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Amikap Pluton
Stratigraphic label: [narc]amk
Map symbol: nAamk

First published: 15 November 2017
Last modified: 27 March 2018

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Translation of original French

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
nAamk2 Granodiorite
nAamk1 Tonalitic gneiss
 
Author:Bandyayera and Daoudene, in preparation
Age:Neoarchean
Reference section:None
Type area:Northeastern Boisrobert Lake area (NTS sheet 32N11)
Geological province:Superior Province
Geological subdivision:La Grande Subprovince
Lithology:Tonalitic gneiss and granodiorite
Type:Lithodemic
Rank:Lithodeme
Status:Formal
Use:Active

Background

The Amikap Pluton is a lithodemic unit introduced to describe an intrusive mass of tonalitic gneiss and foliated granodiorite in the Rupert River area (Bandyayera and Daoudene, in preparation). The elliptical shape of the pluton and its intrusion in the Champion Complex, in contact with massive granodiorite and quartz diorite units, seemed to indicate that the Amikap Pluton was late. Bandyayera and Daoudene (in preparation) proposed a synkinematic emplacement of the pluton in a shear zone based on its highly deformed margin, compared to the core which is rather massive to foliated. New U-Pb data from a sample of tonalitic gneiss gave an age of 2732 ±3 Ma, interpreted as the age of the Amikap Pluton. This age is consistent with synvolcanic intrusions of the Eastmain River volcanic band (Moukhsil et al., 2003). These data suggest that the Amikap Pluton represents an ancient gnessic dome within the Champion Complex.

 

Description

The Amikap Pluton is associated with a strong elliptical magnetic anomaly measuring 14 km x 8 km. It is essentially a homogeneous mass of tonalitic gneiss (unit nAamk1), the centre of which consists of massive to foliated granodiorite (unit nAamk2).

 

Amikap Pluton 1 (nAamk1): Tonalitic Gneiss

Tonalitic gneiss is found on the margin of the Amikap Pluton, in contact with massive granodiorite of the Champion Complex (Achp4), in the south, and with massive to foliated quartz diorite and diorite (Achp3) in the north. Fine to medium-grained rock is locally banded and is light grey in altered surface and fresh exposure. Gneissosity results in alternating light and dark bands generally millimetre-wide, uncommonly centimetre-wide. Dark bands are locally dioritic. Tonalitic to dioritic bands contain 10-30% hornblende, 5-15% biotite, 5% magnetite and 3% epidote.

 

Amikap Pluton 2 (nAamk2): Granodiorite

Unit nAamk2 consists of massive to foliated granodiorite. Homogeneous rock is medium grained, light grey in fresh exposure and beige in altered surface. It contains 15% biotite, 5% magnetite and 2% epidote.

 

Thickness and Distribution

The Amikap Pluton is associated with a strong magnetic anomaly of roughly ovoid shape 14 km x 8 km. The tonalitic gneiss unit (nAamk1) occupies approximately 90% of the intrusive mass.

 

Dating

As previously mentioned, new zircon U-Pb data from a tonalitic gneiss sample (unit nAamk1) yielded an age 2732 ±3 Ma, interpreted as the intrusion age of the Amikap Pluton. This age is consistent with synvolcanic intrusions of the Eastmain River volcanic band (Moukhsil et al., 2003).

 It was not possible to bring out a younger age for overgrowth by analyzing crystal edges at locations identified in cathodoluminescence.

Isotopic SystemMineralInformal SubdivisionCrystallization Age (Ma)(+)(-)Reference(s)
U-PbZirconnAamk1273233David et al., in preparation

Stratigraphic Relationship(s)

The Amikap Pluton is a gneissic to foliated intrusive mass located in contact with massive granodioritic and dioritic units of the Champion Complex. The margin of the pluton is deformed and gneissic. The Amikap Pluton is cut by the Mistassini Dyke Swarm, Matachewan Dyke Swarm, Senneterre Dykes and Abitibi Dykes. The junction of all these diabase dykes is located in the centre of the pluton.

Paleontology

Does not apply.

References

Author(s)TitleYear of PublicationHyperlink (EXAMINE or Other)
BANDYAYERA, D. – DAOUDENE, Y.Géologie de la région du lac Nemiscau : secteur ouest de la rivière Rupert (SNRC 32N06, 32N07, 32N11). Ministère de l’Énergie et des Ressources naturelles, Québec.In preparation
MOUKHSIL, A. – LEGAULT, M. – BOILY, M. – DOYON, J. – SAWYER, E. – DAVIS, D.W.Synthèse géologique et métallogénique de la ceinture de roches vertes de la Moyenne et de la Basse-Eastmain (Baie-James). Ministère des Ressources naturelles, Québec; ET 2002-06, 57 pages, 1 map.2003ET 2002-06
DAVID., J. – BANDYAYERA, D. – HAMMOUCHE, H. – LECLERC, F. – GOUTIER, J. – TALLA TAKAM, F.Datations U-Pb dans la Province du Supérieur effectuées au GEOTOP en 2015-2016. Ministère de l’Énergie et des Ressources naturelles, Québec.In preparation

 

4 février 2019