Petrogenesis of Ultramafic and Ultrabasic Rocks - Review

Abstract

The introductions to each of the preceding chapters (Sections I) have reviewed the conclusions reached, and provided some cross references to other chapters. This final contribution reviews in general and historical terms some of the problems of the petrogenesis of ultramafic and ultrabasic rocks. The greater part of the review deals with the petrogenesis of the alpine-type ultramafic rocks, because these have served as a focus of controversy for many years. The variety of ultramafic rock associations in different tectonic environments, and of the processes involved in their formation, have been emphasized throughout the book. Both are important in considering petrogenesis. Although interpretation of processes may require extensive study, rock associations are more easily distinguished; but the distinctions have not always been made. Hess (1955, p. 394) drew attention to this with the following statement: "Gross errors have probably resulted from applying conclusions drawn from facts related to mica peridotites to alpine peridotites and vice versa. If mica peridotite had been called humpty-dumptyite, these probably would not have arisen."

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