Ophiolites and Their Origins

Ophiolites are suites of temporally and spatially associated ultramafic, mafic, and felsic rocks that are interpreted to be remnants of ancient oceanic crust and upper mantle. Ophiolites show significant variations in their internal structure, geochemical fingerprints, and emplacement mechanisms. These differences are controlled by (1) the proximity, when formed at the magmatic stage, to a plume or trench; (2) the rate, geometry, and nature of ocean-ridge spreading; (3) mantle composition, temperature, and fertility; and (4) the availability of fluids. The oceanic crust preserved in ophiolites may form in any tectonic setting during the evolution of ocean basins, from the rift-drift and seafloor spreading stages to subduction initiation and terminal closure. An ophiolite is emplaced either from down-going oceanic lithosphere via subduction-accretion or from the upper plate in a subduction zone through trench-continent collision. Subduction zone tectonics is thus the most important factor in the igneous evolution of ophiolites and their emplacement into continental margins.