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Geological Society, London, Special Publications; 1990; v. 51; p. 383-393;
DOI: 10.1144/GSL.SP.1990.051.01.25
© 1990 Geological Society of London

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The geochemistry and petrology of the Late Precambrian Georgeville Group: a volcanic arc-rift succession in the Avalon terrane of Nova Scotia

J. B. Murphy1, J. D. Keppie2, J. Dostal3 & A. J. Hynes4

1 Department of Geology, St Francis Xavier University, Antigonish, Nova Scotia, Canada B2G 1CO
2 Nova Scotia Department of Mines and Energy, PO Box 1087, Halifax, Nova Scotia, Canada B3J 2X1
3 Department of Geology, St Mary’s University, Halifax, Nova Scotia, Canada B3H 3C3
4 Department of Geological Sciences, McGill University, Montreal, Canada H3A 2A7

The Antigonish Highlands of northern mainland Nova Scotia lie within the Avalon terrane of the Canadian Appalachians. They are predominantly underlain by late Precambrian interbedded metasedimentary and metavolcanic rocks of the Georgeville Group. In the southern highlands, subaerial volcanic rocks of the Keppoch Formation consist of bimodal, porphyritic and aphyric mafic and felsic flows. Pophyritic mafic flows display volcanic arc calc-alkalic affinities and are extensively fractionated. The aphyric mafic flows are characterized by strong Fe and Ti enrichment and are probably continental tholeiites derived from a heterogeneous metasomatized upper mantle source. Felsic lavas display volcanic arc affinities and were probably derived by anatexis of the crust.

In the northern highlands, mafic flows of the Chisholm Brook Formation are dominated by calc-alkalic basalts and andesites and minor interlayered continental tholeiites. In the central highlands, submarine volcanic rocks of the Clydesdale Formation consist of continental tholeiites and are broadly comparable with those of the Keppoch Formation. The close spatial and temporal association of calc-alkalic and tholeiitic mafic rocks, the felsic rocks with volcanic arc chemistry and the stratigraphy which documents the infilling of a narrow sedimentary basin suggest a rift setting within an ensialic volcanic arc environment. The style of volcanism exhibited in the Antigonish Highlands compares favourably with other late Precambrian successions in Nova Scotia. In general late Precambrian volcanism in northern Nova Scotia is consistent with an ensialic volcanic arc environment with local development of volcanic arc rifts and provides constraints on the evolution of the Avalon terrane as a whole.





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