VUME Upper Mantle of the Earth

Ophiolite and Oceanic Lithosphere.

The ocean basins cover the largest area of the Earth's surface. Ophiolites provide valuable information about how ocean crust develops at spreading centers. Because of plate tectonics, however, most oceanic lithosphere eventually is subducted. So no ocean crust is older than about 200 million years Thus the only existing oceanic lithosphere is younger than about Jurassic in age and occurs at locations farthest from the oceanic spreading centers. Except in areas where magmatism is intense enough to build volcanic structures above sea level, most of the oceanic magmatism is difficult to access. Ophiolites represent the only source of information available about the oceanic crust prior to that time.

Ophiolites are found in all the major mountain belts of the world whether collisional (e.g. Himalayas) or not (e.g. Andes). The subduction-related chemistry of ophiolites and their association with mountain belts suggests that their formation and emplacement are related to oceanic closure and continental collision (final stages of the Wilson Cycle) rather than oceanic opening and seafloor spreading as was first thought.
The nature and origin of ophiolites and oceanic crust and lithosphere are discussed.