Geochemistry of post-tectonic mafic intrusions in the Central Gneiss Terrane of southwestern Newfoundland

Authors

  • K. L. Currie Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE8, Canada
  • J. T. van Berkel Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE8, Canada; Present address: Institute of Earth Sciences, Free University, P.O. Box 7161,1007 MC Amsterdam, The Netherlands Geological Survey of Canada Contribution Number 32288.

DOI:

https://doi.org/10.4138/1682

Abstract

South of Grand Lake, mafic igneous complexes of proven or probable Silurian age intruded quartzofeldspathic gneisses that had been deformed and raised to granulite fades in mid-Ordovician time. The mafic igneous complexes consist of gabbroic units, which locally exhibit igneous layering and contain ultramafic cumulate pods, that grade to and are cut by finer-grained hornblende gabbro. Compositions more felsic than diorite exhibit intrusive to co-mingling relationships with more mafic rocks. Chemical data for possible liquid-derived rocks exhibit characteristics suggesting derivation from diverse mantle sources, followed by varying combinations of fractionation, contamination, mixing and metasomatism by hydrous fluids during ascent and emplacement. The post-tectonic emplacement of the plutons suggests stabilisation of die Central Gneiss Terrane by late Ordovician or Silurian time, when the adjacent terrane to the southeast (Meelpaeg Terrane) was still undergoing deformation and granitic plutonism. RÉSUMÉ Au sud de Grand Lake, des complexes ignés mafiques, dont l’âge est assurément ou probablement silurien, firent intrusion dans desgneiss quartzofeldspathiques qui avaient été déforrnés avaient atteint le faciès des granulites au milieude l’Ordovicien. Les complexes ignés mafiques sont constitues d'unités gabbroiques (montrant localement un aspect rubanné et contenant des lentilles de cumulate ultramaflques) passant graduellement à un gabbro à hornblende moins grenu qui les recoupe aussi. Les compositions plus felsiques que la diorite sont en relation d'intrusion ou de mélange avec les roches plus mafiques. Les données chimiques concernant des roches possiblement derives du liquide montrent des caractéres suggèrant une dérivation à partir de diverses sources mantelliques, suivie d'une combinaison variée de fractionnement, contamination, mélange et métasomatisme par des fluides aqueux durant l'ascension et l’emplacement. L'emplacement post-tectonique des plutons suggère une stabilisation de la lanière Central Gneiss Terrane avant l'Ordovicien tardif ou le Silurien, au moment ou la lanière adjacente au sud-est (la Lanière de Meelpaeg) subissait encore une déformation et un plutonisme granitique. [Traduit par le journal]

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Published

1989-12-01

How to Cite

Currie, K. L., & van Berkel, J. T. (1989). Geochemistry of post-tectonic mafic intrusions in the Central Gneiss Terrane of southwestern Newfoundland. Atlantic Geoscience, 25(3). https://doi.org/10.4138/1682

Issue

Vol. 25 No. 3 (1989)

Section

Articles

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