The Boundaries of Plate Tectonics
Divergent
(Spreading boundary)
*two lithosphere plates move apart
from each other, marked by midocean ridges
•Sea-floor spreading process
(gradual widening of an ocean
basin as new oceanic crust forms at
a mid-ocean ridge axis, moving
away from the axis)
•Buoyancy of oceanic lithosphere
•Subduction process (one oceanic
plate bends and sinks down into the
asthenosphere beneath another plate
Convergent
(Consuming boundary)
*two plates move toward each other, one
plate sinks beneath the other, only
oceanic lithosphere subducts
•Wadati-Benioff zone (belt of
earthquakes in a downgoing plate)
•Accretionary prism (wedge-shaped
mass of sediment & rock scraped off
the top of a downgoing plate,
accreted onto overriding plate
•Fracture zones (narrow belts of brokenup crust, irregular sea floor faults
Transform
(Transform fault)
*one lithosphere plate slips
laterally past another
M. Norma Chavez 11/17/07
•Transform faults (along mid-ocean
ridges; actively slipping segment of a
fracture zone between two ridge
segments
•Transforms link vary and not all occur
in oceanic lithosphere
Alpine Fault (New Zealand) link
trenches, some trench to ridge segment.
San Andreas Fault (California) cuts
across continental lithosphere.
References
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Marshak, S. (2005). Earth: Portrait of a planet (2nd ed). New York, W. W. Norton &
Company.
http://www.geo.arizona.edu/palynology/geos210/converg.gif
http://www.geol.canterbury.ac.nz/research/gis1.gif
http://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/spreading.jpeg
http://courses.science.fau.edu/~rjordan/phy1931/WEGENER/VG23.gif
http://www.tqnyc.org/NYC040792/transform.jpeg
http://www.cornellcollege.edu/geology/rdenniston/NZ%20Pics/group%20on%20transfo
rm.JPG
M. Norma Chavez 11/17/07