Geochemistry of the western part of the Moinian assemblage

Publisher Website
Google Scholar
Abstract
Synopsis: Comparison of chemical analyses of the principal units of the Morar Division suggest that the inter-relationship between psammites and pelitic rocks is dominated by mechanical rather than chemical processes. This conclusion is drawn from similar ratios of Fe 2 O 3 /MgO, K/Rb, K/Ba and Ca/Y, and dissimilar ratios of Ti, Nb and Zr to Fe. Rocks of the Glenfinnan Division differ from comparable members of the Morar Division in having higher Nb/P 2 O 2 and Nb/Y for any given Sr or Fe 2 O 3 /Ni ratio, and higher Sr/Y for any given SiO 2 level. These distinctions may reflect consistent differences in the ratios of quartz and feldspar, ferromagnesians, and accessory minerals. Samples from the Loch Eil Division tend to have higher Zr/P 2 O 5 , Y/P 2 O 5 , CaO/P 2 O 5 , Rb/Sr and lower Ca/Y and K/Rb than their counterparts in the Morar and Glenfinnan Divisions. The Morar Basal Pelite has an immature chemistry showing affinity with the Lewisian basement upon which it rests. It can be distinguished from other Moinian pelitic units by its high Sr/Y. Certain individual psammitic horizons can be distinguished by their contents of P, Ti, Nb and Zr, and sometimes by Cr/Fe. The Morar Division has a chemistry consistent with deposition in a basin close to its supposed Lewisian source. In contrast, the Loch Eil Division may have been partly derived from a (post-Lewisian) sedimentary source, and may rest unconformably upon the underlying Moinian rocks.

This publication has 16 references indexed in Scilit: