Earth Science ENR Plate Boundaries Notes

Transcription

1 Name Earth Science ENR Plate Boundaries Notes Per Tchr Plate Boundary Types: 1) Divergent Plate Boundary (Seafloor Spreading Centers) 2) Divergent Plate Boundary (Continental Rift Valley) 3) Transform Plate Boundary 4) Convergent Plate Boundary (Oceanic - Continental) 5) Convergent Plate Boundary (Oceanic Oceanic) 6) Convergent Plate Boundary (Continental Continental)

2 1) Divergent Plate Boundary (Seafloor Spreading Centers): a. This is the boundary between two sections of oceanic crust on two different plates (oceanic-oceanic divergence) that are moving away from each other. Naval Officer and Geologist Harry Hess ( ) discovered this process and named it Seafloor Spreading. As the plates diverge, magma rises up between the plates forming new basaltic oceanic crust. b. As the magma rises up and breaks through the crust at the spreading center, it uplifts the crust and creates a ginormous underwater volcanic mountain range called a RIDGE. In the very center of the ridge itself, where the plates are spreading and magma rises, is a location called the RIFT VALLEY. The Mid-Atlantic Ridge is one of the most famous ridges. The VOLCANIC MOUNTAINS that make up the ridges can grow upwards to 1 mile above the surrounding seafloor. That s mad high!

3 c. The youngest rock is found at the ridge, and age increases as distance from the ridge increases. Make a graph conveying this information: d. As what was stated in a, b, and c occurs, shallow depth EARTHQUAKES are also quite common.

4 2) Divergent Plate Boundary (Continental Rift Valley) a. This is the boundary between two sections of continental crust on two different plates that are being rifted (torn apart). A crack in this continental crust allows magma to escape the surface, forming new crust and forcing the plates apart. So, VOLCANISM is rampant here. b. A valley forms between the plates and is eventually filled with water to create a young sea, similar to the Red Sea. c. Again, shallow depth EARTHQUAKES are quite common here. d. Best example of this? The East African Rift Valley for sure.

5 3) Transform Plate Boundary: a. This is a boundary in which two plates slide past each other. Friction and pressure are built up as the thick rocky chunks of crust are scraped by one another. b. When the massive amount of potential energy is finally released as kinetic energy, strong, yet shallow EARTHQUAKES occur. c. Mountain building, trenches, and volcanic activity are usually not an occurrence at this boundary type. d. A commonly discussed example of a Transform Plate Boundary is the San Andreas Fault in California. 4) Convergent Plate Boundary (Oceanic Continental) a. This is the boundary between oceanic crust and continental crust that are converging (colliding into each other). The denser, thinner oceanic crust is forced down beneath the less dense, thicker continental crust as they collide. This is called SUBDUCTION, and the boundary where this subduction occurs is called a SUBDUCTION ZONE. Very clever, huh? b. A TRENCH is formed at these subduction zones and

6 c. EARTHQUAKES are quite common. Since there is subduction, shallow, intermediate, and deep earthquakes will occur. d. As subduction occurs, the oceanic plate is forced deep into Earth where it will reach its melting point in the asthenosphere (between km beneath the surface). This melted rock will rise and break through the lithosphere on the continental side of the boundary, forming a CONTINENTAL VOLCANIC ARC. e. Example? 5) Convergent Plate Boundary (Oceanic Oceanic) a. This is the boundary between 2 sections of oceanic crust (on two separate plates). These sections of oceanic crust are converging (colliding into each other). Since both plates are basaltic and dense, they there will be more of a battle between them before the denser basalt is thrust beneath the other. This is called SUBDUCTION, and the boundary where this subduction occurs is called a SUBDUCTION ZONE. Very clever, huh? b. A TRENCH is formed at these subduction zones and c. EARTHQUAKES are quite common. Since there is subduction, shallow, intermediate, and deep earthquakes will occur. d. As subduction occurs, the oceanic plate is forced deep into Earth where it will reach its melting point in the asthenosphere (between km beneath the surface). This melted rock will rise and break through the lithosphere and create

7 volcanic mountains. Since this happens in the middle of the ocean, some of these mountains will rise above the ocean surface to become volcanic islands, creating a VOLCANIC ISLAND ARC. e. Example? 6) Convergent Plate Boundary (Continental Continental) a. This is the boundary between 2 sections of continental crust (on 2 different plates) that are colliding. The uber THICK continents collide with each other, forcing the land to uplift (rise), forming giant, rugged MOUNTAINS. This type of mountain building is termed OROGENY. b. EARTHQUAKES are common at this active plate boundary. The EARTHQUAKES can be shallow or intermediate, but rarely deep due to the thickness of the continental crust (especially beneath the MOUNTAINS. c. Volcanism is rare, as the crust is being forced into the mantle far beneath the mountains. Too deep, yo. d. Example?

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