Lecture4_Plate tectonics_students

Lecture4_Plate tectonics_students - When Plates Collide...

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Unformatted text preview: When Plates Collide Plate Tectonics –  Plates meet at boundaries. •  Divergent •  Convergent •  Transform Convergent Boundaries !  !  What gets created at the spreading centers must get destroyed (Subduc>on). Three types: These blocks have equal volume and are floa>ng in this jar of water. Which one has greater density? A B C= I don’t know Which has the greatest density? A.  Old oceanic lithosphere B.  New oceanic lithosphere C.  New con>nental lithosphere When plates collide, the denser plate sinks! •  Con>nental Lithosphere ~ 150 km thick. –  Grani>c crust + uppermost mantle •  Lighter (less dense) . •  More buoyant – Floats higher. •  Oceanic Crust~ 7 to 100 km thick. –  Basal>c crust + uppermost mantle •  Heavier (more dense). •  Less buoyant – Sinks lower. Convergent boundaries: Three types 1. Ocean-­‐con>nent subduc>on zone Figure 2.23 A Video Oceanic to Con>nental Convergence The Cascades: A Con>nental Volcanic Arc The Cascades result from subduc>on of the Juan de Fuca Plate underneath the North American Plate Convergent boundaries: Three types 2. Ocean-­‐ocean subduc>on zone Figure 2.23 B Video Deep ocean trenches are the surface expression of subduc>on Mariana Trench: Deepest part of the world – 11 km (~36,000 a) deep! Aleu>an Islands: A Volcanic Island Arc That ring of fire… 1.  How many tectonic plates are represented by this ocean profile? 2.  How do you know? Convergent boundaries: Three types 1. Con>nental-­‐Con>nental Convergence •  Con>nental collisions follows aaer ocean-­‐con>nent convergence… •  Con>nental lithosphere is too buoyant to subduct Continent to Continent Convergence Video The Himalayas: Result of a recent con>nental collision (45 Ma-­‐ present) World’s tallest mountain range! Mount Everest = 8,848 metres (29,029 a) Final Boundary Type: Transform Boundaries https://www.youtube.com/watch? v=tIuk2blBzHs Fig. 2-14, p. 24 Multiple boundary types Con>nental collisions •  Con>nents crash together – forming huge mountain ranges. –  E.g. Himalayas, Alps, Appalachians Draw a transect ...
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