarth cause the sections, or plates, to move. |
| Pressure | Force per unit area. As the depth within the Earth increases the pressure on the earth materials increases. |
| P-wave travel time | The amount of time required for a P-wave to travel from the location of an earthquake focus to a seismic recording station. |
| P-waves | Primary waves. Compressional earthquake waves that are the first to reach a seismic station. Pulses of energy that are produced by earthquakes and move through the various portions of the Earth’s interior. |
| Ridge | A long, narrow, steep-sided elevation. |
| Rift Valley | A valley formed between two or more parallel faults; valleys found at diverging plate boundaries such as the mid-ocean ridge system or the Great Rift Valley in Africa. |
| Rigid Mantle/solid upper mantle | The rigid or solid portion of the mantle located directly below the crust and above the asthenosphere. Lithospheric or tectonic plates are composed of crust and rigid mantle materials. |
| Seafloor spreading | The theory that explains the movement of the oceanic crust away from a mid-ocean ridge. As magma moves up from the mantle it pushes lithospheric plates apart at diverging plate boundaries. |
| Sedimentary rock | A layered rock formed by the compaction and cementation of sediments; chemical precipitation; or organic origins. Examples of sedimentary rocks include: conglomerate, sandstone, shale, and limestone. |
| Seismic station | A location that contains instruments that are used to record the occurrence of earthquakes. One seismic station can determine the distance, magnitude, and time of an earthquake. Three stations are used to triangulate the actual location of an earthquake |
| Seismogram | The record of an earthquake that is recorded on an instrument called a seismograph |
| Shadow zone (earthquake) | A zone of Earth in which P-waves and S-waves are not received from a distant earthquake. A zone extending from 103° to 143° from the epicenter of an earthquake. This pattern is the refraction of P-waves and absorption of S-waves by the Earths Core |
| Solid | bonds, forming a crystalline structure. Solids have a definite mass, volume, and shape. |
| Stiffer mantle | The lower mantle or mesosphere. The zone of the Earth’s interior between the fluid (plastic), upper mantle (the asthenosphere) and the core-mantle boundary. The portion of the mantle that extends from approximately 350 km to 2883 km. |
| Subduction zone | A converging plate boundary at which a section of oceanic lithosphere moves beneath another lithospheric plate. Subduction zones are indicated by frequent earthquakes, trenches, volcanic arcs, and volcanic island arcs. |
| Surface ocean currents | Movement of the uppermost sections of the oceans. Movement of the ocean waters as a result of the planetary wind system and the Coriolis effect. |
| S-wave arrival time | The time that the first S-wave arrives at a given seismic station. Since S-waves travel slower than P-waves, the S-wave will arrive at the station after the P-wave. |
| S-waves | Secondary waves. Transverse earthquake waves that arrive after the P-waves. The arrival time difference between the P-waves and the S-waves is used to determine the distance to the epicenter. The S-waves can only pass through solid portions of Earth |
| Tectonic plate | Also called lithospheric plate; one of the twelve or so fragments that make up Earth's solid surface. Lithospheric plates consist of crust and solid upper mantle. Some but not all plates carry continents. |
| Transform boundary | An interface at which two lithospheric plates grind past each other. Transform boundaries are marked by regions with extensive strike-slip (horizontal) fault zones. |
| Trench | Long, linear troughs that form the deepest portions of the oceans. Features formed by the movement of one lithospheric plate beneath another lithospheric plate (subduction). |
| Tsunami | An sea wave that is produced by a submarine earthquake, faulting, or a landslide on the ocean floor. The movement of an earthquake surface wave through water. Incorrectly called tidal waves. |
| Volcanic activity | Any surface or subsurface events associated with the eruption of volcanoes. |
| Weathering | The mechanical or chemical breakdown of rock material as a result of interactions with atmospheric conditions. |
Created by:
bhowell65
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