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|Author(s):||Charette et al., 2016|
|Type area:||Area of Jeannin Lake (NTS sheet 24B)|
|Geological province:||Churchill Province|
|Geological subdivision:||Rachel-Laporte Lithotectonic Domain|
|Lithology:||Meta-arkose and conglomeratic meta-arenite|
The Secondon Suite was introduced in the Jeannin Lake area (Charette et al., 2016) to group well-preserved metasedimentary rock sequences in the south-central part of the Southeastern Churchill Province (SECP). As part of a synthesis of the SECP (Lafrance et al., 2018) and consequently to geochronological results, some rocks previously assigned to this suite have been assigned to the Grand Rosoy Suite in the Baleine Lithotectonic Domain (Lafrance et al., 2020). The Secondon Suite is now restricted to the Rachel-Laporte Lithotectonic Domain (Lafrance and Vanier, 2021).
The Secondon Suite consists of meta-arkose, conglomeratic meta-arenite, metaconglomerate and muscovite-hematite-specularite schist. Metasedimentary rocks are fine grained, non-magnetic, slightly to well foliated and pale, either greenish beige, grey-beige or pink. They commonly display centimetric to metric bedding expressed by variations in quartz, feldspar and muscovite contents, as well as by the presence or absence of felsic rock fragments. Meta-arkose and lithic meta-arenite are generally enriched in quartz (30-85%), depleted in ferromagnesian minerals (2-5%), and contain 10-40% K-feldspar and 15-60% plagioclase. They also contain muscovite (5-35%), small disseminated hematite clusters (2-5%) and specularite (2-15%). This last phase occurs in various forms: disseminated, in clusters, in laminae or in bands regularly arranged along the planes defined by the alignment of muscovite flakes or at the edge of fragments.
In some areas, the rock is more enriched in muscovite and consists of schist. Centimetric bands of muscovite schist are also interstratified in meta-arkose and conglomeratic meta-arenite sequences. Locally, metasedimentary rocks are slightly granular and may be confused with granitic rocks. Intrusive granitic rocks within this suite are not excluded; however, mineral phases present in these lithologies are identical.
Conglomeratic meta-arenite and metaconglomerate are mature and contain 10-55% non-joint and subrounded fragments (0.3-3 cm long by 0.1-1 cm wide, locally up to 20 cm by 4 cm). These fragments consist of white, grey or pinkish pebbles and cobbles, composed of quartz, K-feldspar, granite and granodiorite. In more deformed areas, clasts are lenticular with recrystallization tails.
Metasedimentary rocks are composed of a fine-grained, even-grained quartzofeldspathic matrix. Quartz grains are subrounded to rounded. Plagioclase is weakly sericitized and regularly contains quartz inclusions. Biotite, where present, occurs as small, very pale flakes rarely chloritized. At least two generations of muscovite, one transparent and the other yellowish (ferriferous) in stockier flakes, are observed in thin sections. Micas are most commonly aligned in foliation, but randomly arranged flakes in radial-fibrous form or superimposed on the main foliation are also observed. Muscovite locally forms millimetric to centimetric lenticular nodules in association with quartz and hematite. Accessory minerals include epidote, apatite, zircon and carbonate.
Thickness and distribution
The Secondon Suite forms metasedimentary sequences <6 km wide, located in the south-central part of the Rachel-Laporte Domain. It covers an estimated area of 58 km2.
The Secondon Suite is observed mainly in the vicinity of tectonic slices of the Boullé and Horseshoe complexes. It could thus be derived from the erosion of these rocks (Lafrance and Vanier, 2021). The setting could be similar to that of metasedimentary rocks of the Milamar Formation defined by Dimroth (1978) in the Labrador Trough. This unit consists of arkose, conglomerate and quartzite. Tectonic slices and their cover of sedimentary rocks (Secondon Suite) were then carried (as sheets) over Paleoproterozoic volcano-sedimentary rocks of the Laporte Supersuite during the formation of the New Quebec Orogen (Lafrance and Vanier, 2021).
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Publications Available Through SIGÉOM Examine
CHARETTE, B., LAFRANCE, I., MATHIEU, G., 2016. Géologie de la région du lac Jeannin, Québec, Canada. MERN; BG 2015-01BG 2015-01, 1 plan. Disponible à https://gq.mines.gouv.qc.ca/bulletins-geologiques/lac-jeannin/.
DIMROTH, E., 1978. Région de la fosse du Labrador entre les latitudes 54° 30′ et 56° 30′. MRN; RG 193RG 193, 417 pages, 16 plans. Disponible à https://gq.mines.gouv.qc.ca/documents/EXAMINE/RG193.
LAFRANCE, I., CHARETTE, B., VANIER, M-A., 2018. Sud-est de la Province de Churchill, Nunavik, Québec, Canada : synthèse de la géologie. MERN; BG 2018-12BG 2018-12 Disponible à https://gq.mines.gouv.qc.ca/bulletins-geologiques/churchill/.
LAFRANCE, I., VANIER, M-A., CHARETTE, B., 2020. Domaine lithotectonique de Baleine, sud-est de la Province de Churchill, Québec, Canada : synthèse de la géologie. MERN; BG 2020-07BG 2020-07, 4 plans. Disponible à https://gq.mines.gouv.qc.ca/bulletins-geologiques/churchill/baleine/.
LAFRANCE, I., VANIER, M.-A., 2021. Domaine lithotectonique de Rachel-Laporte, Sud-est de la Province de Churchill, Québec, Canada : synthèse de la géologie. MERN; BG 2021-01, 1 plan.
Ministère de l’Énergie et des Ressources naturelles (MERN). Secondon Suite. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-de-churchill/suite-de-secondon_en [accessed on Day Month Year].
Isabelle Lafrance, P. Geo., M.Sc. firstname.lastname@example.org (redaction)
Mona Baker, P. Geo., M.Sc. (coordination); Thomas Clark, P. Geo., Ph.D. and James Moorhead, P. Geo., M.Sc. (critical review); Claude Dion, Eng., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); Caroline Thorn (HTML editing).
Mehdi A. Guemache, P. Geo., Ph.D. (coordination); Carl Bilodeau, P. Geo., M.Sc. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); André Tremblay (HTML editing).