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09_structure_09_post - 09: Geologic Structures,...

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Unformatted text preview: 09: Geologic Structures, Deformation, and Mountains What is deformation? Change in location, change in orientation, change in size and/or change in shape Folds in Canadian Rockies. Photo: P.L. Kresan Fault offset, 1976 Guatemala earthquake. Photo: USGS Fig. 11.4 Structure: 1 Why is this important? • Folds & faults provide traps for hydrocarbons Structure: 2 Why is this important? • Groundwater & pollution migrate along fractures Anticline in Monterey Formation, Soto Street, Los Angeles. Photo: M.N. Bramlette, Bramlette, U.S.G.S. Photo: J.H. Ramsay Structure: 3 Structure: 4 Types of structures Why is this important? • Fold: bend or warp • Earthquakes (& tsunamis) result from motion on faults Fault scarp from 1983 Borah Peak, ID, earthquake. Photo: M.H. Anders Fault scarp from 1980 El Asnam, Algeria, earthquake. Asnam, Photo: H.C. Shah Structure: 5 Structure: 6 Types of folds Anticline: upfold that contains older rocks in its core. Rt. 23, Newfoundland, NJ. Photo by R.W. Schlische Rt. Types of folds Syncline: downfold that contains younger rocks in its core. Top view Top view Side view Side view Fig. 11.20 Side view Fig. 11.20 Fig. 11.21 Fig. 11.21 Side view Structure: 7 Structure: 8 Types of folds Types of folds Basin: bowl-shaped fold (all side views show synclines; younger rocks at center) (b) Dome: upside-down bowl-shaped fold (all side views show anticlines; older rocks at center) (a) Dome: upside-down bowl-shaped fold (all side views show anticlines; older rocks at center) (a) Top view Side view Side view Fig. 11.23 Fig. 11.23 Structure: 9 Structure: 10 Review Questions Types of structures 1 • Faults: breaks (fractures) along which one side has moved relative to the other. Older rocks in middle Side view 3 Side view Top view 2 See Fig. 11.13 Q1a. Fold 1 is a(n) A. anticline B. basin C. dome D. syncline Q1b. Fold 2 is a(n) A. anticline B. basin C. dome D. syncline Q1b. Fold 3 is a(n) A. anticline B. basin C. dome D. syncline Normal faults in outcrop in southern Utah. Photo: T. Bean Side view Structure: 11 Photo: U.S.G.S. Structure: 12 Types of faults Types of faults Normal fault: the block above the fault (hanging-wall block) moves down relative to the block below the fault (footwall block) Reverse fault: the block above fault (hanging-wall block) moves up relative to block below fault (footwall block) Side view Fig. 10.5 Fig. 10.5 Side view Structure: 13 Photo: J. Ramsay Structure: 14 Types of faults Types of faults Strike-slip fault: the fault motion is horizontal Strike-slip fault: the fault motion is horizontal 1. Left-lateral: far block moves to left relative to near block 2. Right-lateral: far block moves to right relative to near block Fig. 11.14 Fig. 10.5 Photo: P.L. Kresan 1906 magnitude 8.2 San Francisco earthquake along San Andreas fault. Photo: G.K. Gilbert, U.S.G.S. Structure: 15 Structure: 16 Types of faults Other fractures Oblique-slip fault: combines elements of strike-slip faults with normal or reverse faults Normal plus right-lateral Joint: fracture (crack or break) along which the rock has Joint: opened up a very small amount (no sliding as in faulting) Up Down Fig. 11.14 Joint Photo: U.S.G.S. Structure: 17 Review Questions Fault Photo: U.S.G.S. Structure: 18 Experimental Structural Geology 3 1 Cadell (1888) Top view Ernst Cloos, 1955 Side view Q2a. The type of faults in photo 1 is ___. A. left-lateral strike-slip B. right-lateral strike-slip Q2b. The type of faults in photo 2 is ___. A. normal B. reverse 2 Structure: 19 Side view “Experiments have been made ever since the first geologist wrinkled his wife’s tablecloth to wife’ demonstrate folding.” folding.” Q2c. The type of fault in photo 3 is ___. A. left-lateral strike-slip B. normal C. reverse D. right-lateral strike-slip Photo: U.S.G.S. Structure: 20 Experimental Structural Geology Model preparation Hans Cloos, 1929 “True simulation of [structures] and their formation is hindered by the size and time relations. ... When we reduce the [structure] by a factor of 50,000, we have to choose a material which is 50,000 times less strong than [rocks] ... We use natural material [wet clay, dry sand] that satisfies the above requirements concerning low … strengths.” strengths.” Structure: 21 Model preparation Structure: 23 Structure: 22 Model preparation Structure: 24 Model setup--stretching Fixed side Moving end Fixed end Side view Side view Fixed side Structure: 25 Structure: 26 Stretching model Stretching model Top view Top view Top view Side view Side view Structure: 27 Q3. What type of faults? A. Normal B. Oblique-slip C. Reverse D. Strike-slip Structure: 28 Side view Mobile plate Mobile plate Rubber sheet Fixed plate Fixed Wall Rubber sheet Top view Top view Top view Fixed plate Modeling apparatus Plate tectonics--boundaries • Divergent--plates move apart Stretching (rifting) Top view Fig. 4.6a Top view Fig. 4.25 Side view Structure: 29 Side views Shortening Moving Shortening Fixed Landsat image, Gregory rift, Kenya Structure: 30 Top view Fixed Moving Fixed Sand Side views Structure: 31 Structure: 32 Moving Side view Sand Plate tectonics--boundaries Shortening Side view Q4. What type of faults? A. Normal B. Oblique-slip C. Reverse D. Strike-slip Structure: 33 Shearing Moving Moving Fixed • Convergent--plates move toward one another Fig. 4.6b Structure: 34 Shearing Top view Moving Fixed Fixed Moving Moving Fixed Top views Top view Fixed 10 cm Top views Q5. What type of faults? A. Left-lateral-slip B. Oblique-slip C. Right-lateral slip Structure: 35 Structure: 36 Side view Side view Plate tectonics--boundaries Transform plate boundary Top view • Transform--plates slide past one another Fig. 4.19 Fig. 4.6c Structure: 37 San Andreas transform fault, California. Photo: USGS Structure: 38 Transform plate boundary Brittle vs. ductile deformation 1. Ductile deformation: continuous deformation 2. Brittle deformation: discontinuous deformation Brittle: rock breaks or fractures Top view Structure: 39 Q6. What type of faults? A. Left-lateral-slip B. Oblique-slip C. Right-lateral slip Structure: 40 Fig. 11.8 Ductile: rock does not break Brittle vs. ductile deformation Brittle vs. ductile deformation Photo: M.S. Patterson X Y Original sample Brittle: Low T, Low P Ductile: High T, High P Structure: 41 Q7. The faults are ___ faults; layer X deforms ___;mm ~ 10 and layer Y deforms ___. A. normal; brittlely; ductilely brittlely; B. normal; ductilely; brittlely ductilely; Under the same P/T;conditions, some rock types behave C. reverse; brittlely; ductilely brittlely brittlely, others behave ductilely. D. reverse; ductilely; brittlely ductilely; Structure: 42 Mountain-building Mountain-building Convergent plate boundary-subduction Fig. 11.2 Structure: 43 Most mountain belts are related to active or ancient convergent plate boundaries; some are related to rifting; some mountains are volcanoes Fig. 11.33 Structure: 44 Mountain-building Mountain-building Fig. 11.35 Stretching & normal faulting Fig. 11.34 Convergent plate boundary--collision zones Animation--Model--Shortening Structure: 45 Structure: 46 Animation--Rifting Review Questions Mountain-building 9-1. Which type of fold looks like an upside-down U in side view (cross section)? A. anticline B. syncline C. normal D. reverse 9-2. Which type of fold looks like a right-side-up U in side view (cross section)? A. anticline B. syncline C. normal D. reverse 9-3. Which types of folds have older rocks in their cores (centers)? A. anticlines and basins B. anticlines and domes C. synclines and basins D. synclines and domes 9-4. Which types of folds have younger rocks in their cores (centers)? A. anticlines and basins B. anticlines and domes C. synclines and basins D. synclines and domes Haleakala, Hawaii 9-5. A. True / B. False: Movement on faults causes earthquakes. Volcanism Structure: 47 9-6. Which of the following is not a type of deformation? A. change in size B. change in shape C. change in position D. change in orientation E. change in chemical composition Mt. Fuji, Japan Structure: 48 Review Questions Review Questions 9-7. Which type of fault involves the relative upward movement of the block of rock above the fault? A. left-lateral strike-slip fault B. normal fault C. reverse fault D. right-lateral strike-slip fault 9-8. Which type of fault involves the relative downward movement of the block of rock above the fault? A. left-lateral strike-slip fault B. normal fault C. reverse fault D. right-lateral strike-slip fault 9-9. Which type of fault has the fault blocks moving exclusively in a horizontal direction? A. normal fault B. oblique-slip fault C. reverse fault D. strike-slip fault 9-12. If the diagrams above show side views, which diagrams show reverse fault(s)? A. all B. (a) only C. (c) only D. both (b) and (c) 9-13. If the diagrams above show top views, which diagrams show left-lateral faults? A. all B. (a) and (b) C. (c) only D. None 9-14. A synonym for discontinuous deformation is: A. brittle deformation B. ductile deformation C. elastic deformation D. compressive deformation 9-10. Which type of fault is most likely to found at a convergent plate boundary? A. normal fault B. oblique-slip fault C. reverse fault D. strike-slip fault 9-15. The following structures always form during brittle deformation: A. folds and faults B. folds only C. faults only 9-11. Which type of fault is most likely to found at a spreading center? A. normal fault B. oblique-slip fault C. reverse fault D. strike-slip fault 9-16. A. True / B. False: High temperature favors brittle deformation. Structure: 49 9-17. A. True / B. False: Most mountain ranges result from shortening produced at convergent plate boundaries. Structure: 50 ...
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This note was uploaded on 09/25/2011 for the course GEOLOGY 100 taught by Professor Lepre during the Fall '11 term at Rutgers.

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