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Terri Mathews




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Minerals

 

Plate Boundaries

Heat from the Earth's core rises up through the mantle heating the Asthenosphere. The semi-plastic material in the asthenosphere rises as it warms, eventually cools and subsequently sinks setting up Convection Cells in the Asthenosphere.  The heat from the Earth's core continually heats the Asthenosphere, driving the convection cells which are constantly in motion. 

 

 

The lithospheric plates "float" on the asthenosphere and move with the convection cells. Plate tectonic movement results from the rise and fall of convection cell material in the asthenosphere.

The convection cells in the Asthenosphere move upward and reach the bottom of the lithosphere where they move laterally.  This lateral motion forces the lithosphere to split and move away from each other. 

 

The Asthenosphere material cools as it moves laterally and eventually sinks back towards the core.  When it sinks it pulls the lithospheric plate with it. 

 

The movement of the lithospheric plates is caused by the constant movement of the convection cells in the Asthenosphere. 

Three motions characterize interactions at the plate boundaries: separation, collision, or lateral movement. Those motions directly correlate with the categorizations of plate boundaries:

Divergent: lithospheric plates move away from one another

Convergent: lithospheric plates move towards one another

Transform Boundaries: two lithospheric plates move laterally to (slide past) one another  

Each of these plate boundaries is characterized by distinct geographic features and specific geology that vary based on the type of crust involved.

  • Oceanic crust is dense and relatively thin.
  • Continental crust is thick, but much less dense than oceanic crust.

 

 

Aseismic ridge (hot spots) form from volcanic activity in the middle of a tectonic plate. Geologists attribute the activity to a stationary mantle plume. As a tectonic plate moves over top of the mantle plume, a volcano is formed. As the plate continues to move and the plume remains stationary, a chain of volcanoes form.