The interpretation of data for plutonic rocks

Abstract

An important object of any study of igneous rocks in the field is to gain an idea of the volume of the separate units present. Given adequate maps and/or air photographs, assessing the total volume of a lava flow, particularly if it is recent, is a relatively easy matter. Doing the same for a partially exposed pluton is more difficult and frequently only the area exposed is quoted. The time-honoured method of calculating the volume is to extrapolate the boundaries downward to a reasonable depth and model a three-dimensional shape accordingly. That the data so acquired, especially when reassessed in the light of geophysical measurements, provide surprising results is aptly illustrated by the following two examples.