Fnft: The major plates of the earth's crusts
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Transcript of Fnft: The major plates of the earth's crusts
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3 What does the bottom of the ocean look like?
OR
What is the topography or bathymetry of the
ocean floor?
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Fnft: The major plates of the earth's crusts
Courtesy of Reto Stockli, NASA Earth Observatory
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3Topography of the
Ocean Floor
• echo soundings (1920’s)• ocean was not deepest in the center • deepest part of the ocean lie near its edges
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Figure 3.3- Side-scan SONAR (Sound Navigation and Ranging)
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Figure 3.2- Multibeam SONAR (Sound Navigation And Ranging)
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An echo sounder trace. A sound pulse from a ship is reflected off the seabed and returns to the ship. Transit time provides a measure of depth. For example, it takes about 2 seconds for a sound pulse to strike the bottom and return to the ship when the water depth is 1,500 meters (4,900 feet). Bottom contours are revealed as the ship sails a steady course. In this trace, the horizontal axis represents the course of the ship, and the vertical axis represents the water depth. The ship has sailed over a small submarine canyon.
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Ridges/trenches in South Atlantic Sea Floor
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Figure 3.C
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Fig nftBathymetry can tell you wherethings are: Oceanic ridge system
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Figure 3.6
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BATHYMETRY – OCEAN FLOOR CONTOURS
Fig 4-5, g
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AtlanticOcean
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fnft
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Fnft: Some large-scale features of the North Atlantic seafloor
Courtesy National Geophysical Data Center/NOAA
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3Mid-Atlantic Ridge between Florida and western Africa
Canyon in middleof ridge
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3Topography of the
Ocean Floor
REMEMBER: • deepest part of the ocean lie near its edges
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fnft
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3Topography of the
Ocean Floor
• Submerged outer edge of the continents are called continental margins
• Deep-sea floor beyond these is called the ocean basin
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Fig 4-9, g
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Figure 3.8
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Florida coast
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3but
•What goes UP must go DOWN! &
•There are 2 sides to every…OCEAN!
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Figure 3.7
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Fig 4-7, g
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32 types of “margins”
• PASSIVE MARGIN: Continental margins that face diverging plates. These do not coincide with plate boundaries. Little or no activity. Typically associated with the Atlantic.
• ACTIVE MARGIN: Continental margins that face converging plates. These coincide w/plate boundaries. A lot of activity (earthquake/volcano). Typically associated with the Pacific.
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3Continental Margins
•Passive margins – – continental margins not located on
plate boundaries – Atlantic-type margins
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3Continental Margins
•Active margins- – continental margins on the edge of
convergent or transform plate boundaries
– Pacific-type margins
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Fig 4-8, g
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3 Continental Margin:
Continental SHELFContinental BREAKContinental SLOPEContinental RISE
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Fig 4-9, g
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3Continental Margins
(Shelves)•Width of Continental Shelf is
determined by :• proximity to a plate boundary
(active margins have narrow shelves while passive margins have broad shelves)
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3Continental Margins
(Shelves)•Continental Shelves
– Shallow, submerged extension of a continent
– broad, gently sloping – 7.4% of earths Ocean area
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Fig nft
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3Continental (Passive)
Margins•Shelf break –
– transition between the continental shelf and the continental slope
There are also changes from the continental slope (edge of shelf) to the continental rise (ends at edge of ocean floor).
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3Continental Margins
• Continental Slopes– Steeper than the shelf – end at the deep ocean
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Fig 4-9, g
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3Continental Margins
• Continental rises– at the base of continental slope – covered by a blanket of accumulated
sediment– gradual slope
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3Folded ridges of sediment cover the ocean floor west of Oregon
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3Continental Margins
• Submarine Canyons– cut into the continental shelf and
slope – formed by turbidity currents
(avalanche-like sediment movements)
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3SubmarineCanyonOff ofThe coastOf NewJersey
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3What comes next?
• Where the Continental Slope/Rise (granite rock) meets the “deep” ocean floor you get a sediment covered area (Continental Rise) that meets the “true” ocean floor (basalt rock)…what do you find there? What does it look like?
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Fig 4-9, g
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3Ocean Basin
• thick layer of sediment (up to 5 km or 3mi thick) covering basaltic rocks
• Make up more than ½ of the earth’s surface
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Figure 3.15
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3Ocean Basin
•Oceanic ridges– Underwater mountain chain – an active spreading center– offset at regular intervals by transform
faults– You know this as “Sea Floor Spreading”
(divergent plate boundary)
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Fig nftWHERE THE RIDGES ARE!
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Fig. 4-16a, p. 89
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• Midoceanic Ridge Province consists of a continuous submarine mountain range.
• It covers about one third of the ocean floor.• It extends for about 60,000 km around the Earth.
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3Other examples of what
“exists” on the Ocean Floor
• SeaMounts• Guyots• Abyssal Hills• Abysall Plains• Trenches• Island Arcs (seen above “land”)• Hydrothermal Vents
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3Ocean Basin
• Seamounts– Inactive volcanoes that do not rise above
the surface of the ocean– They are tall with steep slopes– (Made of) Basalt!
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3Ocean Basin
• Guyots– Flat-topped seamounts that were eroded
by wave action
• Abyssal Hills– abundant, small sediment-covered extinct
volcanoes
Both still BASALT!
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guyots (G) and seamounts
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Figure 2.26
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3Ocean Basin
• Island Arcs– Curving chains of volcanic
islands and seamounts found paralleling the edge of trenches
– Part of an “Ocean-Ocean” Convergent Plate Boundary geographic result
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3Ocean Basin
• Abyssal Plains– Flat, featureless, sediment-covered ocean
floor
• Trenches– Arc-shaped depression in the deep
seafloor– a converging oceanic plate is subducted
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• Deep Ocean Province is between the continental margins and the midoceanic ridge .
• It includes a variety of features from mountainous to flat plains: – Abyssal plains– Abyssal hills– Seamounts– Deep sea trenches
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Figure 3.12
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3Ocean Basin
• Trenches– Arc-shaped depression in the deep
seafloor– a converging oceanic plate is subducted
(either Oceanic-Oceanic or Oceanic-Continental Crust)
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Figure 3.13
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3Ocean Basin
•Hydrothermal vents– average temp is about 8-16oC (46-61oF)
much warmer than the typical 3-4oC (37-39oF)
– support a unique community of organisms that depend on bacteria
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Approximate locations of confirmed hydrothermal vents and cold seeps
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Cross-section of a ridge axis and the plumbing connected to a vent chimney
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A black smoker on the Galápagos Rift Zone.
Courtesy of UCSB, University S. Carolina, WHOI/NOAA
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Red-plumed tube worms
Courtesy of Monika Bright, University of Vienna, hydrothermalvent.com
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3Importance of
Vent Ecosystem Discovery1. Life in extreme
environments2. Life independent of sun
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3Chemosynthesis = a type of
primary productionPhotosynthesis uses sunlight + carbon dioxide coverts to foodChemosynthesis uses sulfur + carbon dioxide converts to food
Photosynthesis reaction:CO2 + H2O + sunlight CH2O + O2
Chemosynthesis reaction:O2 + CO2 + H2O + H2S CH2O + H2SO4
where H2S is hydrogen sulfide, H2SO4 is sulfuric acid, and CH2O is “food” or organic material
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3PHOTOSYNTHESIS
+
CO2 + H2O O2 + [CH2O]
CHEMOSYNTHESISCO2 + H2O + H2S + O2 [CH2O] + H2SO4 CO2 + H2O + H2S + O2 [CH2O] + H2SO4
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3Importance of Vent
Bacteria
• Base of vent ecosystem -- chemosynthesis• Possible origin of life on Earth• Illustrate link between biology and habitat
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3Coral Reefs?
• All of these different land/(under)water formations can yield MANY different types of coral reefs (a very diverse, valuable, marine community) too!
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3Coral Reef Development
• Fringing reefs – develop along margin of landmass
• Barrier reefs – separated from landmass by lagoon
• Atolls – reefs continue to grow after volcanoes are submerged
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3Coral Reef Development
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Fnft
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Fnft
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Fnft
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Fnft
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Figure 4-6c Present-Day Margin Southeast of Cape Cod
Fnft – Reefs can exist FAR offshore (relics from years ago)