Detailed Textbook Notes Chapter 2

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University of Toronto Mississauga
Earth Science
Terry Botrrill

Pre-Lecture 2 Notes: Crustal Tectonics A Mobile Earth 2.7 What do we mean by Plate Tectonics? The Concept of a Lithosphere Plate Lithosphere: Relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth; constituting crust & top part of mantle Asthenosphere: Layer of mantle that lies between 100-150 km & 350 km deep; asthenosphere is relatively soft & can flow when acted on by force Asthenosphere can undergo convection but lithosphere cant Continental Lithosphere & oceanic lithosphere differ in their thickness; On average, continental lithosphere has thickness of 150 km, whereas oceanic lithosphere has thickness of about 100 km Geoscientists distinguish 12 major plates & several microplates Distinguish 2 continental margins: o Active Continental Margin: Continental margin that coincides with a plate boundary o Passive Continental margin: Continental margin that is not a plate boundary The Basic Principles of Plate Tectonics Earths lithosphere divided into plates that move relative to each other & relative to underlying asthenosphere Plate movement occurs @ rates of about 1-15 cmyear As plate moves, internal area remains largely rigid & intact, but rock along plate boundaries undergoes deformation As plates move, so do continents that form part of the plates, resulting in continental drift Identifying Plate Boundaries 3 types of plate boundaries: o Divergent Boundary: A boundary at which 2 lithosphere plates move apart from each other; they are marked by mid-ocean ridges o Convergent BoundaryA : boundary at which 2 plates move toward each other so that 1 plate subducts beneath the other; only oceanic lithosphere can subduct o Transform Boundary: A boundary at which 1 lithosphere plate slips along the side of another plate 2.8 Divergent Plate Boundaries & Sea-Floor Spreading As plates move apart, new oceanic lithosphere forms along divergent boundary
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