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Lachance Mangerite
Stratigraphic label: [mpro]lhc
Map symbol: mPlhc

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: Morfin et al., 2015
Age: Mesoproterozoic
Reference section: Reference outcrops are located to the SW of the village of Saint-André-du-Lac-Saint-Jean (e.g. 18-AM-124 and 18-AM-125).
Type area: Area south of Saint-Jean Lake (NTS sheet 32A08)
Geological province: Grenville Province
Geological subdivision: Allochton
Lithology: Intermediate intrusive rocks
Type: Lithodemic
Rank: Lithodeme
Status: Formal
Use: Active

 

 

Background

The Lachance Mangerite was introduced by Morfin et al. (2015) during geological survey of the Chambord, Roberval and Notre-Dame-de-la-Doré region (NTS sheets 32A08, 32A09 and 32A10). These authors have grouped several scattered intrusions from the area into this unit. Later, Moukhsil and Daoudene (2019) restricted this unit to a single intrusion that was well circumscribed by the aeromagnetic survey (Intissar and Benahmed, 2015) in sheet 32A08. The latter shows that the intrusion is characterized by an intense magnetic susceptibility along its edges, whereas it appears low to moderate elsewhere.

 

Description

The Lachance Mangerite is a polyphase batholith dominated by mangerite, but syenite and alkaline feldspar granite are also present. The amount of quartz within these rocks varies widely from one outcrop to another, representing between 5 and 30% of the rock.

Mangerite is generally whitish in altered surface and green in fresh exposure. It is characterized by a porphyritic texture with K-feldspar and plagioclase phenocrystals in a medium to coarse-grained matrix consisting of quartz, amphibole, biotite, orthopyroxene and magnetite. The proportion of feldspar phenocrystals ranges from 20 to 30% of the rock and their length is generally between 1 and 4 cm. Phenocrystals are mostly perthitic K-feldspar. Orthopyroxene is observed in ferromagnesian mineral clusters and is partially replaced by biotite and amphibole. Quartz content is variable, but generally relatively low. Quartz forms large zones with undulatory extinction. Magnetite is almost systematically present in mangerite, but its content is highly variable. Mangerite also contains euhedral crystals of magmatic epidote associated with accessory minerals such as apatite and zircon.

The mangerite texture is marked by mild to moderate foliation. At the border of the intrusion, this foliation is often well developed and the rock is finer grained with well-aligned phenocrystals. The apparent increase in strain intensity towards the edge of the intrusion coincides with an increase in magnetic susceptibility.

Syenite is whitish in altered surface and pinkish in fresh exposure. It is mainly k-feldspar porphyritic and massive. It shows the same mineralogy as mangerite, but proportions of the various mineral phases are different. Plagioclase is altered to white mica and K-feldspar is generally perthitic. When present, orthopyroxene appears uralitized. It shows a rim consisting of green hornblende, locally chloritized. These ferromagnesian minerals and biotite form millimetric grain clusters. Syenite locally contains quartz which then forms large zones with undulatory extinction associated with myrmekite grains. Accessory mineral phases are magmatic epidote, opaque minerals (including magnetite), apatite and zircon.

Alkaline feldspar granite is medium grained, pink in fresh exposure, pink-brown in altered patina and shows magmatic foliation. Locally, the rock is deformed and fine grained. This granite contains varying amounts of biotite, orthopyroxene and magnetite. K-feldspar (microcline) is usually perthitic. Biotite and green hornblende are mainly observed as grain clusters. Epidote, apatite and zircon are present as accessory minerals, along with opaque minerals (magnetite, pyrite).

Thickness and Distribution

In sheet 32A08, the Lachance Mangerite forms a dome that looks more or less elliptical on the map with a ~N-S oriented long axis. It extends into the NE corner of sheet 32A01 and covers an area of approximately 150 km2. Other kilometric intrusive bodies associated with the Lachance Mangerite have been mapped in sheets 32A06, 32A09 and 32A10.

Dating

A dating on the sample 2018-AM-0125A was recently carried out.

Unit Sample Number Isotopic System Mineral Crystallization Age (Ma) (+) (-) Reference(s)
mPlhc 2018-AM-0125A U-Pb Zircon 1044,2 6,9 6,9 Papapavlou, 2019

Stratigraphic Relationship(s)

The Lachance Mangerite is in fault contact with the Travers Suite and intrudes into the Belley Plutonic Suite. Highly deformed metavolcanite enclaves are observed in the Lachance Mangerite. These amphibolitized enclaves are centimetric to metric, greenish in fresh and altered surfaces and fine grained. They could correspond to the known Montauban Group volcanics.

 

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.

MORFIN, S., TREMBLAY, C., SOLGADI, F., MOUKHSIL, A., DAIGNEAULT, R. 2015. GEOLOGIE DE LA REGION DE CHAMBORD, ROBERVAL ET NOTRE-DAME-DE-LA-DORE (FEUILLETS SNRC 32A08, A09 ET A10) ET RECONNAISSANCE DES FEUILLETS 32A06, A07 ET A11. MERN, CERM. MB 2015-07, 69 pages and 5 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