|Author:||Verpaelst et al., 2000|
|Type area:||Koroc River area (NTS sheet 24I)|
|Geological province:||Churchill Province|
|Geological subdivision:||Core Zone|
Table des matières
The name “Kangiqsualujjuaq Complex” was introduced by Verpaelst et al. (2000) in the Koroc River area (NTS sheet 24I) to designate a tonalitic gneiss unit that is migmatitized to varying degrees. These authors assigned granitic gneiss and granitic intrusive rocks recognized in the same area to the Baudan Complex. This terminology was not repeated by Simard et al. (2013), Lafrance et al. (2014, 2015, 2016) and Charette et al. (2016), as it did not allow for regional-scale migmatitic zones to be distinguished from gneissic zones, as Taylor had done (1979). The migmatitic zones were thus assigned to the Qurlutuq Complex, while tonalitic and granitic gneiss were grouped together in the Ungava Complex. However, the synthesis work of the southeastern Churchill Province (SECP) has divided this area into various lithotectonic domains. Gneiss observed east of the Moonbase Shear Zone (MSZ) are now recognized as distinct from those identified in the Kuujjuaq and Ungava Bay region west of the Rivière George Shear Zone (RGSZ). Lafrance et al. (2015) noted a larger granitic component in the gneiss located east of the MSZ.
The Kangiqsualujjuaq Complex was redefined to group all the granitic to tonalitic grey gneiss located between the MSZ in the west and the Blumath Deformation Corridor (BDC) in the east. It therefore includes some of the grey granitic gneiss outcrops previously assigned to the Baudan Complex, but excludes migmatitized rocks derived from melting of these gneisses that were instead assigned to the Fougeraye Complex (Mathieu et al. 2018). The name Kangiqsualujjuaq comes from the northern namesake village located in sheet 24I12 at the mouth of the George River.
The Kangiqusualujjuaq Complex consists of gneiss cut by several Proterozoic granitic phases in the form of multiple intrusions and dykes that are an integral part of the complex. Gneiss also contain decimetric to decametric diorite and gabbro horizons and enclaves. The complex consists of three informal units: 1) a tonalitic gneiss unit (ApPkan1); 2) a granitic gneiss unit (ApPkan2); and 3) a banded gneiss unit (ApPkan3).
The gneiss composition of unit ApPkan1 is mostly tonalitic, but locally changes to a quartz diorite. It is medium to light grey and contains between 5 and 25% tonalitic millimetric to centimetric leucocratic bands. Some of these leucocratic bands represent leucosome. The rock is well foliated, fine to medium-grained, and shows partial recrystallization textures and fairly well-defined banding. This banding is generally accentuated by the presence of granitic intrusions subconformable to gneissosity. It contains between 8 and 15% ferromagnesian minerals in varying proportions from band to band. These minerals, mainly brown to green biotite with more variable amounts of hornblende, define strong foliation. Gneiss of unit ApPkan1 may contain up to 5% K-feldspar, interstitial or as exsolution, distributed heterogeneously in the rock. Quartz has ondulating extinction and felsic minerals usually show indented rims, indicating dynamic recrystallization. The main accessory minerals are, in order of importance, apatite, zircon, epidote, opaque minerals, sphene, muscovite and allanite. Plagioclase is weakly sericitized in places.
Kangiqusualujjuaq Complex 1a (ApPkan1a): Fine-Grained Tonalite
In some areas, the Kangiqsualujjuaq Complex contains decametric to kilometric horizons of homogeneous foliated biotite tonalite. These tonalites may represent late, non-foliated and undeformed Archean intrusions that have resisted deformation and partial melting during the Paleoproterozoic. The presence of small centimetric mobilisate bands in the tonalite indicates that it has still undergone some degree of partial melting. Tonalite is fine-grained, homogeneous, light grey to very light grey, even-grained and partially recrystallized. It contains 10-15% biotite and less than 8% K-feldspar.
Kangiqusualujjuaq Complex 1b (ApPkan1b): Dioritic Gneiss
The darkest and predominantly dioritic gneissic rocks have been assigned to subunit ApPkan1b. This unit forms thin klippes less than 2 km wide inside other gneiss units of the Kangiqsualujjuaq Complex. It also occurs as centimetric to metric horizons within the ApPkan1 tonalitic gneiss. The rock is characterized by alternating millimetric to decimetric bands of diorite, quartz diorite and tonalitic whitish mobilisate (10-25%). Some decimetric horizons are more affected by partial melting. Biotite and amphibole are present in greater proportion than in unit ApPkan1 (15-35%), particularly with hornblende. Accessory minerals observed under the microscope are sphene (<1%), K-feldspar (<2%), epidote, apatite, allanite, opaque minerals and zircon. The rock shows a granoblastic texture, but a slight orientation of all mineral phases can be observed. Hornblende contains quartz and plagioclase inclusions.
In outcrop, granitic gneiss of unit ApPkan2 is difficult to differentiate from tonalitic gneiss of unit ApPkan1. It has a light grey colour and contains granitic or granodioritic whitish and pinkish bands that are conformable with gneissosity. Study of thin sections and stains revealed the high percentage of K-feldspar (20-35%) and a lower overall proportion of ferromagnesian minerals (4-12%) in the form of aligned biotite flakes containing zircon inclusions. Gneiss is fine-grained with foliation defined by biotite alignment and a beginning of preferential orientation of the quartzofeldspathic matrix. K-feldspar grains are evenly distributed in rock and have undergone moderate to high recrystallization, as have plagioclase and quartz grains. Quartz has undulating extinction and myrmekites are present. Accessory minerals are sparse and consist of epidote, allanite, apatite, opaque minerals, zircon, hematite, sphene and muscovite. Weak alterations are observed in places such as plagioclase sericitization and biotite choritization.
Kangiqusualujjuaq Complex 2a (ApPkan2a): Monzonitic to Monzodioritic Gneiss
Locally, there is an occurrence of intermediate potassic gneiss that have been grouped together in subunit ApPkan2a. In the field, these gneisses have been described as dioritic gneiss more or less migmatitized similar to those of subunit ApPkan1b. However, study of thin sections and stains revealed the presence of significant amounts of K-feldspar, giving these rocks a composition that varies from monzodiorite to monzonite. The ApPkan2a rocks contain between 20 and 30% green hornblende and brown biotite, and usually contain bands rich in accessory minerals, the main ones being epidote, sphene, opaque minerals, apatite and allanite.
Unit ApPkan3 is characterized by tonalitic gneiss similar to that of unitApPkan1, but contains between 25 and 45% millimetric to centimetric pink granite bands parallel to gneissosity. These bands are fine to medium-grained, partially recrystallized and have undergone the same deformation as the tonalitic portion of the gneiss. This unit could represent areas where Archean tonalites have been cut by pretectonic granite dykes. Both phases would then have been deformed, folded and paralleled by deformation and metamorphism. Gneiss is partially recrystallized and grain rims are generally indented. Ferromagnesian minerals (5-15%) are dominated by biotite, locally partially chloritized, with some hornblende locally. The main accessory minerals are opaque minerals, epidote, sphene, apatite and zircon.
The Kangiqsualujjuaq Complex covers a significant area in the regions of Henrietta Lake (Lafrance et al., 2015), Brisson Lake (Lafrance et al., 2016) and Koroc River (Verpaelst et al., 2000; Mathieu et al., 2018). It is limited to the west by the Moonbase Shear Zone (MSZ), which runs north on the Rivière George Shear Zone (RGSZ), and east on the Blumath Deformation Corridor (BDC). Units ApPkan1 and ApPkan2, which are similar in size, are the most important. They form strips that are several kilometres wide and are followed for several kilometres. The other units and subunits form smaller klippes.
Datings from several gneiss samples (David et al., 2009; Davis et al., 2014, 2018) resulted in Archean crystallization ages and Paleoproterozoic metamorphic ages. The large spread of Archean ages (2.9-2.6 Ga) indicates a complex geological evolution.
Until now, the ages obtained in tonalitic gneiss of the Kangiqsualujjuaq Complex (ApPkan1) have been older than those obtained in the gneiss of the same composition of the Ungava Complex (ApPung2), west of the RGSZ (2723 and 2803 Ma). Metamorphic ages of the Kangiqsualukjjuaq Complex also appear to be older than those of the Ungava Complex, more in line with the deformation associated with the Torngat Orogen (1885-1800 Ma; Charette 2016) than that of New Quebec (1840-1770 Ma).
|Isotopic System||Mineral||Unit||Crystallization Age (Ma)||(+)||(-)||Inherited Age (Ma)||(+)||(-)||Metamorphic Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||ApPkan1||2861||11||11||1874||31||31||Davis et al., 2014 (2011-MS-0070A)|
|U-Pb||Zircon||ApPkan1||2896||5||5||1871||15||15||Davis et al., 2018 (2013-MP-0090)|
|5||5||David et al., 2009 (98-SP-4044A1)|
|U-Pb||Zircon||ApPkan1||>2767||15||15||1848||14||14||David et al., 2009 (98-SP-4044A1)|
|U-Pb||Zircon||ApPkan2||2,62 Ga||David et al., 2009 (98-SP-4079A)|
The Kangiqsualujjuaq Complex is one of the oldest units in the Core Zone. It is the host rock of the majority of Paleoproterozoic intrusive units; it also forms enclaves in these same units. The Kangiqsualujjuaq Complex gneiss enclaves are particularly prevalent in migmatitic rocks and whitish intrusions of the Fougeraye Complex (pPfog), which are interpreted as the result of partial melting of the gneiss.
Does not apply.