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).

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.

Dating

None