The Deep Oceans
Take-Away Points
1. The earth has two kinds of crust
2. Continents have thick, light, granitic crust,
Oceans have thin, dense, basaltic crust
3. How we probe the sea floor
4. Features on the sea floor and edges of
continents are products of plate tectonics
5. Submarine landslides are important on
continental margins
6. Deep ocean sediment comes from the
continents and marine organisms
The TwoStory Planet
1. The earth has two kinds of crust
Earth Has Two Kinds of Crust
2. Continents have thick, light, granitic crust, Oceans have thin, dense, basaltic crust
Continental and Oceanic Crust
Continental Crust (Granitic)
• Residue of Long-Continued Partial Melting
• Thick and Light
• Ancient: > 2.5 b.y.
Oceanic Crust (Basaltic)
• Derived Directly From Mantle
• Thin and Dense
• Young: < 200 m.y.
2. Continents have thick, light, granitic crust, Oceans have thin, dense, basaltic crust
Investigating the Sea Floor
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Coring
Deep-Sea Drilling
Sonar
Seismic Refraction
Gravity Surveys
Magnetic Surveys
3. How we probe the sea floor
Piston Coring
3. How we probe the sea floor
Deep Ocean Drilling
Project Mohole
• Original Intent: Drill to Earth’s Mantle
• Drill in Oceans where Crust is Thinnest
• Hidden Agenda: Complete History of Oceans
• Challenge: Replacing Drill Bits in 5 km of
Water
• Plate Tectonics Showed that Mantle is
Exposed in a Number of Places
3. How we probe the sea floor
Deep Ocean Drilling
• Original Objective Abandoned
• Renamed Deep Sea Drilling Program
• Now Called Ocean Drilling Program
3. How we probe the sea floor
Sonar
3. How we probe the sea floor
Seismic Refraction
3. How we probe the sea floor
Makeup of Ocean Crust
4. Features on the sea floor and edges of continents are products of plate tectonics
Anatomy of a Mid-Ocean Ridge
Continental Margins
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Shelf
Slope
Rise
Active: Subduction Zones. Sometimes Called
Leading Edge
• Passive: No Subduction. Sometimes Called
Rifted or Trailing Edge
4. Features on the sea floor and edges of continents are products of plate tectonics
A Continental Margin
4. Features on the sea floor and edges of continents are products of plate tectonics
Evolution of a Passive Margin
4. Features on the sea floor and edges of continents are products of plate tectonics
Anatomy of a Passive Margin
4. Features on the sea floor and edges of continents are products of plate tectonics
Features of the Deep Ocean
• Mid-Ocean Ridges
• Abyssal Plains
• Fracture Zones
• Oceanic Trenches
• Seamounts
• Submarine Canyons
• Submarine Fans
4. Features on the sea floor and edges of continents are products of plate tectonics
Crest of
the MidAtlantic
Ridge
4. Features on the sea floor and edges of continents are products of plate tectonics
Sea-Floor
Spreading,
Mid-Atlantic
Ridge
1.
Features on the sea floor and edges of continents are products of plate tectonics
Turbidity Flows – Grand Banks, 1929
5. Submarine landslides are important on continental margins
Where Sediment Comes From
6. Deep ocean sediment comes from the continents and marine organisms
Atlantic Sediments
Deep Ocean Sediments
6. Deep ocean sediment comes from the continents and marine organisms
Take-Away Points
1. The earth has two kinds of crust
2. Continents have thick, light, granitic crust,
Oceans have thin, dense, basaltic crust
3. How we probe the sea floor
4. Features on the sea floor and edges of
continents are products of plate tectonics
5. Submarine landslides are important on
continental margins
6. Deep ocean sediment comes from the
continents and marine organisms