Intro to Plate Tectonics

Intro to Plate Tectonics

1. Main compositional zones of the Earth

   • 1. Densie iron rich core, 2. less dense magnesium-silicate rich mantle, 3. thin, light crust composed of mainly silicate

2. Lithosphere and Athenosphere

   • Lithosphere incorporates the crust and parts of upper mante
     • Lithosphere plates - edges of plates are sites of intense geologic activity. Varies from 100-200 km thick.
       • Include both continental and oceanic crust and brittle parts of the upper mantle.
   • Athenosphere- least rigid portion of the mantle. soft, easily flexible

3. Continental drift

   • Continents have moved around. Alfred Wenger - theory of a large landmass called Pangea
     • Pange broke into 2 supercontinents called Gondwana and Laurussia. Seperatedby Tethys ocean.
       • Evidence- fold belts, age of provinces, igneous provinces, stratiographic sections.

4. Seafloor speading

   • echo sounding data from military used to highlight 40,000 km long global mid-ocean ridge system. median valley along the lenght
     • Ocean crust is created at spreading centers by magma that rises from deeper levels.

5. Boundaries

   • Convergent- where oceanic crust collides with continental crust = sinks back into mantle. = SUBDUCTION or two continental crusts collide - mountains
   • Transform- crust neither created or destroyed. earthquakes and volcanic activity occur. e.e San Andreas. WILSON CYCLE
   • Divergent - spreading centre

6. Crusts

   • Oceanic - mafic rocks, young on geological timescale. 6-11 km thick, avg density - 2900/3000 kg/m3
   • Continental - felsic rock, much older than oceanic crust. 30-40 km thick, avg density 2700/2800 kg/m3