Musocho Pluton
Stratigraphic label: [narc]mus
Map symbol: nAmus

First published: 25 July 2018
Last modified:













Translation of original French

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
Author: Holmes, 1959; Racicot et al., 1984
Age: Neoarchean
Reference section: None
Type area: The Muscocho Pluton particularly outcrops along the southwestern shore of Muscocho Lake (northeastern corner of NTS sheet 32G10).
Geological province: Superior Province
Geological subdivision: Abitibi Subprovince
Lithology: Granodiorite
Type: Lithodemic
Rank: Lithodeme
Status: Formal
Use: Active


The intrusion was first named “Muscocho Stock” by Holmes (1959) and Hébert (1979), and later named “Muscocho Pluton” by subsequent authors (Racicot et al., 1984; Daigneault, 1991; Tait, 1992).


According to Tait (1992, p. 43): “It consists of a hornblende granodiorite. The rock is very homogeneous and pink-grey. There are a few more mafic enclaves distributed mainly on the pluton’s edges. Primary foliation, represented by the preferential alignment of tabular hornblende and plagioclase phenocrystals, forms a more or less concentric structure within the pluton. There is an extremely well developed diaclase system, the spacing of which, in places, is in the order of a millimetre. A prominent feature of this granitoid mass is the absence of planar structures that can be correlated with regional schistosity. Contact metamorphism produced an aureole that spreads between 500 and 1000 m through the host volcanics. Very close to contact, rocks reach the amphibolite facies, where the garnet-hornblende-plagioclase paragenesis is observed. Regional schistosity (S2) around the intrusive mass’s edges is destroyed by recrystallization associated with contact metamorphism, which overprints regional metamorphism, confirming the late emplacement of the pluton. The presence of apophysis granodiorite dykes, derived from the pluton and that cut regional schistosity, also confirms this relationship. These dykes are becoming more abundant as we approach the plutonic mass.” 

Thickness and Distribution

The Muscocho Pluton is a 16-km-diameter subcircular intrusion located in the northeastern portion of sheet 32G10.


Sample PM-1 yielded a crystallization age of 2701.2 +1.7/-1.3 Ma (Mortensen, 1993).

Isotopic System Mineral Crystallization Age (Ma) (+) (-) Reference(s)
U-Pb Zircon 2701.2 1.7 1.3 Mortensen, 1993

Stratigraphic Relationship(s)

The Muscocho Pluto cuts mafic volcanic rocks of the Obatogamau Formation.


Does not apply.


Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
DAIGNEAULT, R. Évolution structurale du segment de roches vertes de Chibougamau, Sous-province archéenne de l’Abitibi, Québec. Université Laval; doctoral thesis, 352 pages. 1991
HÉBERT, C. Demie sud du canton de Haüy (comté d’Abitbi-Est) – Rapport préliminaire. Ministère des Richesses naturelles, Québec; DPV-653, 11 pages, 1 plan. 1979 DPV 653
HOLMES, S.W. Région de Fancamp-Haüy, District électoral d’Abitibi-Est. Ministère des Mines, Québec; RG-084, 52 pages, 1 plan. 1959 RG 084
MORTENSEN, J.K. U-Pb geochronology of the eastern Abitibi subprovince. Part 1: Chibougamau – Matagami – Joutel region. Canadian Journal of Earth Sciences; volume 30, pages 11–28. 1993 Source
RACICOT, D. – CHOWN, E.H. – HANEL, T. Plutons of the Chibougamau-Desmaraisville belt; a preliminary survey. In Chibougamau: stratigraphy and mineralization (Guha, J. and Chown, E.H., editors). Canadian Institute of Mining and Metallurgy; volume 34, pages 178-197. 1984
TAIT, L. Géologie de la région du lac à l’Eau Jaune (Territoire-du-Nouveau-Québec). Ministère de l’Énergie et des Ressources, Québec; MB 91-29, 86 pages, 4 plans. 1992 MB 91-29
15 octobre 2019