Transcript Structure of Ocean Floor

The Ocean
• EARTH: The only planet w/ Oceans (or liquid
water)
• Covers 71% of earth’s surface
• “Divided” into 4 large basins
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Pacific (largest, deepest)
Atlantic
Indian
Arctic (smallest, shallowest)
A fifth? The Antarctic…
Ocean basins
Ocean Basin Depths
Interior of Earth
The Difference Between an Ocean
and a Continent…ROCKS!
• Continent: very thick, very old, less dense
and made up of Granite
• Ocean (floor): younger, more dense, not as
thick and made up of Basalt
• Thus, the “Ocean Floor” “sinks” below the
continent(s) and provides the habitats of
marine organisms
Continental Drift
• If we know the Continental Crust and
Oceanic Crust have different
densities…how did they “separate” to
become 7 continents and 4 oceans?
• We start (Pangea) 210 mya!
PANGEA (the super continent)
• 180 million yrs. ago – all continents were
attached together and have slowly moved
apart over time
• Discovered (S. F. Bacon, 1600’s) “Coasts of
continents fit together like a puzzle.”
• Lead to theory of continental drift and plate
techtonics.
Pangea (reptile fossils)
• So…WHERE DID WE
START AND WHERE ARE
WE NOW?
Figure 2.14a
Figure 2.14e
PLATE TECTONICS
• Continental drift leads to the theory of Plate
tectonics
• Although Bacon discussed it in the 1600’s,
it was not understood until the 1960’s.
The Ocean Floor (P. Tectonics)
• Mid-Ocean Ridges
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Underwater mountain ranges
Fault: Crack in earths crust
Rift: Ocean crust separates & creates “cracks”
Earthquakes are common
• Trenches
– Deep depressions in the seafloor
– Mostly in Pacific, Volcanoes common
Major features of Sea Floor
CO 2
Mid-Atlantic Ridge (above sea surface in Iceland)
Sea-Floor Spreading (plate tectonics)
• New sea-floor forms at mid-ocean ridges
(where the edge of these “plates” meet)
• Continental Drift: If the plate (as it spreads
away from the ridge) contains continental
crust (on top) the continents “drift” (move)
apart.
How? Convection and Density!
Sea Floor Spreading:
X-section of sea floor @
Mid ocean ridge
Figure 2.08
Figure 2.07
Paleomagnetism:
Normal magnetism
@ ridge crests (but
Reversed in other
locations)
We get:
• Plate boundaries
• With geologic activity, such as earthquakes,
that (may) correspond w/ these plate
boundaries
Earthquake and Volcano distribution
Lithospheric plate boundaries
How does everything move? Plate
Tectonics!
• The earth’s upper layer, the lithosphere, is
divided into plates
• Plates may contain sea-floor, continents, or
both
• Plates are moving (few cm per year),
floating on top of the earth’s molten mantle
Subduction (plate techtonics)
• sea-floor is destroyed by plunging back into the earth’s
interior at trenches
• When 2 plates collide, 1 dips below the other (in to the
mantle) and 1 is destroyed (causing, sometimes,
earthquakes)
• Ocean vs. Cont. plate: ocean plate destroyed, can get
coastal mountain ranges
• Ocean vs. Ocean plate: 1 dips = volcano or earthquake
• Cont. vs. cont: none destroyed, mnt. Ranges fold
• 2 plates, no collision, lock/shear/earthquake (S. Andreas F)
Figure 2.10
Continental + Oceanic plate collision = trench, earthquake
Figure 2.11
2 oceanic plates collide = trench/earthquake
San
Andreas
Fault
(CA)
Figure 2.13
Sea Floor Regions
• All of this “plate” movement and geologic
activity that occurs under the water yields
different sea floor regions
• Each dependent upon depth, width, slope
etc.
Regions of the sea-floor
• Continental Margins contain continental
shelf, slope and rise
• Cont. shelf = shallow, most “rich” (diverse)
• Deep Ocean Floor, “Abyssal Plain”
• The Ocean “floor” (on average) is 2-3.5
miles BELOW the oceans (water) surface!
Figure 2.17
Continental margin
Active vs. Passive Margins
An active margin
is a geologically
very “active” area;
whereas a
Passive margin is a
geologically
in-active
area.
(Passive Margin) Continental Shelf (19 mi. off of Atlantic City, NJ)
Figure 2.18
Tom’s Canyon
Shelf break
The California Coast
Monterey
Canyon
Active Coast (CA)
Margins
• We know what it looks like at the top of the
(Continental) margin but what does it look
like AT the margin (at the ridge line, deep
under the oceans surface)?
“Black
Smoker”
Hydrothermal
Vent
(at a
Mid
Ocean
Ridge)
Figure 2.24
Black Smoker, cross section
Who are we?
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Iceland, Azores = fault (mountain)
Andes (mts.) = subduction trench (o-c)
Aleutian/Mariana (Is.) = sub. trench (o-o)
Himalayas (mts.) = sub. Trench (c-c)
Hydrothermal vents: Deep Ocean
• See Fig. 2.5 for locations and other “interesting” places to visit.
Major features of Sea Floor