Ask GeoMan...
What are the characteristics of plate boundaries?
Following is a brief summary (in outline form)
Divergent Plate Boundaries
Igneous environment:
Extrusive: Mafic volcanics - very hot and fluid
Basalt flows, pillows, and breccias
Low in gas and water - relatively quiet and non-explosive
Intrusive: Mafic plutons and sheeted dike complexes
Tectonics: Extensional environment
Very thin crust with a high heat flow
Normal faults
Generally shallow focus earthquakes
Relatively low Richter magnitudes
Convergent Plate Boundaries
Igneous environment:
Extrusive: Intermediate volcanics
Andesite breccias, pyroclastics, and flows
High in gas and water - very explosive volcanoes
Intrusive: Felsic to intermediate plutons
Commonly the location of large granitic plutons
Tectonics: Compressional environment
Transitional crust relative to thickness
Reverse faults
Shallow to deep focus earthquakes
Low to very high Richter magnitudes (hang on tight)