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Plate Tectonics
A Major Revolution in Our Understanding of the Earth
There are fossils of marine organisms that can be found
in many of the highest elevations of the world—including the Himalayas
How did rocks that formed on the deep ocean floor near the
equator end up making hills in San Francisco?
Radiolarian chert in San Francisco
If deposited by a great flood—why are
the beds so deformed?
North Eastern Japan March 11th 2011
What is so great about the Theory Plate Tectonics?
Why is it even important?
Volcano Global Distribution
This map does not including all the volcanic activity along the MOR’s
Global Distribution of Earthquake Occurrence
For the most part, earthquakes occur along plate boundaries.
What are the Plate Boundary Types?
• Name a location that you could find each type.
• Is volcanism associated with the plate boundary and
if so what type of volcanism?
• Which types of plate boundaries do you think create
large earthquakes? How about tsunamis?
Divergent Plate Boundary
*
Practice drawing and labeling this picture---you need to know this by memory!
e.g. Mid-Atlantic Ridge
Transform Plate Boundaries
is a strike-slip fault plate boundary.
The San Andreas Fault is an example
(that is where we live!).
Turkey
Oceanic to Oceanic Convergent
Boundary
*
Practice drawing and labeling this picture---you need to know this by memory!
e.g. Japan, Philippines, Indonesia, Aleutian Islands
Continent to Ocean Convergent
Boundary
Practice drawing and labeling this picture---you need to know this by memory!
*
e.g. N. California, Oregon, and Washington, Central and Western S. America
Continent to Continent Convergent
Boundary
Practice drawing and labeling this picture--you need to know this by memory!
India
China
Cratons are very old, stable continental interiors.
Often crystalline metamorphic rock. Cratons are
composed of shields and platforms.
A platform is sedimentary deposits covering the crystalline basement rocks of a shield.
*An important concept:
Temperature change of an
object changes the density
of that object. Density differences
controlled by temperature changes
is what creates convection.
Composition
Felsic vs. Mafic
Motion in the asthenosphere is
what drives plate tectonics!
Pangaea Breakup
Building the Western Margin of
North America
Continents can grow by accretion of terranes.
Much of Western North America
is accreted terranes.
Emperor Seamounts
Hawaiian Island are created by a Hot Spot. This is volcanism
not associated with tectonic plate boundaries. Islands and seamounts
are created by the volcanism over the hot spot but they are carried away
by the moving tectonic plate. They are traveling towards a subduction zone
where they will either be subducted or accreted.
Terrane Formation
Siberian Traps: A massive flood basalt event that is thought to have caused
the largest mass extinction ever to occur. This mass extinction marks the
Permian-Triassic boundary.
Photo by John Stodder;
Image from Woods Hole
Oceanographic Institution.
Flood Basalt
Coincident with the K-T mass extinction 65 Ma
Cretaceous-Tertiary Boundary
(End of the Dinosaurs!)
9 Ma
Continents can grow from volcanism.
From the info given so far,
what two ways do continents grow?
Oceanic to Oceanic Convergent
Boundary
*
Practice drawing and labeling this picture---you need to know this by memory!
e.g. Japan, Philippines, Indonesia, Aleutian Islands
Volcanic Island Arc
Ash plume arising
from Mount Cleveland
on May 23, 2006, as
seen from the
International Space
Station. Astronauts
were the first to realize
the eruption, and
alerted the Alaska
Volcano Observatory
to it.
Cleveland Volcano Aleutian Islands Alaska
Alaska
Aleutian Islands
Trench
Japan
Trench
Indonesia
Trench
Micronesia
and
Melanesia
(South Pacific)
Trench
Australia
Continent to Ocean Convergent
Boundary
Practice drawing and labeling this picture---you need to know this by memory!
*
e.g. N. California, Oregon, and Washington, Central and Western S. America
Continental Volcanic Arc
Large red triangles show
volcanoes with known or
inferred Holocene
eruptions; small red
triangles mark volcanoes
with possible, but uncertain
Holocene eruptions or
Pleistocene volcanoes with
major thermal activity.
Yellow triangles distinguish
volcanoes of other regions.
Central America
and
West Coast of
South America
Trench
Subduction
(a closer look)
Tsunami
Discussion:
What is the difference between an accreted terrane and a accretionary wedge?
What is the ultimate cause of convection?
What type of plate boundary do we live on?
Why did Pangaea break up?
What are some of the
consequences of this break up?
Continental
Rifting
Passive Margin
Example: East Coast of North America
Sometimes called an Atlantic Style continental margin.
Note: The edge of a continent is not necessarily a
plate boundary. Notice that the North American Plate
extends out into the Atlantic ocean to the spreading
center.
Ophiolite Sequence:
They can be scraped off pieces of ocean crust have
been accreted to continents (accreted terrane).
Ocean Crust comparison to the scale of the Grand Canyon.
Serpentinite – Mt Diablo
Vulcan Octopus © Rod Mickens / AMNH
Pogonophora (Tube Worms)
www.ucmp.berkeley.edu
Pillow Basalt
Divergent Plate Boundary
*
Practice drawing and labeling this picture---you need to know this by memory!
e.g. Mid-Atlantic Ridge
Transform Plate Boundaries
is a strike-slip fault plate boundary.
The San Andreas Fault is an example.
Turkey
WHAT KIND OF CONTINENTAL MARGIN DO WE LIVE ON?
Cross-section line through the East Bay
Hills, the Bay, San Francisco and
out the shelf to the Farallon Islands
Home Sweet
Home
The Cascade Range is a continental
volcanic arc. Subduction of oceanic plate
is occurring in the Pacific Northwest.
Subduction ceased in Central and Southern
California when the Farallon Plate
completely subducted, thus we do not have
active volcanism (related to subduction) in
Central and Southern California.
Continent to Continent
Convergent Boundary
Practice drawing and labeling this picture--you need to know this by memory!
India
China
Continental–Continental
Convergence
© 2011 Pearson Education, Inc.
Suture Zone
Continuity of mountain ranges and rock types
Mountains of similar age
and structure show continuity
when continents are joined.
This also suggests the same
mountain building event. The
collision of continents builds
mountains!
Continent to Continent Convergent
Plate Boundary
A real mash up since continents do not want
to subduct. They both are low density
and want to float.
India is still moving North and the
Himalayas are still rising!
We start again in 10 minutes and 32 seconds.
The coordinates of San Francisco is roughly:
North 37 degrees, West 122 degrees
If you wanted a more precise location,
you would need to measure the angle in minutes.
An even more precise measurement would include seconds.
One degree=60 minutes
One minute=60 seconds
Break time!
A jellyfish does not have a brain or central nervous system, and they do not
have specialized digestive, osmoregulatory, respiratory, or circulatory systems.
~90% water
They control movement with
a hydrostatic skeleton
and many can sense light.
Intro to Deformation
Dorset, England
Geothermal Gradient: Near the Earth’s surface the temperature
increases with depth at a rate of about 25 degrees C per km.
Deformation type Causes
Results
Elastic – temporary
deformation
Stress not greater than
elastic limit of rock
Strain released and shape
returns to normal
Brittle – permanent
break
Stress greater than yield
point of rock (usually
colder temperatures –
nearer surface – rapid
stress application)
Strain released with break
in rock (faulting)
Plastic – permanent
ductile deformation
Stress greater than elastic
limit of rock (usually
higher temperatures –
deeper underground –
stress applied slowly
over long time)
Strain is permanent
(folding)
Rocks buried at depth have stress being applied to it equally from all directions.
Plate Tectonics often applies stress to rocks that is
not equal in every direction.
Stress Type: Tension (results in thinning of the crust from being stretched).
Stress Type: Compression (results in thickening/shortening of the crust).
Stress Type: Shear (no change in crust thickness).
Stress types
Plate
boundaries
Fault
types
Crustal
thickening or
thinning or
both/none?
Mountain types
(if any)
Compression
Convergent
Reverse (+
thrust)
Thickening
Fold and Thrust
Tension
Divergent
Normal
Thinning
Fault-Block
Shear
Transform
Strike-slip
None
None
Fault Types
Blind Thrust Fault
Normal Fault
Strike-Slip Fault
(Left-Lateral)
Reverse
Fault
Oblique-Slip Fault
A Thrust Fault is a reverse
fault with dip<45 degrees.
A very low angle thrust fault
is called an over-thrust.
SHEAR
SHEAR
Left-Lateral
STRIKE-SLIP
Right-Lateral
STRIKE-SLIP
REVERSE
NORMAL
HW
FW
FW
HW
Compression
Tension
REVERSE
NORMAL
HW
FW
HW
FW
Tension
Compression
Glacier National Park
What do you see?
Discuss with your neighbor the principle
of superposition.
Where is the oldest rock found?
Y
O
O
Y
O
Syncline
North-Plunging Anticline
Y
South-Plunging Syncline
What type of structure is this?
Wallace Creek
143
Images (c) 2001, 2002 Andrew Alden, licensed to About.com, Inc.
Additional Resources
Quantitative Reasoning #2:
Question:
If the middle of the Atlantic Ocean is discovered, by satellite imagery, to spread, on
average, 2 inches per year, and assuming that rate has been fairly constant through the
development of the Atlantic Ocean, when did spreading first begin?
What do we know?
2 inches of spreading every 1 year
OR
2 inches
year
Distance between the continental shelves of Africa and South America are ~5,000 km
apart (5,000 km = 5 x 103 km)
1 inch = 2.54 cm
100 cm = 102 cm = 1 m
1000 m = 103 m = 1 km
Math:
5 x 103 km x 103 m x 102 cm x 1 in = 5 x 103 x 103 x 102 in = 2 x 108 in
1
1 km
1m
2.5 cm
2.5
2 x 108 inches x 1 year = 108 years or 102 x 106 years = 100 million years
1
2 in
Quantitative Reasoning #2:
Question:
If the fastest spreading center, which is the East Pacific Rise, spreads at a rate of 18
centimeters per year, and it’s been spreading for 100 million years, how much new
Pacific Ocean crust has been formed as a result?
What do we know?
18 cm of spreading every 1 year
OR
18 cm
year
100 million years = 102 x 106 years = 108 years
100 cm = 102 cm = 1 m
1000 m = 103 m = 1 km
Math:
108 years x 18 cm x 1 m x 1 km = 18 x 108 km= 18 x 108 km = 18 x 103 km
1 yr
102cm 103 m 102 x 103
105
= 18,000 km
Earth’s radius = 6400 km
Circumference = 2πr = 40,192 km The Pacific Ocean should be ~ ½ the circumference of
the planet? Is it? If not, where did it go?
Deformation type Causes
Results
Additional Resources
Measuring Speed and Direction
Distance between hotspot and
9 m.y. rock is ~270 km.
distance
Speed =
time
270km
Speed =
9my
Measuring Speed and Direction
km
270km
Speed =
= 30
9my
my
km
cm
÷10 =
my
yr
Measuring Speed and Direction
km
cm
30
÷ 10 = 3.0
my
yr
How fast is the Pacific Plate moving?
Solve then discuss with your neighbor—
make sure you both understand how to
solve this type of problem.
If a region with a rich gold deposit is cut by a
fault that is known from other evidence to move
at a rate of 4 cm/yr. The gold was deposited 10
million years ago. At what distance along the
fault (in the direction of the fault movement)
would one look for the other part of the gold
deposit?
DEFINITIONS
As ultramafic magmas rise
through the crust, they leave
high-density minerals behind,
becoming less dense and
hence also more basaltic
and if travelling long enough
or far enough, more felsic!
Least dense FELSIC – granitic -- continental crust
Intermediate
MAFIC – basaltic -- oceanic crust +
hotspots
Most dense ULTRAMAFIC -- mantle rock