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 *

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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

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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