Chapter 2 Plate Tectonics Theory of plate tectonics

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