Transcript Notes over Plates

Plates
Guest Lecture by Dr. Webster
Vocabulary of the Day
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Asthenosphere
Continental crust
Convergent margin
Divergent margin
Earthquake
Lithosphere
• Oceanic crust
• Plate tectonics
Subduction
• Transform margin
• Volcano
• Volcanoes
Goals
• Distinguish among types of plate tectonic
settings produced by plates diverging,
converging, and sliding past each other.
• Relate modern and ancient geologic features
to each kind of plate tectonic setting.
• Relate certain geologic hazards to specific
plate tectonic settings.
• Universal principles are discovered through
observation and experimental verification.
Prior Knowlege
• Please get out a piece of paper and
write your name on it.
• What do you already know? I’m going to
show you a few geographic features, I
would like you to tell me
• A) What is it (name if you know)?
• B) How it was formed?
Question 1
• A) What is it?
(name if you
know)
• B) How did it
form?
Question 2
• A) What is
it? (name if
you know)
• B) How did
it form?
Question 3
• A) What is it? (name if you know)
• B) How did it form?
Question 4
• A) What is
it? (name if
you know)
• B) How did
it form?
Question 5
• A) What is
it? (name if
you know)
• B) How did
it form?
Question 6
• What ONE idea or concept do all five of
those geographic features have in
common?
Plate Tectonics history
• Plate Tectonics is relatively modern
model to explain many disparate
observations - like the 5 slides from the
beginning.
• Observations supporting a ‘drift’ theory
were made as far back as 1600s
• Taylor and Wegener in early 1900s
published more complete drift theory
Drift
• Observations supporting drift
– Fossils
– Shapes of continents
• BUT - in early 1900’s lacked any way to
explain drift
• What could make rock cross rock?
Post WWII
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Paleomagnetism
Seafloor spreading
+ Drift evidence
Observations all need to be explained
by a coherent model
• Plate Tectonics!
• This was a major shift in the scientific
view of how the world works
Model of Earth Today
• Draw
• Three things can happen at the
boundaries
Today - convergent
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Two types of crust
Drawing
So - can have 3 combos of convergent
Oceanic crust-oceanic crust
Continental crust-continental crust
Continental crust-oceanic crust
Two Types of Crust
• Oceanic
– Thinner (7 km)
– Different material
(basalt)
– More dense
(3 g/cm^3)
– Younger (200 million
years old)
• Continental
– Thicker (10-70 km)
– Volcanic rock with
sedimentary on top
– Granitic materials
– Less dense
(2.7 g/cm^3)
– Older - billions of
years
Model of plate tectonics
• Must explain the appearance of
landscape features - observations
Continental-Oceanic
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Predict - which will go under?
What prior knowledge use to predict?
Draw
Subduction
Melting Temperatures
Material
Melting point (degrees
C)
100
Water
Quartz, K-feldspar, Naplagioclase, micas.
Amphibole, Ca/Naplagioclase
600
Olivine, pyroxene, Ca-rich
plagioclase
1000
800
http://hyperphysics.phy-astr.gsu.edu/HBASE/geophys/meltrock.html
Subduction predictions
• Make a list
• Where do we expect to see continental oceanic crust collisions
SA
• http://geol
ogy.com/
platetectonics.
shtml
You try
• Oceanic crust - oceanic crust
• Label features you expect to see.
Examples on Earth
• http://geology.com/plate-tectonics.shtml
• Top down drawing of area
• Can you identify any other places on
Earth?
Aleutians
Continental-Continental
• Where on the map?
Himalayas
• Folded sedimentary
rock
– Sedimentary suggests ocean bed
– Folding pattern
suggests bottom to
top pressure
http://library.thinkquest.org/10131/geology_visual.html
Hazards associated with
convergent margins
• Volcanoes
• Earthquakes
Summary so far
• The plate tectonic model describes how
plates can collide.
• Colliding plates explain volcanoes,
earthquakes, oceanic trenches, island arcs,
mountains, and the relative positioning of
these features.
• One model - describes many observables.
Plate Tectonics Model
• Hypotheses often cause scientists to
develop new experiments that produce
additional data.
• Think of an experiment that might
support plate tectonics model
More support for plate
tectonics
• And also directly measured motions
with VLBI in 1980’s!
• And ground based positions with
satellites in 1990’s
Assessment
• Write a
paragraph
describing how
the Aleutian
Islands and
nearby
geographical
features formed.
Sketch the
relevant plate
configuration
with features.