Geology 302 Chapter 2.txt

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Geology 302 Chapter 2.txt
2011-09-20 10:59:11
Geology 302 Chapter

Geology 302 Chapter 2.txt
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  1. Alfred Wegener
    1930 German meteorologist. proposed continents were not fixed and they were once fit together called Pangaea.
  2. Continental Drift
    Pangaea fragmented into peices into separate continents that drift apart.
  3. Sea Floor Spreading
    When continents drift apart, new ocean floor forms between them
  4. Seduction
    Continents move toward each other when the old ocean floor between them sinks back down into the Earth's interior
  5. Plates
    The earths lithosphere consists of 20 different pieces that slowly move relative to each other.
  6. Plate Techtonics
    The grand unifying theory of geology, because it successfully explains great many geologic phenomena. It is the theory the plates move relative to each other.
  7. Paleomagnatism
    a record of earths magnetic field in the past. This provided proof of continental drift and contributed to the plate techtonic theory.
  8. Earths Magnetic Field
    Circulation of liquid iron alloy in the outer core of the earth generate a magnetic field. Two ends with opposite polarities.
  9. Magnetic Dipole
    an imaginary arrow that intersets the surface of the planet at two points known as the magnetic poles.
  10. Magnetic Declination
    The angle between the direction that a compass needle points and a line of longitude
  11. Magnetic Inclination
    The angle between a magnetic field line and the surface of the Earth at a given location
  12. Paleomagnetism
    The record of inclination that is not 0. Magnetic Fields of Ancient Rocks indicate the orientation of the magnetic field, relative to the rock, at the time the rock was formed.
  13. How does Palemagnetism develop?
    One process happens when lava (molten rock) cools to form basalt. As it cools and solidifies, time magnetite crystals begin to grow. At first thermal energy causes the magnetic dipole to go crazy and then they settle to permanent parallelism with the Earths magnetic field.
  14. Paleopole
    a term used to refer to the supposed position of the Earths magnetic north pole in the past.
  15. Apparent Polar-wander path
    The successive positions of dated paleopoles trace out a curving line. the continents move relative to a fixed pole. The continents must move with respect to each other. This proved Wegeners was theory of continental drift was correct.
  16. Mid-ocean ridges
    Divergent: The floor beneath all major oceans includes abyssal plains (broad, flat regions in the ocean), mid-ocean ridges (elogate submarine mountain ranges). The crest of the MOR's are the ridge axis. All MOR's are symetrical. Bathymetry is a mirror image on the other side.
  17. Deep Sea Trenches
    trenches where the ocean floor reaches 8-12km deep enough to swallow mt. everest. Along mostly the perimeter of the Pacific Ocean.. Trenches border volcanic arches
  18. Seamount Chains
    Isolated submarine mountains which were once volcanos but no longer erupt.
  19. Fracture Zones
    The ocean floor is diced up by narrow bands of vertical cracks and broken up rock. They lie at right angles to mid-ocean ridges.
  20. Harry Hess and his 'Essay in Geopoetry'
    late 1950 Hess suggest the seafloor had molten rock below it at the ocean ridges which furthered the idea of plate techtonics
  21. Magnetic Anomaly
    is the differnce between the expected strength of the Earths main dipole field at a certain location and the actual measured strength of the magnetic field at the location. Stronger is a positve anomoly, weaker is negative anomoloes.
  22. Magnetic Reversals
    A various times during Earths history the polarity reversed. It alternates between normal polarity and sometimes it is revered polarity.
  23. How to interpret Marine Anomalies
    A positive anomaly occurs over area of sea floor where basalt has normal polarity. This adds to the Earths dipole and creates a stronger magnetic signal than expected. A negative anomaly occurs over regions of sea floor where basalt has reversed polarity.
  24. What is the relationship between anomaly stripe width and polarity chron duration>
    It indicates that the rate of spreading has been constant in the Atlantic for at least the last 4.5 million years.
  25. Is the sediment layer thicker and older away from the axis in sea floor spreading?
  26. What is the outer part of the Eath in two layers?
    Lithosphere: crust plus the top plus the cooler top of the upper mantle.
  27. Asthenosphere: composed of watmer mantle that can flow slowly when acted on by force.
  28. What is the difference between the continental and oceanic lithosphere?
    Their thickness. On average, continental lith has a thickness of 150km. The crustal part of the continental is lower in density. The crustal part of the oceanic lith is on 7-10 km and is highly dense mafic rock
  29. What are the two types of continental margins?
    Active margins (plate boundaries) and Passive Margins are not plate margins. A continental margin a continents coastline.
  30. What is the continental shelf surface like?
    The surface of the sediment layer is a broad, shallow (less than 500m deep) region. Home to the major fisheries of the world.
  31. What are the basic principles of plate techtonics?
    The earths lithosphere is divided into plates that move relative to each other and relative to the underlying asthenosphere. Plate movement occurs 1-15cm a yr. The rocks along the plate boundaries undergo deformation as the plate moves away or into its neighbor. The earth surface constantly changes.
  32. How do you identify plate boundaries?
    it is where earthquakes occur. The Epicenter.
  33. What are three types of plate boundaries?
    based on the relative motions of the plates on either side of the boundary. A boundary that moves away from each other is a divergent boundary, a boundary that moves towards each other is a convergent boundary. A boundary that one plate slips past along side each other is a transform boundary.
  34. What are divergent plate boundaries and sea floor spreading?
    2 oceanic plates move apart by the process of sea floor spreading. When the plates move apart, new floor forms. Takes place a submarine mountian range called a mid ocean ridge that rises 2 km above the adjecent abyssal plains of the ocean..
  35. Divergent Boundary
    Mid-Ocean Ridge MORS MOVING AWAY
  36. What is uniformarism?
    the same laws or process (bio.geo.chem) that are operating on earth today were also operating in the past the same way. "the present is the key to the past"
  37. What happens with a continental-continental collision?
    big ass mountains, no subduction, himilayas, biggest mountians
  38. What were Alfred Wegeners proposal and evidence to plate techtonics?
    He proposed there was a supercontinent (pangaea), continental drift. His evidence was: coastaline match, glaciation patters, ancient rocks match up with climate; fossil distribution.
  39. What are the evidence of plate techtonics?
    magnemitet rocks will aligh with magnetic field; paleomagnatism; polar wander; apparent polar wonder; continental drift;
  40. Who is Harry Hess?
    in the navy hypothesised that heat flow at ridge (magma implies new crust moved up at MOR), sediment depth confirms MOR is younger. Theory for sea floor spreading came up with sebduction
  41. What are characteristics of Mors or divergent boundary?
    The sea floor slopes away from the ridge axis, reaching the depth of the abyssal plain. Either side is symetrical.
  42. How does the Oceanic crust form at the Mid-Ocean Ridge?
    As sea floor spreading takes place, hot asthenosphere rises beneath the ridge. As the asthenosphere rises it begins to melt, producing molten rock, or magma. Magma has a lower density than solid rock, so it rises. It accumulates in the crust below the ridge axis, filling a magma chamber.
  43. What are black smokers?
    the water they emit is black smoke, at the sea floor, which is a suspension of tiny mineral grains that precipitate in the water as the water cools.
  44. Where is the youngest sea floor?
    It occurs on either side of the ridge axis and the sea floor becomes progressively older as it moves away from the ridge. The oldest sea floor lies adjacent to the passive continental margins on either side of the ocean.
  45. How does the Lithospheric Mantle form at the mid ocean ridge?
    AT the ridge axis, such temps occur almost at the base of the crust, because of the presence of rising hot asthensphere and hot magma, so the lithosphere mantle beneath the ridge axis effectively doesnt exist. As soon as the magma cools, it becomes part of the lithosphere.
  46. Is the ocean more shallow or deaper at the older parts of the ocean?
    The lithosphere thickens and gets cooler and denser, it sinks into the asthenophere.
  47. What are convergent plate boundaries?
    two plates, at least one of which is oceanic, move toward one another. One oceanice plate bends nd sings down into the asthensphere beneath the other plate. MOVES TOWARDS
  48. What is the sinking process of one plate?
    Subduction, convergent boundaries are refered to as subduction zones
  49. Why does subduction occur?
    Oceanic lithosphere is denser that sthenopsphere and can sink through the asthensphere.
  50. Can continental crust subduct?
    No, it is too bouyant. the low density rocks acts as a preserver not allowing it to sink
  51. What is the Wadati-Benioff Zone?
    THe belt of the earthquakes in a downgoing plate.
  52. What are geologic features of convergent boundaries?
    an oceanic boundary, an oceanic plate sinks into the mantle beneath the edge of another plate. This process allows the two plates to move toward wach other and ocean basins to close. Trenches and volcanic arcs delinineate convergent boundaries.
  53. What are fracture zones?
    A narrow band of vertical fractures in the ocean floor. Fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.
  54. What is the transform boundary?
    A boundary at which on lithoisphere plate slips laterally past another. A vertical fault on which the slip direction parallels the earths surface.
  55. What are triple junctions?
    Places where three plate boundaries intersect at a point.
  56. What are hot spots?
    Volcanos that exist as isolated points and are not a consequence of a plate boundary movement. A location at the base of the lithosphere, at the top of the mantle plume, where temperatures can cause melting.
  57. What is a mantle plume?
    a column of very hot rock rising up through the mantle to the base of the lithosphere.
  58. What is a chain of extinct volcanos?
    A hotspot track. When the overlying plate moves, it slowly carries the volcano off the top of the plume.
  59. Are hotspots oceanic bound or continental bound?
    Both, ex. Hawaiian Island and Yellowstone national park
  60. What is a continental rift?
    a linear belt in which continental lithosphere undergoes rifting or pulls apart. The lithosphere stretches horizontally so it thins vertically.
  61. What is a collision?
    the process during which two buoyant pieces of lithosphere converge and squeeze together. Ex Himalayas and the Alps, India running into Asia.
  62. What drives plate movement?
    Two hypothesis: ridge push force and slab pull force.
  63. What is ridge-push force?
    the force that drives plates away from a mor. it is caused by the fact that the ridge is elevated relative to the regions of oceanic plate away from the ridge.
  64. What is Slab-Pull Force?
    The force that downgoing plates (or slabs) apply to oceanic lithosphere at a convergent margin. Stanton def: cold dense rock working its way back to earth, pulls rock behind it.
  65. What does high desnity do?
  66. What does low density do?
  67. What is a continental shelf?
    a broad, shawllowly submerged region of a continent along a passive margin.
  68. continental slope
    the slope at the edge of a continental shelf, leading down to the deap sea floor.
  69. What are the earths layers?
    crust, mantle, outer core: liquid metal; inner core; solid metal
  70. Why are the plates moving?
    Convection at the mantle.
  71. What is convection?
    density driven vertical or cyclical movement of material in response to heat.
  72. Describe plate motion?
    Plates move at 1-15 cm/y, about the rate that a fingernail grows. We can describe 'relative motion' of one plate with repect to another or the 'absolute motion' of a plate with respect to the underlying astensphere. GPS can now detect plate motion.