Geochemistry of the granitoid plutons of the Brookville terrane, Saint John, New Brunswick, and implications for development of the Avalon Zone

Authors

  • G. N. Eby Department of Earth Sciences, University of Massachusetts, Lowell, Massachusetts 01854, U.S.A
  • K. L. Currie Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario KlA 0E8, Canada

DOI:

https://doi.org/10.4138/2090

Abstract

The Brookville terrane forms a fault-bounded region, underlain mainly by plutonic and high-grade metamorphic rocks, flanked on one side by a typical Avalonian terrane (Caledonia terrane), and separated from a typical Avalonian terrane (Mascarene terrane) on the other side by the Silurian Kingston Dike Complex. Mafic plutons of the Brookville terrane were derived from a source similar to that of the continental margin basalts of the Coldbrook Group of the Caledonia terrane. Some sialic plutons were probably derived from mixtures of this basaltic component with a component similar to bulk crust. Major element data for most of the plutons fall on smooth curves on Harker diagrams, suggesting that crystal fractionation is the major process controlling the evolution of individual plutons. Trace element modelling indicates that this fractionation was largely due to the removal of hornblende, plagioclase, and alkali feldspar. The presence of A2~type granites of similar age (ca. 550 Ma) in the Caledonia terrane (Bonnell Brook), Brookville terrane (Fairville), and Mascarene terrane (Lingley) suggest that these terranes were amalgamated by 550 Ma. Subsequent magmatism in the Brookville terrane was characterized by emplacement of plutons typical of continental margin magmatism. This period of magmatism ended with the emplacement of A2-type plutons, suggesting that magmatism in the Brookville terrane ceased during post-subduction extension. RÉSUMÉ Le terrane de Brookville forme une région, délimitée par des failles, qui repose principalement sur des roches plutoniques et des roches métamorphiques à haute teneur, accolée d'un côté à un terrane avalonien caractéristique (terrane de Caledonia) et séparée, de l'autre côté d'un terrane avalonien caractéristique (terrane de Mascarene) par te complcxe de filons parallèles siluricn de Kingston. Les plutons mafiqucs du terrane de Brookville sont provenus d'une source semblable à celle des basaltes de la marge continental du groupe de Coldbrook du terrane de Caledonia. Certains plutons sialiques sont probablement provenus de mélanges de ce composant basaltique avec un composant analogue à une masse de croute. Les données sur les principaux éléments de la majority des plutons décrivent des courbes égales et régulieres sur les diagrammes de différenciation, ce qui laisse supposer que la cristallisation fractionnée constitue le principal processus régissant l'évolution de chacun des plutons. La modélisation des éléments traces révèle que cette cristallisation était grandement due au retrait de hornblende, de plagioclase et de feldspath alcalin. La présence de granites de type A-2 d'âige similaire (vers 550 Ma) dans te terrane de Caledonia (Bonnell Brook), le terrane de Brookville (Fairville) et le terrane de Mascarene (Lingley) permet de supposer que ces terranes se sont fusionnés vers 550 Ma. Le magmatisme subsequent dans le terrane de Brookville a été caractérisé par l'intrusion de plutons typiques d'un magmatisme de la marge continentale. Cette période de magmatisme a pris fin avec une intrusion de plutons de type A-2, ce qui amène à penser que le magmatisme à l'intérieur du terrane de Brookville a cessé au cours de l'extension postérieure à la subduction. [Traduit par la rédaction]

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Published

1996-11-01

How to Cite

Eby, G. N., & Currie, K. L. (1996). Geochemistry of the granitoid plutons of the Brookville terrane, Saint John, New Brunswick, and implications for development of the Avalon Zone. Atlantic Geoscience, 32(3). https://doi.org/10.4138/2090

Issue

Vol. 32 No. 3 (1996)

Section

Articles

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