Geology

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• Geology
• Plate Tectonics
• Mid-Ocean Ridge System
• Discovered from sea floor mapping with SONAR
  during and after World War II
• Largest geological feature on Earth
• Ridges displaced in some areas by transform
  faults
• Trenches
• Conspicuous sea floor features
• Especially common in the Pacific Ocean

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http//www.ngdc.noaa.gov/mgg/image/global_topo_lar
ge.gif
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Fig. 2.5
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• Geology
• Plate Tectonics - Evidence
• Ring of Fire
• Geological activity (e.g. earthquakes, volcanoes)
  associated with mid-ocean ridges and with trenches

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Fig. 2.6
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• Geology
• Plate Tectonics - Evidence
• Ring of Fire
• Geological activity (e.g. earthquakes, volcanoes)
  associated with mid-ocean ridges and with
  trenches
• Closer to ridges
• Younger rock
• Thinner covering of sediment
• Magnetic anomalies
• Caused by magnetic field reversals
• Symmetrical on either side of ridge axis

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Fig. 2.7
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• Geology
• Plate Tectonics - Mechanism
• Sea-Floor Spreading
• Mid-ocean ridges contain rifts where two pieces
  of crust are moving apart and new oceanic crust
  is being created (spreading rate ca. 2-18 cm y-1)
• As rift widens, hot mantle material rises through
  rift, cools and solidifies to form new oceanic
  crust
• Ridges spreading centers
• Theory generated by induction explains
  observations
• Younger rock closer to ridges
• Thinner sediment closer to ridges
• Patterns of magnetic anomalies

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Fig. 2.8
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• Geology
• Plate Tectonics - Mechanism
• Sea-Floor Spreading
• Lithosphere made up of lithospheric plates
• Plates may contain continental crust, oceanic
  crust, or both
• Plates rest on asthenosphere (plastic upper
  mantle)
• Plate boundaries correspond to locations of
  mid-ocean ridges and to trenches
• Not all plates completely characterized yet

Fig. 2.9
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• Geology
• Plate Tectonics - Mechanism
• Subduction
• Old crust destroyed when one plate dips below
  another
• Oldest oceanic crust 200 million years old
• Denser plate subducted beneath less dense plate
• Locations oceanic trenches subduction zones
• Recycles crust and supports volcanic activity
• May result from collisions between
• Continental plate and oceanic plate (oceanic
  plate subducted usually forms volcanoes)
• Two oceanic plates (denser plate subducted
  usually forms island arc)

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Fig. 2.10
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Fig. 2.11
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• Geology
• Geological History
• Continental Drift
• All continents joined together 200 mya
• Pangaea supercontinent
• Panthalassa single ocean ? Pacific Ocean
• Tethys Sea Shallow sea between Eurasia Africa
  ? Mediterranean Sea
• Sinus Borealis ? Arctic Ocean
• Laurasia separated from Gondwana 180 mya

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Fig. 2.14
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Fig. 2.14
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Fig. 2.14
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Fig. 2.14
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Fig. 2.14
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Global Plate TectonicsJurassic to Present Day
By L.A. Lawver, M.F. Coffin, I.W.D. Dalziel L.M.
Gahagan, D.A. Campbell, and R.M. Schmitz ?2001,
University of Texas Institute for
Geophysics February 9, 2001
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We wish to thank the PLATES sponsorsfor their
supportConoco, TotalFinaElf, Exxon-Mobil,
Norsk Hydro, and Statoil.
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For more information, contactLisa M.
GahaganInstitute for Geophysics4412 Spicewood
Springs Rd., Bldg. 600Austin, TX
78759plates_at_ig.utexas.edu
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Earth Future Drift
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Earth Future Drift
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Earth Future Drift
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Earth Future Drift
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Earth Future Drift
Link
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• Geology
• Geological Provinces
• Continental Margins
• Boundaries between continental and oceanic crust
• Accumulate sediment deposits from rivers and
  streams
• Continental shelf
• Continental slope
• Continental rise
• Deep-Ocean Basins
• Mid-Ocean Ridges
• Hot Spots

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Fig. 2.17
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• Geology
• Geological Provinces
• Continental Margins
• Continental shelf
• Shallowest part of continental margin
• Underlie 8 of ocean surface
• Richest, most productive parts of ocean
• Some parts exposed during times of low sea level
  and eroded by rivers and glaciers now are
  submarine canyons

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California Coastline
Monterey Canyon
Fig. 2.19
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• Geology
• Geological Provinces
• Continental Margins
• Continental shelf
• Shallowest part of continental margin
• Underlie 8 of ocean surface
• Richest, most productive parts of ocean
• Some parts exposed during times of low sea level
  and eroded by rivers and glaciers now are
  submarine canyons
• Varies in width from 1 km (Pacific coast of S Am)
  to 750 km (Arctic coast of Siberia)
• Ends at shelf break, usually at 120-200 m but up
  to 400 m depth.

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• Geology
• Geological Provinces
• Continental Margins
• Continental slope
• Transition from continent to ocean
• Furrowed with submarine canyons in many areas
• Canyons channel sediment and debris to deep sea
  floor
• Continental rise
• Accumulated sediment, including deep-sea fans
• May be extensive in areas where large rivers
  discharge into ocean

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• Geology
• Geological Provinces
• Continental Margins
• Active margins
• Geologically active
• Usually subduction or transform fault
• Steep, rocky shoreline
• Narrow continental shelf
• Steep continental slope
• Usually lack well-developed continental rise
• Sediment removed by geological activity

Fig. 2.20
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• Geology
• Geological Provinces
• Continental Margins
• Passive margins
• Not geologically active
• Flat coastal plain
• Wide continental shelf
• Gentle continental slope
• Usually well-developed continental rise

Fig. 2.20
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Fig. 2.20
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• Geology
• Geological Provinces
• Deep-Ocean Basins
• Mostly between 3000 and 5000 m
• Predominantly abyssal plain

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• Geology
• Geological Provinces
• Deep-Ocean Floor
• Mostly between 3000 and 5000 m
• Predominantly abyssal plain
• Seamounts Undersea mountains
• Guyots Flat-topped seamounts
• Rises Large table-like features
• Common in Pacific

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California Coastline
Monterey Canyon
Fig. 2.19
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• Geology
• Geological Provinces
• Mid-Ocean Ridges
• Central region rift valley
• Fractures allow sea water to seep into crust

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Fig. 2.23
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• Geology
• Geological Provinces
• Mid-Ocean Ridges
• Central region rift valley
• Fractures allow sea water to seep into crust
• Water is heated by rock and rises back to surface
  of sea floor
• Hot water picks up dissolved minerals (iron,
  manganese, sulfides)
• Hot, mineral-rich water contacts cold sea water
• Precipitate forms
• Black smokers
• May be very hot (350 oC or more)

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Fig. 2.25