2The Plate Tectonic Theory The plate tectonic theory states that the crust of the Earth is broken into several large sections known as crustal or lithospheric plates.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.The interface between two or more plates is known as a boundary.NOTE-- Divergent Boundaries are in blue,Convergent Boundaries are in Red.
3Why do the crustal plates move? Crustal plates may move away from one another, towards one another, or slide against one another. In addition, crustal plates may rise above (uplift) or descend (subsidence) within the Earth.It is theorized that crustal plates move due to the convection currents of heat within the asthenosphere.
4Tectonic Plates of the World “Which tectonic plate is located at 20˚N, 160˚W?”PACIFIC PLATE“What type of boundary is the Mid-Atlantic Ridge?”DIVERGENT PLATE BOUNDARYRT = Pg. 5
5Divergent Plate Boundary A divergent plate boundary is where two plates separate from one another. This separation leads to the rise of magma and igneous intrusions/extrusions at the point of separation.Young CrustAs the plates diverge, magma and lava are forced upward due to convection in the asthenosphere.The molten rock will cool to form new crust.Soon thereafter, new magma will be forced upward and will force the new crust to split and diverge as well.Older CrustWhen a divergent plate boundary occurs under an ocean, it is also referred to as sea-floor spreading.
6Divergent Plate Boundary Dynamic activity associated with a divergent plate boundary includes:Many shallow earthquakesFaulting (sudden uplift of small portions of the crust)Volcanic activityThe creation of a ridge of volcanic mountains (ocean only).When a divergent plate boundary occurs under a continent, it is also referred to as rift valley.
7Convergent 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 CONVERGENCECONTINENTAL-CONTINENTAL CRUST CONVERGENCEOCEANIC-CONTINENTAL CRUST CONVERGENCEOCEANIC-CONTINENTAL CRUST CONVERGENCECONTINENTAL-CONTINENTAL CRUST CONVERGENCEOCEANIC-OCEANIC CRUST CONVERGENCE
8Convergent Plate Boundary: SUBDUCTION ZONE When two plates converge, the denser of the two plates will move and sink under the less dense plate. This process is known as subduction.A subduction zone is an area of tremendous heat, pressure, and dynamic activity. Many features are associated with convergent plate boundaries including:Volcanic activityDeep earthquake activityRegional metamorphismOrogeny – Mountain-building forcesDeep ocean trenchesDeposition basinsOCEANIC-CONTINENTAL CRUST CONVERGENCECONTINENTAL-CONTINENTAL CRUST CONVERGENCEOCEANIC-OCEANIC CRUST CONVERGENCE
9A transform plate boundary is where two plates slide past one another. Dynamic activity associated with a transform plate boundary includes:Many earthquakesFaulting (sudden uplift of small portions of the crust)San Andreas Fault, California: Transform plate boundary between the North American Plate and Pacific Plate
10Appearance of Continents Evidence to Support the Plate Tectonic TheoryAppearance of ContinentsThe outline of many present day continents seem to fit together like pieces of a puzzle.
11Landmass Features/Fossil Record Evidence to Support the Plate Tectonic TheoryLandmass Features/Fossil RecordFossil evidence supports the notion that the continents were once connected.Many rock assemblages are identical in formation and age on different continents.
12Each color represents rocks of similar age. Evidence to Support the Plate Tectonic TheoryAge and Heat Index of Ocean RockIn 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.The red colored rock represents the youngest rock (closest to the source of divergence). The blue colored rock represents the oldest rock.
13Magnetic Polarity Evidence to Support the Plate Tectonic Theory 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.