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Types of Plate Boundaries (finish Chapter 4)
•Hot Spots – more evidence for plate tectonics•Divergent, Convergent and Transform plate boundaries - some examples•California’s complicated tectonic setting – how
it defines our local geography
Ocean island and seamount chainsMost earthquakes and volcanic eruptions occur near plate boundaries – but not all. The Hawaiian Islands are large volcanoes that have formed in the middle of the Pacific Plate. Does this fit into plate tectonic theory?
http://pubs.usgs.gov/gip/dynamic/hotspots.html#anchor19620979
Hot Spots – places where there has been continuous volcanism for a long period of time – sites of ‘leaks’ or
‘mantle plumes’ They provide measurements of absolute rates of plate motion
Subduction zone(crust destroyed)Plates converge (compress)
Midocean ridge (crust created)Plates diverge (move apart)
younger
older
Hot spot
http://volcano.und.edu/vwdocs/vwlessons/hot_spot_pics/ages_of_islands.gif
The hypothesis that islands increase in age with distance from the current hot spot mantle plume is correct
Types of Plate Margins
Figure 4.17, Skinner et al., 1999
•Divergent – new crust is generated where plates pull apart
•Convergent – crust is consumed in the mantle as one plate dives under another
•Transform – plates slide horizontally past one another – crust is neither created nor consumed
Mid-ocean ridges- divergent margins where new ocean crust
is made as plates pull apart
Gakkel Ridge Flyby
Juan de Fuca Ridge
Figure 4.18, Skinner et al., 1999
Mid ocean Ridges
Formation of new crust at MOR
http://oceanexplorer.noaa.gov/explorations/02fire/background/plumes/media/fig2.html
“pillow” lava
Mid ocean ridges are also divergent margins
http://www.geophysics.rice.edu/plateboundary/age.72.gif
Slow spreading rateFast spreading rate
Figure 4.18Skinner et al., 1999
Formation of Divergent Margins
Examples of divergent margins – land being split apart
Gulf of California
Iceland
East African Rift
Convergent Margins:
Collision Zones
Figure 4.24, Skinner et al., 1999
Figure 4.20, Skinner et al., 1999
Convergent MarginsFeatures of Subduction Zones
Convergent Margin examples
http://www.geophysics.rice.edu/plateboundary/aleut1.pdf
Convergent Plate Boundary – Aleutian Arc
http://www.moorlandschool.co.uk/earth/tectonic.htm
200 million years ago to Present
http://www.ucmp.berkeley.edu/geology/tectonics.html
http://www.soc.soton.ac.uk/soc_home2.php?pagetype=news3&idx=212
Tectonic setting for Sumatra/Andaman Earthquakes
Subduction zone
Figure 4.25, Skinner et al., 1999
Transform Margins:The San Andreas Fault
http://www.geophysics.rice.edu/plateboundary/cal1.pdf
California’s complex Tectonic Setting
http://geography.sierra.cc.ca.us/booth/California/1_lithosphere/plates_west_coast.jpg
Volcanoes line up inland of subduction zone
Juan de Fuca plate being subducted under North American plate
Spreading center – splitting Baja California from Mexico and causing Basin and Range crust expansion
California’s big cities are actually on the Pacific plate and moving northwest with it – plate boundary is the San Andreas Fault (a transform fault)
http://www2.nature.nps.gov/geology/usgsnps/province/INDEXbasinRangeSUBS.gif
http://www.gly.uga.edu/railsback/1121NAWestBasin&Range.jpeg
http://geography.sierra.cc.ca.us/booth/California/1_lithosphere/TransRanges_Big.gif