Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 4, 15, 16, 19; Appendix A & B Unit: 4The Forces Within Earth

2. Unit 4: Topic 2.6 Plate Boundaries - Convergence Focus on . . . • describing and giving examples of the three types of collision boundaries. • demonstrating through a drawing the processes associated with plate convergence.

3. Plate Boundaries • According to the Plate tectonic theory, three boundaries exist at the edges of tectonic plates. • Divergent Boundary (Ridge) • Convergent Boundary (Trench) • Transform Boundary Text Reference: Pages 526-539 Figure 19.17, pg. 528

4. Convergent Boundaries (3 Types): • 1) Ocean – Ocean Convergent Boundary • Ocean-ocean collisions involvetwo oceanic plates. • Compressional forces cause theoceanic plates to move together,causing one slab of lithosphere to be consumed into the mantle initiating volcanic activity which creates volcanoes to form on the ocean floor. • The volcanoes produced at this collision boundary are island arc volcanoes; they form a curved arc on the surface (map view). • Features called ocean trenches are formed at these boundaries.

5. Convergent Boundaries (3 Types): • 1) Ocean – Ocean Convergent Boundary • The composition of the moltenmaterial is largely andesitic(intermediate) since the meltingbasaltic (mafic) oceanic crustbecomes mixed with meltingsediments that were located on top of the subducting plate as a result of weathering and erosion from the nearest continent (felsic). • Lithosphere isdestroyedas one oceanic slab descends beneath another. • Example include the Japan island arc and the Japan trench.

6. Convergent Boundaries (3 Types): • 2) Ocean – Continent Convergent Boundary • Ocean-Continent collisions involve anoceanic plate and a continental plate. • Compressional forces cause an ocean plate and a continent plate to move together, due to a greater density (basaltic vs. granitic), the oceanic plate will most likely subduct beneath the continent forming a trench and subduction zone. • In a map view, a volcanic arc is created on the continent as a result of the collision. • Lithosphere is destroyed as one oceanic slab descends beneath another.

7. Convergent Boundaries (3 Types): • 2) Ocean – Continent Convergent Boundary • The composition of the molten material willmost likely be granitic (felsic) since theupwelling magma created by the meltingoceanic crust has to burn through a granitic (felsic) continent. • At depths of about 100 km the oceanic plate and parts of the mantle partially melt producing viscous magmas. This molten rock rises slowly where it cools and solidifies at depths producing plutons. However, some magma may reach the surface and erupt through composite volcanoes as violent volcanic eruptions. • Example include the Rocky mountains in North America and the Andes mountains in South America.

8. Convergent Boundaries (3 Types): • 3) Continent – Continent Convergent Boundary • Continent-Continent collisions involve two continental plates. • Compressional forces cause two continental plates to move together. • Once the oceanic crust between the two continents has been entirely subducted andthe continental shelves have nearly joined,the process of subduction ceases. • Lithosphere is destroyed as one oceanic slab descends beneath another.

9. Convergent Boundaries (3 Types): • Continent – Continent Convergent Boundary • Because of the low density of continental crust neither plate will subduct, both continental shelves get uplifted and deformed, formingfolded mountains. • Such a collision occurred when India collidedwith Asia forming the Himalayan mountainsand also during the formation of the Appalachian mountains • Global examples of continental-continental collisions include the Himalayan and Appalachian mountains

10. Plate Boundaries

11. Example 1: Collision at which plate boundary would result in the tallest mountains?(A) ocean - ocean (C) ocean – continent(B) ocean - fault (D) continent - continent Which is associated with an oceanic to oceanic collision? (A) folded mountains (B) island arc (C) mid-oceanic ridge (D) volcanic arc

12. Example 2: Based on the diagram below, what type of plate collision formed the Himalaya mountain range? (A) continent-continent (B) ocean-continent (C) ocean-ocean (D) seafloor-ocean

13. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: A range of mountains is found on Australia’s east coast. With reference to plate boundaries, explain how this mountain range may have been formed.

14. Solutions . . . Question: A range of mountains is found on Australia’s east coast. With reference to plate boundaries, explain how this mountain range may have been formed. Answer: Mountain ranges are found along convergent plate boundaries. At these boundaries one tectonic plate moves toward and collides with another plate boundary. In the above diagram, an oceanic plate (Pacific) collides with a continental plate (Australian). This collision causes the oceanic plate to subduct beneath the continental plate. These compressional forces generally deform the tectonic plates which result in the continental plate uplifting to form a mountain chain along the length of the convergent boundary.

15. Extra Practice Problems: Which mountain ranges were formed by a collision between continents? (A) Andes and Rockies(B) Andes and Himalayas (C) Appalachians and Himalayas(D) Appalachians and Rockies Which feature is not associated with a convergent plate boundary?(A) deep-sea trench zone (C) mid-ocean ridge (B) earthquake (D) volcanic activity

16. Summary . . . Overview of Points covered: • 3 Types of Convergent Boundaries: • Ocean – Ocean • Ocean – Continent • Continent – Continent • All experience; • Compressional forces • Destruction of lithosphere