Plate Tectonics

Earth’s Interior Earth is made of layers Crust Upper Mantle (asthenosphere) Mantle Outer Core Inner Core Scientists discovered these layers using seismic waves from Earthquakes.

Crust- Lithosphere Outermost layer of the Earth Broken into Tectonic Plates that move around on the upper mantle (asthenosphere) Types of Crust: Oceanic Crust- Basaltic Materials, Heavy and Dense Continental Crust- Granitic Materials, light and less dense than oceanic crust The thickness of the crust ranges from 5-60km thick depending on what type of crust. Oceanic crust is thinner and continental crust is thicker especially in mountainous regions.

Mantle and Asthenosphere Has an upper layer called the Asthenosphere which is responsible for the movement of plates Composed of mostly silicon, oxygen, magnesium and iron Texture is plastic like which has the characteristic of a solid but flows like a liquid when under pressure Approx 2885 km thick Has large convection currents that drive the movement of the plates

Inner and Outer Core Outer Core: Liquid rock composed of Iron, Sulfur and Nickel Approx 2270 km thick Inner Core: Solid dense rock composed of Iron and Nickel Pressure from the upper layers cause it to be solid

Types of Plate Boundaries Divergent- new crust is generated and the plates pull AWAY from each other Convergent- Crust is being destroyed or uplifted and the plates move TOWARDS each other Transform- where crust is neither created or destroyed and the plates that slide horizontally past each other

Divergent Boundaries There are two types of Divergent Boundaries where the crustal plates are pulling away from each other Oceanic-Oceanic- Mid Ocean Ridges This is responsible for Sea floor spreading where new crust is being made as magma rises and cools in the mid ocean ridges

Divergent Boundaries Continued Continental- Continental Divergent When a divergent boundary cuts through a piece of land, the feature called a Rift Valley is formed. Example is Iceland where the North American and Eurasian Plates are pulling apart and the African Rift Valley Volcanoes are created in Rift Valleys as magma plumes up from the separation of the plates Iceland

Convergent Boundaries Two plates move toward each other pushing together Subduction Zone- zone where one plate subsides (goes underneath) another plate Responsible for active volcanism and deep subduction earthquakes There are 3 types of Convergent plate boundaries Oceanic-Continental convergence- subduction Oceanic-Oceanic convergence- subduction Continental-Continental convergence- minimal or ancient subduction and uplifting of large mountains

Oceanic to Continental Convergence When an oceanic plate collides with a continental plate, there is a Subduction Zone A volcanic arc is created inland 100-300km from the coast Trenches are formed off the coast of a subduction zone Oceanic Crust subducts under continental crust because it is more dense

Oceanic-Oceanic Convergence When two oceanic plates converge there is a battle between basaltic crusts until one subducts Volcanic Island arcs are created 100-300km away from the plate boundary – Example: Japan, Aleutian Islands Trenches are created off the plate boundary Cleveland Volcano Aleutian Islands, Alaska

Continental-Continental Convergence When two continental plates collide both are very buoyant and want to stay above each other. They battle towards each other but neither one subducts under the other Builds large mountain chains with very tall mountains No volcanoes because there is not any subduction causing melting of the plates and rising magma ASIA INDIA The ancient Himalayas were volcanoes because as India was pushing towards Asia, there was an ocean between them. This caused a subduction of ocean crust resulting in volcanoes. ASIA INDIA

Transform Boundary Transform boundaries are where two plates slide past each other Usually a part of a system of divergent or convergent boundaries Example is the San Andreas Fault in California Responsible for frequent shallow earthquakes

Hot Spots There are several other volcanoes that are not created near a plate boundary but instead in the middle of a plate They are created when a mantle plume is super heated by the core and burns through the crust building a volcano In the case of an oceanic hotspot, the plate continues to move and the volcano moves off the hotspot, and becomes inactive and just an island. A new volcano will begin to form on the ocean floor and as it peaks above the ocean surface it will become the new active volcanic island in the chain In the case of a continental hotspot, the caldera moves off the hotspot and when there is a new volcanic explosion, a new caldera forms in the chain

Examples of Hot Spots Hawaiian Islands- The active and newest island is the big island of Hawaii, and the oldest inactive island is Kauai. Since the inactive volcanoes are no longer adding to the size of the island, the island will erode away over millions of years until it becomes a seamount where is no longer above the ocean surface. Yellowstone- this is in the middle of a continent causing large scale eruptions that form calderas or collapsed volcanoes. The continental crust is too thick to produce tall standing volcanoes from a hotspot.

Pangaea

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