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Geology 12Geology 12
PresentsPresents
Unit OutlineUnit Outline– Chp 10 Earth’s Chp 10 Earth’s
InteriorInterior– Chp 11 Sea FloorChp 11 Sea Floor– Chp 12 Plate Chp 12 Plate
TectonicsTectonics– Chp 9 Seismic Chp 9 Seismic
(EQ)(EQ)– Chp 13 StructureChp 13 Structure
Chp 11 Seafloor
• Volcanoes outgasses water to fill oceans
• Average depth = 4 km
• Continental Margins mark edge of continent from deep sea floor– 2 types of margins
1. Passive Margin = where oceanic plate is fused to continental plate and large amount of sediment is deposited.– Ex: Eastern N. America
Cont’l PlateOceanic Plate
Cont’l Shelf Cont’l Slope Cont’l RiseAbyssal
PlainSubmarine canyon
Cont’l Margin
fused
• Submarine canyons – Cut into cont’l shelf-slope by:
• a) rivers when sea-level was up to 130 m lower during ice ages
• animation
• b) turbidity currents = underwater landslides that erode slope and travel for 100’s of km
– Sediments are deposited as a deep sea fan as graded bedding
Passive Margins
Hudson River Submarine Canyon
New York
Cont’
slope
Cont’ s
helf
2. Active Margin = where oceanic plate is subducting under continental plate
Ex: W. coast of S. America
Oceanic plate
Abyssal plain
Cont’l plate
Trench
Cont’l slope
Cont’l shelf Volcano
Active Margins
• Oceanic (spreading) Ridge: where new oceanic plate is being created by volcanism
Pillow lava
Sheeted dikes and gabbro
Rift valley
mantleperidotite
seamounts Island/seamount
Ocean Ridge
• Guyots
New volcanic island
Eroded flat by waves Guyot
Guyots & Seamounts
Guyots & Seamounts
• Reefs
Fringing reef
Barrier reef Atoll
Top view
Cross section
lagoon
Fringing Reef Island
Barrier Reef Island
Atoll
• Islands get smaller as they age due to:– a) wave erosion– b) oceanic plate sinks as it moves way from
divergent boundary or hot spot
– See Q14d, p.9 of WS 12.2
Use the diagram of a typical ocean basin to answer question 6.
6. The diagram represents a cross-section of an ocean basin. The number which represents a diverging plate boundary is
A. 1B. 2C. 3D. 4
Read Chapter 11Do WS 11.1
Read Chapter 12
Go to Chp 12 Plate Tectonics