Plate Tectonics The Plate Tectonic Theory The plate tectonic theory states that the crust of the Earth is broken into several large sections known It is theorized that these plates are dynamic and move continually. The interaction between plates produces changes on Earth’s surface such as, volcanoes, mountains, and earthquakes. NOTE-- Divergent Boundaries are in blue, Convergent Boundaries are in Red. Why do the crustal plates move? Tectonic Plates of the World “Which tectonic plate is located at 20˚N, 160˚W?” “What type of boundary is the Mid-Atlantic Ridge?” RT = Pg. 5 Divergent Plate Boundary As the plates diverge, magma and lava are forced upward due to convection in the asthenosphere. The molten rock will cool to form new crust. When a divergent plate boundary occurs under an ocean, it is also referred to as Soon thereafter, new magma will be forced upward and will force the new crust to split and diverge as well. Divergent Plate Boundary When a divergent plate boundary occurs under a continent, it is also referred to as rift valley. Dynamic activity associated with a divergent plate boundary includes: Convergent Plate Boundary A convergent plate boundary is where two plates converge or collide with one another. Convergent plate boundaries can take place in three ways: OCEANIC-OCEANIC CRUST CONVERGENCE CONTINENTAL-CONTINENTAL CRUST CONVERGENCE OCEANIC-CONTINENTAL CRUST CONVERGENCE OCEANIC-CONTINENTAL CRUST CONVERGENCE CONTINENTAL-CONTINENTAL CRUST CONVERGENCE OCEANIC-OCEANIC CRUST CONVERGENCE Convergent Plate Boundary: SUBDUCTION ZONE OCEANIC-CONTINENTAL CRUST CONVERGENCE CONTINENTAL-CONTINENTAL CRUST CONVERGENCE When two plates converge, the denser of the two plates will move and sink under the less dense plate. A subduction zone is an area of tremendous heat, pressure, and dynamic activity. Many features are associated with convergent plate boundaries including: OCEANIC-OCEANIC CRUST CONVERGENCE Transform Plate Boundary Dynamic activity associated with a transform plate boundary includes: San Andreas Fault, California: Transform plate boundary between the North American Plate and Pacific Plate Evidence to Support the Plate Tectonic Theory Appearance of Continents Evidence to Support the Plate Tectonic Theory Landmass Features/Fossil Record Evidence to Support the Plate Tectonic Theory Age and Heat Index of Ocean Rock In a divergent plate boundary, molten rock rises to the surface and cools to become new crust. This newly formed crust is continually being replaced by new molten rock. Older crust diverges and is forced to move away from the area where new molten rock will form into new crust. This image is taken of the Mid-Atlantic Ridge – a divergent plate boundary. Each color represents rocks of similar age. Evidence to Support the Plate Tectonic Theory Magnetic Polarity Earth’s magnetic field has reversed its polarity many times in Earth’s history. Currently magnetic north is close to Earth’s North Pole. Yet, in the past, magnetic north was close to Earth’s South Pole. The nature and frequency of these reversals of magnetic polarity are not fully understood. When molten rock cools at the site of divergence, the minerals within the molten rock begin to crystallize. Many minerals found within igneous rock are magnetic. These minerals will align themselves in the direction of magnetic north. If there is a reversal in magnetic polarity the minerals with igneous rock will align in an opposite pattern. These patterns suggest some plates are moving away from one another.