Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences



Occurrence number: 
Longitude: -57, Latitude: 48.75

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.

A Rb-Sr isochron based on five rocks gave 421±7 Ma (Bell and Blenkinsop, 1981).

BELL, K. and BLENKINSOP, J. 1981. A geochronological study of the Buchans area, Newfoundland. In The Buchans Orebodies (edited by E.A. Swanson, D.F. Strong and J.G. Thurlow). Special Paper, Geological Association of Canada, 22: 91-111.
STRONG, D.F. and TAYLOR, R.P. 1984. Magmatic-subsolidus and oxidation trends in composition of amphiboles from silica-saturated peralkaline igneous rocks. Tschermaks Mineralogische und Petrographische Mitteilungen, 32: 211-22.
TAYLOR, R.P., STRONG, D.F. and FRYER, B.J. 1981. Volatile control of contrasting trace element distributions in peralkaline granitic and volcanic rocks. Contributions to Mineralogy and Petrology, 77: 267-71.
TAYLOR, R.P., STRONG, D.F. and KEAN, B.F. 1980. The Topsails igneous complex: Silurian-Devonian peralkaline magmatism in western Newfoundland. Canadian Journal of Earth Sciences, 17: 425-39.
Whalen and Currie, 1983 and 1984.

Fig. 1_81 Topsails igneous terrane (aftr preliminary map of Whalen and Currie, 1983, Fig. 2.2).
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