Plate Tectonics

Overview: The Lithosphere and the Crust Basic Concepts of Plate Tectonics Plate Movements and Boundaries

Inside the Earth:

The Lithosphere:

The Basic Concepts: - the earth is covered by several large lithospheric plates

These plates move slowly (about a few cm./yr) Due to convection cells in the asthenosphere

Convection movement driven by heat from the core:

Mantle convection produces lateral forces at the boundary between the mantle and the crust

Theory of Plate Tectonics:

Plate Movement and Boundaries Divergent Boundaries oPlates move apart oVolcanic activity oEarthquakes shallow oTwo types of boundaries  Oceanic  Continental

Oceanic divergent boundary Sea-floor spreading of ocean plates Mid-Atlantic Ridge

Page 43, Worrall

Continental Divergent Boundary Continental Rifting, eventually oceanic crust is formed Modern example ; East African Rift

Convergent Boundaries Plates move towards each other Volcanic activity common Deep, medium and shallow earthquakes Three types;  Ocean to ocean  Ocean to continent  Continent to continent

Ocean to Ocean- convergence Subduction - process which one plate slides under the other (subducts) Volcanic arc islands are formed

Ocean to Continent Convergence subductsOcean lithophere subducts under continent

Most tectonic activity occurs at or near these boundaries

Continent to Continent - Convergence Subduction does not occur Mountain building occurs without volcanic activity

Collision of India with Eurasia Height is still increasing

Transform Boundaries Plates slide past each other Little or no volcanic activity Shallow but strong earthquakes Example: San Andreas Fault

West Coast: unstable -subduction zone and transform fault zone

A Divergent B Convergent C Transform plates are moving apart new crust is created Magma is coming to the surface plates are coming together crust is returning to the mantle plates are slipping past each other crust is not created or destroyed

A Divergent B Convergent C Transform Continental crust  rift valley Oceanic crust  mid- ocean ridge 2 continental plates  mountain range Plates move against each other Stress builds up Stress is released  earthquake 2 oceanic plates or oceanic + continental  subduction

The Big Picture