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1
Sea-Floor Spreading, Subduction,& Plate
Boundaries
Lecture 23
Prop: Test 3 Invitations
Geol 101 (Kite) Quiz 9, April 2005
*******************************
* You are cordially invited * Name__________________________* to attend the *
* Geology 101 (Kite) TEST 3 *
* 10:00 a.m. * Student ID____________________
* Tuesday, 18 April 2006 *
* 21 White *
* *
* RSVP, regrets only *
*******************************
Bring this Invitation/Quiz to the Third Test on 18 April.
You must be in class to pick up an invitation. If not download it from the Test and Quizzes Page
Geol 101 (Kite) Quiz 9, April 2006
*******************************
* You are cordially invited * Name__________________________* to attend the *
* Geology 101 (Kite) TEST 3 *
* 10:35 a.m. * Student ID____________________
* Tuesday, 18 April 2006 *
* 21 White *
* *
* RSVP, regrets only *
*******************************
Bring this Invitation/Quiz to the Third Test on 18 April.
You must be in class to pick up an invitation. If not download it from the Test and Quizzes Page
2
Alfred Wegener’s Evidence for Continental Drift
1. Continental “Fit”2. Similar Rocks, Ages
3. Similar Fossils4. Widespread Glaciation
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 Mechanismfor Continents to Plow Through Oceanic Crust
Answer lies on & in the Sea Floor - Ch. 18 + 19 in Text
3
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
Spongebob Theme Song Lyrics
Are ya ready kids?Aye Aye Captain!I CAN'T HEAR YOU!AYE AYE C APTAIN!ohhhhhh!!!!
Who lives in a pineapple under the sea?SPONGEB OB SQUAR EPANTS!Absorbant and yellow and poreous is heSPONGEB OB SQUAR EPANTS!His nautical nonsense be somethin you wishSPONGEB OB SQUAR EPANTS!Then drop on the deck and flop like a fish!SPONGEB OB SQUAR EPANTS!Ready?
SPONGEB OB SQUAR EPANTS!SPONGEB OB SQUAR EPANTS!SPONGEB OB SQUAR EPANTS!
SPONGEYB OB SQUAR EPAAAANTS
Seismic & Sonar Study Reveals
Sea-Floor TopographyGeophysicists’sAnswers Life’s
Important Questions
Know these mega-scale Landforms• Continental Shelf• Continental Slope• Continental Rise• Abyssal Plain• Mid-Ocean Ridge (~ Mid-Ocean Rise)• Trench
Know differences between Oceanic Crust and Continental Crust
4
Ocean Basin BathymetrySee Figures 18.5 to 18.16 in Plummer & Others 10th ed.
Ocean Basin Bathymetry See Figures 18.5, 18.15 in Plummer & Others 10th ed.
Cold WarMore Submarine Science
Magnetic Anomalies in Ocean Basin
5
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
Magnetic Anomalies: Atlantic Ocean South of IcelandNew Ocean Crust Created at MidNew Ocean Crust Created at Mid--Ocean Ridges: Spread CentersOcean Ridges: Spread Centers
6
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
Spreading at the Red Sea: Break-Up of Asia and Africa
Note a “Failed”Arm of Rifting in
East Africa
Birth of an Ocean Basin?
7
Break-Up of a Continent and
Origin of an Ocean Basin
Problem:
If New Crust is Created at Mid-Ocean Ridges,
Where is Old Crust Consumed to Balance the New Crust?
Where is Old Crust Consumed to Balance the New Crust?
Answer Lies in Deep-Focus Earthquakes.
8
Earthquakes Occur in Brittle
(Elastic) Lithosphere
LithosphereAsthenosphere
70 70 -- 100 km100 km
Distribution of All Earthquakes(Deep and Shallow Focus)
Subduction Zones: Ocean-Ocean Margin
9
Subduction Zones: Ocean-Continent Margin
Deep-Focus Quakes Only in
SubductionZones
Isotherms in Subduction Zones
400o
C
600o
C
10
Japan Trench &Volcanic
Arc
Back-Arc and Fore-Arc “Basins”See Figure 19.35 in Plummer & Others 9th ed.
SubductionZones &
Volcanoes
11
Spread Centers Feed Subduction Zones
Missing Mechanisms for Continental Drift:Sea Floor Spreading & Subduction
Continents are Passive “Boats”
Himalayas
How Are Mountains Built?
12
Orogeny(Mountain Building)
in the Himalayas
Continental Lithosphere
Will NOT Flush Down Subduction
Zones
Orogenyin the
Himalayas
13
Orogeny in Himalayas
Orogeny in Himalayas
Orogenyin the
Himalayas
14
Orogeny - Mountain Building - Sediment Supply
Orogeny - Mountain Building - Glaciation
Plate Margins:
• Spread Centers (Mid-Ocean Ridges)• Subduction Zones (Trenches)• Transform Faults
15
Plate Margins:
Transform Faults & Fracture Zones
Transform Faults
16
San Andreas Fault:Right-Lateral
Transform Fault
Left-Lateral Offset!!Why?: Fault is
Produced by Offset, vs. Offset Produced by Fault
Transform Faults:
Offsets in Spread Centers
Plate Motion
on a Sphere
17
Plate Motion on a Sphere Requires
Transform Faults
Because of Different Rates of Motion
The Plates
The Plates: Pacific-Centered View(Distorted by Mercator Map Projection)
18
What Drives Plate Tectonics?
1. Convection Cells in Mantle 2. Sinking of Cool, Dense Plates3. Mantle Plumes - Hot Spots
Convection Cells
19
Convection Cells in MantleConvection Cells in Mantle
Mantle Plumes
20
Mantle Plumes Under Continents
• Known “Hot Spots”
Hawaiian Islands
21
Mantle Plumes - Hot Spots
•
Numbers = Age of Rockin Millions
of Years
Sinking of Cool, Dense Plates
Seamount
Volcanoes Surrounded by Fringing Coral Reefs
22
NASA
Atolls: Submerged Volcanos Support ReefsOnly in Warm Clear Seas
Tuamoto Islands
Quiz 9Chapters on Test III on 18 April
CH 11-19NOT Chapter 20
• Save Questions 6, 7-10 and 12 for Quiz 10
• Turn Whole Quiz 9 in at the test, We will provide a new Quiz 10 on 25 April