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Physical Geography Lecture 12 - Plate Tectonics 111616
The document discusses plate tectonics and the evolution of Earth's crust, emphasizing its ability to bend and maintain equilibrium through processes such as isostasy. It outlines Alfred Wegener's continental drift theory and subsequent evidence supporting the theory, including geological similarities, glacial features, and fossil distributions, leading to a paradigm shift in understanding crustal movement. The theory of plate tectonics is further explained through various plate boundary interactions, including divergent, convergent, and transform boundaries, as well as the concepts of subduction zones and hot spots.
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Physical Geography Lecture 12 - Plate Tectonics 111616
- 1. Plate TectonicsPlate Tectonics Chapter9Chapter 9
- 2. Rigid Earth TheoryRigidEarth Theory It was once believed that Earth’s crust was hard and brittle and could not bend Plasticity We now know that Earth’s crust can bend (like a tough plastic) before breaking
- 3. 33 IsostacyIsostacy • Maintaining equilibriumin the crust • Addition or removal of crustal material causes a sinking or rebounding of crust –A glacier growing or remelting, crust eroding off the surface, sediment deposits, water bodies on land, esp. those created by dams, etc.
- 5. Alfred Wegener andAlfredWegener and His Continental Drift TheoryHis Continental Drift Theory German meteorologist, 1920s--Pangaea (Gk. “whole land”) “The present continents were originally connected as one enormous landmass that has broken up and drifted apart over the last few 100 million years. The drifting continues….” What evidence led him to this theory?
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- 10. 1010 Wegener’s Lines ofEvidenceWegener’s Lines of Evidence Similar geology (rocks and rock structures)… …petrology (rock chemistry), …matching glacial features (U-shaped valleys, glacial deposits, etc.) on continents separated by oceans, …continent shapes that seem to fit together, …patterns in the locations of volcanoes, …paleontology (fossilized plants and animals)... Ex.: S. America/Africa, Madagascar/India, Australia/Antarctica
- 11. 1111 ……but no onebought it.but no one bought it. What do you mean, “The continents are floating???” So why don’t we see the crust ripping apart right now? And hey, what’s the power source driving these movements of all the land masses, anyway??? The crust is too rigid! What a knucklehead.
- 12. Then along cameOceanographerThen along came Oceanographer Harry Hess in the 1960s…Harry Hess in the 1960s…
- 15. The evidence continuedto mount…The evidence continued to mount… • Military seafloor mapping: Seafloor geology—structure,Military seafloor mapping: Seafloor geology—structure, chemistry, and agechemistry, and age – Oceanic crust: only 100 m.y.oOceanic crust: only 100 m.y.o – Continental crust: 4.1 b.y.o.Continental crust: 4.1 b.y.o. • Core samplingCore sampling • Seafloor sedimentSeafloor sediment • Rigid Earth folks retired—paradigm shift to plasticityRigid Earth folks retired—paradigm shift to plasticity • Geologists, geophysicists, seismologists,Geologists, geophysicists, seismologists, oceanographers, physicists, and paleontologists alloceanographers, physicists, and paleontologists all agree the theory fits the evidence gathered within theiragree the theory fits the evidence gathered within their respective fieldsrespective fields • Convection currents as mechanism/power sourceConvection currents as mechanism/power source
- 16. 1616 Convection CurrentsConvection Currents Slow-moving convectioncurrents within the mantle transfer heat from the outer core to the upper mantle Finally, there was a mechanism and a process for moving all those pieces of crust!
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- 18. The Theory ofPlate TectonicsThe Theory of Plate Tectonics Tectonic (crustal) plates Pulling apart (diverging) = Spreading centers Slamming together, sinking (converging) = Subduction zones Sliding laterally (sideways) = Transform fault boundaries
- 19. 1919 African Rift ValleyAfricanRift Valley 1919
- 21. Divergent Plate BoundariesDivergentPlate Boundaries Spreading centers –Crust pulling apart, magma rising to the surface
- 22. Convergent Plate BoundariesConvergentPlate Boundaries Subduction zones –Crust being forced together –Lightest material rises (mountain-building) while the heaviest stuff sinks (pushed back into the mantle) –Remelting (mostly from friction) creates volcanoes –Intense, deep-focus earthquakes
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- 24. 2424 Three Types ofSubduction ZonesThree Types of Subduction Zones 1. Continental crust meets oceanic crust Oceanic crust sinks Big trench offshore Volcanoes on the continental margin Big earthquakes (potential for tsunamis)
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- 26. 2626 Three Types ofSubduction ZonesThree Types of Subduction Zones 2. Oceanic crust meets oceanic crust The older and colder crust will probably sink Big earthquakes and volcanic islands (“island arcs”) Deep ocean trench Potential for tsunamis
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- 28. 2828 Three Types ofSubduction ZonesThree Types of Subduction Zones 3. Continental crust meets continental crust Too light to subduct Mountain-building Big earthquakes Little if any volcanism (mostly intrusive)
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- 30. Transform Fault BoundariesTransformFault Boundaries Tectonic plates slide past one another Earthquakes are less intense than subduction No volcanoes Little or no mountain-building
- 34. 3434 ““Hot spots”Hot spots” •Also called magma plumes • Generally occur some distance from any other type of plate boundary • Unrelated to convergent, divergent, or transform boundaries • Anomalous (odd) “balloons” of rising magma Hot spot stays in one position as the moving, island- covered crustal plate rides away from it
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- 37. 3737 Accreted TerranesAccreted Terranes Amoving continent may pick up new land material as lighter (felsic) material scrapes off of a subducting plate
- 40. 4040 CratonCraton • These terraneswere added to the original material first formed from magma that rose out of Earth’s earliest crust –Craton--the name given to these ancient proto- continents 4040 cratons
- 41. 4141 Continental ShieldsContinental Shields Moremagma material was added to the cratons, forming continents. Continental shields: Where the earliest continental material still exists intact and is exposed at the surface. 4141
- 42. 4242 TopographyTopography • Right fromthe very beginning, the crust was affected by stresses and strains that caused crustal deformations • Over time, the crust has continued to be folded, faulted, broken, eroded and further built upon, creating the topography, the ups and downs of land relief, that we see today