Geo – Chapter 4

Flashcard maker : Charles Clay
What are the three main rock types and what processes (melting, weathering, and metamorphism) cause them to form? Think rock cycle.
IGNEOUS; volcanoes, freezing or slitifcation.
SEDIMENTARY; pressure pushing on all the materials pushing them together, precipitation of water solutions.
METAMORPHIC: changes because of environmental factors; occurs in a solid state.
What is the most abundent rock in the oceanic crust?
What is the most abundant rock type in the Earth’s crust? What is the most abundant rock type we find on the land surface?
Igneous; crust.
Sedimentary; land surface.
How are igneous rocks formed? What are the two types of igneous rocks? How does the location where they cool affect the speed of cooling and crystal size?
They are formed by volcanic eruptions, creating lava flows, and then it hardening. 1. Extrusive; volcanic eruptions ->cools faster, above ground is cooler. 2. intrusive; starts under the ground and gets pushes upwards -> crystal size is smaller, so it’s cooler so it’s more likely to break.
Understand and be able to use (or recognize in slides) the following terms: plutonic, volcanic, intrusive, extrusive, aphanitic, phaneritic, porphyritic, pegmatitic, glassy, vesicular, pyroclastic. What does each texture indicate about the rate of cooling?
plutonic: changes in magma during cooling.
volcanic: eruption.
intrusive: cooling under earth’s surface, magma gets away from the magma chamber.
extrusive: cooling above earth’s surface.
aphanitic: fine-grained crystals.
phaneritic: bigger grained crystals.
porphyritic: larger crystals surrounded by finer crystals.
pegmatitic: coarse grained, cools slower.
glassy: igneous rocks, felsic, high concentration of silica inhibits early growth of crystals.
vesicular: rocks that have bubbles with the open holes within then. i.e. Hummus.
pyroclastic: fragments that are coming out of volcanoes and then consolidate.
Where (in terms of plate tectonic settings) are magmas generated? How do rocks melt (3 ways)? Give an example of a plate tectonic setting that corresponds to each type of melting. What type of magma is produced in Hawaii, Yellowstone, Cascades, Andes?
Magma turns into Igneous Rocks. WHERE: develop upon volcanoes apon oceanic trenches; hot spots, within continental rifts, or along ocean ridges. They can melt up decompression melting (opening of crust allowing rocks to melt, lowering the temperature), heat transfer (melting of crust), or addition of volatiles.
Hot spots can cause magma to form away from plate boundaries. How does the type of melted crust affect the composition of the magma?
…pressure prevents melting, decrease in pressure permits melting. as crust heats up and melts, pressure decreases so more of the mantle magma melts. Melting is caused by a)a decrease in pressure b)by addition of volatiles c) as a result of heat transfer from rising magma. at a volcano, which is a hot spot), the increase in rising magma( from its own \”buoyancy it rises and heat rising etc, all causes such pressure at the earth’s crust that it explodes out like soda from a bottle. continental hot spot causes an effusive and explosive eruption (a volcano).
Igneous rocks are classified based on silica composition. What are the four composition groups? What is the relative melting temperature order for the compositional groups? How do Fe-Mg and Si-Na-K vary in the groups? What minerals would you expect to see in rocks created from Mafic and Felsic compositions? See Figure 4.13 (pg. 108) in the text for help.
…the 4 groups are felsic or silicic magma (66-76%); intermediate magma (52-66%); mafic magma (45-52%);and ultramafic magma (38-45%). the 4 vary in the amounts of silica as compared to the magnesium and iron oxides contained in them. you would expect to see iron in both mafic and felsic because fic means iron. ma means magnesium so expect to see magnesium in mafic.
How does viscosity vary among the compositional groups? How is this related to the magma temperature and magma composition?
…viscosity means resistance to flow. it affects the speed of lava.. low viscosity flows more easily. high viscosity flows more slowly. viscosity depends on temperature, content of volatiles (additives like water and gases), and silica content. hotter magma is less viscous.more volatiles are less viscous than dry. mafic is less viscous than feltic. viscosity is like, syrup flows slower than water, cos its thicker and heavier. so viscosity means, resistant to flowing.
• From magma to igneous rock: What process is involved? What is fractional crystallization? Why does this change the composition of the remaining magma?
• What are other processes that affect magma or igneous rock composition?
• From magma to igneous rock: What process is involved? What is fractional crystallization? Why does this change the composition of the remaining magma?
• What are other processes that affect magma or igneous rock composition?
.the cooling time of magma . 3 factors control the cooling time; the depth of intrusion, the shape and size of the magma body, the presence of circulating ground water. exposure to air, and underground effects above. fractional crystallization is when during freezing of molten rock, cooling takes place, and many minerals form. because some crystallize first, are dense and sink, the process of fractional crystallization takes place, where sequential crystal formation happens. (some cool first, some later) this process progressively extracts iron and magnesium from the magma. the remaining magma, cools later, rises up later, and has a different composition of iron magnesium and silicates. other processes that affect it are freezing, fractional crystallization, earthquakes and underground pressure, pressure from above at the earth crust, temperatures, adding of volatiles (like water) and plate techtonics.
• Be able to identify the different forms of intrusions (sill, dike, batholith: pages 102-105 in textbook) for slides and multiple choice questions. Where do they form? How does magma make its way to the surface?
.sills are parallel to pre existing layers. an intrusion that injects parallel to layering. dikes cut across pre existing layers. they stick up, like a dutch dike. batholiths are an immense mass of igneous rockl the intrusion of numerous plutons in an immense area. like the sierra nevada mountains in california is a batholith. Dikes form in regions where the crust is stretched horizontally, such as a rift. sills occur near the surface of the earth. Batholiths of plutons occur with the process of stoping, when magma assimilates wall rock and pieces break off. Magma rises for two reasons. 1st is buoyancy drives magma upward bec. it is less dense than surrounding rock. 2nd is magma rises bec. the weight of over lying rock creates pressure at depth that literally squeezes magma upwards, like if you step in mud barefoot, the mud squishes up between your toes.
Chapter 5 – Be able to discuss all of the following: Mount St. Helens, Columbia River Basalts, Mt. Rainier, and Hawaii in terms of the dominant landform(s), eruptive style, composition of magma/lava, viscosity of magma/lava, type of plate boundary and any other special textures or volcanic hazards associated with each.

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