Petrogenesis of Palaeocene granites, Island of Skye, N.W. Scotland
This thesis documents an investigation of selected intrusions of the Palaeocene granites on the Isle of Skye, and includes: petrography, mineral chemistry (include REE concentrations) fluid inclusions, whole rock major-, trace- and rare-earth-elements, together with stable oxygen and hydrogen and Sr-Nd isotope geochemistry on whole rocks and mineral separates. The data presented indicate that the granites are geochemically related and have been severely affected by 'associated' hydrothermal fluid(s), especially the Loch Ainort Granite. The hydrothermal fluids most likely represent the limited mixing between magmatic and meteoric waters in Beinn an Dubhaich Granite. In contrast, the other granites are likely to have been affected by meteoric water alone, with water-rock interaction having occurred below 500°C.The coarsening of granophyric texture outwards from alkali feldspar phenocrysts, the low concentration of Fe3+ in pyroxenes, together with the slight variations in Fe2+: Mg ratio of biotites, suggest a slow cooling history for the granites. The (two feldspar) Beinn an Dubhaich and Glamaig granites have small negative Eu anomalies compared with the (single feldspar) Loch Ainort and Marsco granites, suggesting the important role of plagioclase fractionation during granite evolution. The most important reservoirs for the REE in the Skye granites are amphibole, pyroxene and apatite. The inflection present in the plot of MnO against SiO2, the non-linear and divergent relationships between K2O, Rb, Sr and ?Nb against SiO2, and the presence of an anomalous group of granites which are characterised by low Zr, Y and Nb, but with high SiO2 contents, mitigates against simple mixing as the dominant process responsible for the compositional diversity of the granites.