Ophiolite

Article By:

Liou, Juhn G. Geological and Environmental Sciences, Stanford University, Stanford, California.

Maruyama, Shige Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan.

Tsujimori, Tatsuki Institute for Study of the Earth's Interior, Okayama University, Misasa, Japan.

Ogasawara, Yoshihide Department of Earth Sciences, Waseda University, Tokyo, Japan.

Last reviewed:December 2019

DOI:https://doi.org/10.1036/1097-8542.470860

A distinctive assemblage of mafic plus ultramafic rocks generally considered to be fragments of the oceanic lithosphere that have been tectonically emplaced onto continental margins and island arcs. Ophiolite, from the Greek ophios for snake and lithos for rock, was named by A. Brongniart, a nineteenth-century French naturalist, who considered its scaly appearance and the greenish color of its main constituent rock, serpentinite. An ophiolite is a formation made up of an association of particular rocks in a clearly defined sequence. As shown in Fig. 1, a complete idealized ophiolite sequence from bottom to top includes (1) an ultramafic tectonite complex composed mostly of multilayered, deformed harzburgite, dunite and minor chromitite; (2) a plutonic complex of layered mafic-ultramafic cumulates at the base, grading upward to massive gabbro, diorite and possibly plagiogranite; (3) a mafic sheeted-dike complex; (4) an extrusive section of massive and pillow lavas, pillow breccias and intercalated pelagic sediments; and (5) a top layer of abyssal or bathyal sediments, which may include ribbon chert, red pelagic limestone, metalliferous sediments, volcanic breccias, or pyroclastic deposits. Most ophiolites lack complete sections and are dismembered and fragmented. Their estimated original thickness is variable, ranging from about 2 km (1.2 mi) to more than 8 km (5 mi). See also: Earth crust; Lithosphere; Serpentinite

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