Chapter 2: Plate Tectonics Theory of plate tectonics Proposed by Alfred Wegener Earth’s crust consists of plates that move or float on the mantle Movement is fuelled by convection currents Plates diverge, converge or slide past each other

Chapter 2: Plate Tectonics Convection currents Responsible for the movement of plates Magma heats; rises and moves towards the upper mantle 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 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 Older towards continents

Chapter 2: Plate Tectonics Theory of continental drift Suggests that the continents are transported 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. It was effectively 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

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: 1.Divergent (boundaries of construction) 2.Convergent (boundaries of destruction) 3.Conservative (passive boundaries)

Chapter 2: Plate Tectonics 1.Divergent (boundaries of construction) New rock is formed Mid-ocean ridges created Plates separate and move away from each other

Chapter 2: Plate Tectonics 2.Convergent (boundaries of destruction) Three types of destructive boundaries: I.Oceanic-oceanic: where two ocean plates collide II.Oceanic-continent: where an ocean and continental plate collide III.Continent-continent: where two continental plates collide

Chapter 2: Plate Tectonics 2.Convergent (boundaries of destruction) - continued i.Oceanic-oceanic boundaries Heavier, older plate dips Subducted beneath lighter, younger plate Deep sea trench may develop Subducted plate melts as it moves down the mantle Volcanic activity Island arc active volcanoes, e.g. Japan Earthquakes

Chapter 2: Plate Tectonics 2.Convergent (boundaries of destruction) - continued ii.Oceanic-continent boundaries Heavier oceanic plate subducts Ocean trench forms Oceanic plate melts Magma rises to create volcanoes at the continental plate Continental plate is buckled Fold mountains belt formed Faulting Volcanism Earthquakes e.g. The Andes in South America and the Wicklow Mountains in Ireland

Chapter 2: Plate Tectonics 2.Convergent (boundaries of destruction) - continued iii.Continent-continent boundaries Neither plates sink on collision Lithosphere subducts Continental crusts buckle Formation of fold mountains Earthquake activity

Chapter 2: Plate Tectonics 3.Conservative (passive boundaries) Rock 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 Also known as plate boundaries e.g. the San Andreas Fault in California