LAB5_stereonets - Structural Geology Lab 5: I. Introduction...

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1 Structural Geology Lab 5: Introduction to Stereonets I. Graphical Representation of Lines and Planes in Structural Analysis A. Stereonets 1. Stereographic projection of lines and planes onto a circular grid or net a. Essentially taking a 3-D sphere and projecting it to a 2-D piece of paper (analogous to projecting the globe on world maps) b. Schmidt Net or Equal Area Net (1) Areas on the 3-D sphere are preserved as true on the 2-D projection of the net (a) Angles are not preserved, they become distorted (b) Most commonly used since structural problems require assessment of areal density distribution c. Wulff Net or Stereographic Net (1) Areas are not preserved, but angle are. 2. Schmidt Net Basics a. Primitive Circle = outline of sphere b. North-South and East-West Reference Lines c. Plane Projection (1) Lower Hemisphere Projections of Planes (a) Great circles formed by intersection of inclined plane with lower hemisphere of the reference sphere (b) Great circles are plotted on the stereonet i) horizontal plane: dip = 0, plots as great circle on primitive circle of net ii) vertical plane: dip = 90, plots as straight line passing through center
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(2) Lower Hemisphere Projections of lines (a) Lines plot as points of intersection between line and lower hemisphere (b) horizontal lines plot as points on outer primitive circle (c) vertical lines plot as points at center of net. d. Poles to planes (1) Imagine a line drawn perpendicular to plane, passing to lower hemisphere of reference sphere (a) will plot as point on stereonet e. Techniques for Plotting Planes, Lines and Poles to Planes on the Schmidt Net (1) Read detailed instructions on p. 61 and 62 of lab manual II. Stereonets Revisited A. Remember. .. on Schmidt Net (Equal Area Projection) 1. Planes plot as great circles a. given strike and dip of planes, plot as great circles projected to the southern hemisphere of the stereo projection b. types of planes in structural geology (1) bedding planes (2) fault planes (3) joints/fracture planes (4) dikes, sheet intrusives (5) quarry walls, road cuts (6) veins, mineralized zones (7) foliations: planar rock fabric Class Example 1: Draw the great circle projections of the following two planes: Strike = N.38W Dip = 65 SW, Strike = N.60E Dip = 78 NW
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This note was uploaded on 10/02/2011 for the course GEOLOGY 406 taught by Professor Taylor during the Spring '11 term at Western Oregon University.

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LAB5_stereonets - Structural Geology Lab 5: I. Introduction...

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