The Quantitative Mineralogical Composition and Variation of the Lacorne, La Motte, and Preissac Granitic Complex, Quebec, Canada

Abstract

Variation of quartz percentage, colour index, potash feldspar/plagioclase ratio, feldspar percentage, and specific gravity within the Lacorne, La Motte, and Preissac granitic complex is studied by means of trend surface analyses based on 198 specimens. Marked patterns of variation emerge; the more clear-cut patterns relate to massifs with mafic- and potash feldspar-rich centres, and quartzose peripheries. The trend components suggest that the Lacorne massif is a composite body, and re-evaluation of the field evidence supports this prediction. These results are used to demonstrate a quantitative technique and its application to geographically distributed data of granitic complexes; a plea is made for the collection of areally distributed quantitative data of all types.