Plate Tectonics

Composition = Materials Mechanical = Movement Plate Tectonics chemical symbols: Fe = Iron Ni = Nickel

The compositional divisions of Earth were understood decades before the development of the theory of plate tectonics – the idea that Earth's surface consists of large plates that move. By the 1970s, however, geologists began to realize that the plates had to be thicker than just the crust, or they would break apart as they moved. In fact, plates consist of the crust acting together with the uppermost part of the mantle; this rigid layer is called the lithosphere and it ranges in thickness from about 10 to 200 km. Rigid lithospheric plates "float" on a layer called the asthenosphere that flows like a very viscous fluid, like Silly Putty®. It is important to note that although the asthenosphere can flow, it is not a liquid, and thus both S- and P-waves can travel through it. At a depth of around 660 km, the pressure becomes so great that the mantle can no longer flow, and this solid part of the mantle is called the mesosphere. The lithospheric mantle, asthenosphere, and mesosphere all share the same composition (that of peridotite), but their mechanical properties are significantly different. Geologists often refer to the asthenosphere as the jelly in between two pieces of bread: the lithosphere and mesosphere. The core is also subdivided into an inner and outer core. The outer core is liquid molten metal (and able to stop S-waves), while the inner core is solid. (Because the composition of the core is different than that of the mantle, it is possible for the core to remain a liquid at much higher pressures than peridotite.)

Alfred Wegener Evidence for Continental Drift: Considered the father of plate tectonics Proposed continental drift = Hypothesis that all the continents fit together as one mass, & around 200 million years ago, began to break apart from each other. Evidence for Continental Drift: Continental Puzzle (Pangaea) Matching fossils on different continents Matching rock types & mountains on different continents Ancient climates

FUN FACT: = About 95 percent of major earthquakes occur in a few narrow zones near fault lines.

Mechanisms of Plate Movement Mantle convection: movement of heat in the mantle Slab-pull: gravity pulling down on the subducting plate or “slab” & pulling the plate with it Ridge-push: pushing of the plate because of creation of crust at the ridge

Boundary Divergent Convergent Transform Movement: Structures: Sec 9.2 Divergent Convergent Transform Movement: Structures: Examples:

Boundary Divergent Convergent Transform Movement: Structures: Sec 9.2 Divergent Convergent Transform Movement: Moving apart New crust created Coming together Crust destroyed Plates grind past each other Crust neither created or destroyed Structures: Oceanic ridge Rift valleys Subduction zone Deep Trench Volcanic activity Examples: Mid-Atlantic Ridge Andes Mountains San Andreas Fault

Types of Faults Normal = Hanging Wall moves down & Foot Wall moves up -Tension Reverse = Foot Wall moves down & Hanging Wall moves up -Compression Strike-slip = two parts are moving past one another- Shearing Fun...Hurt??? Footwall Up Normal….Hanging Up Reverse Thrust

Activity: create a power point (6 + 1 slides) Suggested name: Plate tectonic formations Picture of formation (real life picture) Explain what caused this formation (using your notes/drawings (there are 6 possible cases) Write about the name and history of this place (see example on next slide) HOT SPOTS – Ex: Hawaii

EXAMPLE The Great East African Rift Valley: 6,000 kilometres (3,700 mi) in length, from Lebanon's Beqaa Valley in Asia to Mozambique in Southeastern Africa. All of the large lakes in Africa (ex: lake Victoria) were formed as part of it. These lakes sustain many different types of natural species and around 33 million people in their basin with their natural resources Caused by divergence of continental plates