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13_tectonics_09_post - Plate Tectonics: Review Plate...

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Unformatted text preview: Plate Tectonics: Review Plate Tectonics: Review 13-1. The theory of plate tectonics ____________. A. incorporates continental drift but not sea-floor spreading B. incorporates sea-floor spreading but not continental drift C. incorporates and explains both sea-floor spreading and continental drift D. does not incorporate sea-floor spreading or continental drift 13-5. Tectonic plates might consist of ____________. A. continental lithosphere only B. oceanic lithosphere only C. oceanic or continental lithosphere or a combination of both D. either oceanic or continental lithosphere, but not both 13-2. Under the theory of plate tectonics, the plates themselves are ____________. A. discrete pieces of lithosphere at the surface of the solid Earth that move with respect to one another B. discrete layers of lithosphere that are vertically stacked one atop the other C. composed only of continental rocks, which plow through the weaker oceanic rocks D. very thick (approximately one-quarter of Earth’s radius) 13-6. Deformed (bent, stretched, or cracked) lithosphere occurs ____________. A. randomly over the surface of Earth B. primarily within the interiors of tectonic plates C. primarily on the margins of tectonic plates 13-3. Continental coastlines that occur within the interior of a tectonic plate are called ____________. A. internal margins B. passive margins C. active margins D. inert margins 13-4. Broad, sediment-covered continental shelves are found along ____________. A. active margins B. passive margins P la te te c to n ic s : 1 Plate Tectonics: Review 13-7. Every plate boundary can be recognized by ____________. A. the presence of active volcanoes B. the presence of an earthquake belt C. a deep chasm which can be seen from space 13-8. At a divergent plate boundary, two opposed plates ____________. A. move toward one another B. move away from one another C. slide past one another P la te te c to n ic s : 2 Plate Tectonics: Review 13-9. At a convergent plate boundary, two opposed plates ____________. A. move toward one another B. move away from one another C. slide past one another 13-14. Deep oceanic trenches are features of ____________ plate boundaries. A. convergent B. divergent C. transform 13-10. At a transform plate boundary, two opposed plates ____________. A. move toward one another B. move away from one another C. slide past one another 13-15. At transform plate boundaries ____________. A. earthquakes are common, but volcanoes are absent B. volcanoes are common, but earthquakes do not occur C. both earthquakes and volcanoes are common 13-11. Mid-ocean ridges are ____________ plate boundaries. A. convergent B. divergent C. transform 13-16. Segments of the mid-ocean ridge system are offset. Between the offset segments we observe ____________. A. a second series of ridges, perpendicular to the main set B. deep ocean trenches C. transform faults 13-12. The youngest sea floor occurs ____________. A. along passive margins B. along active margins C. along spreading centers D. randomly over the entire ocean basin 13-13. Subduction zones are ____________ plate boundaries. A. convergent B. divergent C. transform P la te te c to n ic s : 3 P la te te c to n ic s : 4 13: Plate Tectonics • Divergent boundaries & continental rifting • Convergent boundaries & mountain-building • Hot spots and absolute plate motions • Causes of plate motion Features of divergent plate boundaries • Mid-ocean ridge / spreading center: broad, faulted topographic high with axial depression that marks a divergent plate boundary in the oceans Map Fig. 2.8 Side view P la te te c to n ic s : 5 P la te te c to n ic s : 6 Features of divergent plate boundaries Volcanic / magmatic activity • At surface: small shield volcanoes, pillow basalts. • At depth: intrusion of dikes & mafic rocks (gabbro). Features of divergent plate boundaries Deformation: Fissures (gaping cracks) & normal faults due to stretching Fig. 4.8 Block diagram P la te te c to n ic s : 7 Fig. 9.21 P la te te c to n ic s : 8 Photo: G.E. Sigvaldason Map Features of divergent plate boundaries Earthquake activity: • Spreading centers (ridges): normal faulting (shallow depth) • Transform faults: strike-slip faulting (shallow depth) A g e v s . d e p th Q1. How old is the seafloor present at a depth of 4000 m? A. ~10 million years B. ~20 million years C. ~30 million years D. ~40 million years Fig. 3.8 Surface of sea floor Block diagram Graph P la te te c to n ic s : 9 P la te te c to n ic s : 1 0 A g e v s . d e p th Fig. 4.12 A g e v s . d e p th Q2. At what depth would you expect to find 150 million-year-old seafloor? A. ~5.5x101 m B. ~5.5x102 m C. ~5.5x103 m D. seafloor of that age does not exist • Seafloor depth increases exponentially with increasing age. Fig. 4.12 Surface of sea floor Graph P la te te c to n ic s : 1 1 Fig. 4.12 Surface of sea floor Graph P la te te c to n ic s : 1 2 A g e v s . d e p th A g e v s . d e p th • New oceanic crust forms at spreading centers. • Contracts & subsides as it cools. Fig. 4.12 • New oceanic crust forms at spreading centers. • Contracts & subsides as it cools. Fig. 4.12 Side view Side view Q3. The mid-ocean ridges are elevated above the surrounding seafloor because ____________. A. ridge rocks are hot and therefore of relatively low density B. the lithospheric plates are thickest at the ridges so they stand up taller C. rising ocean currents leave a vacuum above the ridge D. ridge rocks are mafic, whereas the ocean basin crust consists of ultramafic rock P la te te c to n ic s : 1 3 Q4. Oceanic lithosphere thickens away from the mid-ocean ridge primarily due to ____________. A. the addition of new crust due to hot-spot volcanism B. the addition of new crust due to sedimentation C. the addition of new lithospheric mantle as a result of cooling P la te te c to n ic s : 1 4 A g e v s . d e p th Age vs. depth & sea level • New oceanic crust forms at spreading centers. • Contracts & subsides as it cools. Fig. 4.12 Side view Side view Q5. As compared to the density of the asthenosphere, the oceanic lithosphere is ____________. A. always more dense B. always less dense C. initially more dense at the age of formation, but eventually becomes less dense D. initially less dense at the age of formation, but eventually becomes more dense P la te te c to n ic s : 1 5 • Fast-spreading ridges are wider than slow-spreading because more young, hot crust is present P la te te c to n ic s : 1 6 S e a le v e l Continental rifting • Continental rifts: elongate depressions that form when new divergent boundaries develop in continental crust. • Global spreading rates increase --> fast-spreading ridges displace more water --> sea level rises • Example: East African rift system • Global spreading rate is one of the main influence on sea level; glacial ice volume is also important Fig. 13.17 Fig. 4.24 Graph Map P la te te c to n ic s : 1 7 P la te te c to n ic s : 1 8 Features of continental rifts • Basaltic to rhyolitic volcanism • Normal faults Fig. 4.23 Rifting & breakup 1 . S t r e t c h in g , c r u s t a l t h in n in g , n o r m a l f a u lt in g ( T im e 2 t o T im e 3 ) 2 . S e p a r a t io n & s e a - f lo o r s p r e a d in g ( T im e 4 ) 3 . M o r e s p r e a d in g a n d d r if t in g ; c o o lin g & s u b s id e n c e o f c o n t in e n t a l m a r g in ( T im e 5 ) Fig. 4.23 Block diagrams Block P la te te c to n ic s : 1 9 Block diagrams P la te te c to n ic s : 2 0 Rifting & breakup Review Questions 13-17. Which of the following does not characterize spreading centers? A. basaltic magmatism B. fissures C. broad topographic low with central uplift D. normal faulting Produce a passive continental margin 13-18. As compared to a slowly spreading mid-ocean ridge, a rapidly spreading ridge is ____________. A. wider B. narrower C. more silicic in lava composition Thick sediment accumulated during thermal subsidence 13-19. A. True / B. False: A global increase in spreading rate will result in an increase in sea level. 13-20. A. True / B. False: The depth of the seafloor below sea level decreases exponentially with increasing age. Normal faults formed during rifting Thinned crust Block diagram P la te te c to n ic s : 2 1 Convergent plate boundaries: types 13-21. Which of the following is not associated with continental breakup? A. Stretching of the crust and normal faulting B. Separation of the crust and initiation of seafloor spreading C. Drifting of the continental margin away from the spreading center. D. Uplift and erosion of the continental margin P la te te c to n ic s : 2 2 Convergent plate boundaries: types #1. Ocean-continent convergence #2. Ocean-ocean convergence • Subducting plate: oceanic plate • Subducting plate: older, denser oceanic plate • Example: Andes • Example: Japan Side view Side view P la te te c to n ic s : 2 3 P la te te c to n ic s : 2 4 Convergent plate boundaries: types Convergent plate boundaries: types #3. Continent-continent convergence #3. Continent-continent convergence • Subducting plate: continental crust is not subducted, but oceanic crust previously attached to continental crust was subducted Stage 1: Subduction of oceanic crust • Example: Himalayas India Asia Fig. 4.26 Block diagram P la te te c to n ic s : 2 5 P la te te c to n ic s : 2 6 Convergent plate boundaries: types #3. Continent-continent convergence Mt. Everest Stage 2: Suturing and separation of sinking oceanic lithosphere India Asia Convergent boundaries: seismicity • W a d a ti-B e n io ff z o n e : sh a llo w , in te rm e d ia te a n d d e e p -fo cu s e a rth q u a k e s (u p to 6 7 0 k m d e e p ) th a t o ccu r a t th e e d g e o r w ith in th e s u b d u ctin g p la te . Fig. 10.21 • D e e p -fo cu s q u ak es: s u b d u c t in g p la t e r e m a in s c o ld & b r it t le Fig. 4.26 Block diagram Block diagram P la te te c to n ic s : 2 7 P la te te c to n ic s : 2 8 Convergent boundaries: magmatism • Ocean-ocean convergence: andesitic Compression at CPB!s • Accretionary prism: wedge-shaped body of sediment is scraped off the subducting (downgoing) slab; characterized by folds and thrust (reverse) faults • Ocean-continent convergence: andesitic to rhyolitic • Continent-continent convergence: not significant Block diagram • (Fold-and-)thrust belts: regions of folding and reverse (thrust) faulting found in continent-ocean and continent-continent collision zones Side view Fig. 4.15 Composite volcanoes (stratovolcanoes) Mt. Fuji, Japan P la te te c to n ic s : 2 9 P la te te c to n ic s : 3 0 Compression Side view Review Questions 13-22. Which statement concerning the three types of convergent plate boundaries is incorrect? A. For ocean-ocean convergence, the younger oceanic plate subducts. B. For ocean-continent convergence, the oceanic plate subducts. C. For continent-continent convergence, continental crust is not subducted, but oceanic crust attached to the continental crust is subducted. • Fold-and-thrust belts • Example: Valley & Ridge province of Appalachian Mountains. Fig. 11.40 13-23. For an ocean-continent convergent boundary, which sequence of features is listed in the proper order going from the over-riding plate to the subducting (downgoing) plate (Slide 30)? A. accretionary prism, forearc basin, volcanic arc, trench B. volcanic arc, forearc basin, accretionary prism, trench C. trench, accretionary prism, forearc basin, volcanic arc D. trench, accretionary prism, volcanic arc, forearc basin Map Fig. 13.23 13-24. Which match below is correct? A. Andes (South America): ocean-continent convergence B. Himalayas (India/Asia): continent-continent convergence C. Japan: ocean-ocean convergence D. All matches are correct. Side view P la te te c to n ic s : 3 1 P la te te c to n ic s : 3 2 Review Questions 13-25. The material scraped off the downgoing slab forms the ___. A. accretionary wedge B. forearc basin C. volcanic arc D. trench 13-26. The most common type of fault present in an accretionary wedge is a ____. A. normal fault B. left-lateral strike-slip fault C. reverse (thrust) fault D. right-lateral strike-slip fault 13-27. At a subduction zone, the overriding plate ____________. A. is always composed of continental lithosphere B. is always composed of oceanic lithosphere C. may be composed of either oceanic or continental lithosphere 13-28. At a subduction zone (not a collision zone), the downgoing (subducting) plate ____________. A. is always composed of continental lithosphere B. is always composed of oceanic lithosphere C. may be composed or either oceanic or continental lithosphere 13-29. The Wadati-Benioff zone extends down within the mantle to a maximum depth of ____________. A. 30 km B. 150 km C. 670 km D. 990 km P la te te c to n ic s : 3 3 Review Questions 13-30. The Wadati-Benioff zone is a belt of earthquakes found ____________. A. within an otherwise stable continental interior B. within an overriding plate at a subduction zone C. within a downgoing plate at a subduction zone D. along mid-ocean ridges 13-31. A. True / B. False: The Valley and Ridge region is a fold-and-thrust belt related to the Appalachian orogeny. 13-32. A. True / B. False: The Himalayan orogeny began with the subduction of oceanic crust beneath the Indian plate. 13-33. When two bodies of continental lithosphere are pulled together at a convergent boundary, the result is ____________. A. subduction B. collision and mountain formation 13-34. Large, thick, non-volcanic mountain belts, like the Himalayas, are features associated with ____________ plate boundaries. A. convergent B. divergent C. transform P la te te c to n ic s : 3 4 Hotspots: global distribution H o ts p o ts Hotspot: volcanically a ctiv e p a rt o f a lin e a r ch a in o f v o lca n o e s, v o lca n ic isla n d s o r se a m o u n ts th a t fo rm s a b o v e a risin g p lu m e o f h o tte r-th a n -n o rm a l m a n tle ro ck (a lth o u g h th is m a te ria l is still so lid , n o t m o lte n ) Fig. 4.20 Map Fig. 4.23 P la te te c to n ic s : 3 5 Block diagram O c c u rre n c e s : • o c e a n ic lit h o s p h e r e • c o n t in e n t a l lit h o s p h e r e P la te te c to n ic s : 3 6 • p la t e in t e r io r s • p la t e b o u n d a r ie s H o ts p o ts H o ts p o ts Q6. Which of the following Hawaiian Islands contains the youngest volcanic rocks (numbers give ages in millions of years)? A. Hawaii B. Kauai C. Maui D. Oahu Hotspot is fixed Fig. 4.23 Map Animation Age progression Map Plate moves P la te te c to n ic s : 3 7 P la te te c to n ic s : 3 8 H o ts p o ts Q7. What is the trend of the line connecting Necker to Midway? A. ESE B. NNW C. SSE D. WNW Absolute plate motion NNW N Map NNE NE NW ENE WNW W E WSW ESE SE SW SSW S SSE Map P la te te c to n ic s : 3 9 Side views P la t e m o t io n d ir e c t io n : based on lin e a r t r e n d & age p r o g r e s s io n Q8. Prior to 43 million years ago, the direction of plate motion was ___. A. NNW B. ESE C. SSE D. WNW P la te te c to n ic s : 4 0 Map Map Absolute plate motions Absolute plate motions Map • B e n d --> c h a n g e in p la t e m o t io n d ir e c t io n Map Fig. 9.18 Fig. 4.22 Q9. The North American plate is moving to the ___. A. NNE B. ENE C. SSW P la te te c to n ic s : 4 1 D. WSW P la te te c to n ic s : 4 2 Mantle plumes Mantle-plume evolution Mantle plumes: narrow columns of hotter-than-normal (but-still-solid) m a n tle th a t rise fro m th e d e e p in te rio r a n d a re th e d e e p -se a te d ca u se s o f h o tsp o ts 1 (least evolved): minor blob at core-mantle boundary 2, 3: plumes rise with large head and narrow tail 4: plume head flattens and expands at base of lithosphere 5 (most evolved): head has dissipated, only tail remains 1 4 3 5 2 P la te te c to n ic s : 4 3 Side view Side view P la te te c to n ic s : 4 4 Mantle plumes & oceans Plume heads beneath oceanic lithosphere form: oceanic plateaus (e.g., Ontong-Java) P la te te c to n ic s : 4 5 Mantle plumes & oceans Plume tails beneath oceanic lithosphere form: linear seamount chains & hotspot volcanism (e.g., Hawaii). • Basaltic lava • Shield volcanoes P la te te c to n ic s : 4 6 Mantle plumes & continents • Highviscosity rhyolitic magma (very explosive) Yellowstone hotspot • Geysers & other hydrothermal features • Massive ash flows and falls Old Faithful Map P la te te c to n ic s : 4 7 P la te te c to n ic s : 4 8 Photo: R.W. Schlische Y e llo w s t o n e h o t s p o t • Geysers & other hydrothermal features Causes of plate motion • Convection-upper mantle (old idea) Fig. 4.27 Mammoth Hot Springs Side view Photo: R.W. Schlische P la te te c to n ic s : 4 9 P la te te c to n ic s : 5 0 Causes of plate motion Causes of plate motion • Convection: whole mantle, including plumes rising from core-mantle boundary • R id g e p u sh : f o rce th a t d e v e lo p s b e ca u se m id -o ce a n rid g e s (sp re a d in g ce n te rs) lie a t a h ig h e r e le v a tio n th a n th e a b y ssa l p la in , d riv in g th e lith o sp h e ric p la te a w a y fro m th e rid g e . Fig. 4.31 Side view P la te te c to n ic s : 5 1 P la te te c to n ic s : 5 2 Fig. 4.28 Causes of plate motion Causes of plate motion • S la b p u ll : d e n se , d o w n -g o in g s u b d u ctin g p la te (sla b ) p u lls re st o f p la te a lo n g Fig. 4.30 Map Fig. 4.28 Plates with subduction zones generally move fastest. Side view P la te te c to n ic s : 5 3 Review Questions 13-35. Hot spots are caused by ____________. A. friction due to the lithosphere sliding atop the asthenosphere B. unusually dense concentrations of radioactive isotopes in the crust C. hot plumes of molten mantle material that rise up through cooler, denser surrounding rock D. hot plumes of solid mantle material that rise up through cooler, denser surrounding rock 13-36. Hot spots can occur ____________. A. only within continental plates B. only within oceanic plates C. within either continental or oceanic plates D. only when the thickness of the crust is less than 10 km 13-37. A. True / B. False: In a hot-spot volcanic island chain, such as the Hawaiian Islands, all islands possess active volcanoes simultaneously and therefore the risks of volcanic hazards are the same for all islands. P la te te c to n ic s : 5 4 Review Questions 13-39. Which of the following represents a mantle plume in its most advanced stage of evolution? A. plume that lacks a head but has a long tail B. plume with a bulbous head and long tail C. plume with a bulbous head and short tail D. plume with a disk shaped head and long tail 13-40. Iceland is one of the few places in the world that is both above sea level and situated atop a ____________ plate boundary. A. convergent B. divergent C. transform 13-41. A. True / B. False: Slab pull occurs because of downward flowing limbs of convection cells. 13-42. Tectonic plates move at rates that are approximately ____________. A. 1 to 15 mm B. 1 to 15 cm per year C. 1 to 15 m per year D. 1 to 15 km per year 13-38. A. True / B. False: A hot spot, such as Hawaii, is the cause of mantle plumes. P la te te c to n ic s : 5 5 P la te te c to n ic s : 5 6 Review Questions 13-43. Most of the pushing force driving plate motion is produced ____________. A. at spreading centers B. at subduction zones C. at collision zones D. in the interiors of continental plates 13-44. Most of the pulling force driving plate motion is produced ____________. A. at mid-ocean ridges B. at subduction zones C. at collision zones D. in the interiors of continental plates 13-45. Slab-pull occurs because subducting slabs are ____________. A. less mafic, and therefore less dense, than surrounding asthenosphere B. cooler, and therefore more dense, than surrounding asthenosphere C. hotter, and therefore more dense, than surrounding asthenosphere D. cooler, and therefore less dense, than surrounding asthenosphere P la te te c to n ic s : 5 7 ...
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