Term
| What are metamorphic rocks produced from? |
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Definition
| pre-existing igneous, sedimentary, or even from other metamorphic rocks. |
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Term
| Every metamorphic rock has a....? |
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Definition
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Term
| metamorphism leads to changes in what of rocks? |
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Definition
| changes in the mineralogy, texture, and sometimes the chemical composition of rocks. |
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Term
| when does metamorphism occur? |
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Definition
| where pre-existing rock is subjected to a physical or chemical environment that is significantly different from that in which it initially formed. |
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Term
| what kind of changes lead to metamorphism? |
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Definition
| changes in temperature, pressure, and the introduction of chemically active fluids. |
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Term
| where do most metamorphic changes occur? |
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Definition
| at the elevated temperatures and pressures that exist in the zone beginning a few kilometers below Earth's surface and extending into the upper mantle. |
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Term
| What happens when rocks at depth are subjected to directed pressure? |
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Definition
| they slowly deform to produce a variety of textures as well as large-scale structures such as folds. |
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Term
| during metamorphism why must the rock remain essentially solid? |
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Definition
| if complete melting occurs we have entered the realm of igneous activity. |
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Term
| what is the most important factor driving metamorphism? |
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Definition
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Term
| why is heat the most important factor driving metamorphism? |
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Definition
| because it provides the energy to drive chemical reactions that result in the recrystallization of existing minerals and/or the formation of new minerals. |
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Term
| there are two ways that heat affects earth materials, what is one way? |
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Definition
| it promotes recrystallization of individual mineral grains. this is particularly true of clays, fine grained sediments, and some chemical precipitates. |
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Term
| heat affects Earth materials in two ways, what is one of the ways? |
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Definition
| heat may raise the temperature of a rock to the point where one, or more, of the minerals are no longer chemically stable. the constituent ions tend to arrange themselves into crystalline structures that are more stable in the new high-energy environment. such chemical reactions result in the creation of new minerals with stable configurations that have an overall composition roughly equivalent to that of the original material. |
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Term
| where does Earth's internal heat come from? |
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Definition
| mainly it comes from energy that is continually being released by radioactive decay and thermal energy generated during the formation of our planet. |
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Term
| temperatures increase with depth at a rate known as...? |
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Definition
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Term
| what is one environment where rocks may be carried to great depths and heated? |
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Definition
| convergent plate boundaries where slabs of sediment-laden oceanic crust are being subducted. |
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Term
| what does the Gulf of Mexico exemplify? |
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Definition
| rocks may become deeply buried in large basins where gradual subsidence results in very thick accumulations of sediment. they are known to develop metamorphic conditions near the base of the pile. |
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Term
| what do continental collisions cause? |
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Definition
| they result in crustal thickening by folding and faulting, causing rocks to become deeply buried where elevated temperatures may trigger partial melting. |
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Term
| heat may also be transported from the mantle into even the shallowest layers of the crust by... |
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Definition
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Term
| anytime magma forms and buoyantly rises toward the surface, what occurs? |
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Definition
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Term
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Definition
| when magma intrudes relatively cool rocks at shallow depths, the host rock is "baked" |
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Term
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Definition
| with depth as the thickness of the overlying rock increases. |
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Term
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Definition
| where the forces are applied equally in all directions. |
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Term
| confining pressure causes... |
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Definition
| the spaces between mineral grains to close, producing a more compact rock having a greater density. further, at great depths, confing pressure may cause minerals to recrystalize into new minerals that display a more compact crystalline form. |
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Term
| confining pressure does NOT... |
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Definition
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Term
| where does directed pressure occur? |
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Definition
| at convergent plate boundaries where slabs of lithosphere collide. |
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Term
| when forces that deform rock are unequal in different directions, this is called...? |
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Definition
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Term
| what is the difference between confining pressure and differential stresses/directed pressure |
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Definition
| confinding pressure "squeezes" rock equally in all directions, differential stresses are greater in one direction than in others. |
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Term
| rocks subjected to differential stress are often.. |
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Definition
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Term
| along convergent plate boundaries, the greatest differential stress is directed.. |
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Definition
| roughly horizontal in the direction of plate motion. |
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Term
| in surface environments where temperatures are comparitively low, rocks are brittle and tend to fracture when... |
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Definition
| subjected to differential stress. |
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Term
| what kind of fluids are believed to play and important role in some types of metamorphism? |
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Definition
| fluids composed mainly of water and other volatile components, including carbon dioxide. |
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Term
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Definition
| the change in composition by interaction with fluids. |
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Term
| most metamorphic rocks have the same overall chemical composition as the parent rock from which they formed, except for the possible loss or acquisition of.... |
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Definition
| volatiles such as water and carbon dioxide. |
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Term
| texture is used to describe... |
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Definition
| the size, shape, and arrangement of grains within a rock. |
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Term
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Definition
| refers to any planar arrangement of mineral grains or structural features within a rock. |
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Term
| as rock units are folded and gernally shortened during metamorphism, elongated and platy minerals tend to... |
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Definition
| recrystallize perpendicular to the direction of maximum stress. |
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Term
| mechanisms that change the shapes of individual grains are especially important for the development of preferred orientations in rocks that contain minerals such as quartz, calcite, and olivine. When these minerals are stressed... |
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Definition
| they develop elongated grains that align in a direction parallel to maximum flattening. |
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Term
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Definition
| refers to closely spaced planar surfaces along which rocks split into thin, tabular slabs when hit with a hammer. |
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Term
| nonfoliated metamorphic rocks typically develop in... |
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Definition
| environments where deformation is minimal and the parent rocks are composed of minerals that exhibit equidimensional crystals, such as quartz or calcite. |
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Term
| porphyroblastic textures... |
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Definition
| develop in a wide range of rock types and metamorphic environments when minerals in the parent rock recrystallize to form new minerals. |
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Term
| most metamorphisms occur in the vicinity of... |
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Definition
| plate margins, and may are associated with igneous activity. |
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Term
| contact or thermal metamorphism occurs when.. |
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Definition
| rocks immediately surrounding a molten igneous body are "baked" and therefore altered from their original state. |
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Term
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Definition
| the zone where the altered rocks occur |
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Term
| what three things affect the size of the aureole produced |
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Definition
| the size of the magma body, the mineral composition of the host rock, and the availability of water. |
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