Study Guide Exam 3

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South Texas College *

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1403

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Geology

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Apr 3, 2024

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docx

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Physical Geology Study Guide Exam 3 Answer the following questions: 1) Define Metamorphic Rock. Where Metamorphism generally occur? Metamorphic Rocks form by the alteration of preexisting rock because of pressure, high temperature and/or chemically active fluids Metamorphism occurs well below the surface of the earth but at shallower depths and temperatures than would cause rocks to melt. 2) Describe Metamorphism. What are the three agents of metamorphism? What types of rock can be metamorphosed? Metamorphism conditions within the earth result in the changing of the texture and mineral content of a solid rock without melting it. Any type of rock may be metamorphosed- igneous, sedimentary, or even metamorphic. 3) Define Parent Rock. Why are parent rocks important? A Parent rock is the original rock before the metamorphism takes place. In addition to heat pressure and fluid activity, the composition of the parent rock helps determine what metamorphic rock forms. 4) Describe what can be changed during the process of metamorphism. Process of Metamorphism can change both the texture and the mineral composition of the parent rock 5) What is the parent rock for marble? Describe what occurs when this metamorphosis takes place. Does the mineral content change during this process? What happens to fossils? Limestone is the Parent Rock of Marble. When limestone is metamorphosed into marble the crystal size of it changes but not the chemical composition it will recrystallize usually forming larger crystals. 6) What is the parent rock for quartzite? Describe what occurs when this metamorphosis takes place. Does the mineral content change during this process? Why is quartzite a very resistant rock? Quartz Sandstone is the parent rock of Quartzite. Both sandstone and quartzite are composed of SiO2. When sufficient heat and pressure are applied to a sandstone the grain fuses together to form a very resistant rock quartzite. 7) Describe what happens to shale as it undergoes the process of metamorphism. What rocks are formed at low grade metamorphism, medium grade metamorphism, and high-grade metamorphism? Does the mineral content change during this process? Which of these metamorphic rocks has the finest grain size and which of these metamorphic rocks has the coarsest grain size? When shale undergoes metamorphism, it creates new minerals in response to the escalated heat and pressure conditions. Slate is formed at low grade, Schrist at medium,
and Gneiss at high grade metamorphism. The content does change during the process. Slate has the finest grain size, while Gneiss has the coarset grain size. 8) Can slate be formed from any parent rock? Explain why or why not. No, It can only be made from shale or mudstone because every rock has a rock from which it was formed (parent rock). 9) What minerals are almost exclusively found in metamorphic rocks? Kyanite, Sillimanite, and some Garnett. 10) List and describe (in detail) the three basic types of metamorphism. Contact - Occurs when magma comes into direct contact with the parent rock • Changes in the parent rock are primarily due to very high temperatures but not increased pressures • Immediately next to the magma intense metamorphism results in the formation of coarse grained crystals • Moving away from the magma the results in the formation of coarse grained crystals  • Moving away from the magma the resulting rock becomes progressively finer grained • A contact metamorphic zone occurs when a parent rock is intruded by molten magma Sheer - Results from the intense pressures that exist along active fault zones where rock units slide past each other • Mechanical deformation and recrystallization of the minerals result from the heat pressure and movement of fluids as rock units slide or shear past one another Regional - Affects extremely large areas and is caused by a combination of both high temperature and high pressure • Most areas that are affected by regional metamorphism are areas undergoing intense deformation due to mountain building processes 11) Describe how metamorphic rocks are classified. Describe the two types of textures. Metamorphic rocks are classified by texture and mineral composition. Textures • Foliated- rock exhibits layering or color banding • Nonfoliated - rock is nearly uniform throughout 12) Describe how and where foliation occurs. The enormous pressure that accompanies regional metamorphism causes the newly formed mineral grains to align themselves in a distinctly parallel arrangement. Only rocks that are metamorphosed under intense pressure will exhibit foliation. Metamorphic rocks that form entirely due to high temperatures will not have foliation. 13) Describe the progressive patterns of foliation that develop in metamorphosed shale. • Slaty cleavage- develops when a shale undergoes mild metamorphism
• Schistosity - Found in foliated metamorphic rocks with larger, visible crystals. Generally, the result of the parallel arrangement of platy (micas) and ellipsoidal mineral grain. • Gneissic - layering forms under intense regional metamorphism and displays color banding 14) Create a table for the Foliated Rocks that contains Parent Rock, Metamorphic Rock, Key Minerals, and Characteristics. 15) Describe why nonfoliated rocks are nonfoliated. Rocks subjected to uniform pressure from all sides or lacking minerals with distinctive growth habits will not be foliated. The chemical composition of nonfoliate rocks is more consistent than foliated rocks. 16) Create a table for the Nonfoliated Rocks that contains Parent Rock, Metamorphic Rock, Key Minerals, and Characteristics. 17) List and describe the factors that control metamorphic rock characteristics. Mineral Composition of the Parent Rock : The initial rock before metamorphism determines the minerals present, affecting their stability during changes in temperature and pressure. Temperature : Influences mineral stability; certain minerals change or recrystallize at different temperature ranges. Pressure : Alters mineral stability and rock texture. Varying pressures lead to denser rocks and may induce foliation. Fluids (Primarily Water) : Facilitate mineral and ion transfer between and within rocks, expediting metamorphic reactions and aiding in element transportation. Time : Metamorphic processes occur slowly over vast timescales, often associated with slow tectonic activities, such as mountain formation and erosion. 18) Describe the hydrothermal processes associated with metamorphism. What minerals are often associated with hydrothermal veins? •Metamorphism: Water transmits pre-existing ions between grain •Metallic: ore deposits often form this way The minerals often associated with hydrothermal veins include quartz, calcite, sulfides (like pyrite, chalcopyrite, galena, and sphalerite), barite, and fluorite. 19) Define structural geology and geologic structures. Structural geology is the study of the shapes arrangement and interrelationships of rock units and the forces that cause them. Geologic structures are dynamically produced patterns or arrangements of rock or sediment that result from and give information about forces within the earth. Produced as rock change shape and orientation in response to applied stress 20) Define stress. What are the three types of stress and at what type of plate boundary do these occur?
Stress in geology refers to the force applied to a rock per unit area. It's categorized into three main types: Compressive Stress : Forces acting to squeeze or shorten a rock. This stress occurs at convergent plate boundaries, where tectonic plates move toward each other. Tensile Stress : Forces pulling or stretching a rock apart. This stress occurs at divergent plate boundaries, where tectonic plates move away from each other. Shear Stress : Forces causing rocks to slide past each other horizontally in opposite directions. This stress occurs at transform plate boundaries, where tectonic plates slide past each other horizontally. 21) Describe how rocks respond to stress and what is their response dependent upon? Rocks behave as elastic, ductile, or brittle materials depending on: • Amount and rate of stress application • Types of rocks • Temperature and pressure If deformed materials return to their original shape after stress removal, they are behaving elastically. However, once the stress exceeds the elastic limit of a rock, it deforms permanently • Ductile deformation involves bending plastically • Brittle deformation involves fracturing. 22) How are rock structures determined, how are they represented on a map, and what are some of the common structures? Rock structures are determined on the ground by geologists observing rock outcrops. Outcrops are placed where bedrock is exposed at the surface. Geologic maps use standardized symbols and patterns to represent rock types and geologic structures, such as tilted beds, joints, faults, and folds 23) Describe dip and strike. How are they used? Timed beds, joints, and faults are planar features whose orientation is described by their strike and dip • Strike is the compass direction of a line formed by the intersection of an inclined plane with a horizontal plane • Dip is the direction and angle from horizontal in which a plane is oriented 24) What are folds, axial plane, hinge line, and limb? Describe the two types of horizontal folds. • Folds are wavelike bends in layered rocks. Represent rock strained in a ductile manner, usually under compression  • The axial plane do fold into its limbs  • The hinge line (or axis) of the fold is the surface trace of an axial plane. 25) What are plunging folds? Describe the types.
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