Metamorphism and Igneous Action*

Abstract

A PART from the question of the time-continuity of the progressive series represented by, say, the Barrovian zones, there is the chemical continuity to be considered. How far do the zones of Barrow represent an isochemical series of pelitic rocks? The degree to which such processes as meta-morphic differentiation and diffusion have operated obviously affects the compositions of members of the series at any stage. Such possible departures from the isochemical series arise through processes inherent in the rock. There is, however, another aspect of this topic which, though usually ignored in Great Britain, must in my opinion be carefully considered. The possibility of the introduction of material of so-called magmatic origin is one that certainly cannot be dismissed in the higher grades, and one that might apply even to the lower grades of regional metamorphism. It will be convenient for the development of my argument, however, if we transfer ourselves to the domain of ultra-metamorphism, and I discuss the reality of granitization, for, if granitization is real, certain consequences seem to follow.