Themes of the Day:

• Hot Spots
• Subduction Zones & Continental Collisions
• Mountain Belts
• Earthquakes, Faults, and Plate Boundaries Summary

Hot Spots

• Localized upwelling of the Mantle (similar to divergent plate boundaries) - may or may not be located at a plate boundary
• Plate moves over hotspot like cloth through a sewing machine (hotspot = needle, plate = cloth)
• Hotspot at a plate boundary - e.g., Iceland
• Hotspot in the interior of a plate - e.g., Hawaii, Tahiti, (Yellowstone), etc.

Convergent Plate Boundaries: Subduction Zones & Continental Collisions

• Oceanic lithosphere recycled back into the mantle
• When oceanic and oceanic crust collide it is often the older, colder plate that subducts - e.g., Marianas Trench, Izu-Bonin Volcanic Arc, Western Aleutian Islands
• When continental and oceanic crust collide oceanic crust always subducts beneath continental crust - e.g., West Coast of South America, Pacific NW, Alaska Peninsula
• Subduction Zone features:
  • Deep-sea Trenches
  • Earthquakes - Wadati-Benioff Zone
  • Accretionary Wedge
  • Volcanic Arc
  • Forearc/Backarc Basins
• When continental and continental crust collide neither subducts - suture formed - e.g., India-Asia Collision, Himalayan-Alpine mountain chain

Mountain Belts

• Types of Mountain Belts
  • at Divergent Plate Boundaries - Block Faulting, Volcanism - e.g., Mid-Atlantic Ridge, Basin & Range Province (western North America)
  • at Transform Plate Boundaries - from shearing - e.g., Coastal Ranges, Transverse Ranges (California), Anatolian Alps (Turkey)
  • at Subduction Zones - volcanic, compressional - e.g., Andes Mts. (South America), Cascades (Pacific Northwest), Japan
  • at Continental Collisions - Strongly Compressional, fold and thrust belts - Alps (Europe), Himalayas (S. Asia), Appalachians-Caledonides
  • in Plate Interiors - Various - Hawaiian-Emperor Seamount Chain (volcanic hot spot), Rocky Mountain Front Ranges (compressional block faulting)
  • Examples from the Western USA
• Accretionary Processes - oceanic plateaus/island arcs - Cordilleran Accreted Terranes
• Isostacy - long-lived mountains
• Google Earth Mountain Belts Tour

Earthquakes, Faults, and Plate Boundaries Summary

• Continental Margins - boundaries between continental and oceanic crust
  • Active - Plate boundary located at Continental Margin - usually a subduction zone - e.g., West Coast of South America
  • Passive - NO Plate boundary located at Continental Margin - sedimentary wedge overlying rifted continental crust-oceanic crust transition - e.g., East Coast of South America
• Divergent Plate Boundaries
  • Plates move apart - thinning of the crust, creation of new oceanic crust
  • Mid-Ocean Ridges; axial graben; normal faulting; tensional stresses; basaltic volcanism
  • Examples: East African Rift Zone, Mid-Atlantic Ridge
• Convergent Plate Boundaries
  • Plates collide - thickening of the crust, recycling of oceanic crust into the mantle; growth of continental crust
  • Thrust faulting; compressional stresses; andesitic volcanism and granitic plutonism
  • Examples: Western Aleutian Islands (Ocean-Ocean); Western Coast of South America (Ocean-Continent); Indian-Asian Himalayas/Tibet (Continent-Continent)
• Transform Plate Boundaries
  • Plates slip past each other - no net gain or loss of crust
  • Transform or Strike-slip faulting; shearing stresses
  • Examples: Mid-Ocean Ridge offsets; San Andreas Fault

This concludes the material for Exam #2.