2Convergence causes the crust to thicken and form mountain belts. Section 20.2OrogenyConvergence causes the crust to thicken and form mountain belts.Review Vocabularyisland arc: a line of islands that forms over a subducting oceanic plate
3Orogeny - all processes that form mountain ranges also known in geology as orogenic belts
4I. Mountain Building at Convergent Boundaries Most of Earth’s mountain ranges formed along plate boundaries.Fig 20.7Pg. 567
6A. Oceanic-oceanic convergence Subductiona. Plate meltsb. Magma risesFig 20.8Pg. 568
72. Island arc complex a. Aleutian Islands. (Alaska) b. Lesser Antilles 2. Island arc complex a. Aleutian Islands (Alaska) b. Lesser Antilles (Caribbean)
8Hot Spot Island Formation Section 20.2OrogenyHot Spot Island Formation
93. Rock typesa. basaltic and andesitic magmasb. sedimentary rock – uplifted or folded against arc (Japan)
10B. Oceanic-continental convergence Convergence between oceanic and continental plates produces mountain belts that are much bigger and more complicated than island arc complexes.
11Uplift of continental plate (beginning of orogeny) Compression causes continental crust to fold and thickenIgneous activity and metamorphism are common along boundaries.Fig. 20.9Pg. 569
12C. Continental-continental convergence Intense folding and faulting along continental-continental boundaries produce some of the highest mountain ranges on Earth.Fig 20.10Pg. 570
13Another 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.
15II. 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
17A. The early Appalachians 800 to 700 mya -separation from Africaa. two oceans— the ancestral Atlantic Ocean and a shallow, marginal seab. continental fragment
18to 600 myaa. Convergenceb. Island arc east of North America– 400 myaa. continental fragment thrust over younger rocksb. Blue Ridge Mountains
19B. The final stages of formation 400 to 300 myaa. Island arc attachesb. Piedmont Provincec. Blue Ridge rocks pushed farther west
202. 300 and 260 mya a. Pangaea forms b. Extensive folding and faulting c. Valley and Ridge Province
21Visualizing the Rise and Fall of the Appalachians Section 20.2OrogenyVisualizing the Rise and Fall of the AppalachiansThe Appalachians formed hundreds of millions of years ago as a result of convergence.
22Orogeny 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.
23Island 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.
24Examine the illustration. What is happening at this mountain belt?
25Possible 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.