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| rocks that crystallized from molten material |
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| molten rock within the earth; fluid mixture of liquid, solid crystal, and dissolved gases |
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| molten rock that flows above ground |
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| Crystallizes at the Earth's surface from lave (poor in silica) |
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| Crystallizes undergound (poor in silica). |
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| Silica-rich rocks that crystallize under the ground |
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| silica-rich rocks that crystallize at the Earth's surface from lave |
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| Describe magma's cooling process. |
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| Since rocks do not entirely melt at one teperature and pressure, rocks partially melt, with the amont of melt relative to remaining minerals increasing as melting proceeds. Composition changes as minerals of different compositionn begin to melt and contribute different elements to the maga. As it cools, it crystallizes, new bonds form between ions, and tiny crystals begin to appear. As cooling progresses, different minerals crystallize out of the magma at different temperatures. Composition again changes as each crystallized mineral is removed from the magma. Ultimatey, entire body becomes solidified. |
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| Some minerals remain solid (minerals with higher melting points) with the melted portion (the minerals with lower melting points) may flow away as magma |
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| Which factors control the melting of rocks and the creation of magmas? |
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Definition
| heat, pressure, and the amount of water in the rocks |
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| What is the geothermal gradient? |
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Definition
| temperatures in the earth increase with depth |
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| As pressure increases, the temperature at which rocks melt ________. |
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| if the pressure on a rock is removed, the rocks are hot and it leads to a condition of high temperature and low pressure so it partially melts the rocks of the Earth's mantle to produce basaltic magma beneath divergent plate boundaries |
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| Water _____ the melting point of rocks. |
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| Why does water lower the melting point of rocks? |
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| destablizes crystal structures within rock's minerals, promoting breaking of their bonds and lowering it |
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| Hot rocks (magma) _____ relative to cold, solid rocks. |
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| What controls magma's ability to rise |
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| its fluidity, which is governed by its composition and temperature; increased heat=increased fluidity |
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Term
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| a fluid's resistance to flow (opposite of fluidity) |
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| Viscosity ____ with decreasing temperature and _____ with increasing temperature. |
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| Viscosity _____ with silica content. |
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| increases (silica-rich magma is relativel cool; low-silica, basaltic magmas are more likely to rise to the surface and erupt than high silica lavas [rhyolite]) |
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| What does Bowen's reaction series do? |
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Definition
| shows how hypothetically the complete range of the most common igneous-rock compositions could be produced by the same basaltic lava by fractional crystallization; scientists now know does not account for all igneous rocks |
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| When magma is cooling, what happens to crystals that are denser than the surrounding liquid? |
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Definition
| they may sink to the bottom of the magma chamber and become buried by later-settling crystals |
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| fractional crystallization |
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Definition
| a single parent magma can produce a variety of igneous rocks of different compositions |
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| Name two ways besides fractional crystallization that igneous rocks can be formed. |
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Definition
| further melting of already-formed oceanic or continental crust; some mixing of magmas of different compositions |
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| two or more different bodies of magma flow together to form a magma of hybrid composition |
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| How are igneous rocks classfied? |
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| by the size of the mineral crystals in the rock and the rock's composition (texture) which is determined by the rate at which magma or lava cools |
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| the size and shshape of a rock's minerals |
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| intrusive rocks; when we can see the crystals clearly |
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| another name for intrusive rocks |
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| igenous rocks that develop at relatively low temperature from magmas with a high proportion of water; ions move freely enabling crystals to grow unusually large |
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| extrusive rocks; crystals are so small they can barely be seen by the naked eye |
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| another name for extrusive rocks |
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| large crystals are surrounded by regions with much smaller or even invisible grains; form as a result of slow cooling followed by rapid cooling |
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| lava erupts into the air or flows into a body of water and cools so quickly that its ions do not form any crystals at all |
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| name two types of volcanic glass |
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| How are igneous rocks classified based on their silica (oxygen and silicon) contnet? |
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Definition
| ultramafic, mafic, intermediate, felsic |
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| _____ rocks have the smallest proportion of silica to other ions, while _____ rocks have the largest. |
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| What elements do mafic rocks contain? |
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| What is the most common ultramafic rock? |
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Definition
| peridotite which is not technically an igneous rock bc it did not crystallize from magma but they are the dominant rock in the Earth's mantle and they form basalt |
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| What is the silica content of mafic rocks? |
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| magma containing the same mix of minerals as basalt but that cools underground and is basalt's plutonic equivalent, coarse-grained, phaneritic |
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| What is the silica-content of intermediate igneous rocks? |
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Definition
| 55-65%...consists of iron and magnesium silicates like pyroxene and amphibole |
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| Name an intermediate igneous rock and describe its texture. |
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| Andesite, porphyritic, world's most abundant type of volcanic rock |
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| What was andesite named for? |
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Definition
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| What is andesite's plutonic equivalent? |
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| What is the silica content of felsic rocks? |
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| What is the most common felsic igneous rock? |
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Definition
| the plutonic rock granite |
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| What is the result when rising magma forces overlying rocks to bulge upward? |
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Definition
| they form an intrusion within other rocks known as a diapir |
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| moving magma incorporates rock as it rises, some of these melt and assimilate into the magma, unmelted rocks are carried within the magma; when it solidifies, we can see xenoliths, which are the foreign rocks |
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| subsurface intrusive igneous forms created by solidified underground magma |
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| What is another term for preexisting rock? |
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| Where do concordant plutons lie? |
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| parallel to layers of country rock |
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| Where do discordant plutons lie? |
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| cut across layers of country rock |
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| slablike intrusions of igneous rocks that are broader than they are thick, like a table top |
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| When does a tabular pluton form? |
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| if magma flows into a relatively thin fracture in country rock, or pushed into the space between sedimentary rock layers |
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| a discordant tabular pluton that cuts across preexisting rocks; generally steeply inclined or nearly vertical, suggesting that they formed from rising magma |
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| vertical pluton of hard, erosion-resistant volcanic rock that remains in what was once a volcano's central magma pathway |
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| products of deep-seated, extremely gaseous, highly explosive eruptions which contain highly fragmented chunks of lava mixed with rock ripped from the vent wall and masses of rock from deep crust and mantle |
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| a concordant tabular pluton which is produced when intruding magma enters a space between layers of rock, sometimes melting and incorporating adjacent sedimentary material |
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| thick viscous magma intrudes between two parallel layers of rock and lifts the overlying one, it cools to form this mushroom-shaped concordant pluton; many are granitic |
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| saucer-shaped concordant plutons that sag downward...probably produced when mafic magma rises from a deep magma source |
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| massive plutons with surface areas of 100 km squared or more that typically form from intermediate to high viscosity magmas (diorite and granite) |
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| Where do most igneous rocks form? |
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| At or near plate boundaries |
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MORBs
eruptions at oceanic divergent boundaries produce these rocks; solid mantle peridotite rises up and partially melts creating the basalitc magma that then rises and solidifies as ocean crusts; 20% erupts on seafloor |
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| Define oceanic island basalts. |
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| OIBs. Found atop hot spots that lie above deep-mantle heat sources; originate from deep part of mantle; we can see eruptions of OIBs in Hawaii |
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| Where are some places that continental form? |
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Definition
| Partial melting of hot plumes of mantle |
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| What are the primary igneous products of subducting oceanic plates? |
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Definition
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| Name one of the factors that combine to produce igneous rocks of an intermediate composition in a subduction zone. |
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Definition
| water (lowers melting point of rocks) |
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| Which planets of the planets have experienced partial melting? |
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Definition
| terrestrial planets (Mercury, Venus, Earth, and Mars), the Moon, and Io (one of Jupiter's moons) |
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| Name the geological provinces on the Moon. |
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| the highlands and the maria |
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| What are the lunar maria or seas actually made up of instead of water? |
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| What does the relative lack of younger igneous rocks on the Moon's surface today suggest? |
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| its interior is no longer hot enough to produce new magmas |
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| Name somme practical uses of igneous rocks |
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Definition
| gemstones, precious metals, crushed basalt for road construction, decorative building stones, kitchen counter tops, emeralds, topazes, diamonds occur in igneous rock |
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| heat driven subterranean fluids that percolates down through an igneous region and concentrates valuable minerals; converts to steam, then invades surrounding rocks and dissolves soluble minerals in them |
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