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09_structure_09_post - 09: Geologic Structures,...

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Unformatted text preview: 09: Geologic Structures, Deformation, and Mountains Folds in Canadian Rockies. Photo: P.L. Kresan cture: 1 Fault offset, 1976 Guatemala earthquake. Photo: USGS What is deformation? Change in location, change in orientation, change in size and/or change in shape Fig. 11.4 cture: 2 Why is this important? • Folds & faults provide traps for hydrocarbons Anticline in Monterey Formation, Soto Street, Los Angeles. Photo: M.N. Bramlette, U.S.G.S. cture: 3 Why is this important? • Groundwater & pollution migrate along fractures Photo: J.H. Ramsay cture: 4 Why is this important? • 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. Photo: H.C. Shah cture: 5 Types of structures • Fold: bend or warp Rt. 23, Newfoundland, NJ. Photo by R.W. Schlische cture: 6 Types of folds Anticline: upfold that contains older rocks in its core. Top view Side view Fig. 11.20 Fig. 11.21 Side view cture: 7 Types of folds Syncline: downfold that contains younger rocks in its core. Top view Side view Side view Fig. 11.20 Fig. 11.21 cture: 8 Types of folds Basin: bowl­shaped fold (all side views show synclines; younger rocks at center) (b) Dome: upside­down bowl­shaped fold (all side views show anticlines; older rocks at center) (a) Top view Side view Side view Fig. 11.23 cture: 9 Types of folds Dome: upside­down bowl­shaped fold (all side views show anticlines; older rocks at center) (a) Fig. 11.23 cture: 10 10 Review Questions 1 Older rocks in middle 3 Side view Top view 2 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 Side view cture: 11 11 Photo: U.S.G.S. Types of structures • Faults: breaks (fractures) along which one side has moved relative to the other. Side view See Fig. 11.13 Normal faults in outcrop in southern Utah. Photo: T. Bean cture: 12 12 Types of faults Normal fault: the block above the fault (hanging­wall block) moves down relative to the block below the fault (footwall block) Side view Fig. 10.5 cture: 13 13 Types of faults Reverse fault: the block above fault (hanging­wall block) moves up relative to block below fault (footwall block) Fig. 10.5 Side view cture: 14 14 Photo: J. Ramsay Types of faults Strike­slip fault: the fault motion is horizontal 1. Left­lateral: far block moves to left relative to near block Fig. 10.5 Photo: P.L. Kresan cture: 15 15 Types of faults Strike­slip fault: the fault motion is horizontal 2. Right­lateral: far block moves to right relative to near block Fig. 11.14 1906 magnitude 8.2 San Francisco earthquake along San Andreas fault. Photo: G.K. Gilbert, U.S.G.S. cture: 16 16 Types of faults Oblique­slip fault: combines elements of strike­slip faults with normal or reverse faults Normal plus right-lateral Up Down Fig. 11.14 cture: 17 17 Photo: U.S.G.S. Other fractures Joint: fracture (crack or break) along which the rock has opened up a very small amount (no sliding as in faulting) Joint cture: 18 18 Fault Photo: U.S.G.S. Review Questions 3 1 Top view 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 cture: 19 19 Side view 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. Experimental Structural Geology Cadell (1888) Ernst Cloos, 1955 “Experiments have been made eversince the first geologist wrinkled his wife’s tablecloth to demonstrate folding.” cture: 20 20 Experimental Structural Geology 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.” cture: 21 21 Model preparation cture: 22 22 Model preparation cture: 23 23 Model preparation cture: 24 24 Modeling apparatus Fixed Wall Fixed side Moving Moving end end Fixed end Fixed side cture: 25 25 Model setup--stretching cture: 26 26 Side view Mobile plate Rubber sheet Mobile plate Rubber sheet Fixed plate Side view Fixed plate Top view Top view Top view Stretching model Top view Top view Side view cture: 27 27 Stretching model Top view Side view Q3. What type of faults? A. Normal B. Oblique-slip C. Reverse D. Strike-slip cture: 28 28 Side view Plate tectonics--boundaries • Divergent­­plates move apart Fig. 4.6a Side view cture: 29 29 Top view Stretching (rifting) Top view Fig. 4.25 cture: 30 30 Landsat image, Gregory rift, Kenya Side views Moving Fixed Shortening Top view Side view Moving Fixed Sand Sand cture: 31 31 Side views cture: 32 32 Moving Fixed Shortening cture: 33 33 Side view Q4. What type of faults? A. Normal B. Oblique-slip C. Reverse D. Strike-slip Moving Fixed Shortening Plate tectonics--boundaries • Convergent­­plates move toward one another Fig. 4.6b cture: 34 34 Shearing Moving Fixed Moving Fixed Top views cture: 35 35 Top view Shearing Moving Top view Fixed Moving Fixed 10 cm Top views Q5. What type of faults? A. Left-lateral-slip B. Oblique-slip C. Right-lateral slip cture: 36 36 Side view Side view Plate tectonics--boundaries • Transform­­plates slide past one another Fig. 4.6c cture: 37 37 Transform plate boundary Top view Fig. 4.19 San Andreas transform fault, California. Photo: USGS cture: 38 38 Transform plate boundary Top view cture: 39 39 Q6. What type of faults? A. Left-lateral-slip B. Oblique-slip C. Right-lateral slip Brittle vs. ductile deformation 1. Ductile deformation: continuous deformation 2. Brittle deformation: discontinuous deformation Brittle: rock breaks or fractures cture: 40 40 Fig. 11.8 Ductile: rock does not break Brittle vs. ductile deformation Photo: M.S. Patterson Original sample cture: 41 41 Brittle: Low T, Low P Ductile: High T, High P Brittle vs. ductile deformation X Y Q7. The faults are ___ faults; layer X deforms ___; and ~ 10 mm layer Y deforms ___. A. normal; brittlely; ductilely B. normal; ductilely; brittlely Under the same P/T conditions, some rock types behave C. reverse; brittlely; ductilely b reverse; ductilely; brittlely D. rittlely, others behave ductilely. cture: 42 42 Mountain-building Fig. 11.2 cture: 43 43 Most mountain belts are related to active or Most active ancient convergent plate boundaries; some ancient are related to rifting; some mountains are volcanoes volcanoes Mountain-building Convergent plate boundary-subduction Fig. 11.33 cture: 44 44 Mountain-building Fig. 11.34 Convergent plate boundary--collision zones Animation--Model--Shortening cture: 45 45 Mountain-building Fig. 11.35 Stretching & normal faulting cture: 46 46 Animation--Rifting Mountain-building Haleakala, Hawaii Volcanism cture: 47 47 Mt. Fuji, Japan Review Questions 9­1. Which type of fold looks like an upside­down U in side view (cross section)? A. anticline B. syncline C. normal D. reverse 9­2. Which type of fold looks like a right­side­up U in side view (cross section)? A. anticline B. syncline C. normal D. reverse 9­3. 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 9­4. 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 9­5. A. True / B. False: Movement on faults causes earthquakes. 9­6. 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 cture: 48 48 Review Questions 9­7. 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 9­8. 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 9­9. 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 9­10. 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 9­11. 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 cture: 49 49 Review Questions 9­12. 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) 9­13. If the diagrams above show top views, which diagrams show left­lateral faults? A. all B. (a) and (b) C. (c) only D. None 9­14. A synonym for discontinuous deformation is: A. brittle deformation B. ductile deformation C. elastic deformation D. compressive deformation 9­15. The following structures always form during brittle deformation: A. folds and faults B. folds only C. faults only 9­16. A. True / B. False: High temperature favors brittle deformation. 9­17. A. True / B. False: Most mountain ranges result from shortening produced at convergent plate boundaries. cture: 50 50 ...
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