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Andrija Mohorovicic´

The first velocity discontinuity discovered was named for its discoverer. Most people now use a shortened form of the name and call this boundary the Moho. Andrija Mohorovicic´. discontinuities. Each discontinuity marks the boundary between two layers with different physiochemical conditions.

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Andrija Mohorovicic´

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  1. The first velocity discontinuity discovered was named for its discoverer. Most people now use a shortened form of the name and call this boundary the Moho. Andrija Mohorovicic´

  2. discontinuities Each discontinuity marks the boundary between two layers with different physiochemical conditions.

  3. Moho Discontinuity Thickness (km) Density (g/cm3) Typical Rocks Crust 30 2.2 2.9 silica rocks andesite, basalt at base Upper Mantle 720 3.4 Lower Mantle 2,171 4.4 peridodite, eclogite, olivine, spinel, garnet, pryoxene http://www.glossary.oilfield.slb.com magnesium and silicon oxides Outer Core 2,259 9.9 Inner Core 1,221 12.8 Center 13.1 iron+oxygen, sulfur, nickel alloy (liquid) zone including uppermost mantle and lowermost crust is called the aesthenosphere iron+oxygen, sulfur, nickel alloy (solid) http://pubs.usgs.gov/gip/interior/

  4. Major Tectonic Plates There are several large tectonic plates and a number of much smaller plates. The Earth’s continents sit on plates composed of both oceanic and continental crust. The huge Pacific plate is composed almost entirely of oceanic crust, and is being subducted around almost its entire western boundary. Eurasian North American Phillipine Caribbean Pacific Pacific African South American Nazca Australian-Indian Antarctic

  5. The plates “float” on the astenosphere, which is a thin boundary zone where the mantle and crust meet. The asthenosphere is “mooshy” (can be sheared relatively easily) allowing the plates above the slide along.

  6. Oceanic Crust Continental Crust felsic and low density “light and fluffy” mafic and high density “dark and dense” thick and buoyant does not subduct thin and sinks does subduct Mid-Ocean Ridge Aesthenosphere Subducting Slab old crust destroyed Upwelling Magma new crust added Mantle Tectonic plates “float” on the higher density mantle.

  7. Fig. 19.12 The driving mechanism of plate tectonics is mantle convection. Hot mantle material rises at ridges and cooler mantle material sinks at subduction zones.

  8. The contacts along which plates meet are called boundaries. Individual plates move relative to each other in one of three ways: Convergent - moving toward each other. Divergent - moving away from each other Transform - moving past each other Plate Boundaries convergent divergent transform

  9. The different kinds of boundaries have different properties: Convergent – old oceanic crust destroyed through subduction Divergent – new oceanic crust created at mid-ocean ridges Transform – crust neither created or destroyed convergent divergent transform

  10. Convergent Boundaries It is impossible for plates to move toward each other unless crust is “moved out of the way” - usually by subduction and destruction of oceanic crust at trenches.

  11. Convergent Boundaries Oceanic-Continental http://geo.lsa.umich.edu/~crlb/COURSES/270/ Subduction leads to orogeny A sinking slab of oceanic crust will partially melt as it heats up, creating pockets of magma that rise through the crust, forming volcanoes.

  12. Convergent Boundaries Oceanic-Oceanic http://geo.lsa.umich.edu/~crlb/COURSES/270/ When oceanic crust converges with oceanic crust, the denser plate (usually the oldest and coldest) generally subducts. An arc of volcanic islands forms from upwelling magma.

  13. Lesser Antilles Convergent Boundaries Island Arcs http://www.geology.pomona.edu/PETRO/IAMAP.GIF http://www.sabapark.com/research_activities/volcano_monitoring/volcanic_info.htm

  14. Convergent Boundaries Continental-Continental http://geo.lsa.umich.edu/~crlb/COURSES/270/ Since continental crust is buoyant, it does not subduct easily. While the edge of a plate can be dragged under by the weight of attached oceanic crust, it does not go far.

  15. Convergent Boundaries The Himalayas The massive compressive stresses caused by the collision causes huge low-angle reverse faults to form, stacking crust on crust. The crust also thickenes through ductile compression. http://pubs.usgs.gov http://www.high-altitude-medicine.com/photos-mountain.html

  16. Divergent Boundaries Mid-Ocean Ridges Mid-ocean ridges are long mountains formed parallel to oceanic rifts. The plates on either side of the ridge grow as new crustal material is added at the spreading center. Rifts are characterized by relatively shallow earthquake foci along the length of the rift. http://wwwneic.cr.usgs.gov/

  17. Transform Boundaries The San Andreas fault system is part of a system of strike-slip faults caused by the relative motion of the North American and Pacific plates. http://pubs.usgs.gov http://wwwneic.cr.usgs.gov/ http://www.ingv.it/~roma/cultura/ingescuola/terremotopagina/SanAndreas.html

  18. Boundary Type Convergent Divergent Transform Volcanoes yes yes no Mountains yes yes no Earthquakes shallow-deep shallow varies

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