Oceanic crust

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Colors indicate the age of oceanic lithosphere, wherein red indicates the youngest age, and blue indicates the oldest age. The lines represent tectonic plates.

Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however it is denser, having a mean density of about 2.9 grams per cubic centimeter[1] as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter.[2]






Life cycle[edit]


As the mantle rises it cools and melts, as the pressure decreases and it crosses the solidus. The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very slow spreading ridges (<1 cm·yr−1 half-rate) produce thinner crust (4–5 km thick) as the mantle has a chance to cool on upwelling and so it crosses the solidus and melts at lesser depth, thereby producing less melt and thinner crust. An example of this is the Gakkel Ridge under the Arctic Ocean. Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a greater depth, creating more melt and a thicker crust. An example of this is Iceland which has crust of thickness ~20 km.[5]



Magnetic anomalies[edit]

Main article: Seafloor spreading


See also[edit]


  1. ^ Rogers, N.; Blake, S.; Burton, K. An introduction to our dynamic planet. Cambridge University Press. p. 19. ISBN 978-0-521-49424-3. Retrieved January 2008. 
  2. ^ Cogley 1984
  3. ^ D. R. Bowes (1989) The Encyclopedia of Igneous and Metamorphic Petrology, Van Nostrand Reinhold ISBN 0-442-20623-2
  4. ^ Clare P. Marshall, Rhodes W. Fairbridge (1999) Encyclopedia of Geochemistry, Kluwer Academic Publishers ISBN 0-412-75500-9
  5. ^ C.M.R. Fowler (2005) The Solid Earth (2nd Ed.), Cambridge University Press ISBN 0-521-89307-0
  7. ^ Müller, R. Dietmar (April 2008). "Age, spreading rates, and spreading asymmetry of the world's ocean crust" (PDF). Geochemistry, Geophysics, Geosystems (American Geophysical Union) 9 (4). doi:10.1029/2007GC001743.