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Narsajuaq Complex
Stratigraphic label: [ppro]naq
Map symbol: pPnaq

First published: 31 May 2018
Last modified:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Translation of original French

 

 

 

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
pPnaq6 Monzogranite
pPnaq5 Syenogranite
pPnaq4 Monzogranite or syenogranite and clinopyroxene monzodiorite
pPnaq3 Tonalite or granodiorite and monzogranite veins
pPnaq2 Quartz diorite
pPnaq1 Gneiss with tonalite and quartz diorite, granodiorite and monzogranite veins

 

 
Author:Lucas and St-Onge, 1991
Age:Paleoproterozoic
Reference section: 
Type area: 
Geological province:Churchill Province
Geological subdivision:Ungava Orogen / Narsajuaq Arc
Lithology:Plutonic and metasedimentary rocks
Type:Lithodemic
Rank:Complex
Status:Formal
Use:Active

 

 

Background

The Narsajuaq Complex was introduced by Charette and Beaudette (2018) to describe geological units mapped during previous work. These units were previously included in the Narsajuaq Arc, which was defined as a cartographic unit in the synthesis of the Ungava Orogen (Lamothe, 2007). However, Charette and Beaudette (2018) have abandoned this definition of the Narsajuaq Arc, considering it more of a lithotectonic domain. The “Narsajuaq Complex” stratigraphic unit was therefore introduced to comply with the North American Stratigraphic Code.

In addition, in the Cape Wolstenholme region mapped at a 1:100,000 scale by the Ministère in summer 2017, lithologies of the western portion of the arc were instead divided into complexes and suites, the main ones being the Pingasualuit Complex (pPpgs), Suluraaq Suite (pPslq), Nallujaq Suite (pPnal), Tasialuk Allipaaq Complex (pPali) and Sanningajualuk Suite (pPsnn).

 

 

Description

The Narsajuaq Arc consists of an assemblage of highly metamorphosed plutonic rocks and a small amount of sedimentary rocks that have been accreted to the margin of the Superior Province around 1.80 Ga (Lucas and St-Onge, 1992). Located in the northern part of the Ungava Orogen, the Narsajuaq Complex consists essentially of three intrusive suites that account for more than 90% of the arc. These three suites consist of: 1) an older plutonic suite (1863-1844 Ma, St-Onge et al., 1992) composed of tonalite gneiss, granodiorite and quartz diorite (pPnaq1); 2) a younger intrusive suite (1836-1821 Ma, St-Onge et al., 1992; Parrish, 1989) composed of quartz diorite (pPnaq2), tonalite and granodiorite (pPnaq3) and monzogranite or syenogranite (pPnaq4); and 3) a late anatectic suite (1803-1800 Ma; Dunphy et al., 1995; Parrish, 1989) composed of syenogranite (pPnaq5) and monzogranite (pPnaq6). With the exception of the late suite with relatively undeformed units, intrusive rocks of the Narsajuaq Complex are generally gneissic or foliated.

 
1) Older Plutonic Suite: 

The main lithology of the older suite, and of the Narsajuaq Complex as a whole, is a well-banded sequence of tonalite and quartz diorite in which conformable and unconformable granitic veins are found (St-Onge et al., 1992). Units in the older suite have a very homogeneous composition and texture over 250 km. A penetrative tectonic foliation at the granulite facies, parallel to compositional banding at the outcrop scale, characterizes most plutonic rocks of the Narsajuaq Complex (Lucas and St-Onge, 1995).

 

 

Narsajuaq Complex 1 (pPnaq1): Gneiss with Tonalite and Quartz Diorite, Granodiorite and Monzogranite Veins

The older plutonic suite consists of the gneiss unit pPnaq1, a banded assemblage of tonalite and quartz diorite cut by felsic veins whose composition is mostly monzogranitic. Gneiss consists of 70 to 80% biotite-hornblende tonalite. Locally, there is a dominance of hornblende-biotite quartz diorite. Bands are decametre to centimetre thick. Diorite horizons are usually boudinaged and surrounded by tonalite. Decimetric to metric horizons of biotite granodiorite, amphibolite, pyroxenite and peridotite are observed in places. Mafic-ultramafic rocks are in places found as enclaves (St-Onge et al., 1992; Lucas and St-Onge, 1997).

 
2) Younger Plutonic Suite: 

The younger plutonic suite cuts the older plutonic suite as well as metasedimentary rocks of the Sugluk Group. Unlike the older plutonic suite, they consist of kilometric plutons, isolated, usually tabular and occurring as sheets. This younger suite contains quartz diorite, monzodiorite, tonalite and monzogranite with proportions of 50% monzogranite, 35% mafic plutons (diorite and monzodiorite) and 15% tonalite. Plutons in the younger suite show varying degrees of deformation from massive to very foliated. In addition, plutons are composed of various enclaves from the older suite, the Sugluk Group, deep crust lithologies and comagmatic rocks (pyroxenite, diorite, tonalite). Based on the size and degree of homogeneity of the intrusions of the younger plutonic suite, it is believed to have developed in shallow levels of the crust (Lucas and St-Onge, 1997).

 

 

Narsajuaq Complex 2 (pPnaq2): Quartz Diorite

Diorite intrusions are primarily located in the southern portion of the Narsajuaq Arc near the tectonic contact with the Cape Smith Belt. The degree of deformation varies from massive to highly deformed, depending on the proximity of collision faults (Lucas and St-Onge, 1997). Quartz diorite intrusions contain pyroxenite, diorite and tonalite enclaves (St-Onge et al., 1992).

 

Narsajuaq Complex 3 (pPnaq3): Tonalite or Granodiorite and Monzogranite Veins

Hornblende-biotite tonalite kilometric plutons have intruded in the northern Narsajuaq Arc, north of Sugluk Inlet and Charles Island. These are tabular, foliated and parallel to banding of the older suite’s tonalite and quartz diorite. Tonalite is usually medium grained, even grained and contain abundant centimetric to metric enclaves of various compositions (Sugluk Group, gneiss of the older suite, pyroxenite, amphibolite and anorthosite). Biotite monzogranite veins, oriented parallel to or intersecting foliation, cut tonalitic masses (Lucas and St-Onge, 1997).

 

Narsajuaq Complex 4 (pPnaq4): Monzogranite or Syenogranite and Clinopyroxene Monzodiorite

Intrusive bodies of monzogranite form injections that alternate with gneiss of the older suite (pPnaq1) and tonalite of the younger suite (pPnaq3). Monzogranite is composed of hornblende, biotite and clinopyroxene, which are even grained and medium grained. The texture can be megacrystalline towards the centre of intrusions with an abundance of K-feldspar phenocrystals. Monzodioritic intrusions have smaller dimensions (~2 km) along the Narsajuaq Valley, in the southern sector of Sugluk Inlet (Lucas and St-Onge, 1997).

 
3) Late Plutonic Suite: 

Plutonic rocks in this suite consist of small granitic plutons and late-tectonic to post-tectonic, even-grained to pegmatitic veins or dykes. This suite is generally not deformed and not metamorphosed (Lucas and St-Onge, 1997).

 

Narsajuaq Complex 5 (pPnaq5): Syenogranite

The late suite consists of pegmatitic muscovite ± garnet syenogranite. Syenogranite occurs as undeformed dykes and sills that cut surrounding rocks. The dykes show a conjugate series steeply dipping and oriented NE to NW (St-Onge et al., 1992). A dyke from the Sugluk Inlet region cutting a tonalite from the younger plutonic suite was dated 1758 ±1 Ma (Parrish, 1989).

 

Narsajuaq Complex 6 (pPnaq6): Monzogranite

In the late suite, one of the monzogranite plutons in the Duquet Lake area, about 2.5 km in diameter, is egg-shaped, undeformed and non-metamorphosed. The pluton zircon U-Pb dating indicates a crystallization age of 1742.2 ±1.3 Ma (Dunphy et al., 1995). It is potassium-rich, hyperaluminous and has geochemical characteristics related to continental crust-derived granites (Lucas and St-Onge, 1997).

 

Thickness and Distribution

Refer to the above section for information.

 

Dating

Dunphy and Ludden (1998) summarize the ages for each group as follows: 1) the older plutonic suite between 1863 and1844 Ma, 2) the younger plutonic suite between 1836 and1821 Ma, and 3) the late plutonic suite between 1803 and1800 Ma.

SuiteIsotopic SystemMineralAge (Ma)(+)(-)Reference(s)
Older plutonic suite (Gneissic suite)U-PbZircon186322St-Onge et al., 1992
U-PbZircon186122St-Onge et al., 1992
U-PbZircon184855Parrish, personal communication with Dunphy and Ludden, 1994
U-PbZircon184522Parrish, personal communication with Dunphy and Ludden, 1994
U-PbZircon18441310St-Onge et al., 1992
Younger plutonic suiteU-PbZircon18360.50.5St-Onge et al., 1992
U-PbZircon183511St-Onge et al., 1992
U-PbZircon183511Parrish, 1989
U-PbZircon18340.60.6St-Onge et al., 1992
U-PbZircon183022Parrish, 1989
U-PbZircon182611St-Onge et al., 1992
U-PbZircon182533Parrish, 1989
U-PbZircon182111Parrish, personal communication with Dunphy and Ludden, 1994
Late plutonic suite (Anatectic suite)U-PbZircon180333Parrish, personal communication with Dunphy and Ludden, 1994
U-PbZircon180022Parrish, personal communication with Dunphy and Ludden, 1994

 

Stratigraphic Relationship(s)

The Narsajuaq Arc units overthrust the Archean basement (Kovik Antiform). The south front of the Narsajuaq Arc overthrusts the Watts Group units in the Nord Domain. St-Onge et al. (1992) and Dunphy and Ludden (1998) suggest a correlation between the older and younger plutonic suites of the Narsajuaq Complex and the intrusions of the Cape Smith Suite of the Nord Domain. Intrusion ages are grouped in two distinct periods contemporary to the Narsajuaq suites. Geochemical characteristics and similarity in age of the Parent Group volcanics and the Narsajuaq Complex plutonic rocks suggest that the Parent Group could represent a volcanic equivalent of the Narsajuaq magmatic arc, but with less crustal contamination (Picard et al., 1990; St-Onge et al., 1992; Dunphy et al., 1995; Dunphy and Ludden, 1998).

Paleontology

Does not apply.

References

Author(s)TitleYear of PublicationHyperlink (EXAMINE or Other)
CHARETTE, B. – BEAUDETTE, M.Géologie de la région du cap Wolstenholme, Orogène de l’Ungava, Province de Churchill, sud-est d’Ivujivik, Québec, Canada. Ministère des Ressources naturelles, Québec.2018Bulletin géologiQUE
DUNPHY, J.M. – LUDDEN, – J.N. – PARRISH, R.R.Stitching together the Ungava Orogen, northern Quebec: geochronological (TIMS and ICP-MS) and geochemical constraints on late magmatic events. Canadian Journal of Earth Sciences; volume 32, pages 2115-2127.1995Source
DUNPHY, J.M. – LUDDEN, J.N.Petrological and geochemical characteristics of a Paleoprotérozoic magmatic arc (Narsajuaq terrane, Ungava Orogen, Canada) and comparisons to Superior Province granitoids. Precambrian Research; volume 91, pages 109-142.1998Source
LAMOTHE, D.Lexique stratigraphique de l’Orogène de l’Ungava. Ministère des Ressources naturelles, 62 pages.2007
LUCAS, S.B.Structural Evolution of the Cape Smith Thrust Belt and role of out-of-sequence faulting in the thickening of mountain belts. Tectonics; volume 8, pages 6551989Source
LUCAS, S.B. – ST-ONGE, M.R.Evolution of Archean and early Proterozoic magmatic arcs in northeastern Ungava Peninsula, Quebec. Commission Géologique du Canada; papier 91-1C, pages 109-119.1991Source
LUCAS, S.B. – ST-ONGE, M.R.Terrane accretion in the internal zone of the Ungava Orogen, northern Quebec. Part 2: Structural and metamorphic history. Canadian Journal of Earth Sciences; volume 29, pages 765-782.1992Source
LUCAS, S.B. – ST-ONGE, M.R.Syn-tectonic magmatism and the development of compositional layering, Ungava Orogen (northen Quebec, Canada). Journal of Structural Geology; volume 17, pages 475-491.1995Source
LUCAS, S.B. – ST-ONGE, M.R.Géologie, Montagne Pinguk, Québec – Territoire du Nord-Ouest; Commission géologique du Canada, carte 1912A, échelle 1/100 000.1997Carte 1912A
PARRISH. R.R.U-Pb geochronology of the Cape Smith Belt and Sugluk block, northern Quebec. Geoscience Canada; volume 16, pages 126-130.1989Source
PICARD, C. – LAMOTHE, D. – PIBOULE, M. – OLIVIER, R.R.Magmatic and geotectonic evolution of a Proterozoic oceanic basin system: the Cape Smith Thrust-Fold Belt (New Quebec). Precambrian Research; volume 47, pages 223-249.1990Source
ST-ONGE, M.R. – LUCAS, S.B. – PARRISH, R.R.Terrane accretion in the internal zone of the Ungava Orogen, northern Quebec. Part 1: tectonostratigraphic assemblages and their tectonic implications. Canadian Journal of Earth Sciences; volume 29, pages 746-764.1992Source
ST-ONGE, M.R. – SCOTT, D.J. – WODICKA, N.Terrane boundaries within Trans-Hudson Orogen (Quebec-Baffin segment), Canada: changing structural and metamorphic character from foreland to hinterland. Precambrian Research; volume 107, pages 75-91.2001Source

 

 

8 novembre 2018