Some aspects of the igneous and metamorphic geology of central Skye

Abstract

The part of Central Skye investigated and described in the present thesis consists of three adjacent areas the geology of the three regions has not been correlated.

Beinn na Cro consists of a complex of Tertiary basic rocks which are cut by hybrid and acidic net -veins, dykes and great tongues, the latter extending into the basic rocks from the Beinn na Cro granite mass. The rocks comprise lavas which, it is postulated, have been metasomatised into granulite and gabbro and fluidised into dolerite as the result of the uprise of hot supercritical fluids along vertical concentric sub -arcuate fractures. The hybrid and acidic net - veins and dykes appear to have been emplaced partially by the metasomatic alteration of the country rock by acidic fluids and partially as fluidised acidic systems. Quartz- porphyry sheets of magmatic origin cut the other rocks.

bìrea.gan Dubh is formed of a complex of Tertiary gneiss with pyroclastic and basic rocks overlain unconformably by lavas, the entire succession being cut by transgressive agglomerate and quartz -porphyry intrusions. It is suggested that the gneiss has formed as the result of the preferential alteration in situ of laminated and bedded tuff by ascending acidic / acidic fluids without the operation of tectonic forces. The transgressive agglomerate and quartz -porphyry are of magmatic origin.

Glas Bheinn Bheag comprises Jurassic sediments in which a metamorphic aureole around a Tertiary microgranite has been detected. The introduction of heat, alkalies and bases into the sediments from the microgranite has resulted in the granulitisation and chemical alteration of the sediments. The microgranite is considered, at least at its margins, to be metasomatic in origin. Quartz -porphyry sills and dykes of magmatic origin cut the other rocks.