geol101 2006lect22c geophysicstectonicsi -...

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Geophysics

Seismic Waves: Deep Earth ProbesThe Navy Reveals The Sea Floor

CH 17 & 18

SEISMIC WAVES:DEEP EARTH PROBES

Some Waves Reflect Some Waves Refract(Bend)

P Wave Paths

Through Earth

P Wave P Wave Refraction Refraction Produces Produces

Shadow ZoneShadow Zone

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S Wave S Wave Paths Paths

Through Through EarthEarth

S Waves S Waves Absorbed by Absorbed by

the Outer the Outer Liquid CoreLiquid Core

Seismic Waves Reveal Earth’s Layers

Seismic Waves Reveal Earth’s Layers

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Details of Upper Layers

Isostacy~=

Buoyancy

Mountains Have Roots

Mountains Have Roots

Isostacy

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Erosion (Unloading) Causes Uplift; Deposition (Loading) Causes Subsidence

Whole Earth

Structure

Temperatures & Pressures in the Earth

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Rock Strength with Depth

LithosphereAsthenosphere

Earth’s Magnetic Field

May Stem from Convection in Liquid Outer

Core!

Inclination: Deviation from Horizontal

Declination: Deviation from True N-S

Earth’s Changing Magnetic Field

Variable Strength & OrientationNormal: Magnetic N ~ True NReversal: Magentic N ~ True S (last one: 788,000 y)Chrons: Paleomagnetic Time Interval

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How Can We Study PaleomagneticFields? Remnant Magnetism

Remnant Magnetism

Magnetic Anomalies

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Gravity is NOT Constant

High Low“Normal”

Gravity Reveals Underlying Rock

Bouger Anomaly

North American Gravity

Bouger Anomalies

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Alfred Wegener’s Evidence for Continental Drift

1. Continental “Fit”

Include Continental Shelves for Best “Puzzle” Fit

Continental Drift

• Bacon, 1620

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Continental Drift

Alfred Wegener’s Evidence for Continental Drift

1. Continental “Fit”2. Similar Rocks, Ages

Wegener’sEvidence:

Similar Rocks,Similar Ages

Batholith

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Alfred Wegener’s Evidence for Continental Drift

1. Continental “Fit”2. Similar Rocks, Ages

3. Similar Fossils

Similar Fossils

Glossopteris (Common Tree in Coal Seams)Fresh-Water Fish

Mammal-Like Reptiles

http://toad.asu.edu/rschmag/gloss.html

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http://www.dme.qld.gov.au/gsd/fossils/perm.htm

Similar Fossils: Different Continents

Alfred Wegener’s Evidence for Continental Drift

1. Continental “Fit”2. Similar Rocks, Ages

3. Similar Fossils4. Widespread Glaciation

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Widespread GlaciationGondwana Glaciation of Antarctica,

South America, Africa, Australia and India during Permian

Strange Climate Zones

Gondwanaland: Antarctica, South America, Africa,

Australia and India

Laurasia: North America, Europe,

most of Asia

Source:http://vishnu.glg.nau.edu/rcb/Jur.jpg

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Laurasia

Gondwanaland

Source: http://vishnu.glg.nau.edu/rcb/160_1st.jpg

Source:http://vishnu.glg.nau.

edu/rcb/Perm.jpg

Pangaea = Gondwanaland

+ Laurasia

Ice Sheet

Pangaea = Gondwanaland

+ Laurasia

Source:http://vishnu.glg.nau.edu/rcb/Perm.jpg

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Source:http://vishnu.glg.nau.

edu/rcb/Penn.jpg

Pangaea = Gondwanaland +

Laurasia

Source:http://vishnu.glg.nau.

edu/rcb/Penn.jpg

Pangaea = Gondwanaland +

Laurasia

Alfred Wegener’s Evidence for Continental Drifts Was NOT

Accepted in USA.

Problem: No Mechanism for Continents to Plow Through

Oceanic Crust

Answer lies on the Sea Floor & in Ch. 18 + 19

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WW II

Submarine Science

Mapping of Ocean Basins

http://www.spe.sony.com/movies/dasboot/

http://www.geocities.com/Pentagon/2560/bowph1.jpg

http://members.microdsi.net/shirschm/Welcome.index.html

Seismic & Sonar Study Reveals

Sea-Floor Topography

Ocean Basin Bathymetry

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Know these mega-scale Landforms• Continental Shelf• Continental Slope• Continental Rise• Abyssal Plain• Mid-Ocean Ridge (~ Mid-Ocean Rise)• Trench

Know differences betweem Oceanic Crust and Continental Crust

Ocean Basin BathymetrySee Figures 18.6 to 18.12 in Plummer & Others 9th ed.See Figures 18.5 to 18.15 in Plummer & Others 10th ed.

Ocean Basin Bathymetry See Figures 18.5, 18.15 in Plummer & Others 9th ed.

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Cold WarMore Submarine Science

Magnetic Anomalies in Ocean Basin

Deep-Sea Magnetic

Anomalies

Deep Sea Drilling Project (DSDP)Studied Geology of Ocean Basins

Continental Record = IncompleteDeep Ocean Basin Record Was Thought

to be More CompleteGlomar Challenger Harry

Hess

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Magnetic Anomalies: Atlantic Ocean South of IcelandNew Ocean Crust Created at MidNew Ocean Crust Created at Mid--Ocean Ridges: Spread CentersOcean Ridges: Spread Centers

DSDP Surprise Finding:

Ocean Basins are <200,000,000 y OldMuch Younger than the Continents

Very Young Sediments at the Mid Ocean Ridges

Age of the Ocean Basins