ophiolite

Ophiolite is a segment of the Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level, typically as a result of obduction along convergent plate boundaries. Ophiolites provide direct access to rocks that make up the oceanic lithosphere, which is normally lost beneath the oceans.

A classic ophiolite sequence, from the surface downward, begins with deep-sea sediments or pelagic rocks and pillow basalts; beneath these lie the sheeted-dike complex, representing magma conduits that fed the volcanic crust; below this are cumulate gabbros and layered rocks; and at the base a mantle section of ultramafic rocks such as peridotite, often serpentinized. Not all ophiolites show every layer in perfect order, but the overall arrangement is widely used as a diagnostic crystallized record of ocean crust.

Formation and occurrence: Ophiolites form when slices of oceanic plate are thrust (obducted) onto continental margins during plate tectonic collisions. They are preserved in mountain belts and ophiolite complexes around the world, with well-known examples including the Semail ophiolite in Oman and the Troodos ophiolite in Cyprus. These exposures have been central to studies of oceanic crust composition, structure, and the processes of mantle melting and crustal accretion.

Etymology and significance: The term ophiolite derives from Greek ophis, snake, and lithos, stone, in reference to serpentinized rocks commonly associated with ophiolites. Ophiolites remain key to understanding the formation of ocean basins and the history of plate tectonics.