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