The petrogenesis of charnockitic and granitic migmatites of the high-grade metamorphic Precambrian of Rogaland/Vest-Agder, S. W. Norway - A statistical interpretation of major element rock chemistry

Abstract

A charnockitic and granitic rock suite from the high-grade metamorphic Precambrian of southwest Norway was investigated for its geochemical characteristics. Whole rock major element analyses of 37 samples, taken from 8 localities which cover a range of metamorphic grade, were made. Multivariate statistical methods, R-mode and extended Q-mode component analysis, were used to aid the interpretation of the complex data set. Application of these methods resulted in a main division into melanocratic and leucocratic sample groups. A further analysis of the two groups showed that while the melanocratic samples form a homogeneous group, the leucocratic samples display a geochemical variability which is explained here by partial anatexis. Combined geological and geochemical data suggest a primary formation of the rock suite as a series of basic and acid volcanic rocks, that are intercalated with sediments. The charnockitic rock suite (granulite facies) shows no evidence of depletion of magmatophile elements compared to the granitic rock suite (amphibolite-facies).