Deformation of Crystallizing Magma

Abstract

In foregoing paper Professor Grout raises certain objections to processes that I have advocated as significant in petrogenesis, and to some of these objections I wish to take opportunity, offered by editors, of making a brief reply. With particular reference to Duluth gabbro, Grout says that the arguments for circulation are conclusive, but offers no further support for arguments than that formerly offered. The banding and fluxion structures are conclusive evidence of circulation of a sort, perhaps, but not necessarily of convective circulation. Convection suffers from disability of requiring further assumption of rhythmic crystallization, i.e., crystallization which is periodic with respect to nature of substance crystallizing. In this manner it is hoped to obtain alternating layers of different composition, but it would seem much more probable that convection would effect a thorough mixing of successive products. The rhythmical crystallization itself is, moreover, an assumption that has nothing to support it in whole realm of crystallization phenomena. The Liesegang ring effect is a totally different affair, and any assumption of rhythm in crystallization, such as Grout pictures, should be made only in extremis.