geol101 2006lect22c geophysicstectonicsi -...
TRANSCRIPT
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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