Table of Contents

Title: 17.4 Causes of Plate MotionsPage #: 96

Date: 4/10/2013

Objectives

• Students will be able to explain the processes of convection.

• Students will be able to summarize how convection in the mantle is related to the movement of tectonic plates.

• Students will be able to compare and contrast the processes of ridge push and pull slab.

17.4 Causes of Plate Motions

• Convection:

• Pg. 486

• Causes of Plate Motions: • Main Idea: Convection currents in the

mantle cause plate motions.

• Convection: Possible answer to “what causes plates to move?”

17.4 Causes of Plate Motions

• Convection:

• Pg. 486

• Convection Currents: Less dense material rises / More dense material sinks. – Heat causes a decrease in the density of

material.– Hot material rises.– When it gets far enough away from the heat

source, the material cools down.– Cool material sinks back towards heat source.– Up and Down motion called a “Convection

Current.”

Convection Current

17.4 Causes of Plate Motions

• Convection:

• Pg. 486

• Heat in mantle comes from pressure of overlying rock and from radioactive decay of material inside the earth.

• This heat causes huge convection currents.

Heat inside the earth comes from radioactivity and pressure.

17.4 Causes of Plate Motions

• Convection in the mantle:

• Pg. 487

• Convection in the Mantle: Convection currents in the mantle are the driving mechanism of plate movement.

• Steps: 1. Mantle near the core is heated and rises.2. Mantle arrives at base of crust, cools and

sinks.3. Once back at hot core, mantle heats back

up and rises again.

Convection in Mantle.

Mid-Ocean Ridge

Trench Trench

17.4 Causes of Plate Motions

• Plate Movement:

• Pg. 487

• Some rising mantle is turned aside by crust.– The upward and sideways motion of

mantle splits the crust.– Split crust creates a Divergent Boundary

(Mid-Ocean Ridge!)– Downward part of convection currents

occur where a sinking force pulls tectonic plates downward at Convergent Boundaries (Trenches!)

Magma that is pushed to the sides at a Mid-ocean ridge brings overlying crust With it.

17.4 Causes of Plate Motions

• Push and Pull :

• Pg. 488

• Other mechanisms of movement:

• Ridge Push: Process by which dense older oceanic crust is pushed away from a less dense mid-ocean ridge.

• Slab Pull: process by which the weight of a subducting plate pulls the trailing slab into the subduction zone.

Ridge Push Slab Pull