Silicate analyses and normative compositions of the fine fraction of till; examples from eastern Finland

Abstract

Abstract The major element compositions of the fine fractions (< 0.06 mm) of 34 till samples from the vicinity of the Archaean Kuhmo greenstone belt were analyzed by X-ray fluorescence. The normative mineralogy calculated from the chemical composition shows homogeneity amongst the till fines. When plotted on the triangular diagrams normally used for the classification of igneous rocks, the majority of the compositions fall into the fields of the tonalites and granodiorites. Although the influence of the 3-5-km-wide greenstone belt upon the boulder and pebble fractions and upon the trace-element geochemistry of the fines is clear, the picture of the composition of the underlying bedrock obtained from the major element composition of the till lines is obscured by the contribution of material from the vast granitoid area upglacier. This corresponds to the results obtained by direct mineralogical analysis of the till fines. The method introduced here, that usually applied to petrological problems, seems also to be applicable to the study of the finest fractions of the tills.