2 Plate Tectonics

Chapter 2: Plate Tectonics Theory of plate tectonics  “Plate Tectonics” explains why the plates of the earth are moving.  The main idea (theory) was proposed by Alfred Wegener in  Earth’s crust consists of plates that move or float on the mantle  Movement is caused by convection currents in the mantle.  Plates diverge, converge or slide past each other.

Magma Convection currents  Causes the movement of plates  Magma heats; rises and moves towards the upper mantle  The magma flows sidewards, then cools and sinks.  Plate moves with sinking magma  Circular movement fuels plate movement Chapter 2: Plate Tectonics

Sea floor spreading  New rock is formed where plates were split apart (Iceland!!)  Ocean floor widens; magma rises from within the mantle and fills the opening  Magma cools; new ocean floor formed  New sea floor youngest at the mid-ocean ridge  The rocks found further from the plate divide are older so older rocks are found closer towards continents. Chapter 2: Plate Tectonics

Red represents the newest crust of the earth. The further from red the older the crust. Where is Ireland?

Theory of continental drift  Suggests that the continents are moved across the planet by convection currents  Drifting of the continents is still occurring today  Continents were once all joined together in one single landmass known as Pangaea. ……..a supercontinent.  Approximately 200 million years ago Pangaea began to break apart  The continents were fuelled by the convection currents and so they began to drift apart (pangea divided into Laurasia and Gondwanaland…until these broke further apart into todays continents.) Chapter 2: Plate Tectonics

The process of subduction  Continents collide  Oceanic plate is heavier than the continental plate  Ocean floor pulled down into the mantle  Subduction occurs Chapter 2: Plate Tectonics

Plate boundaries There are three types of plate boundaries:  Divergent (boundaries of construction)  Convergent (boundaries of destruction)  Conservative (passive boundaries) Chapter 2: Plate Tectonics

1. Divergent (constructive boundaries)  New crust is formed  Mid-ocean ridges created (Mid-Atlantic Ridge)  Plates separate and move away from each other  Example: American and Eurasian plates

Chapter 2: Plate Tectonics 2. Convergent (boundaries of destruction) Three types of destructive boundaries: I.Oceanic-continent: where an ocean and continental plate collide II.Oceanic-oceanic: where two ocean plates collide III.Continent-continent: where two continental plates collide Heavier, older plate dips Subducted beneath lighter, younger plate Deep sea trench may develop Heavier oceanic plate subducts Magma rises to create volcanoes at the continental plate Continental plate is buckled and fold mountains form Neither plates sink on collision Lithosphere subducts Continental crusts buckle Formation of fold mountains

Chapter 2: Plate Tectonics 3. Conservative (passive boundaries)  crust is neither created nor destroyed  Plates slide past each other  The line along which the plates slide is known as a fault line  Known as transform faults  e.g. the San Andreas Fault in California

1.Who proposed the Theory of Plate Tectonics? 2.What is the main idea of this theory? 3.What causes the plates of the earth to move? 4.What causes magma to move in the mantle? 5.What was Pangea? 6.What proof do we have that the continents of the earth were once all joined together?

7. What are the three types of plate boundary? 8. Name examples of each plate boundary? 9. What feature is generally found at each boundary? 10. Can you name a famous world feature found at each of the main boundary types?