understanding earth fifth edition chapter 2: plate tetonics: the unifying theory copyright © 2007...
TRANSCRIPT
Understanding EarthFifth Edition
Chapter 2:
Plate Tetonics:The Unifying Theory
Copyright © 2007 by W. H. Freeman and Company
Grotzinger • Jordan • Press • Siever
Divergent BoundariesOceanic Plate Separation
Mid-AtlanticRidge
North Am
erican
PlateNort
h Americ
an
Plate
EurasianPlate
EurasianPlate
Divergent BoundariesOceanic Plate Separation
Mid-AtlanticRidge
North Am
erican
PlateNort
h Americ
an
Plate
EurasianPlate
EurasianPlate
Volcanoes and earthquakes concentrate.
Divergent BoundariesContinental Plate Separation
East AfricanRift Valley
Somali Subplate
Somali SubplateAfric
an Plate
African Pl
ate
Divergent BoundariesContinental Plate Separation
East AfricanRift Valley
Somali Subplate
Somali SubplateAfric
an Plate
African Pl
ate
Parallel valleys; volcanoes and earthquakes.
Convergent BoundariesOcean-Ocean Convergence
Mariana Islands Marianas Trench
Pacific PlatePacific PlatePhili
ppine
PlatePhili
ppine
Plate
Convergent BoundariesOcean-Ocean Convergence
Mariana Islands Marianas Trench
Pacific PlatePacific PlatePhili
ppine
PlatePhili
ppine
Plate
Deep-sea trench; volcanic island arc.
Convergent BoundariesOcean-Continent Convergence
Nazca Plate
Nazca Plate
AndesMountains
SouthAmericanPlate
SouthAmericanPlate
Peru-Chile Trench
Convergent BoundariesOcean-Continent Convergence
Nazca Plate
Nazca Plate
AndesMountains
SouthAmericanPlate
SouthAmericanPlate
Peru-Chile Trench
A volcanic belt ofmountains forms.
Convergent BoundariesContinent-Continent Convergence
Himalaya
Mainthrustfault
TibetanPlateau
Indian-Australian Plat
eIndian-Aust
ralian Plate
EurasianPlateEurasianPlate
Convergent BoundariesContinent-Continent Convergence
Himalaya
Mainthrustfault
TibetanPlateau
Indian-Australian Plat
eIndian-Aust
ralian Plate
EurasianPlateEurasianPlate
Crust crumbles, creating highmountains and a wide plateau.
Transform-Fault BoundariesMid-Ocean Ridge Transform Fault
North American P
lateNorth Am
erican Plate
Eurasian Plate
Transform-Fault BoundariesMid-Ocean Ridge Transform Fault
North American P
lateNorth Am
erican Plate
Eurasian Plate
Spreading centers offset.
Transform-Fault BoundariesContinental Transform Fault
North American Plate
North American PlatePacific
PlatePacific
Plate
Transform-Fault BoundariesContinental Transform Fault
North American Plate
North American PlatePacific
PlatePacific
Plate
Offset continental crust.
As platesmove past each other...
As platesmove past each other...
…creek beds are offset
As platesmove past each other...
…creek beds are offset
SanFrancisco
Los Angeles
San Andreas fault
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.
Mid-Atlantic RidgeMid-Atlantic RidgeHigh
intensity
Low intensity
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.
Mid-Atlantic RidgeMid-Atlantic RidgeHigh
intensity
Low intensity
A sensitive magnetometerrecords magnetic anomalies,…
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.
Mid-Atlantic RidgeMid-Atlantic RidgeHigh
intensity
Low intensity
A sensitive magnetometerrecords magnetic anomalies,…
Iceland
Mid-AtlanticRidge
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic Ridge southwest of Iceland, showed an oscillating pattern of magnetic field strength. This figure illustrates how scientists worked out the explanation of this pattern.
Mid-Atlantic RidgeMid-Atlantic RidgeHigh
intensity
Low intensity
A sensitive magnetometerrecords magnetic anomalies,…
Iceland
Mid-AtlanticRidge
…alternating bands of highand low magnetism.
Symmetrical bands on both sides. Why?
Magnetic anomalies also in volcanic lava.
Magnetic anomalies also in volcanic lava.
Normal
Reversed
Magnetic anomalies also in volcanic lava.
Normal
Reversed
Earth’s magnetic fieldreverses direction.
Layers “remember”.
Older layers preservetheir direction.
Scientists constructed a magnetic time scale.
Gilbertreversed chron
Gaussnormal chron
Matuyamareversed chron
Brunhesnormal chron
5.0 Ma Present4.0 3.0 2.0 1.0
Subchrons
Mid-ocean ridge
4.0
3.0
2.0
Oceancrust today
Million years ago (Ma)
5.0
million
years ol
d
3.32.5
0.70 0.7
2.53.3
5.0
ASSEMBLY OF PANGAEARODINIA Late Proterozoic, 750 Ma
ASSEMBLY OF PANGAEARODINIA Late Proterozoic, 750 Ma
Formed about 1.1 billionyears ago; began to breakup about 750 millionyears ago.
ASSEMBLY OF PANGAEA Late Proterozoic, 650 Ma
ASSEMBLY OF PANGAEA Late Proterozoic, 650 Ma
The pre-Pangean patternof continental drift.
ASSEMBLY OF PANGAEA Middle Ordovician, 458 Ma
The pre-Pangean patternof continental drift.
ASSEMBLY OF PANGAEA Early Devonian, 390 Ma
The pre-Pangean patternof continental drift.
ASSEMBLY OF PANGAEA PANGAEA (a) Early Triassic, 237 Ma
ASSEMBLY OF PANGAEA PANGAEA (a) Early Triassic, 237 Ma
Assembled by 237 Ma.
BREAKUP OF PANGAEA (b) Early Jurassic, 195 Ma
BREAKUP OF PANGAEA (b) Early Jurassic, 195 Ma
Signaled by the openingof rifts from which lavapoured; relics can befound today in volcanicrocks from Nova Scotiato North Carolina.
BREAKUP OF PANGAEA (c) Late Jurassic, 152 Ma
BREAKUP OF PANGAEA (d) Late Cretaceous, Early Tertiary, 66 Ma
THE PRESENT-DAY AND FUTURE WORLD (e) PRESENT-DAY WORLD
THE PRESENT-DAY AND FUTURE WORLD (e) PRESENT-DAY WORLD
The modern world hasbeen produced over thepast 65 million years.
THE PRESENT-DAY AND FUTURE WORLD (f) 50 million years in the future
Whole-mantle convection
Uppermantle
Lowermantle
700 km
2900 kmOuter core
Mantle
Outer core
Inner core
Whole-mantle convection
Uppermantle
Lowermantle
700 km
2900 kmOuter core
Stratified convection
Boundary near700 km separatesthe two convectionsystems.