Ophiolites and Their Origins

Ophiolites are the remnants of ancient oceanic crust and upper mantle that were tectonically emplaced into continental margins. They display the only evidence for magmatic, tectonic, and hydrothermal processes associated with seafl oor spreading prior to 170 Ma because no oceanic lithosphere older than this age is preserved in the modern oceans. The occurrence of sheeted dikes, side-byside tabular intrusions of magma, is the primary evidence for the seafl oor spreading origin of ophiolites. Ophiolites are therefore the best archives of the evolutionary history of ocean basins from their rift–drift and seafl oor spreading stages to subduction initiation and fi nal closure. Their recognition as structural analogues for oceanic crust played a signifi cant role in the advancement of the plate tectonic theory in the 1960s, and geoscientists have used ophiolites in investigating the nature of mid-ocean ridge processes, mantle chemistry, the paleogeography of ancient ocean basins, and the tectonic evolution of orogenic belts.