1. Ch. 20 Sec. 2
Orogeny

2. Convergence causes the crust to thicken and form mountain belts.
Section 20.2
Orogeny
Convergence causes the crust to thicken and form mountain belts.
Review Vocabulary
island arc: a line of islands that forms over a subducting oceanic plate

3. Orogeny - all processes that form mountain ranges
also known in geology as orogenic belts

4. I. Mountain Building at Convergent Boundaries
Most of Earth’s mountain ranges formed along plate boundaries.
Fig 20.7
Pg. 567

5. Compressive forces
folding
faulting
metamorphism
igneous intrusions

6. A. Oceanic-oceanic convergence
Subduction
a. Plate melts
b. Magma rises
Fig 20.8
Pg. 568

7. 2. Island arc complex a. Aleutian Islands. (Alaska) b. Lesser Antilles
2. Island arc complex a. Aleutian Islands (Alaska) b. Lesser Antilles (Caribbean)

8. Hot Spot Island Formation
Section 20.2
Orogeny
Hot Spot Island Formation

9. 3. Rock types
a. basaltic and andesitic magmas
b. sedimentary rock – uplifted or folded against arc (Japan)

10. B. Oceanic-continental convergence
Convergence between oceanic and continental plates produces mountain belts that are much bigger and more complicated than island arc complexes.

11. Uplift of continental plate (beginning of orogeny)
Compression causes continental crust to fold and thicken
Igneous activity and metamorphism are common along boundaries.
Fig. 20.9
Pg. 569

12. C. Continental-continental convergence
Intense folding and faulting along continental-continental boundaries produce some of the highest mountain ranges on Earth.
Fig 20.10
Pg. 570

13. Another common characteristic of the mountains that form when two continents collide is the presence of marine sedimentary rock near the mountains’ summits. The marine sedimentary rocks were formed in the ocean basin that existed between the continents before their collision.

14. Orogeny
Convergence

15. II. The Appalachian Mountains—A Case Study
Geologists have divided the Appalachians into several distinct regions. Each region is characterized by rocks that show different degrees of deformation.
Fig Page 571

16. Section 20.2
Orogeny
Folding Rocks

17. A. The early Appalachians
800 to 700 mya -separation from Africa
a. two oceans— the ancestral Atlantic Ocean and a shallow, marginal sea
b. continental fragment

18. to 600 mya
a. Convergence
b. Island arc east of North America
– 400 mya
a. continental fragment thrust over younger rocks
b. Blue Ridge Mountains

19. B. The final stages of formation
400 to 300 mya
a. Island arc attaches
b. Piedmont Province
c. Blue Ridge rocks pushed farther west

20. 2. 300 and 260 mya a. Pangaea forms b. Extensive folding and faulting
c. Valley and Ridge Province

21. Visualizing the Rise and Fall of the Appalachians
Section 20.2
Orogeny
Visualizing the Rise and Fall of the Appalachians
The Appalachians formed hundreds of millions of years ago as a result of convergence.

22. Orogeny refers to all of the processes that form mountain belts.
Convergence causes the crust to thicken and form mountain belts.
Orogeny refers to all of the processes that form mountain belts.
Most mountain belts are associated with plate boundaries.

23. Island arc complexes, highly deformed mountains, and very tall mountains form as a result of the convergence of tectonic plates.
The Appalachian Mountains are geologically ancient; they began to form 700 to 800 mya.

24. Examine the illustration. What is happening at this mountain belt?

25. Possible answer: An oceanic plate is subducting beneath a continental plate. As the subducting plate sinks, it gets warmer and water is released from minerals that contain it.