Topsails

The Topsails complex is one of the largest granitoid bodies in Newfoundland covering an area of 125x50 km. At least four major granite types can be recognized of which only one is peralkaline. The peralkaline rocks comprise granites, quartz- feldspar porphyry dykes and comenditic flows and ignimbrites. The granites contain orthoclase and microcline perthite, 10-15% alkali amphibole, aegirine, aenigmatite and accessory zircon, monazite, allanite, fluorite and magnetite. The porphyries are similar to the granites with, typically, quartz and feldspar phenocrysts and poikilitic microphenocrysts of aegirine and alkali amphibole. In one area they are transitional into peralkaline volcanics, and some samples carry relict fayalite and hedenbergite. Roof pendants consisting of comenditic flows and peralkaline ignimbrites have identical mineralogies to the granite and porphyry dykes. The comendites are the most peralkaline rocks of the suite as a whole. Preliminary results on remapping the complex are reported by Whalen and Currie (1983). Numerous major and trace element analyses are given by Taylor et al. (1980), and Taylor et al. (1981) give REE analyses for a range of the same rocks. Strong and Taylor (1984) have investigated the alkali amphiboles, and Whalen and Currie (1984) discuss the role of magma mixing and transcurrent faulting in the genesis of the peralkaline granite.