Understanding Earth Fifth Edition Chapter 2: Plate Tetonics: The Unifying Theory Copyright © 2007 by W. H. Freeman and Company Grotzinger Jordan Press.

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.