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
10.02.d
4th Piece of Evidence:Magnetic Striping of Sea Floor
Blackboard Exercise: Calculate Sea floor spreading rate…
Thinnest near mid-ocean ridges
Thickest along passive continental margins
Thick offshore of large rivers
5th Piece of Evidence:Sediment Thickness Pattern
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
6th Piece of Evidence:Sea floor heat flow pattern
Earth’s Plates / Plate Tectonic Theory
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
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)
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
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
• 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
Processes Driving Plate Motion
– Convection cells to cycle materials on long residence times (500 my)
– Powered by heat from outer core andradioactivity.
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
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
Plate Boundaries
R. E. Wallace (228), U.S. Geological Survey
Plate Boundaries in the field
W. W. Norton
Application of Plate Tectonics – Hawaiian Island Chain and Plate Motion History
W. W. Norton
Application of Plate Tectonics – Hawaiian Island Chain and Plate Motion History
W. W. Norton
Origin of Hawaiian Island Chain – Hotspot/Mantle Plume
Plate Tectonics and Environmental Geology
Effects• Distribution of mineral
resources• Earthquakes and
volcanoes• Ocean currents and
global climate
Rock Cycle
Rock Cycle
Hydrologic Cycle
Biogeochemical Cycle