105Lab08Structure - Geol 105 Lab 8 Geologic Structure and...

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Unformatted text preview: Geol 105 Lab 8 Geologic Structure and Deformation week of March 5-9, 2012 INTRODUCTION Deformation = all changes in position, shape, and/or volume of a rock body Ductile deformation. From: http://ic.ucsc.edu/~casey/eart150/Lectures/1classIntro/1classintro.html Watch the movie, “Kitchen Geology -- Brittle/Ductile Deformation.” Answer the following: (1) What is the difference between brittle and ductile deformation? (you may use examples) (2) List the 3 controls that determine if you will have brittle or ductile deformation. 1 of 5 STATION 1. SILLY PUTTY BRITTLE FAILURE or DUCTILE DEFORMATION? In near-surface environments, where the confining pressure and temperature is relatively low, rocks are described as brittle because they fracture when deformed. In contrast, at great depths confining pressures and temperatures are high, and rocks become ductile and flow rather than fracture. Remember - One key factor we cannot duplicate in the laboratory is geologic time. If stress is applied quickly, as with a hammer, rocks tend to fracture. If stress is applied over an extended period, rocks may deform like a fluid. Question 1. GIVE IT A TRY! a. BREAK (snap) the silly putty with your hands – is this ductile deformation or brittle failure? b. SLOWLY PULL the silly putty like taffy – is this ductile deformation or brittle failure? c. As instructed by your T.A., compare the silly putty to the chocolate bars. Write a description. Question 2. a. What is your interpretation of samples # 56 (3 rocks) and # 57? b. Identify sample # 57 as igneous, sedimentary, or metamorphic. STATION 2. FAULTS Fractures in the crust along which displacement has occurred. for more info -- http://www.iris.edu/gifs/animations/faults.htm Question 3. MODEL A - FAULT BLOCK MOUNTAINS scale 1 inch = 3 miles a. Find regions 54 and 55 on Model A. The relative motion of these two regional blocks (up and down) has created what is known as "basin and range" topography." 2 of 5 b. Regional block 54 has moved _____________ (downwards or upwards) relative to regional block 55. c. What is the stress type? (see lab manual, page 233) d. What type of fault? e. What is the topographic (surface expression) evidence for a fault? In other words, if you were walking across this landscape, what features might indicate fault movement? (HINT - notice feature X) for your consideration... The features numbered as 46 are alluvial fans - formed as rivers emerge from mountains onto flatter plains, depositing broad, fan-shaped piles of sediment. Question 4. MODEL B a. What type of fault is this? What is the stress type? b. How much displacement? (measure from X to Y with a ruler, convert to feet using scale on block) Question 5. HAND SAMPLE # 48 Evidence for movement along a fault can also be found in rock hand samples. Examine sample # 48 (two rocks from two different areas). What feature indicates rocks have slid past one another? STATION 3. FOLDS Upward or downward bends of rock layers. Antiforms (anticlines) = "upfolds" or convex folds Synforms (synclines) = "downfolds" or concave folds Question 6. a. SATELLITE VIEW OF PENNSYLVANIA Which region - A, B, C - illustrates tightly folded rock layers? scale 1 inch ~ 8 miles b. Lab manual page 245. Complete block diagrams A and B. Be sure to name the structures. 3 of 5 Question 7. MODEL E - FOLDED MOUNTAINS scale 1 inch = 3 miles a. What is the dip direction (such as north, south, southeast, etc.) of the rock layer at Point P? b. At Point R? c. Find the number 141 and 142 on the cross-section view of the model. Name the type of fold: #141 _______________________ #142 _______________________ Question 8. GEOLOGIC MAP - WILLIAMSVILLE QUADRANGLE, VA scale 1 inch = 1 mile a. Find the line B - to - B' on the geologic map, and the corresponding cross- section. You are standing on Little Mt., and want to join your friends over at Jack Mt. To do so, you need to walk across how many rock units? Remember - count only those exposed at the surface. This is a fold, so you might walk over the same unit of rocks more than once! b. What type of fold is this? Question 9. TOPOGRAPHIC EXPRESSION OF FOLDS LOVELAND, CO topo and plastic relief map scale 1 inch = 1 mile Folds are also expressed on topographic maps (remember topo maps illustrate the surface features; the "ups" and "downs" of the ground). Find “feature S” on the Loveland maps, and examine the cross-section. Compare to Fig. 10.7-D on page 234 of lab manual. What type of fold is this? Question 10. ROCK SAMPLES Examine the sample # 7. What has happened to these rocks since their original deposition as horizontal layers? (recall Nicholas Steno's principle of original horizontality) 4 of 5 STATION 4. MODEL Follow the instructions of your T.A., for using the model. Make a sketch (cross-section view) in the space below of the result: 1. Number the layers in relative age order (using #1 as the oldest) as best you can. 2. Label the folds and faults using letters (a, b, c, etc.). Try to determine the type of fold(s) (for example, anticline or syncline), and the type of fault (for example, reverse or normal), and write that information below/beside the sketch. 3. Compare your model to the posters and to the various stations of folds and faults – how is this model similar? 5 of 5 ...
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