May 2004 LIP of the Month

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(corresponds to events 150, 151, and 153 in LIP record database)

Ca. 1880 Ma Circum-Superior LIP

Richard E. Ernst
Geological Survey of Canada 601 Booth St.
Ottawa ON
Canada K1S 2S6

A belt of 1884-1864 Ma mafic- ultramafic rocks surrounds much of the Superior craton. Remarkably extensive, and with relatively tight age concentrations, this belt consitutes a Large Igneous Province (LIP), even though magmas were likely derived from more than one source. The belt continues for more than 3400 km and includes: the New Quebec orogen on the east (also called the Labrador Trough); the Cape Smith belt and eastern Hudson Bay on the north; the Thompson and Fox River belts on the northwest and the Marquette Range Supergroup in the south (Fig. 1). Coeval Pickle Crow dykes cross the interior of the western Superior craton and provide a link between Marquette Range Supergroup magmatism and that of the northwestern part of the Superior craton. The ca. 1880 Ma Circum-Superior belt represents a metallotect because of two major Ni-Cu mining districts, the Thompson Nickel belt in the northwestern Superior craton, and the Raglan and associated deposits in the Cape Smith belt.

The observation that most of this LIP was emplaced along the Superior cratonic margin during the development of adjacent orogens (Trans Hudson, New Quebec, and Penokean) led to models involving back arc rifting and foredeep flexure. However, models involving mantle plumes and breakup of a microcontinent have also been proposed. The ca. 1880 Ma Circum-Superior LIP is a focus of a three-year project by the Geological Survey of Canada (Natural Resources Canada) in collaboration with provincial and territorial partners (Quebec, Ontario, Manitoba, Saskatchewan and Nunavut) and industry.

Figure 1: Elements of the ca. 1880 Ma Circum-Superior LIP (in green). Numbers and letters are explained in Figure 2. Base map modified after Hoffman (1988) and Bleeker (2004).

Figure 2: 1 = Carbonatite feeder (Cheve and Machado 1988); 2 = Montagnais gabbro sills (Findlay et al. 1995; Machado et al. 1997), 3 = rhyodacite (Machado et al. 1997), 4 = Chukotat volcanics (St-Onge et al. 2000; Parrish 1989), 5 = Belcher and Sleeper Island sills (M.A. Hamilton, pers. comm.. 2003), 6 = Fox River sill (Heaman et al. 1986), 7 = Molson dykes (Heaman et al. 1986; Halls and Heaman 2000), 8 = Thompson belt mafic-ultramafic magmatism (Hulbert et al. 2004), 9 = Winnipegosis komatiite (Hulbert et al. 1994), 10 = Hemlock formation (Fralick et al. 2002), 11 = Gunflint formation (Scheinder et al. 2002), 12 = Pickle Crow dyke (Buchan et al. 2003; W. Davis, unpublished U-Pb age).

The Superior craton is the largest piece of Archean crust in the world. It represents the fragment remaining after early Proterozoic breakup on all its margins (e.g. Hoffman, 1988; Bleeker 2003, 2004). Subsequent ocean closure produced orogenic belts that circumscribe the Superior craton. The most prominent is the Trans Hudson orogen, which extends along the west and north sides of the craton (e.g. Hoffman, 1988; Lewry and Stauffer 1990). The Trans Hudson orogen formed during 1900-1800 Ma collision of the Superior craton with the Rae-Hearne craton (e.g. Hoffman, 1988, Van Kranendonk et al. 1993; Zwanzig 1999). Large oroclines are defined by the double promontory structure of the Superior craton (Thompson and Ungava salients) that appear to have originated during initial rifting (Gibb, 1983). On the northeast side of the Superior craton, the New Quebec orogen is linked to closure and collision with the southeastern Rae craton (e.g. Hoffman 1988; Wardle et al. 1990; Van Kranendonk et al. 1993). The southern margin of the Superior craton is marked by the Penokean orogeny, which resulted from 1900-1800 Ma closure of an ocean and a terminal collision with the Wisconsin arc terrane (e.g. Hoffman, 1988; Schneider et al. 2001). The southeast side of the Superior craton, was overprinted by the 1100 Ga Grenville orogen (Hoffman 1988; Rivers et al. in Percival et at. 2004); any Paleoproterozoic collision history in this region has been obscured by the Grenville orogen.

As these 1900-1800 Ma orogenic belts were developing peripheral to the Superior craton, the Superior margin itself was the site of extensive 1884-1864 Ma mafic-ultramafic magmatism. The links between many of these magmatic elements into a Circum-Superior magmatic belt was recognized early (e.g. Dimroth, 1972; Baragar and Scoates 1981, 1987; Arndt et al. 1987). However, inclusion of the Marquette Range Supergroup magmatism on the south side of the craton results from new age dating (Fralick et al. 2002; Schneider et al. 2002), and the discovery of 1880 Ma dykes (Pickle Crow swarm) in the western Superior craton, which link Thompson salient magmatism to the Marquette Range Supergroup (Buchan et al. 2003).

Because of the remarkable extent of this magmatic activity (3400 km measured along the periphery of the Superior craton from northeast to northwest sides, and perhaps another 1000 km to include the magmatism on the south side) and the relatively tight age grouping for magmatism (1884-1864 Ma), we apply the term Large Igneous Province (LIP) (Coffin and Eldholm 1994; Ernst and Buchan 2004). However, basic questions remain about this LIP, including its setting (e.g. plume, rifting, or back-arc), and indeed whether it represents a single event or has multiple causes (cf. plume/LIP cluster idea in Ernst and Buchan 2002).

Below we provide: 1) a brief summary of the magmatic elements of the ca. 1880 Ma Circum-Superior LIP, 2) references and web-links to more detailed information including the associated ore deposits, and 3) a list of outstanding questions related to this LIP that are being addressed by Geological Survey of Canada (Natural Resources Canada) in partnership with the provinces, territories and industry, “The Trans-Hudson / Superior Margin Mettalotect” ( Quoted ages in this article are based on the U-Pb method unless otherwise noted.

New Quebec Orogon (Labrador Trough; region A in figures)
The New Quebec orogen (also known as the Labrador Trough, Figure 1) contains two volcano-sedimentary sequences: Cycle 1, with magmatic ages of 2170-2140 Ma; and Cycle-2 with magmatic ages of 1883-1870 Ma (Le Gallais and Lavoie 1982; Skulski et al. 1993; Clark and Wares 2004). Sedimentary successions in Cycle 2 include turbidites and iron formation. Magmatism associated with Cycle-2 includes 1880 Ma carbonatites and lamprophyres (Dressler, 1978; Chevé and Machado 1988), 1883-1874 Ma mafic (and some ultramafic) magmatism (Willbob and Hellancourt formations and Montagnais sills) (Skulski et al. 1993; Rohon et al. 1993; Findlay et al. 1995; Machado et al. 1993, 1997), and late stage 1870 Ma felsic and carbonatitic magmatism (Machado et al. 1997). Geochemical relationships are detailed in Skulski et al. (1993). Some Cu-Ni-PGE deposits are associated with the Cycle-2 mafic-ultramafic magmatism (Clark and Wares 2004).

The Cycle-2 volcanic-sedimentary eocks have been explained as the deposits of pull-apart basin generated in response to the closing of the SE Rae craton against the Superior craton (Hoffman 1990; Wares and Skulski 1992; Skulski et al. 1993; van Kranendonk et al. 1993). An alternative model suggests this 1880-1870 Ma magmatism records separation of a microcontinent (“Meta Incognita”) from Cape Smith belt region that is now in southwestern Baffin Island (St-Onge et al. 2000).

Ungava Salient (region B in figures)
The Cape Smith belt of the Ungava salient consists of 2040- 1970 Ma Povungnituk volcano-sedimentary Group and the 1880 Ma Chukotat Group (Francis et al. 1983; Picard et al. 1990; St-Onge et al. 2000). The Chukotat Group is estimated to be 5.6 km thick (St-Onge and Lucas 1990), and consists of picritic to tholeiitic basalts intruded by thin mafic and ultramafic sills. Three lava types have been distinguished: olivine phyric, pyroxene-phyric and plagioclase phyric (Francis et al. 1983). The upper Chukotat volcanic rocks are dated at 1870 Ma (St-Onge et al. 2000). The lower Chukotat volcanic rocks have a high-Mg chemistry and are correlated with the Katiniq Suite sills that intrude the lower Povungnituk Group. Although Katiniq sills were dated at 1918 Ma (Parrish, 1989), more recent data and a reinterpretation of the original age suggests a ca. 1880 Ma age for the Katiniq sills (N. Wodicka, pers. comm. 2004). With this reinterpretation the entire Chukotat volcanic package is ca. 1880-1870 Ma.

Associated with the ultramafic Katiniq Suite sills are Cu-Ni deposits including Raglan (e.g. Barnes et al. 1982; Lesher and Keays 2002, and references therein; Naldrett 1999). This region is a focus of significant current exploration for Ni-Cu-PGE ores (

Chukotat Group magmatism may be linked to breakup and separation of a microcontinent (“Meta Incognita”) that is now in southwestern Baffin Island (St-Onge et al. 2000).

Eastern Hudson Bay Area (region C in figures)
Two volcanic sequences, Flaherty and Eskimo volcanics, are distinguished in the eastern arc of Hudson Bay. Based on paleomagnetic correlations, the Eskimo volcanics are linked with Richmond Gulf, Persillon, Pachi and Nastapoka Group volcanics (Chandler and Schwarz, 1980; Schwarz and Fujiwara, 1981; Chandler 1988), and with 1998 Ma Minto dykes (Buchan et al., 1998). The overlying Flaherty group is undated except for a Pb-Pb age of 1960+/-80 Ma (Todt et al. 1984). However, paleomagnetic data suggest a link with the Haig and Sutton Inlier sills (Schwarz and Fujiwara, 1981). Geochemical correlations indicate that the Flaherty group may be linked with the Povungnituk group (Legault et al., 1994; Modeland et al. 2003), and therefore may be 2.04-1.96 Ga. Of particular relevance to the present article, sills in the Belcher Islands and Sleeper Islands have recently yielded a ca. 1.87 Ga (M. Hamilton pers. comm. 2003) confirming that ca. 1880 Ma LIP is also present in this portion of the Circum-Superior belt.

Thompson Salient (region D in figures)
An important concentration of 1880 Ma magmatism is along the periphery of the Thompson salient of the Superior craton. The Fox River belt (Figure 1) consists of volcanics, sills and sediments (e.g. Scoates 1981). The sills have been dated at 1883 Ma (Heaman et al. 1986). Molson dykes parallel the northwest margin of the Superior craton (Ermanovics and Fahrig, 1975; Paktunç, 1987; Scoates and Macek 1978). U-Pb dating and paleomagnetic work distinguish 1883 Ma Molson dykes and an intermixed older 2090-2070 Ma swarm (Heaman et al. 1986; Zhai et al. 1994; Halls and Heaman 2000 and references therein). The Thompson Nickel belt (TNB Working Group 2001) ranks as one of the largest nickel producing areas in the world (Naldrett 1999; Hulbert et al. 2004). The region is also prospective for PGEs (e.g. Peck et al. 2000, 2002; Ernst and Hulbert 2003).

The age of the extensive mafic- ultramafic magmatism that hosts the Ni ore is poorly known. Recently however, an osmium isochron age has been determined for samples from a number of ore deposits that is consistent with a U-Pb zircon age of 1880+/-5 Ma determined for one mineralized sill (Hulbert et al. 2004). The possibly coeval Ospwagan Group (Scoates et al. 1977) is younger than 1974+/-50 Ma, based on the youngest detrital grain (Bleeker and Hamilton, 2001). Located beneath Phanerozoic cover to the southwest is the 1864 Ma Winnipegosis komatiite (Hulbert et al. 1994).

Various settings have been offered for the 1883-1864 Ma magmatism bordering in the Thompson salient of the Superior craton (Hulbert et al. 2004) including a marginal basin rifting event that post-dates F1 deformation (Bleeker 1990).

Marquette Range Supergroup (region in E in figures)
A clastic sedimentary assemblage containing iron formation is widespread in the Marquette Range Supergroup on the southern margin of the Superior craton near Lake Superior. These sediments are associated with magmatism that has recently been dated. The Hemlock formation is a bimodal sequence, and a rhyolite from this formation has now been dated at 1874+/-9 Ma (Schneider et al. 2002). Within the Gunflint formation a similar age of 1878.3+/-1.3 Ma has been obtained for a volcaniclastic unit (Fralick et al. 2002). Additional units that are linked include the Kiernan sills, and the Badwater volcanics (Ueng et al. 1988). These new ca. 1880 Ma ages are consistent with previous models for the origin of the Marquette Range Supergroup and associated magmatism. In one interpretation the volcano-sedimentary sequence may represent a foreland assemblage, with subsidence being driven ahead of the Penokean thrusting (Hoffman 1988; Schneider et al. 2002 and references therein) or may represent a back-arc basin (Ueng et al. 2002; Fralick et al. 2002 and references therein). A third model has been proposed for the magmatism (Buchan et al. 2003), wherein lateral flow through the Pickle Crow dykes (see below) transported magma from the Fox River belt region across the Superior craton for emplacement in the Marquette Range Supergroup. Such a model for long distance magma transport via dykes has also been advocated for the generation of 2215 Ma Nipissing sills from the Ungava radiating swarm of the eastern Superior craton (Buchan et al. 1998), and also in other cases (Ernst and Buchan 1997).

Interior western Superior craton (region F in figures)
Until recently the ca. 1880 Ma magmatism was only known from the margin of the Superior craton, and was unknown from the cratonic interior. However, recent Ar-Ar and U-Pb ages of ca. 1880 Ma on the Pickle Crow dyke (Buchan et al. 2003; W. Davis, pers. comm.. 2003) demonstrate that 1880 Ma magmatism is potentially widespread in the interior of the western Superior craton. The Pickle Crow and associated dykes are traced for at least 400 km and possibly more than 700 km across the western Superior craton from near the Fox River belt in the north to near Lake Superior in the south. As noted above, this craton-crossing magmatism provides a link between ca. 1880 Ma magmatic activity in the northwestern part of the Superior craton and that in the Marquette Range Supergroup on the south side of the Superior craton. Furthermore, the NNW trend of the Pickle Crow dykes and the predominant NNE trend of the Molson dyke swarm converge to a point north of the northwest Superior cratonic margin (Thompson salient), which may locate the center of a mantle plume responsible for part of the ca. 1880 Ma LIP (Buchan et al. 2003).

Outstanding Questions
The ca. 1880 Ma Circum-Superior LIP is a focus of a three-year project by the Geological Survey of Canada (Natural Resources Canada) in collaboration with provincial /territorial (Quebec, Ontario, Manitoba, Saskatchewan and Nunavut) and industry partners ( The ongoing work should provide some answers to outstanding questions related to this LIP, such as:

  1. What is the geodynamic setting for this LIP (e.g. back arc, rifting, plume)? Is a single event represented or are multiple causes required? Is the geochemical signature the same in all areas or are there significant regional differences?
  2. Until recently all the known magmatism has been located around the periphery of the Superior craton. With the discovery of the Pickle Crow dyke swarm cutting across the western Superior craton (Thompson salient), one can ask whether 1880 Ma dykes remain to be discovered elsewhere in the Superior craton particularly in the Ungava salient. Indeed, numerous dyke sets in the Superior craton remain undated (Buchan and Ernst 2004).
  3. Is there a link between 1880 Ma magmatism in the Superior Province, and similar age magmatism in the adjacent Trans Hudson belt (Stern et al. 1999; Zwanzig et al. 2001; Turek et al. 2000) and elsewhere in the world: e.g. East Kimberly event of Australia (event 147 in Ernst and Buchan 2001; Hoatson and Blake 2000) or Mashonaland event of Africa (event no. 157 in Ernst and Buchan 2001; ca. 1860 Ma, Wingate, pers. comm. 2004)? Are there implications for a proposed 1900 Ma global superplume event (Condie et al. 2000)?
  4. What controls the distribution of Ni-Cu-PGE mineralization in this ca. 1880 Ma mettalotect.

Thanks are given to Larry Hulbert for providing a preprint of Hulbert et al. (2004), and Wouter Bleeker for providing the digital basemap for Figure 1. Bill Davis, Mike Hamilton, Mike Wingate and Natasha Wodicka are thanked for allowing reference to unpublished U-Pb ages. This paper has benefited from ongoing discussions with Ken Buchan regarding Large Igneous Provinces.


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