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Global pattern of plates and plate boundaries - Coggle Diagram
Global pattern of plates and plate boundaries
Global patterns of plates and plate boundaries
How plate boundareis were discovered
Testing revealed in the mid 1960s that earthquakes, in particular the high magnitude ones, were spatially concentrated in narrow bands.
In between were large areas that generated little earthquakes.
This suggested the lithosphere and crust were broken up into tectonic plates.
This also showed how in some places plates were moving apart and in others they were converging.
Seven major plates and several minor ones.
Divergent (constructive) plate boundaries
Features
Mid ocean ridges, which are very long chains of mountains.
Pillow lavas
Under water rift valleys
Black smokers
Grabens on continental faults
Processes
Plates are moving apart, due to lava rising through the asthenosphere and forcing its way to the surface.
Convergent (destructive) boundary
Oceanic and continental plates converge in one of three combinations
Oceanic - continental
Oceanic - oceanic
Continental - continental
Oceanic - continental margins
When oceanic and continental plates converge, the denser oceanic plate is forced under the continental plate. This is subduction.
This causes a deepening of the ocean at the plate boundary causing an ocean trench. These are long, narrow depressions with depths of 6000,11,0000m.
This marks the zone of subduction where the oceanic crust descends towards the asthenosphere, pulling the rest of the ocean with it (slab pull)
Subduction creates mountain ranges such as the Andes on the pacific coast of South America
In the benioff zone, where the plate subducts past 45 degrees, there is a build up of pressure and friction. Faulting and fracturing occur in this zone which causes earthquakes.
Also forms volcanoes