I-4 Dynamic Planet Notes

The Earth’s Lithosphere The boundary between the lithosphere and the asthenosphere is a temperature boundary Below the boundary the rocks are hot enough to flow Above the boundary they are cooler and rigid

Two types of lithospheric plates Oceanic crust Continental crust

Oceanic Crust Thickens as it moves away from the hot mid-ocean ridge Thinner More dense Newer crust

Continental Crust Less dense Thicker Older crust

Lithospheric plates The lithosphere is not one continuous piece Made of very large pieces as well as a lot of smaller pieces These pieces are called lithospheric plates

Plate Boundary Where two plates are in contact with each other

Plate Movement 3 Types Plates are in motion relative to one another

Divergent Boundary Plates are moving away from each other Mid-ocean ridges New plate material produced on either side of ridge

Convergent Boundaries Plates are moving towards one another

Transform Boundary Plates slide past one another Example – the San Andreas Fault The Pacific Plate is moving northwest relative to the North American Plate Transform boundaries are sometimes called conservative (lithosphere is neither created nor destroyed)

Subduction Surface area of the Earth is not changing Must be a place where plates are consumed and created

Subduction Zone Plate boundaries where one plate dives underneath another plate The down going plate is an oceanic plate The plate that stays at the surface can be an oceanic plate or a continental plate The place where the down going plate bends downward is marked by a deep trench on the ocean floor Earthquakes and volcanoes are very common

Copy Diagram

Continent-Continent Collision Subduction zones can make an ocean basin close up Two continents may meet at a subduction zone Continents are less dense than the mantle, so they do not go down a subduction zone

When two continents meet, one of the continents is pushed horizontally beneath the other continent The movement eventually stops, when the force of friction between the continents becomes large enough Continent-continent collision zones are where the continent is the thickest

Example India is slowly being pushed under southern Asia Produces the Himalayas – the highest mountain chain Also produces the Tibetan Plateau

AYR Questions 1. What is the difference between crust and lithosphere? What is the difference between oceanic crust and the continental crust? What is the difference between a subduction zone and a continent-continent collision zone? Why do continents not go down subduction zones?

Review and Reflect Questions What type of plate boundaries are found in or along the continental United States? Why does the surface of a thicker continent stand higher above sea level than the surface of a thinner continent?

Answers to I-4 AYR Questions The curst is the outermost shell of the Earth. The lithosphere consists of the crust and the upper, rigid part of the mantle (the part that does not take part in the mantle convection). Continental crust is thicker, less dense, and generally much older than oceanic crust. A subduction zone occurs where oceanic lithosphere is subducted under another oceanic lithospheric plate). A trench forms on the sea floor as one lithospheric plate descends below the other.

In a continent-continent collision, one of the two continental plates slides horizontally under the other for some distance. That thickens the continental crust and forms high mountain ranges.

4. Continents cannot go down subduction zones because continental lithosphere is less dense than the mantle.