09_structure_10

09_structure_10 - 09: Geologic Structures, Deformation, and...

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Unformatted text preview: 09: Geologic Structures, Deformation, and M ountains 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 Folds Anticline in Anticline M onterey Formation, Soto Street, L os Angeles. Photo: M .N. Bramlette, U.S.G.S. 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) r esult from motion on faults Fault scarp from 1983 Borah Peak, I D, Fault earthquake. Photo: M .H. Anders Photo: Fault scarp from 1980 El Asnam, Fault Algeria, earthquake. Photo: H.C. Shah Shah cture: 5 Types of structures • Fold: bend or warp Rt. 23, Newfoundland, NJ. Photo by R.W. Schlische Photo Rt. cture: 6 Types of folds Top view Top view Youngest Side view Oldest Side view Anticline: upfold (upside-down U); layers dip away from center; older rocks in its core. Syncline: downfold (U-shaped); layers dip toward center; younger rocks in its core. Anticline; Away nticline; cture: 7 Syncline; toward 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: 8 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: 9 Types of folds Top view Oldest Side view Youngest Side view Dome: upside-down bowl-shaped fold; layers dip away from center; all side views show anticlines; older rocks at center Basin: bowl-shaped fold; layers dip toward center; all side views show synclines; younger r ocks at center cture: 10 10 Types of folds Dome: upside-down bowl-shaped fold (all side views show anticlines; older rocks at center) Fig. 11.23 cture: 11 11 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: 12 12 Types of structures • Faults: breaks (fractures) along which one side has moved r elative to the other. Side view See Fig. 11.13 Normal faults in outcrop in southern Utah. Photo: T. Bean Geologists have a saying: Sh% & t happens! Sh% Geologists have a saying: Shift happens! Shift cture: 13 13 Types of faults Normal fault: the block above the fault (hanging-wall block) moves down relative to the block below the fault (footwall block) Side view Fig. 10.5 cture: 14 14 Types of faults Reverse fault: the block above fault (hanging-wall block) moves up relative to block below fault (footwall block) Fig. 10.5 Side view cture: 15 15 Photo: J. Ramsay Types of faults Strike-slip fault: the fault motion is entirely horizontal 1. L eft-lateral: far block moves to left relative to near block Fig. 10.5 Photo: P.L. Kresan cture: 16 16 Types of faults Strike-slip fault: the fault motion is entirely horizontal 2. Right-lateral: far block moves to right relative to near block Fig. 11.14 1906 magnitude 8.2 San 1906 Francisco earthquake along San Andreas fault. Photo: G.K. Gilbert, U.S.G.S. Photo: cture: 17 17 Types of faults Oblique-slip fault: combines elements of strike-slip faults with normal or reverse faults Normal plus right-lateral Up Down Fig. 11.14 cture: 18 18 Photo: U.S.G.S. Other fractures Joint: fracture (crack or break) along which the rock has opened fracture up a very small amount (no sliding as in faulting) up Joint cture: 19 19 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: 20 20 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 Experimental Structural Geology Cadell (1888) Ernst Cloos, 1955 “Experiments have been made ever since the first Experiments geologist wrinkled his wife’s tablecloth to demonstrate folding.” folding.” cture: 21 21 Experimental Structural Geology cture: 22 22 Experimental Structural Geology Hans Cloos, 1929 “T rue simulation of [structures] and their formation is True hindered by the size and time relations. ... W hen we r educe 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.” cture: 23 23 M odel preparation cture: 24 24 M odel preparation cture: 25 25 M odel preparation cture: 26 26 M odeling apparatus Fixed Wall Fixed side M oving Moving end end Fixed end Fixed side cture: 27 27 M odel setup--stretching cture: 28 28 Side view M obile plate Rubber sheet M obile plate Rubber sheet Fixed plate Side view Fixed plate Top view Top view Top view Stretching model Top view Top view Side view cture: 29 29 Stretching model Top view Side view Q3. What type of faults? A. Normal B. Oblique-slip C. Reverse D. Strike-slip cture: 30 30 Side view Plate tectonics--boundaries • Divergent--plates move apart Fig. 4.6a Side view cture: 31 31 Top view Stretching (rifting) Top view Fig. 4.25 cture: 32 32 Landsat image, Gregory rift, Kenya Side views M oving Fixed Shortening Top view Side view M oving Fixed Sand Sand cture: 33 33 Side views cture: 34 34 M oving Fixed Shortening cture: 35 35 Side view Q4. What type of faults? A. Normal B. Oblique-slip C. Reverse D. Strike-slip M oving Fixed Shortening Plate tectonics--boundaries • Convergent--plates move toward one another Fig. 4.6b cture: 36 36 Shearing M oving Fixed M oving Fixed Top views cture: 37 37 Top view Shearing M oving Top view Fixed M oving Fixed 10 cm Top views Q5. What type of faults? A. Left-lateral-slip B. Oblique-slip C. Right-lateral slip cture: 38 38 Side view Side view Plate tectonics--boundaries • T ransform--plates slide past one another Fig. 4.6c cture: 39 39 Transform plate boundary Top view Fig. 4.19 San Andreas transform fault, California. Photo: USGS cture: 40 40 Transform plate boundary Top view cture: 41 41 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 Brittle: rock breaks or breaks or fractures fractures cture: 42 42 Fig. 11.8 Ductile: Ductile: rock does rock does not break not break Brittle vs. ductile deformation Photo: M .S. Patterson Original sample cture: 43 43 Brittle: Low T, Low P Ductile: High T, High P Brittle vs. ductile deformation Type of faulting? Brittle or Brittle ductile? ductile? Brittle or Brittle ductile? ductile? X Y Q7. The faults are ___ faults; layer X deforms ___; and Q7. ~ 10 mm layer Y deforms ___. layer 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: 44 44 M ountain-building Fig. 11.2 cture: 45 45 M ost mountain belts are related to active or ancient active ancient convergent plate boundaries; some are related to rifting; some mountains are volcanoes r ifting; M ountain-building Convergent plate boundary-subduction Fig. 11.33 cture: 46 46 M ountain-building Fig. 11.34 Convergent plate boundary--collision zones cture: 47 47 M ountain-building Fig. 11.35 Stretching & normal faulting cture: 48 48 M ountain-building Haleakala, Hawaii Volcanism cture: 49 49 M t. Fuji, Japan Review Questions 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 9-5. A. True / B. False: Movement on faults causes earthquakes. 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 cture: 50 50 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 9-10. 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 9-11. 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 cture: 51 51 Review Questions 9-12. I f the diagrams above show side views, which diagrams show normal fault(s)? A. all B. (a) only C. (c) only D. both (b) and (c) 9-13. I f the diagrams above show top views, which diagrams show right-lateral faults? A. all B. (a) and (b) C. (c) only D. None 9-14. A synonym for continuous deformation is: A. brittle deformation B. ductile deformation C. elastic deformation D. compressive deformation 9-15. The following structures always form during brittle deformation: A. folds and faults B. folds only C. faults only 9-16. A. True / B. False: High temperature favors ductile deformation. 9-17. A. True / B. False: Most mountain ranges result from extension produced at divergent plate boundaries. cture: 52 52 Review Questions 9-18. What is the most important distinction among the major types of faults? A. the relative shape of the faults and the fault blocks B. the absolute amount of displacement of the fault C. the relative motion direction between fault blocks D. the absolute direction of motion between fault blocks 9-19. Which of the following is the best explanation of the difference between a normal and reverse fault? A. Normal faults are usually associated with divergent plate boundaries, whereas r everse faults are usually associated with convergent plate boundaries. B. For normal faults, the hanging wall block moves down relative to the footwall block; for reverse faults, the hanging wall block moves up relative to the footwall block. C. Both A and B. 9-20. I n a near-surface environment, most rocks deform by __________. A. ductile deformation B. brittle deformation C. rocks do not deform here 9-21. The rock above the fault surface is the ___ block, whereas the rock below the fault surface is the ___ block. A. footwall; hanging wall B. hanging wall; footwall D. normal; reverse cture: 53 C. reverse; normal 53 Review Questions 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 9-5. A. True / B. False: Movement on faults causes earthquakes. 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 cture: 54 54 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 9-9. 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 9-10. Which type of fault is most likely to be found at a convergent plate boundary? A. normal fault B. oblique-slip fault C. reverse fault D. strike-slip fault cture: 55 55 Review Questions 9-12. I f the diagrams above show side views, which diagrams show normal fault(s)? A. all B. (a) only C. (c) only D. both (b) and (c) cture: 56 56 Review Questions 9-15. The following structures always form during brittle deformation: A. folds and faults B. folds only C. faults only 9-17. A. True / B. False: Most mountain ranges result from extension produced at divergent plate boundaries. cture: 57 57 ...
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