Ophiolites

An ophiolite (pronunciation: /ˈɒfiəlaɪt/) is a section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. Ophio is Greek for snake (ὄφις), and lite means stone from the Greek lithos (λίθος), after the often-green-color rocks (spilites and serpentinites) that make up many ophiolites.

The term ophiolite was originally used by Alexandre Brongniart for an assemblage of green rocks (serpentine subgroup, diabase) in the Alps; Gustav Steinmann later modified its use to include serpentine, pillow lava, and chert ("Steinmann's trinity"), again based on occurrences in the Alps. The term was little-used in other areas until the late 1950s to early 1960s, with the recognition that this assemblage provided an analog for oceanic crust and the process of seafloor spreading. This recognition was tied to two events: (1) the observation of magnetic anomaly stripes on the seafloor, parallel to oceanic ridge systems, interpreted by Frederick Vine and Drummond Matthews to represent the formation of new crust at the oceanic ridge and its subsequent symmetric spreading away from that ridge, and (2) the observation of a sheeted dyke complex within the Troodos Ophiolite (Cyprus) by Ian Graham Gass and co-workers, which must have formed by repetitive extension of crust and intrusion of magma, resulting in a formation consisting of 100% dikes with no older wall rocks preserved within the complex. Moores and Vine concluded that the sheeted dike complex at Troodos could form only by a process similar to the seafloor spreading proposed by Vine and Matthews. Thus, it became widely accepted that ophiolites represent oceanic crust that had been emplaced on land.

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