Structural Geology of the Mokoman (Knife) Lake-Reindeer River Transect, Northern Saskatchewan

CD. Card 1

Card, C. D. ( 1999): Structural geology or the Mokoman (Knifc)Lakc-Rcindeer Rivt:r Transect. northern Sa~katchewan: in Summary of Investigations 1999. Volume I. Siu;katchcwan Geological Survey, S,t~k. Energy Mines. Misc. Rep. 99-4. 1.

Abstract

The Mokoman (Knife) l ake- Reindeer River area lies within the Scimitar Complex, in the Reindeer Zone of 1he Trans-Hudson Orogen. The Scimitar Complex is located on the eastern flank of the Glennie Domain am/, prior to 1997. their relationship was unclear. The results of the 1997 project suggest that there is no structural or stratigraphic break between the two areas. The assemblage <~(rock types suggests that the Scimitar lake area is an extension of the Flin Flan Domain and represents a p iece of the Glennie-Flin Flan protocontinent.

Five deformation events have been identified in the area. The moderately east dipping regional foliation (S,) is believed to have formed in an axial planar orientation relative to coeval isoclinal fold\·. The second deformation c,vent is poorly developed and observed only in the Gilbert l ake area as part of a type 2 interference pattern. The most common set of.folclr in the area (F3} are generally overturned with north- to north-northwest-striking axial surfaces dipping to the east, north-northwest- to north-northeastward­plung ing axes, and have close to tight interlimb angles. The fourth deformation event is characterized by open to gentle upright fofdr with axial swfaces striking northeast and dipping steeply to either the northwest or southeast and axes plunging gently 10 the norlheast. lnterlimb angles are usually open to gentle. The final phase of deformation (D5) is represented by two sets of lineaments each of which is believed lo mark sleep faults.

The f ive deformation events are linked 10 the tectonic evolution of the Reindeer Zone. Deformation I is consistent with the geometry and characteristics of tectonic imbrication initialed by collision (if the Glennie- Flin F/on protocontinent and the Saskatche wan craton. Deformation 2 also may be related lo this collision. Deformations 3 and 4 are caused by terminal collision of the Superior era/on with the Saskatchewan craton and the overthrust stack of Glennie- Flin Flon rocks. Deformation 5 may represent the late stages of terminal collision.

I Departm~nt of Geology. University o f Regina. Regina, SK S4S OA2

Saskatchewan Geological Survey

l . Introduction

a) Study Area

The Mokoman (Kn ife) Lake- Reindeer River area is part of the structurally complex Reindeer Zone of the Trans-Hudson Orogen. Mapping at I :20 000 scale of a 250 km~ area was undertaken in the summer of 1997 to complete a study of the Scimitar Complex, aimed at establishing the relationship between the Scim itar Complex and adjacent Glennie, Kisseynew, and Flin Flon lithostructural domains and determining the area's mineral potential (Ashton elal., 1996 a, 1996b). Particular attention was paid to the regional context and origin of the Knife Lake Cu-Zn deposit (Harvey, this volume).

The Mokoman (Knife) Lake-Reindeer River study area is located in northeastern Saskatchewan, about 120 km northeast of Missinipe, 75 km north of Pelican Narrows, and 50 km northwest of Sandy Bay (Figure I). The area has a maximum re lief of about 90 m with the high ground dominated by orthogneiss and the low ground mostly underlain by supracrustal rocks. Previous mapping of the area was completed by Pearson ( 1973 ), Fuh ( 1979), and Johnston ( 1984 ).

b) Regional Geology

The "Scimitar Complex' ' (Macdonald, 198 1), is located east of the Tabbernor Fault and Reindeer River, and north of the Churchill River on the eastern tlank o f the Glennie Domain (Figure I). Rocks of the Kisseynew Domain border the northern, eastern, and southern margins of the complex. The rocks of the Scimitar Lake area comprise an upper amphibolite facies volcano~plutonic package with subordinate sediments, and are 111terpreted as an early Proterozoic oceanic island arc complex, similar to that of the Flin Flon area (e.g. Symc, 1990; Ashton et al., 1997). These supracrustal rocks are located on the northwest limb of a regional syn form cored by metasedimentary rocks of the Kisseynew Domain (Figure I). Dominantly volcano-plutonic rocks of the Flin Flon Domain underlie the southeast limb of this regional fold (Lewry et al., 1990; Ashton et al., 1997), suggesting that rocks of the Scimitar Lake area are continuous and broadly correlative wi th those of the Flin Flon Domain beneath the syn form (Lewry et al., 1990; Ashton et al., 1996b; Ashto n et al., 1997).

IOI

The historical boundary between the Scimitar Complex and the G lennie Domain was established during the compilation of regional geological maps for the area (Macdonald, 1981 ). Mapping by Ashton el al. ( 1997) suggested that there is no significant structural o r stratigraphic break between the Scimitar Complex and the Glennie Domain and that the previously defined boundary is main ly a function of inconsistencies in rock nomenclature. As a result Ashton et al. (1997, p6 I) suggested that the tenn Scimitar Complex should be discarded and that the area should now be referred to, in a geographical context, as the " Scimitar Lake area of the Glennie Domain". This implies continuity between the Glennie and Flin Flon domains (Ashton el al., 1997), which supports the idea of a Glennie- Flin Flan protocontinent (Lewry et al., 1996).

c) General Geology

According to Ashton el al. ( 1997), most rocks in the Mokoman (Knife) Lake-Reindeer River area (Figure 2) have been metamorphosed to upper amphibolite facies and appear to be derived from volcanic and plutonic protoliths, although subordinate sedimentary rocks and significant syn-metamorphic melt neosome are also included.

56"30'

The supracrustal assemblage is dominated by amphibolite, carbonatized amphibolite, and migmatitic equivalents of these which are thought to have been derived from mafic volcanic protoliths. lnte1111ediate volcan ic, volcaniclastic rocks, and their migmatitic equivalents, are subordinate and felsic end members rare, occurring mainly in the Mokoman Lake area. Sedimentary rocks include pelitic to psammopelitic, aluminous wackes and a calcic-pelitic package.

Rocks with plutonic protoliths are dominated by granodiorite-tonalite and migmatitic derivatives. Syn­metamorphic neosomal melt rocks are also common: these include leucocratic granodiorite. Late, discordant granitic pegmatite dykes are also common. Metabasites interpreted as being derived from ultramafic to gabbroic intrusions are rare.

d) Purpose

Work completed in 1997 suggested that the Mokoman (Knife) Lake- Reindeer River area underwent polyphase defonnation, with five recognizable deformation episodes. Each episode is defined on the basis of features observed at both the mesoscopic and macroscopic scales. The purpose of th is thesis is to

expand on the structural synthesis

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presented by Ashton et al. ( 1997) by the detailed analysis of the characterist ics of each defonnational episode. Th is study relates these features to tectonic evolution and establ ishes the tectonic setting of the Knife Lake Cu-Zn prospect.

~ : : ; ; ;~i~,4:)!'!~ ; : :

54"30'

Figure I - location of the Scimitar Complex with respect to the lithostructural subdivisions of the southeastern part of the Reindeer Zone of the Precambria11 Shield in Saskatchewan (nwdifiedfrom Ashto11 et al., /99 7). Arrows represent regional, F, axial traces, HLB, Hanson lake Block; and SWSZ, Sturgeo11-weir Shear Zone.

e) Methods

Structural analysis was carried out using the 1 :20 000 scale map and structural data provided by Ashton et al. ( 1997), about half of which were collected by the author. Over 2600 structural measurements, recorded at I JOO stations, have been analysed. In addition, carefu l analysis of air photos and satellite images provided macroscopic information about deformational style. On the basis of structural homogeneity, the area was divided into nine structural domains (Figure 2). The structural characteristics of each domain were detennined using equal area stereonet projections, which were computer generated using the Stereo component of the Rockware 3 .0 software program.

102 Summaryoflnvestigations /999, Volume I

2. Regional Deformation

a) First Deformational Event (D1)

All rocks, other than late pegmatite and aplite dykes and quartz veins, have a weak to strong foliation (S 1).

The S1 regional foliation generally strikes north to northwest, but is locally refolded producing some variations in orientation. Dip varies from about 30°10 75° to the east or northeast (Figure JA). This foliation is assumed to have formed in an axial planar orientation relative to coeval isoclinal folds (Lewry et al. , 1990; Ashton et al., 1997). F I folds are very difficult to distinguish at mesoscopic scale as they are commonly dismembered, with the limbs offset by slip

w E 0 0 0 01

w

ITT rm II ~

~

Syn-metamorphic melts and migmatite

Granodiorite and derived migmatite

Undifferentiated supracrustal rocks

Sedimentary rocks

F elsic-intermediate volcanic rocks and derived migmatite

Amphibolite and derived migmatite

6197000mN

6186500mN

along the axial plane making relict limbs an indistinguishable part of the S, foliation.

The S1 fabric is also defined by a gneissosity, which is present in two varieties in all but pluton ic rocks with low colour indices. A penetrative mineral layering resulting from metamorphic differentiation (Hatcher, 1995) in which many minerals have recrystallized, due to ionic migration, in the plane of the developing gneissosity (e.g. biotite and sillimanite) is exemplified by pelitic rocks, which commonly comprise alternating biotite-rich and quartzofeldspathic layers. The second fonn, stromatic migmatite (Mehnert, 1968), results from the production of neosome (Figure 4), in most

I Structural Domain

/ Structural Domain Boundary

.. ·•···· Eastern boundary of high strain , /

/

Previously inferred Scimitar-Glennie boundary

~ F4 Axial surface trace -(

/ ~ F3 Axial surface trace

~ / Lineaments

0 Kilometres 5

Figure 2 - Geologic map of the Mokoman (Knife) lake area showing structural domains, axial traces of major F1 and F, folds, major Ji11eaments, and the easter,r boundary of the high-strain area (modified from Ashton et al., 1997).

Saskatchewan Geological Survey 103

A N n=99

N n=34

O Axis • F4

I II Ill

n=104 n=137 n=29 N N_

Axis of

• Axis of • F3 F4

IV v VI

n=113 n=227 n=202 N N N -----

Axis of .F3

0 of

VII VIII IX

Figure 3 -A) Equal area stereonet projectio11s of the poles to S, in structural domains I through IX. Heavy solid Ji11e represents great circle girdles to F1 folding; heavy dashed li11e represents great circle girdles to F, folding. B) Equal area stereoneJ projectiom of the axes of F1 minor folds/or structural domains Va11d Vil. C) Equal area stereonet projections of the axes of F1 minor folds/or structural domains I and Ill.

/04 Summary of Investigations 1999. Volume I

quartzofeldspathic rocks, by partial melting. One part icularly common ncosome type in the g neissic granodiorite contains about 20 percent hornblende± biotite and probably resulted from the reaction: biotite+plagioclase+quartzc=homblende+ K-feldspar­rich melt±sphene±magnetite (Winkler, 1974, p298).

Layering was formed by in situ generation and/or local injection of melt neosome in layers of varying width, paralle l to S,. In situ neosome generally contains both leucosome and melanosome; however, injected neosome contains only leucosome. Locally, metre­scale bands of injected neosome alternate with paleosomal gneisses. The presence of both injected and in situ anatect ic melt defines S, suggesting that partial melting of these rocks began early in their tectonic history.

B N=1 3

v

c

(J I

Heterogeneous strain in the area west of Gilbert Lake has produced numerous metre-scale zones of protomylonite and mylonite. The S, fabric is locally mylonitic (Figure 4). Distinct strain gradients may be observed locally, w ith protomylonite grading into mylonite. Mylonites are most obvious in leucocratic granodiorites considered to be syn-metamorphic melt rocks (Ashton et al., 1997); however, it is likely that all rocks have been subjected to high strain . The absence of obvious mylonitic fabrics in other units may be due to their more competent nature during conditions of high stress.

The mylonitic rocks are typically S-L tectonites, but a lso include some highly stretched L-S tectonites (Hatcher, 1995). The L, linear component is a penetrative stretching lineation plunging gently to moderately (5° to 40°) north to northeast (Figure SC

N n=14 --~

~

0 VII

N n=24

Oo III

Figl4re 3 (contitlued).

Saskatchewan Geological Survey 105

Figure 4 - Feldspar beading in a migmatitic and mylonitic Kranodiorite. Leucosomal layen clearly define the S , regio11alfoliation; western shore oftl,e "central" Reindeer River area.

and D). Although generally associated with mylonites, L1 is a lso common in rocks that lack a mylonitic foliation . It is typically defined by stretched and smeared quartz and plagioclase grains, generally in leucosome (Figure 6), but is also defined by dimensional preferred elongation of hornblende grains in paleosome or homblendic melts within non­mylonitized rocks. Injected leucosome is commonly well lineated. High strain seems to be focussed in syn­metamorphic melt rocks (leucocratic granodiorite) suggest ing that these layers may have been lacking in bulk strength, likely due to e levated temperatures.

Rare 8-porphyroclasts in the mylonitic rocks generally indicate a reverse-dextral shear sense (Fig ure 7) (Ashton et al., 1997) suggesting south- to southwest­verging tectonic transport (Ashton et al., 1997), although such tectonic indicators may have been reoriented during subsequent deformation.

b) Second Deformational Event (D2)

All rocks have been affected by 0 2 deformation with the exception of discordant pegmatite/ap lite dykes and quartz veins. 0 2 exists as tight to isoclinal fold ing of the S1 fol iation . It is unclear whether such fo lds formed late in the D1 event or represent a d istinct 0 2 event, which has been assumed in this study.

F2 fo lds have north-northwest to north-northeast striking axial surfaces, which dip moderately either to the west or east and plunge north-northwest to north­northeast. These orientat ions are attributed to later refo lding. No S2 fabric was recog nized altho ugh it is likely that any coeval foliation would be subparallel to S1, except in the F2 hinges, d ue to the iso~l inal_nature of the folds. It is likely that 0 2 is correlative with the second isoclinal fo lding event suggested by Lewry et al. ( 1990).

c) Third Deformational Event (03)

All the rocks have been affected by 0 1 deformation, except for late pegmatite and aplite dykes and quartz veins. The F3 fo lds, defined in all cases by refolding of

/ 06

the regional fol iation, are typically close (30° to 70° interlirnb angle) to tight (0° to 30° interlimb angle) (Hatcher, 1995), with 30° to 60° ang les most common (Figure 8). Fl folds are generally overturned to the west but in rare cases remain upright. Axial p lanes strike north to north-northwest (commonly north-northwest, west of Gilbert Lake) and generally dip moderately to steeply (45° to 60°) east to east-northeast at both mesoscopic and macroscopic scales (but range to upright). Axes generally plunge gently, north­northwest to north-northeastward (Figures 3 B and SA) with rare east- and southeast-plung ing axes, probably resulting from later refolding.

Structural domains I and V provide good examples of macroscopic F3 axial traces that trend northwest to north-northwest (Figure 2). Equal area stereonet projections of the axial planes of F3 minor folds in these domains illustrate this orientation (Figure 9A). Figure 3A d isplays equal area stereonets of S 1 foliat ion in each of the nine structural domains. The poles to the great circle girdles shows that Fl axes plunge gently north to north-northwest, w ith north-northwest plunges more common west of G ilbert Lake. The north­northwest to north-northeast p lunge is illustrated by equal area stereonet plots of the axes of Fl minor folds in domains I and III (Fig ures 5A and 58) and V and VII (Figure 3 B). Southeast-plunging axes are rare.

An S3 fabric, typically in the form of a quartz flattening foliation (Ashton el al., 1997), is developed in an axial planar orientation relative to F3 minor folds (Figure 10). Thin sections of biotite-rich rocks near Mokoman Lake (Harvey, this volume) display reoriented biotite grains defining the weak S3 fabric . A rare S/ S1

intersection lineation is locally developed coax ial to F 3

fold axes. Rare mineral lineations, defined mainly by hornblende, are also coaxial to F3 fo ld hinges.

The orientation ofF3 minor fo ld axes is generally close to that of the L 1 stretching lineation, lead ing to uncertainty in distinction of the latter from LJ lineations. The L1 lineations are represented by pronounced quartz and feldspar smearing and rodding and are best developed in 0 1 high-stra in (mylonitic) zones. Since the 0 1 mylonites are refolded by F3, it follows that L1 stretching lineations shou ld also be folded by F3 and should not be coaxial. Equal area stereonet projections of L 1 and F 3 axes in structural domains I and Ill (areas in which L1 is most strong ly developed) suggest that the two linear features are sim ilar but not coaxial (Figure 5). Attitudes of the f-'; axes show significant scatter, with some axes plunging to the southeast. L 1 consistently plunges to the northeast to north-northeast, but never to the southeast.

The abundance of L1 lineations is far greater west of G ilbert Lake, in the area of high strain attributed to 0 1•

There is no corresponding evidence of variation in the intensity of F 3 folding providing furth er evidence that the stretching lineation is re lated to D1 rather than 0 3•

The broad similarity in orientat ion o f L1 and F 3 may be due to rotational transposition o f L1 toward the F3 ax is during D3 refolding but a more likely possibil itx i~ that the F3 fo ld axes were superimposed on a pre-existing

Summmy of /nvestigmions 1999. Volume I

n=23 B N n=26

0 I III

c N n=38 D

I III

Figure 5 - Equal urea stereonet projection.5 of FJ axes versus stretching lineations. A) and B) represent F_1 axes in structural domains I anti lll. Note the large scatter of data and the presence of southeast-plunging axes. C) and DJ represent L , lineations for structural domains I and Ill. Note the consistent north to northeast plunge.

regionally lineated crust and simply mimicked that line of weakness.

d) D1-Di/D3 Fold Interference

Refolding of D1 and/or 0 2 structures by 0 3 has produced both type 2 and 3 fold interference patterns (Ramsay, 1967). A macroscopic type 2 fold interference pattern, expressed as a boomerang pattern, is located in the Gilbert Lake area of structural domains IV and V (Figure 2). This structure is difficult to interpret due to a lack of outcrop control (Gilbert

Saskatchewan Geological Survey

Lake partially obscures the structure) but it is clear that the later fold set responsible for this pattern is F3. Since closures of the early folds are defined by the S I foliation, they are assumed to be part of a 0 2 folding event.

Mesoscopic type 3 fold interference patterns were also observed in the Reindeer River area (Figure 11 ). It is unclear whether the isoclinal folds, refolded by F3,

represent F, or F2. Although no macroscopic examples were observed, they do occur farther east in the Scimitar Lake area (Ashton et al., l 996b).

I ()7

Figure 6- Quartz and feldspar roddi11g and nneari11g represe11t the l I stretching li11e11tio11. Note that the lineation is better developed in the leucosome; we.ft shore of "lo11g Bay", soutliwestem Reindeer River.

Figure 7 - o-porphyroclasts in my/011itized leucocratic granodiorite indicating dextral .rhear; from large lake east of Reindeer River in structural domain JI/.

Figure 8 - F1 folds in migmatitic, il1lermediate volcanic rocks. Folds are best defined hy leucosome; southwestem Reindeer River.

108

The types of fold interference patterns provide clues as to the initial geometry of the f 1 and F2 fold sets. Type 2 interference patterns form when near upright folds (F, folds are moderate to upright) deform gently dipping. overturned to recumbent folds with axial planes striking perpendicular to the later folds and whose fold axes plunge at a sim ilar orientation to those o f the earlier set (Ramsay, 1967). Type 3 interference requires that near upright folds deform an ear lier set which has reclined axial p lanes and whose strike is nearly parallel to that of the former (Ramsay, 1967). The o lder fo ld sets, interacting with F1, would requ ire axial planes that were nearly normal to each other. in order to produce both type 2 and 3 interference, under ideal, end member conditions. Thus, it is probable that 0 2±0 1 folds were gently dipping and oriented broadly east-west.

e) Fourth Deformational Event (04)

All rocks were affected by the 0 4 event. The F4 minor fo lds, which deform all previous structurns, are coaxial with regional folds of the same generat ion. They are generally upright structures with open to gentle interlimb angles. Fo ld hinges plunge gently to the northeast and axia l planes are northeast-southwest striking although dips vary from steeply northwest to steeply southeast (Figure 98).

Several macroscopic F4 folds with axial traces striking northeast to east-northeast are recognizable in the Mokoman (Knife) Lake- Reindeer River area (Figure 2). In structural domain Ill (Figure 3C), they gently refold S1; in other areas (e.g. structural domain VIII) they also refold regional F 3 structures.

In structural domains I, II, Ill , IV, VIII , and IX great circle girdles to the S1 foliation illustrate the northeast to north-northeast plunge of F4 fold axes (Figure 3A). The orientation of the axes of F 4 minor folds in structural domains I and Ill (domains w ith well-defined regional F4 folds) also show a generally northeast plunge (Figure 3C).

F4 folds are defined by the gentle warping ofS1 and more rarely gentle refolding of F J fo lds, commonly resulting in type I fold interference patterns. At macroscopic scale, this refolding is expressed as rotation of older structural trends from north-northeast in the east, to northwest in the west (Figure 2), as for example the change in orientation of F 3 axes from north-plunging east of Gilbert Lake, to north-northwest p lunging west of Gilbert Lake (Ashton et al., 1997). The northwest rotation of F.1 axes and the z-asymmetry of F 4 minor folds is consistent with the area's location on the z-l imb of a megascopic F 4 anti form (Figure I).

A suite of pegmatite and aplite dykes, discordant to the regional foliation, are affected by 0 4 deformation. The dykes generally strike northwest-southeast and dip steeply to the southwest, but strike may vary from east­west to north-south (Figure I 2). These dykes are usually rectiplanar, but in rare cases they appear to be gently folded by F4, although not to the same degree as the surrounding rock. The northeast-southwest-striking

Summa,y of Investigations /999. Volume I

A N ~-------------. n=28 N n=12

I

B N n=25 1--,=--~

N n=15 ----------~

()

------III VII, VIII, IX Figure 9 -A) Equal area stereonet projections of the poles to F1 axi"/ pla11es in structural domaifls I and V. The poles show that the strike of F1 axial planes ranges from north to 11orthwest and dipping moderately to the northeast. B) Equal area stereonet proj ections of the poles to FJ axial planes i11 structural domains /I/and VI/-IX. The poles show that the strike of F, axial pla11es is generally northeast to east-northeast aml dip direction i.{ either northwest or .,·outheast at steep angles.

axial p lanes of most F4 folds implies a northwest­southeast direction of maximum shortening. The regional orientation of the dykes is consistent with the probable orientation of brittle fractures resulting from such shortening (Hatcher, 1995) suggesting that dyke emplacement was contro lled by the 0 4 stress system. Northwest-southeast-striking dykes likely fi ll extension fractures related to 0 4 shorten ing. North-south and east-west dykes are likely fi ll ing a conjugate set of strike-s lip fractures which are consistent with the orientation expected during 0 4 shortening. The consistent orientation and folding of the dykes by F.

Saskatchewan Geological Survey

suggests that the dykes may have been intruded during late stages of the o. event. Thus, age dat ing of these dykes would constrain the age of the 0 4 event.

f) D/ 0 4 Fold Interference

Gentle refolding of 0 3 by 0 4 structures is common. Rarely, this produces macroscopic type I dome and bas in interference patterns, such as the large type I basin structure in structura l domain II (Figure 2). Relative orientation of F\ and F 4 ax ial surfaces (upright and at high angles to each other) is likely to produce

/09

Figure JO - F_, fold with a we/I-developed axial planar fabric. Note that SJ foliation is best developed in the /eucosomal layers; from large lake east of Gilbert lake in structural domain VII.

Figure I I - F1 (?) folds refolded by FJ and displaying a type 3 fold interference pattern. Note the characteristic hook pattern in the core of the bottom fold; west shore, 11ortheastern Reindeer River.

this pattern (Hatcher, 1995). Good examples of gentle refolding of F3 folds by F4 were also observed at mesoscopic scale (Figure 13).

g) Fifth Deformational Event (D5)

The 0 5 defonnation is expressed by map-scale fracture lineaments visible on air photos and regional satellite images. The linearity, continuity and discordance of these features suggest that they post-date the folding.

There are at least two sets of fracture lineaments in the Mokoman (Knife) Lake-Reindeer River area. One set strikes northwest to west-northwest. One good example is the lineament extending from Scimitar Lake to the Reindeer River (Figure 2). The second, north- to northeast-striking fracture set is subparallel to the Tabbemor Fault and probably represent splays from this regional structure (Ashton et al., 1997). A long, linear bay in the lake east of Gilbert Lake probably be longs to this set (Figure 2). Johnston ( 1984) suggested that linear sections of the Reindeer River may also be controlled by this set.

110

..

. .

N . . . . .

. . . . . ,•. . . ··~·· ... : : . ....... ..

. .

• . . ..

. . . . . . .

n=103

Figure 12- Eq11al area stere011et projection of the poles to pegmatite dykes and quartz veins. Dykes generally strike east-west to 11orth-south.

Figure 13- A (top) An intermediate structure between types I and 1 f old interference end members. Here an FJ fold is refolded by an F,fold; east shore of the central Reindeer River. B (bottom) Type I fold interference due to F, refolding of FJf olds. Note the FJ closure in the leucosome left of the scale card; east shore of the central Reindeer River.

Summary of Investigations 1999, Volume I

Both sets of lineaments are believed to mark steep faults but there is no evidence of any significant offset across these features at the I :20 000 scale. Such offset, if any, is likely to be no more than a few tens of metres (Ashton et al., 1997). Evidence from the Knife Lake property suggests that the northwest-striking set displays dextral offset (Ashton et al., 1997). The north to north-northeast set, if part of the Tabbernor Fault system, may have sinistral offset (c.f. Ashton et al., 1997; Tran, 1997; Hartlaub et al., 1997). The orientation of the fault sets and their related offset may suggest that they are conjugate (Hatcher, 1995). A conjugate set with these orientations is consistent with northwest-southeast shortening and may relate the set to 0 4 defonnation. As the lineaments are discordant to F4 , folds they probably represent the final stages of 0 4

shortening.

3. Discussion and Conclusions

The five defonnational events documented in the Mokoman (Knife) Lake- Reindeer River area can be interpreted in the context of the plate tectonic history of the Trans-Hudson Orogen. 0 1 is characterized by isoclinal folds whose axial planar fabric represents the regional S, foliation and heterogeneous high strain, particularly in the western portion of the map area. The extensive mylonitic S1 fabric there, may be broadly correlative with mylonites of the Pelican Decollement Zone, south of the area (Hartlaub et al., 1997). Kinematic indicators suggest south to southwest, reverse-dextral tectonic transport, consistent with documented transport direction across the Pelican Decollement Zone (Lewry et al. , 1996; Ashton et al., 1997). These shear zones may represent higher level splays coeval with and rooting in the Pelican Decollement Zone (Ashton et al., I 997), relating 0 1 to collision of the Glennie- Flin Flon protocontinent with the northeast convergent Saskatchewan craton prior to 1.835 Ga (Lewry et al., 1996).

Outcrop relationships of migmatitic rocks in the western part of the study area and the growth of high temperature minerals (sillimanite) within the plane of S,, suggest upper amphibolite facies conditions of metamorphism during 0 1• Stromatic migmatites appear to have fonned by injection of anatectic melt along S, foliation planes. Neosome in these migmatites generally appears to have been affected by D, strain and commonly the L 1 stretching lineation is more prominently developed in these layers than in the surrounding paleosome, even where both components are of similar composition . This suggests that the neosome may have been hot or partially molten at the time of deformation allowing these layers to focus the strain.

In the eastern part of the area, migmatitic neosome seems to be mostly of in situ derivation. West of Gilbert Lake, however, injection migmatites become more abundant and are generally dominant, although in situ neosome persists. This increase in injected neosome correlates broadly with the documented increase in D, strain and suggests the two features may

Saskatchewan Geological Survey

be related. Injected neosome might have used structural discontinuities (i .e. shear zones) as conduits to intrude the country rocks. An example is leucocratic granodiorite, the most commonly mylonitized rock unit, which are interpreted as syn-metamorphic melt rocks by Ashton et al. ( 1997). If th is is the case, minimum melting temperatures (upper amphibolite facies) are broadly synchronous with shearing (defonnation) related to the collision between the Saskatchewan craton and the Glennie-Flin Flon protocontinent. These high-grade conditions are thought to persist until 0 4 _ at which time pegmatite and aplite dykes, whose magmas are of metamorphic origin, were emplaced.

The 0 2 event comprises a second set of isoclinal folds and may or may not be a distinct event relative to 0 1

making it difficult to relate to regional tectonic models. It is likely that this folding event is a result of continued deformation due to the collision between the Saskatchewan craton and the Glennie- Flin Flon protocontinent, perhaps being related to post­collisional shortening(?).

0 3 is characterized by upright to overturned folds with north- to northwest-striking axial surfaces and a weak axial planar fabric. These refold 0 1 and 0 2 structures resulting in type 2 and 3 fold interference patterns. The regional context of 0 3 structural development is uncertain. It has been argued that this north-south folding is related to initial interaction of the Superior craton with the newly welded and still defonning Saskatchewan craton and Glennie- Flin Flon protocontinent (Tran, 1997). The resolution of these two stresses is thought to have produced the north­south geometry of the F3 fold set. Tran ( 1997) suggested that early interaction of the Superior craton with the Saskatchewan craton and Glennie-Flin Flon protocontinent and F3 folding likely occurred between 1.82 and 1.805 Ga.

0 4 is characterized by upright folds with northeast­southwest striking axial surfaces. In the west, these folds result in the counterclockwise rotation of the previous structural fabrics to the northwest. 0 4 is thought to be related to post-collisional shortening following post 1.8 Ga (Lewry et al.,1996) terminal collision of the Superior craton . Discordant dykes of late 0 4 age may be used to constrain the age of 0 4, but accurate age dates are not available for these rocks. Similar dykes have been dated at I . 77 Ga (Bickford et al. , 1987). It is important to note that regional F4 fold axial traces consistently strike northeast (Figure 1) whereas, in this area, axial traces approach easterly strikes (Figure 2). This is interpreted as being a local phenomenon.

0 5 is characterized by macroscopic lineaments, believed to be steep faults, of at least two orientations, striking northwest to north-northwest and north to north-northeast. This faulting postdates 0 4 folding, as indicated by the linear nature of the faults. The orientation of the two sets of lineaments and the related sense of inferred displacement suggest that these faults

JI I

may be conjugate and related to the final stages of 0 4 shortening.

4. Acknowledgments This study fonned the basis of a B.Sc. Honours thesis completed at the University of Regina. The assistance and d irection provided by Dr. K.E. Ashton and Dr. J.F. Lewry, in the field and as thesis co-supervisors, was greatly appreciated.

5. References Ashton, K.E., Card, C.D., and Harvey, S.E. (1997):

Geology of the Mokoman (Knife) Lake-Reindeer River area: The Scimitar Complex and its relationship to the Glennie Domain; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p55-64.

Ashton, K.E., Hartlaub, R.P., Therens, C., and Legault, A. ( I 996a): The Scimitar Complex- Kisseynew Domain boundary in the Wintego Lake area (part of 63 M-1 O); in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p219-37.

Ashton, K.E. , Therens, C., and Legault, A. ( I 996b): Geology of the Scimitar Lake area (part of63M-15), east-central Scimitar Complex; in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p22-28.

Bickford, M.E., Van Schmus, W.R., Collerson, K.D., and Macdonald, R. ( 1987): U-Pb zircon geochronology project: New results and interpretat ions; in Summary of Investigations 1987, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 87-4, p76-79.

Fuh, T.M. ( 1979): Geology of the Gilbert Lake West Area; Sask. Dep. Miner. Resour., Rep. 187, 17p.

Hartlaub, R.P., Ashton, K.E., and Lewry, J.F. ( 1997): Geology of the Ourom-lskwatam lakes segment of the Churchill River: Boundary relat ions between the Scim itar Complex, Kisseynew Domain, and Glennie Domain; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p 65-71.

Hatcher, R.D. ( 1995): Structural Geology: Principles Concepts and Problems; 2nd ed., Prentice Hall, Englewood Cliffs, New Jersey, 525p.

Johnston, W.G.Q. (1984): Geology of the Royal Lake and Laird Lake (east) areas; Sask. Energy Mines, Open File Rep. 83-1 , 80p.

Lewry, J.F., Lucas, S., Stem, R., Ansdell, K., and Ashton, K. ( 1996): Tectonic assembly and

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orogenic closure in the Trans-Hudson Orogen; in Program with Abstracts, GAC-MAC Annual Meeting, May 1996, Winnipeg, v2 I, pA56.

Lewry, J.F., Thomas, O.J., Macdonald, R., and Chiarenzelli, J. ( 1990): Structural relations in accreted terranes of the Trans-Hudson Oro gen, Saskatchewan: Telescoping in a collisional regime?; in Lewry, J.F. , and Stauffer, M.R. (eds.), The Early Proterozoic Trans-Hudson Orogen of North America, Geol. Assoc. Can., Spec. Pap. 37, p75-94.

Macdonald, R. ( 198 1 ): Compilation bedrock geology: Pelican Narrows and Am isk Lake areas (NTS 63M, 63L, part of 63N and 63K): Preliminary geological map and report; in Summary of Investigations 198 1, Saskatchewan Geological Survey, Sask. Miner. Resour., Misc. Rep. 81 -4, p 16-23.

Mehnert, K.R. ( l 968): Migmatites and the Origin of Gran itic Rocks; Elsevier Publish ing Company. Amsterdam, 393p.

Pearson, D.E. ( l973): The Geology of the Scimitar Lake area (east half), Saskatchewan; Sask. Dep. Miner. Resour. , Rep. 156, I 7p.

Ramsay, J.G . ( 1967): Folding and Fracturing of Rocks; McGraw-Hill , New York, 568p.

Syme, E.C. ( 1990): Stratigraphy and geochemistry of the Lynn Lake and Flin Flon Metavolcanic Belts, Manitoba; in Lewry, J.F., and Stauffer, M.R. (eds.), The Early Proterozoic Trans-Hudson Orogen of North America, Geol. Assoc. Can., Spec. Pap.37,pl43- 16 1.

Tran, H. T. ( 1997): Structural relations and thennotectonic history of the Med icine Rapids­Grassy Narrows area, northern Saskatchewan, Canada; unpubl. M.Sc. thes is, Univ. Regina, 226p.

Winkler, H.G .F. (1974): Petrogenesis of Metamorphic Rocks; 2nd ed., Springer-Verlag, New York, 298p.

Summary of lnvestlga1ions 1999. Volume I