DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Author:||Simard et al., 2013|
|Type area:||Kuujjuaq and Ungava Bay area (NTS sheet 24K)|
|Geological province:||Churchill Province|
|Geological subdivision:||Rachel-Laporte Lithotectonic Domain|
|Lithology:||Metamorphosed volcano-sedimentary rocks|
In the 1940s, geologists at Labrador Mining and Exploration introduced the term “Laporte Series” to describe schists, gneiss and amphibolites located NE of Schefferville, in the Laporte Lake area (Frarey and Duffell, 1964). Harrison (1952) formalized this unit as the Laporte Group. In the southern portion of the Quebec part of the New Quebec Orogen, Baragar (1967) designated metamorphosed rocks located east of the Labrador Trough as the Younger Complex, considering that metamorphism had obliterated primary structures of rocks and that the relative age of these units could not be established. However, this term was not used in subsequent work, as authors preferred the term “Laporte Group” (Frarey, 1967; Dimroth, 1978; Dressler, 1979; Girard, 1995). In the Kuujjuaq area (sheet 24K), Goulet (1995) assigned metamorphosed rocks equivalent to the Laporte Group to the Thévenet Formation (Sauvé and Bergeron, 1965), a term that was not used in subsequent work. In the Déborah Lake area, Girard (1995) reassigned some of Laporte Group rocks to the Deborah Formation, considering that in this area, paraschists have a mappable extent, consistency, internal homogeneity and established stratigraphic position. Metamorphosed rocks of the Laporte Group were considered by various authors to be equivalent to several units of the Kaniapiskau Supergroup (Labrador Trough). However, the metamorphic grade achieved in these rocks resulted in them losing their primary structures, which led Simard et al. (2013) to replace the term “Laporte Group” with “Laporte Supersuite”. This designation places this regional-scale unit among higher-ranking lithodemic units, equivalent to a supergroup, in accordance with the North American Stratigraphic Code (1983, 2005). The Laporte Supersuite thus combines all Paleoproterozoic metamorphosed supracrustal rocks of the Rachel-Laporte Lithotectonic Domain.
The New Quebec Orogen is divided into two large lithotectonic units: the Labrador Trough to the west and the Rachel-Laporte lithotectonic domain to the east. Several names were used to designate the Rachel-Laporte Lithotectonic Domain. The term “Rachel Zone” was used in the northern portion (Wares and Goutier, 1989, 1990; Wardle et al., 1990; Hall et al., 2002) and the names “Laporte Terrane” (Wardle et al., 1990; Hall et al., 2002) and “Laporte Domain” (Van der Leeden et al., 1990) in the southern portion. Wardle and Van Kranendonk (1996), then Wardle et al. (2002) used the term “Rachel-Laporte Zone” to refer to the lithotectonic domain forming the eastern part of the New Quebec Orogen. This term has also been used by Hammouche et al. (2011) in the southern part of the Southeastern Churchill Province (SECP), and by Simard et al. (2013), Lafrance et al. (2014) and Charette et al. (2016), in the northern and central parts of the SECP. In 2018, Lafrance et al. proposed the new name “Rachel-Laporte Lithotectonic Domain” as part of the SECP regional synthesis. As mentioned above, Simard et al. (2013) assigned all Paleoproterozoic metamorphosed volcano-sedimentary rocks of the Rachel-Laporte Lithotectonic Domain to the Laporte Supersuite. The Rachel-Laporte Lithotectonic Domain also contains Archean structural complexes connected to thrust sheets in fault contact with Paleoproterozoic metamorphosed volcano-sedimentary rocks.
A regional compilation of the southern part of the SECP by the Ministère’s geologists in 2003 divided rocks of the Rachel-Laporte Lithotectonic Domain (pPLAP) into 14 informal units. In the Bonaventure Lake area, Hammouche et al. (2011) recognized units pPLAP1 and pPLAP5, and defined two new informal units (pPLAP15 and pPLAP16). As part of the SECP regional synthesis (Lafrance et al., 2018), these informal units were abandoned. They were reassigned to the Freneuse, Klein or Grand Rosoy suites, depending on their composition and origin.
In the Déborah Lake area, Girard (1995) divided the Laporte Group (now Laporte Supersuite) into four lithodemic packages: the Deborah Formation, Grand Rosoy Formation, De Jeu Gabbro and Manereuille Complex. With the exception of the Grand Rosoy Formation (now redefined as the Grand Rosoy Suite and reassigned to the Baleine Lithotectonic Domain), rocks of other units were also reassigned to the Freneuse and Klein suites, depending on their composition.
The Préville Suite was later introduced in the Jeannin Lake area (Charette et al., 2016).
The Laporte Supersuite was divided into two suites by Simard et al. (2013): the Klein Suite, which includes all metamorphosed mafic and ultramafic rocks of effusive or intrusive origin, and the Freneuse Suite, which groups metasedimentary rocks. In the Jeannin Lake area, Charette et al. (2016) added a third suite, the Préville Suite, to group mafic calcosilicate rocks and carbonate gneiss. In the southern part of the SECP, the Grand Rosoy Suite, which consists of meta-arkoses and paraschists, was also included in the Laporte Supersuite.
The Laporte Supersuite is the dominant unit of the Rachel-Laporte Lithotectonic Domain that represents the eastern part of New Quebec Orogen. It is ~550 km long and 20-35 km wide, along general NW-SE orientation, and is adjacent to the eastern limit of the Labrador Trough.
Protoliths of Laporte Supersuite metamorphic rocks have not been dated. It is possible that Laporte Supersuite rocks are largely equivalent to rocks of the Kaniapiskau Supergroup (Simard et al., 2013), located in the Labrador Trough just to the west. However, recent mapping indicates that the metasedimentary rocks of the Laporte Supersuite (Freneuse Suite) differ from those of the Labrador Trough by a greater apparent thickness and a more homogeneous composition.
The Labrador Trough consists of a Paleoproterozoic volcano-sedimentary sequence deposited at the margin of the Archean Superior Craton between 2.2 Ga and 1.87 Ga (Clark and Wares, 2004). This sequence was folded, overthrusted and metamorphosed during collision between the Superior and the Core Zone during the New Quebec Orogenesis (1.82-1.77 Ga).
The Laporte Supersuite covers the entire Rachel-Laporte Lithotectonic Domain, which forms the eastern part of the New Quebec Orogen. It is limited to the west and east by thrust faults. It is also in fault contact with various Archean or Proterozoic structural complexes that are, north to south: the Boulder, Rénia, Highfall, Boullé, Wheeler and Giton complexes (Simard et al., 2013; Lafrance et al., 2014; Charette et al., 2016). These complexes correspond to thrust sheets that overthrusted Paleoproterozoic rocks during the New Quebec Orogenesis.
Volcano-sedimentary units of the Laporte Supersuite are locally intruded by dykes or sills of granite and pegmatitic granite of the Mercier Suite.
Does not apply.