Plate Tectonics
A Brief Overview
The Earth’s Plates
http://www.nature.nps.gov/geology/usgsnps/pltec/pltec2.html
Layers of the Earth
• Chemical
• Physical
http://www.burkemuseum.org/static/geo_history_wa/The%20Restless%20Earth%20v.2.0.htm
Layers of the Earth and Food
• Lithosphere
– Chocolate: when it’s cold, it’s hard and breaks, but
as it warms up it can bend and eventually melt
• Asthenosphere
– Honey: it’s thick and sticky, but it flows
• Mantle
– Crumbled cookies: it’s solid but can move and
convect
• Outer core
– Milk: liquid
• Inner core
– Peach pit: solid
Plate Boundaries
Stern, R. J., Subduction zones, Rev. Geophys., 40(4), 1012, doi:10.1029/2001RG000108, 2002
Margins: Divergent
• Mid-Ocean Ridges
– Mid Atlantic Ridge
http://www.phschool.com/atschool/phsciexp/internet_acti
vity/cfd-1014_midocean.html
• Continental Rifts
– East African Rift Valley
http://www.talktalk.co.uk/reference/encyclopaedia/hutchi
nson/m0006339.html
Margins: Convergent
• Ocean-ocean subduction
– Island arc: Marianas
http://www.see.leeds.ac.uk/structure/dynamicearth/subduction/cordillera_islandarc.htm
Margins: Convergent
• Ocean-continent subduction
– Volcanic arc and mountains: Andes
http://www.see.leeds.ac.uk/structure/dynamicearth/subduction/cordillera_islandarc.htm
Margins: Convergent
• Continent-continent collision
– Large mountain range: Himalayas and Alps
http://www.unil.ch/igp/page23575_en.html
Margins: Transform
• Marine
– Transform faults:
• Mid Atlantic Ridge
• Terrestrial
– Strike-slip faults:
• San Andreas Fault
http://geomaps.wr.usgs.gov/archive/socal/geology/inland_empire/socal_faults.html
Evidence for Plate Tectonics
• Fit of the continents
• Sea floor ages and magnetic anomalies –
evidence of ocean spreading
• Paleontology – similar species on now widely
separated continents
• Seismicity and volcanism concentrated at
plate boundaries – evidence of oceanic
subduction
• Hot spot tracks – record movement of plates
over “fixed” hot spot
• GPS