Objective • Students will be able to describe how Earth’s tectonic plates result in many geologic features. • Students will be able to compare and contrast the three types of boundaries and the features associated with each. • Student will be able to generalize the processes associated with subduction zones.

Word of the Day • Mid-Ocean Ridge: A major feature along the ocean floor consisting of an elevated region with a central valley.

Plate Boundaries • Main Idea: Volcanoes, mountains and deep-sea trenches for at the boundaries between plates. • Scientists look at features on ocean floor and asked “What may have caused this?”

Plate Boundaries Theory of Plate Tectonics Pg. 480 Evidence of Seafloor spreading suggests that continental and oceanic crust move as enormous slabs. Tectonic Plates: huge pieces of crust and rigid upper mantle that fit together at their edges to cover Earth’s surface. Plate Tectonics: The theory that describes how tectonic plates move and shape Earth’s surface. (Plates move a few centimeters per year.) • Plate tectonics unifies the theories of continental drift and seafloor spreading.

Plate Boundaries Theory of Plate Tectonics Pg. 480 There are 12 tectonic plates that interact with each other at their boundaries. • Plate tectonics unifies the theories of continental drift and seafloor spreading.

Plate Boundaries Divergent Boundaries Pg. 481 Divergent Boundaries are where 2 tectonic plates move apart from one another. Found at rift valleys. Magma rising through rift’s faults forms a mid-ocean ridge and new seafloor. • Where crust is formed.

Divergent Boundary: Plates move apart from Each other. Mid-Ocean Ridge.

Plate Boundaries Convergent Boundaries Pg. 482 Where 2 tectonic plates move towards each other and collide. Subduction: During collision denser plate submerges below the less dense plate. • Where crust is destroyed. • Subduction occurs at “subduction zones.”

Plate Boundaries Convergent Boundaries Pg. 482 3 Types of Convergent Boundaries: Classification is based on the type of crust involved. Oceanic Crust: Basaltic, dark in color, lots of iron and magnesium (metals.) Dense!! Continental Crust: Granitic, light in color, feldspar and quartz. Less Dense!! • Where crust is destroyed.

Plate Boundaries Convergent Boundaries Pg. 482 3 Types of Convergent Boundaries: Oceanic – Oceanic: One oceanic plate (denser one) will descend below the other one at a subduction zone. Creates an ocean trench. Creates an island arc as subducting (descending) plate melts and material returns to the surface. Example: Aleutian Islands in North Pacific. • Where crust is destroyed.

Oceanic-Oceanic Convergent Plate Boundary creates a trench And a volcanic island arc.

Plate Boundaries Convergent Boundaries Pg. 482 3 Types of Convergent Boundaries: Oceanic – Continental:Denser oceanic plate descends under less dense continental plate. Produces a trench and a volcanic arc at edge of continental plate (not an island chain.) Arc is characterized by mountain chain and many volcanoes. Example: Preu-Chile trench and Andes Mountains. • Where crust is destroyed.

Oceanic- Continental Convergent boundary results in a trench and an on land Volcanic mountain chain.

Plate Boundaries Convergent Boundaries Pg. 484 3 Types of Convergent Boundaries: Continental – Continental: Happens long after ocean-continent convergence (when oceanic plate is completely subducted.) Continents are passengers that ride on oceanic crust. Because both continents are not very dense, neither sinks. Continents become crumpled, folded and uplifted. Forms mountains. Example: Himalayas • Where crust is destroyed.

Continent-Continent convergence results in huge mountains. Example: The Himalayas.

Plate Boundaries Transform Boundaries Pg. 484 3 Types of Convergent Boundaries: Transform Boundaries: When two plates slide past each other in opposite directions. Crust becomes deformed and fractured.

Transform Boundaries are found where two plates slide past each other.

Example: San Andreas fault. Note: Folds and deformation.

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