Transcript Chapter 10 - Continents

Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 10:
HISTORY OF THE CONTINENTS
© 2011 by W. H. Freeman and Company
Chapter 10:
History of the
Continents
About Evolution of the Continents
• Nearly two-thirds of the Earth’s surface –
all of the oceanic crust – was formed
over the past 200 million years.
• However, rocks of the continents are much
older, as old as 4 billion years.
• Studying the continents tells us how the
continental lithosphere formed and
evolved.
Lecture Outline
1. The structure of North America
2. Tectonic provinces around the world
3. How continents grow
4. How continents are modified
5. The origin of cratons
6. The deep structure of the continents
1. The Tectonics of North America
● The stable interior
● Canadian shield
● interior platform
● basins and uplifts
1. The Tectonics of North America
● The Appalachian fold belt
● Valley and ridge province
● Blue ridge province
● Piedmont
● Coastal Plain
1. The Tectonics of North America
● The North American cordillera
● uplift and orogeny
● rejuvenation
● crustal stretching
2. Tectonic Provinces
around the World
● Types of tectonic provinces
● shield
● platform
● continental basin
● orogen
● extended crust
2. Tectonic Provinces
around the World
● Ages of tectonic provinces
● Archean
● Early Proterozoic
● Middle Proterozoic
● Late Proterozoic
● Paleozoic
● Mesozoic and Cenozoic
Thought questions for this chapter
Figure 10.8b shows more continental crust of MesozoicCenozoic tectonic age than continental crust of any
geologic period. Does this contradict the hypothesis that
most of the continental crust was differentiated from the
mantle in the first half of Earth’s history?
3. How Continents Grow
● Modes of growth
● Magmatic addition
● Continental accretion
● accreted terrains
● exotic terrains
Terrain
accretion
Terrain
accretion
Aleutian
Trench
Wrangellia
Subduction margin
(convergent boundary)
Cascadia
Trench
NORTH
AMERICA
San Andreas
Fault
Spreading center
(divergent boundary)
Transform
fault
Island arc
Submarine deposits
Ancient ocean floor
Displaced continental
fragments
Wrangellia was
transported from
5000 km away …
to the
Southern
Hemisphere!
Much of western North
America is made up of exotic
terranes accreted over the
past 200 million years.
Aleutian
Trench
Wrangellia
Subduction margin
(convergent boundary)
Cascadia
Trench
NORTH
AMERICA
San Andreas
Fault
Spreading center
(divergent boundary)
Transform
fault
Island arc
Submarine deposits
Ancient ocean floor
Displaced continental
fragments
Thought questions for this chapter
How would you recognize an accreted terrane? How
could you tell if it originated far away or nearby?
4. How Continents are Modified
● Modification by plate collision
● Alpine-Himalayan orogeny
● Assembly of Pangaea
● The Wilson Cycle
Alpine-Himalayan Orogeny
Alpine-Himalayan Orogeny
Alpine-Himalayan Orogeny
Alpine-Himalayan Orogeny
Alpine-Himalayan Orogeny
Wilson
Cycle
Geologic Time Scale of Events
in the History of Earth’s Continents
4. How Continents are Modified
● Modification by epeirogeny
● cooling and heating of
lithosphere
● weight of accumulating
sediments or glacial ice
Thought questions for this chapter
How would you recognize an accreted terrane? How
could you tell if it originated far away or nearby?
How would you identify a region where active orogeny is
taking place today? Give an example.
Would you prefer to live on a planet with orogenies or
without them? Why?
5. Origin of Cratons
● Archean cratons
● granite-greenstone
terrains
● high-grade metamorphic
terrains
Thought questions for this chapter
Why are the ocean basins just about the right size to
contain all the water on Earth’s surface?
6. Deep Structure of the Continents
● Structure of the craton
● continental crust
● cratonic keel
Thought questions for this chapter
What would happen at the surface if the cold keel beneath
a craton suddenly heated up? How might this effect be
related to the formation of the Colorado Plateau?
Key terms and concepts
Accreted terrane
Accretion
Active margin
Craton
Cratonic keel
Epeirogeny
Glacial rebound
Magmatic addition
Orogen
Orogeny
Passive margin
Rejuvenation
Shield
Tectonic age
Key terms and concepts
Tectonic province
Wilson cycle