Intermission:

Plate Tectonics

National Oceanic and atmospheric Administration/National

Geophysical Data Center

AlfredWegener

Evidence:(1)

Continents Fit

Together

Evidence:

(2) Rocks & Structures Match

Up

Evidence: (3) Glacial Features

Evidence: (4) Fossils

Pangea

Animation Link

“If we are to believe Wegener’s Hypothesis,

we must forget everything which has been learned in the last 70 years and start over again.”

–Critic of Continental Drift in

1928

HarryHess

Evidence:

Seafloor

Seafloor Spreadin

g

Seafloor Age

Seafloor Age

Plate Tectonics

• Earth’s “surface” (lithosphere) is broken into plates

• Plates move on asthenosphere

• “Geology happens” where the plates interact with one another

Basic Plate Tectonics

What do we mean by the Outer

Part of the

Earth?

Three Layers:Based on CompositionLayer Composition

Crust Rock: Felsic & Mafic

Mantle

Rock: Ultramafic

Core Metal: Iron & Nickel

Crustal Properties

CrustCrust DensityComposit

ionThickne

ssAge

continecontinentalntal

~2.8 g/cm3 Felsic

Thick:20-70 km

Old:up to4 Byrs

oceanicoceanic ~3.2 g/cm3 Mafic

Thin:2-10 km

Young:<200 Mys

Five Layers:Based on Physical

PropertiesLayer “State”

Lithosphere

Solid / Rigid

Asthenosphere

Partly Liquid / “Plastic”

Lower Mantle

Solid

Outer Core Liquid

Inner Core Solid

Part #1of Plate Tectonics

DefinitionEarth’s “surface” is broken into rigid plates

Surface = Lithosphere

(includesContinental Lithosphere and

Oceanic Lithosphere)

Part #2of Plate Tectonics

DefinitionPlates move…

…on the “plastic” Asthenosphere

…at about 1-10 cm/yr

Part #3of Plate Tectonics

Definition“Geology happens” where the plates interact with one

another

Earthquake Distribution

Volcanoes and Plate Tectonics

Part #3of Plate Tectonics

Definition“Geology happens” where the plates interact with one

anotherHow do they interact?

1. Pull Apart from one another (Diverge)(New rock is formed)

2. Push into one another (Converge)(Rock is destroyed)

3. Slide past one another(Rock is conserved)

Divergent Boundary

Results in the formation of Oceanic Crust

Examples:

Transform Boundary

Transform Example

San Andreas Fault

Convergent Boundary: Subduction

Results in the formation & growth of Continental Crustand destruction of Oceanic Crust

Melting

Produces More Felsic Magma

Example:Pacific

Northwest

Example:Andes

Mountains

Convergent Boundary: CollisionResults in the growth of Continental Crust

1. Earth’s lithosphere is broken into 12-24 rigid plates

2. Plates move about 1-10 cm/yr on the plastic Asthenosphere

3. “Geology happens” where the plates interact with one another along Divergent, Transform, Subduction and Collisional Boundaries

Basic Plate Tectonics - Revised

What Drives Plate Tectonics?

Internal Heat

Convection Models

Set the “Wayback Machine” to return to

the Hadean…

Return to Hadean ppt