The interpretation of two-element variation diagrams

Abstract

The preceding chapters covering simple experimental systems give an indication of the ways in which natural magmas might be expected to evolve by processes involving liquid—solid fractionation during melting and crystallisation. This knowledge is part of the essential background to hypothesis formation. It enables us to make sensible initial guesses as to possible ways in which particular magmatic series may have formed. We also require a method of examining the compositional data of natural rocks which will enable the formulation of precise hypotheses and thus refine and test the initial ideas. However, this is only part of the problem and we shall see in later chapters how a consideration of the petrography of rocks and of melting experiments carried out on natural samples both contribute further to the refinement of hypotheses.