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Bourguet Syenite
Stratigraphic label: [mpro]bog
Map symbol: mPbog

First published: 26 January 2018
Last modified:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Translation of original French

 

 

 

 

 

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
mPbog2 Fe-Ti-P oxide gabbronorite, feldspar xenocrystal porphyritic
mPbog1 Alkali feldspar-megacristic biotite-clinopyroxene-apatite syenite, alkaline syenite dykes, granite, websterite

 

 
Author: Moukhsil et al., 2015
Age: Mesoproterozoic
Reference section: Reference outcrops 14-AM-007 (mPbog1) and 14-TC-5022 (mPbog2)
Type area: NTS sheet 32B02
Geological province: Grenville
Geological subdivision: Allochton
Lithology: Syenite, granite, websterite, gabbronorite
Type: Lithodemic
Rank: Lithodeme
Status: Formal
Use: Active

 

 

Related unit(s)

None

 

 

 

 

Background

The Bourguet Syenite was identified by Moukhsil et al. (2015) during mapping of the Parent region, Haut-Saint-Maurice.

 

 

Description

 

 

Bourguet Syenite 1 (mPbog1): Alkali Feldspar-Megacristic Biotite-Clinopyroxene-Apatite Syenite, Alkaline Syenite Dykes, Granite, Websterite

This unit is the main facies of the Bourguet Syenite. It occupies the centre of the intrusion and consists of megacristic syenite with bluish grey K-feldspar phenocrystals (up to 4 cm long). It also contains magnetite, biotite, clinopyroxene, apatite and traces of ilmenite and titanite. K-feldspar phenocrystals are perthitic, contain apatite and biotite inclusions, and locally have Carlsbad twinning (orthose) without significant deformation. Phenocrystals display a slight preferential orientation, thus testifying to a magmatic texture of syenite. On the other hand, the host of the intrusion is highly deformed, developing mylonitization (shearing); straight and banded gneiss are observed.

Salmon-pink alkaline syenite dykes and minor amounts of websterite and granite are associated with this unit. Syenite dykes are fine-grained and cut the main facies. They are foliated and perthitic K-feldspar megaporphyric (40-65% of the rock, 1-3 cm long). Both types of dykes are composed of interstitial biotite, with small amounts of orthopyroxene, magnetite, ilmenite and apatite as accessory minerals. Websterite is green in fresh exposure, medium grained and contains clinopyroxene, orthopyroxene, biotite, olivine and green hornblende. Accessory minerals are apatite and ilmenite. Granite associated with syenite is pinkish and coarse grained. It is composed of quartz, plagioclase, K-feldspar, usually perthitic and opaque minerals.

 

Bourguet Syenite 2 (mPbog2): Fe-Ti-P Oxide Gabbronorite, Feldspar Xenocrystal Porphyritic

This unit is located on the northern periphery of the intrusion. It consists of Fe-Ti oxides-apatite gabbronorite (type OAGN = Oxide Apatite Gabbronorite, acronym according to Dymeck and Owens, 2001), characterized by a porphyritic texture with K-feldspar xenocrystals. These rectangular-shaped xenocrystals (2 mm to 1 cm long) are of the same composition as phenocrystals of the main syenite unit (mPbog1). Gabbronorite is medium to coarse grained, highly magnetic, consisting of poikiloblastic biotite crystals (~1 cm long), clinopyroxene, orthopyroxene, plagioclase, magnetite, hornblende, apatite and trace sulphides (pyrrhotite, chalcopyrite). There is also the presence of normative ilmenite.

Thickness and distribution

This intrusion is roughly elliptical, approximately 7.5 km long and 4 km wide, with a NW-SE orientation. Two small intrusions are also visible northwest of the main intrusion.

Dating

Unit mPbog1 was dated during mapping of the Parent region and gave a crystallization age of 1038 +15/-13 Ma.

Isotopic System Mineral Crystallization Age (Ma) (+) (-) Reference(s)
U-Pb Zircon 1038 15 13 Augland et al., 2016

Stratigraphic Relationship(s)

The Bourguet Syenite intrudes into the Dugré Plutonic Suite and Wabash Complex.

Paleontology

Does not apply.

References

Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
MOUKHSIL, F. –  SOLGADI, F. – BELKACIM, S. – AUGLAND, L.E. – DAVID, J. Géologie de la région de Parent, Haut-Saint-Maurice (Partie ouest du Grenville). Ministère de l’Énergie et des Ressources naturelles, Québec, 62 pages, 1 map. 2015 RG 2015-04
DYMEK, P.F. – OWENS, B.E. Petrogenesis of apatite-rich rocks (nelsonite and oxyde-apatite-gabbronorite) associated with massif anorthosites. Economic Geology, volume 96, pages 797-815. 2001 Source

AUGLAND, L.E. – MOUKHSIL, A. – SOLGADI, F.

Mantle influence of syn- to late-Grenvillian alkaline magmatism in the Grenville Province: causes and implications. Canadian Journal of Earth Science, volume 54, pages 263-277. 2016 Source

 

 

 

13 février 2019