chapter 2: plate tectonics
DESCRIPTION
Chapter 2: Plate Tectonics. Tectonic Plates of Earth. Pangaea. Pangaea: Pan = all Gaea = Earth Panthalassa Thalassa = sea AKA Tethys Sea. Continental Drift. Progressive breakup of Pangaea into modern continents Similar to sea ice. Wegner’s Evidence. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 2: Plate Tectonics
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Tectonic Plates of Earth
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Pangaea Pangaea:
Pan = all Gaea = Earth
Panthalassa Thalassa =
sea AKA Tethys
Sea
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Continental Drift
Progressive breakup of Pangaea into modern continents
Similar to sea ice
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Wegner’s Evidence Present-day
shorelines fit like puzzle pieces
Better fit from continental shelves
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Fossil Evidence Identical fossils
present in S. Amer. & Africa
e.g. Mesosaurus
e.g. Glossopteris
e.g. Marsupials
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Geologic Evidence Identical rocks on
different continents e.g. 2.2Ga igneous
rocks in Brazil & Africa
Similar Mountain Ranges e.g. Appalachian Mts
~ Caledonian Mts
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Mesozoic Supergroup Identical
package of rocks & fossils found in S.Amer., Africa, Australia & Antarctica
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Paleoclimatic
Evidence Paleo = ancient Climate =
weather conditions
Glacially transported sediments
Glacial striations
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Rejection of Continental Drift Hypothesis
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
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Earth’s Magnetic
Field Similar to
bar magnet Magnetic
materials align themselves to magnetic field
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N-S Orientation & Dip Magnetic
orientation has 2 dimensions North-South Dip angle
(Inclination) Curie point (T) Fossil Magnetism /
Paleomagnetism
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Magnetic Inclination Magnetizatio
n = degrees from N pole
Magnetization + Latitude = 90°
e.g. Lavas from Puerto Rico show 75 ° from N pole & Puerto Rico = 15 ° from equator
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Apparent Polar Wander
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Seafloor Spreading
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Paleomagnetism
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Progression of Seafloor Spreading
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Plate Boundaries
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Plate Boundarie
s Correspond
s to Earthquakes & Volcanoes
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Plate Boundarie
s Three Types
Divergent AKA
Rift Convergent
AKA Subduction
Transform AKA Strike-
slip
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Divergent Boundaries AKA
Spreading Centers
AKA Rifts Largest
mountain chains
Plates move apart due to eruption of lava New lava =
new oceanic crust
Oldest oceanic crust 180Ma
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Pillow Basalts Form when
lava extruded under water
Immediately outer layer freezes
New material pushes through like toothpaste
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Continental Rifting Rifts also can form in
continental settings Linear depressions
Lakes, valleys, etc. Asthenosphere thins
due to tension e.g. East Africa Rift
Zone, Mt. Kilimanjaro
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Continental Rifting (con’t) If tension
continues, eventually continental rift develops into oceanic spreading
e.g. Red Sea, Sea of Cortez
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Convergent Boundaries Old oceanic crust
dense & heavy Heavy vs. light
=> subduction AKA destructive
margins Large earthquake
& explosive volcanoes
Melting triggered at ~100km depth
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Oceanic-Oceanic Convergence
e.g. Virgin Islands, Japan, Philippines
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Oceanic-Continental
e.g. Andes, MesoAmerica, Italy
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Continental-Continental
e.g. India
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Hot Spots
Caused by mantle plumes
Plumes do not move, plates do
Bend at 40Ma Major
change in plate motion
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Relative Plate Motions Relative to
Hot Spots & other plates
Measure motions with Paleo-magnetism
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Forces Driving Plate Motions Convectio
n of Mantle
Upwelling Mantle Ridge-
push Slab
Suction AKA
Slab-pull
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Layer-Cake Model Two zones of
convection, above & below ~660km
Explains why mid-ocean ridge basalt different than hot spot basalt
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Whole Mantle Convection Cold oceanic
crust descend to bottom of mantle, “stirring” it
Hot plumes rise from core-mantle boundary Bring “primitive”
mantle to surface Not popular b/c
complete mixing in 100s Ma
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Deep Layer Model Heat from Earth’s
interior causes two layers to shrink & swell Similar to lava lamp
Small amt of material rises to surface to create hot spots
Little seismic evidence to support this model
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Importance of Plate Tectonics
First theory to provide comprehensive view & explain: Earth’s major surficial processes Geologic distribution of earthquakes,
volcanoes & mountain ranges Distribution of mineral resources &
ancient organisms