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DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
| Author: | Beauchamp, 2020 |
| Age: | Neoarchean |
| Stratotype: | None |
| Type area: | Cadieux Lake area (NTS sheet 33A02) |
| Geological province: | Superior Province |
| Geological subdivision: | Opinaca Subprovince |
| Lithology: | Tonalite and granodiorite |
| Category: | Lithodemic |
| Rank: | Lithodeme |
| Status: | Formal |
| Use: | Active |
None
Background
Hocq (1985) assigned felsic rocks outcropping in the Otish Mountains from the south part of sheets 33A01 and 33A02 to the Lac Barou Massif. This massif was decomposed into several units during the summer 2017 Ministère‘s mapping of sheet 33A01 (Beauchamp et al., 2018). The Barou Intrusion and Martel Pluton were then introduced. Mapping of sheet 33A02 allowed for the creation of a distinct unit at the western end of the Otish Mountains, the Pisim Pluton, which consists of tonalite and granodiorite (Beauchamp, 2020).
Description
The rock is very homogeneous and consists of weakly foliated medium-grained tonalite and granodiorite. The rock is pale grey to whitish grey in altered patina and fresh exposure. Plagioclase damouritization gives a greenish colour to the rock in fresh exposure. The Pisim Pluton contains 5 to 15% ferromagnesian minerals (biotite ± hornblende ± magnetite). Sericite-calcite ± hematite alteration is common in this unit. Staining reveals that the rock is rather poor in K-feldspar. Indeed, the microcline content varies between 2 and 15%. The Pisim Pluton is cut by a weakly hematitized massive granite that contains biotite ± hornblende ± magnetite.
From a geochemical perspective (Beauchamp, 2020), rocks of the Pisim Pluton are of calc-alkaline affinity (Frost et al., 2001). They are peraluminous and type I (Maniar and Picolli, 1989). They fall in the volcanic arc granite field (Pearce et al., 1984). The rare earth profile shows light rare earth enrichment over heavy rare earths and a small positive Eu anomaly. Negative anomalies in Th, Nb and Sm, and positive anomalies in La, Ce, Zr and Hf are present on spider diagrams normalized to the primitive mantle (McDonough and Sun, 1995).
Thickness and Distribution
The Pisim Pluton is located at the top of the Otish Mountains, more specifically at its western end (SE portion of sheet 33A02). It measures 4.5 km by 2.5 km.
Dating
None.
Stratigraphic Relationship(s)
The Pisim Pluton cuts metasedimentary rocks of the Laguiche Complex and intrudes the Martel Suite to the east.
Paleontology
Does not apply.
References
Publications Available Through Sigéom Examine
BEAUCHAMP, A.-M. 2020. Géologie de la région du lac Cadieux, sous-provinces d’Opatica et d’Opinaca, Eeyou Istchee Baie-James, Québec, Canada. MERN. BG 2019-02, 2 plans.
BEAUCHAMP, A.-M., MASSEI, F., DAOUDENE, Y. 2018. Géologie de la région de l’île Bohier, au contact entre les sous-provinces d’Opatica, d’Opinaca et le bassin d’Otish, au nord de Mistissini, Eeyou Istchee Baie-James, Québec, Canada. MERN. BG 2018-02, 2 plans.
HOCQ, M. 1985. GEOLOGIE DE LA REGION DES LACS CAMPAN ET CADIEUX, TERRITOIRE-DU-NOUVEAU-QUEBEC. MRN. ET 83-05, 190 pages and 4 plans.
Other Publications
FROST, B.R., BARNES, C.G., COLLINS, W.J., ARCULUS, R.J., ELLIS, D.J., FROST, C.D. 2001. A geochemical classification for granitic rocks. Journal of Petrology; volume 12, numéro 11, pages 2033-2048. doi.org/10.1093/petrology/42.11.2033.
MANIAR, P.D., PICCOLI, P.M. 1989. Tectonic discrimination of granitoids. Geological Society of America Bulletin; volume 101, pages 635-643. doi.org/10.1130/0016-7606(1989)101<0635:TDOG>2.3.CO;2.
MCDONOUGH, W.F., SUN, S.S. 1995. The composition of the earth. Chemical Geology; volume 120, pages 223-253. doi.org/10.1016/0009-2541(94)00140-4.
PALME, H., O’NEILL, H.S.C. 2004. Cosmochemical estimates of mantle composition. In Treatise on Geochemistry. (Holland, H.D. and Turrekian, K.K. editors), Elsevier, Amsterdam, The Netherlands; volume 2, pages 1-38. doi.org/10.1016/B978-0-08-095975-7.00201-1.
PEARCE, J.A., HARRIS, N.B.H., TINDLE, A.G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology; volume 25, pages 956-983. https://doi.org/10.1093/petrology/25.4.956.
Suggested Citation
Ministère de l’Énergie et des Ressources naturelles (MERN). Pisim Pluton. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-du-superieur/pluton-de-pisim_en [accessed on Day Month Year].
Contributors
|
First publication |
Anne-Marie Beauchamp, Eng., M.Sc. anne-marie.beauchamp@mern.gouv.qc.ca (redaction) Mehdi A. Guemache, P. Geo., Ph.D. (coordination); Patrice Roy, P. Geo., M.Sc. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); Ricardo Escobar Moran (HTML editing). |