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Ch 6 ReveiwQuestions
Question | Answer |
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how is the process of freezing magma similar to that of freezing water? how is it different? | They are similar in that they transform a liquid into a solid, they are different because water freezes at 0º C and magma freezes at high temperatures (650º |
What is the source of heat in the Earth? How did the first igneous rocks on the planet form? | The source of heat on earth is its core. The first igneous rock was formed as a result of Mar sized object colliding with earth, making earth so hot and partially molten on its surface |
Describe 3 processes that are responsible for the formation of magmas? | Melting as a result of a decrease in pressure, melting as a result of the addition of volatiles, melting as a result of heat transfers from rising magma |
Why are there so many different types of magmas? | because the proportion are different as far as composition |
Why do magmas rise from depth to the surface of earth? | first magmas rises because its less dense than the surrounding rock, thus more buoyant. Second it rises because of the weight of the overlaying rock creates pressure at the depths which literally squeezes the magma upward |
What factors control the viscosity of a melt? | magmas viscosity depends on temperature, volatile content, and silica content |
What factors control the cooling of magma within the crust? | the depth of the intrusion, the shape and size of the magma body, the presence of circulation groundwater |
How does grain size reflect the cooling time of magma? | a melt that cools rapidly forms fine grain (aphanitic) rock, melts that cool slowly forms a coarse grained (phanaretic) rock. |
What does the mixture of grain size in a porphyritic igneous rock indicate about its cooling history? | This indicates that some cooled slowly at depth, so that large phenocrysts form, then the melt erupted and the remainder cools quickly. |
Describe the ways magmas are produced in subduction zones? | When the mantle subducts, volatile compounds separate into the athenosphere, the addition of volatiles causes the ultramafic rock to partially melt to produce basaultic magma. Some gets trapped from reaching the surface in magma chambers beep in the surf |
What processes in the mantle may be responsible for causeing hotspot volcanoes to form? | Researchers think that many hot spot volcanoes form above plumes of hot mantle rock that rise from the core mantle boundary. |
Describe how magmas are produced at continental rifts? | |
What is a large igneous province? How might the formation of of LIPs have affected the earths systems? | provinces with large volumes of igneous rock. LIPs have a profound affect on the environment and any changes in ocean chemistry, global temperature, and atmospheric clarity triggered by an LIP eruption could even cause the extinction of a life form |
Why does melting take place between the axis of mid ocean ridges? |