Structural Geology

Structural Geology - Structural Geology Objectives: At the...

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Structural Geology Objectives: At the end of this lab you will be o Familiar with the different types of rock deformation. o Be able to determine the forces and plate tectonic setting that cause deformation. o Become familiar with geologic maps. o Construct a geologic map. o Interpret the geologic structure from a geologic map. Introduction Structural geology is the study of rock deformation. This deformation can take place at a small scale (e.g., crushing of a mineral grain) or a large scale (e.g., plate boundaries). Structural geology is also one of the major features shown on geologic maps and cross sections and has significant economic value. Often the geologic structures are an important part in determining where oil and natural gas accumulates and may control the location ore bodies such as gold or silver. So, knowledge of structural geology is an important part of geology. The timing of rock deformation is also important. Geologists use relative, correlative and absolute age dating techniques to determine when faults have broken rocks during earthquakes or if a fold is old enough to trap oil or contain ore. The style of deformation and forces that caused the deformation is also valuable information for geologists to determine both the present and past (paleo) plate tectonic setting. Ductile, Elastic and Brittle Rocks deform in two main ways: ductile and brittle. Ductile deformation is bending without breaking. Brittle deformation is breaking of rocks. Think of pulling on a piece of
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chewing gum (chewed or unchewed). As you pull only a small amount on the gum, initially the gum bends and changes shape without breaking (ductile deformation). Rocks are ductile because they do not return to their original shape. Materials that deform elastically do not return to their original shape. Go back to the piece of gum. If you stretch the gum and then let go, the gum will not return to its original shape – meaning that the gum is not elastic. If you pull more, eventually cracks form in the gum and the gum breaks into two pieces (brittle deformation). Whether a material, including rocks, is ductile or brittle is dependent not only on the type of material, but also the temperature and force exerted on the material. Probably the most famous and tragic example of temperature dependent deformation is the space shuttle Challenger disaster. With the temperature above 40 degrees Fahrenheit, the O-rings on the Challenger fuel cells are ductile and maintain a tight seal. At temperatures below 40 degrees, the O-rings are brittle and crack when a force is exerted on them. Just like the O-rings, rocks buried deep in Earth experience higher temperatures and are ductile. Rocks close to Earth’s surface are cooler and deform by brittle deformation. The discussion above includes discussion of forces and changing shape. A force exerted
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This note was uploaded on 04/07/2008 for the course GEOLOGY 101 taught by Professor Wareham during the Spring '08 term at CSU Fullerton.

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Structural Geology - Structural Geology Objectives: At the...

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