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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.)
What constitutes the Theory of plate tectonics?
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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
Testing the hypothesis
The Glomar
Challenger
drilling ship
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Current drilling vessels
JOIDES Resolution
Texas A&M and
Columbia Universities
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)
Chikyu
JAMSTEC
What kind of data did the
ocean drilling program collect?
Magnetic Reversals on Earth
• 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?
Normal polarity (today)
Reverse polarity
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Magnetic reversals in the Pacific
Magnetic Reversals and Age
Ages of Sediments
Data from Deep-sea Drilling Project
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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
The big picture
Also identified changes in climate, ocean chemistry and marine
plankton assemblages over 100 m.y. time scales.
Ridge Crest
Sediment
Oceanic crust
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
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Types of plate boundaries
Types of plate boundaries:
Transform faults Divergent Convergent
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)
Figure from USGS
Important examples of important plate boundaries
Blanco Fracture Zone
Transform boundary
San Andreas fault zone
Convergent plate boundary:
continental-continental crust
Himalayan mountains
All three types of plate
boundaries off WA coast
• Juan de Fuca ridge
• Blanco Fracture zone
• Cascadia subduction zone
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“Hot spots” and island chains
Island and seamount formation
Do hotspots stand still?
Tarduno et al. Science, August 22, 2003
Where does the hot stuff in
hotspots come from?
Hand, 2015, Science
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Patterns and observations
Mantle-core
boundary
French and Romanowicz, 2015, Nature
Tale of two coastlines …
Ocean margins and bathymetry
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
Ch. 3, The sea floor and its sediments
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http://pubs.usgs.gov/publications/text/historical.html
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
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1.6 m
1.6 m
Geometry of passive continental margins
Primarily rocky
coastline
Primarily sandy
beaches
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Atlantic
continental
slope
http://ccom.unh.edu/images/lots/atlantic/Atlantic_North_bathy.jpg
Maryland
Seafloor at 740 m, Block Canyon
How do these canyons form?
New Jersey
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Breaking of transatlantic cables
Nov 18, 1929
Nova Scotia
Grand Banks
Earthquake
Epicenter
Sediment sources for continental rise:
1: Continental erosion and transport across continental shelf
2: Slow accumulation of biogenic particles from open ocean
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 Deposits
Why are these deposits restricted to passive margins?
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Active versus passive continental margins
Cascadia
Subduction
Zone
Image from USGS
Hydrothermal vents: E.g., Axial volcano of the Juan de Fuca ridge
from: http://www.rsmas.miami.edu/personal/schuller/images/map_juan_de_fuca_subduction2.gif
http://www.pmel.noaa.gov/vents/
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Hydrothermal vents
“Black smoker” and tube worms at Juan de Fuca ridge
hydrothermal vent system
http://www.pmel.noaa.gov/vents/
HDTV photo of Juan de Fuca Ridge sediment
Photo: http://www.visions05.washington.edu/
11:00 AM
http://novae.ocean.washington.edu/story/Ashes_CAMHD_Live
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Passive margin
Active margin
Image from NOAA
Image from NOAA
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
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