La nature et l'évolution du contact entre le Domaine de Kovik ...

© Thierry Karl Gélinas, 2022

La nature et l’évolution du contact entre le Domaine de Kovik et le Domaine Nord, Orogène de l’Ungava, Nord

du Québec

Mémoire

Thierry Karl Gélinas

Maîtrise interuniversitaire en sciences de la Terre - avec mémoire

Maître ès sciences (M. Sc.)

Québec, Canada

La nature et l’évolution du contact entre le Domaine de

Kovik et le Domaine Nord, Orogène de l’Ungava, Nord du

Québec

Mémoire par insertion d’article

Thierry Karl Gélinas

Sous la direction de :

Carl Guilmette, directeur de recherche

Kyle Larson, codirecteur de recherche

ii

Résumé

L’Orogène de l’Ungava correspond à la branche nord-est de l’Orogène Trans-Hudsonien et

est situé sur la péninsule de l’Ungava dans le nord du Québec. La présence d’une éclogite de

1,8 Ga au sein du Domaine de Kovik dans l’Orogène de l’Ungava a été utilisée pour proposer

une tectonique des plaques moderne active au Paléoprotérozoïque. Cette étude vise à

contraindre la cinématique, la température et la chronologie de la déformation associée à une

structure interprétée comme ayant permis l’exhumation de cette éclogite, la zone de

cisaillement séparant le Domaine de Kovik du Domaine Nord. Nous avons combiné les

observations de terrain le long de transects à travers le contact entre le Domaine de Kovik et

le Domaine Nord, l’analyse microstructurale du quartz et de la titanite et des datations U-Pb

sur titanite. Deux zones de cisaillement, localisées dans les orthogneiss du domaine de Kovik,

ont été identifiées. La zone de cisaillement principale, distale au contact, est caractérisée par

une cinématique de sommet-vers-le-sud et des fabriques d’axes-c du quartz associées à une

déformation en aplatissement. La zone de cisaillement secondaire, proximale au contact, est

caractérisée par une cinématique de sommet-vers-le-nord et des fabriques d’axes-c du quartz

associées à une déformation plane. La température de déformation est contrainte à 627 et 580

± 50°C pour les zones de cisaillement principale et secondaire, respectivement. La

géochronologie U-Pb sur titanite a permis de définir deux populations de titanite. La vielle

population, contrainte à 1890 Ma, est contemporaine de la mise en place de la grande

province ignée du Circum-Supérieur. La jeune population, contrainte à 1740 Ma, est

interprétée comme représentant la réinitialisation de la vieille population pendant un épisode

de déformation tardive possiblement relié à l’effondrement de l’orogène. Nous interprétons

que le contact entre le Domaine de Kovik et le Domaine Nord représente un détachement.

iii

Table des matières

Résumé ................................................................................................................................... ii

Table des matières ................................................................................................................. iii

Liste des figures ...................................................................................................................... v

Liste des tableaux .................................................................................................................. vi

Remerciements .................................................................................................................... viii

Avant-propos ......................................................................................................................... ix

Introduction ............................................................................................................................ 1

Contexte géologique ............................................................................................................ 2

Chapitre 1: Constraining the nature and timing of the contact between the Kovik Domain

and Northern Domain, Ungava Orogen, Northern Québec .................................................... 5

1.1 Résumé .......................................................................................................................... 5

1.2 Abstract ......................................................................................................................... 6

1.3 Introduction ................................................................................................................... 7

1.4 Geological setting ......................................................................................................... 8

1.4.1 The Ungava Orogen ............................................................................................... 8

1.4.2 Tectonic and metamorphic history of the Kovik Domain .................................... 12

1.5 Field observations and sampling ................................................................................. 15

1.6 Methodology ............................................................................................................... 18

1.6.1 Petrography .......................................................................................................... 18

1.6.2 Quartz c-axis analysis........................................................................................... 19

1.6.3 Opening angle and deformation temperature ....................................................... 19

1.6.4 μ-XRF Maps and titanite grains imaging (EPMA/EBSD) ................................... 20

1.6.5 U-Pb geochronology and geochemistry by Laser Ablation Inductively Coupled

Plasma Mass Spectrometry (LA-ICPMS) ..................................................................... 21

1.6.6 Zr-in-titanite thermometry.................................................................................... 22

1.7 Results ......................................................................................................................... 22

1.7.1 Petrography and microstructures .......................................................................... 22

1.7.2 Quartz c-axis analysis........................................................................................... 26

1.7.3 Opening angles and deformation temperature ..................................................... 29

1.7.4 Microstructural features and trace element zoning of titanite .............................. 30

iv

1.7.5 Titanite U-Pb geochronology ............................................................................... 31

1.7.6 Zr-in-titanite thermometer .................................................................................... 33

1.8 Discussion ................................................................................................................... 34

1.8.1 Microstructures and temperature of deformation ................................................. 34

1.8.2 Structural interpretations ...................................................................................... 35

1.8.3 Interpretation of titanite geochronology ............................................................... 37

1.8.4 Evolution of the contact between the Kovik Domain and the Northern Domain 40

1.8.5 Comparison between the Kovik Domain and the Tso Morari Nappe .................. 40

1.9 Conclusion .................................................................................................................. 42

1.10 Acknowledgements ................................................................................................... 44

1.11 References ................................................................................................................. 45

1.12 Supplementary data: BSE, EPMA, EBSD and tables ............................................... 45

Conclusion ............................................................................................................................ 61

Bibliographie ........................................................................................................................ 63

v

Liste des figures

Figure 1: Simplified geological map of the Ungava Orogen in northern Québec, Canada

…………………………………………………………...…………………………………11

Figure 2: Comparison between the regional antiform model of the Kovik Domain and the

upper crustal features of many ultra-high-pressure rocks complex.

…………………………………………………………...…………………………………14

Figure 3: Field observation photos…………………………………………………………17

Figure 4: Schematic cross section across the Kovik Domain and Northern Domain Contact

……….…………………………………………………………………………...………...18

Figure 5: Microstructural and textural observations in thin section………………………24

Figure 6: Kinematic indicators from the lower shear zone and the upper shear zone…….25

Figure 7: Lower hemispherical, equal area projections of quartz c-axis fabrics from the USZ

and LSZ…………………………………………………………………………………….28

Figure 8: Temperatures of deformation of each fabric along the transects projected with

respect to their horizontal distance from the Kovik Domain and Northern Domain

contact……………………………………………………………………………………...29

Figure 9: BSE, EPMA, misorientation and kernel average misorientation maps of titanite in

the LSZ……………………………………………………………………………………..31

Figure 10: Tera-Waserburg diagrams of specimens TG-4015, TG-4022 and TG-4023…..33

Figure 11: Calculated temperature of crystallization of titanite from Zr-in-titanite

thermometry.…………………………………………..………………………...…………34

Figure A1: Y distribution, BSE, misorientation and KAM maps from titanite TG-4015-4 and

TG-4015-1 with the 238U/206Pb corrected for the 207Pb age plotted…………………….50

Figure A2: Y distribution, BSE, misorientation and KAM maps from titanite TG-4015-2

with the 238U/206Pb corrected for the 207Pb age plotted………………………………… 51

Figure A3: Y distribution, BSE, misorientation and KAM maps from titanite TG-4022-1

with the 238U/206Pb corrected for the 207Pb age plotted…………………………………52


TG-4023-7 with the 238U/206Pb corrected for the 207Pb age plotted…………………….53


TG-4023-2 with the 238U/206Pb corrected for the 207Pb age plotted……………………54

vi

Liste des tableaux

Table 1: Isotopic ratios of specimen TG-4015…………………………………………… 55

Table 2: Isotopic ratios of specimen TG-4022…………………………………………….56

Table 3: Isotopic ratios of specimen TG-4023…………………………………………….57

Table 4: Geochemistry analysis by LA-ICPMS on titanite from specimen TG-4015, TG-

4022 and TG-4023…………………………………………………………………………58

vii

Liste des abréviations et sigles

UO: Ungava Orogen

THO: Trans-Hudson Orogen

Zr: Zirconium

Y: Yttrium

Nb: Niobium

E: East

W: West

N: North

S: South

GBM: Grain boundary migration

SGR: Subgrain rotation

C-M: Core-and-mantle structure

EPMA: Electron Probe Micro-Analyser

EBSD: Electron backscatter diffraction

BSE: Backscatter electron

LA-ICP-MS: Laser Ablation Inductively Coupled Plasma Mass Spectrometry

KAM: Kernel Average Misorientation

LIP: Large igneous province

MORB: Mid-ocean ridge basalt

viii

Remerciements

Un petit merci à François pour ses conseils sur la pêche à la mouche et à Sacha pour son

amour des grands discours sur l’amour. Un grand merci à Alexandra pour son support et ses

beaux yeux et une mention honorable à la pandémie de Covid 19 sans qui, ce mémoire aurait

déjà été terminé.

ix

Avant-propos

Ce mémoire comprend un article s’intitulant «Constraining the nature and timing of the

contact between the Kovik Domain and Northern Domain, Ungava Orogen, Northern

Québec» destiné à la revue «Precambrian Research». Thierry Karl Gélinas est le premier

auteur de cet article et a rédigé son entièreté. La contribution de chaque co-auteur est précisée

au tableau ci-dessous. L’article n’est pas encore soumis.

Contribution Coauteurs

Conception du projet de maîtrise Carl Guilmette

Travaux sur le terrain Thierry Karl Gélinas, Kyle Larson, Carl

Guilmette, Marc-Antoine Vanier

Microstructures Thierry Karl Gélinas, Kyle Larson

Fabriques d’axe <c> du quartz Thierry Karl Gélinas, Kyle Larson, Marc-

Antoine Vanier

Datation U-Pb sur titanite Thierry Karl Gélinas, Kyle Larson

Thermométrie du Zr dans la titanite Thierry Karl Gélinas, Kyle Larson

Interprétation et discussion Thierry Karl Gélinas, Kyle Larson, Carl

Guilmette, Marc-Antoine Vanier

Rédaction de l’article Thierry Karl Gélinas

Lecture critique Kyle Larson, Carl Guilmette et Antoine

Godet

1

Introduction

Les processus associés aux mouvements des plaques tectoniques sont relativement bien

compris. Toutefois, le moment de l’initiation de la tectonique des plaques est l’un des sujets

les plus controversés en géosciences. La récente découverte d’un fragment éclogitique dans

l’Orogène de l’Ungava (OU) au Canada et plus précisément dans le Domaine de Kovik est

interprétée comme le signe qu’une tectonique des plaques modernes était déjà établie au

Paléoprotérozoïque (Weller and St-Onge, 2017). L’OU est la branche nord-est de l’Orogène

Trans-Hudsonien (OTH). L’OTH est considéré comme étant l’un des Cycles de Wilson le

mieux préservé sur Terre (Corrigan et al., 2009) et résulte de la collision entre la plaque

inférieure du Supérieur et de l’amalgamation de micro-continents et de croûte juvénile

formant la plaque supérieure du Churchill (Corrigan et al, 2009; St‐Onge et al., 2006).

Plusieurs auteurs considèrent l’OTH comme un analogue ancien à l’Orogène de l’Himalaya-

Tibet (OHT) sur la base de leurs géométries et de leurs évolutions temporelle, structurale,

magmatique et thermale (Corrigan et al., 2009; Corrigan et al., 2021; St‐Onge et al., 2006;

Weller et St-Onge, 2017). Notamment, l’association spatiale du Domaine de Kovik et du

Domaine de Nord, hôte d’un fragment éclogitique et d’une ophiolite, respectivement, a été

utilisée comme analogue au complexe de roche d’ultra-haute pression (UHP) du Tso Morari

dans l’OTH (Weller and St-Onge, 2017).

L’histoire tectono-métamorphique de la Nappe du Tso Morari est bien caractérisée et sa

configuration actuelle a été atteinte rapidement après la collision initiale entre l’Inde et l’Asie

(Leech et al., 2005; Epard et Steck, 2008). À l’inverse, l’exhumation du Domaine de Kovik

est moins bien contrainte avec quelques âges Ar40/Ar39 sur micas et hornblende indiquant un

refroidissement de plusieurs dizaines de millions d’années après la collision (Kellett et al.

2020; Skipton et al., 2020). La nature et la chronologie de l’activité de la zone de cisaillement

séparant le Domaine de Kovik et le Domaine Nord sont inconnues et pourraient s’avérer

importantes quant à la compréhension des processus tectoniques actifs au

Paléoprotérozoïque.

Ce mémoire de maîtrise se concentre sur la zone de cisaillement séparant le Domaine de

Kovik et le Domaine Nord dans l’Orogène de l’Ungava. Les objectifs sont de préciser la

2

cinématique, la température et la chronologie de la déformation de la zone de cisaillement

entre le Domaine de Kovik et le Domaine Nord. Ce mémoire de maîtrise documente les

observations de terrains le long de de trois transects recoupant le contact entre le Domaine

de Kovik et le Domaine Nord, ainsi que les résultats d’une étude pétrologique et structurale

détaillée incluant une analyse des indicateurs cinématiques, des pétrofabriques du quartz, de

la thermométrie et des dates U-Pb sur titanite. Une discussion sur les similarités entre la

Nappe du Tso Morari et le Domaine de Kovik sera également présentée.

Contexte géologique

L’Orogène de l’Ungava (OU) correspond à la branche Nord-Est de l’Orogène Trans-

Hudsonien et est situé sur la péninsule de l’Ungava au Nunavik où il s’étend d’est en ouest

sur ~300 kilomètres (Figure 1). Le Ministère de l’Énergie et des Ressources naturelles

(MERN) divises l’OU en cinq domaines lithotectoniques, qui sont du Sud vers le Nord, la

Province du Supérieur, le Domaine Sud, le Domaine Nord, le Domaine de Kovik et le

Domaine de Narsajuaq (Lucas et St-Onge, 1992; St-Onge et Lucas, 1992; St-Onge et al.,

1999; Lamothe, 2007; Charette et Beaudette, 2018; Vanier et Lafrance, 2019).

Le Domaine Sud est composé du Groupe de Povungnituk et du Groupe de Chukotat. Le

Groupe de Povungnituk consiste en un assemblage de roches volcanosédimentaires de ~2.04-

1.96 Ga (Machado et al., 1993), en contact stratigraphique sous-jacent au Groupe de Chukotat

(Bleeker and Kamo, 2017). Le Groupe de Chukotat est composé principalement de roche

volcanique mafique de composition MORB et d’une quantité mineure de roche sédimentaire

(Hynes et Francis, 1982; Picard, 1989; Beaudette et al., 2020). Le Groupe de Povungnituk

est interprété comme s’étant déposé sur la marge du Supérieur lors d’un épisode de rift

continental (e.g. Machado et al., 1993). Alternativement, les basaltes tholéitiques de la

Formation de Beauparlant du Groupe de Povungnituk pourraient être reliés à la grande

province ignée de Minto-Povungnituk (Kastek et al., 2018). Le Groupe de Chukotat est

interprété comme faisant partie de la grande province ignée du Circum-Supérieur (e.g.

Bleeker and Kamo, 2017).

3

Le Domaine Nord est composé de trois Groupes distincts soit le Groupe de Watts, le Groupe

de Spartan et le Groupe de Parent. Le Groupe de Watts est composé d’un assemblage de

roches volcaniques et plutonique, mafique à ultramafique de 2.0 Ga (St-Onge et al., 1989;

Parrish, 1989). Le Groupe de Watts, dont l’origine est encore incertaine (e.g. Kastek et al.,

2018), est interprété comme étant l’une des plus vieilles ophiolites du monde (Scott et al.,

1989; Parrish, 1989). Les Groupes de Spartan et de Parent corresponds respectivement à des

roches sédimentaires clastiques ayant un âge de déposition maximal de 1,85 Ga (Davis et

Sutcliffe, 2018) et à des volcanoclastites et volcanites d’arc mises en place entre 1,92 et 1,86

Ga (Beaudette et al., 2020; Lamothe et al., 1984; Machado et al., 1993). Le Groupe de Parent

et le Groupe de Spartan sont interprétés comme un complexe d’avant-arc (St-Onge et Lucas,

1992). Le Domaine Nord and le Domaine Sud sont séparés par la Faille de Bergeron, orientée

est-ouest et à vergence Sud permettant au Domaine Nord de chevaucher le Domaine Sud.

Cette structure est interprétée comme une zone de suture (Corrigan et al., 2021; Hoffman,

1985; St‐Onge et al., 2006).

Le Domaine de Kovik est principalement composé d’orthogneiss felsiques archéen, daté

entre 2882 et 2737 Ma (Parrish, 1989; Scott et al., 1995) et d’un âge paléoprotérozoïque ca.

1850 Ma (Davis et Sutcliffe, 2018). Depuis plus de 30 ans, le Domaine de Kovik est interprété

comme étant le socle archéen de la Province du Supérieur remobilisé entre le Domaine de

Narsajuaq et le Domaine Nord et Sud résultant de plissements tardifs à l’orogène contraints

entre 1758 et 1742 Ma (Dunphy et al., 1995; Hoffman, 1985; Parrish, 1989). Le Domaine de

Kovik et le Domaine Nord sont séparés par une zone de cisaillement, nommée la zone de

cisaillement de base (e.g. St-Onge et al. 1995) ou la zone de cisaillement de Françoys-

Malherbe et de Lecorré (Mathieu and Beaudette, 2018). À des fins de clarté, cette zone de

cisaillement sera référencée dans ce mémoire par le contact entre le Domaine Nord et le

Domaine de Kovik. Une récente étude a mis en évidence la présence d’un fragment mafique

éclogitique au sein du Domaine de Kovik , impliquant une subduction profonde de la

Province du Supérieur (Weller and St-Onge, 2017). Une telle évolution requiert une

exhumation importante du Domaine de Kovik, qui pourrait représenter une nappe ductile

exposée le long de détachements (e.g. Long et al., 2020), tout comme son analogue du dôme

du Tso Morari (Epard and Steck, 2008).

4

Le Domaine de Narsajuaq correspond quant à lui à la partie continentale du Block de Sugluk

(Corrigan et al.,2009; 2021). Ce dernier est interprété comme un microcontinent archéen

s’étant formé entre 2794 et 2560 Ma (Davis et Sutcliffe, 2018) et est l’hôte d’intrusions

paléoprotérozoïques (Corrigan et al., 2021; Dunphy et Ludden, 1998). Le secteur ouest du

Domaine de Narsajuaq a fait l’objet de levé géologique récents (Charrette and Beaudette,

2018; Vanier and Lafrance, 2020). Ces travaux révèlent une prédominance d’orthogneiss

intermédiaires à felsiques au sein desquels sont intercalées des unités méta-sédimentaires et

mafiques. Le Domaine de Narsajuaq et le Domaine de Kovik sont séparés par la zone de

cisaillement de Sugluk, interprétée comme un chevauchement vers le sud avec une

composante dextre s’étendant sur environ 150 km dans l’axe OSO-ENE (Charette and

Beaudette, 2018; Vanier and Lafrance, 2020;).

5

Chapitre 1: Constraining the nature and timing of the

contact between the Kovik Domain and Northern Domain,

Ungava Orogen, Northern Québec

GÉLINAS, Thierry Karl1 GUILMETTE, Carl1, LARSON, Kyle P2, VANIER, Marc-

Antoine3, GODET, Antoine1.

Département de Géologie et de Génie Géologique, Université Laval, Québec, QC G1V 0A6,

Canada, (2) Earth, Environmental and Geographic Sciences, University of British Columbia

Okanagan, Kelowna, BC V1V 1V7, Canada, (3) Ministère de l’Énergie et des Ressources

naturelle, 5700 4e Av O, Québec, QC G1H 6R1

1.1 Résumé

Le Domaine de Kovik et le Domaine Nord contiennent respectivement des unités

ophiolitiques et éclogitiques de l’Orogène Paléoprotérozoique de l’Ungava, et sont clés quant

à la compréhension de son évolution tectonique. Cette étude vise à contraindre la

cinématique, la température et la chronologie de la déformation du contact séparant ces deux

domaines. Les observations de terrains, l’analyse des microstructures et des datations U-Pb

sur titanites ont été combinées. Deux zones de cisaillement ont été identifiées, les zones de

cisaillement inférieure (LSZ) et supérieure (USZ). La LSZ est caractérisée par une

cinématique de sommet-vers-le-sud et une température de déformation de 627± 50°C. La

USZ est caractérisée par une cinématique de sommet-vers-le-nord et une température de

déformation de 580 ± 50°C. Les datations sur titanite ont permis de contraindre la

déformation entre 1737 et 1752 Ma. Nous interprétons que le contact entre le Domaine de

Kovik et le Domaine Nord représente un détachement.

6

1.2 Abstract

The Ungava Orogen is located on the Ungava Peninsula, northern Québec and corresponds

to the northeastern branch of the Trans-Hudson Orogen. The discovery of eclogite in the

Kovik Domain in the UO has been used to propose it as an analog to modern tectonic

archetypes of ultra-high pressure complex such as the Tso Morari Nappe (TMN) of the

Himalaya-Tibet Orogen. Ultra-high-pressure complexes are typically associated with

extensional structures that have helped to exhume the deeply buried rocks. The aim of this

study is to investigate the kinematics, timing, and temperature of deformation at the contact

between the Kovik Domain and adjacent Northern Domain to determine if it could have acted

as such an extensional structure. To do so, we have combined field mapping, microstructural

analysis of quartz, and titanite and U-Pb in situ geochronology on titanite. Analysis of the

multi-variate dataset has revealed two shear zones. The structurally lower shear zone (LSZ),

distal to the contact, is characterized by a top-to-the-south sense of shear and quartz c-axis

fabrics that indicate overall flattening strain. The upper shear zone (USZ), proximal to the

contact, is defined by a top-to-the-north sense of shear and is associated with quartz c-axis

fabrics that approximate plane strain. The temperatures of deformation in the LSZ and USZ,

as informed by the quartz c-axis fabric opening angle thermometer, are 627 and 580°C ±

50°C, respectively. U-Pb geochronology on titanite from orthogneiss from the LSZ yielded

two distinct populations: an old population of 1894 ± 31 Ma and a young population with

ages between 1752 ± 40 Ma and 1737 ± 7 Ma. The ca. 1740 Ma population is interpreted to

reflect the time of movement along the LSZ. Although we interpret the LSZ as a detachment,

the results of this study are hard to reconcile with the Kovik Domain as an analog to the

TMN.

7

1.3 Introduction

The onset of modern plate tectonics is one of the most heated debates in geosciences (Brown

and Johnson, 2018; Palin et al., 2020; Shirey et al., 2008). Geological records are ambiguous,

but combinations of geological elements, especially those found in the Ungava Orogen (UO)

of Canada, have been interpreted as a sign that modern tectonics was already ongoing by 1.8-

2.0 Ga (Weller and St-Onge, 2017; Scott et al., 1989). The UO corresponds to the

northeastern branch of the larger Trans-Hudson Orogen (THO). The THO is a

Paleoproterozoic orogen located within the North American continent and is thought to have

remarkably preserved geological archives of one the oldest Wilson-Cycles on Earth

(Corrigan et al., 2009; Hoffman, 1988). The THO resulted from the collision between the

Superior lower plate and amalgamated microcontinents and juvenile crusts, forming the

Churchill upper plate ca. 1830 Ma (Corrigan et al., 2009; St‐Onge et al., 2006). Many authors

consider the THO and the Himalaya-Tibet Orogen as analogous based on their geometry,

duration, and structural, magmatic and thermal evolutions (Corrigan et al., 2021; Corrigan et

al, 2009; St‐Onge et al., 2006; Weller and St-Onge, 2017). Recently, the ophiolite-eclogite

association of the Northern and Kovik Domains, respectively, in the UO have been proposed

as analogs to modern tectonics archetypes like Tso Morari Nappe and Indus ophiolites of the

Himalaya-Tibet Orogen (Weller and St-Onge, 2017). Although the Northern Domain and

Kovik Domain show the appropriate spatial and structural relationships, the timing of their

assembly remains unconstrained. The tectono-metamorphic history of the Tso Morari Nappe

and the overlying ophiolite in the Himalaya-Tibet Orogen is well characterized and they

reached their current configuration in the earliest stages of collision between India and Asia

(Leech et al., 2005; Epard and Steck, 2008). The exhumation of the Kovik Domain, in

contrast, is only loosely constrained, with a few Ar40/Ar39 ages in the Kovik Domain and

overlying rocks clustered around 1700-1750 Ma that seem to indicate very late cooling,

several Ma after the initial collision (Kellett et al., 2020; Skipton et al., 2020).

In this contribution, we focus on an exceptionally well-exposed shear zone in the eastern

segment of the orogen. It separates the Northern Domain from the underlying Kovik Domain,

and was initially interpreted as a folded thrust (e.g. St-Onge and Lucas, 1995). The

occurrence of eclogite in the Kovik Domain (Weller and St-Onge, 2017), however, indicates

8

a significant metamorphic gap between the Kovik and Northern Domains and the shear zone

between them may have acted as a detachment fault. Here we report field observations,

kinematic indicators, quartz c-axis fabrics, thermometry and U-Pb geochronology on titanite

for this shear zone. We interpret shear sense, conditions and timing of the deformation and

discuss similarities with the Tso-Morari Nappe modern analog.

1.4 Geological setting

1.4.1 The Ungava Orogen

The UO is composed of five principal lithotectonic domains. From South to North, these are

the Superior Province, the Southern Domain, the Northern Domain, the Kovik Domain and

the Narsajuaq Domain (Figure 1). The Superior Province is the largest Archean craton of the

Canadian Shield and in the study area, is mainly composed of ca. 2.7 to 3.0 Ga felsic plutonic

rocks (Percival and Skulski, 2000; Percival et al., 1994). The Southern Domain is composed

of the Povungnituk and the Chukotat Groups. The Povungnituk Group consists of ca. 2.04-

1.96 Ga volcanosedimentary rock assemblage (Machado et al., 1993; Parrish, 1989) in

stratigraphic contact with the overlying Chukotat Group (Bleeker and Kamo, 2017). The

Povungnituk Group is interpreted to have been deposited on the Superior Province margin

during a continental rift (e.g. Machado et al., 1993) and is mainly allochthonous within the

Southern Domain, with locally autochthonous clastic sedimentary rocks capped by the basal

décollement of the orogen (St-Onge and Lucas, 1992). It is also possible that the tholeiitic

basalt of the Beauparlant Formation in the Povungnituk Group may be part of a large igneous

province (LIP), the Minto-Povungnituk LIP (Kastek et al., 2018). The Chukotat Group is

mainly composed of a ca. 1.88-1.87 Ga mafic volcanic rocks with MORB-like (Mid-ocean

ridge basalt) composition and sedimentary rocks (Hynes and Francis, 1982; Picard, 1989, St-

Onge et al., 1992; Parrish, 1989; Bleeker and Kamo, 2018). The Chukotat Group is

interpreted to be part of the Circum-Superior LIP (e.g. Bleeker and Kamo, 2017).

The Northern Domain consists of the Watts Group, composed of ca. 2.0 Ga mafic to

ultramafic plutonic and volcanic rocks (Parrish, 1989; St-Onge et al., 1992), the Spartan

Group, corresponding to clastic sedimentary rocks with a maximal deposition age of 1852

9

Ma (Davis and Sutcliffe, 2018) and the Parent Group, composed of volcanosedimentary

rocks constrained between 1917-1860 Ma (Machado et al., 1993; Lamothe et al., 1984;

Beaudette et al., 2020). The Watts Group, whose origin remains unclear (e.g. Kastek et al.,

2018), has been interpreted as one of the oldest ophiolites on Earth (Scott et al., 1989), while

the Parent and Spartan Group are interpreted as a forearc complex (St-Onge et al., 1992).

The Southern and Northern Domains are separated by the Bergeron Fault, a major structure

that extends across Ungava from Hudson Bay to Wakeham Bay (Figure 1). It is interpreted

as having accommodated thrust-sense displacement verging towards the South (Bergeron,

1957; St-Onge et al., 1999). Additionally, the Southern and Northern Domains are dissected

by a series of east-west trending faults with southerly displacement that are locally crosscut

by out-of-sequence structures (Lucas, 1989).

The Kovik Domain (Vanier and Lafrance, 2020), is mainly composed of tonalite and

granodiorite of Archean age, between 2882-2737 Ma (Parrish, 1989; Scott and St-Onge,

1995) and one Paleoproterozoic age, ca. 1850 Ma (Davis and Sutcliffe, 2018), with minor

ultramafic to mafic and sedimentary enclaves (St-Onge et al., 1992). Sedimentary bands

dominated by pelite and semipelite are also present (Charette and Beaudette, 2018; St-Onge

et al., 1992). The Kovik Domain rocks are locally migmatized and crosscut by granitic

injections (Vanier and Lafrance, 2020). This domain is interpreted as reworked Archean

basement of the Superior Province (Hoffman, 1985; St-Onge et al., 1999). The structural and

metamorphic history of the Kovik Domain will be discussed in further details in the following

section. The Kovik Domain and the Northern Domain are separated by a wide shear zone

(Figure 1), which has been referred to as the ‘basal shear zone’ (e.g. St-Onge and Lucas.

1995) or the Françoys-Malherbe and the Lecorré shear zones (Mathieu and Beaudette, 2018).

For clarity, this deformation zone will be referred to here as the contact between the Kovik

Domain and the Northern Domain.

The Narsajuaq Domain (Vanier and Lafrance, 2020), is composed of intermediate to felsic

orthogneiss with minor metasedimentary and mafic units bracketed between 2794 and 2560

Ma (Davis and Sutcliffe, 2018) with intrusions of Paleoproterozoic felsic rocks (Dunphy et

10

al., 1998). The Narsajuaq Domain is interpreted as the penetratively deformed continental

part of the Sugluk block (Corrigan et al., 2009, 2021), an Archean micro-continent. The

Narsajuaq Domain is separated from the Northern and Kovik domains by the Sugluk shear

zone, a ~150 km long WSW-ENE thrust toward the SSE with a dextral component (Figure

1; Vanier and Lafrance, 2020; Charette and Beaudette, 2018).

The timing of deformation along the main structures mentioned above in the UO is currently

poorly constrained and are loosely bracketed either by intrusions crosscutting the structures

(e.g. Dunphy et al., 1995), the presence of the youngest unit in a given area (e.g. Lucas and

St-Onge, 1992; St-Onge et al., 1992), or by its inferred correlation with the growth of

metamorphic minerals dated outside of the structure (e.g. Scott and St-Onge, 1995). Direct

assessment of the timing of deformation through in situ geochronology is, therefore, essential

to understand the relationships between each domain. This is especially true for the contact

between the Kovik Domain and the Northern Domain, whose nature and timing of activity

remain unclear (see following section).

11

Figure 1: Simplified geological map of the Ungava Orogen in northern Québec, Canada

(modified from SIGÉOM, 2021 and St-Onge et al., 2006). The transects B-B’, C-C’, D-D’

12

and E-E’ crosscutting the Kovik Domain and Northern Domain contact are shown in Figure

4.

1.4.2 Tectonic and metamorphic history of the Kovik Domain

In the eastern segment of the UO, Kovik Domain rocks are characterized by metamorphic

conditions range from amphibolite to granulite facies assemblage (St-Onge and Lucas, 1995;

St-Onge and Ijewliw, 1996). Although all units contain local granulite facies assemblages,

such assemblages dominantly occur between 5 km and 20 km north of the contact between

the Kovik Domain and the Northern and Southern Domain (Figure 1; St-Onge et al., 1995).

South of this limit, the granulite facies assemblage is overprinted by an amphibolite facies

assemblage. The transition between the amphibolite-granulite facies is marked by the

absence or presence of clinopyroxene-orthopyroxene (St-Onge and Lucas, 1995). Granulite

facies metamorphism is associated with temperatures and pressures of ~860-920°C and 3.5

kbar (St‐Onge and Lucas., 1995; St-Onge and Ijewliw, 1996). U-Pb geochronology on a

metamorphic zircon overgrowth yielded an age of 2.73 Ga and is interpreted to represent the

timing of the granulite metamorphism (Scott and St-Onge, 1995). Amphibolite facies

metamorphism, in contrast, records temperatures and pressures of ~640-715°C and 7.7-9.8

kbar (St-Onge and Ijewliw, 1996) and has been associated with titanite growth between 1814

+19/-8 Ma and 1789 Ma (Scott and St-Onge, 1995). Titanite is interpreted as a marker of the

amphibolite overprint as it occurs as coronitic overgrowth around ilmenite, as inclusions in

hornblende and garnet, but is never associated with pyroxene and is absent from granulite

facies domain (Scott et St-Onge, 1995; St-Onge and Ijewliw, 1996; St‐Onge and Lucas,

1995). Multiequilibrium thermobarometry on titanite-bearing assemblage in the Kovik

Domain yielded temperatures of crystallization of 660-700°C (Scott and St-Onge, 1995).

Granulite facies metamorphism is interpreted to be coeval with the development of the

foliation affecting the plutonic rocks of the Kovik Domain (Lucas and St-Onge, 1995). The

Archean foliation appears to be reworked by two Paleoproterozoic deformation events. The

first is mainly concentrated between the Southern-Northern Domain and the Kovik Domain

forming a 0.5 to 400 m thick shear zone interpreted as the result of south-directed thrusting

the Southern Domain and Northern Domain over the Kovik Domain (St‐Onge and Lucas,

1995; Lucas et St-Onge, 1992). This deformation was accompanied by the imbrication of

13

several map-scale basement slices (Figure 1; Lucas, 1990). The significant extent of this

shear zone at the contact between the Kovik Domain and Northern Domain (Figure 1) can be

attributed to the presence of folds and by the possible internal imbrication of the Kovik

Domain (St-Onge and Lucas, 1995). Compilations of structural data from the Geological

Survey of Canada and the MERN at the contact between the Kovik Domain and Northern

Domain in the investigated area indicate a strong E-W foliation, locally mylonitic, a North-

plunging mineral and stretching lineation and a South-directed shear sense (St-Onge and

Lucas., 1997; St-Onge et al., 1990; Mathieu and Beaudette, 2018). The second

Paleoproterozoic deformation event is expressed by two folding episodes (Figure 1), which

also affect all tectonic domains of the UO (Lucas and Byrnes, 1992; St-Onge et al., 1990).

The first episode of folding is recorded as east-trending folds, ranging from meter to map

scale with a south to southwest-verging asymmetry (Lucas and Byrnes, 1992; Lucas, 1990).

The east-trending folds are refolded by north to northeast-trending folds (St-Onge et al.,

1990; Lucas and Byrnes, 1992). U-Pb geochronology on zircon from crosscutting intrusions

constrained the east-trending and north to northeast-trending folding event between 1758+/-

1 Ma and 1742 +/-1 Ma, respectively (Parrish, 1989; Dunphy and Ludden, 1995).

For the past ~30 years, the Kovik Domain has been interpreted as reworked Archean

crystalline basement of the Superior Craton (Hoffman, 1985; St-Onge et al., 1999) exposed

in a tectonic window following post-orogenic folding. As a corollary of that interpretation,

the basal shear zone located between the Superior Province and the Povungnituk group

should be exposed (Figure 2) between the Kovik Domain and Northern Domain (Hoffman,

1985; St-Onge et al., 1995). This interpretation is mainly supported by the continuity between

the Kovik Domain and the Superior Province in the east without a structure separating them

(Figure 1; Taylor, 1982), the inferred structural architecture (Figure 2) (Hoffman, 1985), and

the Archean age of the Kovik Domain (Parrish, 1989; Scott and St-Onge, 1995). However,

Weller and St-Onge (2017) described a mafic eclogite in the Kovik Domain which they

interpreted to be the result of a deep subduction of the Superior Province and compared it to

the Tso Morari Nappe in the Himalaya-Tibet Orogen. Although the presence of an eclogite

is not necessarily diagnostic of a subduction (Palin et al., 2020), the similarities between the

UO and the Tso Morari eclogite in terms of their field relationships, such as boudins of mafic

14

eclogite in felsic orthogneiss and similar peak metamorphic conditions of metamorphism (St‐

Onge et al., 2013; Weller and St-Onge, 2017) are interpreted to reflect the presence of

subduction processes in the UO. This evolution implies that the Kovik Domain might have

evolved as a ductile nappe bounded by detachments that accommodated its exhumation

(Figure 2).

Figure 2: a) Regional antiform model where the Kovik Domain represents the post-orogenic

folding of the Superior Province exposing the basal shear zone (modified from St-Onge et

al., 1999). Transect line A-A’ is shown in Figure 1. b) Cross-section of upper crustal features

of many ultra-high-pressure rocks complex such as the Tso Morari, Himalaya-Tibet Orogen

(modified from Beaumont et al., 2009).

a)

b)

15

1.5 Field observations and sampling

Three transects crosscutting the Kovik Domain and the Northern Domain contact have been

investigated. Two North-South (transect B-B’ and D-D’, Figures 1 and 3) and one East-West

(transect C-C’, Figure 1 and 3) traverses were carried out across a Northern Domain klippe

affected by North and East-axis folds inside the Kovik Domain. An additional composite

North-South transect (E-E’) across the main contact was interpreted from structural and field

observation data (Figure 1). Together the transects comprise over 5000 meters of horizontal

distance of almost continuous outcrop, accounting for a 600m structural thickness (Figure 3).

As the fabrics are very gently dipping, our lowest structural sample was collected in the

deepest valley nearby and was still within the shear zone. Accordingly, we have no clear

control on the true structural thickness of the shear zone. The main lithologies encountered

in the Kovik Domain include biotite-muscovite orthogneiss (Figure 3b) with locally

decametric to plurimetric horizons of metagabbro and metasediments. Garnet-rich

metagabbro and metapyroxenite are observed in the Northern Domain, where the garnet

content locally exceeded 40% of the mafic and ultramafic rocks. Between the Kovik Domain

and the Northern Domain, a thin layer of metasedimentary rocks and amphibolite are

observed and are correlated with the Nituk Formation (Figures 3c-d), belonging to the

Southern Domain. The orthogneiss, metasediment and amphibolite-gabbro and pyroxenite

sequence occurs at the Northern Domain klippe and at the main contact (Figure 3e-f and 4).

The foliation is defined by aligned biotite and muscovite in the orthogneiss from the Kovik

Domain, by chlorite, hornblende and biotite in the metasedimentary rocks and amphibolite

of the Nituk Formation, and by the preferred orientation of layer-rich garnet and by

hornblende in the Northern Domain metagabbro and metapyroxenite. The average foliation

plane from the two North-South transects strikes SE-NW and dips gently toward the SW

(Figure 4). For the East-West D-D’ transect, the average mineral foliation plane strikes N-S

and dips gently toward the W (Stereonet, Figure 4). The stretching and mineral lineations are

defined by quartz and biotite, respectively, in the orthogneiss from the Kovik Domain. In the

metasediment and amphibolite of the Nituk Formation and the metagabbro and

metapyroxenite from the Northern Domain, the mineral lineations are marked by aligned

16

chlorite and hornblende, respectively. The average mineral and stretching lineation across all

transects plunges gently toward the South (Figure 4).

Decametric to metric horizons of mylonite are observed (Figure 3b-d-e) within the

orthogneiss from the Kovik Domain and the metasediment and amphibolite from the Nituk

Formation. Between ~600 and ~140 meters (structural distance) away from the contact

between the Kovik Domain and Northern Domain, almost no asymmetric fabric elements are

observed except for rare sigma-type feldspar porphyroclasts (Figure 3d) consistent with a

weakly developed top-to-the-south sense of shear. Within ~140 structural meters of the

contact between the Kovik Domain and the Northern Domain, a change in the sense of shear

is observed and the asymmetry of the fabrics in the rocks are well developed. Several shear-

sense indicators are observed in the metasedimentary unit of the Nituk Formation including

C-S and C-C’ fabrics (Figure 3e). Those indicators, along with feldspar sigma-type

porphyroclasts in the orthogneiss of the Kovik Domain, define a top-to-the-north sense of

shear. Two distinct deformation events are, therefore, identified in the transects based on

stark differences in shear sense and the asymmetry of the fabrics. The dominantly

symmetrical, weakly developed top-south deformation event is referred to as the Lower shear

zone (LSZ) and the well-developed, asymmetrical, top-north deformation event is referred to

as the Upper shear zone (USZ) (Figure 4, composite transect). No direct crosscutting relations

between the USZ and LSZ are observed as they are parallel.

17

Figure 3: a) Almost continuous outcrops in the LSZ and USZ. b) Mylonitic biotite-muscovite

orthogneiss. c) Thin layer of metasedimentary unit at the contact between the Kovik Domain

and Northern Domain. d) Sigma-type feldspar porphyroclasts in the orthogneiss defining a

top-to-the-south sense of shear (LSZ). e) C-S fabric in the Nituk Formation defining a top-

to-the-north sense of shear (USZ). f) Sheared contact between the metasedimentary unit of

the Nituk Formation and the orthogneiss of the Kovik Domain.

a) b)

d)

e) f)

c)

18

Figure 4: Schematic cross section across the Kovik Domain and Northern Domain Contact.

The E-E’ transect represents a composite of the structural data from transect B-B’, C-C’ and

D-D’ where the two shear zones identify are color coded.

1.6 Methodology

1.6.1 Petrography

Over 50 oriented specimens were sampled along the transects. These oriented specimens,

including all observed lithologies and transposed quartz veins, were cut perpendicular to the

foliation and parallel to the lineation (representative of the XZ plan) to produce oriented thin

sections used to investigate the sense of shear, quartz and titanite microstructures and

microtextural relations between phases.

19

1.6.2 Quartz c-axis analysis

Quartz c-axis analysis was used to assess the kinematic and the 3D strain history (Lister and

Hobbs, 1980; Passchier and Trouw, 2005). Quartz c-axis orientations were obtained from 13

oriented thin sections with a Russell-Head Instruments G60+ Automated Fabric Analyser at

the University of British Columbia, Okanagan. Quartz c-axis fabrics were generated based

on one representative point per grain using the instrument’s software package. Quartz c-axis

were plotted in lower hemisphere, equal area projections such that the lineation plots as an

E-W horizontal line and the foliation plots as a vertical, E-W striking plane. The plots were

constructed using the FabricPlotR scripts from Larson (2021) for the open and free R

software environment.

1.6.3 Opening angle and deformation temperature

The relationship between increasing opening angle of the fabric arms of quartz c-axis

orientations and increasing temperature (Tullis et al., 1973; Kruhl, 1998) has been widely

used to infer the temperature of deformation of quartz-rich rocks (Faleiros et al., 2016; Law,

2014). Other than the temperature of deformation, parameters such as strain rate, critically

resolved shear stress, and hydrolytic weakening can potentially influence the opening angle

of quartz c-axis fabrics (see review by Law, 2014). Making the assumption that the main

factor controlling the differences observed in crystal fabric development is the deformation

temperature, this thermometer can provide a ±50°C estimation (Law, 2014; Faleiros et al.,

2016). The non-linear thermometer defined in Equation 3 of Faleiros et al. (2016) was used

to determine the deformation temperature. This thermometer is defined by the following

equation:

𝑇(°𝐶) = 483.75𝑙𝑛𝑂𝐴(𝑑𝑒𝑔𝑟𝑒𝑒𝑠) − 1499

OA represents the opening angle between the fabric arms of quartz c-axis fabric. The quartz

c-axis fabrics opening angles were calculated with the FabricPlotR scripts from Larson

(2021).

20

1.6.4 μ-XRF Maps and titanite grains imaging (EPMA/EBSD)

Over 50 oriented thin sections were mapped at the micron scale using X-ray fluorescence

spectroscopy (μ-XRF). μ-XRF maps were acquired to document the mineral distribution at

thin sections scale, microstructural relations and to locate titanite. μ-XRF maps were

performed with a M4 TORNADO at the microanalysis laboratory of Laval University. The

maps were collected using a step size of 20μm, and a 5ms dwell time per pixel. The X-ray

tube was set at 50keV and 300nA. The maps were then processed with the instrument

software.

Y, Zr and Nb maps and BSE maps on titanite grains were acquired to document internal

zoning patterns such as patchy zoning, oscillatory zoning and sector zoning, as well as to

identify inclusions and cracks to avoid during the LA-ICPMS analysis. Grains selected after

petrographic and μ-XRF investigation were mapped with a CAMECA SX-100 five

wavelengths dispersive spectrometer electron probe microanalyzer at the microanalysis

laboratory of Laval University. The maps were collected using a 1μm pixel size, a 30ms

dwell time per pixel and a beam current of 150nA.

Electron backscatter diffraction (EBSD) analysis of titanite grains was performed using a

TESCAN Mira3 XMU Field Emission Scanning electron microprobe (SEM) equipped with

an Oxford Instruments Nordlys EBSD in the Fipke Laboratory for Trace Element Research

(FiLTER) at the University of British Columbia, Okanagan. Thin sections were polished for

2 hours in an alumina solution using an ATM Saphir Vibro-polisher, coated with 10nm of

graphite and contoured with a copper tape to enhance conductivity. The specimens were tilted

to 70° during the analysis, which was performed with a step size of 1-1.5μm. To remove wild

spikes and zero-solution pixels, the data of each titanite map was denoised using a Channel5

(Oxford instruments). The Tango software was used to produce misorientation maps. The

data was then treated in MTEX 5.6, a toolbox for modeling and analyzing crystallographic

textures from EBSD data on Matlab (Hielscher et al., 2019), to produce kernel average

misorientation (KAM) maps. The misorientation maps represent the difference in the

orientation of a pixel and a manually selected point and the KAM maps represent a

measurement of the average misorientation of a pixel compared to a kernel of neighboring

21

pixels. Both maps were used to target grains, subgrains and local dislocations during the LA-

ICPMS analysis.

1.6.5 U-Pb geochronology and geochemistry by Laser Ablation Inductively Coupled

Plasma Mass Spectrometry (LA-ICPMS)

The U-Pb isotopic analysis was performed on titanite using a Photon Machines Analyte 193

Excimer Laser coupled with an Agilent 8900 QQQ-ICP-MS in the FiLTER facility in the

University of British Columbia, Okanagan. The analysis was performed using a 40 µm

diameter spot size, a laser repetition rate of 4 Hz and a fluence of 5.0 J/cm2. Analyses of

primary and secondary standards from bracketed titanite unknowns. ‘MKED1’ (Spandler et

al., 2016) was used as a primary and ‘Mount McClure’ (Schoene et al., 2006) as the secondary

reference material with expected 206Pb/238U ages (ID-TIMS) of 1517.32 ± 0.32 Ma and

207Pb/235U age of 523.26 ± 1.27 Ma (ID-TIMS), respectively. The ‘NIST610’ reference

material was used to optimize the analytical setup for maximum signal. The Iolite software

package (v.4) was used to monitor and correct the instrumental drift and down-hole

fractionation based on the primary reference material (Paton et al., 2011; Paton et al., 2010).

Three analytical sessions were performed across three thin sections, specimens TG-4015,

TG-4022 and TG-4023 from the LSZ. The analysis of the secondary reference material

yielded 206Pb/238U age corrected for 207Pb (Stacey and Krammer., 1975) of 515 ± 4 Ma

(MSWD=0.73; n=8), 520 ± 2 Ma (MSWD=2.47; n=8) and 533 ± 3 Ma (MSWD=0.29; n=8)

for TG-4023, TG-4022 and TG-4015, respectively, all within 2% of the accepted values.

Isoplot R (Vermeesch, 2018) was used to generate Tera-Wasserburg diagrams (Tera and

Wasserburg, 1972).

29Si, 43Ca, 44Ca, 88Sr, 89Y, 90Zr, 93Nb, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 157Gd, 159Tb,

163Dy, 165Ho, 166Er, 169Tm, 172Yb, 175Lu and 232Th elements concentration were measured with

the U-Pb isotopes of titanite in specimens TG-4015, TG-4022 and TG-4023. Iolite software

(v.4) (Paton et al., 2011) was used to calculate the trace elements concentration with Ca as

the internal standard with NIST610 (Jochum et al., 2005) as the primary reference material.

22

The expected values of trace elements concentration for the NIST610 are generally matched

within 5% (GeoReM database, Jochum et al., 2005).

1.6.6 Zr-in-titanite thermometry

The Zr-in-titanite thermometer (Hayden et al., 2008) relies on the substitution of Ti4+ for Zr4+

in titanite with varying temperatures and pressures and has been widely used across orogens

to estimate the temperature of crystallization of titanite (Garber et al., 2017; Kohn, 2017;

Kohn et al., 2011; Spencer et al., 2013). The calibration of Hayden et al. (2008) is defined by

the following equation:

(𝑍𝑟𝑡𝑖𝑡𝑎𝑛𝑖𝑡𝑒 , 𝑝𝑝𝑚) = 10.52(±0.10) −7708(±101)

𝑇(𝐾)− 960(±10)

𝑃(𝐺𝑃𝐴)

𝑇(𝐾)− 𝑙𝑜𝑔(𝛼𝑇𝑖𝑂2) − 𝑙𝑜𝑔 (𝛼𝑆𝑖𝑂2)

The Zr-in-titanite temperature was calculated for rutile absent, quartz and titanite bearing

assemblages assuming a αSiO2 =1.00 and αTiO2 = 0.75 ± 0.25 (Kapp et al., 2009), where 𝛼

stands for activity. Zircon and quartz are commonly observed to coexist with titanite grains.

Pressures in the shear zone between the Kovik Domain and the Northern domain have not

been formally calculated, so a ‘representative’ pressure of 0.9 ± 0.1 GPa was assumed from

previous thermobarometric works in the Kovik Domain in the study area, that range from

0.77 to 0.98 GPa (St-Onge and Ijewliw, 1996). Uncertainties of each parameter were

propagated.

1.7 Results

1.7.1 Petrography and microstructures

All specimens of orthogneiss from the Kovik Domain present a similar mineral assemblage

composed of quartz-feldspar-biotite-muscovite-epidote-zoisite-titanite ± hornblende ±

allanite. The specimens contain a strongly developed foliation mainly defined by muscovite

and biotite. Titanite, hornblende, epidote and zoisite are also deformed and aligned along the

foliation, locally forming porphyroclasts (Figure 6a-b,f). The titanite grains are euhedral to

23

anhedral (Figure 5h), generally free of any inclusions and are characterized by undulous

extinction and subgrains (Figure 5g). Feldspar is sericitized and locally exhibits core-and-

mantle structures (Figure 5f). Such a texture is consistent with dynamic recrystallization by

subgrain rotation (SGR) mechanisms (Passhier and Trouw, 2005; Pryer, 1993).

Quartz grains often forms elongated clusters along the foliation, which are characterized by

variable grains size with lobate to amoeboid grain boundaries (Figure 5a-e). This

microstructure is consistent with dynamic recrystallization of quartz by grains boundary

migration (GBM) (Passhier and Trouw, 2005). Internal subgrains on quartz grains affected

by GBM and small individual grains with straight boundaries are also observed (Figure 5a).

This microstructure is consistent with dynamic recrystallization of quartz by SGR (Passhier

and Trouw, 2005). Locally, quartz meets at 120° triple junctions. This geometry is consistent

with grain boundary area reduction during static recrystallization (Passhier and Trouw,

2005). Quartz and feldspar microstructures are homogeneous across all specimens from the

orthogneiss. In the metasedimentary rocks horizon in the Kovik Domain, the mineral

assemblage is composed of hornblende-biotite-chlorite-quartz. The foliation is well

developed and marked by the biotite, hornblende and chlorite. Quartz in these rocks

frequently exhibit subgrains. In the Nituk Formation, the mineral assemblage of the

metasedimentary rocks and amphibolite consists of garnet-zoisite-epidote-hornblende-

chlorite-plagioclase, all of which contribute to defining the foliation. The metapyroxenite and

metagabbro from the klippe of Northern Domain present a mineral assemblage including

clinopyroxene-plagioclase-garnet-zoisite-ilmenite-titanite. Titanite in these rocks occurs as

corona around ilmenite grains locally.

As noted previously, shear sense indicators in the LSZ are rare and commonly ambiguous.

Those observed in thin section are sigma-type porphyroclasts and C-S fabric in the

orthogneiss and metasedimentary rocks horizon. They generally indicate a top-to-the-south

sense of shear (Figure 6a-c). This sense of shear is compatible with the field observations.

Contrary to the LSZ, the USZ exhibits abundant asymmetrical microstructures in thin section

including delta and sigma-type porphyroclasts in the orthogneiss as well as C-S fabrics and

sigma-type quartz aggregates porphyroclasts in the metasediment. All kinematics in the USZ

indicate top-to-the-north shear (Figure 6d-g).

24

Figure 5: a) to e) Quartz textures observed across the transect. Textures are marked as follows: GBM: grain boundary migration, SGR:

subgrain rotation, ISG: internal subgrains. f) Feldspar porphyroclast forming a core-and-mantle structure (C-M). g and h) Titanite

showing extinction by domain. i) Euhedral titanite.

a) b) c)

d) e)

f)

g) h) i)

25

Figure 6: a-c) Sigma-type porphyroclasts in thin sections from the LSZ. d) C-S fabric and e-f) sigma-type porphyroclasts in thin sections

from the USZ. g) and h) uXRF elementary maps showing shear-senses indicators from the USZ.

a) b) c)

d)

e)

f)

g) h)

26

1.7.2 Quartz c-axis analysis

Si, Na, Ca, K μ-XRF maps were superposed and used to ensure that only quartz grains and

subgrains were selected and feldspars excluded. Between 270 and 1136 individual quartz c-

axes were obtained from each of the thirteen specimens investigated from the Kovik Domain.

Approximately 600 m structural distance separates the structurally lower specimens from the

structurally higher specimens and include both shear zones. The structurally lowest sample

is still within the LSZ, for which as mentioned before we could not assess the true thickness.

The quartz c-axis fabrics of each specimen are depicted with respect to their structural

distance between the Kovik Domain and Northern Domain contact (Figure 7). The quartz c-

axis fabrics from the two shear zones will be discussed separately.

Quartz c-axis fabrics from the LSZ were measured to specimens TG-4017, TG-4018, TG-

4022, TG-A1, TG-A2, TG-A3 and TG-A4. Excluding TG-4018, this group is characterized

by strongly developed fabrics with a combination of rhomb<a> and basal<a> slips defining

small circles normal to the flow planes, which are linked with a weak central girdle consistent

with some measure of prism <a> slip. Fabrics with similar patterns are generally associated

with flattening strain (Lister and Hobbs, 1980). TG-4018 differs from the other quartz c-axis

fabrics of the LSZ and presents a combination of basal <a>, prism<a> and rhomb<a> slip

forming a weakly developed type II cross girdle (Lister, 1977). Type II cross girdles are

associated with constrictional strain (Lister and Hobbs, 1980). TG-4017, TG-4022, TG-A2

and TG-A3 quartz c-axis fabrics are characterized by a weak asymmetry toward the south,

defining a top-to-the-south sense of shear. This sense of shear is compatible with the field

and oriented thin section observations. TG-A4 quartz c-axis fabric is characterized by a very

weak asymmetry toward the South. TG-4018 did not yield an interpretable sense of shear.

The quartz c-axis fabrics from the USZ correspond to the specimens TG-4026A2, TG-

4026A3, TG-4026B, TG-4034, TG-A7 and TG-A8. Specimens TG-4026A3, TG-4026B,

TG-A7 and TG-A8 are characterized by rhomb <a>, basal <a> and prism<a> slips generally

forming type I cross girdles (Lister, 1977) indicative of plane strain deformation (Lister &

Hobbs, 1980). The specimen TG-4026A3 yielded a fabric defined by a combination of

27

rhomb<a>, prism<a> and basal<a> and forms a single girdle, which is also compatible with

plane strain deformation. Specimen TG-4034 yielded more complex fabrics characterized by

a combination of rhomb<a> and basal<a> slips that form small circles normal to the flow

plane linked by a weak central girdle formed by prism <a> slips. This pattern is similar to

that observed in the LSZ, implying a component of flattening strain (Lister and Hobbs, 1980).

All quartz c-axis fabrics, however, including TG-4034, yielded a strong asymmetry towards

the north, defining a top-to-the-north sense of shear. This sense of shear is compatible with

the field and oriented thin sections observations.

29

Figure 7: Lower hemispherical, equal area projections of quartz c-axis fabrics. Left are

scatterplots and right are the density contour plots. All specimens are oriented with the North

to the left and South to the right. Specimens are plotted according to their horizontal distance

with the contact between the Kovik Domain and Northern Domain.

1.7.3 Opening angles and deformation temperature

With the exception of TG-4026A2, all of the quartz c-axis fabrics comprise diverging arms

that define an opening angle. The opening angles range between 68° and 87°, corresponding

to temperatures of deformation of 535 to 661 ± 50 °C, using the pressure independent

calibration from Faleiros and al. (Equation 3; 2016). The deformation temperatures for each

specimen were projected with respect to their structural distance from the Kovik Domain and

Northern Domain contact (Figure 8). The temperature of deformation is similar for both shear

zone with no sharp break between the LSZ and the USZ. The deformation temperature

averages ~610°C ±50 °C across the transect.

Figure 8: Temperatures of deformation of each fabric along the transects projected with

respect to their horizontal distance from the Kovik Domain and Northern Domain contact.

30

1.7.4 Microstructural features and trace element zoning of titanite

Twelve titanite grains from specimens TG-4015, TG-4022 and TG-4023, were imaged using

EPMA, BSE and EBSD techniques. Distribution maps of Y, Zr and Nb were initially

performed on two titanite to investigate zoning. Only the Y concentration map showed any

zoning. Y distribution maps were subsequently made for each titanite grain investigated.

Generally, titanite presents a homogeneous distribution of Y but local zoning is observed

(titanite TG-4023-1-2-4 and TG-4022-1; Supplementary data). Where present, Y zoning is

patchy across the cores and the rims of titanite grains. BSE response maps are also typically

homogeneous in the titanite grains. In two specimens, small dark and bright domains are

observed (TG-4023-1-4-5 and TG-4022-1) matching high Y distributions.

Crystal lattice orientation maps, based on EBSD data (Fig 8), outline titanite grain and sub-

grain boundaries (misorientation of 10° or more), and the sub-grains a misorientation

between 2 and 10° (Lloyd et al., 1997) (Figure 9). The manually selected reference points in

each titanite’s misorientation map, from which the misorientations are calculated are

represented by a red cross. A maximum threshold of 2.5° for the misorientations was applied

in the KAM maps to remove most sub-grains boundaries and accentuate local dislocation.

EBSD analyses of the titanite grains show that all titanite investigated display the

development of grains, sub-grains and local dislocations (Figure 9; Supplementary data),

consistent with dynamic recrystallization. Misorientations vary between 6° (TG-4022-1) and

115° (TG-4023-7). Networks of local dislocations, as illustrated by the KAM maps, occur in

most titanite. Local straight dislocations (TG-4023-1 and TG-4023-6) are interpreted to be

the result of interference from scratches related to incomplete polishing. The microstructures

identified with the misorientations and KAM maps generally do not follow Y zoning and

BSE domains. One exception is the TG-4023-1 titanite where a Y-rich and brighter BSE

domain partially matches with a sub-grain (Figure 9).

31

_

Figure 9: From top to bottom are BSE, EPMA, misorientations and Kernal average

misorientations from titanite in the shear zone distal from the contact. The ages plotted are

LA-ICP-MS age of the 238U/206Pb corrected for the 207Pb from Stacey and Krammer (1975).

1.7.5 Titanite U-Pb geochronology

73 analyses were performed on 12 titanite grains from specimens TG-4015, TG-4022 and

TG-4023 from the LSZ (Supplementary data). Analyses targeted the Y and BSE internal

zoning, grains and subgrains determined from the misorientation maps and local dislocations

32

identified in KAM maps. Tera-Wasserburg diagrams from each specimen are presented in

Figure 10 using a Model-1 (Vermeesch, 2018) regression. All uncertainties are presented as

2 standard error of the mean (SE). Data near the Y axis are scattered and the spread of the

analysis along the discordia regression is not evenly distributed. The discordia regression line

should therefore be anchored for a 207Pb/206Pb isotopic ratio. Previous data on titanite in the

Kovik Domain indicate its association with the amphibolite assemblage overprints (Scott and

St-Onge, 1995), which is consistent with Zr-in-titanite temperature from this study (see

discussion). Discordia regression lines were therefore anchored at isotopic ratio 207Pb/206Pb

of 0.98 based on crustal Pb evolution model ca. 1800 Ma (Stacey and Krammer, 1975), the

approximate age of amphibolite metamorphism in the study area (Scott and St-Onge, 1995).

The data define two populations of titanite. The oldest population yielded an age of 1894 ±

31 Ma (n=7, MSWD= 1.6) and is only present in the specimen TG-4023. The youngest

population has overlapping ages between 1752 and 1737 Ma (TG-4015: 1752 ± 40 Ma, n=5,

MSDW=5.2; TG-4022: 1737 ± 7 Ma, n=22, MSWD=4.2; TG-4023: 1751 ± 13 Ma, n=14,

MSWD= 1.6).

238U/206Pb ages, corrected for initial common 207Pb ratios as mentioned above were

superposed on Y, BSE and microstructural maps (Figure 9) to investigate potential

correlation between ages and zoning or microstructural features. The old population is co-

located with young analyses in TG-4023-1, TG-4023-2 and TG-4023-5 (Figure 9,

Supplementary data). No correlation between ages and Y and BSE internal zoning is

identified except in titanite TG-4023-1 where high Y concentrations correlates with a

younger age and old analyses are associated with lower Y concentrations. Ages also typically

varies depending on the position of the analysis site and their proximity to microstructural

features such as grains, sub-grains and local dislocations. Such association are observed in

titanite TG-4023-3 and TG-4023-5 (Figure 9, A1) where younger ages are locally associated

with increased densities of dislocations. Conversely, strain free domains are generally

associated with older ages. Titanite TG-4023-1 (Figure 9) also illustrates a spatial

relationship with microstructural features and the ages where the two populations, located

within a single titanite grain, are restricted to different sub-grains.

33

Figure 10: Tera-Waserburg diagrams of TG-4023, TG-4022 and TG-4015. TG-4023-a and

TG-4023-b representing the old and young populations, respectively, present in TG-4023.

1.7.6 Zr-in-titanite thermometer

Calculated temperatures of crystallization of titanite from Zr-in-titanite thermometry using

the calibration from Hayden et al. (2008) are shown in Figure 11. The analyses form a single

population that varies between 737 ± 37°C and 648 ± 31°C with a Tukey’s biweighted mean

yielding a temperature of 677 ± 4°C. No difference in Zr temperature is noted between the

34

old and young populations, which yield temperatures of 675 ± 25°C and 674 ± 5°C,

respectively.

Figure 11: Calculated temperatures of crystallization of titanite from Zr-in-titanite

thermometry using Hayden et al. (2008) calibration.

1.8 Discussion

1.8.1 Microstructures and temperature of deformation

Fieldwork, thin section observations, and quartz c-axis fabric analysis highlight the presence

of two parallel, gently dipping but distinct shear zones at the contact of the Kovik Domain

and the Northern Domain, the LSZ and the USZ (Figure 4). Quartz c-axis fabric analyses

constrained the extent and kinematics of both shear zones. The LSZ is located at least

between ~600 and ~140 structural meters below the contact along the investigated transects

and is generally defined by a weak, top-to-the-south sense of shear characterized by

significant foliation normal flattening. The lower extent of the LSZ has not been observed

and, therefore, no approximation of its overall structural thickness can be inferred. The USZ,

located between ~140 and 0 meters below the contact, is defined by a plane strain dominant,

top-to-the-north sense of shear.

Correlations between the temperature of deformation and observed dynamic recrystallization

mechanisms of quartz should be used cautiously since many factors can influence the

35

dominant mechanisms (Law, 2014; Passchier and Trouw, 2005). The original calibration of

microstructures against the estimation of deformation temperature reported by Stippet al.

(2002a,b) is valid only for the water content and strain rates of the mylonites sampled in their

studies. Nonetheless, this microstructural thermometer was used to qualitatively assess the

relative temperatures of deformation of the LSZ and USZ for comparison with the quartz c-

axis opening angle thermometer. The main recrystallization mechanism of quartz observed

in the LSZ and USZ is GBM and to a lesser extent, SGR (Figure 5) indicating deformation

at moderate temperatures (between 500 and 700°C in Stipp et al., 2002a,b). The core-and-

mantle texture of the feldspar porphyroclasts (Figure5f) observed has been described to be

an efficient recrystallization mechanism at temperatures in excess of 450°C (Passchier and

Trouw, 2005), which is consistent with the temperature indicated based on the Stipp et al.

(2002a,b) quartz textural calibration.

The quartz c-axis opening angle thermometer provides further information about deformation

temperatures. This thermometer was calibrated with LS tectonites and its application with

S>L or L>S tectonites may have an effect of over- and underestimating the temperature of

deformation, respectively (Faleiros et al., 2016; Law, 2014). Except for TG-4018, quartz c-

axis fabrics from the LSZ are associated with flattening strain (S>L tectonites), which could

overestimate the temperature of deformation. The average temperature of deformation from

these fabrics (removing temperature of deformation of TG-4018) is 627 ± 50°C and is

therefore considered as a maximum temperature for the LSZ. Fabrics with deformation that

approximate plane strain (LS tectonites) from the USZ (fabrics TG-4026A3, TG-4026B, TG-

A7, TG-A8), which do not suffer the same potential problems, yielded an average

temperature of 580 ± 50°C. No sharp break in temperature of deformation can be resolved

between the USZ and LSZ, which is compatible with the similar quartz and feldspar textures

along all transects.

1.8.2 Structural interpretations

The LSZ is generally defined by a top-to-the-south sense of shear associated with quartz c-

axis fabric with a weak to absent asymmetry and patterns characteristic of flattening strain.

The flattening pattern combined with the weak to absent asymmetry of the quartz c-axis

36

fabrics and the general absence of shear-senses indicators in the field and oriented thin

sections are consistent with an important component of pure shear deformation since coaxial

deformation tends to form symmetrical structures (Fossen, 2016). The top-to-the-south shear-

senses are compatible with the sense of shear documented in earlier works (e.g. Lamothe et

al., 1984; Lucas and St-Onge, 1991) and are consistent with the interpretation that this

structure represents the exposed basal shear zone of the orogen since a folded thrust, as

proposed by previous workers (e.g. Hoffman, 1985), would yield a top-to-the-south sense of

shear (see Figure 2). Top-south kinematics are also compatible with a model in which this

shear zone represents a detachment (inferred from Weller and St-Onge, 2017), since a

detachment between the foreland and the UHP complex would also yield top-to-the-south

shear sense along a south dipping SZ (see Figure 2).

In contrast to the LSZ, the USZ is defined by a top-to-the-north sense of shear and strongly

asymmetric quartz c-axis fabrics that approximate plane strain (Figure 7). These observations

are consistent with a significant component of simple shear strain in the USZ (Passchier and

Trouw, 2005). Critically, the top-to-the-north kinematics within the USZ has not been

reported by previous workers.

The quartz c-axis fabric extracted from TG-4034, within the USZ, helps mark the switch

between the top-to-the-south sense of shear LSZ and the top-to-the-north sense of shear of

the USZ (Figure 7). This fabric contains a c-axis orientation pattern characteristic of a

component of flattening strain, similar to the fabrics from the LSZ. It also, however, records

top-to-the-north sense of shear, characteristic of the USZ. Quartz c-axis fabrics have been

documented to record multiple strain histories within single specimen (e.g. Kirschner and

Teyssier, 1991; Larson and Cottle, 2014). The presence of a hybrid fabric may indicate the

overprinting of the LSZ by the USZ or the opposite. Alternatively, the absence of crosscutting

relationships in the field, similar quartz and feldspar microstructures and temperatures of

deformation, constrained between 627 and 580°C ± 50°C for the LSZ and USZ respectively,

might indicate coeval activities (e.g. Dutta et Mukherjee, 2021). Future work on the timing

of deformation of the USZ should be assessed to better understand the overall interaction

between the USZ and LSZ.

37

1.8.3 Interpretation of titanite geochronology

Titanite can occur as a primary igneous and/or secondary metamorphic mineral (Frost et al.

2001; Kohn, 2017). The U-Pb system in titanite can record multiple crystallization events

and can be reset by thermally mediated volume diffusion, interaction with fluids, or by plastic

deformation (Garber et al., 2017; Holder and Hacker, 2019; Spencer et al., 2013; Stearns et

al., 2015). Our titanite dates could represent protolith ages (for igneous titanite), cooling (for

thermally diffused titanite), metamorphic ages (for metamorphic titanite) or reset ages

reflecting recrystallization during deformation. Assessing potential Pb diffusion mechanisms

in the titanite grains is thus critical to our geological interpretation of ca. 1740 Ma and 1894

Ma populations obtained in this study.

Titanite dates have been interpreted as cooling ages because of their historically low closure

temperature estimations, initially thought to be between 450 and 600°C (Cherniak, 1993;

Mattinson, 1978). However, recent studies have demonstrated the robustness of titanite to

thermally mediated volume diffusion of Pb and calculated relatively high closure

temperatures, bracketed between 700 and 850°C (Gao et al., 2012; Garber et al., 2017; Kohn,

2017; Kohn and Corrie, 2011; Spencer et al., 2013, Holder et al., 2019). Kirkland et al. (2016)

demonstrated that titanite grains with a diameter of ≥ 210 µm were only partially reset under

temperatures of 695-725°C. Similarly, Spencer et al. (2013) concluded that titanite grains as

small as 200 µm can preserve their crystallization age even after reaching temperatures over

750°C for 40 Myr. Titanite grains from this study are 260 µm in size on average (ranging

from ̴150 to ̴1000 µm) and the amphibolite-grade metamorphic event they are associated

with in the Kovik Domain reached temperatures of 640-715°C (St-Onge and Ijewliw, 1996).

The large size of our titanite grains and the limited peak metamorphic temperatures likely

limited the effectiveness of thermally mediated Pb diffusion. Accordingly, the ages

determined are not considered to be cooling ages.

Zr-in-titanite is a thermometer that could help differentiate between igneous and

metamorphic titanite ages (e.g. Olierook et al., 2019). Temperatures obtained with the Zr-in-

titanite thermometer from this study are of the same order are similar (Tukey weighted mean

38

of 677 ± 4°C) to those reported for the amphibolite facies metamorphism associated with

titanite growth (~640-715°C; Scott et St-Onge, 1995, St-Onge et Ijewliw, 1996) We interpret

that the ca. 1890 Ma population of titanite outlined in this study, therefore, do not represent

a protolith age, but a metamorphic age. This metamorphic age is ~80 Ma older than

previously reported metamorphic titanite ages (Scott and St-Onge, 1995). The titanite

geochronology presented in Scott et St-Onge (1995) is based on an anion-exchange

chromatographic technic and, therefore, may represent mixing between different titanite

domains, highlighting the potential importance of in situ dating. A ca. 1890 Ma metamorphic

age could be related to the ca. 1880 Ma Circum-Superior LIP emplaced around the Superior

Province (Bleeker and Kamo, 2017) leading to the initial hydration of the Archean basement.

As for the younger ca. 1740 Ma population, the spot analyses that define it have an

indistinguishable Zr temperature from the older population: 675 ± 25°C and 674 ± 5°C for

the 1894 Ma and ca. 1740 Ma populations, respectively. The younger age could be explained

through plastic deformation and/or fluid-mediated resetting or a young crystallization event

(Garber et al., 2017; Holder and Hacker, 2019; Spencer et al., 2013; Stearns et al., 2015).

Plastic deformation is an important mechanism of Pb diffusion in titanite (Spencer et al.,

2013; Stearns et al., 2015; Gordon et al., 2021) where it can create pathways for fast diffusion

of Pb. The apparent control of the age by grains, sub-grains and the correlation between high

strain domains and young ages and low strain domains and old ages illustrated in KAM maps

(Figure 9) are consistent with partial resetting of Pb in titanite grains through dynamic

recrystallization.

Multiple crystallization events are unlikely, given the general lack of spatial association of

young ages with only the outside portions of grains. Moreover, the absence of correlation

between the 238U/206Pb ages, corrected for common 207Pb contamination (Stacey and

Kramers, 1975) and differences in BSE response maps (Figure 9, supplementary data)

supports a single crystallization event (e.g. Gao et al., 2012, Papapavlou et al., 2017). Titanite

is prone to developing sector zoning, which presents as the difference in composition

controlled by the crystallography (Kohn, 2017). The differences in Y distribution and BSE

response maps observed in titanite from this study may be ascribed to such zoning.

39

Although plastic deformation is interpreted as the main mechanism responsible for Pb

diffusion, fluid-titanite interaction could also have contributed. Fluid-mediated resetting of

titanite is envisioned to take place by interface-couped dissolution-precipitation reactions

(ICDR) and is hypothesized to be the primary mechanism by which titanite dates are reset

below the temperature of closure (Holder and Hacker, 2019). ICDR, where an older titanite

is partially replaced by a younger titanite with different compositions as a result of the

interaction with a fluid, will lead to patchy, lobate and oscillatory zoning and the presence of

inclusions and porosity in titanite grains (Holder and Hacker, 2019; Putnis, 2009). Some of

these features are present in titanite grains in this study, such as local patchy zoning, which

might indicate that fluid-mediated resetting could have been involved perhaps in conjunction

with plastic deformation.

Because plastic deformation and fluid-titanite interaction can lead to Zr diffusion (e.g. Stearn

et al. 2015), we must assess the robustness of the crystallization temperature from the Zr-in-

titanite thermometry. The lower temperature of crystallization of TG-4022 (Figure 11) could

indicate that the Zr might have slightly diffused out of the titanite from specimen TG-4022

during the deformation. However, Pb has been observed to be more mobile than Zr in titanite

grains following plastic deformation and fluid-titanite interaction (Gordon et al., 2021;

Holder and Hacker, 2019). Because the Zr-in-titanite temperatures between the old and

young populations from this study are nearly identical (675 ± 25°C and 674 ± 5°C,

respectively, Figure 11) it would be unlikely that the old population preserved its

crystallization age but not its temperature. This indicates that the temperatures of

crystallization of the titanite calculated from Zr-in-titanite thermometry are robust and likely

represent the temperature of crystallization of titanite at ca. 1894 Ma and therefore, the

estimation of temperature for the amphibolite facies. Moreover, the temperatures of

crystallization of titanite in this study overlap with the previous estimate of 660-700°C on

titanite grains located outside of the contact between the Kovik Domain and the Northern

Domain (Scott and St-Onge, 1995).

40

1.8.4 Evolution of the contact between the Kovik Domain and the Northern Domain

Our ca. 1740 Ma shearing ages predates or overlap with most biotite, muscovite, and

hornblende 40Ar/39Ar dates reported from the Southern Domain, Northern Domain and Kovik

Domain (Kellett et al., 2020; Skipton et al., 2020), which range between 1750 and 1700 Ma.

This indicates that the late amphibolite-grade top-to-the-south shearing event recorded in the

LSZ was contemporaneous with the onset of regional cooling. Kellett et al. (2020) identify

significant and widespread exhumation following lithospheric delamination as a likely

process to explain relatively high post-terminal THO cooling rates. We suggest that the

contact between the Kovik Domain and the Northern Domain may be one of the structures

that accommodated the exhumation of rocks in the UO. The ca. 1740 Ma timing of shearing

at the contact between the Kovik Domain and the Northern Domain also indicates that it was

coeval with the formation of the dome structure of the Kovik Domain, previously suggested

to have occurred between 1758+/-1 Ma and 1742 +/-1 (Parrish, 1989; Dunphy et al., 1995).

The kinematics and timing of the LSZ and the structural architecture of the Kovik Domain

are, therefore, consistent with a model in which the latter is a post-orogenic metamorphic

dome. In such a model, the LSZ, south dipping, would have acted as a detachment at the

southern margin of this dome, providing a potential explanation for the pressure gap inferred

from the presence of an eclogite in the western Kovik Domain and the amphibolite

metamorphic condition of the Northern Domain. Such model would be compatible with the

overall upper structural features of many UHP complex (Figure 2b). As for the USZ, its

interpretation remains ambiguous as no data were collected that can inform its movement

timing relative to that along the LSZ.

1.8.5 Comparison between the Kovik Domain and the Tso Morari Nappe

Weller and St-Onge (2017) suggested that the Kovik Domain represents a Paleoproterozoic

analog to the Tso Morari Nappe in the Himalaya-Tibet Orogen. Although the Tso Morari

Nappe and the Kovik Domain share apparent similarities such as comparable timing-lag of

eclogite metamorphism (Weller and St-Onge, 2017; St‐Onge et al., 2013; Leech et al., 2005),

and similar structural characteristics such as size, ophiolite association and the dome structure

(Epard and Steck, 2008; St-Onge et al., 1999), the overall tectono-metamorphic histories

diverge significantly.

41

Collision ages of ca. 55 Ma for India-Asia (Najman et al., 2017; Zhu et al., 2015) and ca.1830

Ma for Churchill-Superior (St-Onge et al., 2006; Corrigan et al., 2009) are used for the

following explanation. After reaching peak UHP conditions within ~10 Myrs after the

collision (pc) between India and Asia (Leech et al., 2005; St‐Onge et al., 2013; Donaldson et

al., 2013), the Tso Morari Nappe detached from the Indian subducting crust and exhumed

via extensional shearing that may have been active until 25 Myrs post-collision (Long et al.,

2020). The exhumation of the Tso Morari Nappe to mid-crustal levels was accompanied by

amphibolite facies metamorphism within ~7-10 Myrs post-collision (Epard and Steck, 2008;

St‐Onge, 2013; Wilke, 2015). The structural doming of the Tso Morari Complex formed by

~8-25 Myrs post-collision and was driven by the emplacement and the exhumation of the Tso

Morari Nappe to structurally higher rocks of the subducting Indian margin (Epard and Steck,

2008).

In the Kovik Domain, eclogite metamorphism was also reached within ~10 Myrs post-

collision (Weller and St-Onge, 2017). However, the shearing between the Kovik Domain and

the Northern Domain and the formation of the structural dome happened later than in the Tso

Morari Nappe and are constrained between ~78-93 Myrs post-collision (this study) and ~72-

88 Myrs post-collision (Parrish, 1989; Dunphy, 1995). The granulite facies assemblage is

overprinted by an amphibolite facies assemblage, as marked by the growth of titanite ca. 64

Myrs post-collision (this study). The emplacement of the Tso Morari Nappe to its current

location was a rapid process achieved at least within 25 Myrs following the collision. In stark

contrast, the final configuration of the Kovik Domain was achieved ~90 Myrs after initial

collision. The dissonance between the rapid exhumation of the Tso Morari Nappes and the

slow evolution of the Kovik Domain following the collision imply that the latter did not

evolve similarly as the Tso Morari or, at least, on a significantly different timescale.

42

1.9 Conclusion

Investigation of the contact between the Kovik Domain and the Northern Domain

highlighted the following:

• Based on fieldwork and thin section observations, and quartz c-axis fabric analysis,

two distinct shear zones were identified at the contact of the Kovik Domain and the

Northern Domain

• The LSZ is located at least ~within 600 and ~140 structural meters of the contact, as

the northern extent of this shear zone has not been investigated and is defined by a

top-to-the-south sense of shear associated with quartz c-axis patterns characteristic of

flattening strain.

• The USZ is located within ~140 structural meters of the contact and is defined by a

top-to-the-north sense of shear and quartz c-axis fabric characteristic of deformation

that approximates plane strain.

• The temperatures of deformation of the LSZ and USZ are constrained at 627 ± 50°C

and 580°C ± 50°C, respectively.

• Two populations of titanite are identified. The old population yielded an age of 1894

± 31 Ma and the young population yielded an age at ca. 1740 Ma.

• The old population is interpreted as metamorphic titanite related to the ca. 1880 Ma

Circum-Superior LIP emplaced around the Superior Province (Bleeker and Kamo,

2018) leading to the initial hydration of the Archean basement causing the

amphibolite facies overprint. The young population is interpreted to represent

resetting of the titanite via dynamic recrystallization during deformation within the

LSZ.

Although we interpret LSZ as a detachment, the results of this study are hard to reconcile

with the modern plate tectonic model exhuming UHP complex as seen in the Tso Morari in

43

the Himalaya-Tibet Orogen and imply that the Kovik Domain evolved differently, or at least

on different timescales.

44

1.10 Acknowledgements

This project was funded by the Ministère de l’Énergie and des Ressource Naturelle du

Québec (MERN) and by a NSERC grant RGPIN-2020-06400 to CG. The authors would like

to thank Edmond Rousseau, Suzie Côté, Riccardo Graziani and Mark Button for the sample

preparation, X-ray fluorescence analyses, EBSD analyses and LA-ICPMS analyses,

respectively.

45

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1.12 Supplementary data: BSE, EPMA, EBSD and tables

Figure A1: From top to bottom are BSE, EPMA, misorientation and Kernal average

misorientation from titanite in the shear zone distal from the contact. The age plot are LA-

ICP-MS age of the 238U/206Pb corrected for the 207Pb.

53




54




55




56




57

Table 1: Isotopic ratios of specimen TG-4015

* Analysis not used in the age calculation.

Specimen-grains-spot U Th Pb U/Th 238U/206Pb 2σ (%) 207Pb/206Pb 2σ (%) 207Pb/235U 2σ (%) 206Pb/238U 2σ (%) rho206Pb/238U Age(Ma)

207 Corr2σ (abs) 2σ (abs)

TG-4015-1-1* 0.84 0.10 6.5 8.80 0.4431 5.51 0.7804 4.01 252.8323 6.72 2.3507 5.39 0.80 4775 183 688 34

TG-4015-1-2* 0.66 0.04 1634 18.83 0.0074 70.48 0.9387 8.13 63423.8749 46.43 490.2346 45.72 0.98 4850 1418 687 34

TG-4015-1-3* 0.71 0.03 46.6 25.15 0.1272 16.94 0.8432 6.23 1083.7326 18.54 9.3261 17.46 0.94 4972 576 686 34

TG-4015-2-1 6.62 0.29 5.5 23.20 2.2260 1.83 0.3867 4.70 24.0583 5.15 0.4514 2.12 0.41 1707.5 27.4 691 34

TG-4015-2-2 5.63 0.42 16.8 13.48 1.4508 4.21 0.5261 5.43 50.9012 7.03 0.7021 4.47 0.64 2065.7 74.2 681 33

TG-4015-2-3 6.29 0.50 13.7 12.53 1.6748 3.37 0.4933 4.57 41.1107 5.87 0.6046 3.68 0.63 1882 55 690 34

TG-4015-2-4 9.97 0.33 9.1 30.11 2.3472 3.23 0.3566 5.36 21.2068 6.35 0.4316 3.40 0.54 1702.4 48.2 682 34

TG-4015-3-1* 0.17 - 4.4 - 0.1461 9.81 0.9553 4.60 1012.7275 10.48 7.6921 9.42 0.90 4748 314 692 34

TG-4015-4-1 1.67 - 4.5 - 1.1470 4.44 0.6889 4.55 83.7547 6.27 0.8821 4.31 0.69 1551 61 691 34

TG-4015-4-2* 0.55 - 3.5 - 0.5359 7.89 0.8554 4.52 236.2158 9.01 2.0036 7.79 0.87 5035 274 682 34

Concentrations (ppm) Mesured isotopic ratios Isotopic ages Zr-in-titanite temperature

Temperature (°C)

58




207Pb Corr.2σ (abs) 2σ (abs)

TG-4022-1-1 6.00 0.72 7 8.30 2.4944 2.87 0.3397 5.91 18.8576 7.69 0.40 4.92 0.64 1643.2 41.6 658 32

TG-4022-1-2 5.43 0.64 18 8.47 2.2435 4.23 0.3568 5.90 22.3662 8.15 0.45 5.63 0.69 1785 66 656 32

TG-4022-1-3 46.91 4.82 15.4 9.73 3.1581 1.27 0.1399 3.34 6.1198 6.02 0.32 5.01 0.83 1710.3 19.08 659 32

TG-4022-1-4 13.32 1.52 6 8.78 2.9164 1.92 0.2049 4.82 9.6921 6.84 0.34 4.85 0.71 1707.7 28.8 659 32

TG-4022-1-5 47.39 4.72 17 10.05 3.0198 1.03 0.1574 3.55 7.1924 5.93 0.33 4.75 0.80 1750.66 15.72 663 32

TG-4022-1-6 43.65 4.67 15.1 9.34 3.0918 1.19 0.1474 3.22 6.5829 5.86 0.32 4.89 0.84 1731.08 18 664 32

TG-4022-1-7 48.11 5.06 17.5 9.50 3.0366 1.19 0.1489 3.77 6.7690 6.11 0.33 4.81 0.79 1758.92 18.36 661 32

TG-4022-1-8 2.72 0.31 8.1 8.72 1.5760 5.14 0.5483 5.40 48.7933 7.66 0.65 5.44 0.71 1755 79 674 33

TG-4022-1-9* 0.29 0.09 3.9 3.28 0.5050 9.87 0.9568 6.06 276.1782 12.06 2.09 10.42 0.86 5188 352 688 34

TG-4022-1-10 11.09 1.03 6.4 10.72 2.7071 3.60 0.2586 8.34 13.3852 10.06 0.38 5.62 0.56 1711.1 54.2 674 33

TG-4022-1-11 8.90 1.00 8.1 8.93 2.1805 2.40 0.3322 5.21 21.1442 6.64 0.46 4.11 0.62 1916.3 39.8 654 32

TG-4022-1-12 21.21 2.23 8.9 9.53 2.9319 1.64 0.1923 4.25 9.0708 6.40 0.34 4.78 0.75 1726.5 24.8 654 32

TG-4022-1-13 11.22 1.22 6.2 9.17 2.5827 1.93 0.2652 3.05 14.2287 5.34 0.39 4.39 0.82 1778 30 654 32

TG-4022-1-14 28.21 2.64 11.2 10.69 3.1098 1.90 0.1639 4.46 7.2884 6.81 0.32 5.14 0.75 1687.2 28.2 665 32

TG-4022-1-15 9.52 1.10 7.1 8.66 2.4226 2.35 0.3194 3.80 18.2984 5.80 0.42 4.38 0.76 1751 36 683 34

TG-4022-1-16* 0.08 0.01 4.9 12.92 0.0580 13.12 1.0488 3.82 2872.2026 12.82 19.87 12.24 0.95 4579 430 685 34

TG-4022-1-17* 0.06 0.01 3.3 4.64 0.0673 25.23 1.0272 6.49 4391.2373 39.93 31.02 39.40 0.99 4632 834 667 33

TG-4022-1-18 24.28 2.81 9.6 8.63 3.0067 1.27 0.1840 3.67 8.4541 6.03 0.33 4.79 0.79 1701.43 18.98 660 32

TG-4022-1-19 3.02 0.46 6.3 6.51 2.0196 6.44 0.4116 6.66 28.7397 9.61 0.51 6.93 0.72 1811.2 101.8 683 34

TG-4022-1-20 32.04 3.58 15.9 8.95 2.7651 1.30 0.2388 3.10 11.9032 5.44 0.36 4.47 0.82 1721.65 19.6 660 32

TG-4022-1-21 22.13 2.01 8.8 11.01 2.9535 1.42 0.1862 3.71 8.6942 6.05 0.34 4.78 0.79 1727.1 21.4 665 32

TG-4022-1-22 39.73 4.03 14.5 9.86 3.0021 1.09 0.1564 3.42 7.1943 5.84 0.33 4.74 0.81 1762.84 16.76 655 32

TG-4022-1-23* 0.09 0.22 4.2 0.39 0.0802 18.73 1.0312 4.37 2459.1480 21.03 17.30 20.57 0.98 4603 616 683 34

TG-4022-1-24* 0.13 0.22 6.2 0.59 0.0758 9.16 0.9525 3.65 1802.1736 7.99 13.73 7.11 0.89 4800 310 676 33

TG-4022-1-25 15.73 2.04 10.6 7.71 2.8321 2.88 0.2260 6.06 11.0561 7.98 0.35 5.19 0.65 1710.2 43.4 665 33

TG-4022-1-26 23.22 2.19 21 10.59 2.7376 2.12 0.2192 5.34 11.0758 7.11 0.37 4.69 0.66 1786 33 677 33

TG-4022-1-27* 0.29 0.20 9.5 1.44 0.1079 8.33 0.8861 3.48 1201.2134 9.01 9.84 8.31 0.92 4907 286 693 34

TG-4022-1-28* 1.53 0.15 11.6 10.27 0.6768 4.77 0.7802 5.09 161.8211 6.95 1.50 4.72 0.68 4710.6 159.4 680 33

TG-4022-1-29* 0.09 0.20 502 0.45 0.0145 49.58 0.8746 4.04 75741.7980 38.79 628.36 38.58 0.99 4937 1710 671 33

TG-4022-1-30 23.75 2.71 84 8.78 1.4144 5.95 0.5405 5.05 54.6257 8.62 0.73 6.99 0.81 2052.8 104.6 648 31

TG-4022-1-31* 1.37 0.75 24.5 1.84 0.2402 4.47 0.8911 2.80 519.7217 5.00 4.23 4.14 0.83 4852.8 152.4 682 34


Temperature (°C)

59




207 Corr2σ (abs) 2σ (abs)

TG-4023-1-1 27.4 0.3 17.46 107.7 2.6194 2.31 0.2597 5.33 13.6930 5.86 0.3825 2.44 0.42 1766.6 35.8 690 34

TG-4023-1-2 34.6 0.3 15.83 129.1 2.8834 1.96 0.2054 7.40 9.8575 7.74 0.3482 2.27 0.29 1726.0 29.6 691 34

TG-4023-1-3* 1.3 0.1 10.22 19.8 0.3776 6.26 0.7244 3.44 272.9343 7.27 2.7338 6.41 0.88 4316.9 196.8 735 37

TG-4023-1-4 2.7 0.0 3.06 251.4 1.8513 4.26 0.4135 5.78 31.4930 7.31 0.5527 4.48 0.61 1987.4 72.8 651 32

TG-4023-1-5 8.4 0.3 8.01 75.4 2.0933 3.25 0.3548 5.24 23.6746 6.21 0.4841 3.32 0.53 1928.8 54.2 655 32

TG-4023-1-6 4.5 0.1 6.10 33.5 1.6964 8.21 0.4703 6.34 40.4298 9.72 0.6238 7.36 0.76 1954.3 138.4 737 37

TG-4023-1-7 28.7 0.3 16.85 114.9 2.4633 4.47 0.2992 8.35 17.0823 9.61 0.4143 4.74 0.49 1775.6 69.4 690 34

TG-4023-2-1* 16.2 1.4 21.74 12.7 1.9676 5.81 0.5308 5.67 37.9229 8.70 0.5184 6.59 0.76 1419.1 74.0 683 34

TG-4023-2-2* 5.7 0.2 6.59 45.9 2.3351 5.69 0.4224 5.24 25.5755 7.78 0.4394 5.75 0.74 1515.0 76.8 677 33

TG-4023-2-3* 5.5 0.2 5.26 44.9 2.3150 3.05 0.4160 5.92 24.7867 6.74 0.4323 3.23 0.48 1548.6 42.0 698 35

TG-4023-2-4 14.8 0.5 15.33 37.2 2.0974 2.74 0.3524 5.41 23.2294 6.04 0.4783 2.69 0.44 1932.7 45.8 667 33

TG-4023-2-5 41.5 0.4 18.75 100.4 2.9438 1.90 0.1776 7.35 8.3515 7.69 0.3413 2.25 0.29 1751.6 29.0 701 35

TG-4023-2-6 41.8 0.4 17.04 113.2 3.0434 1.61 0.1619 7.15 7.3584 7.42 0.3298 1.96 0.26 1727.8 24.4 700 35

TG-4023-2-7 17.1 0.1 27.85 170.1 1.6520 2.82 0.4828 4.17 40.4326 5.15 0.6076 3.02 0.59 1960.0 47.6 685 34

TG-4023-2-8 19.7 0.2 10.19 136.8 2.7726 2.10 0.2156 7.72 10.7856 8.07 0.3630 2.35 0.29 1771.4 32.6 679 33

TG-4023-2-9* 26.6 0.4 11.68 69.3 3.1508 3.25 0.1993 6.56 8.8440 7.45 0.3219 3.54 0.47 1592.7 45.8 678 33

TG-4023-3-1 24.3 0.5 11.71 52.0 2.9181 1.93 0.1873 6.67 8.8884 7.01 0.3443 2.18 0.31 1745.6 29.4 677 33

TG-4023-3-2 28.8 0.4 12.95 73.6 3.0051 2.00 0.1904 6.88 8.7804 7.25 0.3345 2.27 0.31 1688.6 29.6 689 34

TG-4023-3-3* 21.5 0.4 13.44 52.6 1.7481 14.05 0.3007 12.00 29.4544 20.42 0.7107 16.52 0.81 2565.0 298.0 686 34

TG-4023-3-4 26 0.4 12.02 69 2.8068 1.77 0.2032 6.70 9.9865 7.04 0.3567 2.17 0.31 1778.4 27.4 686 34

TG-4023-3-5 30.7 0.4 13.43 73 2.8970 1.75 0.1701 7.35 8.1263 7.63 0.3466 2.04 0.27 1796.2 27.4 689 34

TG-4023-4-1 36.5 0.4 15.88 101.9 2.9521 1.91 0.1765 6.96 8.2804 7.30 0.3405 2.21 0.30 1749.1 29.2 694 34

TG-4023-4-2* 12.0 0.2 7.01 62.3 2.1914 4.17 0.2679 6.19 17.2003 7.61 0.4659 4.42 0.58 2100.4 74.8 671 33

TG-4023-4-3 23.0 0.3 10.02 88.8 2.9194 2.03 0.1817 7.18 8.6221 7.53 0.3444 2.28 0.30 1757.2 31.2 689 34

TG-4023-5-1 14.6 0.8 9.27 17.7 2.7138 3.08 0.2475 7.56 12.6130 8.16 0.3698 3.09 0.38 1733.7 46.8 677 33

TG-4023-5-2* 14.3 0.5 17.44 32.2 2.6984 2.63 0.5598 3.03 28.8586 4.21 0.3741 2.92 0.69 913.6 22.4 659 32

TG-4023-5-3 14.3 0.8 9.22 17.4 2.5109 3.68 0.2700 8.57 15.1499 9.67 0.4071 4.46 0.46 1817.8 58.4 667 33

TG-4023-5-4* 10.1 0.5 9.65 20.0 2.5124 2.49 0.3983 4.87 22.0236 5.63 0.4012 2.82 0.50 1469.1 32.6 667 33

TG-4023-5-5 9.0 0.5 6.63 18.6 2.3790 2.46 0.2733 5.91 15.9556 6.46 0.4236 2.61 0.40 1912.7 40.8 668 33

TG-4023-6-1 13.8 0.7 12.98 19.1 2.1230 2.19 0.3790 4.11 24.6547 4.69 0.4720 2.26 0.48 1821.9 34.8 681 33

TG-4023-6-2* 36.6 1.2 20.70 30.1 2.8493 1.72 0.2655 4.68 12.8974 5.12 0.3525 2.08 0.41 1608.5 24.6 692 34

TG-4023-6-3* 8.8 0.3 8.62 32.3 2.2709 2.57 0.4055 4.99 24.8224 5.67 0.4442 2.70 0.48 1613.6 36.6 673 33


Temperature (°C)

60

Table 4: Geochemistry analysis by LA-ICPMS on titanite from specimen TG-4015, TG-4022 and TG-4023

Specimen-grains-spot Sr Y Zr La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

TG-4015-1 57 73 53 1.2 BelowLOD 1.4 7.9 4.8 2.6 6.4 1.3 10.4 2.6 8.4 1.3 9.4 1.3

TG-4015-2 32 70 52 0.63 3.8 0.8 5.5 3.9 2.4 5.8 1.3 10.7 2.6 8.4 1.2 8.8 1.3

TG-4015-3 32 66 51 0.7 4.2 0.9 5.7 4.2 2.4 6.1 1.3 9.6 2.3 8.1 1.2 9.3 1.3

TG-4015-4 36 338 57 5.5 37.6 9.5 66 38 21.7 54 9.6 63 12.5 37 5.0 35 4.9

TG-4015-5 31.7 308 45 4.8 30.6 8.4 59 36 21.7 52 9.0 58 11.4 32.7 4.5 29.8 4.2

TG-4015-6 33.7 317 55 5.3 34.0 8.9 62 37 22.6 53 9.1 59 11.9 34 4.8 32 4.6

TG-4015-7 47 437 47 7.72 54 14.6 105 62 36.3 85 14.1 87 16.6 45 6.0 39 5.3

TG-4015-8 41 3.9 58 0.32 2.0 0.37 1.7 0.7 1.6 0.6 0.06 0.4 0.10 0.6 0.20 2.4 0.45

TG-4015-9 38 152 56 1.64 10.9 2.4 14.9 10.2 11.6 15.6 3.3 24 5.5 17.8 2.5 19 2.5

TG-4015-10 39 68 47 0.58 3.5 0.8 4.7 3.6 3.9 5.5 1.3 10 2.3 7.6 1.2 9.1 1.2

TG-4022-1 27.2 345 27.7 1.8 10.3 2.4 16.0 11 38 20 4.4 37.6 9.4 35 5.7 40 5.7

TG-4022-2 27.1 335 25.9 1.6 9.5 2.3 15.2 10.0 36.7 17.5 4.3 35 9.1 34 5.4 38 5.1

TG-4022-3 27.6 2003 28.3 13.5 76 19.3 137 107 198 191 42.9 321 68 199 25.1 148 17.2

TG-4022-4 26.8 906 27.8 4.4 25 6.6 49 39 69 72 17 131 30 95 13.9 85 10.8

TG-4022-5 28.3 2236 30.5 15.0 79 20.0 143 109 209 206 47 356 77 222 28.4 163 18.7

TG-4022-6 29.8 2078 31.2 13.6 76 18.7 134 105 188 195 42.7 335 71 206 27.0 153 17.3

TG-4022-7 27.9 2297 29.6 14.6 79 19.8 142 112 205 211 46.9 366 78 229 29.6 167 18.9

TG-4022-8 42 98 38.8 1.9 5.3 1.5 9 5.5 11 10 2.1 15 3.4 10.0 1.4 9.0 1.2

TG-4022-9 44 40 53 2.1 2.0 0.7 2.1 1.0 2.0 1.5 0.4 4.1 1.2 5.1 0.9 6.0 0.7

TG-4022-10 39 605 39 3.4 18 4.6 31 27 49 51 12 97 22 63 8 46 5.1

TG-4022-11 27.4 458 25.0 2.8 15.8 3.8 28 18.9 52 32 7.2 58 13.6 45 6.9 45 5.9

TG-4022-12 28.0 827 25.0 6.6 36 9.0 64 44 103 78 16.6 124 27.0 80 11.1 67 8.2

TG-4022-13 28.0 443 25.1 3.9 20.0 5.0 34 21.7 64 35 7.3 57 12.8 42 6.4 42 5.6

TG-4022-14 34 1427 32.0 9 46 12 84 68 124 130 30 232 49 143 19 107 12

TG-4022-15 40 349 48 5.3 18.5 4.8 30 19 42 33 7.2 54 11.4 34 4.5 27 3.0

TG-4022-16 45 7.5 50 0.02 0.09 Below LOD Below LOD 0.2 0.3 0.3 0.06 0.8 0.21 0.7 0.15 1.5 0.24

TG-4022-17 42 2.9 33.6 0.3 0.3 0.08 Below LOD 0.2 0.2 0.3 0.05 0.4 0.11 0.3 0.05 0.3 0.03

TG-4022-18 30.9 781 29.0 9.2 44 10.8 73 49 112 79 16.3 119 24.7 73 9.9 60 7.6

TG-4022-19 40 284 48 4.1 7.2 2.0 11 7 17 14 3.7 34 9 35 6 41 4.9

TG-4022-20 29.2 1094 28.9 14.2 62 15.2 98 66 148 107 23.1 171 36 104 13.7 82 9.9

TG-4022-21 34.9 1032 31.8 6.4 36 9.3 65 52 95 92 21.0 163 34 101 13.6 78 8.6

TG-4022-22 27.5 1368 25.8 12.6 68 17.2 115 82 167 135 28.1 215 44 129 16.8 103 12.2

TG-4022-23 45 2.3 47 1.8 1.8 0.6 2.0 0.5 0.3 0.2 0.06 0.4 0.06 0.21 0.04 0.2 0.03

TG-4022-24 44 5.1 41 4.1 3.2 1.2 4.2 0.7 0.3 0.5 0.09 0.5 0.13 0.5 0.12 1.0 0.15

TG-4022-25 28.8 716 32 15 39 10.5 58 36 81 59 12.9 102 22.4 70 10.2 66 8.2

TG-4022-26 35.4 1139 42 8.0 40 10.0 69 52 101 98 23.3 182 40 119 15.8 90 10.1

TG-4022-27 45 12 59 5.0 3.8 1.6 4.9 1.2 0.9 1.0 0.21 1.6 0.4 1.3 0.21 1.4 0.17

TG-4022-28 41 179 45 0.6 2.7 0.6 4.5 3.6 10 7.5 2.0 20 5.6 22 3.8 27 3.4

TG-4022-29 41 4.9 36.9 3.4 2.7 1.0 3.3 0.7 0.2 0.6 0.08 0.6 0.1 0.6 0.15 1.4 0.2

TG-4022-30 26.7 785 21.6 14.5 56 14.9 93 56 111 87 17.6 129 28 79 10.7 63 7.0

TG-4022-31 45 49 47 17 25 6.1 20 5.2 3.1 4.4 1.0 7.0 1.6 5.3 0.9 6.6 0.9

TG-4023-1-1 22 316 55 7.5 41 8.7 47 22 22 34 6.3 47 10.9 34 5.2 36 5.6

TG-4023-1-2 23 261 57 9 48 9 50 22 29 29 5.7 37 9 27 4.2 32 4.8

TG-4023-1-3 12 5.3 138 47 64 5.1 14 1.5 9.6 1.1 0.1 0.9 0.2 0.5 0.1 0.7 0.1

TG-4023-1-4 12.1 26 23 18 20 1.8 6 2.2 5.1 2.6 0.5 3.8 0.9 2.8 0.5 3.5 0.5

TG-4023-1-5 47 79 25 21 43 6 23 7 7.7 9 1.7 12 2.8 8.6 1.4 10 1.2

TG-4023-1-6 14 20 145 89 138 12 32 5 18 3.2 0.5 3.1 0.6 2.1 0.4 3.4 0.6

TG-4023-1-7 38 383 56 7.5 37 8.1 46 24 28 38 7.5 58 13 41 6.5 45 6.5

TG-4023-2-1 60 81 47 59 135 17 58 13 11 12 2.0 13 2.8 9 1.5 12 1.8

TG-4023-2-2 23 45 42 43 75 8 29 6 6.4 4.7 0.8 6.0 1.4 5.0 0.9 8 1.3

TG-4023-2-3 18 37 66 24 39 4.4 17 4.3 6.5 3.6 0.8 5.2 1.4 4.2 0.8 7 1.1

TG-4023-2-4 25 133 33 22 61 9.9 47 19 12 21 3.4 22 4.7 14 2.0 14 1.9

TG-4023-2-5 24 342 70 11.4 59 12.0 66 29 37 40 6.9 51 11 36 5.4 41 6.1

TG-4023-2-6 23 305 68 10.2 53 11 61 27 34 37 6.7 47 10.2 33 5.0 36 5.4

TG-4023-2-7 21 203 50 12 32 4.8 23 10 13 15 3.7 28 7 22 3.8 30 4.9

TG-4023-2-8 20 194 43 4.3 22 4.7 26 12 18 18 3.6 27 6.3 22 3.4 25 3.7

TG-4023-2-9 17 593 43 5.7 29 6.3 37 23 30 47 11 90 21 67 10 68 10

TG-4023-3-1 26 246 42 10.6 56 11.9 66 29 17 37 6.5 42 9.0 26 3.6 25 3.2

TG-4023-3-2 24 339 54 10 52 11 63 29 19 39 7.2 51 11.5 36 5.5 39 5.4

TG-4023-3-3 22 273 51 13 67 14 77 31 18 39 6.9 44 9.2 28 4.0 27 3.9

TG-4023-3-4 21 323 51 8.6 47 9.6 55 26 19 37 7.0 49 11.3 35 5.3 38 5.1

TG-4023-3-5 22 358 55 9.8 57 11.1 63 29 20 42 8.0 56 12 39 5.8 40 6

TG-4023-4-1 23 311 61 10.9 58 11.9 65 28 27 38 6.9 48 10.4 33 4.8 34 4.8

TG-4023-4-2 18 91 37 57 129 14 53 13 20 14 2.1 15 3.0 10 1.5 10 1.6

TG-4023-4-3 19 177 54 37 93 13 54 18 25 22 3.9 28 5.9 18 3.0 20 2.9

TG-4023-5-2 16.0 61 28 21 51 10.9 46 13 7.5 11 1.7 10 2.1 6.4 1.1 8 1.5

TG-4023-5-3 21 100 34 11.1 51 10.3 54 18 13 18 3.0 18 3.5 11 1.5 11 1.8

TG-4023-5-4 19 64 34 16 50 8.8 41 11 8.1 11 1.8 10.4 2.1 6.6 1.1 8.7 1.5

TG-4023-5-5 16.6 79 35 26 100 18.1 85 22 10.8 17 2.6 15 2.7 7.8 1.2 8.9 1.4

TG-4023-5-6 21 123 42 8.5 42 8.7 46 17 14 18 2.9 20 4.0 13 2.0 14 2.2

TG-4023-6-1 50 113 46 32 67 9.9 44 16 12.1 18 2.9 19 4.1 12 1.8 14 2.1

TG-4023-6-2 24 194 58 18 66 13.9 68 24 27 26 4.4 29 6.3 20 3.1 22 3.7

TG-4023-6-3 18 110 38 13.1 34 5.9 31 14 9.3 16 3.0 19 4.2 12 1.8 12 1.7

Concentration (ppm)

61

Conclusion

La présente étude du contact entre le Domaine de Kovik et le Domaine Nord a permis de

souligner les informations suivantes :

• Deux zones de cisaillements entre le Domaine de Kovik et le Domaine Nord ont été

identifiées sur la base d’observations de terrains, de lames minces orientées de

d’analyse des axes-c du quartz.

• La LSZ est située à au moins entre ~600 et ~140 mètres structurellement du contact,

puisque son étendue Nord n’a pas été investiguée. Elle montre une cinématique de

sommet-vers-le-sud et des fabriques d’axes-c du quartz caractéristiques d’une

déformation en aplatissement.

• La USZ est située entre ~140 et 0 mètre structurellement du contact et montre une

cinématique de sommet-vers-le-nord et des fabriques d’axe <c> du quartz

caractéristiques d’une déformation plane.

• Les températures de déformation de la LSZ et de la USZ de cisaillement sont

contraintes à 627 ± 50°C et 580 ± 50°C, respectivement.

• Deux populations de titanite ont été identifiées. La population la plus vieille est datée

à 1894 ± 31 Ma alors que la population la plus jeune est datée à 1737-1752 Ma.

• La population la plus jeune représente la réinitialisation de la population la plus vieille

lors de l’activité de la LSZ. La population la plus vieille est interprétée comme étant

reliée à l’emplacement de la grande province ignée Circum Supérieur.

Bien que nos résultats supportent que le contact entre le Domaine de Kovik et le Domaine

Nord correspond à un détachement, la chronologie des événements tectono-métamorphiques

du Domaine de Kovik est difficilement corrélable avec celle observée dans la nappe du Tso

Morari dans l'Orogène Himalaya-Tibet.

62

Pour de travaux futurs, la USZ observée au contact Domaine de Kovik et Domaine Nord

devrait être datée en combinant les données du EBSD et de datation U-Pb in situ sur titanite

afin de comparer la chronologie de son activité avec celle de la LSZ. D’autres transects à

travers le Domaine de Kovik et le Domaine Nord pourraient être effectués dans la partie

occidentale du Domaine de Kovik afin de pouvoir mieux définir l’étendue et la cinématique

des zones de cisaillement identifiées dans ce mémoire.

63

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