Petrology, geochemistry, and tectonic setting of some Carboniferous plutons of the eastern Cobequid Hills

Authors

  • G. Pe-Piper Department of Geology, St. Francis Xavier University Antigonish, Nova Scotia B2G ICO, Canada
  • J, B. Murphy Department of Geology, St. Francis Xavier University Antigonish, Nova Scotia B2G ICO, Canada
  • D. S. Turner Department of Geology, St. Mary's University, Halifax, Nova Scotia B3H 3C3, Canada

DOI:

https://doi.org/10.4138/1669

Abstract

The Early Carboniferous Pleasant Hills and Hart Lake - Byers Lake granitoid plutons are the youngest plutons in the eastern Cobequid Highlands. In both plutons, coarse-grained granites predominate, but both also include fine-grained phases, most common at their margins. Modally, these granites fall in the "alkali-feldspar granite" field of the IUGS classification. Geochemically, both alkaline and subalkaline granites are present. The graniies have relatively low concentrations of Al2O3 and CaO, high alkali content, and molar (Na2O+K2O)/ Al2O3 in the range 0.84 to 0.99. The granites have within-plate trace element characteristics and are more alkaline and less aluminous than similar Early Carboniferous within-plate granites in the western Cobequid Highlands. This entire suite of Early Carboniferous granites in the Cobequid Highlands is approximately synchronous with extrusion of die Fountain Lake Group volcanic rocks. This igneous activity is apparently related to local extension along the Cobequid and other major strike-slip faults. RÉSUMÉ Les plutons granitoides éocarbonifères de Pleasant Hills et de Hart Lake - Byers Lake sont les plus jeunes plutons de l’est des Monts Cobequid. Les granites à grain grossier prédominerit au sein de l'un et l’autre pluton quoiqu'on y retrouve aussi des phases à grain fin, les plus souvent près des marges. En termes de mode, ces granites tombent dans le domaine des "granites à feldspath alcalin" de la classification IUGS. Du point de vue de la géochimie, les granites sont aussi bien alcalins que subalcalins. Leurs concentrations en Al2O3 et CaO sont relativement basses, leurs teneurs en alcali hautes et leurs rapports molaires (Na2O+K2O)/ Al2O3 vont de 0.84 à 0.99. Les granites renferment des éléments en traces à caractére intraplaque; ils sont plus alcalins et moins alumbieux que leurs homologues de l'ouest des Monts Cobequid. Ce cortège entier de granites éocarbonifères dans les Monts Cobequid est approximativement synchrone de l’extrusion des volcanites du Groupe de Fountain Lake. Cette activité ignée semble liée àune extension locale le long de la Faille de Cobequid et d'autres décrochements majeurs. [Traduit par le journal]

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Published

1989-04-01

How to Cite

Pe-Piper, G., Murphy, J. B., & Turner, D. S. (1989). Petrology, geochemistry, and tectonic setting of some Carboniferous plutons of the eastern Cobequid Hills. Atlantic Geoscience, 25(1). https://doi.org/10.4138/1669

Issue

Vol. 25 No. 1 (1989)

Section

Articles

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