HISTORY AND CURRENT STATUS OF THE OPHIOLITE CONCEPT

Ophiolites represent on-land exposures of oceanic crust and mantle formed at oceanic spreading centers. Ophiolites represent one of the most important components of orogenic belts. The development of ideas about ophiolites paralleled those of the nature of orogeny up to, during, and after the 1960-1970 Plate Tectonic Revolution.

Brongniart (1813, 1827) first named ophiolites for exposures in the Alpine-Mediterranean region, Suess (1909), Steinmann (1905, 1927), Benson (1926), and Hess (1939, 1955) noted ophiolites' presence in worldwide orogenic belts. Steinmann recognized the deep-sea nature of sediments associated with the peridotite (serpentinite), and pillow lava of what became known as an ophiolite sequence. Hess pointed out the tectonic significance of ophiolite emplacement as the first major deformation of an intracontinental orogenic belt.

We now recognize a typical ophiolite sequence, comprising from bottom to top, mantle (tectonite) peridotite, mafic-ultramafic cumulate rocks, a dike-within-dike sheeted complex, and extrusive pillow lavas, overlain by pelagic or volcaniclastic sediments. Examples range from Archean to Cenozoic in age.

Much recent work on ophiolites has focused on the composition of their magmas as indicating a origin in a forearc, intra-arc, or back-arc setting. Recently recognized silicic mid ocean lavas complicate facile interpretations of the environment of ophiolite origin, based on geochemistry, however. Pelagic sediments on some complexes indicate an open ocean environment of formation. Hess's (1939, 1955) tectonic observations of ophiolites have been interpreted in plate tectonic terms as collision of a continental margin with a subduction zone dipping away from the continent (e.g., Moores, 1970, 1982, Wakabayashi et al., 2003; Searle et al., 2003).

The complex tectonics, sedimentology, petrology, and geochemistry of ophiolites argue for a multidisciplinary, rather than a specialized, approach to their study and interpretation.