1. Mountain building & the evolution of continents
Chapter 20
Mountain building & the evolution of continents

2. 1) Mountain belts “Orogenesis” = mountain building
Mountain belts = continuous mountain ranges
Huge horizontal forces in the crust build mountains
Signs of such forces: folding, faulting, metamorphism, igneous activity

3. 2) Isostacy and crustal uplift
Abundant evidence for uplift exists

4. 2) Isostacy and crustal uplift
Let’s talk about gravity.
“isostacy” = gravitational balance

5. 3) Mountain building
many “young” mountain belts ( < 100 million years old)
mountain belts usually parallel folded/faulted ridges
sedimentary or volcanic rocks, usually intruded by igneous bodies
- Western Americas
- Himalayas
- NW Pacific, etc

6. 3) Mountain building Subduction zones (convergent plate boundaries)
Ocean-ocean boundaries (Aleutian-type)
Generates a
volcanic arc
Ocean-continent boundaries (Andean-type)
1st: a passive continental margin (like east coast of US)
2nd: turns into an active margin, subduction initiates
3rd: deformation, metamorphism: 2 parallel zones:
accretionary wedge and volcanic arc

8. Appalachians 3) Mountain building
Subduction zones (convergent plate boundaries)
Continental collisions
Appalachians

9. Formation of the Appalachians

10. 3) Mountain building “Continental accretion”
Small island arcs or “mini-continents”
can be added to continents
Example: Western N. America

11. Endicott Mtns, Alaska

12. 4) Evolution of continental crust
Not well known. Different ideas:
Continents evolved early in Earth’s history
Gradual evolution of the continents
During Earth formation, light stuff quickly rose to surface and formed crust
Continents slowly grow in the process of recycling
oceanic crust

13. 4) Evolution of continental crust
T&L Figure 20.19

15. Current uplift or subsidence in the U.S.