G145

 

Features of Plate Boundaries

 

Divergent boundaries  (Constructive)

            Mostly found in oceanic crust

            Shallow earthquakes

            High heat flow

            No sediments

            Symmetrical rise forming low profile mountain chain

            Medial valley

            Symmetrical distribution of age of rock on each side of the rise

            Symmetrical paleomagnetic reversal patterns on each side of the rise

            Creates new ocean crust in medial valley of basaltic composition (volcanic)

            Associated rocks:  basalt, gabbro, pillow structures are common

 

Subduction Zones (convergent boundary…destructive)

Shallow, intermediate, and deep focus earthquakes associated with descending  

                oceanic plate

            Possibility of a deep trench (ocean to ocean interaction) or accretionary wedge

    (continental to oceanic interaction)

            Volcanoes on overriding plate (volcanic island arcs or continental arcs)

            Volcanic are often intermediate (andesite/diorite) in composition

            Orogenic zone on continental coast when oceanic crust meets continental crust. 

     Mountains intruded by plutonic bodies

 

Transform boundaries (conservative)

            Located in alternating fashion on ridge system

            Strong shallow earthquakes (<70km) responsible for most damage

            Relative rate and direction of movement has been measured along most transform

     Faults

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sept ‘04