Français
 
Mimosa Plutonic Suite
Stratigraphic label: [mpro]mim
Map symbol: mPmim

First published: 14 June 2019
Last modified: 17 January 2020

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Translation of original French

 

 

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.

None

 

Author: Moukhsil and Daoudene, 2019
Age: Mesoproterozoic
Reference section: Reference outcrop 18-AM-120 located approximately 1.32 km east of Castor Lake
Type area: NE corner of NTS sheet 32A07
Geological province: Grenville Province
Geological subdivision: Allochton
Lithology: Felsic, intermediate and mafic intrusive rocks
Type: Lithodemic
Rank: Suite
Status: Formal
Use: Active

 

 

Background

The Mimosa Plutonic Suite was defined by Moukhsil and Daoudene (2019) in NTS sheets 32A07 and 32A08 during mapping of the SW area of Lake Saint-Jean. Analysis of regional aeromagnetic maps (Intissar and Benahmed, 2015) suggests that the plutonic suite extends northward in sheet 32A10.

 

Description

The Mimosa Plutonic Suite is a polyphase batholith whose composition is highly variable from one outcrop to another. It consists of quartz syenite, hypersthene syenite, mangerite, granite, orthopyroxene granite, alkaline feldspar granite, granodiorite, quartz monzodiorite and minor amounts of jotunite and gabbronorite. The suite is highly magnetic and its extent is easily located on aeromagnetic maps (Intissar and Benahmed, 2015).  

Quartz syenite and hypersthene syenite are both whitish to brownish in altered patina and greenish in fresh exposure. With the exception of the hypersthene content that differs from one lithology to the other, they show similar petrological characteristics. They are both K-feldspar-plagioclase porphyritic to locally megacristic. Feldspars make up a total of 40% of the rock. Phenocrystals are 1 to 5 cm long and can reach 7 cm locally. In addition to hypersthene, biotite and hornblende are the other ferromagnesian mineral phases occurring in clusters. Hypersthene is altered and frequently shows a hornblende rim. K-feldspar is perthitic and quartz forms large zones with undulatory extinction. Quartz is in places in contact with myrmekite. For both types of syenite, the most common accessory mineral phases are apatite, zircon and epidote.

Quartz mangerite is magnetic, porphyritic, greenish in fresh exposure with a similar appearance to syenites. The difference with syenites lies in its greater plagioclase content, approximately 25%. In mangerite, foliation is visible where there are clusters of ferromagnesian minerals such as orthopyroxene, hornblende and biotite.

Granite is fine to medium grained, locally containing orthopyroxene (charnockite). It is grey-pink in altered patina and pinkish grey in fresh exposure. Granite is composed of K-feldspar, plagioclase, quartz, biotite, zircon, apatite and opaque minerals.

Alkaline feldspar granite is salmon pink in fresh and altered surfaces, fine grained and foliated. It contains microcline, quartz forming large zones with undulatory extinction and ~1% biotite. Accessory mineral phases are apatite and zircon.

Quartz monzodiorite is magnetic, grey-white in altered patina and grey-black in fresh exposure. It is medium grained and migmatitic with the presence of leucosome veins, which vary in composition from tonalitic to granitic. These veins are both conformable and unconformable to foliation. Quartz monzodiorite is composed of slightly sericitized plagioclase grains, locally perthitic K-feldspar, hornblende, biotite, apatite and zircon.

Granodiorite is fine to coarse grained, locally containing orthopyroxene (opdalite). It is homogeneous, beige to grey in fresh exposure and beige-brown to pink in altered patina. It is foliated and contains quartz in large zones, K-feldspar and fractured plagioclase filled with white mica. Granodiorite also contains biotite, hornblende, magnetite and accessory zircon and apatite.

 

Jotunite and gabbronorite represent minor proportions of this suite. Jotunite (hypersthene monzodiorite) is brownish in fresh exposure and grey-brown in altered surface. It is medium grained and foliated. Jotunite is composed of plagioclase, K-feldspar, quartz, orthopyroxene, clinopyroxene, biotite and accessory phases such as apatite and opaque minerals. Ferromagnesian minerals are either in clusters or disseminated throughout the rock.

Gabbronorite is coarse grained and magnetic. It contains pyroxene, hornblende and biotite in lesser amounts. Gabbronorite is locally migmatitic, which allows it to be differentiated from the Claire Gabbronorite.

Fine-grained grey diorite dykes with K-feldspar xenocrystals intrude into quartz syenite of the Mimosa Plutonic Suite.

 

Thickness and Distribution

On the map, the Mimosa Plutonic Suite is mainly represented by a large batholith with an area of approximately 270 km2. This batholith was originally mapped in the NW corner of sheet 32A07 (Moukhsil and Daoudene, 2019), but aeromagnetic imaging (Intissar and Benahmed, 2015) suggests that it extends northward in sheet 32A10. In both sheets, the batholith shows a coarsely arced shape, with a long N-S axis in the northern part, which curves along a NNW-SSE orientation in the southern part. Two other plutons of the Mimosa Plutonic Suite outcrop south of the main batholith (sheet 32A07); they cover areas of 10 km2 and 22 km2.

Dating

A dating on the sample 2018-AM-0116A was recently carried out.

Unit Sample Number Isotopic System Mineral Crystallization Age (Ma) (+) (-) Reference(s)
mPmim1 2018-AM-0116A U-Pb Zircon 1003 18 18 Papapavlou, 2019

Stratigraphic Relationship(s)

The Mimosa Plutonic Suite intrudes into the Barrois Complex. It is cut by centimetric to metric dykes of granitic, syenitic and dioritic composition. The unit contains centimetric to metric paragneiss enclaves (Barrois Complex unit mPboi4).

Paleontology

Does not apply.

References

Publications available through Sigéom Examine

INTISSAR, R., BENAHMED, S. 2015. LEVE MAGNETIQUE AEROPORTE DANS LE SECTEUR OUEST DU LAC-ST-JEAN, PROVINCE DE GRENVILLE. MERN, GOLDAK AIRBORNE SURVEYS. DP 2015-06, 7 pages and 2 plans.

MOUKHSIL, A., DAOUDENE, Y. 2019. Géologie de la région du lac des Commissaires, Province de Grenville, région du Saguenay–Lac-Saint-Jean, Québec, Canada. MERN. BG 2019-01.

PAPAPAVLOU, K. 2019. U-Pb geochronology report, Grenville 2018-2019. UQAM. MB 2019-11, 21 pages.

 

 

11 novembre 2019