The stratigraphy and geochemistry of late Devonian to early Carboniferous volcanic rocks of the northern Chignecto peninsula, Cobequid Highlands, Nova Scotia

Authors

  • David J.W. Piper Atlantic Geoscience Centre, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
  • Georgia Pe-Piper Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada
  • David J. Pass Department of Geology, Saint Mary's University, Halifax, Nova Scotia B3H 3C3, Canada

DOI:

https://doi.org/10.4138/2077

Abstract

The volcanic succession of the Fountain Lake Group of the northern Chignecto peninsula consists of basalt and andesite flows, rhyolite shallow intrusions and minor flows, and rhyolitic pyroclastic rocks. Fault scarp breccia, fluvial conglomerate and sandstone, and lacustrine siltstone and minor limestone are interbedded with the volcanic rocks. The succession is cut by mafic dykes, some of which predate and others postdating brittle north-vergent thrusting. Detailed geochemical and petrographic study shows that the volcanic rocks geochemically resemble the plutonic rocks of the Cape Chignecto pluton that are thrust over the volcanic succession. Diabase dykes may record the contamination of gabbroic magma by residual basc-of-crust plagioclase-pyroxenc granulite from which felsic magma had been extracted. Fractionation of this mafic magma resulted in enrichment in incompatible elements in some dykes. Andesites evolved from basaltic parents cither by fractionation or by melting of hydrous gabbros. Much of the volcanic succession shows low-temperature alteration including silicification. RÉSUMÉ La succession volcaniquc du Groupe du lac Fountain dans la partie septcntrionale de la péninsule de Chignecto comprend des ccoulcments de basalte et d'andésite, des intrusions peu profondes de rhyolite et des écoulements mineurs, de même que des roches pyroclastiques rhyolitiques. Des breches d'escarpements de failles, du grès et un conglomerat fluvial, ainsi que du siltstone lacusfre et une faible quantité de catcaire sont interstratifiés-de roches volcaniques. La succession est entrecoupeé par des filons intrusifs mafiques, dont certains sont antérieurs et d'autres postérieurs à une poussée fragile orientée vers le nord. Une étude géochimique et pétrographique détaillée montre que les roches volcaniques ressemblent géochimiquement aux roches plutoniques de l'intrusion ignée de Cape Chignecto qui recouvrent la succession volcanique. Des filons intrusifs diabasiques peuvent enregistrer la contamination du magma gabbroique par la granulite résiduelle de ptagioclase-pyroxène de la base de la croûte de laquelle du magma felsique avait été extrait. Le fractionnement de ce magma maflquc a produit un enrichissement en éléments incompatibles de certains filons intrusifs. Les andésites ont évolué è partir de parents basaltiques, par fractionnement ou par fusion de gabbros aqueux. Une vaste part de la succession volcanique rcvele une altération, notamment une silicification, à basse température. [Traduit par la rédaction]

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Published

1996-04-01

How to Cite

Piper, D. J., Pe-Piper, G., & Pass, D. J. (1996). The stratigraphy and geochemistry of late Devonian to early Carboniferous volcanic rocks of the northern Chignecto peninsula, Cobequid Highlands, Nova Scotia. Atlantic Geoscience, 32(1). https://doi.org/10.4138/2077

Issue

Vol. 32 No. 1 (1996)

Section

Articles

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