10.02.d
DESCRIPTION
4 th Piece of Evidence: Magnetic Striping of Sea Floor. 10.02.d. Blackboard Exercise: Calculate Sea floor spreading rate…. 5 th Piece of Evidence: Sediment Thickness Pattern. Thickest along passive continental margins. Thinnest near mid-ocean ridges. Thick offshore of large rivers. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/1.jpg)
10.02.d
4th Piece of Evidence:Magnetic Striping of Sea Floor
Blackboard Exercise: Calculate Sea floor spreading rate…
![Page 2: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/2.jpg)
Thinnest near mid-ocean ridges
Thickest along passive continental margins
Thick offshore of large rivers
5th Piece of Evidence:Sediment Thickness Pattern
![Page 3: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/3.jpg)
Age increases systematically out from ridge
Mid-ocean ridges less deep because young
Deepest seafloor is oldest
Age patterns truncated at trenches
Depth (dark is deep)
Age (orange is young)
Correlation of sea floor depth and age
![Page 4: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/4.jpg)
6th Piece of Evidence:Sea floor heat flow pattern
![Page 5: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/5.jpg)
Earth’s Plates / Plate Tectonic Theory
![Page 6: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/6.jpg)
Current Plate Tectonic Theory
"Chocolate covered cherry" analogy
Rigid outer shell
Solid core
Moveable liquid between the two
Earth's Structure
• 6371 km mean diameter
• Internal structure characteristics
Composition and density
Behavior (solid:liquid; weak:strong)
Unifying concept of geology
Evolution to biology
Relativity to physics
![Page 7: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/7.jpg)
Current Plate Tectonic Theory
Tectonics (Greek tecton = builder)
Movement of Lithospheric Plates • Large scale geologic processes
(landforms, ocean basins, and mountains)
• Driven by forces deep within the Earth
Lithosphere: 12 major plates (boiled egg-shell mode)
• Plate tectonics: processes related to creation, movement, and destruction of plates
• Plates may include both continents and parts of ocean basins or ocean basins alone; may large (Pacific Plate) or small (Juan de Fuca Plate)
![Page 8: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/8.jpg)
How do we know Internal Structure?
Primarily based on seismology (earthquakes and seismic waves)– Primary waves (compressional)
propagate the fastest (6.5 km/sec in the crust) and pass through liquids and solids.
– Secondary (shear) waves propagate through solid materials, but not through liquid; about 4 km/sec in crust
– Focus--the site where energy is first released
– Focus depth--distance below the surface
Link to seismic waves animation:http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization
![Page 9: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/9.jpg)
Internal Structure
Inner core (1,300 km dia.)• Mostly iron (90%); Some Ni, S, and O
Outer core (2,000 km dia.)• Liquid similar in composition to inner core • Densities of inner and outer cores about same =10.7 g/cm3
Earth's average density; ~5.5 g/cm3
Mantle (3000 km dia.)• Average density=4.5 g/cm3
• Iron & magnesium silicates• The Mohorovicic discontinuity = Between the crust and lithosphere• Lithosphere – Made up of the rigid mantle and crust – Cool, strong, outermost layer of Earth; averages about 100 km thick– Thin at mid-oceanic ridges; 120 km under oceans– 40-400 km thick under continents• Asthenosphere– Hot, slowly flowing layer of relatively weak rock– Low seismic velocity zone
![Page 10: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/10.jpg)
• Crust– Top of the lithosphere– Less dense than mantle
– Oceanic crust » 6-7 km thick
» More dense than continental crust
» Less than 200,000 My years old
– Continental crust » May be billions of years old
» Different geologic histories
» Average thickness about 35 km (70 km max.)
Internal Structure Continued
![Page 11: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/11.jpg)
Processes Driving Plate Motion
– Convection cells to cycle materials on long residence times (500 my)
– Powered by heat from outer core andradioactivity.
![Page 12: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/12.jpg)
Internal Structure
– Epicenter-- surface projection from center through the focus
– Seismic waves can be reflected and refracted (Snell's law: n1sin1 =n2sin2)
– P-waves show low velocity zone at core-mantle boundary; some reflected or refracted
– S-waves dissipated at the core-mantle boundary suggesting a liquid outer core
![Page 13: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/13.jpg)
Plate Boundaries
Divergent (spreading centers)– Mid-Oceanic ridges– Iceland– African Rift Valley
Convergent (subduction)– Ocean-ocean (Japan and other Pacific
trenches)– Ocean-continent (Andes Mts. in Latin America)– Continent-continent (Himalayan Mts. between
India– and China)
Transform (San Andreas fault)
Triple junctions (Mendocino triple junction, Red Sea, and others)
Show animation (Atwater) of plate boundary movement/migration
![Page 14: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/14.jpg)
Plate Boundaries
![Page 15: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/15.jpg)
R. E. Wallace (228), U.S. Geological Survey
Plate Boundaries in the field
![Page 16: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/16.jpg)
W. W. Norton
Application of Plate Tectonics – Hawaiian Island Chain and Plate Motion History
![Page 17: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/17.jpg)
W. W. Norton
Application of Plate Tectonics – Hawaiian Island Chain and Plate Motion History
![Page 18: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/18.jpg)
W. W. Norton
Origin of Hawaiian Island Chain – Hotspot/Mantle Plume
![Page 19: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/19.jpg)
Plate Tectonics and Environmental Geology
Effects• Distribution of mineral
resources• Earthquakes and
volcanoes• Ocean currents and
global climate
![Page 20: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/20.jpg)
Rock Cycle
![Page 21: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/21.jpg)
Rock Cycle
![Page 22: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/22.jpg)
Hydrologic Cycle
![Page 23: 10.02.d](https://reader035.vdocuments.us/reader035/viewer/2022070413/56814d69550346895dbab487/html5/thumbnails/23.jpg)
Biogeochemical Cycle