Alpine-type sensu strictu(ophiolitic) peridotites: Refractory residues from partial melting or igneous sediments? A contribution to the discussion of the paper: “The origin of ultramafic and ultrabasic rocks” by P.J. Wyllie

Abstract

Abstract Although Alpine peridotites and basaltic lavas are widely associated in eugeosynclines and oceanic areas, their genetic ties are obscure. Three major characteristics of olivine-rich Alpine peridotite and dunite—relict cumulus textures, aggregated masses of chromitite, and intimate association with magnesium-rich gabbro — cannot be explained by partial melting of garnet peridotite to form tholeiite. Association of magnesium-rich gabbro with the chromite-bearing and so-called high-temperature Alpine peridotites is believed to present problems that have not been considered by advocates of the partial-melting hypothesis. The chromite-bearing Alpine peridotites and related feldspathic rocks are believed to have formed near the top of the mantle by gravitational differentiation processes which are largely independent of the melting processes that produce basaltic magma at depths of 50 km or more.