Petrogenesis of Ultramafic and Ultrabasic Rocks - Review

The introductions to each of the preceding \nchapters (Sections I) have reviewed the conclusions reached, and provided \nsome cross references to other chapters. \nThis final contribution reviews in general \nand historical terms some of the problems of the petrogenesis of ultramafic and ultrabasic \nrocks. The greater part of the review \ndeals with the petrogenesis of the alpine-type \nultramafic rocks, because these have \nserved as a focus of controversy for many \nyears. The variety of ultramafic rock associations \nin different tectonic environments, \nand of the processes involved in \ntheir formation, have been emphasized \nthroughout the book. Both are important \nin considering petrogenesis. Although interpretation \nof processes may require extensive \nstudy, rock associations are more \neasily distinguished; but the distinctions \nhave not always been made. Hess (1955, \np. 394) drew attention to this with the following \nstatement: "Gross errors have probably \nresulted from applying conclusions \ndrawn from facts related to mica peridotites \nto alpine peridotites and vice versa. \nIf mica peridotite had been called humpty-dumptyite, \nthese probably would not have \narisen."