Ophiolite

ophiolite [′äf·ē·ə‚līt]

(petrology)

A distinctive assemblage of mafic plus ultramafic rocks, generally considered to be fragments of oceanic lithosphere that have been tectonically emplaced onto continental margins and island arcs.

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Ophiolite 

a group of ultrabasic and basic intrusive (dunites, peridotites, pyroxenites, various gabbros, tonalites), effusive (primarily basalts and their tuffs), and sedimentary (pelagic oceanic deposits) rocks that are found together.

The concept of ophiolite was introduced by the Swiss scientist G. Steinmann in 1905. Ophiolites are usually associated with the manifestation of magmatism in the early stages of the formation of geosynclinal systems.

During the 1960’s and 1970’s, in connection with intensive study of the oceans, the problem of ophiolites attracted a great deal of attention. Scientists began viewing ophiolites in folded regions as relics of oceanic crust tectonically moved to the margins of the continents. Moreover, serpentinized ultrabasites are viewed as part of the mantle; gabbroids, as the “basalt layer”; and the effusive sedimentary series, as an analogue of the “first” and “second” layers of the present-day oceanic crust. A partial disruption of this sequence of rocks results from the tectonic factors that cause the development of a specific geological formation, a serpentinite rock, in which all members of the ophiolite group, as well as other rocks, are chaotically intermixed and “cemented together” by serpentinites.

Ophiolites are a common component of the earth’s linear folded regions. They are widespread in geosynclinal systems, forming within them protrusions (rock masses tectonically intruded in the solid state into the deposits covering them) or nappes thrust over the miogeosynclinal or platform sediments that overlie the continental crust. The study of ophiolites is important in discovering deposits of chromium, nickel, platinum, gold, mercury, and other ores genetically related to ophiolites, and for studying the historical development of the earth’s crust.

REFERENCES

Peive, A. V. “Okeanicheskaia kora geologicheskogo proshlogo.” Geotektonika, 1969, no. 4.
Hess, H. H. “History of Ocean Basins.” In Buddington Volume. New York, 1962.

A. L. KNIPPER