Mohorovičić discontinuity

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The Mohorovičić discontinuity is located at letter A

Ordovician ophiolite in Gros Morne National Park, Newfoundland. This rock which formed in the Moho is exposed on the surface.

The Mohorovičić discontinuity (Croatian pronunciation: [mɔhɔːrɔvitʃitɕ] (Moh-ho-row-ree-chich)), usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. The Moho serves to separate both oceanic crust and continental crust from underlying mantle. The Moho mostly lies entirely within the lithosphere; only beneath mid-ocean ridges does it define the lithosphere-asthenosphere boundary. The Mohorovičić discontinuity was first identified in 1909 by Andrija Mohorovičić, a Croatian seismologist, when he observed the abrupt increase in the velocity of earthquake waves (specifically P-waves) at this point. Ophiolites are sections of oceanic crust and possible mantle rock that have been obducted into the continental crust during plate collisions.^{[citation needed]}

The Mohorovičić discontinuity is on average 7 km below the ocean floor and 30 to 50 km beneath typical continents. It is deepest beneath the Tibetan Plateau, where it is approximately 75 km below the surface.^{[citation needed]}

During the late 1950s and early 1960s, a proposal was taken up in the executive committee of the National Science Foundation to drill a hole through the ocean floor to reach this boundary. However the operation, named Project Mohole, never received sufficient support and was mismanaged; it was canceled by the United States Congress in 1967. Simultaneous efforts were made by the Soviet Union at the Kola Institute, which reached a depth of 12,260 meters (40,226 feet) over 15 years   the world's deepest hole to date   before that attempt was also abandoned.^[1]

Reaching the discontinuity remains an important scientific objective. A more recent proposal considers a self-descending tungsten capsule heated by radiogenic heat to explore Earth’s interior near the Moho discontinuity and in the upper mantle.^[2] The Japanese project Chikyu Hakken ("Earth Discovery") also aims to explore this general area.

[edit] See also

• Brittle-ductile transition zone
• Gutenberg discontinuity
• Kola Superdeep Borehole
• Lehmann discontinuity

[edit] References

[edit] Bibliography

• Harris, P. (1972). "The composition of the earth". in Gass, I. G. et al. (eds). Understanding the earth: a reader in the earth sciences. Horsham: Artemis Press for the Open University Press. ISBN 0-85141-308-0. 
• "Schlumberger Oilfield Glossary". Schlumberger. http://www.glossary.oilfield.slb.com/default.cfm. Retrieved on 2008-07-17. 
• Dixon, Dougal (2000). Beginner's Guide to Geology. New York: Bounty Books. ISBN 0-7537-0358-0. 

[edit] Notes

This section needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (April 2009)

[edit] External links

• Britt, Robert Roy (2005-04-07). "Hole Drilled to Bottom of Earth's Crust, Breakthrough to Mantle Looms". Imaginova. http://www.livescience.com/technology/050407_earth_drill.html. Retrieved on 2008-07-17. 
• "Digging a Hole in the Ocean: Project Mohole, 1958-1966". National Academy of Sciences. http://www.nas.edu/history/mohole/. Retrieved on 2008-07-17. 
• Map of the Moho depth of the European plate