Plate tectoncis 2012

Motion in the

solid earth:

Mt. Everest Marianas Islands Challenger Deep S e

a _le ve_l

Depth (km)

Elevation (km) Typical

elevation

of land surface is 0—1 km

The rocks at the bottom of

the Grand Canyon are 1.7–2.0 billion years old.

The most recent layer is about 250 million years old.

The rocks at the bottom of

the Grand Canyon are 1.7–2.0 billion years old.

The explosive impact of a meteorite created this

4560 Ma Earth and planets form 4510 Ma Moon forms 4470 Ma Oldest lunar rocks 4000 Ma Oldest continental rocks 3800 Ma

Evidence of erosion by water

2700 Ma

Start of rise of

atmospheric oxygen

3500 Ma

Record of magnetic field Fossils of primitive bacteria

2500 Ma Major phase of continent formation completed 542 Ma Evolutionary “Big Bang” 443 Ma Mass extinction 420 Ma Earliest land animals 125 Ma Earliest flowering plants 5 Ma First hominids 0.2 Ma First appearance of our species,

Homo sapiens

Mass extinctions

359 Ma 251 Ma 200 Ma 65 Ma Present

Building a planet requires building materials. The two types of materials that were used are represented by rocky and metallic meteorites. The Earth is a mixture of these components.

Today the Earth is a layered body.

Crust Mantle

Solid iron inner core Liquid iron

THE CLIMATE SYSTEM

Cryosphere

Hydrosphere

Biosphere

Atmosphere

The Earth system

THE PLATE TECTONIC SYSTEM

Asthenosphere

Deep mantle Lithosphere

THE GEODYNAMO SYSTEM

Inner core

0 (km)

Continental crust (2.8 g/cm3)

Moho

discontinuity Horizontal distance not to scale

Mantle

(3.4 g/cm3)

Oceanic crust (3.0 g/cm3)

10 20 30 40 50

Less dense continental crust floats on denser mantle.

0 (km)

Continental crust (2.8 g/cm3)

Moho

discontinuity Horizontal distance not to scale

Mantle

(3.4 g/cm3)

Oceanic crust (3.0 g/cm3)

10 20 30 40 50 ‘Mafic’

magnesium and iron (ferrum) rich

‘Felsic’

K-feldspar and

silica rich

Density of Earth’s Major Layers Crust Mantle Outer core Inner core Depth (km) D e n si ty ( g / cm 3 ) Depth (km) CRUST Silicon (28%)

Aluminum (8%) _{Iron (6%)}

Magnesium (4%) Calcium (2.4%) Other (5.6%) Oxygen (46%) Silicon (21%)

Aluminum (2.4%) Iron (6.3%)

Magnesium (22.8%) Calcium (2.5%) Oxygen (44%) MANTLE Nickel (5%) Iron (85%)Iron

(85%) Sulfur (5%)

Sun

The Sun drives Earth’s external engine.

Solar energy is responsible

for our climate and weather.

Earth’s internal engine is powered by trapped heat…

…and radioactivity in its interior.

Heat radiating from Earth balances solar input and heat from interior.

Meteors move mass from the cosmos to Earth.

Convection causes hot water to rise…

...where it cools, moves laterally, sinks,…

…warms, and rises again.

Hot matter from the

mantle rises,… …causing plates toform and diverge. Where plates converge, a cooled plate is dragged under… …sinks, warms, and rises again.

The Earth’s outermost rigid layer (lithosphere) is broken up into a number of large fragments called plates.

Divergent Boundaries

Mid-Atlantic Ridge

North Am

erican Plate

North Am

erican

Divergent Boundaries

Mid-Atlantic Ridge

North Am

erican Plate

North Am

erican

Divergent Boundaries

Continental Plate Separation

East African Rift Valley

Somali Sub_plate Somali Sub_plate African Pl

ate

African Pl

Divergent Boundaries

Continental Plate Separation

East African Rift Valley

Somali Sub_plate Somali Sub_plate African Pl

ate

African Pl

ate

Convergent Boundaries

Mariana Islands Marianas Trench

Pacific Plat_e Pacific Plat_e Philippine

Plate

Convergent Boundaries

Mariana Islands Marianas Trench

Pacific Plat_e Pacific Plat_e Philippine

Plate

Philippine Plate

Convergent Boundaries

Ocean-Continent Convergence

Nazca Plate

Nazca Plate

Andes

Mountains

South

American Plate

South

American Plate

Convergent Boundaries

Ocean-Continent Convergence

Nazca Plate

Nazca Plate

Andes Mountains South American Plate South American Plate Peru-Chile Trench

Convergent Boundaries

Indian-Australian Plate Indian-Australian Plate

Eurasian Plate

Convergent Boundaries

Indian-Australian Plate Indian-Australian Plate

Eurasian Plate

Eurasian Plate

Whole-mantle convection

Upper mantle

Lower mantle 700 km

2900 km Outer core Mantle

Whole-mantle convection Upper mantle Lower mantle 700 km 2900 km Outer core Mantle Outer core Inner core Stratified convection Boundary near

The slab—how low does it flow?

Tomographic image of the oceanic slab

penetrating

Transform-Fault Boundaries

North American Pl

ate

North American Pl

ate

Eurasian Pla_te

Transform-Fault Boundaries

North Americ_{an Plate} North Americ_{an Plate}

Pacific Plate

Convection in the outer core creates the Earth’s magnetic field

Somehow—changes in convection regime cause polarity reversals of the Earth’s magnetic field, so that the SOUTH pole

becomes the NORTH pole.

The ploarity today is called NORMAL, whereas the opposite mode is called

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 Ridge

Mid-Atlantic Ridge

High intensity

Low intensity

A sensitive magnetometer

records magnetic anomalies,…

Iceland

Mid-Atlantic Ridge

…alternating bands of high and low magnetism.

Mid-ocean ridge

4.0

3.0

2.0

Ocean crust today

Million years ago (Ma)

5.0 million years old

3.3 2.5

0.7 0 0.

7 2.5 3

40

K-

Ar dating of basaltic lava flows relates allows

Pangea

~250 million years ago

Pangea

~250 million years ago

Alfred Wegener and the Continental Drifters

1880-1930

"Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine 'truth' here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw.”

ASSEMBLY OF PANGAEA

ASSEMBLY OF PANGAEA

RODINIA Late Proterozoic, 750 Ma

Formed about 1.1 billion years ago; began to break up about 750 million

ASSEMBLY OF PANGAEA

ASSEMBLY OF PANGAEA

Late Proterozoic, 650 Ma

ASSEMBLY OF PANGAEA

Middle Ordovician, 458 Ma

ASSEMBLY OF PANGAEA

ASSEMBLY OF PANGAEA

ASSEMBLY OF PANGAEA

PANGAEA (a) Early Triassic, 237 Ma

BREAKUP OF PANGAEA

BREAKUP OF PANGAEA

(b) Early Jurassic, 195 Ma

BREAKUP OF PANGAEA

BREAKUP OF PANGAEA

THE PRESENT-DAY AND FUTURE WORLD

Compression wave

Shear-wave crest

Wave direction

Surface waves ripple across Earth’s surface.

The ground surface moves in a rolling, elliptical motion.

Wave direction

Focus 0 Seconds_{Rupture expands circularly on}

fault plane, sending out seismic waves in all directions.

5 Seconds

Rupture continues to expand as a crack along the fault plane. Rocks at the surface begin to rebound from their deformed state.

10 Seconds

The rupture front progresses down the fault plane, reducing the stress.

20 Seconds

Rupture has progressed along the entire length of the fault. The earthquake stops.

Fault cracks at surface

Recording pen

Earth

moves up

Upward movement of the Earth causes

Earth

moves left

Earth

moves right

Earth

moves side to side

Seismograph

Focus Seismograph

Seismograph

Epicenter

Seismic waves arrive at distant seismographic

Minutes

Surface waves

The body waves travel at different speeds

and so arrive at the seismograph station at

different times.

0

P S

Distance traveled from earthquake epicenter (km) T im e e la p se d a ft e r st a rt o f e a rt h q u a k e ( m in ) 3-minute interval at 1500 km

2000 4000 6000 8000 10,000 25 20 Seismogram A 11-minute interval at 8600 km 8-minute interval at 5600 km 15 10 5 0 Seismogram B Seismogram C S wave P wave

Because P waves travel faster than S waves, the interval between their travel-time curves

increases with distance.

By matching the observed interval to the curves, a

1500 km 1500 km A A B B Epicenter Epicenter 5600 km 5600 km 8600 km 8600 km C C

1500 km 1500 km A A B B Epicenter Epicenter 5600 km 5600 km 8600 km 8600 km C C

If the geologist then draws a circle around each seismographic station,…

…the point at which the circles

Focus

Mantle

Seismograph Core

S P

Seismic waves travel through

Earth and over its surface.

Seismic rays are refracted

away from the normal as they penetrate the earth, which

causes them to bend, because each lower layer in the earth’s mantle becomes progressively more dense due to the weight of overlying rock.

High density

Low density

i

r

Seismic ray

It is the analysis of seismic wave propagation in the Earth, stemming from from earthquakes and nuclear detonations, that allowed the layered structure of the Earth to be

elucidated.

S-wave paths through Earth’s interior. Focus S-wave shadow zone 0° 105° 105° Inner core Mantle Outer core S wave shadow zone between 5 and 105 degrees

The pattern of P-wave paths through Earth’s interior.

Focus P-wave shadow zone 0° 105° 105° 142° 142° P wave shadow zone between

105 and 142 degrees

In order for rocks to melt within the earth, the melting curve for rock must be to the left of the geotherm (the earth’s temperature with depth). Note that this occurs only in the outer core and

asthenosphere. It is even more interesting to consider that the melting curve for rock in this figure is for a wet asthenosphere. If the asthenosphere were dry, the melting

Focus Solid inner core Liquid outer core Mantle Seismographic stations

Seismic tomography uses the travel times from many

The slab—how low does it flow?

Tomographic image of the oceanic slab

penetrating

North

America Africa

…and the

remnants of the Farallon Plate under North

American Plate.

ISOSTASY: measurements of the rate of glacial isostatic rebound provides estimates on the

World seismicity from 1976 to 2002 EUROPE AFRICA ASIA INDIAN OCEAN AUSTRALIA SOUTH AMERICA NORTH AMERICA ANTARCTIC OCEAN

PACIFIC OCEAN _ATLANTIC OCEAN

≤ 50 km deep (shallow focus) 50–300 km deep

Lithosphere

Lithosphere

Asthenosphere

Asthenosphere

Transform fault (lateral shearing)

Rift valley (divergence) Normal faulting

Mid-ocean ridge (divergence)

Lithosphere

Lithosphere

Asthenosphere

Asthenosphere

Deep-ocean trench (convergence)

Large shallow

earthquakes occur

mainly on thrust faults.

Southern California fault traces

San Andreas fault San Gabriel Mountains

North American Plate North American Plate Pacific Plate Pacific Plate Los Angeles

Southern California fault traces

San Andreas fault San Gabriel Mountains

North American Plate North American Plate Pacific Plate Pacific Plate Los Angeles

Motion of Pacific Plate relative to motion of North American Plate

Southern California fault traces

San Andreas fault San Gabriel Mountains

North American Plate North American Plate Pacific Plate Pacific Plate Los Angeles

Motion of Pacific Plate relative to motion of North American Plate

The “Big Bend” causes the Pacific Plate to compress against the

North American Plate, causing thrust faulting.

Southern California earthquakes (July 1970-June 1995)

Northridge 1994

Magnitude 6.9 San Fernando 1971Magnitude 6.7 Landers 1992Magnitude 7.3

July 1970–June 1995

July 1970–June 1995 Key:

Tsunami generation

Thrust fault

Shallow w

Tsunami generation

Thrust fault

Shallow w

ater

An earthquake produces a surge of water that

Tsunami generation

Thrust fault

Shallow w

ater

An earthquake produces a surge of water that

moves outward as a tsunami.

A tsunami is only a few centimeters high in the deep ocean but can

Computer simulation of tsunami radiation.

Hawaii

4 hr 42 min North America

North America

Computer simulation of tsunami radiation.

Hawaii

4 hr 42 min North America

North America

Epicenter