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Chapter 2: Plate Tectonics
Tectonic Plates of Earth
Pangaea
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Pangaea:
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Pan = all
Gaea = Earth
Panthalassa
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Thalassa = sea
AKA Tethys Sea
Continental
Drift
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Progressive
breakup of
Pangaea into
modern
continents
Similar to sea
ice
Wegner’s Evidence
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Present-day shorelines
fit like puzzle pieces
Better fit from
continental shelves
Fossil Evidence
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Identical fossils
present in S.
Amer. & Africa
e.g. Mesosaurus
e.g. Glossopteris
e.g. Marsupials
Geologic Evidence
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Identical rocks on
different continents
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e.g. 2.2Ga igneous rocks in
Brazil & Africa
Similar Mountain Ranges
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e.g. Appalachian Mts ~
Caledonian Mts
Mesozoic Supergroup
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Identical
package of
rocks &
fossils
found in
S.Amer.,
Africa,
Australia
&
Antarctica
Paleoclimatic
Evidence
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Paleo = ancient
Climate = weather
conditions
Glacially
transported
sediments
Glacial striations
Rejection of Continental Drift
Hypothesis
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No evidence of continents “breaking
through” oceanic crust
Tidal forces necessary would halt Earth’s
rotation
Danish scientists found no astronomical
evidence of drift from 1927-1948
Earth’s
Magnetic
Field
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Similar to bar
magnet
Magnetic
materials
align
themselves to
magnetic field
N-S Orientation & Dip
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Magnetic orientation
has 2 dimensions
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North-South
Dip angle (Inclination)
Curie point (T)
Fossil Magnetism /
Paleomagnetism
Magnetic Inclination
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Magnetization
= degrees from
N pole
Magnetization
+ Latitude =
90°
e.g. Lavas from
Puerto Rico
show 75 ° from
N pole &
Puerto Rico =
15 ° from
equator
Apparent Polar Wander
Seafloor Spreading
Paleomagnetism
Progression of Seafloor Spreading
Plate Boundaries
Plate
Boundaries

Corresponds
to
Earthquakes
& Volcanoes
Plate
Boundaries
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Three Types
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Divergent
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Convergent
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AKA
Rift
AKA
Subduction
Transform
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AKA
Strike-slip
Divergent Boundaries
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AKA
Spreading
Centers
AKA Rifts
Largest
mountain
chains
Plates move
apart due to
eruption of
lava

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New lava =
new oceanic
crust
Oldest oceanic
crust 180Ma
Pillow Basalts
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Form when lava
extruded under
water
Immediately
outer layer
freezes
New material
pushes through
like toothpaste
Continental Rifting
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Rifts also can form in
continental settings
Linear depressions
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Lakes, valleys, etc.
Asthenosphere thins
due to tension
e.g. East Africa Rift
Zone, Mt. Kilimanjaro
Continental Rifting (con’t)
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If tension
continues,
eventually
continental
rift develops
into oceanic
spreading
e.g. Red Sea,
Sea of Cortez
Convergent Boundaries
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Old oceanic crust
dense & heavy
Heavy vs. light =>
subduction
AKA destructive
margins
Large earthquake
& explosive
volcanoes
Melting triggered at
~100km depth
Oceanic-Oceanic Convergence
e.g. Virgin Islands, Japan, Philippines
Oceanic-Continental
e.g. Andes, MesoAmerica, Italy
Continental-Continental
e.g. India
Hot Spots
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Caused by
mantle
plumes
Plumes do
not move,
plates do
Bend at 40Ma
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Major
change in
plate motion
Relative Plate Motions
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Relative to
Hot Spots
& other
plates
Measure
motions
with Paleomagnetism
Forces Driving Plate Motions
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Convection
of Mantle
Upwelling
Mantle
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Ridgepush
Slab
Suction
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AKA Slabpull
Layer-Cake Model
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Two zones of
convection,
above & below
~660km
Explains why
mid-ocean ridge
basalt different
than hot spot
basalt
Whole Mantle Convection
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Cold oceanic
crust descend to
bottom of mantle,
“stirring” it
Hot plumes rise
from core-mantle
boundary
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Bring “primitive”
mantle to surface
Not popular b/c
complete mixing
in 100s Ma
Deep Layer Model
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Heat from Earth’s
interior causes two
layers to shrink &
swell
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Similar to lava lamp
Small amt of
material rises to
surface to create hot
spots
Little seismic
evidence to support
this model
Importance of Plate Tectonics
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First theory to provide comprehensive view
& explain:
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Earth’s major surficial processes
Geologic distribution of earthquakes, volcanoes
& mountain ranges
Distribution of mineral resources & ancient
organisms