chapter_15_powerpt.CM-11e

chapter_15_powerpt.CM-11e - Geologic Structures Physical...

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Steve Kadel, Glendale Community College Geologic Structures Physical Geology 11/e, Chapter 15
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Geologic Structures To date we have discussed how rock at the surface of Earth is affected by the atmosphere, hydrosphere, and the biosphere. We now turn our focus to processes in the solid Earth or geosphere. In this chapter we will explain How rocks respond to tectonic forces How geologists study the resulting geologic structures The purpose of this chapter is to Help you recognize certain geologic structures Understand the forces that caused them To thus determine the geologic history of an area
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Geologic Structures 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 rocks change shape and orientation in response to applied stress Structural geology is the study of the shapes, arrangement, and interrelationships of bedrock units and the forces that cause them Fig. 15.1 Folded and faulted sedimentary beds exposed in a road cut
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Fig. 15.1
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Cover 15. Rocks that once were horizontal have been contorted into folds during mountain building; Africa.
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Stress and Strain Stress is a force per unit area The three basic types of stress are compressive , tensional and shear Strain is a change in size or shape of a rock body in response to stress Structures produced are examples of strain that are indicative of the type of stress and its rate of application, as well the physical properties of the rock or sediment being stressed
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Fig. 15.2 The effects of compressional and tensional stresses
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Shear Stress Modeled By A Deck of Cards (From Tarbuck & Lutgens, 8e)
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Rock Responses to Stress and Strain Rocks behave as elastic , ductile or brittle materials depending on: amount and rate of stress application type of rock temperature and pressure If deformed materials return to 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
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Fig. 15.4 Fig. 15.4 Graph shows the behavior of rocks with increasing stress and strain
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A rock showing results of ductile behavior (From Tarbuck & Lutgens, 8e)
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This note was uploaded on 06/13/2011 for the course GEOL 1403 taught by Professor Mulcahey during the Spring '11 term at Lone Star College System.

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chapter_15_powerpt.CM-11e - Geologic Structures Physical...

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