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Announcements

• Textbooks?

• ESCI 322 – Meet in Env. Studies Bldg Rm 60, 1 PM

• Marine geology problem set

• Today, finish plate tectonics, cover ocean margins

and bathymetry, start sediments?

• Thursday, finish sediments, quiz on Booth 1994 and

discussion on Puget Sound formation. (Lots of odd

terms in Booth paper – look them up as you read.)

Patterns and observations? Continental drift hypothesis

Early evidence for “continental drift”

Edward Bullard plot – 60’s

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Similar mountains and rocks across the AtlanticE.g., turbidite deposits in Maine

Distribution of earthquake epicenters

What constitutes the Theory of plate tectonics?

• The earth’s crust is made of plates

• New crust is created at spreading centers

• Old crust is destroyed at subduction zones

• Plates move from spreading centers toward subduction zones and mountains, volcanoes, and earthquakes form by plate motion

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Testing this hypothesis

• What kinds of data would you collect?

• What kind of equipment would you use?

Testing the hypothesis

The Glomar

Challenger

drilling ship

Current drilling vessels

JOIDES Resolution

Texas A&M and

Columbia Universities

Chikyu

JAMSTEC

Deep-sea drilling program: 1968 - 1983

Ocean drilling program: 1983 - 2004

Integrated ocean drilling program: 2004 - present

(> 36,000 cores from > 600 locations collected

through ODP)

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What kind of data did the

ocean drilling program collect?

• If crust were created at spreading

centers, the age of the crust would

increase as you move away from the

spreading center.

• How do you date the seafloor crust?

Magnetic Reversals on Earth

Normal polarity (today) Reverse polarity

Magnetic Reversals and Age

Magnetic reversals in the Pacific

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Ages of Sediments

Data from Deep-sea Drilling Project

Major findings of Deep-sea drilling project:

Sediment depth increases away from ocean ridges

Sediment age and age of the crust increases away from ridges

-magnetic and radiometric dating

Also identified changes in climate, ocean chemistry and marine

plankton assemblages over 100 m.y. time scales.

Ridge Crest

Sediment

Oceanic crust

The big picture

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Putting the pieces together

• What forces cause continents to move?

• How can plate tectonics explain our observations

about the distributions of mountains, trenches, and

earthquakes?

Driving force: Gravity

- Leading edges of plates pulled

deep into the mantle at trenches

(slab pull)

- Trailing edge of plates slide off the

ridges (ridge push)

- Convection cells inside the earth

create divergent boundaries, rifts

Types of plate boundaries:

1: Divergent plate boundary: “spreading center” where

crustal formation occurs

2: Convergent plate boundary: “subduction zone” where

crust is destroyed

3: Transform plate boundary: “transform faults” where plates

move past each other (intense seismic activity)

Types of plate boundaries

Figure from USGS

Transform faults Divergent Convergent

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Important examples of important plate boundaries

Convergent plate boundary:

continental-continental crust

Transform boundary Himalayan mountains

San Andreas fault zone

All three types of plate

boundaries off WA coast

• Juan de Fuca ridge

• Blanco Fracture zone

• Cascadia subduction zone

Blanco Fracture Zone

“Hot spots” and island chains

Island and seamount formation

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Do hotspots stand still?

Tarduno et al. Science, August 22, 2003

Where does the hot stuff in

hotspots come from?

Hand, 2015, Science

Mantle-core

boundary

French and Romanowicz, 2015, Nature

Patterns and observations

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Tale of two coastlines …

Ocean margins and bathymetry

Take-home messages

- Know the differences between active and passive margins

- Know the structures and provinces of the ocean floor from

the coast to the deep sea

- Understand the origin and significance of turbidite deposits

- Understand the processes that create hydrothermal vents

Ocean margins and bathymetry

Ch. 3, The sea floor and its sediments

http://pubs.usgs.gov/publications/text/historical.html

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Appalacian Mountains:

Sedimentary rock, deformed

from collision between N. Am

And Europe, ~480 mya

Supercontinent forms ~400

mya, more mountain building

Coastal rock formations

similar to those in Europe

and Africa. Ripped off

Pangaea when Atlantic

Ocean formed ~150 mya.

Primarily rocky

coastline

Primarily sandy

beaches

1.6 m1.6 m

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Primarily rocky

coastline

Primarily sandy

beaches

Geometry of passive continental margins

Atlantic

continental

slope

http://ccom.unh.edu/images/lots/atlantic/Atlantic_North_bathy.jpg

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Maryland

New Jersey

Seafloor at 740 m, Block Canyon

How do these canyons form?

Sediment sources for continental rise:

1: Continental erosion and transport across continental shelf

2: Slow accumulation of biogenic particles from open ocean

Breaking of transatlantic cables

Nov 18, 1929

Nova Scotia

Grand Banks

Earthquake

Epicenter

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Ancient turbidites along coast of Maine

Recent turbidite from the base of Zhemchug

Canyon, the largest submarine canyon in

the world (Bering Sea, 3600 m water depth)

Abyssal Plains Turbidite DepositsWhy are these deposits restricted to passive margins?

Active versus passive continental margins

Image from USGS

Cascadia

Subduction

Zone

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from: http://www.rsmas.miami.edu/personal/schuller/images/map_juan_de_fuca_subduction2.gif

Hydrothermal vents: E.g., Axial volcano of the Juan de Fuca ridge

http://www.pmel.noaa.gov/vents/

Hydrothermal vents “Black smoker” and tube worms at Juan de Fuca ridge

hydrothermal vent system

http://www.pmel.noaa.gov/vents/

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HDTV photo of Juan de Fuca Ridge sediment

Photo: http://www.visions05.washington.edu/ http://novae.ocean.washington.edu/story/Ashes_CAMHD_Live

11:00 AM

Image from NOAA

Passive margin

Image from NOAA

Active margin

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Summary of margins and bathymetry

I. Continental margins consist of shelf, slope, and rise

II. Coastlines are shaped by tectonic history, sea level

rise and (in northern latitudes) glaciations

III. Submarine canyons convey coastal sediments to the

deep sea forming the continental rise along passive

continental margins

IV. Active continental margins typically have a narrow

shelf and slope and no rise due to subduction

V. Geochemical processes at hydrothermal vents

affect elemental cycles and support chemosynthetic

communities of organisms