Geology of the Northwest

James Hutton“The Father of

Geology”

Uniformitarianism

Scientific Method

• Raise question

• Gather data

Scientific Method• Raise question

• Gather data

• Form hypothesis

• Test and modifyhypothesis

• Scientific Theory

• Scientific Law

1. Earth’s “surface” is broken into rigid plates

2. Plates move

3. “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 Composition

Layer Composition

Crust Rock: Felsic & Mafic

Mantle Rock: Ultramafic

Core Metal: Iron & Nickel

Crustal Properties

CrustCrust Density Composition Thickness Age

ContinentalContinental ~2.8 g/cm3 FelsicThick:

20-70 km

Old:up to

4 Byrs

OceanicOceanic ~3.2 g/cm3 MaficThin:

2-10 kmYoung:

<200 Mys

Four Layers:Based on Physical Properties

Layer “State”

Lithosphere Solid / Rigid

Asthenosphere Partly Liquid / “Plastic”

Lower Mantle Solid

Outer Core Liquid

Inner Core Solid

Part #1of Plate Tectonics Definition

Earth’s “surface” is broken into rigid plates

Surface = Lithosphere

(includesContinental Lithosphere and

Oceanic Lithosphere)

The Major Plates

Part #2of Plate Tectonics Definition

Plates move…

…on the “plastic” Asthenosphere

What Drives Plate Tectonics?

Internal Heat

Part #3of Plate Tectonics Definition

“Geology happens” where the plates interact with one another

How 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

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

Note Alternative Names:

1. Divergent (also called Spreading Ridges, Rifts, and Mid-Ocean Ridges)

2. Transform (also labeled as Strike-Slip Faults)

3. Convergent: Oceanic-Continental (also labeled as Subduction Zones)

4. Convergent: Continental-Continental (also labeled as Collision Zones and Thrust Faults)

Volcanoes

Earthquake Distribution

Topography

Rock Age

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