Plate Tectonics
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Transcript of Plate Tectonics
Plate TectonicsPlate Tectonics The theory --the surface of the Earth is The theory --the surface of the Earth is
broken into large plates. The size and broken into large plates. The size and position of these plates change over position of these plates change over time. The edges of these plates, where time. The edges of these plates, where they move against each other, are they move against each other, are sites of intense geologic activity, such sites of intense geologic activity, such as earthquakes, volcanoes, and as earthquakes, volcanoes, and mountain building. mountain building.
Plate tectonics is a combination of two Plate tectonics is a combination of two earlier ideas, continental drift and sea-earlier ideas, continental drift and sea-floor spreading. Continental drift is the floor spreading. Continental drift is the movement of continents over the movement of continents over the Earth's surface and in their change in Earth's surface and in their change in position relative to each other. Sea-position relative to each other. Sea-floor spreading is the creation of new floor spreading is the creation of new oceanic crust at mid-ocean ridges and oceanic crust at mid-ocean ridges and movement of the crust away from the movement of the crust away from the
mid-ocean ridges.mid-ocean ridges. http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/introduction.htmlhttp://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/introduction.html
Earth StructureEarth Structure
Mexico quake-- magnitude at 7.0, and epicenter was in Mexico quake-- magnitude at 7.0, and epicenter was in the western Pacific state of Michoacan. Its depth was about the western Pacific state of Michoacan. Its depth was about 40 miles40 miles
Indonesia-- earthquake off coast of Indonesia Wednesday, Indonesia-- earthquake off coast of Indonesia Wednesday, April 11 with magnitude of 8.6, sparking tsunami warningsApril 11 with magnitude of 8.6, sparking tsunami warnings
LithosphereLithosphere
Consists of continental, Consists of continental, oceanic and upper part of oceanic and upper part of mantlemantle
Continents composed of granite-type rock, quartz and feldspar minerals, density+2.8g/cm3
Oceanic crust formed of basalt; basalt rich in iron/magnesium minerals, density+3.0 g/cm3 Lithosphere is rigid layer of crust and mantle overlying partially-molten asthenosphere
Continental Drift EvidenceContinental Drift Evidence
– Geographic fit of continentsGeographic fit of continents– FossilsFossils– MountainsMountains– GlaciationGlaciation
Evidence supporting the idea that the continents had drifted.
Researchers noted geographic fit of continents– e.g. Africa and S. America– Atlantic formed by separation of Africa from S.
America Seuss, 1885, proposed super continent by studying fossils, rocks, mountains
Wegener and Taylor, early 1900’s, proposed continental drift and Pangaea
Continental Drift Continental Drift Geographic FitGeographic Fit
Continents seem to fit together like pieces of a puzzleContinents seem to fit together like pieces of a puzzle
Continental DriftContinental DriftFossilsFossils
Similar distribution of fossils such as the Similar distribution of fossils such as the MesosaurusMesosaurus
Continental DriftContinental DriftMountainsMountains
Mountain ranges match across oceansMountain ranges match across oceans
Continental DriftContinental DriftGlaciationGlaciation
Glacial ages and climate evidenceGlacial ages and climate evidence
ObjectionsObjectionsto theto the
Continental Drift ModelContinental Drift Model
Wegener did not Wegener did not provide a plausible provide a plausible mechanism to explain mechanism to explain how the continents how the continents could have drifted.could have drifted.
Seafloor SpreadingSeafloor Spreading
Continental drift reexamined in 1960’s with new Continental drift reexamined in 1960’s with new informationinformation
– World seismicity
New theory developed – Seafloor spreading Supporting evidence for seafloor spreading
Theory combining continental drift and seafloor spreading termed “Plate Tectonics”
– Volcanism– Age of seafloor
– Heat flow
– Paleomagnetism
Seafloor SpreadingSeafloor Spreading
New sea floor created at the mid-ocean ridge and New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenchesdestroyed in deep ocean trenches
Evidence for Seafloor SpreadingEvidence for Seafloor SpreadingWorld SeismicityWorld Seismicity
Earthquake distribution matches plate boundariesEarthquake distribution matches plate boundaries
Evidence for Seafloor SpreadingEvidence for Seafloor SpreadingVolcanismVolcanism
Volcanoes match some plate boundaries; some are hot spotsVolcanoes match some plate boundaries; some are hot spots
Evidence for Seafloor SpreadingEvidence for Seafloor SpreadingAge of SeafloorAge of Seafloor
Youngest sea floor is at mid-ocean ridgeYoungest sea floor is at mid-ocean ridge Oldest sea floor away from mid-ocean ridgeOldest sea floor away from mid-ocean ridge
Evidence for Seafloor SpreadingEvidence for Seafloor SpreadingPaleomagnetismPaleomagnetism
When rocks cool at the Earth’s surface, they record Earth’s When rocks cool at the Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity)magnetic field (normal or reverse polarity)
Earth has a magnetic field - Probably caused by rotation of solid inner core in liquid outer core (both mostly Fe)
Evidence for Seafloor SpreadingEvidence for Seafloor SpreadingPaleomagnetismPaleomagnetism
Paleomagnetic studies indicate alternating Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the stripes of normal and reverse polarity at the mid-ocean ridge.mid-ocean ridge.
Seafloor SpreadingSeafloor SpreadingHeat FlowHeat Flow
In 1960, convection currents were proposed as driving In 1960, convection currents were proposed as driving force to move continentsforce to move continents
Theory of Plate TectonicsTheory of Plate Tectonics
John Tuzo Wilson combined ideas of continental drift and John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics”seafloor spreading into “Plate Tectonics”
Principles of Plate TectonicsPrinciples of Plate Tectonics
Earth’s outermost layer composed of thin rigid Earth’s outermost layer composed of thin rigid plates moving horizontallyplates moving horizontally
Plates interact with each other along their edges (plate boundaries)
Plate boundaries have a high degree of tectonic activity– mountain building– earthquakes– volcanoes
Plate BoundariesPlate BoundariesThree typesThree types
Plate BoundariesPlate BoundariesDivergentDivergent
Plates move away from each otherPlates move away from each otherNew crust is being formedNew crust is being formed
Divergent Plate BoundariesDivergent Plate BoundariesExamplesExamples
East African Rift Mid-Atlantic Ocean Ridge
Plate BoundariesPlate BoundariesConvergentConvergent
Plates are moving toward each otherPlates are moving toward each otherCrust is being destroyedCrust is being destroyed
Three Types:Three Types:
Ocean-continentOcean-continent
Ocean-oceanOcean-ocean
Continent-continentContinent-continent
Convergent Plate BoundariesConvergent Plate BoundariesExamplesExamples
Mount Lassen, California
Andes, South America
Mount Fuji, Japan
Plate BoundariesPlate BoundariesTransformTransform
Plates slide past one anotherPlates slide past one another Crust is neither created nor destroyedCrust is neither created nor destroyed
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Transform Plate BoundariesTransform Plate BoundariesExamplesExamples
San Andreas Fault
Calexico, California
Carrizo Plains, Central California
Stop HereStop Here
Origin of the EarthOrigin of the Earth
Meteors and Meteors and Asteroids bombarded Asteroids bombarded the Earththe Earth
Gravitational compressionGravitational compression
Density Stratified planetDensity Stratified planet
Earth’s InteriorEarth’s Interior
Crust Crust Outermost layerOutermost layer ContinentalContinental – granite-type, – granite-type,
density=2.8 g/cm density=2.8 g/cm OceanicOceanic – basalt, density=3.0 g/cm – basalt, density=3.0 g/cm Rigid Rigid
CoreCore– densedense– Nickel and IronNickel and Iron– Inner coreInner core – solid – solid– Outer coreOuter core – liquid – liquid
MantleMantle– Less dense than coreLess dense than core– Iron and Magnesium silicatesIron and Magnesium silicates– Partially moltenPartially molten
Evidence of Internal StructureEvidence of Internal Structure
Granite Density
– calculate density of Earth– Speculate on probable compositions
Basalt
Meteorites– Use composition and age to
determine composition and age of Earth
Seismic waves– Travel times and direction
give indication of internal structure of Earth
Types of Seismic WavesTypes of Seismic Waves
S wavesS waves– Secondary, shaking, side-to-sideSecondary, shaking, side-to-side– Slower (average 4 km/sec)Slower (average 4 km/sec)– Travel through solids onlyTravel through solids only
P waves– Primary, pressure, push and pull– Travel fastest of the seismic waves (average 6 km/sec)– Travels through solids and liquids
Seismic Waves Through EarthSeismic Waves Through Earth