Plate Tectonics

Afred Wegener  

  • Matching shapes of continent  

  • Geographic distribution of fossil, rock types, paleoclimate belts, glacial deposits 

  • Proposed idea of “continental drift” in 1915 

  • Generally rejected by geologists in USA/Great Britain 

 

Defined climate belts and set by the global dynamics' axis tilt.  

Seafloor mapping showing global ocean ridge system 

Magnetic reversal in ocean crust  

Generally young seafloor age 

Increasing sediment thickness as crust gets older  

 

Allowed for age- dating oceanic crust  

Youngest crust near ridges  

 

 

Calculation of spreading rates  

Oldest near trenches and edges of continent away from ridges  

 

 

Key evidence for seafloor spreading  

 

 

 

The farther it moves from the rift, the older it is. 

 

Its magnetic field makes it stick up like a compass pin.  

Map on the ocean floor, where it was normal or reversed.  

 

Spreading rates = distance/time  

= 250/25=10ka  

Full spreading rate=½ srx2=20ka  

They found trenches, the deepest part of the ocean 

Subduction Zone  

Seafloor Spreading  

Hess, Matthew and Vine in early 1960’s  

Seafloor spreading is the mechanism for continental drift  

General structure of the Earth  

Compositional structure of the earth  

  • Core 

  • Inner  

  • Outer  

  • Mantle  

  • Crust  

Mechanical structure of the earth 

  • Mesospheric mantle  

  • Asthenosphere(Closes to being melted, softest)  

  • Lithosphere (Fairly cold, and bitter rocks)  

Heat is constantly trying to get out  

Idenfitcation of Plate Boundaries  

Earthquake activity  

Volcano activity  

Mountain building  

Oceanic trenches  

Volcanic island arcs 

Continental volcanic arcs  

Divergent= plates moving away from each other  

Convergent= “towards”  

Transform= plates sliding past each other  

Types of Plate Boundaries  

Divergent Convergent Transform  

Ocean-ocean Ocean continental Continent- Continental