Intermission:
Plate Tectonics
National Oceanic and atmospheric Administration/National Geophysical Data Center
Alfred
Wegener
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
Harry
Hess
Evidence:
Seafloor
Seafloor
Spreading
Seafloor Age
Seafloor Age
Plate Tectonics
Basic Plate Tectonics
• Earth’s “surface”
(lithosphere) is
broken into plates
• Plates move on
asthenosphere
• “Geology happens”
where the plates
interact with one
another
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
Crust
Density
continental ~2.8 g/cm3
oceanic
~3.2
g/cm3
Composition Thickness
Felsic
Thick:
20-70 km
Mafic
Thin:
2-10 km
Age
Old:
up to
4 Byrs
Young:
<200 Mys
Five Layers:
Based on Physical Properties
Layer
“State”
Lithosphere
Solid / Rigid
Asthenosphere
Partly Liquid / “Plastic”
Lower Mantle
Solid
Outer Core
Liquid
Inner Core
Solid
Part #1
of Plate Tectonics Definition
Earth’s “surface” is broken into rigid plates
Surface = Lithosphere
(includes
Continental Lithosphere and
Oceanic Lithosphere)
Part #2
of Plate Tectonics Definition
Plates move…
…on the “plastic” Asthenosphere
…at about 1-10 cm/yr
Part #3
of Plate Tectonics Definition
“Geology happens” where the plates interact
with one another
Earthquake Distribution
Volcanoes and Plate Tectonics
Part #3
of 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
San Andreas
Fault
Convergent Boundary: Subduction
Melting
Produces
More
Felsic
Magma
Results in the formation & growth of Continental Crust
and destruction of Oceanic Crust
Example:
Pacific
Northwest
Example:
Andes
Mountains
Convergent Boundary: Collision
Results in the growth of Continental Crust
Basic Plate Tectonics - Revised
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
What Drives Plate Tectonics?
Internal Heat
Convection Models
Set the “Wayback Machine” to
return to the Hadean…
Return to Hadean ppt