The Theory of Plate Tectonics 4.2 Plate Tectonics Greek tektonikos = “construction” Tectonics is the study of the formation of features in the earth’s crust. Review of earth’s make up 2 types of crust: Continental and oceanic crust Lithosphere: Crust + ridgid upper mantle. Athenosphere: Plastic rock that flows slowly when under pressure. Lithosphere is broken into separate plates that “ride” on the athenosphere. 30 plates have been identified. Some are moving together…some apart this constant movement has created earth’s major surface features. Divergent Boundaries Divergent- 2 plates moving apart. Asthenospere flows upward to fill the open space. Forms new rock forms. Mostly occurs on ocean floors. Rift Valleys are formed: Red Sea occupies a huge rift valley of when African and Arabian plate seperated. Convergent Boundries 2 plates coming together and colliding 3 types: 1) Oceanic vs. Continental: continental crust is subducted under oceanic crust: Produces Volcanic mountains or a ocean trench. 2) Continental vs Continental: Neither plate is subducted. Edges are crumpled upward and produce large mountains (hymliays) 3) Oceanic vs oceanic: One goes under the other and the subducted plate produces magma that forms and rises to form an island arc. Transform Boundaries Transform Boundaries forms when the two plates are grinding past each other. They scrape each other and make earthquakes. San Andreas fault Causes of Plate Motion Convection: Transfer of heat through the movement of heated material. Cycle of warm water rising and then cooling create convection currents. Scientist hypothesize that the earth has hot low-density plumes from mid-ocean ridges when it moves away from mid ridge it becomes more dense and begins to subduct into asthenosphere. Questions still remain though. Microplate Terranes Theory of Microplate Terranes: Continents are actually a patchwork of the lithosphere. 1)Terrane contains rock and fossils that differ from neighboring terranes. 2)Major faults at the boundaries of the terrane 3) Magnetic properties do no match those of neighboring terranes.