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