Geochemical studies of the Moine rocks in western Inverness-Shire

The aims of this work were to make a statistical study of variations in chemical composition within and between two major pelitic units in the Moine Series of Morar, western Inverness-shire, and to assess the metamorphic grade across the area by means of the calc-silicate bands found. Two of the major pelitic units, the Lochailort Pelitic Group and the Garnetiferous Pelite, were sampled to a rigid sampling plan which allowed analysis of variance techniques to be applied to the results, in a study of chemical variation within each of the units. Stepwise linear discriminant function analysis of the data was also undertaken, to provide functions which could be used to separate the two units on the basis of their chemical compositions. These derived functions could also be used to classify unknown samples and assign them to their correct stratigraphic position. Calc-silicate bands found as a minor rock type within the area may be used as precise indicators of metamorphic grade, since their chemistry determines their mineralogical response to metamorphism in a predictable fashion. Evidence from the less responsive pelites indicates that metamorphic grade rises generally eastwards across Morar, and a study of the calc-silicates, while confirming this, also provided evidence of a later, retrogressive event in the east of the area. In order to obtain large numbers of chemical analyses, rapid X-ray fluorescence analytical techniques were employed. For major element analysis a fusion method of sample preparation was adopted, and a new method of calibration was devised which allows a large range of rock compositions to be analysed using a single set of linear calibration regression equations.