Types of igneous cumulates

Abstract

The term 'cumulate ' is proposed as a group name for igneous rocks formed by crystal accumulation. After accumulation of the crystal precipitate, various ways of completing the crystallization process lead to differences in the rock finally produced. The various types of cumulates which have so far been distinguished are briefly described. I N layered intrusions the lower levels contain minerals of presumed high-tem-perature crystallization and upwards the minerals are of progressively lower temperature type. This relationship, together with textural features, has led to the view that discrete crystals successively separated from the magma and accu-mulated, as a result of their greater density, at the bottom of the liquid, building up gradually to form a layered series. Crystal accumulation without remelting was advocated by Bowen for the origin of certain ultrabasic rocks (1928, p. 167), and the term 'accumulative rocks ' has gradually appeared in petrological literature. Now that an origin by crystal accumulation has been widely accepted for certain eucrites, gabbros, and ferrogabbros as well as for various extreme rock types suc