Lab 10

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San Diego State University *

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CHEM 200

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Geology

Date

Apr 3, 2024

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pdf

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9

Uploaded by ColonelHareMaster108

Name: m%r;m Jalnnzon Structural Geology Introduction Structural geology is a subdiscipline of geology that investigates rock deformation (bending and breaking or folding and faulting) on both the small (microscopic) and .Iarge (mountains, oceans, and continents) scale. For the purposes of this lab we are going to focus on the large-scale structural features associated with folding and faulting of rocks and their identification. Structural geologists (you) seek to use their observations a_t thg surface of the Earth to interpret what the structures look like below the surface, which is hard to observe directly. In this lab we will discuss two different ways of looking at the Earth, map view and cross-sectional view (figure 1). Map view is what you see when you look straight down onto the surface of the Earth or as in figure 1A the top of a cake. Cross sectional view is what the crust looks like if you were to take a slice out of the Earth or cake (figure 1B). We use cross sections to project the structures we observe at the Earth’s surface into the subsurface. A. Map view D = 3 £ ) " o i £ - » 4 & “3 ] 3 : : A B. Cross sectional view 4! . \ E P : youngest ¥ = ¥ })’ N 4 layers b : j}‘ " B - oldest Figure 1: A. Map view of the top of a cake as an analogy for map view of the Earth. B. A slice of the cake in A as an example of cross-sectional view. Without cross sections we would not have a way to project what we observe on the surface of the Earth into the subsurface. Notice that the slice of cake has 5 horizontal layers and the oldest layer is at the bottom and that the youngest layer is at the top. Strike and Dip In our discussion of geologic time in lab 7 we learned six principles of relative dating, one being original horizontality. The idea that all rocks on the Earth are originally deposited in essentially horizontal layers and that if the rocks are currently not horizontal then some younger event must have disturbed their original horizontality.
time the topographic high will erode to a flat surface leaving the youngest unjl 3 ir_l the (.'cnlcr of the s);nclinj:. Rllrlkc and dip symbols with dips towards the center of the fold indicate the limbs of lhc‘lnld dip towards each other. Along the axis of the fold is the map symbol for a syncline. Below is a fold found along the northwestern coast of Africa near Algeria. Use this screenshot from Google Earth to answer questions 1 - 4. } g S ¢ g g 3 i i = > G g . e il e T 2%y e T | e e ————— e | > \§v . = | % «foi Mg A% ks = AN ){ . 9 ? | G % 2t . - " FONEAE 1. By examining the dip directions on the strike and dip symbols, which direction is the north limb (upper half) dipping (north, south, east, or west)? What about the south limb (lower half)? No HWmb 1% d|f>pm;j, Nov ¥ . SouHa limbp > ulpr,m\a soutn., 2. What is the dip direction on either side of the fold axis (white line)? Using a pen or pencil, draw an arrow on either side of the fold axis indicating the dip direction. Refer to figures 3C and 4C for examples. SR, )Hydm ot reenshet 3. Based on your answers to questions 1 and 2 what type of fold is this, syncline or anticline? anAcliing
4. Would the limbs on this fold form a topographic high or a topographic low? Topograpue i '(«]'m Below is another fold found along the central portion of Iran. Use this screenshot from Google Earth to answer questions 5 - 8. 1km Ly i ! NN LT oo LS MGt 5. By examining the dip directions on the strike and dip symbols, which direction is the east limb (upper half) dipping (north, south, east, or west)? What about the west limb (lower half)? East |imls E S| PPN south. Weat limbh ul,fipmaf norHn, 6. What is the dip direction on either side of the fold axis (black line)? Using a pen or pencil, draw an arrow on either side of the fold axis indicating the dip direction. Refer to figures 3C and 4C for examples. iqum@&,6%4h SIS 7. Based on your answers to questions 1 and 2 what type of fold is this, syncline or anticline? ‘gu{)y\(flw&/ 8. Would the limbs on this fold form a topographic high or a topographic low? H)PQ'AODYQPH\Q (Do 5
: in what we call As you may have imagined anticlines and synclines Oflendform;fig:;hfirrming together. a fold system where you have several folds, a_ntlclmes an s'yn ot outorop or hillside These fold systems can occur at very small m‘|crosco>p|c sca es,Shot o okl plstsl TS scale, and also at large continental scales. Figure Sis a screeZ| 8. Ite important to of a series of folds along the northwestern coast of Africa near/ g e How you answer mention that these folds are plunging, but this fact has no beaAnn? . Fold symbols the questions below. A plunging fold dips into the Earth along its lengtn. i i d di have been drawn along the axis of several folds along with several strike and dip symbols. Use figure 5 to answer questions 9 - 12. ] | Fold G R ‘ Bkl A 1‘ S\ ‘\ e - ‘ g f . A ; i X Y / . y { g RO T‘K ——— ,f y i 3 ¥ 4 " t A | f ASes ™ \ 2 ] | v o / Wy | A A & A T [ — Fold A Y / |4 PR o TN DR Mg N 3oiRAL, 4| Figure 5. Plunging fold system located along the northwestern coast of Africa near Algeria. Fold axes are outlined and labeled with map symbols, as are strike and dip symbols. Line DE is for question 12, 9. How many anticlines are in figure 5? i 10. How many synclines are in figure 5? 3 11. Based on the fold pattern you observe in figure 5 what type of fold would you hypothesize to be located to the north of fold G? And similarly, to the south of fold A? | 1"?} poHesize HWrt would e o mncling, folon loceta) To Hhe norta of fold & AND 200 o fold B
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