1Plate TectonicsChapter 2Interactions at plate boundaries depend on the direction of relative plate motion and the type of crust.Which kind of plate boundary is associated with Earthquake activity?A. Divergent BoundaryB. Convergent BoundaryC. Transform-fault BoundaryD. All of the aboveInteractions at plate boundaries depend on the direction of relative plate motion and the type of crust.Which kind of plate boundary is associated with Earthquake activity?A. Divergent BoundaryB. Convergent BoundaryC. Transform-fault BoundaryD. All of the aboveAt which kind of plate boundary is new oceanic lithosphere formed?A. Oceanic transform boundaryB. Oceanic divergent boundaryC. Ocean-ocean convergent boundaryD. Ocean-continent convergent boundaryInteractions at plate boundaries depend on the direction of relative plate motion and the type of crust.At which kind of plate boundary is new oceanic lithosphere formed?A. Oceanic transform boundaryB. Oceanic divergent boundaryC. Ocean-ocean convergent boundaryD. Ocean-continent convergent boundaryInteractions at plate boundaries depend on the direction of relative plate motion and the type of crust.Plate Tectonics:Learning Goals•Scientific Method–Development of Plate Tectonics Theory•Lithosphere vs Asthenosphere•Crust vs Mantle•Plates contain continent and ocean•Plate boundaries (where the action is)–Convergent Boundaries–Divergent Boundaries–Transform Boundaries2Divergent, Convergent and Transformplate boundariesCrust and Mantle vsLithosphere and AsthenospherePlates are lithosphere:Both continent and ocean crustScientific Method•1. Observation (fact)– This is a repeatable measurement or experiment•2. Hypothesis– One or more possible explanations to link observations •3. Testing– Further experiment or observation to test hypothesis– Non-testable hypotheses also rejected•4. Theory– A grand or unifying hypothesis that has survived tests– Relativity, Evolution, Plate tectonics1. Observation:Early Evidence (Wegener)•The geometric fit of the continents. •The similarity in rock age groups between adjoining regions. •The similarity in Paleozoic fossils between adjoining areas. •The distribution of Paleozoic glaciation in S.America, S.Africa, Australia, and India. The geometric fit of the continents.3Similarity of Paleozoic Fossils in adjoining regions. Early Objections•Mantle is solid –(Transmits Shear waves).•How can continents move and remain intact?•What is the driving force?1960s: Compelling New Evidence: Magnetic Anomalies•Magnetic minerals such as magnetite (Fe3O4) record Earth’s magnetic field.•They also perturb the field by a small amount.•Perturbations are called magnetic anomalies.•Anomalies can be mapped using magnetometers dragged behind aircraft or ships.Magnetic Anomalies•Anomalies were first solid evidence of sea-floor spreading.•Here was a credible hypothesis that demanded testing.2. The Hypothesis:•The continents have moved (drifted) over geologic time so that North and South America have separated from Europe and Africa.43. Test the Hypothesis•The hypothesis makes several predictions that allow it to be tested by further observation.–Rocks in adjoining parts of Africa and South America should be similar in age and type.–Rocks on Atlantic floor should get younger toward the mid-ocean ridge.–New bathymetric measurements define the continental crust boundary. Do South America and Africa still fit together? –If crust is being created at mid-ocean ridges, it should also be consumed. Where is the crust consumed?–There needs to be a driving force.3. Test the Hypothesis•Rocks in adjoining parts of Africa and South America were age-dated using new radio-isotopic methods: they matched perfectly. •Rocks were dredged from the sea floor: they showed ages symmetrically increasing away from the ridge. There were no old rocks (>250MY) . •The fit of continents was revised using the edge of the continental slope rather than the coastline: the match was nearly perfect.Rocks were dredged from the sea floor:They showed ages symmetrically increasing away from the ridge.There were no old rocks (>250MY).3. Test the Hypothesis4. Theory of Plate Tectonics•There appear to be 13 major plates that cover the globe. •The plates can contain oceanic, or continental crust or both. •New oceanic crust is created at the mid-ocean ridge (divergent boundary). •Old oceanic crust is consumed (subducted) at convergent plate boundaries.Continental Margins: Passive and Active5Divergent, Convergent and Transformplate boundariesTransform, Divergent, and Convergent plate boundariesCrust and Mantle vsLithosphere and AsthenosphereCrust and Mantle vsLithosphere and AsthenosphereInteractions at plate boundaries depend on the direction of relative plate motion and the type of crust.Key Figure 2.6 (pages 26-27)Go to next slide to beginDivergent BoundariesOceanic Plate SeparationMid-AtlanticRidge6Divergent BoundariesOceanic Plate SeparationMid-AtlanticRidgeVolcanoes and earthquakes concentrate.Divergent BoundariesContinental Plate SeparationEast AfricanRift ValleyDivergent BoundariesContinental Plate SeparationEast AfricanRift ValleyParallel valleys; volcanoes and earthquakes.Divergent Boundaries•Mid-Atlantic Ridge•East Pacific Rise•Red Sea-East Africa rift7Divergent, Convergent and Transformplate boundariesConvergent BoundariesOcean-Ocean ConvergenceMariana IslandsMarianas TrenchConvergent BoundariesOcean-Ocean ConvergenceMariana IslandsMarianas TrenchDeep-sea trench; volcanic island arc.Convergent BoundariesOcean-Continent ConvergenceAndesMountainsSouthAmericanPlateSouthAmericanPlatePeru-Chile TrenchConvergent BoundariesOcean-Continent ConvergenceAndesMountainsSouthAmericanPlateSouthAmericanPlatePeru-Chile TrenchA volcanic belt ofmountains forms.8Convergent BoundariesContinent-Continent Convergence(No Volcanoes)MainthrustfaultTibetanPlateauEurasianPlateEurasianPlateHimalayaConvergent BoundariesContinent-Continent ConvergenceHimalayaMainthrustfaultTibetanPlateauEurasianPlateEurasianPlateCrust crumbles, creating highmountains and a wide plateau.Convergent Boundaries•Ocean – Ocean –Tonga trench–Marianas Trench•Ocean - Continent–West coast South America–Japan Trench–Aleutians•Continent – Continent–Himalayas–AlpsDivergent, Convergent and Transformplate boundariesTransform-Fault BoundariesMid-Ocean Ridge Transform FaultTransform-Fault BoundariesMid-Ocean Ridge
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