THE THEORY OF PLATE TECTONICS

Chapter 14 lesson 3

The Plate Tectonic Theory

So we learned that new crust forms at the mid ocean ridges, but what happens to the older oceanic crust?

Plate tectonics states that Earth’s surfaces is made of a series of rigid slabs of rock or plates that move with respect to each other

Tectonic plates

17 total plates8 major plates and 9 smallerLargest plate- the Pacific plate

Lithosphere

Outermost layer of EarthConsists of the crust and the solid, upper

mantle

Asthenosphere

Directly below the lithosphereVery hot part of the mantleSolid but behaves like a liquid plastic

material that flows

Plate boundaries

3 typesDivergentConvergentTransform

Divergent

Two plates are separatingCan occur at a mid ocean ridge

Oceanic and Oceanic plateCan also occur in the middle of a continent

Continental and Continental plate Rift Valley like the Eastern African Rift Valley

Convergent

When two plates come together or collideThe denser plate sinks below the less dense in a

process called subduction.Continental and Continental

Neither plate sinks below the other because the plates are of the same density

Mountains are formed like the Himalayas

Oceanic and Continental Oceanic plate is dense compared to a continental plate Oceanic plate subducts or sinks below the continental plate Deep ocean trench and line of volcanoes occur

Transform

Two plates slide past each otherAs they move, it is common for the plates to

get “stuck”Stress builds up and the rocks breakThis leads to earthquakes and fault lines

What causes the plates to move

Convection Currents- the circulation of material caused by differences in temperature and density.

Convection in the mantle- hot mantle rises toward the crust, it cools, and sinks back down only to be heated again.

Forces causing plate motion

Basal Drag- convection currents in the mantle act like a conveyor belt in the lithosphere

Ridge Push- Rising mantle material at mid-ocean ridges creates the potential for the plates to move away from the ridge.

Slab pull- the denser plate is called a slab when it collides with a less dense plate.

As the slab sinks it pulls on the rest of the plate with a force called a slab pull.

Theory in Progress

Still many unanswered questionsWhy is Earth only planet in solar system with

plate tectonic activity?

Why do earthquakes and volcanoes happen away from plate boundaries?

What forces dominate plate motion because we can’t measure convection currents?