Volume 17, numéro 4, december 1990

EN :

The eastern Churchill Province, which separates the Archean cratons of the Superior and Nain provinces in the eastern Canadian Shield, is a rare example of a two-sided EarlyProterozoic orogenic belt. The interior of the eastern Churchill Province is composed largely of reworked Archean rocks, which appear to form an extension of the Rae Province, sutured against the adjoining Superior and Nain provinces by the New Québec and Torngat orogens. Both orogens contain continental margin sequences that record the transition from initial rift to fore deep environments. Deformation was predominantly of transpressional character and was controlled by oblique convergence of the Superior and Nain cratons on the Rae Province. The New Québec and Torngat orogens have a mirror-image symmetry defined by outward-verging fold and thrust belts associated with dextral (west) and sinistral (east) transcurrent shear on their interior margins. The dominant feature of the New Québec Orogen isits broad fold and thrust belt which is developed in low- to medium-grade rocks and is analogous to the foreland zones of Phanerozoic orogens. The Torngat Orogen, however, is dominated by an extensive sinistral shear system, developed in granulite-facies crust, that provides an excellent lower crustal analogue for modern crustal-scale transcurrent fault systems.

EN :

A tectonic model is proposed, based on the Cenozoic evolution of Southeast Asia, in which the southeast arm of the Rae Province rotated clockwise in response to collision alindentation of the Superior Province. A dextralpull-apart basin characterized by mafic sill-sediment complexes formed along the leading edge of the rotating block. Relics of this basin, analogous to the Andaman Sea basin of Southeast Asia, were subsequently thrust onto the Superior Province margin where they occur as allocations in the Labrador Trough.A wedge-shaped ancestral Baffin basin, analogous to the South China Sea, opened simultaneously in the wake of the rotating block.The margins of this basin are delineated bythe Foxe-Rlnkian and Dorset fold belts; their convergence and disappearance westward reflect the primary shape of the basin. North-west-dipping subduction beneath the mouth of the basin accommodated convergence of the Burwell and Nain provinces from the southeast and gave rise to the Cumberland batholith. Docking of the Burwell and Nain provinces caused compressional collapse ofthe ancestral Baffin basin and sinistral transpression of the Torngat Orogen, respectively.The model is well constrained by existing U-Pb geochronological data and makes predictions which can be tested by additional data.

EN :

Previous work has shown that a major part ofthe Early Archean (>3500 Ma) rocks in Labrador north of Nain were reworked undergranulite-facies conditions between 2800and 2700 Ma. New U-Pb zircon data show that Middle Archean gneisses are more abundant than previously recognized. Their metamorphic histories differ from the historyof the Early Archean rocks. Part of the Middle Archean gneiss suite was emplaced direct lyin granulite faciès between 3250 and 3200Ma and was partly retrogressed at the time of granitoid veining ca. 2990 Ma. Only after ce.2700 Ma do Early and Middle Archean gneisses have similar histories. We suggest that the terrane model proposed for SW Greenland can be applied to Labrador and that terrane intercalation took place ca. 2700Ma. The Middle Archean gneisses north of Nain are likely to be tectonic slivers equivalent to the Maggo gneiss of the Hopedale area to the south. Correlation between the Middle Archean terrane of Labrador and the Akia terrane in SW Greenland is suggested.

EN :

The high-grade gneisses of the Archeannian Province were formed through Early and Late Archean orogenlc cycles. Late Archean structural development consistedof pre-thermal-peak isoclinal folding and thrusting in allochthonous Upemavik supra-crustal rocks, followed by regional, recum-bent, isoclinal folding and upright refolding ofthe Upernavik suite and reworked Early Archean gneisses under amphibolite- to granulite-facies conditions. Style and sequence of the Late Archean structures closely resemble those described by previous workers from the Early Archean gneiss complex ofthe North Atlantic craton, from Precambriangreenstone belts, and from Phanerozoic orogenic belts, suggesting that no principal differences exist in the structural evolution of these types of terrain.

EN :

The Kuujjuaq terrane of the New Québec Orogen may represent a northern extension of the De Pas batholith, which is thought to be the remnant of a lower Proterozoic continental magmatic arc. Collision between the Kuujjuaq terrane and the Labrador Trough to the west produced intense deformation, associated with large-scale, southwest-directed transport. The Kuujjuaq batholith, thought to be a subduction-related granitoidsuite, was emplaced at a late stage in the deformation. Extensive post-tectonic metamorphism involved retrogression of early granulite-facies mineral assemblages. Our interpretation is that the Kuujjuaq terranewas subjected to deep and protracted burial(>40 m.y.). This is consistent with, and most easily explained by, its development within a major continental collision zone such as that between India and Asia.

EN :

The westernmost hinterland zone of thenorthern Labrador Trough is characterized by four NW-trending, Archean basement bodies overlain by an upward-coarsening, amphibolite-facies volcano sedimentary cover sequence correlative with the Kani-apiskau Supergroup of the Labrador Trough.Two of the gneissic basement bodies occurin anti formal cores, but two occur in the cores of synforms. The synformal gneissesare thought to represent the down folded lower limb of a single, basement-cored nappe floored by a large thrust that roots down into one of the basement domes. The history of this area during the Hudsonian Orogeny involved initial westerly imbrication and transport of the cover succession along a thin décollement zone at the basement-cover interface. This was followed by NW-directed, basement-involved thrusting and associated folding, and large-amplitude, up-right to SW-vergent, SE-plunging folding.The NW-vergent, basement-involved event appears to be restricted to this portion of the hinterland zone.

EN :

The northern segment of the New Québec Orogen is divided into 4 zones, based on lit hostrat I graphic assemblages and deformational style. The tectonic fabric Is the result of WSW-SW transport during the third deformation event, which, in the foreland, consists of two stages. A basât décollement,low-angle thrust faults and bedding-parallel gliding in the western foreland are important features of the early D3 stage. The bulk of crustal shortening occurred during the late D3 (D3.) stage, which is characterized by large-scale, high-angle out-of-sequence thrusts, and folds. The hinterland records more complex pre-D3, deformation, which cannot presently be correlated with early deformation in the foreland. The D3. out-of-sequence geometry is probably the result of syntectonic erosion of the orogenic wedge, but there is little geological evidence in the foreland supporting this premise. This apparent paradox can be explained by Invokinga two-sided, double-wedge orogenic model, which links erosion and uplift In the hinterland to out-of-sequence thrusting in theforeland.

EN :

La partie septentrionale de l'orogène du Nou-veau-Québec se divise en quatre zones enfonction des assemblages lithostratigra-phiques et du style structural. Le grain tec-tonique régional résulte d'un transport deces zones vers le WSW-SW lors de la troisiè-me phase de déformation qui comprend,dans l'avant-pays, deux phases. La phaseprécoce (D3) est caractérisée par un dé-collement basai et des chevauchements ensérie dans la partie est de l'avant-pays et pardes glissements parallèles aux strates dansla partie ouest. La phase tardive (D3-), surtout responsable de l'épaississement crus-tal, est caractérisée par un ensemble géné-ralisé de grands plis et de failles de chevau-chement hors série abruptes. Larrière-paysprésente des structures pré-D3, plus com-plexes qui ne peuvent être corrélées aveccelles de l'avant-pays. L'agencement hors-série D3- provient probablement de l'érosionsyn-orogénique du prisme tectonique, maison observe peu d'évidence de cette érosiondans l'avant-pays. Cette disparité corres-pond peut-être au modèle de double prismestectoniques opposés, qui relie l'érosion et lesoulèvement de l'arrière-pays aux chevau-chements hors série de l'avant-pays.

EN :

Detailed gravity data, collected along an east-west transect across the northern New Québec Orogen near Leaf Bay, provide constraints on the deep structure of this segment of the orogen. The Bouguer anomaly profilecontains long and short wavelength compo-nents. A steep gravity gradient and a strongpositive anomaly near the centre of the orogen are related to the presence of densemafic volcanic rocks in the shallow crust. Two alternative models are presented that are compatible with the long wavelength gravity data. The authors prefer to interpret the long wavelength components in terms of crustal thickening beneath the orogen and increased crustal density in the Rae Province, to the east. A scenario based on this crustal density structure is suggested for the evolution of the orogen. It calls for (1) the formation of a small ocean separating the Superiorand Rae provinces; (2) subduction of this ocean beneath the Rae Province; and (3) complete closure of the basin with over-thrusting of the Superior margin and, possibly, obduction of the Rae Province onto the Superior Province craton.

FR :

Un profil gravimétrique est-ouest à traversla partie nord de l'orogène du Nouveau-Québec a fourni des données sur la structureprofonde de ce segment de l'orogène.L'anomalie de Bouguer contient des courteset grandes longueurs d'onde. Un fort gradientet une anomalie positive près du centre del'orogène sont causés par des roches vol-caniques mafiques dans la croûte supér-ieure. Deux modèles sont compatibles avecles anomalies de grande longueur d'onde.Les auteurs préfèrent évoquer un épaississement de la croûte sous l'orogène et uneaugmentation de sa densité moyenne versl'est, dans la Province de Rae. Un scénario,basé sur cette structure de densité de lacroûte, est suggéré pour expliquer l'évolutionde l'orogène. Les étapes principales en sont :(1) la formation d'un mini-océan entre lesblocs du Supérieur et de Rae; (2) la subduc-tion de l'océan sous la Province de Rae; et(3) la fermeture du bassin avec chevauche-ment de la marge du Supérieur et, peut-être,l'obduction du bloc de Rae sur le craton duSupérieur.

EN :

This paper presents new data from an area ofthe Rae (eastern Churchill) Province where migmatite and gabbro-anorthosite complexes are intruded by metamorphosed diabase dykes. The pre-dyke rocks are lithologically comparable to Archean components in the Nain Province and may be correlative with them; the dykes may be equivalents of the Eariy Proterozoic dyke swarms of the Nain Province. It is proposed that this area comprises Archean crust that has escaped pervasive Early Proterozoic structural overprint, but was affected by the prevailing metamorphism. Preservation of these types of relationships may be more widespread in the Rae Province than presently recognized. Some tectonic implications of the data are discussed.

EN :

In Labrador, the northerly-trending zonesof the Churchill Province are truncated at their southern margin by rocks of the Labrador Orogen within the Grenville Province. Churchill Province rocks locally extend into the Grenville Province where they are grada-tionally reworked. This paper describes thegeology of the central part of the Churchill Province (the Rae Province) in a 3700 km2 area lying astride the Grenville Front.

The eastern part of the area, the Ormadomain, consists of supracrustal rocks intruded by, and infolded into, orthogneiss. The supracrustal unit is dominated by maficvolcanic and pelitic rocks with subordinate psammite, felsic volcanic rocks, quartzite and conglomerate. The orthogneiss unit consists of foliated to gneissic tonalité andgranodiorite. Both units are intruded by aplutonic suite of granite, diorite and gabbro.U-Pb zircon geochronology of four tonalité samples indicates that the majority of orthogneiss in the Orma domain was empiaced in the Late Archean (2682-2675 Ma). These data confirm earlier ideas that parts of the Rae Province consist of reworked Archean crust. U-Pb results of both zircon and titanite analyses from the same samples indicate a Labradorian Pb-loss, but show no influence by either the Hudsonian or Grenvillian orogenies on the U-Pb isotopic systematics.

FR :

La suite intrusive de Pallatin, sise près ducisaillement de la rivière George, dans Carriè-re-pays de la Fosse du Labrador, se compo-se d'un ensemble magmatique blmodal gra-nodioritique et gabbroTque. Les filons-cou-ches et massifs tabulaires de cette suite sonten continuité avec les basaltes, dacltes,rhyolites et volcanoclastites du complexe deNtshuku. La séquence s'est mise en placedans un environnement bathyal sur un soclegneissique archéen en subsidence rapide.Le complexe et la suite, métamorphisés aufaciès des am phi oolites inférieures, sont re-couverts de sédiments épicratoniques pro-térozoiques inférieurs affectés d'un méta-morphisme au faciès des schistes verts.

Les roches magmatiques montrent unesignature géochimique typique d'un environnement supra-subductifensiallque. La proxi-mité du batholithe de De Pas (type andin) etdu bassin Intra-arc du complexe d'Atsha-katsh supporte cette assertion. Toutefois,l'âge U/Pb sur zircon de 2.3 Ga obtenu sur lagranodiorite de Pallatin rend ambiguë sonaffiliation à un événement précoce-hudso-nien ou tardi-kénoranien.

EN :

The Pallatin intrusive suite, located near theGeorge River Shear Zone, is a granodioritic-gabbroic hypabyssal sill complex. It is continuous, through a dyke swarm, with basaltic and dacitic lava flows, rhyolite domes, andturbiditicvolcaniclastic sediments belong into the Ntshuku complex. The sequence was developed in a bathyal environment and was just exposed upon a gneissic Archean base-ment. Affected by a lower amphibolite-faclesmetamorphism, the Ntshuku complex Is unconformably covered by greenschist-facleslower Proterozoic eplcratonic sediments.

The magmatic rocks show an ensialic arcgeochemlcaJ signature. This Is supported bytheir close association with the Andean-type Hudsonian De Pas bathotith and the intra-arcAtshakatsh complex. However, the grano-diorite yielded an enigmatic 2.3 Ga U/Pbzircon age, which could be assigned to either an eariy-Hudsonian or a late-Kenoran event.

EN :

The NW-trending Torngat Orogen in eastern Ungava Bay, which contains Early Protero-zofc sedimentary rocks and Archean ortho-gneiss, is subdivided into the Burwell terrane, Tasiuyak gneiss, Lake Harbour Group and the George River segment. The Burwell terrane. a granulite-facies migmatitic complex, grades to the southwest into the Tasiuyak gneiss composed of plagioclase-garnet-quartz-sillimanite and graphite. Further to the southwest, the Tasiuyak gneisspasses gradationally into amphlbolite-faciespelitic gneiss, quartz!te and marble of the Lake Harbour Group, which is associated with granodioritic Archean orthogneiss of the George River segment. The 15 km wide Abloviak shear zone, a high strain zone with-in the eastern Torngat Orogen, overprints and subvertically transposes the Tasiuyakgneiss, part of the Lake Harbour Group and its Archean basement. D, deformation is interpreted to have resulted In development of early foliation, and west- to southwest-verging thrusts that interleaved Lake Harbour Group rocks and George River segmentgneiss. D2 was a transpressional deforma-tion event responsible for refolding in the Lake Harbour Group and development of mylonitic fabrics in the Abloviak shear zone.The latter comprises medium- to highly strained rocks (mylonites) formed in a major transcurrent sinistral shear environment. The Lake Harbour Group is deformed into km-scale NNW-trending dome-and-basin structures, involving Archean basement, that were vertically transposed in a northwest ward direction toward the Abloviak shear zone.

FR :

Lbrogène Torngat est orientée NO à l'est dela baie d'Ungava et contient des roches sô-dimentaires protérozoïques et des ortho-gneiss archéens. Le complexe de Burwell,un terrane mlgmatltique au faciès granulltepasse graduellement vers le SO dans lesgneiss de Tasiuyak composés de plaglo-clase-grenat-quartz-sllltmanite et graphite.Au SO, les gneiss de Tasiuyak sont Intercalésavec des métasédlments du groupe de LakeHarbour. Plus à l'ouest, le groupe de LakeHarbour formé de quartzita, de marbre et deparagnelss au faciès amphibolite supérieurest associé à des gneiss granodiorittquesarchéens du Segment de Kuujjuaq. On infèrequ'une phase D, est la cause d'une foliationprimaire et de chevauchements à vergenceSO Intercalant les roches du groupe de LakeHarbour et des gneiss du segment de RivièreGeorge. D2 est une phase en transpressionreprenant les plis dans le groupe de LakeHarbour et développant des mylonites sur 15km dans le cisaillement d'Abloviak. Il s'agit degneiss transposés et de mylonites définis-sant un cisaillement majeur, décrochant etsenestre. Le Groupe de Lake Harbour estformé de structures en dômes et bassinsd'échelle kilométrique à l'interface socle/couverture; elles sont orientées NNO et sonttransposées verticalement en sapprochantdu cisaillement d'Abloviak.

EN :

Detailed gravity data, collected in the northern part of Québec along a SW-NE transectacross the northern Torngat Orogen, provide constraints on the deep structure of this segment of the orogen. The section, located inthe Rae Province east of Ungava Bay, traverses the Archean gneissic terrane of theGeorge River segment, the Early Proterozoic metasedimentary rocks of the Lake Har-bour Group, the Abloviak shear zone and thegranullte-facies migmatttlc complex of the Burwell terrane. The Bouguer gravity profile indicates four distinct zones: (1) in the SW, a low density zone from George River to theeast of Keglo Bay; (2) a zone of intermediate density further to the NE from the Lake Harbour Group extending to Abloviak Fiord; (3) a steep, narrow, Bouguer gravity gradient {positive to the N) which is prominent along the Abloviak shear zone; and (4) a high density zone in the extreme NE of the area. The gravity trend on the contoured Bouguer gravity map is NE in zones 1 and 2, where as it is E-W in zones 3 and 4 and could be correlated with a similar trend in the northern part of the Superior Province west of Ungava Bay. Short wavelength anomalies in zone 1indicate the presence of basin-and-domestructures in the gneissic terrane.

FR :

La structure interne de l'orogène Torngatnous est dévoilée à partir de données grav-imétriques obtenues dans la partie sep-tentrionale du Québec et du Labrador, le longd'une section orientée SO-NE. Le chemine-ment situé sur la côte orientale de la baie d'Ungava recoupe le terrene de gneiss ar-chéens du segment de la rivière George, lesmétasédlments du Groupe de Lake Harbour(ProtérozoTque inférieur), la zone de cisaille-ment Abloviak et le terrane de Burwell, uncomplexe migmatlttque au faciès granulite.Le profil gravimétrique de Bouguer indiquequatre zones distinctes : (1) dans le SO, unezone à faible densité à partir de la RivièreGeorge jusqu'à lest de Keglo Bay; (2) unezone de densité intermédiaire plus loin versle NE, soit à partir du groupe de Lake Har-bour jusqu'au fiord Abloviak; (3) une zoneétroite et montrant une pente abrupte dugradient gravimétrlque de Bouguer (positifvers le N) qui prédomine le long de la zone decisaillement d'Ablcviak; et (4) une zone à trèshaute densité à l'extrémité NE de la région.L'orientation du patron gravimétrlque est NEdans les zones 1 et 2 alors qu'elle est E-0dans les zones 3 et 4 et as dernières zonespourraient se corréler avec des orientationssemblables dans la province du Supérieur,solt à l'ouest de la Baie d'Ungava. Les ano-malies de faible longueur d'onde de la zone 1nous indiquent la présence de structure endome et bassin dans le terrane gneissique.

EN :

The Archean Nain Province of northern Labrador displays a variable imprint of Early Proterozoic thermotectonism several tens of kilometres east of its collisional boundary (Torngat Orogen) with the Archean Rae (eastern Churchill) Province, the latter extensively reworked by Early Proterozoicevents. This imprint is discerned by the west-ward increase in metamorphic grade in the Early Proterozoic Domes diabase dykes and from the degree of retrogression of Archeangranulite-facies gneisses. Early Proterozoictectonic effects also include the translation of Raman Group cover rocks over their Ar-chean basement, and the subsequent folding of both the basement décollement and the cover. Later steep reverse faults dissect the boundary zone between the Rae (Churchl) Province and the Archean foreland. All these features are believed to be related to Earty Proterozoic oblique continental collision between two Archean crustal blocks.

EN :

The Archean Nain Province, part of the North Atlantic craton, collided obliquely with the eastern Churchill Province 1900-1800 million years ago. The eastern Churchill Province (Rae Province) and portions of the western Nain Province were deformed by sinistral transcurrent shear at syn- and post-peakgranulite- to amphibolite-facies conditions during the collislonal phase of the Torngatorogeny. Tectonic remnants of the Early Proterozoic Ramah Group were structurally inter-leaved with Nain Province rocks in the tectonic foreland during this orogeny. In the Churchill Province, the orogeny deformed felsic and mafic igneous rocks intruded into sediments deposited on a foredeep shelf of inferred metaplutonic rocks of the eastern Churchill Province. The effects of orogeny extend east of the tectonic foreland as waning metamorphic grade across 85 km of the Nain Province.

EN :

The Hudsonian Torngat Orogen In the North River map area, Labrador, evolved through: (1) early thrusting and associated isoclinal folding in lower Proterozoic supra crustal cover rocks, and the development of a regional tectonic fabric at peak metamorphic grade; (2) folding and intense shearing on subvertical planes, characterized by a sub-horizontal NNW-plunging extension llneation during sinistral transpression; and (3)Å-directed thrusting during uplift of the orogen. These structures are Interpreted as progressive features that resulted from E-Woblique collision of the Archean Nain and Rae continental blocks across a 160°-striking boundary.

EN :

Granulite-facies gneisses in the Ablovlak shear zone in the internides of the Torngat Orogen are characterized by subvertical shear fabrics and associated subhorizontal stretching lineations. P-T vectors, derived from individual samples of these gneisses by conventional geothermobarometry of equilibrium core, rim and replacement symplectite assemblages, yield evidence of over 3k bars decompression associated with cooling of approximately 150°C. When the sample population is considered together, a P-T-fpath involving over 5 kbars decompression and 250°C cooling is defined. Such paths are compatible with theoretical models of synmetamorphic uplift following doubling of crustal thickness during thrusting, and imply that transcurrent motion took place in tectonically thickened crust, and was coeval with uplift. In a regional context, the Torngat Orogen preserves evidence of the oblique collision of two Archean cratonic blocks, the Nainand Rae provinces, during the Early Proterozoic and their a malgamation with Laurentia.

EN :

The Hopedale block of the southern ArcheanNain Province forms a wedge between the Early Proterozoic Makkovik and Churchill provinces. Lower Proterozoic supracrustal rocks, deposited on the Hopedale block following intrusion of tholeiitic dykes ca. 2200Ma, were reworked at amphibolite faciès, and thrust westward against undeformed portions of the block during orogeny in theMakkovik Province. The Makkovik/Hopedaleblock structural boundary Is marked by alate, greenschist-facies dextral shear. By contrast, the boundary between the Hope-dale block and the Churchill Province to the west is a fault zone that separates lower Proterozoic supracrustal rocks, deposited on a protocontinent of Churchill Provincerocks, from fundamentally different rocks ofthe Nain Province. The intensity of Early Proterozoic deformation and metamorphismrises progressively from sub-greenschist fades In the Hopedale block to granulite fades in the interior of the Churchill Province.

EN :

Preliminary precise age determinations of tectonic and metamorphic events across a transect of the Torngat Orogen have shown atime-span of 80 million years between the oldest synmetamorphic intrusions and the latest uplift of the orogen. Two tectonothermal peaks have been determined at 1844 Ma (eastern and central part of the transect) and at 1826 Ma (western part of the transect).

FR :

Les premiers résultats d'une étude géochro-nologique de l'orogène de Torngat, axée surla datation précisa d'événements tecton-iques et métamorphiques, ont montré qu'unedurée de 80 millions années (entre 1860 Maet 17È0 Ma) sépare les premières intrusionssynmétamorphes de la surrectîon finale deia chaîna. Deux "pics" de déformation et demétamorphisme ont été déterminés à 1844Ma (au centre et à l'est de la chaîne) et à 1826Ma (à l'ouest).

FR :

Le segment est de l'orogène Trans-Hudsonse compose d'un terrain gneissique polycy-clique coincé entre les orogènes hudsonlensdu Nouveau-Québec et de Torngat. L'inter-face entre ce terrain gneissique et les cra-tons de Nain à l'est et Supérieur à l'ouest estmarqué par les failles de Komaktorvik à l'estet du Lac Tudor à l'ouest, lesquelles montrentdes directions de transport opposées. Simi-lairement, le terrain interorogénlque est dis-séqué de cisaillements à déplacementslatéraux montrant une direction de mouve-ment cohérente avec celles des failles limi-trophes, soit senestre à l'est dans les cisaille-ments d'Ablovlak, Falcoz et Moonbase Lake,et dextre à l'ouest pour le cisaillement de larivière George. La relation temporelle entreces différents systèmes de failles est in-certaine.

EN :

The eastern part of the Trans-Hudson Orogen is composed of a gneisslc polycyclic terrain caught between the Torngat and New Québec orogens. Its boundaries with the adjacent Archean Nain and Superior cratons are expressed by the sinistral Komaktorvik shear in the east and the dextral Lac Tudorfault in the west. Their common gneissichinterland is dissected by two networks of transcurrent faults, the sinistral Abloviak--falcoz-Moonbase Lake shear system inthe east and the dextral George River shearin the west. Timing relationships between these fault systems is still unclear and is essential to the unravelling of the link between both orogens.

EN :

The Nagssugtoqidian mobile belt Is a ca. 300km wide Proterozoic tectonic zone, extending across Greenland, in which Archean basement rocks have been tectonically reworked and subjected to high-grade metamorphism. It is regarded as part of an originally continuous orogenic belt (Figure 1) which included the Tomgat Orogen of Labrador (Korstgard et al.. 1987) and the thrustbelts of Northern Norway and the Kola peninsula (Marker, 1988). All the segments are dominated by thrust tectonics and pressures up to 12 kb. In North Norway and West Greenland, juvenile Proterozoic sialic crustformed in association with sutures within the mobile belt. In East Greenland, Juvenile Prot-erozoic magmas are represented by basic intrusions emplaced into Archean continental crust. The location of the East Greenland section of the mobile belt is thought to have been controlled by pre-existing Late Archeanand very early Proterozoic structures.