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Narsajuaq ArcTranslation of original French

 

 

First published: 24 May 2018
Last modified: 

 

 

Background

The Narsajuaq Arc was first mapped by Taylor (1982). The latter assigned an Aphebian age (Paleoproterozoic) to intrusive rocks located north of the Sud Domain (also known as the Cap Smith Belt and Ungava Trough). The works of Parrish (1989), St-Onge and Lucas (1990) and Lucas and St-Onge (1991) characterise this plutonic (and sedimentary) assemblage as two entities: one of Archean age, the Kovik Antiform, and the other of Paleoproterozoic age, the Narsajuaq Arc. The term “Narsajuaq Arc” was defined as a mapping unit in the synthesis of the Ungava Orogen (Lamothe, 2007). Charette and Beaudette (2018) abandoned this Narsajuaq Arc definition, considering it rather a lithotectonic domain. These authors then introduced the Narsajuaq Complex cartographic unit to describe the geological units mapped during historical work. In addition, in the Cape Wolstenholme region mapped at a scale of 1:100,000 by the Ministère in summer 2017, lithologies of the western arc were instead divided into complexes and suites, the main ones being Pingasualuit Complex (pPpgs), Suluraaq Suite (pPslq), Nallujuaq Suite (pPnal), Tasialuk Allipaaq Complex (pPali) and Sanningajualuk Suite (pPsnn).

Description

The lithotectonic domain of the Narsajuaq Arc is located in the northern portion of the Ungava Orogen at the northern tip of Quebec. This domain is in tectonic contact with the Kovik Antiform to the south. It also forms an axial trough in the centre of the antiform, separating the northern bedrock into two blocks (east and west antiform). In the western portion of the arc, the Sugluk Suture marks the southern boundary of the west Kovik Antiform.

Geology

The Narsajuaq Arc consists of gneissic, intrusive and metasedimentary units with metamorphic facies ranging from granulites to amphibolites. Paragneiss klippes are generally limited in thickness within the arc, with the exception of the northern portion of the Cape Wolstenholme region where larger strips were observed. In this area, Charette and Beaudette (2018) report that orthogneiss is distinguished from the rest of the arc by its amphibolite facies metamorphic assemblages and its intense deformation. These authors believe the presence of folded mylonites would indicate a polyphase evolution and therefore a tectonometamorphic signature different from the rest of the Narsajuaq Arc.

Relationships between the units are usually obliterated by the E-W regional fabric, which induces fine imbrication of lithologies on an hectometric to kilometric scale. However, it is possible to recognize the emplacement of intrusive rocks, synchronous or posterior to the Ungava Orogen, such as granulitic felsic intrusions (Navvaataaq Suite), likely polyphase potassic granitoids (Tasialuk Allipaaq Complex and Sanningajualuk Suite) and intermediate and mafic intrusions (Ivitaruq Suite and Nauyuk Suite).

Geological Evolution

The Narsajuaq Arc is interpreted as a magmatic terrane comprising three phases of intrusions (Dunphy and Ludden, 1998 and references cited), namely the ancient plutonic suite (1863-1844 Ma), the recent plutonic suite (1836-1821 Ma) and the late plutonic suite (1803-1800 Ma). The petrogenesis of these intrusive rocks implies significant crustal contamination (Dunphy and Ludden, 1998). In addition, the geological evolution of this terrane is polyphase.

First, the ancient plutonic suite would have intruded around 1860 Ma, possibly into an Archean craton. This hypothesis is based on: 1) Sm-Nd model ages obtained from samples belonging to the ancient plutonic suite (extraction age of the depleted mantle varying from 1.97 to 3.11 Ga; Dunphy and Ludden, 1998); and (2) on Rb-Sr isochrone timelines of metasedimentary rocks of the Sugluk Group that indicate their source is possibly Paleoproterozoic to Archean (Doig, 1987). For example, several authors have defined an Archean to Paleoproterozoic terrane that includes intrusions of the magmatic arc, sedimentary rocks and possibly the Archean bedrock. Several names have been given to this terrane, such as the Ungava Terrane (St-Onge et al., 2001), the Sugluk Terrane or Block (Hoffman, 1985; St-Onge and Lucas, 1990; Corrigan et al., 2009) or the Narsajuaq Terrane (Lucas and St-Onge, 1991; St-Onge et al., 2009).

Intrusive rocks of the ancient plutonic suite are the only ones to have recorded an intra-arc tectonometamorphic event (D1-M1) associated with metamorphic conditions of the granulite facies (Lucas and St-Onge, 1992). These conditions would have developed during accretion of the magmatic terrane in the Meta Incognita Peninsula around 1.85 Ga (Corrigan et al., 2009). The recent and anatectic plutonic suites, sometimes denoted Narsajuaq Arc sensu stricto, intrude into the ancient plutonic suite and Meta Incognita block.

The collision between the Narsajuaq-Meta Incognita assemblage and the Superior Province would have occurred during the Ungava Orgenesis, approximately 1.82 to 1.80 Ga. This collision would have resulted in regional deformation and metamorphism to the amphibolite facies affecting all of the Narsajuaq Arc lithologies, with the exception of post-tectonic intrusions.

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 de l’Énergie et des Ressources naturelles, Québec2018Bulletin géologiQUE
BARAGAR, W.R.A.Geology of part of Kovik Bay map area (NTS 35-F). Geological Survey of Canada; Open File 7846, 21 pages.2015Source
CORRIGAN, D. – PEHRSSON, S. – WODICKA, N. – DE KEMP, E.The Paleoproterozoic Trans-Hudson Orogen: a prototype of modern accretionary processes. Geological Society, London, Special Publications; volume 327, pages 457-479.2009Source
DOIG, R.Rb-Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith fold belt, Quebec. Canadian Journal of Earth Sciences; volume 24, pages 813-825.1987Source
DUNPHY, J.M. – LUDDEN, J.N.Petrological and geochemical characteristics of a Paleoproterozoic magmatic arc (Narsajuaq terrane, Ungava Orogen, Canada) and comparisons to Superior Province granitoids. Precambrian Research; volume 91, issues 1-2, pages 109-142.1998Source
HOFFMAN, P.F.Is the Cape Smith belt (northern Quebec) a klippe? Canadian Journal of Earth Sciences; volume 22, pages 1361-1369.1985Source
LAMOTHE, D.Lexique stratigraphique de l’Orogène de l’Ungava. Ministère des Ressources naturelles, Québec; DV 2007-03, 62 pages.2007DV 2007-03
PARRISH, R.R.U-Pb geochronology of the Cape Smith Belt and Sugluk block, northern Quebec. Journal de l’Association Géologique du Canada, Volume 16, numéro 3, pages 126-130.1989Source
ST-ONGE, M. R. – VAN GOOL, J.A.M. – GARDE, A. A. – SCOTT, D.J. Correlation of Archean and Palaeoproterozoic units between northeastern Canada and western Greenland: constraining the pre-collisional upper plate accretionary history of the Trans-Hudson orogen. Geological Society, London, special publication; volume 318, pages 193-235.2009Source
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
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. Revue canadienne des sciences de la Terre; 1992, volume 29, n°4, pages 765-782.1992Source
ST-ONGE, M.R. – LUCAS, S.B.Early Proterozoic collisional tectonics in the internal zone of the Ungava (Trans-Hudson) orogen, Lacs Nuvilik and Sugluk map areas, Québec. Commission Géologique du Canada; papier 90-1C, pages 119-132.1990
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
TAYLOR, F.C.Reconnaissance geology of a part of the Canadian Shield, northern Quebec and Northwest Territories. Commission géologique du Canada; Mémoire 399, 32 pages.1982Source

 

 

16 octobre 2018