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4_Ocean Floor and Margins 2010

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									        Formation of Planets
•    Accretion of dust in space due to
     GRAVITATIONAL FORCES
    – Dust
    – Asteroids
    – Planets
      1. accretion of Heavy elements
      2. attraction of Light gases to dense
         nucleus
Origin Solar System
        Formation of Planets
•    Recent planets were HOT
    – Compressional Heating
    – Impact Heating
    – Radioactive Decay


• The Earth is layered by Densities
    – Densest Core
    – Lightest Crust
                  Earth’s Layers
•   Core (Fe, Ni)
    –   Inner Core (solid)
    –   Outer Core (liquid)
•   Mantle (plastic) –    very close to melting point
    –   Inner Mantle
    –   Asthenosphere
•   Lithosphere (rigid)
    –   Upper Mantle (~100km) (Lithosphere)
    –   Crust
        •   Oceanic
        •   Continental
Earth’s Core, Mantle and Crust
Ocean Floor and Margins
If the entire history of the earth were 1 year long:

  •Origin of Earth 4600 MY


                                         •Oceans first form 4000 MY



                    •Oldest dated rocks 3800 MY                   •First life form 3600 MY




                                      MY
 •Ocean – Atmosphere equilibrium 1000•Multicelular complex organisms 700 MY



              •Beginning of well known Geology
                   600 MY
                                       •First FISH!
                                      •First510 MY
                                             Land Plants 430 MY
                                                                               *
DECEMBER




     Dinosaurs
       evolve




                 Dinosaurs
                  extinct




 *
           December 31st
• 9:15 pm Homo sapiens evolves
• Historical Times = 1 minute 18 sec.
• Columbus discovers America = 3 sec. till
  midnight
• HMS Challenger Expedition = 0.9 sec.
  till midnight
• You have been around for ~0.13 seconds
Asthenosphere & Lithosphere
                        Crust
• Oceanic Crust
  –   Density: ~2.9 g/m3
  –   Mineral composition: Basalt (Fe, Mg, SiO2)
  –   Thickness: ~5-10 km
  –   Elevation: ~ 3800m below sea level
  –   Age: <200 MY
• Continental Crust
  –   Density: ~2.75 g/m3
  –   Mineral Composition: Granite (Na, K, SiO2)
  –   Thickness: ~20-90 km
  –   Elevation: ~840m above sea level
  –   Age: <3800 MY
Lithosphere
   Study of Earth’s Interior
• Rock Sampling & Drilling
• Meteorites
• Seismic Studies
                  Rock Drilling




ODP (Ocean Drilling Program)
Meteorites




    http://www.nmnh.si.edu/minsci/images/gallery/43.htm
                                Seismic Studies




http://pangea.stanford.edu/~sklemp/




                                      http://www.oceanmarine.com/
          Seismic Studies
• Differential speed of seismic/sound
  waves due to density differences
  – Pressure Waves (p)
    • Parallel to direction of motion
    • Travel through liquids
  – Shear Waves (s)
    • Perpendicular to direction of motion
    • DO NOT travel through liquids


  Seismic waves refract & reflect at density
   boundaries
Seismic Waves
Seismic Waves
Convection Processes




Shallow and deep mantle convection cells
Convection Processes
    Divergent Margins - Ridges
• New oceanic crust formation
• Spreading
Convergent Margins - Trenches
• Oceanic crust Destruction
• Convergence & Subduction
Lithosphere Plates
               Earthquakes




Shallow (0-70 km)   Medium (70-300 km)   Deep (>300 km)
250 – 225 MY
Spreading Cycles
Hot Spot
Hot Spot
Loihi Volcano
                Evolution of
                Coral Reefs
Fringe reefs




Barrier reefs




Atolls
Hot Spot Map
       Convergent Margins
• Continental Convergent Margins
  – Oceanic crust / Continental crust
  – Pacific Coast South America
• Oceanic Convergent Margins
  – Oceanic crust / Oceanic crust
  – Aleutian Trench, Caribbean Arch

• Continental Collision Margins
  – Continental crust / Continental crust
  – Himalaya mountains
Continental Convergent Margins




Oceanic Convergent Margins




Continental Collision Margins
Continental Convergent Margins

Andes Mountains
  Oceanic Convergent Margins

Caribbean Island Arch
Convergent margin vulcanism




                       St Helens
          Convergent margin vulcanism




http://www.rsiphotos.com                        http://www.montserratreporter.org/
                           Soufriere - Montserrat
   Continental Collision Margin
Himalaya Mountains
          Divergent Margins
• Oceanic Divergent Margins
  –   Two spreading plates, upwelling magma
  –   Central Rift Valley and Oceanic Ridge
  –   Mid Atlantic Ridge (Slow 1-5 cm/year)
  –   East Pacific Rise (Fast 9-18 cm/year)

• Continental Divergent Margins
  – Crustal upwarp, Rift Valley, Linear Ocean
  – East African Ridge, Red Sea
Continental Divergent Margins

  African Rift Valley
Mid Atlantic Ridge




                 http://www.ngdc.noaa.gov/
Mid Atlantic Ridge




           http://faculty.washington.edu/lyn4/images/iceland.jpg
Mid Atlantic Ridge




        httphttp://www.geomorph.org/gal/mslattery/IAG1.jpg
East Pacific Rise




                    http://www.ngdc.noaa.gov/
East Pacific Rise




                    http://geologyindy.byu.edu/
East Pacific Rise
Divergent margin vulcanism
Divergent margin vulcanism
Ocean Crust Age
Convection Processes




Shallow and deep mantle convection cells
Passive Continental Margins
Figure 2.28
        Transform Faults

• Two plates slide by each other
• Numerous earthquakes along faults
• Common in divergent and convergent
  margins
Transform Fault
Mid Atlantic Ridge




                 http://www.ngdc.noaa.gov/
        San Andreas Fault
between Pacific & N. American plates




                       •http://quake.wr.usgs.gov/kap/carrizo/
   Plate Tectonics History
• Alfred Wegener (1915)
  – Continental Drift Theory
  – Panagea (200-250 MY)
   Plate Tectonics History
• Alfred Hess (1960)
  – Seafloor spreading theory
  – Geo-Poetry




   WHAT DATA PROVES PLATE
         TECTONICS?
Figure 2.17
Magnetic Anomaly
Reversal
 Earth’s
Magnetic
Polarity
Sediment Thickness
         Ocean Sediment Drilling




ODP (Ocean Drilling Program)
Age Difference
      Ocean Crust: <200 MY
      Continental Crust: <3800 MY
Earth Quake
Distribution
Earthquakes

Shallow (<100km)




Deep (>100km)
Continent Fitting
Paleomagnetism
Direct Movement
Measurements

								
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