The origin, structural style, and reactivation history of the Tabbernor Fault Zone, . Saskatchewan, Canada
BY James R. Davies
A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillmeot of the requirements for the degree Master of Science
Department of Earth and Planetary Sciences McGill University, Montreal
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Wollaston Lake at sunset, summer of 1996 Abstract
The Tabbernor ~aunzone (TFZ) in Saskatchewan is a >1500krn geophysical, topographie and geological lineament that trends approximately northward dong the province's eastern boundary. Detailed field mapping and petrographic analyses, coupled with remote sensing and geophysical evidence have shown that the TFZ is a fundamental structure within the Trans-Hudson Orogen (THO), separating and offsetting severai lithotectonic domains.
Eariiest deformûtion presewed within the TFZ in the Wollaston Lake area is the transposition of a regionai gneissic foliation ont0 a northeast-trending fiattening piane, within north-trending sinistral shear zones. The transposed fabnc is characterized by folded and attenuated remnants of the gneissic foliation. together with boudinaged leumgranitic sheets and dykes. Within these shear zones a shear fabric is developed parailel to the margins in several locations. The shear fabric offsets dl earlier foliations with consistent sinistrai offset. Adjacent to the shear fabric, structures are reoriented to lie dose to the shear plane.
The fault and its associateci structures controlleâ the intrusion of grmitic and pegrnatitic dykes which were subsequently weakiy deformed. These intrusives relate to a regionai magmatic episode assouated with the culmination of the second tectonornorphic event in the THO at 1815Ma. Post-collisional adjustments caused localized reactivation of stnictures and assoaated retrogresive metamorphism.
Brittle overpnnting of ductile fault features is widespread. Mineralized fault planes display well-developed slickenlines which formed during more than one reactivation episode. Reactivation may have been coevai with the age of formation of large uranium deposits in the irnmediately adjacent Athabasca Basin. Structural similafiaes between the TF2 and rninerdized areas suggest that the fault may have had a control on the location of minerakation.
Sedirnentary features, apatite fission track data, and uranium mineralogical studies ail show that the TFZ was readvated at least twice in Phanerozoic times. Late Devonian tectonic events associated with the Antler Orogen caused reactivation of the TF2 dong much of its length. In southern Saskatchewan fault reactivation cuntrolled depositional patterns and structures within the Williston Basin. Further north. fault reactivation resulted in the widespread rernobilization of uranium-bearing minerais. Reactivation in the Eady Cretaceous Pefiod, associated with Cordilleran orogenic activity. had similar affects. The identification of multiple reactivations of an intracratonic structure calls into question the model of a 'stable' craton. La zone de la faille de Tabbemor (ZFï). situde en Saskatchewan, reprdsente un lineament g6ologique. topographique et gdophysique de plus de 1500km. Elle présente une orientation nord, longeant la frontière Est de la province. Une cartographie detailiee et une Btude petrographique, jumelés aux donnees de télédetedion et aux Bvidences geophysiques illustrent dairement qu'il s'agit d'une structure fondamentale au sein de I'orogène Trans-Hudsonienne (THO)l séparant et décalant plusieurs domaines lithotectonics.
Dans la region du Lac Wollaston, les premieres evidences de d6formations observées au sein de la ZFT sont caracterisees par la transposition d'une foliation gneissic regionale dans un plan nord-est. Ce plan est situ6 A l'intérieur d'une zone de cisaillement qui est orienté vers le nord et & ddplacement sénestre. La fabrique transposee est caracteris& par des plis et des traces résiduelle de la foliation gneissk accompagne de feuillets leucogranitique et de dykes boudin&. A diffhnt endroits. plusieurs de ces zones de deformation possedent une fabrique de cisaillement paraiMe aux marges, deplaçant les foliations precedentes avec un mouvement s6nestre. Aux abords des plans de cisaillement, les structures sont rborientées de façon à être similaire aux fabriques de cisaillement.
La faille de Tabbernore ainsi que les structures associées contrôlent l'intrusion de dykes granitiques et pegrnatitiques qui furent par la suite faiblement déformés. Ces intrusions sont associées à un épisode magmatique régional. associé avec la culmination du second 6venement tectonomorphique dans la THO. à 1815Ma. Des ajustements post-collisionnaux? ont causé la réactivation des différentes structures ainsi qu'un mdtamorphisme rétrograde.
iii La superposition de structures cassantes sur les zones de faille ductile est trbs fr6quente. Les pians de failles min6raJises possèdent des "did Les caractéristiques s6dimentaires. les donnees de fission de I'apatite? ainsi que les résultats des Btudes sur la minhiagie des min6raux uranifhres démontrent tous que la rbactivation. Phan6rozoïque de la ZFT semble s'être produite a deux reprises. Les Bvenements tectoniques du DOvonien tardif associés B IOrogéne d'Antier, ont causds la r6activation de la ZFT sur presque toute la longueur de celle-ci. Dans le sud de la province du Saskatchewan. la réactivation de la faille contrôle les patrons de ddpdt ainsi que les structures a I'intdrieur du bassin de Williston. Plus au nord. la rdactivation de la faille a produit une rembilisation génerale des mineraux d'uranium. Cette rembilisation des mineraux uranifhres s'est aussi produite lors de la r6activation de la ZFT au Crétace Inférieur lors de I'Orog8ne CordilliBflenne. L'identification de plusieurs phases de rdactivation d'une structure intracratonique remets en question le modele d'un craton "stable". This thesis consists of four chapters, the second and third of which are in manuscript form. and are intended for submission to a refereed journal. In accordanœ with McOill thesis preparation guidelines the candidate is required to make an explicit statement on the authonhip of dl work submitted as part of the thesis: The analyses of two rock sarnple suites from the Wollaston Lake and Neilson Lake areas were undertaken by Dr. Barry Kohn, at the Australian Geodynarnics Cooperative Research centre. La Trobe University, Bundoora, Victoria. The samples were analyzed to provide an apatite fission track age for each sample. As well as the results, Dr. Kohn also provided a preliminary interpretation of the fission track age data within the context of the North Amencan continental history. Ail subsequent interpretetion of the data in relation to the cunent study is the work of the author. The Neilson Lake sample suite was collected by Colleen Elliott. Ail other data collection, preparation. analyses and presentation within the thesis was conducted entirely by the author. The thesis supervisor, Colleen Elliott of Concordia University. has reviewed both manuscri pts. Acknowledgements The author would like to acknowledge the role of his field assistants Luke Willis, Gary Smith, and Rami Mirshak for their patient and diligent work dunng two summers of fieldwork on Wollaston Lake. Additional field logistics were supplied by Gary Delaney, Tom Sibbald and Bruno Lafrance (dl Saskatchewan Energy and Mines). Laboratory preparation and results of fission track analyses on two sample suites was provided by Barry Kohn at La Trobe University. Victoria. Supervision of the Masten program was undertaken by Colleen Elliott of Concordia University. Colleen Elliott aiso gave review and cornments that greatly improved the organization 'and preparation of the two manuscripts. French translation of the thesis abstract by tissa Morotti and Annick Chouinard is gratefully acknowledged. I am especially indebted to Gary Delaney, lnhne Annedey (Saskatchewan Research Council), Don Baker, and Andrew Hynes (both McGill University) for their continued comments and advice during the cornpletion of this project. Funding for this project was provided by a LITHOPROBE supporting geosciences grant awarded to Colleen Elliott. To al1 the additional friands, family, and ailleagues who go unmentioned here but without whom this thesis would have gone unfinished, "1 wish you al1 that you would wish yourselves!". Table of Contents Résume ...... iii Preface ...... v Table of Contents ...... vii List of Figures ...... x List of Tables ...... xii List of Plates ...... xiii Chapter 1: Thesis Introduction ...... 1 Generai Statement ...... 1 Objectives of Research ...... 2 Review of Previous Work ...... 2 Chapter 2: Structural Investigation of the Tabbernor Fault Zone. Wollaston Lake: Implications toi Regional Deformation Associateâ with Post-collisional Tectonics In the Tnns-Hudson Otogen . . 5 Abstract ...... 5 1 . Introduction ...... 7 2 . Regional Geology ...... 8 3 . Previous Work on the Tabbernor Fault Zone ...... 11 3.1 Geometry ...... 11 3.2 Deformational Character ...... 12 3.3 Offset ...... 12 3.4 Timing of Movernent ...... 13 4 . Previous Work in the Wollaston Lake area ...... 14 4.1 Stratigraphy ...... 14 4.2 Structure ...... 16 4.3 Timing and Metamorphism ...... 18 vii 5.CunentWork;...... 20 5.1 Geophysical Interpretaüon ...... 20 5.2 Field Mapping ...... 23 5.2.1 Hidden Bay area ...... 23 5.2.2 Compulsion Bay area ...... 28 5.2.3 Small-scale Reactivation Features cornmon to both Hidden Bay and Compulsion Bay ...... 31 6 . lnterpretation of Data ...... 33 6.1 Ductile Defoimation Associated with the Trans-Hudson Orogen 33 6.2 Briffle Reactivation of Hudsonian Features ...... 38 7. Discussion ...... 40 8 . Importance of the TFZ to Uranium Exploration ...... 43 9. Conclusions ...... 46 Link: The Rob of Proterozoic Fault Delormtion in Controlling Phanerozoic Fault Reactivation ...... Chapter 3: Evidence for Orogeny-drfven Phanerozoic Reactlvations of the Tabbernor Fault Zone. Saskatchewan. Canada ...... 49 3. Reactivations in Western Canada ...... 52 3.1 Regional Stratigraphy ...... 53 3.2 Dnving Mechanisms for Tectonic Deformation ...... 55 4 . The Tabbernor Fault Zone ...... 57 4.1 Introduction ...... 57 4.2 Deformational Character and Geometry ...... 58 4.3 Geophysical Characteristics ...... 60 4.4 Offset ...... 61 4.5 Absolute Ages of Movement ...... 62 viii 5 Phanerozoic History of the TFZ ...... 5.1 Previo~sWork ...... 5.2FissionTrad Chapter 4: Summary and Conclusions ...... General Conclusions ...... Contributions to Knowledge ...... References and Bibliography ...... List of Figures Figure 2.1 Simplified Geologicaî map of the exposed THO and boundary regions. Figure 2.2 lnterpretation of the internai geometry of the THO. Figure 2.3 Age constraints on ductile deformation within the Tabbernor Fault Zone in the Neilson and Wollaston Lake areas. Figure 2.4 Simplified geological map of the southern Wollaston Lake area showing the location of the data collection areas. Figure 2.5 Schematic stratigraphie column for the Wollaston Lake area of the Wollaston Dornain. Figure 2.6 lnterpreted vertical gradient aeromagnetic map of the NENIAEA Athabasca test area. Figure 2.7 Fom Surface map of the Hidden Bay area. Figure 2.8 Contoured stereographicai projections of structural data from the Hidden Bay area. Figure 2.9 Stereographical projections of fold data from the Hidden Bay area. Figure 2.10 Location rnap of the Compulsion Bay mapping area. Figure 2.1 1 Stereographical projections of structural data from the Compulsion Bay area. Figure 2.1 2 Detailed field map of the location 520201. Figure2.13 Stereographical projection of fold data from the Compulsion Bay area. Figure 2.14 Stereogiaphicai projections of bnttle fault data from the Hidden Bay area. Figure 2.1 5 Stereographicai projections of brime fault data from the Co mpufsion Bay area. Figure 2.16 lnterpretative cartoon showing the evolution of the THO. Figure 2.1 7 Compilation map of a selected area of northern Saskatchewan showing the relationship between aeromagnetic lineaments that define the trace of the TFZ and major lithotedonic boundaries. Figure 3.1 Phanerozoic elements of the western North American continent. Figure 3.2 Tectonic domains of the western Canadian basement. Figure 3.3 Constraints on the development of a ciassicai foreland basin. Figure 3.4 Simplified Geologicaî map of the exposed THO and boundary regions. Figure 3.5 Simplified geological map of the Athabasca Basin and adjacent basement domains. Figure 3.6 lnterpretation of the internai geometry of the THO. Figure 3.7 Age constraints on ductile deformation within the Tabbernor Fault Zone in the Neilson and Wolfaston Lake areas. Figure 3.8 Location and apatite fission-track ages of sarnples collected dong the Neilson Lake transect. Figure 3.9 Location and mefission-track ages of sarnples collectecl dong the Hidden Bay transect, Wollaston Lake. Figure 3.1 0 Isopach map of the Woodbend (374370Ma)-Winterbum (370-362Ma) and equivalent groups of the Upper Devonian Period, Saskatchewan. Figure 3.1 1 lsopach map of the Cretaceous Upper Manville Group (and equivalents) in Saskatchewan. Paleogeographical reconstruction of Cretaceous middle Upper Manville Group (and equivalents) geography in Saskatchewan. Figure 3.1 2 Secondary isochron plots of =pb?pb and p7~b1204~b ratios in sulfide and sulfate rninerals of varying paragenesis from the Athabasca Basin. List of Tables Table 3.1 Compilation of Phanerozoic radiogenic age data derived from U-Pb dating rnethods on uranium minerakation. xii List of Plates Plate 2.1 Second-generation pegmatite dyke, north shore of Pow Bay. Plate 2.2 Developrnent of foliation boudinage at location 21071. southeast shore of Parker Island. Plate 2.3 Small-scale ductile fault with adjacent st rong sinist rd drag . location 2 1041 , southeast shore of Parker Island. Plate 2.4 Extensive boudinage of pegmatitic materiai within well- foliated, fine-grained biotitequartz gneiss. location 25021 . Plate 2.5 Closely-spaced shear deavage in Archean gneiss of the Johnson River Inlier, location 520201, west of Compulsion Bay. Plate 2.6 Granite dyke intruded into the shear deavage, location 520201, same as plate 2.5. Plate 2.7 Photomicrograph of the margin of a dyke int~dedinto the shear deavage, from location 520201. Plate 2.8 Photornicrograph of quartz from a vein intnided into a fault plane. xiii Chapter 1 Thesis Introduction General Statement . It can be reasonably assumed that a person who has lived for 80 yean will have had more life expeiienœs than a child of 5 or 6. The same can be said for faults. Thus, if the tectonic conditions are right, it should corne as no surprise to find many ancestral faults have a repeated history of reactivation. The processes that accompany the formation of faults. both ductile and brittle. assure that the structures will never regain the same strength as the previously unaltered rock. Mineralogical weakening of fault zones has been shown to dramatically reduœ the strength of a fault (Wintsch et al.. 1995), and may be the cause of seismic activity in modem strike-slip faults such as the San Andreas Fault, which fail under stress conditions lower than those expected by modeling. The fundamental loss of strength is espeaally true of deep-rooted fault structures such as interplate transform faults. During continental assembly these fault structures may becorne situated within the cratonic interior but their inherent incornpetence means that they will aiways be among the weaker parts of the crust. These faults myin fact focus intraplate stresses far from the cratonic margins because of their predisposition for reactivation (Heller et al., 1993). Over the last decade or more the study of fault reactivation has become more prevalent in structural geology. Advances in the field have culminated in recent publications, such as the thematic set ansing from the Tectonic Studies Group meeting (Butler et al.. 1997) held at Budington House, 6-7 March 1996. Fluid processes. both during and after initial fault formation. also have a very important role in the evolution of a fault system. An exceilent review of the involvement of fluids in faulting can be found in Hickman et al. (1995. and references therein). Objectives of Research This project was formulateci with the goal of expanding and refining cunent knowiedge of the Tabbemor Fault zone (TFZ). The study is part of a larger research program ai- at working out the timing and kinemtic hidory of the Tabbernor Fault, and adjacent structures. in the context of the assembly of the North American continent. Phanerozoic reactivation of the fault was known to have occurred pnor to the undertaking of this thesis (Byen, 1962; Elliott. 1995), and the research group aiso covered this aspect of the fault's history. The fieldwork component of the project was restncted to the fault where it is exposed on Wollaston Lake, Saskatchewan. Exposures of the fault to the south have been examined by Prof. Colleen Elliott. Spedfic goals established at the outset were to evaluate kinematics and significanœ of dudile fabrics dong the fault in the Wollaston Lake area, and to assess the potential links between faulting and U- mineralization in the Athabasca Basin. Subsequent to the start of the project it became clear that there was the potential for a strong causai Iink between Phanerozoic fault reacüvation and remobilization of mineralization within many of the major uranium deposits. The project was wnsequentiy expanded to explore this avenue of research. Review of Previous Work The Tabbemor Fault has been identified as a s1500km geophysicai (Green et al., 1985; Jones and Craven, 1990) and topographie (Elliott and Giroux. 1996) lineament that extends from the Northwest Territories to North Dakota, with a north-south trend. Earliest geologicai studies to indude parts of the Tabbernor Fault (Budding and Kirkland, 1956; Wailis, 1971 ; Scott, 1973; Sibbald, 1978; Lewry et al., 1981) ail canduded that the fault had a sinistral sense of displacement but did little to darify the kinematic history. Recent studies have initiated much debate over the significance of the fault in the regional tectonic framework of the Trans-Hudson Orogen. Lewry (1981) suggested that the Tabbernor Fault was a transform junction between t ha Glennie Microcontinent and the Kisseynew Domain. More recently, Lewry et al. (1990) downplayed the importance of the Tabbernor Fault, suggesüng that eafly ductile mylonites seen in the exposed southem segment of the fault are only locally coincident with the fault. lnstead they suggest that these rnylonites relate to an eailier refolded, and over-steepened, high-strain nappe de. Uliott (1994a. 1995) used the kinematics of the eady ductile deformation, in relation to dated deformed intrusives to bracket the timing of movement between 1848+6/-5Ma and 1737eMa. Elliott (1996b) also suggested that the combination of geophysical evidence and well- developed kinematic features indicate that the Tabbernor Fault did have an important role in the evolution of the Trans-Hudson Orogen. Reviews of the regional geology assocjated with the Trans-Hudson Orogen are numerous, but the rost comprehensive can be found in Lewry and Stauffer (1990, and references therein). Lucas et al. (1993), and Clowes (1997, and references t herein). The Phanerozoic history of the Western Canadian Sedimentary Basin is covered by excellent publications such as Mossop and Shetson (1994), Savoy and Mountjoy (1 995), and Macqueen and Leckie (1992). For tectonic modelling of the Western Canadian cratonic rnargin the reader is refend to Leckie and Smith (1992), Fermor and Moffat (19W), Quinlan and Beaumont (1984), and Stockmal et al. (1992). More speafic studies of the role of the Tabbernor Fault in the Phanerozoic eon cm be found in Byen (1962), Gerhard et al. (1987). Haidl (1988), and Elliott (1995). The process of fault reactivation, and its recognition. is covered by Butler et al. (1997, and references therein) and Heller et al. (1 993). The study of unconformity-type uranium deposits. as found in the Athabasca Basin, immediately adjacent to the Wollaston Lake field area is extensive. Recent reviews concentrate on the geochemistry and origin of ore-forming luids and associated alteration minerakation (Kotzer and Kyser, 1993, 1995; Komninou and Sverjensky, 1996; Fayek and Kyser, 1997). Previous work (Cameron, 1983; Sibbald and Petruk, 1985; Evans. 1986) mncentrated more on the structural and stratigraphic settings of the deposits. as well as paragenetic minerai studies. Varying aspects of the deposits are stress& in individuai studies but it is probably true that structure9fluid composition, lithology. and alteration al1 have an important role in determining the position and composition of the deposits. Chapter 2 Structural Investigation of the Tabbernor Fault Zone, Wollaston Lake: Implications for Regional Deformation Associated with Post-collisional Tectonics in the Trans-Hudson Orogen J. R. Davies, Dept. of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC. H3A 2A7, CANADA. Abstract The Tabbernor Fault zone (TFZ) in the area of Wollaston Lake. northern Saskatchewan, is a series of poorly defined NNE-trending sinistral shear zones with a repeated history of fault mwement. The region is within the northwestern hinteriand of the Trans-Hudson Orogen VHO). An eaily episode of regional orogenic deformation (Dl) resulted in an extensive, EN€-stfiking, moderately to steeply S-dipping, gneissic foliation (SI). This eady fabric is transposed ont0 a NE-striking. steeply SE-dipping, flattening foliation (S. Transposition is characterized by folding and boudinage of the original gneissic foliation and is limited to Tabbemor-related shear zones such as the Parker Island shear zone (PISZ). These can be tracad back to the main fault in the Reindeer zone. Within the highest strain zones the S2 foliation is modified by the development of a coeval NNE-striking, verticai sinistral shear deavage. Metre-scale ductile and brittle-ductile faults parallel the main shear zones. Previously identified TFZ fault zones, that are N-trending and show little offset. are probably synthetic 'Riedel' faults. Regionally, D2 deformation probably occuned dunng or after terminai collision in the THO, and was concentrated in shear zones which allowed post- collisional orogenic shortening and 'escape' tectonics. Intrusion of leucogranitic and pegmatitic sheet-like dykes into the sinistral shear fabrics postdates the bulk of 02 deformation. These intrusives are similar to 1815Ma Hudsonian granites seen elsewhere in the Wollaston Dornain and bracket the lower limit of lming of Dt deformation. Continued ductile detonnation during late Hudsonian deformation events caused restrided sinistral shearing. Brittle overprinting of the dudile shear zones is a cornmon feature and consists of brecaation and th8 development of slickensided fmlt planes. Two generations of cogenetic faults have ben identified by the fault-slip inversion method. Brittle fault features are accompanied by mineral growth that suggests extensive ffuid circulation accornpanied fault rnovement. 1. Introduction Anal ysis of LITHOPROBE THOT seismk line 9 (Hajncil el al.. 1992; Lucas et al.. 1993) has show that the western margin of the Trans-Hudson Orogen (THO) in Saskatchewan is dominated by a sucœssion of westedy to noithwesteily dipping juvenile tenanes. subducted beneath the eastern mrgin of the Hearne Province (Figs. 2.1 and 2.2). Above, and to the wst of th8 subduction zone, sediments of the Wollaston Group were deposited in a rift to continental margin setting. Dunng oblique collision events that cha*iderized the dimax of the THO, Wollaston Group sediments were complexly folded and metamorphased. The nature of deformation and metamorphic events within the Wollaston Domain (containing Wollaston Group rocks as well as exposed Archean inliem. and Hudsonian-age intrusives) is not well defined. Neither is the relationship between deformation in the Wollaston Dornain, and deformation elsewhere in the THO. This study atternpts to explain some of the structural relationships in the Wollaston Lake area of the Wollaston Domain (Fig. 2.1). The lake is on the eastern margin of Athabasca Basin, the western world's largest uranium producing region. 01 particular interest is the age and nature of defomtion associated with the Tabbemor Fault system (TFZ). The TFZ crossaits and borders several distinct tedonic domains of the THO (Le- et al., 1990). It is a longitudinal geophysical and topographical lineament which is c1500krn long (Elliott and Giroux, 1996). Its noithern limits can be traced to the northern border of Saskatchewan, and airphoto anaiysis shows that the southem limits extend under the Phanerozoic cover into North Dakota (Giroux. unpublished M.Sc. thesis). In addition there are a number of extensive regional lineaments, parallel to the TFZ. which occur in Saskatchewan and Manitoba (Elliott, 1996a). The study was organized with the goal of fitting Tabbemor-related deformation into the larger picture of deforrnation in the Wollaston Domain and the THO. Figure 2.1. Simplltkd Gwloglcat map of the exposed THO and bounday mglons. Lithotectonic zonas are sub-dlvldd lnto domalns e.g. Flin Flon, Klsseynew etc. Abbnvlatlons: C.S.B.Z. = Churchill - Superlor Boundary Zone; f.FZ. = Tabkrnor FauHZone; N.F.SZ = Needk Falls Shnr Zone; B.R.S.B. = Blrch Raplds StraigM Bdt; S.82. - Stanley Shear Zone; P.L.SZ. = Parker Lake . Shear Zone; 8.T.Z = Snowblrd Tedonlc Zone. Red dots ma* locations dlscuuod In the tex-; 1 = Wollaston Lake; 2 - Nelkon Lake. Nok that only major TF2 huit splays am shown In tha northern half of.the map. By lncludlng mlnor TFZ splays the longltudinal extent of the fault zone exbndr for approxlmatoly 170km. Map k adapted after Lewry et al. (1890); Iithotactonlc dlvislons as of Clowes (1997). Flgum 2.2. InterpmWIon of the Intemal geometiy of the THO. A)GeoIoglcal cross-sectlon showlng prlnclpal tectonostmtlgmphlc unltm of the Tmns-Hudson Orogen (fmm HaJnalet al.. 1992). The medon 1s con.tn1n.d by THOT reflectlon praflk B. 6) Inamt of the migrated wlsmlc profile. The sectlon is / from O to 12 wconds (TWT), and aquat.. to a dapth of approxlmately 36km. The TFZ k charadmalzed by a zone of low refiectance. Note that althouah decton In the lomr crust appear to truncate the TFZ they am not contlnuous acrosr the fiult wlth the samo mfioctance. 2. Regional Geology The THO is a 500km-wide belt of exposed Eaily Proterozoic orogenic rocks. The western segment of the orogen has an arcuate form that changes from s- trending in Saskatchewan and western Manitoba, through th8 'Big Bend' to W- trending across northern Manitoba and into Hudson Bay. Subsurface extensions. buried beneath Phanerozoic rocks of the Western Interior Platform. continue southward into North Dakota and Montana (Nelson et d., 1993). Recent summaries of the THO have divided the geology up into 4 distinct lithotectonic zones: The Churchill-Superior Boundary Zone (CSBZ) (Fig. 2.1) is a narrow foreland zone, bordering the Superior Craton to the southeast. The zone is composed of reworked Archean rocks of the Superior Craton. together with Paleoproterozoic supracrustai rocks of the Thompson belt and vanous Hudsonian-age intnisives. To the northwest the CSBZ is fault-contacted with the Reindeer Zone that composes the juvenile core of the THO (Fig. 2.1). It is subdivided into sevenl domains distinguished by rock type, structural continuity, radiornetric age and style of deformation within. Geochernicai and isotopic work suggests that most of these rocks evolved in an oceanic to transitionai. subduction-related an: setting (Clowes, 1997). The age of the Reindeer Zone jwenile rocks is arca. 1.9-1.8Ga (Clowes, 1997). Beneath these juvenile domains there is strong geophysical and geochemical evidence for an Archean crustctl block, termed the Sask Craton (Lucas et al., 1993; Ansdeil et al., 1995) (Fig. 2.2). This Archean 'micro-continent' does not appear to be connected to either the Superior or Rae/Hearne Provinces, and where exposed in 'basernent windows', such as the Pelican Window (Lewry et al., 1989). structurai evidence suggests that the juvenile terranes were thrust southwestward over the Sask Craton at cira. 1.81Ga (Heaman et al-, 1995). The Wathaman-Chipewyan Batholith (Fig. 2.1 ) is an Andean-type mgmtic arc. The southern margin of the batholith forrns the northem and western boundary of the Reindeer Zone. The batholith fomied as a result of continued westerly subduction of oceanic material beneath the continental rnargin. It is a moderately heterogeneous granite-granodiorite body, and contacts between the batholith and the Reindeer Zone appear intrusive (Lewry and Collenon, 1990). Emplacement of the batholith is though to have ocairred in a restricted geological time frame, at approximately 1855Ma (Mayer et al., 1992). The western boundary of the THO is forrned by the Northwestern Hinterland Zone (NHZ) (Fig. 2.1). As with the CSBZ, it is a mmbination of reworked Archean basernent rocks, overiain by Paleoproterozoic sediments. Unlike the CBSZ, the NHZ is a wide belt, dominated by defomed matasedirnentary rocks of the Wollaston Group. These were deposited in a rift to miogeodinal setting (Money, 1968; Ray, 1979; Delaney, 1995). Where the orogen is N- to NE- trending in Saskatchewan, the contact between the NHZ and the Wathaman batholith is marked by a 400km-long dextral fault, the Needfe Falls Shear Zone (NFSZ) (Fig. 2.1). Studies show that the NFSZ was active somewhere between 1857Ma and 1760Ma. with ductile kinematics (Stauffer and Lewry, 1993; Fedorowich et al., 1995), and later with ductile-brittle to britüe shearing. West of the 'Big Bend' the contact relationship between the batholith and the NHZ appean to be largely intrusive (Lewry and Collenon, 1990). lntraplate transcurrent faults and sub-horizontal shear zones dissect the entire orogenic belt into thrust sheets (Lewry et ai., 1990). It has been suggested that many of these steep faults and detachment shear zones were active lata in the main phase of orogenic activity, allowing orogen-parailei extension (Hoffman, 1988; Stauffer and Lewry, 1993; Hajnal et al., 1996). or orodinal rotation of the southern part of the orogenic belt (Symons, 1991, 1994). In the modal of Hajnal et al. (1996) the escape of the central-western Reindeer zone to the southwest, dunng these orogenic adjustments, was facilitated by dominantly dextral stnke- slip shear dong omgen-parailel shear zones on the western margin (eg. NFSZ), and sinistrai strike-slip movement on the Tabbernor Fault (TFZ). All of this ocarrred in response to contraction aaoss the Reindeer Zone. due to oMique convergence with the Superior craton during postcollisional deformation (Bleeker. 1990; Stauffer and Lewry, 1993) 3. Previous Work on the Tabbernor Fault Zone 3.1 Geometry The TFZ is one of several largescale shear zones and linear belts which help to subdivide the THO into lithotectonic domains (Fig. 2.1). What is unusual about the TFZ is that it is oMique to main fabric trends in the orogen. Between the Glennie Domain and the Hanson Lake Block the TF2 is a domain boundary, but in other places, such as the Wollaston Domin, the fault crosscuts domains. The effect is to deflect and offset eartier fabrics within a domain. It is well documented that the fault offsets eariier Hudsonian structures in both the central Neilson Lake area (Elliott, 1994a) and further north in the Wollaston Lake area (Wallis. 1971; Davies, 1996). with a consistently sinistrd sense. Seismic imaging of the TFZ, as part of the LfTHOPROBE Trans-Hudson Orogen Transect, has revealed the TFZ to be a wide vertical zone of low reflectance (Hajnal et al., 1992; Lucas et a/.,1 993) (Fig. 2.2b). Strong reflecton terminate at the TFZ through much of the crustai profile. Hajnai et al. (1992) interpret the TFZ as -terminating on a shailowiy dipping lower crustal retlector, probably a detachment thrust, and therefore suggest that it is not a through-going crustai structure (Fig. 2.2a)..The migrated profile published in their paper, and that of Lucas et al. (1993). is incondusive and aithough reflecton seem to correlate on both sides of the fault they are not cantinuous with the same reflectance right across the fault zone. Nemeth and Hajnal (1 996) suggest that veloàty anisotropy in the upper-lithospheric mantle beneath the northern Reindeer Zone and NHZ can be attributed to reonentation of the mantle fabnc by the TFZ and adjacent NFSZ. This would suggest that the TFZ is a through-going cnistal structure. penetrating the Moho boundary, although this may not necessarily have always been the case during its evolution. 3.2 Deformational Chwactar The character of the TF2 changes dong its length. Between the Glennie Domain and Hanson Lake Bock the eailiest fabrics developed in the fault are characterized by sinistral ductile shear and development of eafiy, upright, mylonites (Elliott, 1994a). Minerai lineations within the mylonitic fabric change orientation acrosç the fault. They are Werately to steeply S-plunging in the east, changing to Werately N-plunging in the west. These two distinct domains are separated by a bnttle to semi-brittle fault trace with subhonzontal slickenside lineations t hat overprint the eariier ductile fabrics (Elliott, 1994a). As the fault progresses northward its mrphology changes from a single. or several anastornosing, splay(s) with restncted longitudind extent. to a bifurcating array of discrete fault splays and topographical lineaments which extend from 102OW to 1OSOW (Fig. 2.1 ). This is a width of approximately 170km. compared to maximum width of 2km in the Neilson Lake area (Elliott, 1994a). in the Reindeer Zone. The change in style of the fault coincides with the transition from where the fault separates the Glennie Domain from the Hanson Lake Bock and Kisseynew Domain, to where it penetrates into the La Ronge Dornain and extends northward to the Wollaston Domain (Fig. 2.1). 3.3 Offset Magnitude of offset across the TF2 varies with location but the sense is consistently sinistral. Offset of a north-east dosing fold hinge, across a single Tabbernor splay in the Neilson Lake area, was documented to be 2km (Elliott. 1994a). From this it was argued that the offset across the main fault trace was greater than 2km. Further north, in the Wollaston Lake area, offsets across individual fault splays have been suggested to be <500m-3000m+ (Wallis. 1971). based on field mapping augmented by aeromagnetic interpretations. Metamorphic isograds mapped by Sibbald (1978) and Wilcox (1991) in the Neilson Lake\ Pelican Narrows area suggest post-metamorphic sinistral displacement across the entire fault of 6-8km. although these isograds are argued to be controlled by lithology (Elliott. 1994a) and not to reflect tnie displaœment. 3.4 Timing of Movernent. Timing of fault movement is not well understood. Deformation associatecl with the formation of the mylonitic strain zone in the Neilson Lake area is constrained by cross-cutting relationships between 1848+6/-5Ma and 1737&2Ma (Elliott. 1995) (Fig. 2.3). The only constraint on movement along the TFZ in the Wollaston Domain is that it is younger than the Hudsonian fabncs that it deflects and offsets. The earliest Hudsonian deformation accurred at approximately 1840- 1850Ma (see below). Brittle deformation in both locations overpnnts ductile fabrics and is therefore younger. Reactivation of the TFZ is known to have occurred at least once during the Phanerozoic eon (Byers, 1962; Elliott. 1995). Current work suggests that there hava been severai reactivation events. the most significant of which occuned dunng the Late Devonian and Early Cretaceous penods (Davies. in press b). No ages have been determined to more preasely constrain early ductile or bnttle movement along the TFZ. Despite its dimensions and evident regional significanœ, the importance of the TF2 has been downplayed by several recent authors (Lewry et el., 1990. Tran et al., 1996. Maxeiner, 1996) due to the lack of significant offset of lithologies. Flgure 2.3. Aga constralnts on ductlk ddonnatlon wlthln the Tabbernor Fauk Zona In the NeIlson and Wollaston Lake areas. Tho aga constralnts In tha NaIlson Lakm ana am from the NeIlson Lake pluton and a crosscuttlng pogmatite (Elllott, 1O95); aga . constralnts In the Wollaston Lake ana am bamd on the dlsruptlon of D, fabrltr In the vlclnity of Tabkmor Fault .play.. D, deformation has bwn dateâ at 1.a54 .Ma(Annerley et al., 1996., 1897). In southam Saskatchewan, kmk movementr on the TF2 are known to have occumd afbr depositlon of aarly Sllurlan strata (Elllott, 1B9S). 4. Previous Work in the Wollaston Lake area 4.1 Stratigraphy Much of the previous work in the Wollaston Lake area was driven by the discovery of the Rabbit Lake uranium deposit in 1968 (located on figure 2.6). and subsequent need for better understanding of the Wollaston Domain geology beneath the Athabasca basin (Fig. 2.4). The firçt detailed mapping of the basement geology in the area was undertaken in the Hidden Bay (64L - 4) area (Wallis. 1971) at 1 :63 360. Together with work to the south of Hidden Bay in the Nekweaga Bay (west half) (64E - 13 - W) and Morell Lake (west half) (64E - 12 - W) areas (Chadwick. 1966, 1967). and subsequent work southwest of Hidden Bay in the Compulsion bay area (part of area 64E - NW) (Lewry et al., 1981). it has produced a dear picture of the local stratigraphy (Fig. 2.5). The idealized stratigraphic succession starts with the Archean basement gneisses and granites. Above the basement rocks a 'basal' pelite forms the lowest unit of the Aphebian Wollaston Group supracrustai rocks. lnterbedded with the pelites are semi-pelites. metaquaitrites and cabsilicate horizons. Above the pelites is a thick sequence of arkosic rocks that contains more quartz-rich horizons. Locafly t hase are intnided by abundant pegmatites (Lewry et al., 1981 ; Thomas. 1983). In the Hidden Bay area Wallis (1971) identified the Hidden Bay assemblage that consists of meta-quartzite overiain by biotite psammite, rneta-arkose, garnet- amphibole rock, marble and cabsilicate rock. In the study of the Compulsion Bay area (Lewry et al.. 1981) no similar package of rocks was found. Wallis considered this to be a distinct package of sedimentary rocks. overlying the pelites and quartzites. Alternatively it has been suggested that the Hidden Bay assemblage either represents the uppermost part of the Wollaston Group, equivalent to other mixed sedimentary rocks seen elsewhere (Lewry and Sibbald, 1980), or the lateral faaes equivaient of the psamrnitic rocks found elsewhere in the upper Wollaston Group (Ray, 1979). In 1978 an area north and northwest of Hidden Bay was chosen as the site of the NEA/IAEA test area, a multidisciplinary exploration study for uranium deposits assoaated with the unconformity-type Ffgum 2.4. Slmplitkd goologlcil nup of th. .outhm Wollamton Lake arw showlng th. Iowtlon d th d.h odl.ctlon amu. the cores of mJor rtructuril dom# Wh rn rmglonal no*adrrly trend. Aphebianrgo mdasdlmontary gnebm (no pitbni) unconformably wdk th. Ardian gri.k.w. and t#m th. majority of thm oxposd roda In the Wollaston Domain. Hudsonlan-ige Inttllalv# (cm88p.tbni) mm 8 common fadur, of the rma and occur at al1 scdos. Flat-lylng wdlnnntiry rodu dthe Athabasca Group (mndom stlpplm) unœnformIibly ovdkroda of the Wollaston Domaln in th. wmst of thm map ama. Tho Hlddan Bay and Compulsion Bay d.b wlloctlon mIk. am shown by the huavy black boxas. Addltlonal data wlkctlon amam away fbm the maln Hldden Bay amam Indi- by th0 wrouin. Also shown am the the locatlon of ne* Idontltlod, Tabkrnor~lated,Wult splays (solid lines). Identification 1s basd on g.ophyslcal anomaly patterns and mapplng whero Ilmlted expomun allowa. Abbmvlatlons: S.I.G. - &ndy klinds Gmbbm complox; R.L.T. - Rabbit Lake Thnist; TwNmGm- Tmut N8mows Gmnlk; K.L.G. - Kldd Lake Granlt.; HwIwGm= Hocton Island Gmnb; K.L.F. = Kldd Lake Fault; and JrnRrnIm - Johnson Rkw Inlier. Map b adapteâ from Chadwlck (10; Lowry et al. (1981); and Thomas (1B83). I I Wollaston 1 ! Lake Flgun 2.5. Schmmatlc stmtlgmphlc column for #a Wollaston Lakm ana of the Wollaston DomaIn. Adamafbr Lowry etml. (1081) and Slbbald (1O83). Tho column Ir not to s#k. Athabasca Group, fluviatile quartz sandstones and conglomerates Ulc ' 'Hidden Bay assemblage' dominated by quartzite and amphibolite rocks, minor metaarkoses, semipelites, calc A ...... <...... nudsonian intrusives ...;_ .- . .... .:.. Arkosic sequences, thick meta- arkose and biotite-rich psammite, interbedded with pure quartrites, .. . . . plagioclasites and calc-silicate horizons . . , i. -- i. - i. Pelites, 'basal' pelite in part graphitic, grading into semipelites with interbedded metaquartrites and calc-silicate horizons Basement gneiss, foliated, exposed in the cores of basement domes such as the Johnson River Inlier and Trout Narrows Granite; highly strained at contact with unconformably overlying Aphebian pelites model (Fig. 2.4; Carneron, 1983). Wolk on the geology of the test area (SiWald. 1979, 1983). induding the Hidden Bay area, has done much to improve the understanding of the Hidden Bay assemblage leading to the recognition of a varied st ratigraphy, folded and faulted du ring polyphase deformations. Many Hudsonian-age intnisives have been reporteci in the area. Most are granitic or leucogranitic in composition. but more mafic intrusions, such as the Sandy Islands Gabbro cornplex (Madore and Annesley. 1996), are aîso present (Fig. 2.4). The main phase of granitic intrusions is interpreted to be synchronous with the end of peak rnetamorphism circa. 1815Ma (Annesley et al., 1997; Madore and Annesley; 1998). There is some evidence that the intrusives are deforrned along their margins suggesting that they were intruded into active shear zones (Heine, 1986; Madore and Annesley. 1992; Annesley pen. corn. 1998). The Wollaston Group is overlain by the Paleohelikian Athabasca Group (Figs. 2.4 and 2.5). which is interpreted to have been deposited unconfombly on top of the basement rocks at circa. 1700Ma (Cumming et al., 1987; Kotzer et al., 1992). It is composed of fluvial to marine dastic sediments. dominantly sandstones (Ramaekers, 1983). At the base of the sandstones a well-developed basement regolith is present in some paieo-depressions. The thidviess ranges from O-Som. The regolith is a major host of unconfomity-type uranium minerakation (Saskatchewan Geologicai Survey, 1994). Several large, SW-trending diabase dykes intrude the Wollaston Domain and Athabasca Basin. They rarely outcrop in the area but their traces are deaily seen on the verticai gradient aeromagnetic maps (Kornik, 1983. Fig. 2.6). Diabase is also found in drillare from the Midwest Lake uranium deposit (Fig. 2.6. Ayres et al., 1983). The dykes are assumed to belong to the Mackenzie dyke swarm, dated at 1267I2Ma (Cumrning and Kntic, 1992, and references therein). 4.2 Structure The earîiest regional Hudsonian-age deformation event preserved is the development of an early gneissic foliation parallel to the basement-cover contact in the Archean gneisses. and the sedimentary layering in the Wollaston Group rocks. This foliation development has been suggested to have resulted from the rise of a sub-horizontal thermal front eaily in the THO (Lewry and Sibbdd, 1980). This early gneissic foliation is folded into a senes of northeasterly trending. shallowly doubly-plunging domes by a second major deformational event. It is in the cores of these domes that Archean basement rocks are exposed, such as the Trout Narrows Granite (Wallis. 1971) and the Johnson River lnlier (Lewry et al., 1981) (Fig. 2.4). A third minor deformational event was reported by Wallis (1971). In the Hidden Bay area (Fig. 2.4) two prominent foliations have been distingukhed (Wallis, 1971). The first foliation, SI, typidly trends 070'. and is defined by compositional layering and by biotite and amphibole preferred orientations. The second foliation, Sp, also ocairs as compositionai layering and as an orientation fabric. but trend is typically doser to 050". Wallis (1971) noted tha-t where only one of the fabrics is present there are no distinguishing criteria. The SI fabnc is commonly seen axial planar to FI folds, but F2 fol& are only rarely seen with a well developed axial planar fabric. More typically the F2 folds are distinguished by the occurrence of the SI foliation folded about Fz fold hinges. FI axial planes typically strike 060-070°, whereas F2 axial planes are more variable about a strike of 040-050'. Fg folds are minor, smali-scaie concentric folds or kinkfolds. with the axial plane variable about a trend of 320°. No axial planar foliation is associated with these folds. In the Compulsion Bay area (Fig. 2.4) two foliations were also recognized. The first, Si, is cornposed of transposed primary layering, gneissic segregation, and preferred orientation of biotite, amphiboles, sillimanite, feldspar, gamet and cordiente. SI is axial planar to FI folds, that are generally isoclinal and commonly have disconnected fold noses (Lewry et al., 1981). The Si foliation is refolded about minor F2 isodinal folds, commnly plunging at low to rnoderate angles to the southwest. S2 axial planar sdiistosity is rare except for the more pelitic interlayers. Thus, DI and D2 events observed in the Wollaston Lake area, both in the Compulsion Bay and Hidden Bay areas. appear to cornelate with the DI and Dt regionai deformation events for the Wollaston Dornain described above. Similar late small-sale folding. such as the 03event of Wallis (1971) is seen elsewhere in the Wollaston Domain (Scott.1 973; Delaney et al., 1995) Faulting in the Wollaston Lake area is widespread. and is of vanous styles and presumabiy ages. The eailiest fault structures observed by Wallis (1971) are a series of NE-trending, SE-dipping, ouique reverse faults. such as the Kidd Lake fault (Fig. 2.4). At Kidd Lake, faulting produced a new penetrative foliation in the highly deforrned footwall rocks. Fault slickenlines, quartz rods and fold axes of minor folds in the imparted foliation trend 2Q8Olplunging 11 OS. This suggests that movement was dominantly sinistrai with a small, reverse. east side-up component. Two roughly E-trending faults have been located in the Hidden Bay area. The most important is the Rabbit Lake Th~st(the name 'Pow Bay Fault" was given to the structure by Wallis (1971). but was renamed by Sibbald. 1983) that regionaily strikes 075" and passes through the Rabbit Lake pit (Fig. 2.4 and 2.6b). Where exposed in the pit walls the fault strikes 06S0. dipping 35-65" southeast. It consists of a black gouge, in part graphitic, varying in width from 1- 35m. The amount and sense of displacement on the fault is not known (Heine, 1986). The second fault forms the topographic low between Ashley lnlet and Otter Bay (Fig. 2.4 and 2.6b). It is well exposed along the south shore of the Ashley lnlet and on the south shore of mer Bay. The fault strikes 090°, and dips 35"s. Kinematic indicators suggest sinistral rnovement (Wallis. 1971 ). Many authors have reported the occurrence of Tabbernor-related faults in the Wollaston Lake area (Chadwick 1966, 1967; Wallis, 1971; Chandler, 1978; Ray, 1978; Lewry et al., 1981 ; Sibbald, 1983). N-trending topographic lowç, steep diffs and bluff sections. and intense brecciation define the most prominent fault splays. In the Compulsion Bay area there is a very conspicuous N-trending linear bay to the west of Compulsion Bay itself (Figs. 2.4 and 2.10). This trend continues southward of the bay as a nanow area of swamp and muskeg, and a narrow linear lake. Such N-trending topographic features are also common in the Hidden Bay area. Both Wallis (1971) and Sibbald (1983) reported prominent north-south fault depressions and abrupt bluffs at Pow Bay, Dragon Lake, north of Ahenakew Lake, and the west shore of Otter Bay (Fig. 2.4 and 2.6b). At these localities the rocks are strongly brecciated but no new foliation is imparted (Wallis, 1971). The breakdown of feldspan to kaolin and widespread hematization are also common features. Sibbald (1983, p. 10) noted that - ".. .quartrites intersected..[by north-trending faults]..are strongly fractured, hematized and permeated by microcrystailine opalescent quartz", whereas, "rocks intersected by reverse faults tend to be extensively affected by argillic and chloritic aiteration". Offset along the former faults is deemed to be sinistral, ranging from 500m-3000m+ (Wallis, 1971). No kinematic indicators were recorded to indicate the displacement vector. 4.3 Timing and Metamorphism The basement rocks of the Wollaston Domain record a polyphase metamorphic history. The earliest. metamorphic event produced a high-grade metamorphic assemblage across most of the Wollaston Lake area. Both Sibbald (1 983; Hidden Bay) and Lewry et al. (1981 ; Compulsion Bay) conduded that the first metamorphic event attained upper arnphibolite - lower granulite faaes conditions at low to medium pressure (700-750°C, 5-6kban). The first rnetamorphic event Ml, was synchronous with. or imrnediately postdatecl, the 01 deformational event. These metamorphic conditions amtinued through to the end of the Do deformational event (Lewry et al., 1981). In contrast, Wallis (1971) suggested that metamorphic grade in the Hidden Bay area only reached mid-amphibolite facies th tempe rature and pressure at 600-65û°C and 3kbars. respectively. Retrograde metamorphisrn accompanied minor Da deformation that is seen locally in the Hidden Bay area (Wallis, 1971 ; Hoeve and Sibbald. 1978). Recent worù (Madore and Annesley, 1993; Madore et al., 1996; Annesley et cil., 1996a, 1997) has conœntrated on the tectonotherml history of the Wollaston Dornain, especiaify in the Wollaston Lake area Madore and Annedey's study area is essentiaily the same as the current rnapping area, augmented by drillcore samples from basement rocks to the immediate west. They condude that the Wollaston Domain underwent three rnapr thermotectonic events (using the notation of Mn1-3 and D~1.3). The first event MHI, occurred at 1840-1850Ma, synch ronous wit h, or immediateiy proceeding DH~.Peak pressures of 5-8kban were obtained duting MHI. Granulite-faaes peak metamorphic conditions were attained dunng MH~,aevi with DH~,at 1812-1830Ma. Pressures and tempe ratures reached 4-6kban and 725-77S°C, respdvely. The third event, MH~,occurred between 17751795Ma. This was an amphibolite-facies, retrograde metamorphic event that ocairred during uplifi-driven decompression, and tranpressional shearing. Retrograde metamorphisrn continued with uplift through untii 1752Ma. and a minor greenschist to lower amphibolite-facies rnetamorphic event, MH~(Annesley et al., 1997). Thus, it is noted that with the addition of several refinernents by the later studies, the metamorphic conditions indicated here are broadly sirnilai to those proposed by Lewry et al. (1981) and Sibbald (1 983). 5. Current Work 5.1 Geophysical Interpfetation To help in the interpretation of the structural history of the Wollaston Lake area it was decided to try and reevaluate the geophysical data available. The whole of northern Saskatchewan is covered by aeromagnetic field data collected dong flight lines with a 350m line spaang. and pubiished by Saskatchewan Department of Mineral Resourœs. It shows the broadly NE-trending grain of the Wollaston Domain. It aiso shows magnetic highs that correspond to the outcrop patterns of the douôly-plunging basement gneiss domes, which core the fold patterns in the domain. The Archean basement gneiss has a high magnetic response in cornparison to the metasedimentary rocks of the Wollaston Group. Although this gives a broad picture of the structurai styie in the Wollaston Domain it does not help resolve srnaller-scale fault and fold structures. As part of the NWIAEA study extensive aeromagnetic surveys were flown over the test area to aid in the interpretation of basement geology ôeneath the Athabasca Group and later Quaternary cover. Line spacing on the survey was 300m, flown east-west, with readings taken every 0.5 seconds, equivalent to approximately 40m. The results of the survey are discussed in Komik (1983). In an attempt to improve the resolution of basement fault features the raw data file from the original survey was obtained from the GSC Regional Geophysics branch. Two sets of readings were taken in the sunrey, total magnetic field (nT) and vertical gradient (nT/m). The vertical gradient reading provides better resolution of near surface magnetic features, and thus was chosen for interpretation of surface geology. A map of the contoured vertical gradient data is shown in figure 2.6a. The disadvantage of the vertical gradient measurement sh~wsin the western half of the rnap where up to 300m of sandstone cover decreases the resolution and amplitude of top to basement anomalies. The colour scheme Figure 2.6. lnterpreted vertical gradient aeromagnetic map of the NENIAEA Athabasca test area. A) shaded relief map of the vertical gradient data. See text for explanation of colour scheme. 6) interpretation of the underlying geology based on the magnetic response of the rocks coupled with knowledge of geology from previously published and unpublished reports. Abbreviations:- (structures) P.I.S.Z. = Parker Island Shear Zone; R.L.F. = Rabbit Lake Thrust; C.B.F. = Collins Bay Thrust; M.L.F. = Moffat Lake Thrust; (Locations) H.B. = Hidden Bay; O.B. = Otter Bay; A.P. = Ashley Peninsula; B.I. = Black Island; PB. = Pow Bay; P.I. = Parker Island; N.I. = North Island; H.P. = Harrison Peninsula; S.I. = Snowshoe Island; K.L. = Kewen Lake. Shading:- red indicates high magnetic response, probably Archean basement gneisses; unshaded indicates moderate to low magnetic response, dominantly Aphebian paragniesses with subordinate Hudsonian intrusives; solid blue lines indicate position of diabase dykes; horizontal green stripes indicates limits of the P.I.S.Z.; thin green Iines indicate possible position of additional Tabbernor-related fault zones. Red dots show the locations of major uranium deposits: 1 = Midwest Lake; 2 = Dawn Lake; 3 = JEB; 4 = McClean Lake; 5 = Sue; 6 = RavenlHorseshoe; 7 = Rabbit Lake; 8 = Collins Bay 'B' zone; and 9 = Eagle Point. chosen for the map is not related to a linear increase in the vertical g&ent. but is modified to best pi& out the changes in field patterns assodated with basement fault features. Thus no deis show and no inferences about the absolute value of the verticai gradient should be drawn. Reds and oranges represent relatively high values, and Mues and greens represent low values. The east-west 'stripes' are an artifact of the greater line spaang than sample spaang along the lines. The map is dominated by a NE-trending high in the centre. and similady trending lows to the northwest and southeast. The high has been interpreted as the axial trace of a Dz antiform with Archean rocks creating the high. This fold in fact contains two separate cores termed the Hanison and McClean massifs (nomenclature of Suryam. 1984). The abrupt deep lows on the north and west sides of the basement doms, as compared to the mare graduai change in field to the south and east, suggests that the antiform is not upright. The axial plane appears to strike northeast and dip to the southeast, with the sense of vergance to the northwest. As noted above, Tabbemor-related fault features show intense oxidation and brecciation of the basement rocks associated with them. Because of this the faults should appear on the map as a decrease in the vertical gradient. Cornparison of the known topographie lows that coinude with the rnapped Tabbernor Fault traces (at Ahenakew Lake, Dragon Lake and Pow Bay) to the vertical gradient map shows that there is no offset of the dominant northeasterly trend across these faults. within the resolution of the rnap (compare figures 2.6a and 2.6b). There is certainly not the 3000m+ suggested by Wallis (1971). There is however a small decrease in the vertical gradient assoaated with the faults. This is in agreement with the observation of oxidation and breakdown of the rnagnetic rninerals in the vicinity of the fault. The most obvious feature affecting the regionai trend of the vertical gradient map is a zone 1-3km wide, trending 015-025' aiong the western shore of Otter Bay. through Black Island, Harrison Peninsula, and Snomhoe Island (Fig. 2.6a). It is characterized by a visiMe sinistral displacement of the magnetic highs and a lowering of the gradient field in cornparison to those rocks either side dong strike. This feature is herein after refened to as the Parker Island shear zone (PISZ) (Fig. 2.6b), as it is at this locality that the features related to its structural history are best devdoped. lopographidly the PIS2 is hidden beneath the waters of Wollaston Lake for much of its length. Where it does intersect the shore it is usually in areas of liffle or no exposure. There are several other wïde basernent zones that trend approximately 020° and appear to offset the regional trend sinistraily (Fig. 2.6a). The rnost prominent of these is a 2km wide zone. 5km west of Kewen Lake. These zones are not as well defined as the PISZ but this is probably due to the greater Athabasca Group cover to the west. There are also severai visibie lineaments in the Harrison massif on the north shore of Collins Creek (Fig. 2.6a). These lineaments trend approximately northward and correspond to a decrease of the verocal gradient. As such they appear similar, geophysically, to the Tabbemor Fault traces discussed eariier. There are no corresponding topographie features on the surface. but this area is covered by Athabasca Group sandstones and is in a wide zone of swamp and general low relief. Both these features would combine to mask any expression of basement brecciation and glacial erosion seen at the other locations. The Rabbit Lake Fault does not show up on the map but the larger Moffatt Lake Fault dearly shows up as a lineament along the northern edge of the Harrison massif, and continues west where it has apparent sinistral displacement. Unfortunately such good geophysicai data are not available for the Compulsion Bay area and therefore no similar interpretation can be made for that area. 5.2 Field Mnpping Detailed field mapping was camed out during the coune of summer seasons in 1996 and 1997. Because of poor inland exposure the mapping was almost exclusively along the shoreline of Wollaston Lake. Two areas, Hidden Bay and Compulsion Bay (Fig. 2.4), were chosen as they were reasonably accessible by boat and previous mepping had shown outcrop adjacent to welldefined TFZ splays. The ernphasis of mapping was to wlled as much structurai data as possible, espeaally adjacent to the TFZ splays. The mpping and correlation of lithological units was not attempted, but descriptions of lithology were still recorded at al1 locations and these generally agreed Ath the earlier reports of Wallis (1971 ), Lewry et al. (1981 ), and Sibbald (1983). The orientation of rock fabrics was recorded wherever seen almg with a description of the fabric type, Le. cornpositional layering or the prefened orientation of minerais. Orientations of pegmatitic and leucograniüc intrusions, and quartz veins were recorded as it was apparent from prelirninary observations and previous reports that several generations of intrusive events had taken place. Brittle features such as joints and micro faults were noted as well as the sense and amount of displacement where evident. The results of the data collection in the Hidden Bay and Compulsion Bay areas are shown in figures 2.7 to 2.13. 5.2.1 Hidden Bay area On the basis of the vertical gradient map interpretation, the area has been divided into two domains (Fig. 2.7). The division is based on those outcrops that lie within. or adjacent to, the PISZ, and those that do not. The second domain was modified to include data from a small group of islands within Hidden Bay and at the southern point of the bay. The reason for this modification has to do with the dominant lithology at these locations and will be discussed in more detail later. The two dornains will be discussed separately as their structural elements show a marked difference in orientation and presurnably history. Flgun 2.7. A) Form surha map of the HMdan Bay arma. Tha devalopmant of S1 1s Intwpmted as klng a widaspmad event assoclatad wlth early Hudsonlan datomatlon. Sa18 mlatad to post- colllslonal daformation In the THO. and k mtrlcted to Tabkrnor- relakd hult zones. The exwptlon Is calc-slllcak and marbk unlts exposed on Islands within Hidden Baym8, 1s dominantly defined by the transposition of S1 on to the D, dafomratlon plane, but at H mlneml fabrlc thd overprlnb 8,. Tha solld llnw that deflne the boundarles of the PIS2 also deflna the llmb of data Included ln domaln II.The orkntatlon and genamtion of fabrlca has been extmpolated to amas wham thmm Is Insufflclant exposum, uslng the modal for davelopment of S1 and Sahbrlcs. 6) Inset showing cartoon Illustmtlon of foilatlon orlentatlons In the PI=. The shear zone contalns motless folds and boudins pamllel to the Sa follatlon. ln hlgh stmin areas the follastlon may be norlentated to IIe parallel to the shear zone. or a new shear cbavage may be developed. Dornain 1: outside the PIS2 Foliation readings outside the PIS2 am consistent about an average strike of 06P (Fig. 2.8a). The dip varies from moderately- to steepiy-dipping to the southeast (counting peak of 53O). The foliation is typically defined by fine. millimetre-de, altemating bands and blebs of quartz and feldspar, with more mafic segregations in which biotite flakes show a strong prefened orientation. Typically the foliation is not observed in relationship to any other fabric. and forrns massive, monotonous outcrops of gneiss. This indicates that the previously existing sedirnentary layering has been obscured by development of the gneissic foliation. In locations where quarute outcrops north of Hidden Bay the original protolith contained little or no mafic component. Here occasional oxidized seams and mica flakes define a discontinuous foliation. Fold data collected outside the PIS2 show that folding in the dornain is consistent w'th one phase of deformation that produced the previously mentioned foliation (Fig. 2.9b). The fold axes fit well on a great cirde, the pole to which is coincident with the pole to the average of the foliation readings. This agrees with the field observations that fofded veins and dykes are tightly folded and often rwtless. with the foliation Ming planar to the folds. The fact that the fdd axes are not co-linear shows that the dykesîfoliation were not CO-pîanarprior to deformation. This may be due to an earlier unrecognised deformation event, pobsbiy the early thermally-controlled doming of the basementcover contact (Lewry and Sibbaid, 1980). Alternatively the dykes may have been intnided into the rnetasedirnentary rocks discordant to the foliation. Although not as consistent, the axiai plane data also have a counting peak coincident with the average foliation reading. A plot of the axiai trace data shows that the average stnke of the folds is 067O. again consistent with the foliation and fold axes data. Flgure 2.8. Contoumd stemogmphlcal pmJactlons of .tructuml data fmm the Hlddm Bay ama. Thesa and al1 prowadlng stereonets am lower hamisphan, equal-rma, .trmogmphlcal proJectlons. Whan stemoneîs are contourad It 1s dom udng Gausslan countlng method wham th. axp.ckd count for a random dlstrlbutlon, E-m. Contoum am dmovwy 20 abovm the expected count. AC= Domaln 1. A) pohs to gnolulc (bllaüon; 8) poles to dykes; C) polas to velna; DQ - Domaln II. D) polos to gnelsslc follllon; E) polas to dm;F) polos to velni. Figure 2.9. Stereographical projections of fold data from the Hidden Bay area. A) al1 fold data from Hidden Bay area; 8) fold data from Domain I-outside P.I.S.Z. Shown for reference is a stereonet of foliation data from Domain 1. (as figure 8a). Data suggest that folds are compatible with formation during the development of the gneissic foliation (S,); C) fold data from Domain II-inside P.I.S.Z. Shown for reference is a stereonet of foliation data from Domain II. (as figure 8d). Data suggest that folds are compatible with formation during the transposition of the gneissic foliation (S,) ont0 the plane of flattening to produce (S,), inside the P.I.S.2. Fold Axes Axial Planes Axial Traces N N N / I \ Foliation b) Domain 1 - Outside P.I.S.Z. Foliation N T *= FOI^ Axes = Axial Planes Axial Axial Traces Domain II - lnside P.I.S.Z. Axial Planes Axial Traces N LI Granitic and leucogranitic intrusives are cornmon in this domain. There appear to be at lest two separate generations of intnisives. The first generation appean as pale pink quartr and feldspar veins and dykes which Vary in thickness from 1cm-50cm. The intnisives crosscut the foliation at a low angle and generally show evidence of gentle folding and/or boudinage. The plane of flattening appears to be the plane of the foliation. although the data suggest that the dyke orientation is more variable than the foliation (Fig. 2.8b). Mafic minerals are generally absent but occasional tourmaline crystalline aggregates were seen intergrown with quartz. The second generation of intrusives crosscut the foliation at a high angle, in contrast to the eariier generation. and where the two are seen together the later generation crosscuts the eadier one. They range in thickness from 2cm-2m and are rectilinear. These later intrusives are similar in composition to the first, king cornposed al most entirely of quark and feldspar. Rare. large, biotite books ocair in the second-generation intnisives but these are the exception. The biotites show no preferred orientation and no foliation is developed. Hematite is a ubiquitous accessory minerai in late fractures and dong deavage planes in the feldspars. The two generations of intrusives can be distinguished on the basis of colour, the second generation being a more vivid deep pink or red. Another distinguishing characteristic of the second generation of pegmatitic intnisives is the angular nature of the wall contacts. Dyke (sensu lato) walls show sharp, planar contacts with the sunounûing rocks (Plate 2.1) with no indication that melt rnatenal migrated from the irnmediate surroundings. Dykes also exhibit sharp changes of direction, suggesting they were intruded into brittle fractures. Rafts of country rock can be cleariy made out in several dykes. These rafts can easily be correlated to sections of the adjacent wall rock, suggesting that the dykes did not under go significant lateral movernent across them dunng emplacement. There is a strong preferred orientation to these dykes, tightly dustered around a strike of Plah 2.1. Secondqomraüon pogmitlk dyka, nonh shom of Pow rlgM of the plctun. This dyk. shom wvml of ai. dlagnostlc Laturw of socondganwatlon Int~shms.Flrstîy, nnd the sharp contact ktween th. dykm and th. adjacent roda. Al80 note the angular natum of the bloda of country mck whlch have spalkd , frorn the dyke wall during intrusion. Secondly, the dyke Is unaMedby deformation, and no follatkn k developod withln lt. Flnally, the dyka trends appmxlmately northward, am do many other dykes of thk genemtlon. Thk partlcular dykm k wldar than the avemga, it 1Om*. For scak th. wmpau la lOcm long. 350-005" and verücally ôipping (Fig. 2.8b). The lad< of significant offset suggests that the second generation of intrusives were emplaced during an extensionai event, perpendiwlar to the dyke orientation. Quartz veins appear to follow the same broad trends as the pegmatite intrusives. bath mineralogically and stnictuially (Fig. 2.û~).Examples intemediate between dykes and quartz veins exist. with quartz-feldspar margins and a pure quartz core. Actinolite laths up to Smm long were observed in a series of quartz veins at locality 18081 (Fig. 2.7). The orientation of quartz veins is sirnilar to the dykes with the second generation of veins trending 330-000" and vertically dipping. Domain n: lnside the PlSZ Foliation readings within the PIS2 are far less consistent in orientation than those outside (Fig. 2.8d). 60th strike and dip Vary by about 60-70 degrees, but as a general rule the foliation is steeper and closer to NE-trending than the foliation in domain 1. This is reflected in the counting peak for the foliation within the PIS2 which is 048/7S0. The nature of the foliation is sirnilar to that in dornain 1. It is typicaily defined by compositional variations consisting of aiternating bands of qua* and feldspar, with nanower more mfic bands of quartz+feldspa»biotite smphibole. There is more evidence of boudinage in the foliation in the PIS2 than outside, and grah flattening and elongation is cornmon. Outcrop-scale folds within the foliation, which are rare in the foliation outside the PISZ, are also more abundant. At location 21071 (Fig. 2.7) on the eastern shore of Parker Island, a gneissic foliation striking 020" is seen to tnincate a foliation. of what appears to be the same generation, striking 360" (Plate 2.2). If these two foliations are of the same generation then their discordant relationship can be explained by asyrnmetric foliation boudinage (Lacassin. 1988) of this competent layering. The initial break in the foliation may have evolved into a 'C' type shear plane with sinistral shear displacement. This would explain the cuirent geometry of the foliation and the Plate 2.2. Devalopment of asymmetrlt follatlon boudlnage at location 21071, south east ahor, of Parker Island. The follitton to the far Ieft of the photograph, trrndlng 020°, truncatm the folillon In the centra, tmndlng 36Um.60th kllatlons am defined by gnelulc layering In quarkdch gnmki.. and quublt.. th.1 pmdomlnate on Parker Island. The mxplinmtlon ghn for thmlr cunrnt discordant mlationshlp b th1thoy have bwn dkloorkd along a plane whlch nins pamllel to ai@ fdMlon on the kCI, but cub acroms foliatlon to the flght This dlrlocitlon occumd during Iarge~cale foliatlon boudlnaga of the compooltlonal Iaymring. Seo text for more cornpleb descrlptlon of the structure. orientation of the break between the blodrs, which is approxirnately parallel to the plane defined by the PISZ. Generally on the Parker ldand outaops the main foliation is north to NE-trendhg and subvertical. Two locallies (21021 and 22021 ; Fig. 2.7) show a well defined stretching lineation on the main foliation plane. and in elongated quartz dasts. These lineations plunge 39" towards 232'. in a foliation 21 7/76". Still on Parker Island at outcrop 21041 (Fig. 2.7) a dudile fault with the orientation l95/85"offsets the foliation sinistrally with an unknown displacement (Plate 2.3). Adjacent to the fault the foliation is rotated around until it lies paraflel. It appean as though at least sorne of the offset dong this fault was achieved by foliation-parallel slip. Eight more small-scale faults with similar orientation and style of ductile sinistral offset were obsewed in or adjacent to the PISZ. A mixture of quartz and feldspar has intruded five of these faults. Folding is cornmon in the rocks exposed on Pafker Island, such as on the srnall islands of the northeast point, where the foliation and dykes are folded into üght to isoclinal folds with fold hinges that plunge moderately NNE-SSW. The data for domain II show that the folds lie on a plane of flattening which is coinadent with the counting peak for foliation readings within the PISZ, Le. 0W5O (Fig. 2.9~). Axial plane readings within the PIS2 are consistent with the average foliation plane, and axial traces show a maximum trend of 048'. This suggests that the folds are examples of SIisodinaîly folded ont0 the 02plane of flattening, with the limbs being transposed ont0 S2. It is possible that these folds represent FIfolds transposed ont0 the 02 plane of flattening. and this explanation should not be discounted. Abundant boudinage of the foliation-parallel leucogranitic dykes and resistant bands in the gneissic foliation suggests that flattening onto the plane of the foliation has been extensive in dornain II (Plate 2.4). 'Chocolate tablet boudinage' structures seen in some locations indicate that extension occurred in two Plate 2.3. SrnaIl-k ductltlk huit with nljawnt mngslnlstml dmg, location 21041. souanist ahom of Parker kbnd. Tho f.uM plane .Mk# 185., dlpplng 115. to tha south. Thk Ir slmllar to the lnfernd orknbtion of the PIS& and the 8Inl.tril .bar fibric mn In the Compuklon Bay ama (seu section Sm2.2). On the rlght-hand side of the huit a slngk prk puarbrlch kymr, appmxlmibly 6cm wide, has boon tlattonod parrlkl to th. f.uk plan.. Thm tnincation of adjacent layon In tha gnablc folktlon auggmb the 1hast soma of the dkplacement on thk hua was achleved by Iayer pamllel slip. Compau k 1Ocm long. Plate 2.4. Ext.nshm boudlnage of pogmatltlc materlal wlthln well- follated, finegralned blotltequarh gneiss, locatlon 25021. Thls location Is north d the Hidden Bay arma In one of the additlonal mapplng amas. ît k loatmd wlthln a strong topogmphlc Ilneament, trendlng 02S0, thmugh Greenaway Island on Wollaston Lake. The M follatlon strlkas 220°, whlch Is about the average for domaln II of the Hldden Bay ama. Tho boudlnagmd material may dthr k part of an eariy 'in-mlk18mdtsegmgatlon or a Iater Intrushm dyke. In the cantm of the phatogmph small hocllnal, motleu fold withln a section of pm#mdto Indlcib. th. ûmnsposltlon of the aarliw follatlon onto the cumnt Watbnlng' follatlon. Hmmer In shot Ir 3Ocm long. directions TighUy folded quartz veining at IocaOons 13021-13061 and 29061- 29091 show i~odinalfolâing with wavelengths of 2-1 Ocm. about a well developed axial planar fabric. The folding shows approximately equal amounts of 'S'- and '2'-folds, suggesting that there was no strong wmponent of shear parallel to the foliation during deformation. Dyke and vein orientations (Fig. 2.80 and f) show that both types of intrusives have strongly dustered orientations parallel to the foliation. 5.2.2 Compulsion ûay am As vertical gradient suwey data were not available for the Compulsion Bay area no similar means of subdividing the data into structural domains was available. Because of this the domains were distinguished by the occurrence of a visible shear cleavage. Despite the recognition of this new fabric it has not been possible to define a continuws zone of shear like that in the Hidden Bay area. Thus for this study the areas displaying the shear deavage are treated as isolated regions in an otherwise unaffected dornain (Fig. 2.1 0). Domain 1: amas umffected by sheai developmnt As with the Hidden Bay data, the main foliation is defined by compositional layenng on a millimetre to centirnetre de.In more micaceous horizons the mica flakes (predominantly biotite) have a strong prefened planar orientation that gives nse to strong schistosity. Much of the mapping included areas of basernent gneiss outcrop and at these locations the foliation is poorly developed. Where present, it is defined by the preferred planar orientation of discrete biotite flakes that make up 2-10 percent of the rock. There is considerable variation in the strike of the foliation but it is consistently steeply NW- or N-dipping. The counting peak for foliation readings in the regions unaffeaed &y sheai is 253/76O (Fig. 2.1 1 a). The granitic intrusives are similar to second generation of dykes in domain 1 of the Hidden Bay area. The dykes are leucogranitic, with occasional rnafic Flgun 2.10. Loatlan map of tha Compublon Bay mpplng am. BIack ddr Indiatm th. Ioaüons af outcmpm dlsplaylng shou fabrlcs, and thmforr Intludd In domaln lZ (mae tmxt for explination). Tha solid linos mpmaont the Imation of TFZ huit splays, and dashed llna IndIcabs the pmbabk posltlon of a major TFZ huit spiiy bmwd on mignotic flald p.tbms and llmttod mapping. Figure 2.11. Stwwgmphlul pto).dlom of 8~cturilddi from th. Compulsion Bay 8ri.o. AC - Domaln 1. A) pd.o to gnokdc foliation; 6) pohs to dykw; C) pok. to wlrm; O+ - Domaln II. 0) poksto grniulctollatlon; E) polos to dyk.8; F) polos to vmlns. Domain I Domain II Veins rninerals, planar with sharp wails, and unfdded. Hematite is an important accessory mineral as is magnetite at certain locations. Zircon has been noted in thin section as well as several other unidentifid acçessory phases. A few of the dykes show shear of the foliation adjacent to the dyke margins. consistent Ath sinistral shear, but the majority show no evidence of deformation. Even in those dykes where there is evidenœ of shear adjacent to the margins the dyke rock is unsheared, and composeci of 1-2cm feldspar crystals in a coarse-grained mat rix. Typicai dyke width is 2-15cm. Several dykes show a transition to quartz- dorninated or even monomineralic quartz veins. The dykes are dustered about a peak orientation of 350/83O (Fig. 2.1 1b). The number of quartz vein readings is small but severai of the veins follow a similar trend. Dornain II: areas showlng development of shear featuies As mentioned above the diagnostic feature of sites induded in this subset is the presence of a shear deavage or parallel joints. Reagnition of these features is based on severai criteria. First, the shear planes and joints have a very consistent orientation. They are tightiy dustered about an average of 014/86". Second, shear deavage development is associateci with strong deflecüon or drag of the foliation with a wnsistently sinidrai sense. Third, both the shear deavage and joints show patchy to continuous rdhernatite coating the surface of the planes, which may be in part siiicified. Quartz fiII in open planes, or dilations on inegular planes, is cornmon and mineral growth steps and slickenlines suggest sub-horizontal sinistral movernent. Locally joints and deavage planes have an associated, pink aiteration halo 1-5mm either sida of the plane that is preferentially eroded on weat hered or glaaated surfaces The counting peak for the main foliation is 229ff8O although, as in domain ïï in the Hidden Bay area, the range in foliation orientation is larger than in dornain 1 (Fig. 2.1 1d). The foliation is more obvious at locations displaying the shear fabric, especially where exposure is of basement gneiss. In contrast to basement gneiss outcrops elsewhere that show scattered biotite flakes, these outcrops have semi- wntinuous seam of biotite, appmximately Imm thidc Quartz grains are severely flattened into ribbons of quartz aggregates parallel to the foliation. The sheared foliation is displayed in location 520201 (Fig. 2.1 2, Plate 2.5), where the shear deavage is also well developed. Hem the shear planes are approximately 5mrn apart. discontinuous and easily identifiable with the naked eye. In thin section the rock shows strong ribboning of quartz aggregates and strong alignment of biotite flakes parailel to the foliation. Adjacent to shear planes the quartz and feldspr show drastic grain-size reduction. A new generation of biotites has grown along the shear plane, or the existing mineral grains have been reon'ented parailel to the shear plane. These biotites have undergone pervasive chloritization (see sedion 5.2.3). From visual inspection alone (Plate 2.5) it appean as though this new shear deavage is in fact a classical S-C fabric. Although the similarity is striking the author is reluctant to use this terrninology. The reason for this-~eluctanœis that although the gniessic layering resembles the 'S or flattening plane it is not a new fabnc developed simultaneously with the 'C' or shear plane, as shown by Berth& et al. (1979). Lister and Snoke (1984) argue that the 'S and 'C fabric elements need not be developed simultaneously although they still infer fabric development dunng the same deformation episode, which is contrary to the mode1 argued for the development of the tabric shown here. In addition the sde of fabric development is larger than that typically associated with S-Gtype fabrics (Lister and Snoke, 1984; Blenkinsop and Treloar, 1995). in which are C planes are sepaiated by prn or mm. Deformation associated with small-sale ductile faulting is restricted to rocks immediately adjacent to faults. A foliation swing of 34 degrees over 2m was recorded adjacent to a small ductile fault, orientated 013î74°, at location 490701 (Fig. 2.10). Similar deflections of the foliation were recorded adjacent to faults at locations 580301 and 61 0201 (Fig. 2.1 0). Both of these locations show granite pegmatites intruding the fault planes. Shearing of the pegmatite is only seen at the rnargins of the intrusives at location 580301. Figure 2.12. D.trlkd tkld m.p of ldlon52û201. Tho location h an outcrop of Archan b.#mmt ginlu(part of th8 Johnson Rlvw adjacent TF2 f.uh sply. Dnormmtlon k ch.mkrbd by Inbiislffatkn of th. gri.k.lc folktlon and dovmkpmont of a cleavagm planas by qrinMc mît rnmîmrlml hrkd to many cloi.ly- spadnarrow gmnltlc dyk.8 whlch pmmlkl the mhur dlrrctlon. Sem figure 10 for location. Plate 2.5. Closely-spaced shear cleavage in Archean gneiss of the Johnson River Inlier, location 520201, west of Compulsion Bay. Note the extreme development of a flattening foliation, defined by elongate quartz 'ribbons' and biotite seams. This is in contrast to the poorly-developed foliation elsewhere in Archean basement rocks. The shear cleavage, striking 00g3 and dipping 86O west, is patchy but where present it has rotated the foliation with consistent sinistral sense. The photograph is 2Ocm from top to bottom. Folds are uncornmon in the Compulsion Bay area, espedally in the granite gneisses which fonthe Johnson River Inlier. Fold orientation data is shown in figure 2.1 3. The dykes within domain II are bimodd in orientation. One group of dykes is sirnilar in al1 charaderistics to the dykes from the dornain unaffected by the shear foliation. trending 335-360" (Fig. 2.1 le). The second set of dykes is parallel to the shear fabric. Le. trending 010425°, and shows lots of examples of sinistral shear in the wall rock adjacent to the dyke (Plate 2.6). At two outcrops the dykes themselves are sheared, with minor biotite flakes afigned parallel to the dyke walls, but only at the edges of the dyke. The cores of the dykes remain undeforrned. As with other locations the qua- veins appear to rnirror the orientation and style of the quartz-feldspar dykes. They are composed of two populations, one intruded into shear planes and showing strong deformation. the other trending 330-350"and undeforrned (Fig. 2.1 le). 5.2.3 Srnall-scale Reactivation Fmtures common to both Hldden Bay and Compulsion Bay Reactivation of ductile fault features. filled by intrusive material, is not comrnon but where it occurs it follows a consistent pattern. 60th dykes and veins show eari y ductile shearing of coane-grained quartz and feldspar. Biotites show occasional kink bands. Deformation is associated with biotite alteration and/or replacement. This style of dyke deformation is well displayed at location 520201 (Fig. 2.10). Here 2-3cm thick dykes deariy intnide shear deavage planes with a separation of 50cm or less. Thin section anaiysis of the dykes shows a discontinuous zone on both margins of the dyke about 2mm wide. Within this zone quartz and feldspar grains have been sheared out into elongated aggregates that display a drastically reduced grain size as cornpared to the rest of the dyke (Plate 2.7). Seams of heavily altered biotite are aligned parallel to the Compulsion Bay ama. All th. fold data wi. calkcbd hmdomaln ïï amas. Shown for nnirnœ am pdœ and planos for both th. avamge follatlon phnm and the avmg. 8h.u cloawgo plane (u FIg. 11d). Nd. thl both the told .x.r and th. otld plan- Ik somewhem betwun th. avmg. follmtlon plam and the shear plana suggosüng thit thmy hmundorgona -Ion tomrûs th. shear plan. r mrmsult d hlgh -ln In th. rock. Plate 2.6. Gmnlk dyke 1ntnid.d lnto the ah- claavage, location 520201, samm u platm 2.5. fhm gmnlk-pogmatItIc dyke 1s hfnt (dashed whwhlk Ilma show thm dg-), but k deflnd by the Iack of follatlon devdopment, and darkmr plnk colour with hemltte . stalnlng. Folldon planes In th. gnak. am ahumd out wlth obvlous slnlstml dmg but th. dyk. ahom no dgna of dudlo defonnatlon. The da* lmguhr llm ninnlng domthe centre af the dyke (whlte amw) k hctumpkm thldevmloped durlng bMe reactivatlon of th. 8h.u niMc. Duk patchms on the gnelss an Ilchen growth. Thm dykm k 8ppmxim.kly 3cm wldm. Plate 2.7. Photomlcrogmph of tha maigln of a dykm Intruded lnto the rhaar cleavaga, from locatlon 520201. Thlr clrrly shom the localkation of shaaring withln tha dyka. Tha corn (uppmnast and to the right) Is composed of coanegmlrnd quark and hldapar gralns whlch am i.latlvely unddonnd. Tha only aitomtlon k wmak the dgeof the dyka shom oxtnma anln si20 mludlon of qua- and feldspar ln nsponse to shearlng. The shearing is accompanld by the Introduction of ahoargamlkl ah- of blotlb (swn as bright layem due to hlgh blmfrîngenœ). Thosa hmbnn alkmd to a mMum of chlorlb, wrlclte (llllt.3) and mlnorapldok. shear plane. These are now replaced by what appean to be a Cnegrained phyllosilicate aggregate, induding chlorite, sencite and minor epidote. Quartz veins contain rafts of highly-strained, undulose quartz in a finegrained recrystallized quartz matrix, with strong flow banding (Plate 2.8). The margins of the intrusives are more heavily deformed than the cores. Later deformation consists of brinle fractures that crosscut both quartz and feldspar grains. Hematite staining is assoaated with many of these late fradures. It is not uncornmon for the fractures to be filled by a new generation of quartz. At location 18081 (Fig. 2.7) severai parailel quartz veins show extensive brittle deformation. The fractures crosscut and offset actinolite needles in the vein. The fractures are filled by a cornplex assemblage that indudes euhedraJ zoisite (Fe-poor epidote). surrounded by a halo of fine-grained carbonate and then by seriate. Many of the intrusives are reactivated as brittle faults with well identifiabie slickenline lineations. One example of a granitic dyke reactivated as a brdated fault zone was seen at location 560501 (Fig. 2.10). The core of the dyke now consists of subangular fragments of quartz and feldspar in a silicified hematite mat rix. Small-scale brittle fault planes are common in both field areas. They are typically reactivated joints or. in the Compulsion Bay area, deavage planes. Minerai growth steps ailow the determination of movement sense where present. Minerakation on the fault surfaces is typically quartz and hematite although chlorite, epidote and unidentified day minerais are also present on some surfaces. The faults are more common in the Archean basement gneiss than in the overlying ~phebiangneiss. Plate 2.8. Photomlcmgraph of qua- from vdn Intnidad lnto fault plane. The eadlest oh8ervabk ovent k charactorhed by the crystalllzllon of coamegmln.d queIn the veln. Subsequont ductilo deformatlon resulted ln the mcrystalllzatlon of much of thls and the dawlopmant dflow bandlng wlthln the quark. Wlthln thls flnerqmlnad, mcrystallkad quark tham am romnant 8mb'of the origlnal quartz whlch hava a chamcterlstlc undulma texture due to the straln asaoclatmd with m.ctlvaüon. Later roactlvatlon causd brittlo fmcturlng that crosa~cutmboth ganemtlons of quark gmwth. 6. Interpretation of Data 6.1 Ductik ûefomiation Assoclateâ with the Tmns-Hudson Orogen In agreement with previous studies of the Hidden Bay and Compulsion Bay areas two foliations have been recognized. The first foliation (SI) in areas unaffected by shearing is reasonably consistent in its trend of 067-247' in the Hidden Bay area, and 063-243" in the Compulsion Bay area (Figs. 2.8a and 2.1 1a). The dominant southeasteily dip direction in Hidden Bay is consistent with the area ocaipgng the southeastem flank of major structural dome, cored by Archean gneisses of the Harrison and McClean massifs (Figs. 2.4 and 2.6). Likewise the northwesterly dip direction in the Compulsion Bay area rnay be the result of its position on the northwest flank of the Johnson River Inlier, another Archean are to a major structural dome (Fig. 2.4). Alternatively. the change in dip direction has been attributed to a division of the Wollaston Domain into a western segment where dips are to the southeast. and an eastem segment where dipû are to the northwest (Annesley pers. comm., 1998). A dominandy low aerornagnetic field to the West and a dorninantly high aeromagnetic field to the east distinguish the two segments. The lineament separating the two segments passes just south of the Hidden Bay area. There is some evidenœ supporting this later hypothesis as readings from northwest of the smaller Trout Nanows granite (Fig. 2.4) indicate a southeastward dip, contrary to what would be expected of this location if the SI foliation dip were controlled by position relative to the basement domes. Folding in these structural domains is consistent with flattening ont0 the plane of the SIfoliation, typified by tightly folded pegmatic segregatians. As noted earlier. the lack of CO-axiallywithin the fold axes suggests that the foliation was not co- planar and may indicate a prior deformation episode not distinguished here. The limited amount of data shown in the paper rneans that little importance can be placed on this distribution, and the proceeding arguments on the nature of deformation within the TF2 are not affected by the earlier deformations. The folded dykes are not evident in the ~orn6ulsionBay data because the host lithology is dorninantly basement gneiss that did not Contain many early mît segregations. The limited fold axes data suggest that there was little rotation of the axes to towards parallelism. indicating that there was not a strong constrictional strain (Fig. 2.9b). Unlike the results of previous studies, it is dear from the data here that the second foliation (S4 is not a universai overprinting fabric, but is restricted to narrow belts that trend between 010-020". The most easily definable of these is the PIS2 although it is dear from the Compulsion Bay data that such a shear zone, or zones, must exist in that area as well. These shear zones offset the lithology and Sc foliation consistent sinistral sense. As with the SI foliation. the orientation of the S2 foliation in Hidden Bay is comparable with that in Compulsion Bay, being 048ffS0SE and 229/78*NW respectively (Figs. 2.8d and 2.1 id). Thlsauggests that shear zones in the Hidden Bay and Compulsion Bay areas underwent a similar degree of shean'ng and sinistral rotation of the local plane of flattening. The only exceptions to S2 being confined to the linear belts or shear zones are found on severai srnqll idands in Hidden Bay (Fig. 2.7). The dominant lithology at these locations is cabsilicate rich arkoses and dirty marbles. These lithologies are considered to be the mstductile within the mapping area. It is not surprising then that these rocks should take on the characteristics of the D2 deformation, whereas other lithologies outside the shear zones do not. The fact that S2 is generally not seen in relation to SI suggests that S2 is developed by transposing the eailier gneissic fabric onto the 02 plane of flatteni ng . The transposition was accompanied by intensification of the g neissic foliation, tight folding and boudinage. This is well displayed at location 25021 (Plate 2.4). Folding of the transposed SI foliation about F2 folds was noted on the outcrop scafe but no regionai scale folds have been identified. The fold data from the PIS2 show that fold axes are flattened ont0 a plane parallel to Si (Fig. 2.9~). This may be a combination of neMy fomed F2 folds, and FI fol& rotated to lie on the 02plane of flattening. Results from the Compulsion Bay area show that a third deformational fabric. in the form of a shear deavage, is present in areas where S2 is weII developd. The fact that &and the shear fabric occur at the same localif es and that SZoccurs in belts parallel to the shear fabnc suggest that the two were developed during the same deformation episode. As discussed above Sz develops paralel to the 02 plane of flattening, whereas the shear foliation is developed parallel to the component of simple shear within the shear zone. Location 520201 (Fig. 2.10) displays the best-developed strain features as a result of the D2 deformation. What is noticeable at this location is that the S2 foliation is strongly sheared out adjacent to the deavage (Plates 2.5 and 2.6). This effect is seen on a larger scale at location 540101 (Fig. 2.10) where the foliation deflection is in the order of 25 degrees over 20m adjacent to rdoxide-stained joint planes that are interpreted as being part of the shear deavage. Fold data from Compulsion Bay also show the effect of the sinistral sheanng (Fig. 2.13). Fold axes and axial planes lie somewhere between the plane defined by & average and the plane of shearing. Thus the fol& are assumed to have developed on the D2 plane of flattening, but in zones of high strain the plane of flattening has rotated towards the shear plane. This shear fabnc has been recognized at several locations in the Compulsion Bay area but not the Hidden Bay area One explanation may be that the host lithology controls the occurrence of the shear deavage, and that it was not developed in the more ductile rocks of the Hidden Bay assemblage. On Parker Island the more northeily strike of the foliation. existence of foliation boudinage, and mineral stretching lineations point to high strain accommodation in the rock. An alternative explanation is that the deavage may have developed at both locations but outcrops in the Hidden Bay area are not preserved. The occurrence of the shear planes causes the rock to possess a fielity, even in the mechanically resistant granitic gneisses where it is be$t dispiayed. In less resistant rock this fissility could result in a dramatic increase in amount of surface erosion, espeaaily by recent glacial activity. As noted, the PlSZ is characterird by very poor outcrop along its length, and it defines the shoreline on much of its western rnargin. Another possible reason is that the shear deavage was not recognized as a separate fabric and grouped Ath the other joints. Reanalysis of the joint data from the Hidden Bay area shows that severai of the joints orientated paraltel to the shear plane do show the characteristic red oxide- staining seen on shear joints in Compulsion Bay. Several others have slickenside lineations. which are also characteristic of shear planes in the Compulsion Bay area. The previously defined Tabbemor Fault lineaments, typically N-trending, do show weak reorientation of the foliation, consistent with sinistral shear, but this is normally confined to a few meters either dde of the overprinting brittle fault planes. They also appear to have a restricted laterai extent, suggesting that they die out or rnerge into the main shear structures, trending 020". The mst plausible explanation of these structures is that they are 'Riedel-like' in origin, seperated by an angle of approximately 20 degrees from the main TF2 structures (Fig. 2.7). The intrusion of pegrnatites and quartz into srnall-scale faults and shear zones appears to be a widespread feature of structures associated with the D2 event. The trend of dykes within the Compulsion Bay area and their structural characteristics suggest that many of them are intruded into D2 deformation structures, but the lack of strong deformation or Row structures within most dykes suggests that they were emplaced after the bulk of deformation. The lack of deformation and foliation development is a feature they share with the second generation of pegmatite dykes in domain 1 of Hidden Bay. They are also superficially similar in mineralogy, and trend. Because of these observations, the intrusion of second-generaüon dykes is tentaüvely attributed to the same event as the intrusion of pegmatites and quartz veins into the D2 fault features. Intrusion occuned in response to an approwimately east-west tensional event. after 02, that caused the formation of new tension garhes in the unsheared areas. These filled with melt material ascending from below. In those areas affected by Dz shearing the shear deavage and parailel joints provide a pre- existing weakness plane that is utilized as a conduit for magrna ascent. Subsequent reactivation of the 02 structures caused deformation at the margins of severai dykes, but for the most part ductile deformation appeared to have ended before the intrusion of the pegmatites. On a larger scale, late-Hudsonian porphyritic granites such as the Kidd Lake granite, Horton Island granite and smaller granitic bodies identified by Wallis (1 971), Chadwick (1966; 1967) and Sibbald (1983) occur throughout the Wollaston Lake area. These are described as deep pink, unfofiated, homogenous granites. Despite this last statement Wailis (1 971) noted that some of the srnaller intrusions "...grade through foliated granite porüons into pegmatized, pink. meta- arkose." It was also noted that the Kidd Lake granite is foliated irnmediately adjacent to the Kidd Lake Fault. The lack of a foliation to the cores of the intrusions suggests that they were intnrded after 02 deformation. The devalopment of a foliation at the margins of dykes and smaller intrusives and adjacent to faults indicates there was localized reactivation of structures dunng or after intrusion. It would appear that the location of lager granite bodies was controlled by pre-existing or active structures such as the Kidd Lake Fault. Thus both mineralogidly and stnicturally the larger granitic intrusives are very sirnilar to the small-scale intrusive dykes noted in this study. Wallis made the same genetic link between the Hudsonian granitic bodies and late, rectilinear pegmatites in Hidden Bay (P3 generation of Wallis, 1971. p. 39). As noted earlier, the most recent radiogenic data from these granitic bodies suggest that they were intruded circa. 1815Ma (Annesley et al.. 1997; Madore and Annesley, 1998) dunng the peak of Hudsonian thermal metamrphism. This means that deformation associated with the Oz event ocairred before 1815Ma. Subsequent ductile deformation of the intrusives is likely linked to late transpressionai sheaiing during retrogressive rnetamorphism, as noted by the alteration of biotites associated with the deformation event. 6.2 Brittle Reactivation of Hudsonian Features The reactivation of joint and shear planes as brittle faults is a cornmon occurrence in both areas. Orientation data were analyzed to see if the faults were caused by a single recognizable event or due to localized stress buildups with no widespread coherency. The orientations of the fault planes and slickenline lineations were entered into a data file dong with the movement sense. This file was entered into the BRUTE3 fault-slip data inversion program (Hardcastle and Hills, 1991). BRUTE3 caiculates the best-fit stress tensor for the recorded fault data. The vaiues of cohesion. C. the coefficient of friction, p. and the fluid pressure, Pw. were. assigned as 0, 0.4. and 0.5 respectively, using values suggested by Hardcastle and Hills (1991). Where two or more subsets of unrelated faults exist they maybe subâivided using the accornpanying SELECT prog ram. Modeling of the Wollaston Lake data is shown in figures 2.14 and 2.15. Figure 2.1 4b shows that of the 64 faults recarded in the Hidden Bay data set. 38 (59%) are compatible with a single stress tensor. Another 15 (23%) are compatible with a separate stress tensor (Fig. 2.14~).The Compulsion Bay data show that 50 of 62 faults (81%) fit a single stress tensor (Fig. 2.15b). As a test of the method's reliability the values of p and PRU~were varied from 0.1 to 0.8 to see if it would significantly alter the orientation of the resultant stress tensor. The results showed that neither the values of p nor Ptl"~had a significant effed on the orientation of the stress tensor or the inclusion of individual faults into a genetically-related subset. Flgun 2.14. S~mphlcalpm~ons of britth hult data hm the Hldden Bay ami; A) stemogmm showlng the orlentalon of al1 brittle faub Includd In the maln data set. The small dots repmrnt thetrund and plunga ofth. Ilneatlons on thehult planes. The IlnaatJons may lia sIlgMly off the plane definhg the fault, due to mors asaoclated with field mmsummants, but If th. llnutlon Is more than 10. out d the hult plain both the f.uk and the Ilinatlon were culled hmthe data ad; B) poIm to Mitpknas Included In sub set 1, and thm orknhtlon of thm dafinoâ paleodmss bnror. Prlnclpal st- ut- am 0, -1 S61ûOa, a, = O6Wû(r, a, - 2W4'; C) poles to huit planes Included In sub sut 2, and the orlentatlon of the defïned paleo+tmss tonsor. Prlnclpal strass axes am a, =142Mm,a, - 276148., a#=034/24@. a) All Fault data N b) Sub Set 1 c) Sub Set 2 N Sinistral fault plane Sinistral fault plane lineation Dextral fault plane = Dextral fault plane lineation Flgure 2.15. Skrmgmphlcal pmJectIonr of brlttk huit data hm the Compuldon Bay ana; A) sbmognm showlng the orlentitlon , of al1 brittle hub lncluded in th. maln data set. nia data Ir dbplayed as In figum Ils; 6) polos to fruit pknm included In sub set 1, and the orkntatlon of the d.flnod pako-stmss bnsor. a) All Fault data N b) Sub Set 1 N Sinistral fault plane Sinistral fault plane lineation Dextral fault plane Dextral fault plane lineation The results of the fault-Jip data inversions are significant. The similanty between the first subset from the Hidden Bay data and the Compulsion Bay data strongly suggest that these two paleostress tensors are part of a widespread basement reactivation event that affected the Wollaston Lake area sometime after the intrusion of the granite pegmatites, i.8. 1815Ma. No definitive age can be assigned to this tectonic event but it is possible that it is related to the Dm or DH~ events of Annedey et al. (1997). Altematively this tedonk event may linked to widespread Hudsonian fault reactivation that accompanied the main phase of uranium minerakation in the Athabasca Basin 'unconformity-type' deposits (1400-1 500Ma; Saskatchewan Geologicai Survey, 1994). The possibility of a link between small-scale reactivated faults and uranium mineralization is enhanced by the similar nature of fault plane mineralogy and alteration associated with many deposits. The typical hematite and quartz mineralization that forms on fault surfaces is similar to the outer alteration haloes sunounding uranium deposits (Komninou and Sverjensky, 1996; Wilson and Kyser, 1987; Kotzet et el., 1992). Alsol the orientation of the stress tensor is compatible with reverse movement on the northeast-trending thnist faults such as the Rabbi Lake thrust and the Collins Bay thnist, hosts to severai large deposits (Fig. 2.6). Seismic pumping (Sibson et al., 1975; Sibson. 1990) due to tedonic reactivation is a very effective fluid circulation mechanism to concentrate the uranium in the absence of an eievated heat source. There is no obvious geologicai event to account for the second stress tensor in the Hidden Bay area. It may be related to one of the late Hudsonian events. to the uranium mineraking event, or even to tectonic effects associated with the intrusion of the Mackenzie dyke swarm at circa 1265Ma. 7. Discussion The eailiest recognized gneissic fabnc in the Wollaston Lake ama is SI,which is seen in the unsheared areas of the Wollaston domain. Its average trend of 070- 250' is not compatible with the average trend of the aeromagnetic anomaiies in the area, which is approximately 045-225'. Thus the current trend of the orogenic belt, which is parallet to the regional magnetic anomalies. is not due to deformation associated with the formation of SI alone. The S2 foliation, trending 048-228O, could account for the current trend of the aeromagnetic anomalies but data anaiysis suggests that S2 is confined to north-northeast-trending belts of restricted areai extent. The S2 shear fabnc, which trends approximately 01 SO, is certainly not compatible w-th the bulk trend of the orogen. This suggests that the shear fabric is restrided to a few high strain zones, or the magnetic anornaly patterns would have an orientation doser to that of the shear fabric. The conclusion frorn this research is that the current bulk trend of the orogenic belt is due to a combination of the Sr foliation and pooily-defined shear zones where the SI foliation is transposed on S2 and then sheared out dong the S2 shear plane. The poor exposure in these shear zones probably led to lack of recognition of this by eailier workers. In order to amunt for the regionai geometry of the Wollaston domain, there would need to be a large number of previously unmapped TF2 fault spîays. This is considered a reasonable possibility as there is very little structurai modification assoaated with the shear zones, except in the highest strain zones. On top of this much of the ductile deformation is obscured by later brittle faulting and glacial erosion. Topograpghic lineaments and sinistrai offsets of the magnetic anomaly patterns are seen throughout the ~ollastondomain. This geometry of TFZ fault zones would give the Wollaston belt a 'staircase' profile on aerornagnetic maps. Such an effect can be seen on the outline of the McClean massif (Fig. 2.6a). East of the Wollaston Lake area the Wollaston Domain rotates around to be f- trending across Manitoba and into Hudson Bay. To the west the dornain trend continues to rotate counter-dockwise until it straightens out, trending 025O parallel to the NFSZ, at a longitude of 104O30' (Stauffer and Lemy, 1993). The longitudinal limits of this change in trend are approximately the Iimits to which splays of the TFZ are seen (Fig. 2.1). As noted earlier. the eastem contact between the NHZ and the Wathaman-Chipewyan bathdith is an intrusive contact whereas the western and southem margins are in fault contact, dong the NFSZ. Thus a scenario is required whereby the western segment of the NHZ - Wathaman-Chipewyan batholith contact is activated as a dedral fault, but the eastern segment stays undefomied. Given the immediate proximity of the TFZ to the terminus of the NFSZ and the western 'big bend' it is reasonable to speculate that they may be linked. The timing of movement along the NFSZ is constrained between 1857Ma and 1760Ma. most ductile sh8ating havïng taken place before 1785iUla (Fedorowich et al.. 1995). Timing of ductile movement on the TF2 is constrained between 1848+6/-5Ma and 1737i2Ma (Elliott. 1995). with results of the cunent study suggesting that the bulk of ductile mwement occuned before 1815Ma. Thus the two faults could have been adve synchronously as ductile features between 1848Ma and 1815Ma. This would be somewhere between the regionai DI and 02 eve nts. The geometry and mavernent sense of the faults would result in the southwestward escape of the bulk of the Glennie dornain. La Ronge domain. Rottenstone dornain and Wathaman-Chipewyan. This scenario is the one favored by Hajnal et al. (1996) where the NFSZ is one of several shear zones that facilitate the escape of the western internal domains. Ejection of these domains would result in a void space at the NFSZ - TFZ junction. Such a void could be dosed by severe north- or northwestward compression of the juncticn and anticlockwise rotation of the western segments of the Wollaston domain. Rottenstone domain and Wathaman-Chipewyan batholith (Fig . 2.1 6). The northern segment of the TFZ, from the Glennie domain noithward, is redundant in this simple 'wedge escape' mode1 but may aa as a transpressional structure to Figure 2.16. IndwpmWüvo cartoon mhowlng th. avolutlon of the THO. A) Posltknof th.mmln trcdonlc domalm er0, dmfonnatlon domain huaIr#dy docidta th. southam mqlnaf thm Hmmm Craton, and thrtth. Smk Cnton Is klngovwthrust by oœanlc uc tomnes of tha Gknnk. Hinson Wtr and Flln Flon domalna. 8) Posllon of th. nuln t.ctonlc domalns dbr4 defomatlon In the Wollaston Lake am. clma. 1800Ma. Ex'tmnslncni.trl ImMdon usoclatmd wtth th. Gdlklon of th. Suparior Cmton k 8up.rcd.d aid escape and orodinal rotation of the western intemal domains. Intensive folding with north-trending axid surfaces at the teMnus of the Erch Rapids Strait Belt (BRSB, Schwerdtner and Hirsekom, 1995) (Fig. 2.17) and in the Numabin Complex (Le- et al., 1990) indicates that the TFZ in that area is indeed assoaated with strong compression across the fault. As the fault splays bifurcate northward it appears that the compressional component of deformation decreases as tight north-trending fol& are not reported in the Wollaston domain. But the strong boudinage assodated with the PIS2 suggests that even well into the northern hinterland of the THO the TFZ is a transpressional structure. Throughout the THO the TF2 has been recognized as a sinistral fault system. Within the western Wollaston domain there are several fault splays with north- or northwesterly strike and sinistral offset. These faults have ben previously classified as Tabbernor-related because of their similar characteristics, but the aeromagnetic lineaments suggest that they do not link with the main trace of the Tabbernor Fault in the Glennie domain (Fig. 2.17). Most of the faults appear to die out where they intersec( the NFSZ or its easterly extensions, the Parker and Reilly Lake shear zones (Lafrance and Varga. 1996) (Fig. 2.17). This supports the idea that the TFZ and northeast-trending shear zones such as the NFSZ and the BRSB were active synchronously during regionai post-collisionai deformation. Figure 2.17. Compllation map of a sekct.d ama of northam Saskatchewan showlng the nlatlonshlp ktwwn aemmagnetlc Ilneamenb that dnlm the tram of the T.FZ and major lithotectonlc boundarles. Nd6 the apparent dlsappearance of many of the aeromagnetlc Ilneaments (dashed Ilnes) 8s they InteMct major .tnictuml hlummuch as the N.F.SX or RL.S2. Abbnviatlons:- R.D. - Rotbnstorn domaln; M.L.B. Mackan Lake Belt; N.F.82. = Nodk Falls Shear Zone; P.L.SZ. = Parker Lake , Shear Zone; RLSZ- Rellly Lake Shear Zone; T.FZ. = Tabkrnor Fauk Zone; 6.RS.B. - Blrch Raplds StralgM 8.k W.L. - Wollaston Lake; R.L. - Rolndeer Me.Box- 1ndlcate:- 1. = Hldden Bay arma; 2.- Compulrlon Bay ama; N-EA = aeromagnetlc test ama. Aeromagnatic Ilneamenta mi, traceâ from 1:63,36û scale map sheets publlrhd by Saskatchewan Geologlcal Survay. The domaln boundarks mmSaskatchewan Geologlcal Sumy (1994). Posltlons of the N.F.SZ., P.L.S.2.. and R.LS.2. hmStaufhr and Lewry (1993). Poslon of the B.R.S.B. (dam gn,y)from Lewry et a$. (1990) and Schwmrdtner and Hlrsekorn (1995). I 1 Kisseynew ' 8. Importance of the TF2 to Uranium Exploration As noted previously, the Wollaston domain beneath Athabasca Group sandstones is a highly productive area of highgrade uranium minerditation. Most of these deposits are of the 'unconfomiity-type', which are fault-controlled at or near the unconformity contact. Although none of the wrrently known deposits have been directly linked to the TFZ it is becoming dear that shear zones such as the PIS2 may have a direct link to the location of mineralization. Given that the major deformation a-at with the TF2 trends 010-020'. and not 350-000° as previoudy defined by discontinuous topographic lineaments such as the Dragon Lake lineament, it can be seen that several deposits have strong Tabbernor-like characteristics. Deposits such as the Sue (Mattheus et al., 1997), Midwest Lake (Ayres et al.. 1983), and Dawn Lake (Clarke and Fogwill. 1986) ail are aligned on trends that are much doser to the 010-020' trend than the regionai trends of 067O for Sl. or 048O for S. The McClean Lake deposits trend approximately east-west and are not aligned parallei to the Tabbernor trend. The limits of minerakation are, however, contained within a 10Wm+ corridor that trends 021 (Wallis et al., 1983b, p. 107). which is again much doser to the Tabbernor trend than to the regionai trend. Also conductive horizons defined during exploration show a pattern that can be reasonably explained by rotation into a sinistral shear zone passing through this location, dong a trend of approxirnately 020° (Wallis et al.. 1983a. p. 60) Better structurai evidence for TF2 control on mineralization cornes from the Rabbit Lake Pit where the highest grade ore is contained in a microgranite- breccia zone (Heine, 1986). The microgranite is dyke-like and '..appears to have been emplaced along an old fracture zone, and was itself subsequently broken up by continued movement along this break." (Heine. 1986, p. 139) The microgranite is rnineralogically very similar to circa. 1815Ma granites described earlier, and is only 2km from Hudsonian granites of similar affinity (Madore and Annesley. 1992; Annesley et al.. 1996b). The trend of the intrusion is approximately 0200 though the central part of the pit. Also, within the pit the hanging wall rocks have ben folded into a series of major antidines and a syncline. w*th axial traces variable but northeily trending. The fold axes plunge about 6 degrees to the north (Heine. 1986). Both the brecciated microgranite and the folds are features identifiable as having an ongin related to the Tabbemor Fault in this report. South of the Rabbit Lake pit. dong a trend of 020° are the Raven and Horseshoe deposits (Figs. 2.6 and 2.7). At a drill camp. west of Horseshoe Lake. is an example of a well-developed S2 'straight* gneissic foliation. trending 0 15". abuîting what is interpreted as SI& trending 063O. An inegular body of pegmatite obscures the contact between the two. This relationship. as with the sirnilar discordant foliation relationship on Parker Island, can be explained by foliation boudinage. Nearby the SIfoliation is folded into an outcrop-sde open fold. Developed within the fold is a very weak shape fabric defined by the orientation of mafic grains. This fabric is axial pianar to the foldi ng in the gneissic foliation. The shape fabnc trends 050° and is steepiy dipping either side of vertical. Intersection lineations defining the fold axis pîunge 56O towards 024". This is interpreted to be the only example of S2 developed axial pîanar to a fold in SI seen during mapping. Again, these structures are typicai of those developed within sinistral shear zones such as the PISZ. On a quartzite ridge midway between the Rabbit Lake and RavenlHorseshoe deposits (Fig. 2.6) SIstnkes consistently between 050-060". At one outcrop the foliation trend changes abruptly to 208O. in an area of strong brecciation. This location is exactly along strike between the Rabbit Lake and Horseshoe Lake locations. If this 015020° trend is continued southward it would pass dose to the Kidd Lake granite, and a northward extension would pass through the topographie low defined by Collins Creek. lt is noticeable that the Collins Bay Thrust, a regionaîly important rninerdized structural feature, changes trend from 060" to approximately 030° at a point where it intersects the northward extension of this zone (Sibbaid, 1983) (Fig. 2.6). Thus it appears as though there is strong evidence for a shear zone developed west of Hidden Bay and that passes through several important uranium dep~sits.The detailed verücal gradient map does not show any evidence of sinistrai shear but the area is one of generai low gradient and structural features are hard to distinguish. A model for TFZ fault-control on mineralization would rely on ductile deformation to estabiish the fault splays as preexisting weaknesses in the rock. This is achieved by the development of closely spaced planar fabnc Ath low shear strength, i.e. the shear deavage, and associated mineraiogical changes that weaken the rocks around the fauits. These fault zones will then preferentially reactivate during brittle deformation assoaated with the mineralizing event. The fault would allow deep circulation of fluids within the basement rocks, causing reduction of the fluid by interaction with graphitic gneiss horizons. These ffuids then migrate up to the unconfomity contad where they interact with a uranium- bearing oxidized fluid and cause the precipitation of uranium mineralization (Kotzer and Kyser, 1993, 1995; Komninou and Sverjensky, 1996). The rnost likely site for mineraiization would be at the intersection of TF2 fault spiays and other faufts such as the Rabbit Lake thrust and Collins Bay thrust. This is a preliminary analysis, without detailed structural mapping and dating at any of the mineraiized locations, but in light of this observed structural similarity it is suggested that more comprehensive follow-up work be undertaken to see if the link between the TFZ and uranium mineralization can be substantiated. 9. Conclusions The TFZ in the Wollaston Lake area is defined by disaete transposition of Sl ont0 a NE-trending, steeply dpping & plane. Transposition is generally confined to continuous zones trending approximately OIS0. Folding and boudinage suggests that the transposition was accompanied by reorientation of preexisting structures ont0 the S2 plane of fiattening. In the zones of highest strain a new shear fabric is developed paralfel to the trend of the shear zones. The shear fabric is developed as either a spaced deavage or joints and shows consistent sinistral offset of the SIISI foliations dong fi. Small-scale sinistral faults with ductile drag parallel the shear zones. Intrusion of granitic or pegmatiüc melts was controlled by the occurrence of TF2 structures that acted as conduits for magma ascent. The age of intrusion is circa. 1815Ma, late in the main phase of regional D2 metamorphism and deformation. The melts were emplaced as dyke-structures that were weakly deformed dunng subsequent retrogressive metarnorphisrn and shearing. Later readivation of the faults caused a brittle overprinting of the eailier deformation. Intensive fluid circulation associated with reacti-vation caused quartz predpitation and widespread oxidation of the basernent rocks, concentrated dong the Tabbernor features. This britüe deformation event may be synchronous with the formation of economically important uranium deposits, and on a regionai scale the mineralization may have been controlled by the occurrence of TFZ shear zones. Link: The Role of Proterozoic Fault Detonnation in Controliing Phanerozoic Fault Reactivation All evidence presented in chapter 2 shows that the deformation assoa'ated with the TFZ dunng the Proterozoic era had a fundamentai effect on the properties of the fault rocks. It has been show that the deformation caused the transposition of SIonto the S2 foliation plane, and folding and boudinage in the Wollaston Lake area. This would have an effect on the rheology of the rock, espeaally in regard to the development of a strength anisotropy. Also, the development of the shear cieavage would drasücaliy reduce the shear strength of the rock within the shear zones. The development of mylonites in the Neilson Lake area would have had a sirnilar effect on the fault rocks at that locality. All of this is overprinted by briNe- ductile and bnttle fault fabrics developed dun'ng the waning stages of the THO. In the Wollaston Lake area this manifests itself as lodized shearing of the granitic and pegmatitic intnisivei;'and development of mineraiized briffle faults and micro-faults. Intense fluid circulation dunng this hime led to hematization, chloritization, illitization, and siliafication. Mfferent minerals have conflicüng effects on rock strength but the resultant minerai assemblage is weaker than the pre-aiteration assemblage (Wintsch el el., 1995). As well as the change in the rock properties of the exposed rock, consideration should be given to the rocks at mid-trustai levefs, and deeper. In any mode1 of crustal-scale. strike-slip fault development the rocks at greater depth are hotter and at greater pressure than those at surfaœ. In the Wollaston Lake area the rocks currently at surface are indicated to have been at a depth of 15-23km (denved from the estimate of 4-6kbars of Annesley et al., 1997. and a cnrstai density of 2700 kg m'3, suitable for granitic rocks) and a temperature of 725- 775°C (Annesley et al., 1997) during MH~.At this depth the dominant quanz- feldspar mineraiogy would have responded in a ductile manner to applied forces, assuming a moderate main rate. The same is true of the fault rocks that currently occupy that crustal position. Thus the low strength of any fault zone is dominantly due tu the rocks at midcnistal depths, and not to those that currently ompythe top several kilometres of the cnist. Deep crustal deformalion. induding structures going fight through to the upper mantle (Nemeth and Hajnal, 1996), make the fault even more susceptible to reactivation. The debate as to whether the TFZ is tnrly a through-going cnistai structure, or terminates on a low-angle detachment thrust in the midcrust (Lucas et al., 1993), is unresolved but it has a significant bearing on the reactivation potentiai of the TFZ. Chapter 3 Evidence for Orogeny-driven Phanerozoic Reactivations of the Tabbernor Fault Zone, Saskatchewan, Canada J. R. Davies. Dept. of Earth and Planetary Sciences. MiIl University. 3450 University Street. Montrad, QC, H3A 2A7, CANADA. Abstract Phanerozoic reactivation of the Tabbernor Fault in Saskatchewan has occurred during at least two separate episodes. A strong tectonic episode related to the Late Devonian Antler orogeny caused fault reactivation and syn-sedimentary fault control on the depositional patterns of the Wwdbend and Winterburn Groups within the Williston Basin. Saskatchewan. Fault movement also breca'ated previously depoôited Ordovician and Silurian strata. Further north the fault reactivation caused rembilization of U and Pb in the mpr uranium deposits of the Athabasca Basin. A second reactivation episode related to Cordilleran orogenic adivity during the midGretaœous Period had a similar effect on depositionai patterns and U-minerakation. Minor tectonic episodes may also have caused localized reactivation of fault drudures during the Eady Permian Period and Late Triassic-Eariy Jurassic Penods. 1. Introduction The central western portion of the Canadian Shield. comprising the exposed shield in Saskatchewan and Manitoba as well as the southern continuation buned beneath the Western Canadian Basin (Fig. 3.1), is traditionally thought of as a stable tectonic Mock which responds uniformly to extemal stresses at the shield margin. The Canadian Shield acaimulated during several orogenic events in eaily- and middle-Proterozoic times. Reactivated and reworked Archean crustal blocks such as the Superior Province and the Heame Province (Fig. 3.2) are therefore separated by jwenile orogenic belts containing major fault systems that acted as ancestral weaknesses to control locaiized reactivation of the Canadian Shield during Phanerozoic tectonic events. Reactivation of the Proterozoic Canadian Shield in central Canada is contrary to traditionai t houghts on continental accretion which treat the craton as a stabie block unaffected by marginal processes. The objective of this paper is to diswss the evidence for reactivation of the Tabbernor Fault zone and adjacent structures in the Phanerozoic eon. Evidence is set forth for discret9 intra-cratonic adjustments in response to changes in the tectonic regime at the cratonic margin. These adjustments control depositionai patterns in the acaimulating Phanerozoic rocks as well as reworking preexisting uranium deposits in the PaleoHelikian Athabasca Basin. Flgum 3.1. Phainmoolc mlomonb of th@ w#tnn North Anmlcan continent. MJor .tructuml akmrint. show am th- whlch hmm had a rrw contrd on ..dhiwntitkn durlng th. Phinwosolc ai. Th. llgM gmy pa(bm ls th. cumnt llmlt of outcrop (or rock. in wmtmm Canada. Tho duk gmy mmk tha llmlt of âoop basln sedlmontuy rodu In th. Al- and Wlllkton blns. Tha black patbrn Indlcrit.. tha Ilmit af L.b Davonkn. Laduc Fornilion mf buIldup.. Ako shown am th. appr0xlrn.b. llmlb of the Antlar-age orog.nlc front, and the Cordllkmn-agm ormgenIo front. Adapted from Wright etal. (1994); 8wlb.r et dm(lm); Hayes et al. (1894); &voy and Mouqoy (1985). Flgure 3.2. Tdonlc domalns of th. mrtem Cinadlan buement. Modlfied from Ross et d. (1SW). Expo~dsub4lvlslons of the - mns-Hudson Orogan (shadeâ) hmClow# (1897). Duhed box Indlcates Inset flgum 3.4. 2- Reactivation Reactivation is defined as qhe accommodation of geologically separaMe displacement events (intervals >1Ma) dong pre-existing structures" (Hddswrth et al., 1997). Traditionai approaches to the study of crustal structures have concentrated on the kinematics and history assoa-ated with the structures' formation, typically during orogenic events and cnistal accumulation. e.g. Ramsay and Graham (1970). or Stauffer and Lewry (1993). More recently researchers have begun to address the significance of reactivation on pre- existing structures assoQated with postsrogenic deformation (Butler et al.. 1997, and references thenin). The reactivation may have the same sense of displacernent as eahevents, kinernatic reactivation, or a different sense, geometric readvation. The recognition of separate episodes of reactivation along major intra-continental shear zones has lad to the rethinking of cratonic blocks reacting uniformly to external forces and changes in the intemal stresses. Studies on structures such as the Archean Thabatirnbi-Murchison Linearnent, S. Africa (Good and De Wit, 1997). and ltacaiunas Belt, Brazil (Pinheiro and Holdsworth, 1997) have shown that reacüvation of cnistal-scale shear zones can occur over large time intentais. with different reactivation geornetries. presumably relecting changes in the regionai stress field. Eariy ductile mylonitic fault tabrics have been shown to control the occurrence of later britüe-ductile and brittle fabrics that are dated by radiometric studies of the mineralogy in the fault zone. Other methods for recognizing reactivation include stratigraphic control on syn- tectonic 'pull-apart' basins (Pinheiro and Holdsworth, 1997); changes in the distribution and nature of deformation within faults and I or shear zones (Imber et al., 1997; Hanmer, 1997); and focused plutonic activity in shear zones (Hanmer, 1997; D'Lemos et al., 1997). In al1 studies the long-ten weakening of the shear zones by a variety of kinematic and mineralogical processes is fundamental to t heir role as reactivated structures. 3. Reactivations in Western Canada Although the role of basement structures has long been considered to have been important in controlling sedirnentary fades in western Canada (Rutherford. 1954). little condusive evidence has been found to link the two elements. Recent work in the Western Canadian Sedirnentary Basin (Fig. 3.1) has been driven by the economic irnpohce of basement structures in controlling the build-up of Late Devonian-age carbonate reefs in central Ai berta (Greggs and Greggs. 1989; Savoy and Mountjoy, 1995; Edwards and Brown, 1996). In assessing the question of basement involvement in the control of Upper Devonian reef chain distribution, such as the Rimbey-Meadowbrook and Bashaw-Duhamel (Leduc Formation) reef chains (Fig. 3.1). Edwards and Brown (1996) conduded that low angle thnists emanating from the basernent may offset the basement cover contact. These offsets produced subtie changes in relief in the overlying sedimentary cover. These low-relief topographic highs are considered to have been sufficient to locally control the developrnent of Leduc Formation reef complexes. Although local mntrol by basement fault structures was found to affect the position of overlying reef complexes no dominant basement controls were found on the regional-scaie distriMion of Leduc carbonate reefs. Basement structures may have dso pîayed an important role in the distribution of linear sandbodies in the Western Canada Sedirnentary Basin dunng the Cretaceous Penod. Recent studies in the Alberta Basin (Bergman and Waiker, 1996; Enckson and Bergman, 1997) and Peaœ River Arch area (Bergman and Walker, 1996; Chen and Bergman, 1997) (Fig. 3.1) suggest that the distribution of Cretaceous sandbodies is controlled by a complex combination of syn- depositional tectonism, eustatic sea-level change and change in sedi ment supply. In a similar study, Collom (1997) suggests that reactivation of basernent fault structures in the Peace River Arch area (Fig. 3.1). during the Upper Cretaceous Penod. affected deposition of Dunvegan-Cardium Formations (-97- 87k2.5Ma1). He proposes a link between basement reactivation and teirane accretion or subduction dong the western margin of the North American craton. Chen and Bergman-(1997) ai= suggest a link between reactivation of the basement and tectonism on the western margin of the craton, but imply that the controlling mechanism was a change in the direction of regional compression. 3.1 Regional Stmtigraphy The western Canadian continental margin was a passive margin where carbonates and dastics forw in miogeodinal seas throughout most of the Paleozoic era (McCrossan and Glaister. 1964). From eaily Givetian time (-380118Ma) onward, significant build up of increasingly deeper-water facies sediments occurred in the Western Canadian Sedimentary Basin (Oldale and Munday, 1994; Switzer et al., 1994). During deposition of the Woodbend Group megacycie (374370k15Ma) (Savoy and Mountjoy, 1995) in centrai Alberta the steady deposition of the Cooking Lake Formation platform carbonates gave way to the Duvernay Formation artoxic Mack shaies. This was accompanied by rapid rise in sea level (Johnson et al., 1985; Savoy and Mountjoy. 1995). Subsidence was synchronous with Antier-age orogenesis involving arecontinent collision (Burchfield and Royden, 1991; Smith et al, 1993; Savoy and Mountjoy, 1995 and references therein), -and Leduc Formation reef cornplex growth (Dwernay Formation is equivaîent in age to the middle Leduc Formation) (Fig. 3.1). This adds credibility to the idea of a basement-reactivation control on reef distribution in a tectonicaily active setting. As with the Late Devonian-Early Carboniferous intetval, the Late Jurassic-Eariy Tertiary stratigraphic sequence in the Western Canadian Sedimentary Basin staits with an abrupt change from miogeoclinal or platformal deposits to increasingly deep-water faaes. black shales, limestones and thin sandstones (Fermor and Moffat, 1992; Poulton et al., 1994). A westedy derived source is t AI1 &tes quoicd in thc papcr arc umvcrtcd ban ihc pcriod or agc quotcd in lhc source Lo bc concordant with the DNAG gcdogic tirne de(Palma, 1983) identified for Oxfordian-Tithonian (163-1 50k15Ma) siitstones and sandstones, interbedded with marine shaies of th8 Femie Formation and basai Nikanassin Formation, indicating orogenic uplift to the west (Poulton. 1984; Stott, 1984; Fermor and Moffat, 1992). This is succeeded by shallow marine sandstones of the Kootenay Group (156-1 44SMa), indicating sedirnentation kept place with rapid cnistal subsidence (Beaumont, 1981 ). This unconfomity-bound package of Fernie Formation and Kootnay Group (and equivaients) forms Cyde 1 of Lecke and Smith (1992), and first dastic wedge of Stott (1984). A second cyde of sedimentation (Cyde 2 of Leckie and Smith, 1992; second dastic wedge of Stott. 1984) followed trends broadly similar to the fint although there was less deep water facies sedimentation than that associated with the onset of the first 'megacycle'. Cyde 2 is typified in central Alberta by a basai chert in the Cadornin Formation (120-1 18SMa) which is overiain by the Manville Group (120- 108BMa), composed of sandstones, interbedded siltstones and occasional shales (Hayes et al., 1994). and lower Colorado Group (104-94MMa) induding interbedded shales and sandstones (Leckie et al.. 1994; Reinson et al.. 1994). The unconformity that separates the first and second rnegacydes appears to represent significant isostatic adjustment of the craton (Stott, 1984; Femr and Moffat, 1992). A third rnegacycle, unconfoltnity-bound like the first two, extends frorn early Campanian (84i4.5Ma) to early Paleoœne times. or even younger (<66Ma) (Fermor and Moffat. 1992). Leckie and Smith (1992) divide the sedimentary succession into 5 cydes, and Stockmal et al. (1 992) into 6 dastic wedges, but the pnnaple of cydic deposition controiled by tectonic processes associated with Cordilleran-age orogenesis is evident in each study. Studies of syn-depositionai wntrols on Cretaœous sandbodies diswssed above (Bergman and Walker, 1996; Enckson and Bergman, 1997; Chen and Bergman, 1997; Collom. 1997) ocair broadly within the time frame of cycle 2 of Leckie and Smith (1992). 3.2 Driving Mechanlsms for Toctonlc üafomutlon The mst widely acœpted geodynamic mode1 for the production of a foreland basin, with assodated sedirnentary facies changes, is one of elastic (or visco- elastic) flexunng or downflexing of the continental lithosphere (Beaumont. 1981; Quinlan and Beaumont, 1984; Cant and Stockmal, 1989; Stockmal et al, 1992; Fermor and Moffat, 1992) in response to loading of the fithosphere by overthnisting of accreted terranes. Modeling shows that, in addition to the foreland basin, the tectonic loading produces a peripheiai bulge ahead of the foredeep (Fig. 3.3a). 60th of these elements will migrate cratonward as terrane accretion continues. As terrane accretion ceases the penpheral bulge migrates back towards the foredeep, and the basin deepens because of relaxation of the bending stresses in the overth~stplate (Quinlan and Beaumont. 1984) (Fig. 3.3b). This may be counteracted by basin iebound as the tectonic load is rernoved (Stockmal et al., 1992), produang an unwnformity surface across the entire basin (Fig. 3.3~).H is a combination of the above effects that best explains the unconformity-bound dastic wedges seen in many foredeep basins. The work described above parüaily resolves the question of how marginal orogenic events affect the North American craton, espetiaily the link between tectonism and sedimentary cycles. It is now widely accepted that tectonic processes linked to convergence at the craton margin control megacycles of inboard deposition, such as the Late Devonian megacycles (Savoy and Mountjoy. 1995) or Cretaceous megacyles (Stott, 1984; Leckie and Smith, 1992). In contrast, the mechanisms that link these marginal tectonic processes to syn- sedimentary basement tedonism and localized sedimentary control are still poorly understood. Other mechanisms cited as being important in controlling sedimentary basin developrnent. and which rnay also play a role in basement reactivation indude: 1) tilting of continentai interiors by dynamicaf effects of subduction (Mitrovica et al.. 1989); 2) depression of the continental cnist above subduction zones (Gurnis, Figure 3.3. Constraints on the development of a classical foreland basin. A) Development of a foredeep due to loading of the cratonic rnargin by the allochthonous terranes, and infilling of the foredeep by sediments; B) thermal relaxation of bending stresses within the continental plate causes additional subsidence of the foredeep and migration of the peripheral bulge back towards the orogen; C) syn- and post-orogenic erosion of the thrust sheets causes widespread rebound of the craton, most apparent close to the orogenic front. Adapted from Quinlan and Beaumont (1984), Stockmal et al. (1992). Orogen 1 - Peripheral Bulge C ------\ Basin rebound - Epeirogenic uplifl Allochthonous terranes Shallow water molasse sediments Deep water sediments Additional basin fiIl 1993). (the latter two~rnodelsare similar in effect and rely on the rate and angle of the subducüng plate); 3) mantle dynamics and dramatic downwelling beneath continental lithosphere (Pysklywec and Mitrovica, 1997); 4) mantle convection and assembly of supercontinents (Kominz and Bond. 1991); 5) syndepositional. fault-controlled, local basin development (ünk et al., 1993); 6) waxing and waning compressive in-plane stresses transmitted through the foreland lit hosphere, reactivating pre-existing fault stmctures (Dorobek et al., 1990). 4. The Tabbernor Fault Zone 4.1 Introduction The Tabbernor Fault zone (Tm)is a cim. 4 500km. N-trending, topographid and geophysical lineament in eastem Saskatchewan (Elliott and Giroux, 1996) (Figs. 3.1 and 3.2). lt is defined as a fault system through Archean and Proterozoic rocks from north of the 60°N parallel, to the contact with Phanerozoic-age cover rodo southeast of La Ronge. From there it extends southward at least as far as 4g0N latitude, as a purely topographicsil Iinearnent defined by dry creek valleys, river channels, and soi1 color variations (Elliott and Giroux, 1996). Geologicaily it is an important structurai element of the Trans- Hudson Orogen (THO) (Fig. 3.4) and is believed to have formed in association wit h late orogenic effects of the THO (Lewry, 1981 ; Elliott. 1995) . - The THO is one of a nurnber of known Proterozoic orogens (Fig. 3.2). the final collision of which led to th8 formation of Laurentia. The orogen can be broken down into four distinct zones (Hoffman. 1988; Lemy and Collerson. 1990; Clowes, 1997) dependent upon the rock type. radiometric age. and style of deformation within. In northern Saskatchewan and Manitoba the cor6 of the orogenic belt is composed of an matetelescoped collage of 1.9-1.8Ga juvenile terranes, termed the Reindeer Zone (Le- et al., 1990) (Fig. 3.4). The Reindeer Zone is bounded on either side by vanously reworked Archean cnistal blocks. To the southeast it is bounded by the Churchill-Superior Boundary Zone, and to the northwest by the Noithwestern Hinteriand Zone. Separating the Reindeer Zone from the Northwestern Hinterland Zone is the Andean-type Wathaman Batholith. This was intruded at the junction of the subducting juvenile crust and the Archean continental cnrst at circa. 1.855Ga (Meyer et a.. 1992). The Northwestern Hinterland Zone is composed of Archean basement rocks overîain by early to middle Aphebian rift (Delaney, 1995) and platformal sediments which have been affected by Hudsonian thermotectonism. Early (pre-1.85Ga) deformation (Dl), possibly assoaated with arc-continent collision, was followed by the main phase Figure 3.4. Slrnp1M.d geologlcal rnap of expowd THO and bounday nglons. Llhotectonlc zonas am sub-dlvlded lnto domalns mg. Flin Flon, Kissoynm etc. Abbmvlatlons: C.S.B.Z. = Churchlll - Sup.rior Boundary Zone; T.FZ. - Tabkrnor Fauk Zone; . N.F.SX. = Nwdh Falk Shew Zone; B.R.S.B. - Blrch Raplds Stmlght 8eIt; 8.82. - Stanley Shew Zone; P.L.82. - Parker Lake Shaar Zone; S.TZ - Snowblrd T.ctonIc Zone. Red dab mark locations dkcusseâ In the bxt; 1 - Wollaston Lake; 2 - Neilson Lake; 3 = Llmestona Polnt Lake. Mappd Is adapbd dbr Lamy et al. (1990); llthokctonlcdlvklons a8 of Clowms (1997). of deformation (Da). a 1.83-1.8ûGa nappe-fofmïng event dunng continent- continent collision (Bickford et al., 1990). This is in dose agreement Ath stuclies by Annesley et al. (1996a) and Madore et al. (1996) in the Wollaston Domain (Figs. 3.2 and 3.4) which indicate a 1.84Ga MIrnetamorphic event, followed by peak metamorphism and plutonism. M2, at 1.82-1.81 Ga. The later studies also report a third retrograde mtamorphic event. &, at -1 -80-1.775Ga. 4.2 ûeformational Chancter and Geometry The TFZ is one of several large-scale shear zones and linear belts which help to subdivide the THO into tectonic domains (Fig. 3.4). What is unusuai about the TFZ is that it is oblique to the main fabric trend in the orogen. Between the Glennie Domain and the Hanson Lake Block the TF2 is a domain boundary. but in other places. such as the Wollaston Domain. the fault deflects and offsets fabncs within a single domain. It is well documented that the fault offsets earlier Hudsonian structures in both the centrai Neilson Lake area (Elliott. 1994a) and further north in the Wollaston Lake area (Wallis, 1971; Davies. 1996). with consistently sinistral offset (Fig. 3.4). The character of the TF2 changes along its length. Between the Glennie Domain and Hanson Lake Block the eailiest rnovernent is characterized by sinistral ductile shear and development of an eady mylonitic fabric. Mineral lineations within this mylonitic fabric change across the fault. They are moderately to steeply S-plunging in the east, changing to moderately N-plunging in the west. These two distinct dornains are separated by a brittle to semi-brittle fault trace with subhorizontal slickenside lineations that overprint earlier ductile fabrics (Elliott, 1994a). As the fault progresses northward its rnorphology changes from a single or severai anastomosing splay(s) with restricted longitudinal extent, to a bifurcating array of discrete fault splays and topographical lineaments which extend from 102OW to 105OW. This is a width of approximately 170km. The change in style of the fault coincides with the transition from where the fault -pantes the Glennie Domain from the Hanson Lake Biock and Kisseynew Domain. to where it penetrates into the La Ronge Domn and extends northward to the Wollaston Domain (Fig. 3.4). As in the Glennie Domain, brittle deformation overptints earlier ductile deformation, but brittle deformation is the dominant style in bath the Hidden Bay and Compulsion Bay areas of Wollaston Lake (Fig. 3.5b). Mapping as pait of this study, and previous dudies. wggest that major fault splays in the Wollaston Lake area are approxirnately 2-5km apart. Minor structures are less continuous and therefore harder to map. but rnay be separated by distances of as little as 1km. This means that TFZ structures are very impoitant to the geology of the Wollaston Lake area, and more generaîly throughout the Wollaston Domain. Brittle deformation is characterized by quartrcMorite mineral fibres defining a subhorizontal lineation and sinistral movement sense on small-sde fault planes. Elsewhere the fault splays are topographie lows, where intense brecdation is amrnpanied by hematite staining. The most notaMe difference between the TF2 in the WoHaston Lake area and its counterpart in the Neilson Lake area is the la& of mylonitic fabrics developed in the former. Ductile deformation there is restricted to rotation of earlier Hudsonian fabrics, and isolated development of a weak shear fabric. Another significant difference between the TFZ in the two study areas is the intrusion of post- D2,s harp-walled granitic, leucogranitic and pegmatitic int~sions into the trace of the fault. and adjacent faults, in the Wollaston Domain (Heine, 1985; Davies. in press a). No dates have been determined for the age of these intrusions in the TFZ. Flgum 3.5. A) Slmplllhd gdoglal map of tha Athabasca Basln and adJaœnt bvwmont domilna, modl(l.d dtmr Snkitchwan showing th. Ilthotdmnlc domrln boundrrk.. Amam of mapplng , by the author irm Indlwbâ by bluk box#. 0ash.d Ilnos show TF2 splays Indlatod by g.ophy.lc.1 llnmmo& ind by bodrock mapplng whom I1rnlt.d oxpaaun allam. Both m.p. rhow tha locatlon of mJor umnlum d.pos)b and mlna s)b. dkcussod In the text. 4.3 Geophyslcal Chafact@firtlcr Seismic imaging of the TFZ. as part of the LITHOPROBE Trans-Hudson Orogen Transed, has reveaîed the TFZ to be a mde verticai zone of iow reflectanœ (Hajnal et al., 1992; Lucas et ai., 1993) (Fig. 3.6). Strong reflectors teminate at the TFZ through much of the trustai profile. Its verticai extent is undear. Lucas et al. (1993) interpreted the TFZ to teminate on a shallowly dipping lower crustal reflector, and therefore not a throughgoing cnistd structure. The migrated seismic profile is incondusive, and though reflectors correlate on both sides of the fault, they are not continuous with the same reflectance nght across the fault zone. However, Nemeth and Hajnal (1996) suggest that velocity anisotmpy in the upper-lithospheric mantle can be attributed to reorientation of the mantle fabric by the TFZ and adjacent Needle Falls Shear Zone (NFSZ). This would suggest that the TFZ does penetrate through the mho boundary, making the TF2 a through-going crustai structure. Magneticafly the TF2 is well defined by a corridor of N-trending magnetic anomalies that diverge from the regionai NE-trending foliation (Jones and Craven, 1990). The southern extrapoîation of the m. south of the Canada- United States border, is defined by the boundary between moderate- to highly- magnetic rock to the east and weakly magnetic rocks to the west (Green et a., 1 985). The gravity anomaly associated with the TFZ is not highly conspicuous. If the previously defined magnetic lineament is supetimposed on the gravity map. the TFZ can be seen as a steep gradient in the Bouguer gravity anomaly field (see Jones and Craven, 1990, Fig. 6; Green et al., 1985, Fig. 5), corresponding to juxtaposed domains with different cnistai properties. This observation is supported by magnetoteliuric data collected across the TFZ. near the shield margin (Ferguson et al., 1996). These show conductive rocks in the mid to lower Flgure 3.6. Interpmtatlon of the Interna1 geometry of the THO. A)Geologlcal cross-sectlon showlng prlnclpal tectonostmtlgmphlc unlta of the Tmns-Hudson Orogen (hm HaJaalet al., 1882). The section Is constmlrid by THOT mflactlon , profila 9. B) Innt of the mlgmtmd aeismlc profile. The wdlon Is from O to 12 wconds (TWT), and rquatms to a dmpth of approxlmatoly 36km. The TF2 is charackrized by a zona of low reflecbhnco. Nok that although reflecton In the lomrcru.1 appear to tnincate the TFZ, they ara not contlnuous acrou the fault with the same Mectance. crust. below the Hanson Lake Bock. terminating a! a position irnmediately below the TFZ. and having no equivaîent to the west of the fault. This also suggests that the TF2 separates domains with dffering characteristics at a austal scaie. 4.4 Offset Magnitude of offset across the TFZ varies with location but the sense is consistently sinistral.. Offset of a north-east dosing fold hinge, across a single Tabbernor splay in the Neilson Lake area, was documented to be 2km sinistrally (Elliott, 1994a). Frorn this it was argued that the offset across the main fault trace was greater than 2km. Further north, in the Wollaston Lake area, offsets across individual fault splays have been suggested to be 400rn-3000m+ (Wdlis. 1971; Davies, 1996). bas& on field mapping augmented by aeromagnetic interpretations. In addition to the well defined geologicel and topographiml fault traces the author has doairnented nurnerous, northedy-trending, srnall-scale fault features Ath 10's of cm's sinistral displacement. and condudes that total displacement summed across Tabbemor-related structures is significantiy greater than that recoided on the main spiays aione. Metamorphic isograds mapped by Sibbald (1978) and Wilcox (1991) in the Neilson Lake\ Pelican Narrows area suggest sinidrai displacernent across the entire fauH of 6-8km. although these isograds are argued to be mntrolled by lithology (Elliott, 1994a) and do not reflect true displacement. Despite its size, character and evident regional significance, the importance of the TF2 has been downplayed by severai recent authors (Lewry et al., 1990; Tran et al.. 1996; Maxeiner. 1996) due to the Jack of significant offset of lithologies. 4.5 Absolut. Ag88 ot Movmmt Deformation assoa*ated 4th the formaüon of the myionitic strain zone in the Neilson Lake area is constrained. by aoss-cutüng relationships, between 1848+6/-5Ma and 1737I2Ma (Elliott, 1995) (Fig. 3.7). Constraints on mvement along the TFZ in the Wollaston Domain suggest that the fault zone initiated after DI that is synchronous with Ml rnetamorphism, dated at 1840-1850Ma by Annesley et ai. (1996a). A lower limit on âucüfe defoimation is suggested by the intrusion of undeformed granitic and pegmatitic dykes into the trace of the Tm. These intnisives are tentative1y conelated to adjacent granitic bodies. intruded at circa. 1815Ma (Annedey et al., 1997; Madore and Annesley, 1998). Brittle deformation in both locations overprints ductile fabrics and is therefore younger (Fig. 3.7). Flgun 3.7. Aga constralnts on ductlle ddonnllon wlthln the Tabbernor FauIt Zona In the Neilson and Wollaston Lako amas. Tha aga constralnts In the Nailson Lako ami mm from th. Nalkon Laka pluton and i cross.cutting pogmatlt. (Elllott, 1985); aga constmlnts In the Wollaston Lake ana are bawd on the dlsruptlon of D, hbrla, dabd at 1.05-1.840. (Annadey et& 18H, 1897), and .an assumad aga of 1815Ma for und.formd pogmrtld, dykn Intruded lnto the TFZ (se. text for explandon). 5. Phanerozoic History of the TF2 5.1 Previous Woik Little evidence has been collected to show the Phanerozoic history of the TFZ. Byers (1962) reported that topographic linearnents in the shield could be traced southward into Silurian strata. In addition to this. work by Giroux (unpubîished M.Sc. thesis) shows that lineaments in airphoto and satellite images extend 500+km south of the sedimentary cover contact. Examination of two drill cores intersecting the trace of the TFZ showed that there are anomalous breccias in the Upper Ordoviaan and Silurian strata (Haidl. 1988). Further examination of the cores by Kent Wilcox (unpublished MSc. thesis) and Elliott (1995) demonstrated that the breccias were tectonic in origin. If these observations are to be believed then the wnstraint on Phanerozoic reactivation of the TFZ is that it was active after lithification of lower Silurian carbonates. A study of an outlier of deformed Ordoviaan limestones at Limestone Point Lake (Fig. 3.4) by Elliott (199413, 1996a) wnduded, in agreement with the previous observations, that deformation took place after lithification and dolomitization. The outlier lies above one of a series of parailel, N-trending basement linearnents defined by the truncation of regionai magnetic anomalies (Elliott, 1996a). It was suggested that these basement linearnents may be related to the TFZ. The traang of topographic lineaments of the TF2 into Silurian strata by Byers (1962) may further constrain the upper limit on the timing of deformation. Alternatives to this last observation are that the lineament could have resulted from a solution collapse breccia forming in the Silurian strata above the fault, or that there were. in fact, severai pulses of reactivation of the TFZ during the Phanerozoic eon. and that movement could have occurred both before and after Sifurian carbonate deposition. 5.2 Fission Tmck Analyrh Fission track andysis of rodes from two transeds orthogonal to the trace of the fault indicates that t here has been rneasurable Phanerozoic displacement across the TFZ. The Neilson Lake transect (Fig. 3.8) shows that apatite from samples east of the fault yield younger fission track dates than samples to the west and within the fault. The younger samples indicate a slightly deeper. hotter pre-ugift crustal level. The explanation for this is that there has been east-side up vertical movement across the fault. The diffetence in the ages of samples suggests that there was between 250-400m of vertical displacernent (pers. comm. B. Kohn). The constraint on the timing of rnovement is that it was after the date given by the youngest sample, i.e. 316k15Ma. The exact age of movement is not known but companson to other studies in the Canadian Shield indicate that it is definitely late Phanerozoic (pers. cornm. B. Kohn). The second transect was taken across the eastem shore of Wollaston Lake (Fig. 3.9). The 15km long transect crosses several defined and probable TFZ fault splays. The results of the analysi$ were surprising in that there was no identifiaMe rnovement on many of the fault spiays. The rnost signifiant sample is 3701 1. This sample is the most easteriy in the transed and yields an age much younger than samples immediately to the west, samples 11021 and 1 1Oïl. A prominent N-trending topographic lineament. passing through the locality known as Trout Nanows separates these samples fmm sample 3701 1. This lineament is the probable location of a Phanerozoic fault splay. As m'th the Neilson Lake area the recording of younger ages from samples east of the fault indicates that rocks to the east were exhumed from a deeper level. Apparently the other fault splays were either not reactivated or the movement is not resolvable using this rnethod. Flgure 3.8. Ldomand mlb fblon.brdr ag# of umpk. callectod dong Nmlkon Wu b.nwct. Linas n-nt ml1 ddnad TFZ huit rplays (ml#) and mlnor or probibk TF2 fiun Flgum 3.9. Location and .prtlt. fbkn4ack .g.. d .rnpk. colloctoâ dong Hlddmn Bay trinaoc& Wolk.ton Idm. Llnos rapraaont ml1 ddnoâ TF2 hlt.play. (h.ivy d88h.d) and mlnor or probabk TF2 hum 8pl.y. (fim dniud). Nob th. sIgnMt.ntiy youngr aga d thumpk furlh..t .wt (37011), In th. location which codod from a dœpor prm-upllftdmpth than mckm to th. dm The posltion of th. huit accmrnmodatlng dHhrrnflal upltft mua II. betwemn thla ampk and sunpk. 11021\11071 on khky Paninsula. It k Ilbly Lat It runs dong thm topogmphlo low that definma thm Tmut Numm. Tha umnooumly old aga of tha samplm 27021 is dw to tha high chlorlna In th. aprtld., Incm~Ingthm 5.3 Williston Wnoiporltkn Phanerozoic sedimentation in southern and central Saskatchewan started in the Cambrian Period ad continued through until the Terüary Pedod. Structure maps and isopach maps, for ail the major inteivais are awered in Moasop and Shetson (1 994). Like the foreland basin of Alberta the Williston Basin in Saskatchewan shows changes in stratigraphy and depositional rates that reflect the role of orogenesis on the basin (Kent and Christopher, 1994). An isopach map for the Late Devonian Woodbend (374-370115Ma) and Winterbum (370-36211 1Ma) Groups (Fig. 3.10) show that sedimentary thickness in the Williston Basin exceeds 200m in parts of southern Saskatchewan for these groups. The map also shows that the deposition is irregular. with areas undergoing differentiai sedirnentation. lllustrating this, the 200m isopach for the combined Woodbend and Winterbum age sedirnents shows a marked change in trend, from roughly east-west to north-south, approximately coincident with the 103OW line of longitude. The Winteibum zero edge (limit of deposition of the group) is strongly aligned dong a similar noithedy-trend. The Jgnificance of this abrupt change in trend is that 1 lies dong strike of the TF& as it disappears beneath the Phanerozoic cover 350km due north (Fig. 3.1 0). It is also coinadent with the rerote sensing lineament that is interpreted to be the extension of the TFZ to the south (Elliott and Giroux, 1996). There is a second lineer trend in the 200m isopach at approximately 102W. which may also be rnatched by a similar trend in the Winterbum zero edge. The significance of this second linear trend is discussed later. The distribution of the isopachs shows that deposition was greater to the West of both lineaments than it was to the east. This is compatible with the fission track analysis suggesting east-side up rnovement dunng the late Phanerozoic eon. The sarne linear trends are obsenred in the isopach mp for the Ctetaceous middle Upper Manville Group (-1 13-108MMa) (Fig. 3.1 la). While most of the southeastern part of Saskatchewan was submerged beneath shailow seas or Flgum 3.10. hop.ch mmp of th. Woodknd (374470Ma)- Winterbum (370462Ma) and oquM.nt groupa of th0 Uppw depositlonal adgo of tha group.. Tho dots mpfmsont contiol mlk; O 100 miles 54' / zero/ edge I I ,Lineuvents offecting II isopach Figure 3.11. A) Isopach map (in metru) of Cmtaceous Upper Manvllle Gmup (and equlvalents) In Saskatchmwan (adapted alter Hayes et a&., 1994). 6) PaIeog.ogmphlanl ncon8trudlon of Ctetaceous mlddte Upper Manvlllm Gmup (and equlvalenb) ~~gmphyIn Saskatchewan (adamdbr SmHh. 1994). Shadlng denotes: da& gmy = fluvlal sysbms; llgM giry = progrrdlng deltalc; patternad = amas sufbrlng woslon dufing Upper Manvllle tlm. Also shown Is the known trace of the Tabbernor fault In the exporeâ shkld to cornpan agmlnat the pakogeogmphy and Isopach brnd Ilnes; the dasheâ Ilnos mpresant the bopach Ilneaments tmced hmfigure 3.10. forrned deltaic systems, certain locations were emergent highlands (Kg. 3.1 1b). These highlands follow the east-west trend of the Punnichy Arch. in centrai Saskatchewan, and the southem end of the Birdtail-Waskada Axis in Manitoba and southeastem Saskatchewan (compare Fig. 3.1 wi-th Figs. 3.1 la and b). 60th these structurai features have been suggested to be tectonically contmlled and reactivated periodically dunng the evolution of the Williston basin (Kent and Christopher, 1994; Poulton et al., 1994). The eastern edge of the highlands coincident with the Punnichy Arch teminates at 103OW, the same longitude as the Late Devonian isopach lineament. The western limit of the highlands forrned by the Birdtail-Waskada Axis teminates at -1 02OW. again coincident with a Late Devonian isopach lineament (Fig. 3.1 1b). Unlike those eailier lineaments, the Manville Group highlands do not show the same sense of verticai displacement. The termination of the eroded highland at 103°W, indicatesdeposition to the east of the lineament, whereas the lineament at 102OW shows deposition to the west. This suggests that the TF2 spîay at 103W aitered from being an east-side up fault in the Late Devonian Period to a west-side up fault during the Early Cretaceous Period. The second lineament at -1 02W parallels the trace of the Setting Lake Fault zone in the subsurface (te& the Thompson Boundary Fault in its subsurface extension by Baird et al., 1992). The northern extension of this fault in the exposed basement rocks is the eastern boundary of the Reindeer Zone, separating the Kisseynew Domain to the east from the reworked Archean rocks of the Thompson Belt to the west (compare figures 3.1 0 and 3.1 1 with figures 3.2 and 3.4 showing the basement tectonic domains). As such it is a major Iitho- tectonic boundary between the Churchill-Supenor Boundary Zone and the Reindeer Zone. 5.4 Geochionology and Isotope Syrtomaüca trom Umnlum ûeposlt Mineralogy Reactivation of basernent structures has affected the uranium deposits of the Athabasca Basin and sunounding districts. Beck (1970) suggested that reactivated fault movements were linked to anomalously young radiometric dates from deposits on the northem shore of Lake Athabasca. PuMished within that paper were K-Ar radiogenic dates of 467f28Ma and 486255Ma,taken from an ultramylonite at Cluff Lake (Fig. 3.5) having a protolith denved from both basernent granite and Athabasca sandstone. Also puMished were two U-Pb agas f rom pitchblende in Athabasca sandstones at Stewart Island (Fig. 3.5) yielding dates of 41 8Ma and 448Ma (no errors given). The deposits are of two broad types. The Cnt are the econornically significant 'unconformity-type' deposits, such as Collins Bay '6' zone and Key Lake (Fig. 3.5). These are fault-controlled and lie at or near the unconfomity between Wollaston Domain basernent rocks and overlying PaJeoHelikian sandstones of the Athabasca Basin (Tremblay, 1982; Cameron. 1983; SibbaU and Petnik, 1985; Evans, 1986). Disaissi*on on the formation of wch 'unconfomity-type' deposits can be found in Komninou and Sverjensky (1996). and Fayek and Kyser (1997). The second type, les econornically signifiant but more nurnerous, are the 'fracture-type' deposits. They are al1 basement hosted, in faults and fractures t hat may or may not be part of large-scale fault systerns (Beck, 1969). The largest concentration of 'fracture-type' deposits is found on the north shore of Lake Athabasca, north of the Athabasca Basin (Fig. 3.5). The term 'fracture-type' has been used here to clarify the more confusing 'simple mineraiogy' and 'cornplex mi neralogy' classification of Beck (1969), and 'cornplex vein-type' of Kotzer and Kyser (1993). It denotes only that the mineralization is hosted by once-open fractures in the basement and makes no inference regarding source or composition of the mineralization. Many fracture-type deposits are thougM to have fomied during late-Hudsonian tectonic events at 1750Ma. whereas the unconforrnity-type deposits give U-Pb ages for prirnary minerakation that indicate formation around 1400-1500Ma (Saskatchewan Geologicel Survey, 1994). Som deposits rnay show elements of both types of minerakation. but the host seming is not important to the ensuing arguments. Numerous radiometric data have been extracted from various minerals associated with both 'unconformity-type' and Yracture-type' deposits. These typically make use of the U-Pb or Pb-Pb systems in the main ore mineral. U02. This occurs either as a cubic crystalline form, uraninite, or as a sooty black, massive variety, pitchbiende, which is charaderistic of lower temperatures (Tc250°C: Fryer and Taylor, 1987). More recently, stabie isotope evidence has been used to show that fracture-controlled kaolinites around the McArthur River deposit formed from rock interacting with a fluid equivaient to modern meteoric waters, and that this was controfled by readivated faults (Kotzer and Kyser, 1995). A summary of radiometric data, giving Phanerozoic ages. from Udeposits in and adjacent to the Athabasca basin is show in Table 3.1. This shows that there is li mited concordance of dates between different radiogenic dating methods. Despite this some cornparisons can be drami between radiogenic age data from the various deposits and systerns. Ali the chernical U-Pb ages for stage two and three uraninites. pitchblendes, coffinites and Ca-U hydrates as reported by Fayek and Kyser (1997) are significantly younger than earlier (as established by growth relationships) stage one uraninites and pitchblendes. There is some correlation between stage-3 uraninite ages, as three of the analyses overlap within analytical error at approximately 370Ma and a fourth is slightly out at 403Ma. Two ages from McClean Lake (Sue zone) overlap between 125-132Ma. Table 3.1. Cornplfation of Phanerozolc mdloganlc aga data derlved from U-Pb dllna mathodo on unnlum mlnemllzatlon. The locations of tha dapoolta clkd In the tut ank found In Flgum 5. Rehmnces: a - Cummlng and Rlmalk, 1878; b - Fayak and Kysar, 1897; c - Hoave et dm,1885; d - Cummlng and Krstlo, 1992; O - Andrade, 19119; f - Budsgurd of#& ISû4; g -PhIllppa et& 1883; h - Phllippe and Lancol* 18û8; I - HOmdorf et al., 1885; J - Trockl et alm,1984; k - Ruz~c,~~1986. . Prim. and sec. pitch. from Rabbit Cake Coricordia L. 1. Coffinite from McCiean Lake Chernical Age Primary pitchbiende from Rabbit Lake Comadia L. 1. Stage 3 uraninite from Midwest Lake Chemical Age Late pitchblende from McArthur River Corwxndia U. 1. Uraninite from Eagle Point Concordia C. 1. Primary pitchblerde from Midwest Lake Goricordia L. 1. Coffinite from Midwest Lake Chemical Age Primary pitchblerde frun Midwest Lake Corwrndia L. 1. Prirnary uraninite from Cigar Lake Corwxndia L. !. Stage 3 uraninite from Eagie Point Chernical Age Prim. uran. and @ch, frm Cigar Lake Concardia L. 1. W. R., mineralized zones from Key Lake Concordia L. 1. W. R., mineralized zones from Key Cake Concordia L. 1. Primary uran. and pitch. from Cigar Cake Coricordia L. 1. W. R., mineralized zones fiom Key Lake Concordia L. 1. Pitchblende from Rav- Concordia U. 1. Stage 3 uraninïîe from McArthur River Chemical Age Ca-U hydrate fmEagle Poirit Chernical Age Secondary pitchblenôe from Rabbit Lake Concordia U. 1. Primary uraninite fiom Key Lake Concordia L. I- Secondary pitchblende from Rabbit Lake Concordia U. I. Coffinite from Eagle Pois Chemical Age Late pitchblende f rom McArthur River Concordia U. 1. Stage 3 uraninile from Cigar Lake Chemical Age Sec. uran. and pitch. from Cigar Lake Concordia L. 1. Stage 3 uraninite from McClean Lake Chemical Age Prim. pitch. and CM.from Midwest Lake Coricordia L. 1. Primary pitchblende frun Key Lake Concordia L. 1. Stage 3 uraninite from McClean lake Chemical Age Ca-U hydrate from Key Lake Chemical Age Late pitchblende frorn McArthur River Concordia L. 1. Ca-U hydrate from McArthur River Chemical Age Sec. pitch. and coff. from Midwest Lake Concordia L. 1. Ca-U hydrate from McClean Lake Chemical Age ~bbreviations:Ref. - Reference; prim. - pn'mary; sec. - samd bitch. - piîchblende; eoff. - &inil& Na - wor nd availabte. Summary description of andyzad matorid based on mare cornplet@descriptions given by the author in the referenced paper. '~ethodof dating either UPb chernical age or UPb concordia mahod (U. 1. = Upper Intercept; L. 1. = Lower Intercept). 'Given in Ma. Concordia method lower intercepts frorn six samples of eaily minerakation give ages between 322i38Ma and 340hk. These are interpreted as indicatin9 there was a major episode of minera1 remobikation affecting the 8ady U- mineralization. Another lower intercept from Midwest Lake gives an age of 12W17Ma. This is -compatible with the U-Pb chernical ages from stage 3 uraninites at McClean Lake. Of the 'unconformity-type*deposits listed in the table, many are dong or near to northerly-trending fault features which are interpreted to be splays of the TFZ. For instance the Collins Bay 'B* zone deposit omnin a segment of northeast- trending, southeast-dipping reverse fault. Mineralkation is concentrated where the thrust deviates from its northeastedy trend to a northerly trend. This is coincident with a weak north-trending aeromgnetic lineament considered to be the geophysicai expression of a TFZ fault splay. The Key Lake deposit consists of two tabular ore bodies on the same thnist fault separated by a distance of approximately 1km (Dyck and Boyle. 1980; Tremblay, 1982; de Cade, 1986). 60th orebodies are cut by several north-northwest trending faults that are considered to be part of the Tabbernor Fault grouping, as they have the same orientation as faults seen at the nearby Janice Lake copper showing (Fig. 3.6). These have been rnapped by severai authors as being connected to the TFZ (Scott. 1973; Delaney et al., 1995; this study). In at least one instance at Key Lake, the Tabbernor lineament coincides with a dilution of the mineralization. De Carie (1986) noted that repetitive movement on north- nort hwest trending faults has '. .. brecciated, remobilized and, locall y, displaced the deposits". indicating fault movement post-dates ore deposition. Other deposits such as those at Rabbit Lake and Eagle Point show no evidence of Tabbernor Fault splays cross-cutting them, but are w'thin 1km of minor Tabbernor Fault splays (Heine, 1986; Ruzicka 1986; this study). A few such as the Midwest Lake and McClean Lake deposits (Aryes et al.. 1983; Wallis et al.. 1983) are not dose to identified Tabbernor spiays. Despite this it is reasonable to assume that with the high density of aeromagnetic lineaments and minor Tabbemor-related faults in the basement. as rnapped on the shore of Wollaston Lake to the east. the reactivation of the TF2 would result in a general fluid circulation event throughout the basement. 5.5 Field Evldence of Qhanerozoic Reactivation of thTFZ Field evidenœ for Phaneroroic reactivation is poor. Whilst mapping over two field seasons in the Wollaston Lake area produced ample evidence for the brittle reactivation of Tabbemor-related structures, none of t hese cm be confident1y assigned to the Phanerozoic eon. Early Hudsonian age deformation. which is characterized by discrete ductile sheanng, but no rnyionite development. is overprinted by hematization, brecciation and horizontal quartz - chlorite growth fibres on slickensided joint planes. Brirle fault features are widely distributed in the basement rocks exposed in the Wollaston Lake area, but become more densely distributed around TFZ fault spiays. Poor exposure and lad< of good rnarker horizons predudes assignrnent of the relative displacements to the ductile or brittie phases of deformation. Individuai brittle rnovement planes show offsets between 4cm - Sm. Work on the nature of britlle faulting in the Wollaston Lake area suggests that the rnajority of these feahires are not Phanerozoic (Davies. in press a). They were formed during a widespread basement reactivation. possibly in the middle Proterozoic eon synchronous with the early stages of U-minerakation. The cleaily defined trace of a mafic dyke on the aeromagnetic field map of the area (Kornik, 1983) shows no offset across any of the major Tabbernor Fault splays. The dyke is assumed to belong to the Mackenzie dyke swarm, dated at 1267eMa (Cumming and Krstic. 1992, and references therein). Thus JI significant horizontal displacernent on the fault splays in the area, within aeromagnetic field map resolution (300m line spaang), ended before dyke emplacement and well before any Phanerozoic reactivation. 6.1 Timing of Phanerozoic Basement Reactîvatîons Tectonic reactivation of basement structures in the western Canadian Shield is an idea that has gained much aîtention in recent tirnes. Because of the inherent weakness of fault rocks and change in cnistal properties that commonly oaxin across large-scale cn~staifaults. they will preferentially accommodate intraplate stresses (Heller et al.. 1993). The TFZ in the exposed shield. and presumably under the Williston Basin, shows many properties that would rnake it a favorable locus for tectonic reactivation. Therefore it should corne as no surprise that the TFZ should show ample evidenœ of reactivation during the Phanerozoic eon. Fission track data from transects across the fault show that there was rneasurable vertical movement across the fault in two locations, with east-side up movement sense. The timing of movernent is canstrained to be les than the date given by the youngest rocks, i.e. 316î15Ma for the Neilson Lake transect and 338I14Ma for the Wollaston Lake transect. Fault reactivation also manifests itself as dilution and brecciation of uranium mineralization at the Key Lake deposit. The constraint on the timing of fault reactivation here is oniy that it be younger than the mineralization. This is loosely dated at - 1400I50Ma Brecciation of the Ordovician and Silunan carbonates in drillcores intersecüng the trace of the TF2 show that tectonic movement must have occurred after lithification of the strata. The age of lithification is not known but it is estimated that the strata were lain down at -438st12Ma. Assuming that fault control on depositional patterns in the Williston Basin was syn-sedimentary, then the best evidence for the timing of TFZ reactivation cornes from the Upper Devonian Woodbend (374-37Oi15Ma) and Winterburn (370- 362i11 Ma) Group. with the Winteikim Group being the more strongly affected. The Eariy Cretaceous upper Manville (113-108f4Ma) Group also shows evidence of fault activity during deposition. The Setüng Lake Fault was aiso active during both these periods. As with the Tabbernor Fault it is a structure that can be reasonably expected to readivate preferentially during a major tectonic episode. Evidence for such reacüvations is given by Bezys (1996). U-Pb data (Table 3.1) show that concordia method lower intercept ages from eariier stages of minerakation (-320-340Ma) are consistently younger than the U-Pb chernical ages from late stage mineraiization (-370Ma). The reason for this is probably due to amtinued remobilization of both U and Pb by interaction with oxidizing groundwaten. A possible expianation for why older generations of uraninite and pitchblende are more susceptible to Pb-loss than younger minerakation lies in the valence of the uranium ions. The ideal formule of U02 is based on the assumption that ail the uranium is in the ub onjdation state. In nature this is rarely the case, especiaily in the unconfonnity deposits, and the m'nerai is always somewhat oxidized, with the conversion of U& in part to U~ (Fryer and Taylor. 1987). This can conf nue up to a poorly defined limit (Frondel. 1958) without modification of the crystal structure. but beyond this the minerai will start to bewme anisotropic. The change in the valence state of the uranium is cornpensated for by the entrance of oxygen into vacant positions in the crystal lattiœ. lt is believed that this structural modification will aid the migration of lead. and maybe uranium. out of the mineral. * The early formed uraninites are comrnonly identified optically by their botryoidal texture. lighter colour and high-reflectance (Cumming and Krstic. 1992: Cari et a 1992; Phillipe et al., 1993; Fayek and Kyser, 1997) which indicates a high degree of crystallinity. Later, dtered, generations of uraninite that forrn as rims and fracture fillings to the earlier minerai. are darker, less refleclive. These probabl y result from oxidation of earlier formed uraninite and concomitant breakdown of the crystd latüce. The latest, stage3 mineralization identified by Fayek and Kyser (1997). appean to be extremely pristine and is characterized by low to moderate Pb contents. Their condusion was that this represents either the introduction of new ore, or the cornpiete recrystallization of previoudy deposited ore. The fonner explanation is favored hem. The earlier rnineralization is interpreted to have precipitated at the rnixing front of an oxidizing basinal fluid and a reduung basement fluid (Kotzer and Kyser. 1995). Interaction between these eariier generations of mineralization and extre me1y oxidized fiuids t hat characterized basin fluid incursions du ring the Phanerozoic eon would lead to extensive uranium oxidation, 4th associated U and Pb remobilization. This in turn would lead to relative Pb-loss out of the mineral and enoneously young agec for lower intercepts from eadier mineralization. The latest stage of mineraiization. i.e. rnineraiization foming after -500Ma bop.. precipitated in equilibrium with these oxidized fluids and wuld not suffer the same level of oxidation as the earlier ores. Therefore they suffer less from U and Pb remobilization. This is reflected in their high reflectivity. lad< of alteration features and more concordant ages. Thus the goal of this discussion is to show that in attempting to estirnate the timing of U-remobilization. and by association fault reactivation, the data from the late mineralization gives better indication of timing than data from the eaiiier mineralization. Wlh this in mind it is evident that U-Pb ages for late rnineralization are in strong agreement Ath the ages of fault reactivation indicated by the control on depositional patterns in the Williston Basin, i.e. 370Ma and -1 20Ma. These two dates ernphasized in the discussion of stage03 mineraiization take on greater significance when wmbined with the data from Pb/Pb analysis of sulfide and sulfate minerais from the Key Lake. McArthur River and Eagle Point depodits (Kotzer and Kyser, 1993) (Fig. 3.1 2). These minerals are intimately assodated with U-minerdiration and their =pbP~band m7~bp~bratios suggest a highly uranogenic source (Cumming et al.. 1984; Kotzer and Kyser, 1990) i.0. the altered U-mineras. Using the secondary isochron equations of Cumming et al. (1984), Kotzer and Kyser (1993) showed that Pb ratios in the late-formed sulfides and sulfates are compatible with uranogenic Pb evdving in a dosed system (i.e. the U-bearing minerals) until disniption of the system and incorporation of the radiogenic Pb into the sulfides and .sulfates. The samples give ages of 369Ma (Key Lake. Fig. 3.1 2a) and 130Ma (McArthur River and Eagle Point. Fig. 3.1 2b) which represent the time at which the system was disnipted and S-bearing mineras were precipitated. These show good agreement with the U-Pb ages from the late mineralization and dates from depositionai data in the Williston Basin. The Late Devonian data show an especiaily strong correlation. The possibility exists that there were more than the two reacüvation events discussed so far. For example, there are several deposits for which the concordia lower intercepts from prirnary mineralization give ages of 232-41 Ma to 30MMa (TaMe 3.1). In addition, two concordia upper intercepts from late rnineraiization give ages of 21 0fGMa and 275f25Ma (Table 3.1 ). Whether these data represent real episodes of rembilization of the ore. or are simply due to more recent continuai diffusion of Pb out of the U-minerals is unclear. The lack of supporting U-Pb chernical ages from late U-minerais. or Pb-Pb ages from late sulfides and sulfates. suggests these ages are not as significant as the other data. However, Chipley and Kyser (1996) published ages of haiite recrystallization from the Middle Devonian Prairie evaporite Formation in southern Saskatchewan. The ages published, 371 Ma, 284Ma. 214Ma and <35Ma. are in excellent agreement with the concordia upper intercepts for late- mti- In aultld. and su- minmin of vuylng -18 from thm Ath.b..a Bwin (tom u\d Km1993). Symbd8 mpi#.nt Pb ritk. dobrmlnoâ in gmkm 1C#n Pmdopomlb .t Key Lakm U om d.poilb (md# Wangk.), pyrb and niw#.itm in undstori.. and fmcturr 1K.y Wt., YokLhur Rlm. and Eagk Point (opan cirok.), mngiaitm in abrdundatanom pmximil do Kay Wro U or, doposb (0p.n aquai..). 8CIcmy3(rrmom gmwth cunn shown for i.hmnca (6btry and Krifmm, 1O75). a) Socoriduy kodiron plot comprklng Pb müa mmgakna 1 Key Lmko. Aga cmlculatod umlng wconQy kochron oqudons (a.g., Cummlng ot al., WW),murnlng an mg. af 1400 Ma lbr th. mdloganlc Pb aoum. b) mndmry bochron plot comprklng Pb ratIo8 hmpyrlt., rnammlt., and 8ngk.b .t bykk. (1- kCt) and from h.cturm-fmW cubk Wrl(, .t McMhur Rlvor and Eagia Point. Aga calcuiatd using wtondwy koohmn oquitlons (~mgm~ Cummlng at d.. 1@64),mumlng th. aga d thm mdlogmnlc Pb soum wu 800 Ma, rimilu to thm aga of ~umcontrolioâ comnlb formitkn Inth. min(HOhndorf of al., 1-1. Key Lake slope =O. 1 004 MSWD = 9.5 Age = 369Ma McArthur River + Eagle Point slope = 0.0724 MSWD = 41.6 Age = 130Ma stage minerdiration. This would suggest that there is additional evidence for repeated basernent reacüvation through much of Saskatchewan during the Phanerozoic eon. Chipley and Kyser (1996) suggested that halite recrystallization was related to tectonic events in the cordillera to the west. Summarizing al1 the data presented it is possible to present a tima frame for TFZ reactivation during the Phanerozoic eon. This started with a stmng episode of fault movement at 370Ma that controfled sedimentation in the Williston Basin and remobilized U and Pb from deposits in the Athaôasca Basin. This event can dso be used to explain the anornalous breccias observed in Ordoviaan and Silurian rocks. This event cannot, however, explain the fission track data which show that there was vertical movement on the fault after -325Ma. This vertical movement is probably related to the episode of Eaily Cretaceous fault reactivation that is poorly constrained somewhere around 110-1 20Ma. Alternatively the vertical movement can be attributed to one of the minor basement reactivation events that may have occurred at circa. 280Ma and 21 0Ma. 6.2 Cause and Mechanisms of Reactivation As noted earlier rnany authors have proposed links between a variety of tectonic and stratigraphie features in the western sedirnentary basin and orogenic activity on the western margin of the North American continent. Cornparison with the best estimates on the timing of Cordilleran tectonics shows that there is an excellent correlation between basernent reactivation and major collisional episodes on the western cratonic margin. Earliest orogenic activity is suggested to have begun in the Middle to Late Devonian Period with the Antler Orogen (see references given earlier). Successive sequences of terrane accretion resulted in the Late Permian (258-245&24Ma) Sonoma Orogen, Jurassic (208- 14421 8Ma) Nevadan Orogen (Windley. 1995). Early Cretaceous (1 19-1O5I9Ma) Columbian Orogen (Pavlis. 1989; Sprinkel, 1992). and Late Cretaceous (97.522.5Ma) Laramide-Sevier Orogen (Windley, 1995). These events are in excellent agreement with al1 the ages given for reactivation for the TFZ. Discussion of the nature of the mechanisms connecting marginal tectonic events to reactivation of th8 Tabbemor Fault and other basement ieatures is at best speculative. The main reason for linking the tm, processes is the strong correlation in the timing of the episodes. This suggests that the rnechanism(s) that link orogenic ad-vity to basement reactivation must transmit the stresses needed to initiate reactivation extremeiy rapidly, geologically speakhg. The mechanism of lithospheric flextufing discussed at the beginning of this paper would certain1y have an eff ect on the stresses within the conti nentai lithosphere. Helier et al.. (1993) discuss the cause of tectonic reactivation in the Rocky Mountain region, related to Cordilleran orogenic activity. They condude that reactivation of pte-existing basement structures can be brougM about by West changes in intraplate stress fields. Far-field processes such as plate-margin orogenesis, or local effects, such as intraplate loading and flexure can bring about these changes in intraplate stress magnitudes andlor orientations. Pavlis (1989) suggested that the Cdumbian Orogen on the noithwestern margin of the North American continental margin was characterlzed by a cornplex arrangement of extensional and contractionai tectonism associated with the th rusting of the Wrangdlian composite terrane beneath previously accreted terranes. Extensional tectonics at this time may explain why the TFZ reactivated as a west-side up fault dunng Mannville Group deposition, as opposed to east- side up movement during the dorninantly contractional Ant!er Orogen. Other mechanisms cited at the beginning of the paper, such as supercontinent assembly by mantle convection and tilting of continental interiors by dynamitai effects of subduction, could aiso bring about changes intraplate stresses, but it would be difficult to link them to the timing of orogenic activity. 7. Conclusions The Tabbernor Fault is a long-lived fault zone that has undergone repeated reactivation duri ng the Phanerozoic eon. The most signifiant reaaivation events probably occurred in the Late Oevonian (-370hk) and Early Cretaœous (-120Ma) Periods. aithough there may have been severai other reactivation episodes. The readivation of the fault dong rnost of its length led to significant controi on depositioncil patterns in the Williston Basin, and remobilizationl preapitation of uranium-bearing minerais in high-grade deposits of the Athabasca Basin. Apatite-fission track analyses of rocks froni the exposed basement in northem Saskatchewan show that there was differential uplift across the TFZ dunng the Phanerozoic eon, with vertical. east-side up, movement and an unknown component of horizontal movement. The ultimate cause of fault reactivation was linked to orogenic activity at the western continental margin. which was synchronous with reactivation. There is supporting evidence that the reactivation of the TFZ was part of a larger scaie reactivation of the western continental basement structures, due to the differentiai accommodation of strain within the lithosphere. Chapter 4 Summary and Conclusions General Conclusions As a result of wrk camed out during th8 cornpletion of this project severai new discoveries have been made on the history of the Tabbernor Fault zone. These are listed below in point form: 1) The earliest movement along the TFZ in the Wollaston Lake area is characterized by the tranposition of the regional SIfabric ont0 an upnght NE-trending plane of flattening, produang Sn. This transposition is typified by tightly folded and boudinaged pegmatite segregations within an intensified gneissic foliation. The limits of this tranposition are defined by NNE-trending sinidrd shear zones such as the Parker Island shear zone. 2) In high strain zones the newly developed s2 fabric is modified by a near vertical, NNE-striking, sinistrai shear deavage. As a result of modification. the foliation and associated fold structures are rotated away from the regional 02plane of flattening towards the shear plano. 3) The fault and assodated parallel structures controlled the intrusion of a granitic or pegmatitic melt phase during a break in deformation. This intrusive event ocarrred after the bulk of sinistral sheanng that affected the adjacent rocks. Mineralogical and structural similarities between the intrusive phase in the TFZ and a regional phase of Hudsonian granitic intrusions dated at -1815Ma suggest that the Tabbernor Fault was active prior to 1815Ma. 4) Given the assurnptions made above the most likely explmation for origin of the TFZ is as a strike-slip fault that accomrnodated sinistral rnovement during post-collisional escape of the 'Sask' craton beneath the Reindeer Zone. riming of this post-cdlisional event is indicated to be synchmnous with peak metamorphism at arca. 1815-1 830Ma. 5) Subsequent renewal of ductile shearing caused localized reactivation of TFZ structures and rninor development of shear fabrics with the intrusives. This was related to late orogenic adjustrnents of the THO dunng Dm and DH~tectonomorphic events. 6) The TFZ rnay have a strong role in wntrolling the location of major uranium deposits in the Athabasca Basin. Not only rnay the fault act as a fluid conduit. ailowing deep circulation of the ore-forming fluids, but structural evidence from identified deposits suggests that they are situated within ductile, Tabbernor-related, structures. 7) Readivaüon of TFZ structures oaxrrred over much of the fault's length during the Phanerozoic Eon. Evidenœ from as far afield as the Williston Basin and the Athabasca Basin ail wggest that the TFZ was active during the Antier Orogeny and the Laramide-Sevier Orogeny. Reactivation caused differentiai upiift of basement rocks, depositional control of active sedimentation, and extensive uranium mobilization. Contributions to Knowiedge This study is the first investigation focusing solely on the TF2 within the Wollaston Domain. As a result of work published here the probable age of the eariiest ductile movernent within the fault has ben narrowed to a window of 1815-1848Ma. This indicates that fault movernent was refated to major orogenic events, rather than minor pst-orogenic adjustments as suggested by some worken. lt is also the first wrk to compile geologic data coming from the known geographic and temporal extent of the TFZ. From this it is possible to present an intermittent history of the fault over >1 Sa. This is the first puMished study to identify a possible link between the TFZ and uranium mineralization. This link, if substantiated, rnay be of extrerne importance in the future exploration for 'unconformity-type' uranium deposits in the eastem Athabasca Basin. A test of this hypothesis would be to try and ide~tifyoutcrop- scale fault features that are sirnilar to those seen within TFZ spiays mapped on the shore of Wollaston Lake. To the south, the link between the FZ,sedirnentary patterns, and structures within the Williston Basin has the potentiaî to control the economic occurrence of hydrocarbon piays. One oil and gas field. the Minton field. has already been located immediately above the TFZ. The idea of intracratonic stability is put into further question by the knowledge that the TFZ has had a very long, repeated history of reactivation. This is despite being oblique to the active plate margins during the THO and far removed frorn any active plate margin subsequently. References and Bibliography Andrade, N., 1989: The Eagle Point uranium deposits, northern Saskatchewan. Canada. In: Uranium resources and geology of North America. International ~tomicEnergy Agency Technical Document. 500, p. 455- 490. Annesley, 1. R., Madore, C., and Shi, R., 1996a: U-Pb geochronology and thermotectonic history of the Wollaston Domain in the Wollaston Lake area, Hearne Province, Saskatchewan. In: GAC-MAC program with abstracts, v. 21, p. A4. Annesley, 1. R., Madore, C., Shi, R., and Krogh, T. 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