Geology 1 MT2 advanced tectonics

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kjel
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84782
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Geology 1 MT2 advanced tectonics
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2011-05-09 15:25:44
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Geology MT2 advanced tectonics
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Geology 1 MT2 advanced tectonics
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  1. structure of oceanic lithosphere
    ophiolite
  2. layers that make up ophiolite:
    • ocean seds
    • pillow basalts [extrusive mafic]
    • sheeted dikes of basalt [extrusive mafic]
    • gabbro [intrusive mafic]
    • ...............................................................crust
    • peridotite [intrusive ultra-mafic]
    • .............................................................mantle
  3. pillow basalt
    • a structure that forms when lava erupts underwater
    • due to rapid cooling because water has high heat capacity
    • any incidence of pillow lavas, on continent or in the ocean, indicates the lava erupted under water
  4. dike
    igneous intrusion that forms when magma intrudes other rocks
  5. sheeted dikes
    • dikes of basaltic magma
    • intrusion continues through the weakest point
    • weakest point will be the seams of dikes or hot regions
  6. magma chamber
    • find xenoliths
    • differentiation occurs
    • leave behind the makings of gabbro
  7. ridge-push
    volcanic eruptions at the mid-ocean ridge are pushing the plates apart
  8. slab-pull
    metamorphism increases the density of subducted rocks which pulls the plate along
  9. plate-sliding
    plates are dragged around on top of moving convection cells in the mantle
  10. black smokers
    • hydrothermal vents found on the seabed cause mineralization
    • responsible for ore-formation
    • pyrite, chalcopyrite, sphalerite, etc.
  11. how continents grow:
    • magmatic addition; the most buoyant, silica-rich crust is formed over subduction zones; both continental and island arcs play a role
    • continental accretion; buoyant portions of crust are attached during plate movements; individual fragments are called accreted terranes
  12. the Wilson cycle
    • describes the plate movements that open and close basins and also describes the effect on continents
    • 1. rifting splits the continent...
    • 2. ...leading to the creation of new oceanic crust
    • 3. passive margin -- oceanic and continental lithosphere are in direct contact with no active tectonic boundary
    • 4. convergence begins; an oceanic plate subducts beneath a continental plate, creating a volcanic chain
    • 5. terrane accretion welds material to the continent
    • 6. orogeny thickens the crust and builds mountains forming a new super continent
    • 7. the continent erodes, thinning the crust. rifting may begin the process again

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