2The Earth’s Lithosphere The boundary between the lithosphere and the asthenosphere is a temperature boundaryBelow the boundary the rocks are hot enough to flowAbove the boundary they are cooler and rigid
3Two types of lithospheric plates Oceanic crustContinental crust
4Oceanic Crust Thickens as it moves away from the hot mid-ocean ridge ThinnerMore denseNewer crust
6Lithospheric plates The lithosphere is not one continuous piece Made of very large pieces as well as a lot of smaller piecesThese pieces are called lithospheric plates
7Plate BoundaryWhere two plates are in contact with each other
8Plate Movement3 TypesPlates are in motion relative to one another
9Divergent Boundary Plates are moving away from each other Mid-ocean ridgesNew plate material produced on either side of ridge
10Convergent Boundaries Plates are moving towards one another
11Transform Boundary Plates slide past one another Example – the San Andreas FaultThe Pacific Plate is moving northwest relative to the North American PlateTransform boundaries are sometimes called conservative (lithosphere is neither created nor destroyed)
13Subduction Surface area of the Earth is not changing Must be a place where plates are consumed and created
14Subduction ZonePlate boundaries where one plate dives underneath another plateThe down going plate is an oceanic plateThe plate that stays at the surface can be an oceanic plate or a continental plateThe place where the down going plate bends downward is marked by a deep trench on the ocean floorEarthquakes and volcanoes are very common
16Continent-Continent Collision Subduction zones can make an ocean basin close upTwo continents may meet at a subduction zoneContinents are less dense than the mantle, so they do not go down a subduction zone
17When 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 enoughContinent-continent collision zones are where the continent is the thickest
19Example India is slowly being pushed under southern Asia Produces the Himalayas – the highest mountain chainAlso produces the Tibetan Plateau
20AYR 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?
21Review 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?
22Answers 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.
23In 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.
244. Continents cannot go down subduction zones because continental lithosphere is less dense than the mantle.