DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Author:||Charette et al., 2016|
|Type area:||Jeannin Lake area (NTS sheet 24B)|
|Geological province:||Churchill Province|
|Geological subdivision:||Rachel-Laporte Lithotectonic Domain|
|Lithology:||Migmatites of sedimentary origin|
The Giton Complex was introduced in the Jeannin Lake area (Charette et al., 2016) to group heterogranular diatexites (ApPgit2) circumscribed to a thrust sheet of the Rachel-Laporte Lithotectonic Domain. Hence it is a structural complex. During the regional synthesis of the Southeastern Churchill Province (SECP), a second slice was identified in the Recouet Lake area and incorporated into this unit. The increased amount of migmatized paragneiss in this area led to the introduction of a new informal unit (ApPgit1).
The Giton Complex groups migmatites of sedimentary origin that form two thrust sheets in the Rachel-Laporte Lithotectonic Domain. This unit, characterized by a magnetic signature distinct from surrounding volcano-sedimentary rocks, is clearly visible on aeromagnetic maps. Migmatites were divided into two informal units: migmatized paragneiss (ApPgit1) and heterogranular diatexite (ApPgit2).
Migmatized paragneiss of unit ApPgit1 varies in composition from metapelite to meta-arenite to metawacke. Changes in the main minerals’ content locally induce banding. The amount of millimetric to centimetric leucosome bands fluctuates with the protolith (≤20%), increasing the banded appearance of the rock. Paragneiss is generally homogeneous and fine-grained. It is grey with a lighter alteration patina, locally beige to brownish. In thin sections, the matrix is well recrystallized. Micas (biotite and muscovite) make up 10-25% of the rock and form millimetric laminae marking foliation. Garnet commonly occurs as brown to pinkish crystals or porphyroblasts (1-5 mm). Staurolite locally occurs as small subhedral crystals within biotite and muscovite laminae. Accessory minerals (chlorite, opaque minerals, sphene, apatite, zircon and allanite) are also observed in small amounts. In places, actinolite forms felt clusters that preserve clinopyroxene cores. In some areas of unit ApPgit1, muscovite-biotite-garnet paraschist and garnet amphibolite form metric to hectometric layers.
Unit ApPgit2 consists of homogeneous diatexite whose composition varies from granodiorite to quartz monzodiorite. The rock is heterogranular, yellowish to brownish grey, and shows a well-developed foliation associated locally with a protomylonitic texture. Diatexite regularly contains 15-30% centimetric phenocrystals of plagioclase and K-feldspar. It also includes 15-25% quartz and 5-20% microcline, interstitial or as phenocrystals. Silicate minerals float in a fine-grained matrix rich in brown biotite (20-40%) containing sphene and zircon inclusions. The rock also contains some hornblende (<5%), as well as zoisite and allanite. Plagioclase is slightly sericitized. Quartz displays undulatory extinction and partial recrystallization at the edge of larger crystals. Diatexite contains up to 10% centimetric to decimetric enclaves and layers (“schollen” or rafts) of variably migmatized biotite ± garnet paragneiss similar to that of unit ApPgit1. Certain metre-wide diatexite layers show greater deformation indicated by anastomosed foliation and the transformation of phenocrystals into sigmoid porphyroclasts associated with recrystallization tails.
The Giton Complex is located in the southern portion of the Jeannin Lake area (Charette et al., 2016) and in the northern portion of the Recouet Lake area, where it forms two sheets oriented NW-SE within the Rachel-Laporte Lithotectonic Domain. The first sheet is ~28 km long by 7 km wide and consists mainly of unit ApPgit2 diatexite. The second form a 37 km-long by 8 km-wide antiform and consists mainly of unit ApPgit1 paragneiss.
Rocks of the Giton Complex have not been dated. However, in the Ungava Bay (Simard et al., 2013) and Saffray Lake (Lafrance et al., 2014) areas, protoliths of gneiss and deformed intrusive rocks that form thrust sheets of the Rachel-Laporte Domain are all Archean (2668-2883 Ma). These various thrust sheets are interpreted as having overthrusted Paleoproterozoic rocks during the New Quebec Orogenesis (1.82-1.77 Ga).
Wardle et al. (2002), Corrigan et al. (2009) and Simard et al. (2013) suggest that part of the Core Zone represents a fragment that separated from the Superior Province during rift opening in the Paleoproterozoic. Archean diatexites in this area could be correlated with units of the same type in the Ashuanipi Subprovince just west of the New Quebec Orogen. However, rocks of the Giton Complex could also be younger as they are similar to diatexites of the Winnie Suite whose crystallization was dated to ~1838 Ma.
Pending the results of geochronological analyses, Charette et al. (2016) interpreted migmatitic rocks of the Rachel-Laporte Domain like ancient rock slices that overthrusted rocks of the Laporte Supersuite during the New Quebec Orogenesis.
The presence of diatexites in the Rachel-Laporte Lithotectonic Domain suggests that the Giton Complex represents thrust sheets. This unit is therefore in fault contact with volcano-sedimentary rocks of the Laporte Supersuite.
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