|Author:||Dunphy and Ludden, 1998|
|Type area:||Ungava Orogen Northern Domain: Kovik Bay (NTS sheet 35F), Nuvilik Lakes (sheet 35G) and New Quebec Crater (sheet 35H)|
|Geological province:||Churchill Province|
|Geological subdivision:||Ungava Orogen / Ungava Trough / Northern Domain|
Taylor (1982) was the first to recognize the existence of a late intrusive assemblage in the northern part of the Ungava Orogen. The work of Lamothe et al. (1984, 2007), Tremblay (1989, 1991), Barrette (1990a, 1990b), St-Onge and Lucas (1993) and Dunphy (1994) showed that the suite’s lateral extension covers all units of the Northern Domain, namely the Watts, Parent and Spartan groups. Mathieu and Beaudette (2019) later introduced several plutons to individualize local intrusions in the Northern Domain.
The Cape Smith Suite is a series of peridotitic to granitic plutons located essentially in the Domain. They are massive and homogeneous in some areas, but more generally foliated or highly deformed. Larger intrusive bodies commonly exhibit compositional zoning or magmatic layering. The intrusive nature of contact with the host rock is generally clearly defined. Hornblende-biotite±clinopyroxene assemblages are largely replaced by epidote, tremolite-actinolite and chlorite, while plagioclase is almost entirely sericitized. This assemblage suggests metamorphism ranging from the greenschist to the lower amphibolite facies, similar to that of host rocks.
Cape Smith Suite 1 (pPcsi1): Peridotite, Pyroxenite
Intrusions of this unit occur in sheets 35G13, 35G14, 35G11 and 35G10, in the central portion of the Northern Domain. They are metric to kilometric in size (Taylor, 1982; Lamothe et al., 1984; Tremblay, 1991; Dunphy, 1994). A grey pyroxenite pluton previously part of the Watts Group (St-Onge and Lucas, 1989) was individualized by Mathieu and Beaudette (2019) and identified as the Illuinaqtuut Pluton.
Cape Smith Suite 2 (pPcsi2): Gabbro
Gabbroic intrusions of this unit are located in the centre of the Northern Domain, in sheets 35G11 and 35G12, and at the southern limit of the Northern Domain, in sheets 35F06, 35F07, 35G08 and 35G05. In the southern part, intrusions are elongated and parallel to regional foliation (Taylor, 1982; Lamothe et al., 1984; Moorhead, 1994; Tremblay, 1991; Dunphy, 1994).
Cape Smith Suite 3 (pPcsi3): Diorite, Monzonite
Several kilometric intrusions are hosted in the Watts, Spartan and Parent groups. They vary in composition from dioritic to monzodioritic, monzonitic and tonalitic. Most are massive to weakly foliated (Taylor, 1982; Lamothe et al., 1984; Tremblay, 1989, 1991; Barette, 1990a, b; Dunphy, 1994; St-Onge and Lucas, 1993). Mathieu and Beaudette (2019) report a zoned and layered intrusion (tonalite-diorite and diorite-gabbro) immediately west of Watts Lake (sheet 35G16), named Kinguppak Pluton.
Cape Smith Suite 4 (pPcsi4): Granodiorite, Granite, Tonalite
A total of ~15 kilometric hornblende-biotite tonalite plutons belonging to this subdivision cuts the Watts Group (St-Onge and Lucas, 1993). In addition, a large granodiorite pluton intruding into the Parent Group has been identified. It cuts a dioritic intrusion and contains diorite enclaves near the contact. This intrusion is deformed and composed of quartz, twinned plagioclase, microcline and perthite, as well as ferromagnesian minerals and muscovite. In south central sheet 35G15 (~8 km west of Serpentine Lake), the Watts Group is also cut by a pluton described as massive, unfoliated alaskite (Dunphy, 1994). Mathieu and Beaudette (2019) introduced the Qimmiq and Purtuniq plutons to individualize two tonalitic intrusions cutting the Watts Group, in sheets 35G16 and 35H13.
Thickness and Distribution
The size of these intrusions ranges from a few metres to >10 km in width.
This suite was dated (U-Pb) across its entire extent at several locations by Parrish (1989) and Machado et al. (1993). Ages range from 1898 +12/-9 Ma to 1836 ±3 Ma. The similarity of ages and compositions, coupled with the proximity of the suite to intrusive units of the Narsajuaq Arc, suggests a comagmatic relationship between the two plutonic units (St-Onge et al., 1992; Dunphy, 1994; Dunphy et al., 1995).
The Cape Smith Suite intruded into all Northern Domain allochtonous units and Parent Group units in sheets 35F06, 35F07 and 35F10 (Lamothe, 2007). The suite has a range of geochemical compositions very similar to the various intrusive suites of the Narsajuaq Arc. Also, the time interval for the emplacement of these two assemblages is very similar (Dunphy and Ludden, 1998). However, the isotopic signature of the Cape Smith Suite is more juvenile than that of the Narsajuaq Arc, indicating a low-intensity crustal contamination. The tectonic model proposed by Dunphy and Ludden (1998) involves partial melting of oceanic crust in an ocean-ocean subduction zone. Magmas from the Cape Smith Suite were reportedly intruded in an ocean crust assemblage (Watts Group), overlain by calc-alkaline volcanic units (Parent Group) and sedimentary units (Spartan Group). This island arc assemblage and its ocean floor were dismembered during the orogeny and accreted to the South Domain (Lucas and Onge, 1992; St-Onge and Lucas, 1992).
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Publications available through SIGÉOM Examine
Barrette, P D. 1990. Géologie de la région du lac Bolduc (Fosse de l’Ungava). MRN. ET 89-03, 48 pages and 3 plans.
Dunphy, J. 1994. Évolution des roches plutoniques du Domaine Nord de la Fosse de l’Ungava. MRN. MB 94-58, 54 pages.
Lamothe, D., Picard, C., Moorhead, J. 1984. Région du lac Beauparlant, bande de Cap Smith-Maricourt. MRN. DP-84-39, 2 plans.
Lamothe, D. 2007. Lexique stratigraphique de l’Orogène de l’Ungava. MRNF. DV 2007-03, 66 Pages et and Plan.
MATHIEU, G., BEAUDETTE, M. 2019. Géologie de la région du lac Watts, Domaine Nord, Fosse de l’Ungava, Nunavik, Québec, Canada. MERN. BG 2019-04.
Tremblay, G. 1989. Géologie de la Région du Lac Vanasse (Fosse de l’Ungava). MRN. ET 87-08, 29 pages and 2 plans.
Tremblay, G. 1991. Géologie de la région Du Lac Lessard (Fosse de l’Ungava). MRN. ET 88-09, 32 pages and 2 plans.
Dunphy, J.M., Ludden, J.N. 1998. Petrological and geochemical characteristics of a Paleoproterozoic magmatic arc (Narsajuaq terrane, Ungava Orogen, Canada) and comparisons to Superior Province granitoids. Precambrian Research; volume 91, pages 109–142. doi.org/10.1016/S0301-9268(98)00041-2.
Parrish, R.R. 1989. U-Pb geochronology of the Cape Smith Belt and Sugluk Block, northern Québec. Geoscience Canada; volume 16, pages 126–130. Source.
St-Onge, M.R., Lucas, S.B. 1989. Géologie, Lac Watts, Québec. Geological Survey of Canada, « A » Series Map 1721A, 1 sheet. doi.org/10.4095/127673.
St-Onge, M.R., Lucas, S.B., 1993. Geology of the eastern Cape Smith belt: parts of the Kangiqsujuaq, cratère du Nouveau-Québec, and lacs Nuvilik map areas, Quebec. Geological Survey of Canada, Memoir 438, 110 pages. doi.org/10.4095/183988.
Taylor, F.C. 1982. Reconnaissance geology of a part of the Canadian Shield, northern Quebec and Northwest Territories. Geological Survey of Canada, Memoir 399, 32 pages (7 sheets). doi.org/10.4095/109241.