8 3 Causes of Plate Movement Objectives 1

8. 3 Causes of Plate Movement Objectives: 1) Explain the “mantle convection hypothesis”. 2) Compare and contrast ridge push and slab pull.

Introduction � 3 major hypotheses describe how tectonic plates move � Mantle convection � Ridge push � Slab pull � Asthenosphere � Provides the plates with a surface on which they can move � Pliable � Rock materials are hotter than those in the lithosphere

Mantle Convection � The mantle may be moving the plates along with it as it convects � Magma that is hotter and less dense than its surroundings rises upward at a mid-ocean ridge � It drags the lithospheric plate with it as the current moves away from the midocean ridge � Cooler, denser rocks of the lithospheric plate sink down at a subduction boundary

Ridge Push � “Gravitational Sliding” � Molten magma rises at the mid- ocean ridge � Heats the rock around it � Surrounding rock is heated to expand elevate � Creates a slope � New rocks are less dense and more buoyant � Becomes denser as it cools � Gravity causes older, denser rock to slide away from the ridge down the slope � New molten magma wells up (etc. )

Slab Pull � The edge of the subducting plate is much colder and heavier than the mantle � It continues to sink, pulling the rest of the plate along with it � Definition: the force that the sinking edge of the plate exerts on the rest of the plate � Scientists think this is a stronger factor than ridge push or mantle convection in driving plate movements

8. 3 Exit Ticket �Answer the following 1) What is the “mantle convection questions. hypothesis”? �Use complete 2) Compare and contrast sentences. ridge push and slab �You may NOT use your pull. (use a Venn book. You MAY use diagram) your notes. �This is a quiz grade