The ultramafic belts

Abstract

One petrological approach to upper mantle studies is to determine which ultramafic rocks represent mantle material. Ultramafic rocks occur in a variety of field and petrographic associations: in recent reviews, Wyllie [1967b, 1968] outlined eleven petrographic associations, some with subdivisions. In this summary, it is convenient to consider these in four larger groups: (1) layered, stratiform, and other intrusions involving gabbro or diabase, together with accumulations or concentrations of mafic minerals; (2) the alkalic rocks, including kimberlites, mica peridotites, members of ring complexes, and ultrabasic Java flows; (3) the several serpentinite-peridotite associations often classified together as alpine-type intrusions; (4) serpentinites and peridotites of the oceanic regions.

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