Structure and composition of the oceanic lithosphere created at different spreading rates

The specific features of the oceanic lithosphere (the petrography, the mineral composition, and the petrochemistry of igneous rocks and restites) that indicate its formation at different spreading rates, from the extremely slow to fast, are considered. This evidence may be used for solution of the inverse problem of estimating, at least qualitatively, the rate of paleospreading from the structure and composition of rocks pertaining to the ophiolitic association. The use of petrochemical data as the criteria of paleospreading rate is limited. The anomalous composition and structure of the oceanic crust may be due to factors unrelated to the spreading rate. The well-studied cases of ophiolites interpreted as fragments of the ancient oceanic lithosphere formed under conditions of fast, slow, and extremely slow spreading rates are discussed. It is concluded tentatively that the fast spreading is typical of the ophiolites obducted on passive margins (the Periarabian, Uralian, and Appalachian-Caledonian belts) as fragments of ensimatic suprasubduction basins formed at the final stages of the evolution of paleooceans (Tethys and Iapetus). Ophiolites as products of slow spreading are commonly localized in accretionary (subduction-related) orogens at the present-day and older active continental margins.