Theory of Plate Tectonics Theory is a well tested, widely accepted scientific idea Plate is a large, rigid slab of solid rock Tectonic comes from Greek word “to build” Theory of plate tectonics states that Earth’s lithosphere is broken into plates that move because of convection in the mantle

Three types of plate boundaries Moving plates collide, pull apart and slide past each other. Plate boundaries are classified according to the type of movement. Three types of plate boundaries Divergent Convergent Transform

Divergent Boundary As plates move apart molten magma erupts to fill the gap....seafloor spreading...rift valley Divergent Plate Boundary Animation

Iceland is on the Mid-Atlantic Ridge Divergent plate boundary

Convergent Boundary Where plates collide Three types of collisions possible: Continent-continent collision Continent-oceanic crust collision Ocean-ocean collision Convergent boundaries are where the plates move towards each other. There are three types of convergent boundary, each defined by what type of crust (continental or oceanic) is coming together. Therefore we can have: continent-continent collision, continent-oceanic crust collision or ocean-ocean collision….

Continent-Continent Convergent Boundary Continental crust is less dense – buoyant and thick When continents collide they buckle, crack and push each other up forming mountains Continent-Continent Collision Animation

Himalayas India collides with Asia creating the Himalayan Mountains

Continent-Oceanic Crust Collision Called SUBDUCTION .... Denser oceanic crust sinks beneath less dense continental crust Ocean-Continent Convergent Boundary Animation

Subduction Oceanic lithosphere sinks underneath the continental lithosphere Melting slab forms volcanoes Continental crust buckles forming mountains Andes Mountains of South America The Andes mountain range along the western edge of the South American continent is an example of a mountain belt formed by subduction. The continental crust of the South American plate has buckled under the compressional strain of converging with the Nasca and Antarctic plates. Additionally there are many volcanoes, the result of melting of the subducting slab and the production of new material that has risen through the crust to the surface.

Ocean-Ocean Convergent Plate Boundary When two oceanic plates collide, one pushes over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. Ocean-Ocean Convergent Boundary Animation

Transform Plate Boundary Where plates slide past each other Above: View of the San Andreas transform fault More Animations!

Map of tectonic plates showing relative directions and velocities NASA plate motion maps Cornell University - Discover our Earth link

Ridge-push Hypothesis ...one idea of how convection in the mantle moves tectonic plates

Slab-Pull hypothesis ...another idea of how convection in the mantle moves tectonic plates

Magma Plumes hypothesis ...another idea....maybe all three mechanisms are at work moving tectonic plates

WORKS CITED Kious, W. Jacquelyne, and Robert I. Tilling. "USGS Developing the Theory." This Dynamic Earth: The Story of Plate Tectonics. USGS Publications Warehouse, n.d. Web. 6 Apr. 2012. http://pubs.usgs.gov/gip/dynamic/dynamic Plummer, Charles, David McGeary, and Diane Carlson. "Chapter 19 Plate Tectonics Animations and Movies." Physical Geography Online Learning Center. Version Nonthe Edition. McGraw-Hill, n.d. Web. 6 Apr. 2012. <http://highered.mcgraw-hill.com/sites/0072402466/sitemap.html>. "Discover Plate Boundaries." www.geo.cornell.edu. N.p., n.d. Web. 6 Apr. 2012. <http://www.geo.cornell.edu/hawaii/220/PRI "Earth Science." ClassZone. N.p., n.d. Web. 6 Apr. 2012. <http://www.classzone.com/books/earth_science