The Sudbury Basin, the Southern Province, the Grenville Front, and the Penokean Orogeny

STEPHAN J. BROCOUM* IAN W. D. DALZIEL** Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964

ABSTRACT The Sudbury Basin in the Canadian Shield has been proposed as a meteorite impact site subsequently deformed by en- dogenic tectonism. Detailed study of the structural geology strengthens this hypothesis and strongly suggests that the deformation of the basin was coeval with major folding and flattening (2.0 to 1.6 b.y. ago) of the rocks of the eastern Southern province and the northwesternmost Gren- ville province. The structural geometry indicates that most of these rocks have a similar strain history. Finite-strain analysis of deformed concretions within the Sudbury Basin sug- gests that originally it was almost circular in outline. Key words: structural geology, deformation, finite-strain indicators, folds, impact features, meteor crater, orogeny, Precambrian, structural analysis, tectonic Figure 1. Geological setting of the Sudbury Basin. fabric. sublayer (Souch and Podolsky, 1969), 1972) or suevite breccia (Peredery, 1972) INTRODUCTION which apparently also intrudes the country has increased the number of workers who The Sudbury Basin, Ontario, is situated rock as radial and concentric dikes called believe that the Sudbury Basin was formed just north of Lake Huron near the intersec- offsets (Fig. 2; Naldrett and others, 1971). at least in part by the impact of a hyper- tion of the Superior, Southern, and Gren- The sublayer and offsets of the irruptive velocity bolide. ville provinces of the Canadian Shield (Fig. are, at present, the world's largest single Geologists who argue against the meteor- 1). The basin is 60 km long and 27 km source of nickel, as well as an important ite impact hypothesis interpret the breccia- wide. It is topographically and structurally source of copper, cobalt, iron, platinum, like Onaping Formation as an ash flow or defined by the Nickel Irruptive, which con- and 11 other elements. tuff (Stevenson, 1972). They emphasize the sists of a lower (outer) layer of augite- The origin of the Sudbury Basin has long facts that the Sudbury Basin is not circular norite, an upper (inner) layer of been a topic of debate, increasingly so since (Fig. 2), that it occurs on a domal structure granophyre, and a "transition zone" of Dietz (1964) proposed that it was formed and appears to be associated with a re- quartz gabbro between the two (Naldrett by meteorite impact. The presence of shat- gional positive gravity-magnetic anomaly at and Kellerud, 1967; Naldrett and others, ter cones in the surrounding country rocks the intersection of major fault systems in 1970, 1971); it is believed to have the shape (Dietz and Butler, 1964; Guy-Bray and the Canadian Shield (Card and Hutchinson, of an asymmetric lopolith (Popelar, 1972). others, 1966; Dietz, 1968, 1972), evidence 1972; Card and others, 1972a; Popelar, At the base of the augite-norite, there is a of shock metamorphism in the Onaping 1972; Fig. 1), and that the entire region discontinuous zone of inclusion and Formation at the base of the section within may represent a special metallogenic prov- sulfide-rich igneous intrusions known as the the basin and in the country rocks north of ince in which the Sudbury Irruptive is only the basin (French, 1967, 1968a, 1968b, one ore-bearing element (Card and Hutch- 1970; Fig. 2), and the interpretation of the inson, 1972). * Present address: Department of Geology, Texas Onaping as a "fall-back" breccia (Dietz, The present study was undertaken to in- Christian University, Fort Worth, Texas 76129. 3 * Also of: Department of Geology, Columbia Uni- 1964; French, 1967, 1968a, 1968b, 1970; vestigate the internal structure of the Sud- versity, New York, New York 10027. Guy-Bray, 1971; Dence and Guy-Bray, bury Basin and its relation to the apparently

Geological Society of America Bulletin, v. 85, p. 1571-1580, 4 figs., October 1974

1571

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/10/1571/3418075/i0016-7606-85-10-1571.pdf by guest on 27 September 2021 Kl Olivine-Diabase Dikes (generalized) E Chelmsford Fm Onwatin Fm [ÔU Onaping Fm nn m Norite Nipissing Diabase E3 Creighton (CG) and Murray (MG) Granites • Mississagi Fm McKim, Ramsay Lake and Matinenda Fms Mafic and Felsic Volcanlcs

Bedding, uninverted Bedding, overturned Bedding, facing direction unknown Layering First Folds; upright, overturned Second Folds, overturned Grenville Front, transitional Grenvilie Front, faulted Faults

Figure 2. Generalized geologic map of the Sudbury Basin and eastern Southern province. After Card (1969), with modifications.

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complex structural geometry and tectonic larly demonstrated by concretions in the cannot be sustained. The paleo-flow indi- history of the surrounding rocks. Chelmsford Formation, which [with the ex- cators of Cantin and Walker were likely ro- ception of misleading locally variable tated toward and concentrated near the THE SUDBURY BASIN shapes due to coalescence of adjoining con- long axis of the basin during the The deeper structure of the Sudbury Ir- cretions and (or) preferential development northwest-southeast shortening of the ruptive, including possible feeders, is un- in certain beds] are always flattened in the basin. Rotation of linear and planar struc- known. The sedimentary rocks of the foliation surface and therefore must have tures during strain are well documented Whitewater Group that infill the basin form been originally spherical or nearly so. If (Flinn, 1962; Ramsay, 1967, p. 461-517). a doubly plunging synclinorium. The outer they were not originally nearly spherical, Removal of the effects of the strain would surface of the underlying irruptive plunges they would not always be flattened in the result in a much weaker preferred orienta- steeply southwestward at the northeast foliation surface (Ramsay, 1967, p. tion of the paleo-flow indicators but would closure and moderately northeastward at 204-205, and Figs. 5-20 to 5-22). The bed- still suggest a source of the Chelmsford the southwest closure (Speers, 1957). The ding and the foliation pass through them Formation from the northwest quadrant. northwest limb dips gently to moderately without deviation. Thus, these bodies can As mentioned above, all the rock units of southeastward. The more steeply dipping be used as finite-strain ellipsoids reflecting the Whitewater Group have gradational southeastern limb is locally thrust and over- the deformation undergone by the and conformable contacts and the same tec- turned northwestward (Naldrett and Chelmsford Formation. Finite strain tonic and metamorphic history. others, 1971; Card and Hutchinson, 1972; analysis (Brocoum and Dalziel, 1974) sug- Metamorphism was limited to lowest Fig. 2). gests that the Chelmsford was shortened greenschist facies and to local contact ef- The Whitewater Group consists., from approximately 30 percent of its original fects of the Irruptive (Card and Hutchin- bottom to top, of the Onaping Formation, a length normal to the cleavage, and ex- son, 1972; Rousell, 1972). tufflike breccia unit with little or no dis- tended 10 percent subhorizontally and 40 Finally, over-all fold vergence, the cernable mesoscopic stratification; the On- percent subvertically in the plane of cleav- asymmetry of the basin, and the decrease in watin Formation, a thinly bedded car- age (assuming no change in volume). The the amount of strain toward the northwest bonaceous slaty shale; and the Chelmsford axial ratio on a horizontal surface of the de- indicate compression from the south and Formation, a carbonaceous and arenaceous formed concretions varies between 1.7 to 1 east to account for the deformation that proximal turbidite (Rousell, 1972; Cantin and 1.8 to 1, somewhat less than that for must postdate the emplacement of the and Walker, 1972; Fig. 2). The rare un- the Nickel Irruptive (approximately 2.2 to 2.0-b.y.-old Irruptive (Gibbins and faulted contacts exposed between the units 1). This means that the Sudbury Basin (or at McNutt, 1972; Gibbins, 1973, personal are conformable and gradational. No rocks least the depositional area of the commun.) and predate the northwest- correlative with the Whitewater Group Chelmsford Formation) may have been al- southeast-trending olivine-diabase dike have been positively identified outside the most circular prior to deformation. swarm that cuts the basin and its structures basin. The Onaping Formation and the (Figs. 1, 2). The true age of the olivine- The most prevalent imposed structural granophyre layer of the South Range have a diabase dikes is still uncertain, but the most element in the Sudbury Basin is a slaty-type strong lineation within the foliation surface recent date is about 1.46 b.y. B.R, based cleavage which strikes east-northeast paral- (Fig. 3). This lineation is formed by elon- on the Rb-Sr whole-rock isochron method lel to the long axis of the basin and dips gated minerals and rock fragments. It sug- (Gates and Hurley, 1973). The Irruptive steeply but variably (Fig. 3). The grains are gests that the finite deformation ellipsoid in was formerly regarded as 1.7 b.y. old (Fair- flattened in the plane of this cleavage that is those rocks was triaxial with a steeply bairn and others, 1969), and the dike strongly developed in the southern two- northwesternly plunging axis of maximum swarm as 1.2 b.y. to 1.66 b.y. old (Van thirds of the basin but absent in the North finite extension. Finite-strain analysis Schmus, 1965; Fairbairn and others, 1969; Range Nickel Irruptive and the adjacent (Brocoum and Dalziel, 1974), using the Gates, 1971,1972). Onaping Formation (Fig. 3). Folds in the rock and mineral fragments in the Onaping Chelmsford Formation are open and up- Formation, suggests that it was shortened THE SOUTHERN PROVINCE right. The foliation is axial planar to them, approximately 40 percent normal to the The eastern part of the Southern province and its intersection with bedding is sub- foliation, extended 140 percent parallel to (eastern Penokean fold belt), immediately horizontal, indicating that the associated the lineation, and shortened 30 percent south of the Sudbury Basin, consists of a folds plunge very gently northeast and normal to the lineation in the foliation wedge of metasedimentary and basal southwest (Figs. 2, 3, 4D). The slaty cleav- plane (assuming no change of volume). metavolcanic rocks as much as 10,500 m age of the poorly exposed Onwatin Forma- Whether the embayment at the eastern thick, the Huronian Supergroup. It was de- tion is clearly the same as the foliation in end of the Sudbury Basin (Fig. 2) is an orig- posited unconformably upon the Archaean the Chelmsford turbidites. The Whitewater inal feature of the basin is not known. In basement (>2.5 b.y. old) that is exposed Group and the Irruptive have undergone the vicinity of Val Therese, the immediately north of the basin, and in- the same deformational history. Structural east-northeast—striking axial-surface folia- truded by the Nipissing diabases 2.15 b.y. variation can readily be ascribed to differ- tion of the southwestern part of the basin ago (Figs. 1 and 2; Van Schmus, 1965; ences in location and rheologic behavior. bifurcates to strike north-northeast and Fairbairn and others, 1969). The lowest For instance, in the South Range, the southeast, axial planar to the two folds on unit, known as the Elliot Lake Group granophyre is highly deformed, and the either side of the embayment (Fig. 3). If the (Table 1), consists of mafic volcanic and in- augite-norite is only locally foliated; but in embayment was an original feature of the terbedded sedimentary rocks (Stobie and the North Range, both are virtually unde- Irruptive, it has since been highly modified Elsie Mountain Formations), felsic vol- formed. by strain. There is no suggestion that more canics (Copper Cliff Rhyolite), distal to No preferential grain elongation is ap- than one period of deformation was in- proximal turbidites (McKim Formation), parent in the foliation of the Chelmsford volved in producing this conjugate struc- and quartzites (Mississagi and Matinenda and Onwatin Formations, and this suggests ture. Formations). The upper three units (Hough that the finite deformation ellipsoid in those The suggestion that an originally approx- Lake Group, Quirke Lake Group, and units is within the field of flattening with imately circular Sudbury Basin was de- Cobalt Group) consist of gross repetitions the axis of maximum shortening strain formed into a more elongate shape prior to of conglomerate, pelite, and orthoquartzite. normal to the foliation (Ramsay. 1967, p. the deposition of the Chelmsford Forma- It has been suggested that each represents a 136, Fig. 4-11). This flattening is spectacu- tion (Cantin and Walker, 1972, p. 100) glacial cycle (Frarey and Roscoe, 1970;

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TABLE 1. FORMATIONS OF THE HURONIAN SUPERGROUP moderately, northeast and southwest, form- IN GENERAL STRATIGRAPHIC ORDER* the rocks of the eastern Southern province, ing elongate basins and domes often clearly wi.h the exception of the volcanics at the

Cobalt Group outlined by the essentially concordant in- base of the Huronian succession and the Bar River Formation (sandstone) trusions of Nipissing diabase and trending Creighton and Murray granites, have the Gordon Lake Formation (siltstone) Lorrain Formation (sandstone) parallel to the Sudbury Basin (Fig. 2). Be- same strain history as those of the Sudbury Gowganda Formation (conglomerate, sandstone, cause most of the rocks involved are mas- siltstone) Basin, and their structural geometry sug- Quirke Lake Group sive quartzite (Mississagi Formation) and gests that they were deformed by strains Serpent Formation (sandstone) diabase, the foliation is not everywhere well ranging from pure flattening to pure plane Espanola Formation (calcareous siltstone, limestone) Bruce Formation (conglomerate) developed. However, it becomes more strain (that is, k-values ranging from 0 to 1; Hough Lake Group prominent toward the Grenville Front, Flinn, 1962; Ramsay, 1967, p. 137). Mississagi Formation (sandstone) Pecors Formation (siltstone) where the Nipissing diabase outlines large The Huronian rocks of the Sudbury dis- Ramsay Lake Formation (conglomerate) isoclinal folds in the Mississagi Quartzite, trict are locally highly brecciated on a mi- Elliot Lake Group McKim Formation (graywacke, siltstcne) and the foliation, now of mylonit:c charac- croscopic, mesoscopic, and macroscopic Matinenda Formation (sandstone, corglomerate) ter, is still axial planar to these folds (Figs. scale (there are breccia blocks as much as Copper Cliff Formation (mafic and f'elsic volcanics) Elsie Mountain-Frood—Stobie Formal-ions (mafic 2, 3, 4D). 0.3 km across). These singular breccias are volcanics and graywacke) Only near the Grenville Front, where referred to as Sudbury or Sudbury-type * Modified after Card, 1971a, 1971b. large Z-shaped asymmetric folds with an breccias (Speers, 1957; Card, 1965, 1968). associated (but localized) east-north- According to the impact hypothesis (Dietz, east-trending axial planar foliation deform IS64) they, like the shatter cones, resulted Card and others, 1972a and 1972b; both limbs of the isoclinal structures out- from the passage of shock waves through Church and Young, 1972). lined by the diabase sills is there evidence of the target rock. It is possible that disorien- The Elliot Lake Group, from its base refolding (Grant and others, 1962, map tation and uplift of large blocks of the through the McKim Formation, forms a 2017; Brown, 1968, PI. 1; Dalziel and Huronian during brecciation and heaving, nearly vertical south-facing homocline others, 1969; Fig. 2). Elsewhere in the perhaps due to impact, may explain the ir- along the southeast margin of the Sudbury Southern province, younger crenulation regular bedding-foliation relations ob- Basin from the vicinity of Garson Junction cleavages, that in places form conjugate served in the homocline south of the basin. in the northeast to Worthington in the sets, provide the only evidence of another After the event that caused brecciation, southwest (Figs. 2, 3, 4D). Folding in this ductile, but nonpenetrative, deformation. heaving, and uplift, the individual blocks part of the section is limited to a few minor Thus it appears that all the rocks of the had slightly differing attitudes, but gener- structures. Southwest of the basin, and west Sudbury Basin, and tie Huronian succes- ally they all faced south and had steep dips. of Worthington, there are folds in the Elliot sion of the eastern Southern province were When the foliation was imposed on these Lake Group (Figs. 2 and 3), and higher up affected by the same major deformational blocks with slightly varying attitudes, the the succession to the southeast, folds are event. result was the variable bedding-foliation re- present both north and south of the Murray Southwest of the Sudbury Basin, the lations described above (Figs. 4C, 4D). Fault (Fig. 1). The Irruptive was apparently Baldwin Antiform (Fig. 1), a major struc- Generally the main penetrative foliation emplaced in a breccia near the contact be- ture in the Huronian that appears to fold of the Sudbury Basin and the eastern South- tween the Huronian and the Archaean intrusions of Nipissing diabase (Thomson, ern province rocks cuts both the blocks of basement. It has been suggested that the 1952; Card, 1971a), has an axial planar the breccia and the surrounding matrix. homocline of basal Huronian rocks repre- foliation of the same character and attitude This relation agrees with the hypothesis sents the remnant of the upturned "collar" as that described in the rocks in and south- that the breccias were formed instanta- of a simple crater (Deitz, 1964) or of the east of the basin. Card and others (1972a, neously in time, as a result of impact, and central uplift of a deeply eroded complex 1972b) have maintained that major folds of prior to the deformation of the Sudbury crater 80 km in diameter (Dence, 1972), more than one generation, the earliest pre- Basin; this is best seen in the argillaceous both caused by meteorite impact. dating (Church, 1966) or accompanying McKim Formation where the foliation is a The most prevalent structural element (Church and Young, 1972) emplacement of slaty cleavage. However, Sudbury-type imposed on the Huronian rocks southeast the Nipissing diabases, are present in the breccias in the Creighton granite (Fig. 2) of the Sudbury Basin is a penetrative folia- Southern province north of Lake Huron. contain highly foliated granite blocks with tion due to flattening. It is similar in nature To us, the Huronian Supergroup near the the foliation randomly oriented. The matrix and attitude to the one described in the Sudbury Basin appears to be a succession is also foliated, though the foliation is not rocks of the basin (Fig. 3), and we see no folded only by one major event which post- as strong as that in the disoriented blocks. reason to doubt that they resulted from the dates intrusion of the Nipissing diabases The mafic volcanics at the base of the same deformational event. (2.15 b.y. ago) and predates the intrusion of Fluronian succession (Elsie Mountain or In the homocline at the base of the Huro- the olivine diabase dikes (1.46 b.y. ago) Stobie Formation, Fig. 2) and intruded by nian succession, the intersection of cleavage which cut across the structures of the east- the Creighton granite contain breccias with (foliation) and bedding is highly variable ern Southern province. The folds resulting a well-developed tectonic foliation ran- (Figs. 2, 3, 4D). The relation between the from this deformation are upward facing, domly oriented with respect to the foliated two surfaces in some places indicates an an- upright, or with steeply southeast dipping matrix. In some blocks, the foliation is tiform to the north and in others a synform axial surfaces (Figs. 2, 4D; also see section folded. (Fig. 4D). Yet the beds everywhere face C-D in Card and others, 1972a, p. 352). In In both these cases, a foliation was south. This seems to indicate that they had this area, they become tighter as the Gren- clearly imposed prior to brecciation. This a variable but steep attitude at the time the ville Front is approached, and, as men- can be explained by assuming more than foliation was imposed on them. Yet there is tioned above, only there are they affected one period of deformation, more than one almost no evidence of earlier tectonic fold- by macroscopic refolding. A downdip min- episode of brecciation, or both. Speers ing. If the beds had been affected by earlier eral elongation lineation like that in the (1957) and Card (1968) believed that folding, then they would not: all face south. Onaping Formation and granophyre of the Sudbury-type breccias were produced over In the rocks between the homocline and South Range of the Sudbury Basin is locally f. significant period of time, but those who the Grenville Front, the foliation is axial present in the axial surface foliation, par- support the meteorite impact theory assume planar to the folds present. The hinge lines ticularly in the core of the Baldwin An- that the breccias formed at one instant in of these folds plunge gently, and sometimes tiform and near the Grenville Front. Thus time (for example, Dietz, 1964, 1972;

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French, 1967, 1968a, 1968b, 1970, 1972; Supergroup metasediments occur axial surfaces trending almost east-west Dence, 1972; Guy-Bray, 1972). It is possi- (Wynne-Edwards, 1964, 1969; Krogh and (Warren, 1967; Brown, 1968; Dalziel and ble that compression from the southeast Hurley, 1968), in the northwestern part of others, 1969) appear to be the same age as started before the crypto-explosion event. the province adjacent to the Grenvilie some of the major second folds mapped in Another possibility is that the Creighton Front, there is evidence only of faulting, re- the Southern province adjacent to the granite and mafic volcanics represen t up- latively brittle deformation, and a thermal Grenvilie Front. Farther west into the lifted Archean basement with an older foli- event that "reset" the isotopic "clocks." In- Southern province, this period of deforma- ation than that imposed on the basin and deed, where the Grenvilie Front has been tion appears to be characterized by minor Huronian rocks. However, whereas pet- studied in the greatest structural detail near and sporadic crenulation cleavages which rologic similarity of the volcanics of the Sudbury, it appears that the structures im- appear unrelated to any major folds. Southern province and those of Archean mediately to the southeast of the front are Metamorphism to upper almandine- greenstone belts of the Superior province is the same age as those in the adjacent rocks amphibolite facies within the Grenvilie frequently noted (Robertson, 1971; Ros- of the Southern province to the northwest. province predates the earliest recognizable coe, 1971), the former are generally re- Work on the structural geology by Warren event (Brown, 1968; Dalziel and others, garded as an integral part of the Huronian (1967), Brown (1968), Dalziel and others 1969). However, metamorphism, from succession (Young and Church, 1966; Card (1969), Henderson (1972) and by the au- lower greenschist to lower almandine am- and others, 1972a). Also, the foliation in thors; and on the geochronology by Davis phibolite facies in the Southern province the Creighton granite may not be due to and others (1967 and 1970), Krogh and seems to postdate the major folds and pre- tectonism but to forceful intrusion (Card, others (1968 and 1971), Krogh and Davis date the crenulation cleavages and kink 1968). Thus the relation of brecciation and (1969, 1970a, 1970b), and Krogh (1971) bands (Card, 1964; Card and others, 1972a deformation still poses a major problem. all suggest that the Grenvilie Orogeny (1.0 and 1972b). Our work indicates that the As the Irruptive is older than the oldest b.y. ago) was represented only by a thermal earliest folds in the Southern province are tectonic structures visible in the overprint and possibly brittle deformation, equivalent to the earliest recognizable folds metasedimentary rocks of the eastern in the northwesternmost Grenvilie province in the northwestern Grenvilie province Southern province, it would be expected in the vicinity of Sudbury. Most recently, (Figs. 3, 4). If our conclusions are correct, it that the offsets are also older. The Worth- Krogh and Davis (1972b, 1973) have pre- follows that major metamorphism in the ington Offset, which cuts the homoclinal sented data suggesting that Grenvilie pro- northwestern Grenvilie province climaxed Huronian rocks near Worthington (Figs. 2 vince rocks at French River, Ontario, about (? or began) earlier than it did in the South- and 3), must be older than the earliest de- 50 km southeast of the Grenvilie Front, un- ern province (Table 2). It is possible that formation, because the earliest tectonic derwent amphibolite-facies regional still older structures in the Grenvilie prov- foliation in the Southern province cuts the metamorphism in the period 1.3 to 1.0 b.y. ince have been obliterated. It would be offset. The field relations between the Cop- ago; but despite the work of Lumbers unusual for migmatization and high-grade per Cliff Offset and the structures of the (1972), there is no strong evidence of pene- metamorphism to have occurred in previ- Southern province are not yet clear. The trative deformation along the Grenvilie ously undeformed rocks. offset cuts the foliation in the Creighton Front at that time. granite, but this foliation may be the one We are convinced that the early isoclinal CONCLUSIONS that predates the Sudbury-type breccias folds southeast of the Grenvilie Front near We see no reason to doubt that the main farther west, and is, therefore, older than Sudbury (Figs. 2, 3, 4D) and their mylonitic structures of the Sudbury Basin, of the the foliation seen in Southern province axial planar foliation are the same age as Huronian rocks of the eastern Southern metasedimentary rocks. Thus, although the the main folds and their axial surface folia- province, and of the northwesternmost Worthington Offset is older than the tec- tion in the Mississagi Quartzite to the Grenvilie province are related and essen- tonic structures of the Southern province, northwest (also see Warren, 1967; Brown, tially coeval (Table 2). They were formed, this relation cannot at present be 1968; Dalziel and others, 1969). Current for the most part, after the event, be it generalized to the other offsets which in- and graded bedding are preserved in the meteorite impact or cryptovolcanic explo- trude the Huronian rocks. quartzite, yet there is no evidence that sion, that initiated the Sudbury Basin, after structures in the Grenvilie province over- the deposition of the Whitewater Group, THE GRENVILLE FRONT print structures in the Southern province. after the formation of the Sudbury-type The Grenvilie Front, situated 8 to 16 km The mylonitic foliation in the rocks of the breccias, and after the intrusion of the southeast of the Sudbury Basin, is the Grenvilie province near the front, like that Nickel Irruptive (2.0 b.y. ago; Table 2), but northwestern boundary of the Grenvilie in many Southern province rocks, has a before the intrusion of the olivine diabase province. The latter is characterized by steeply downdip plunging mineral elonga- dike swarm (1.46 b.y. ago; Table 2). This metamorphic and igneous rocks that yield tion lineation. Hence the geometry of finite single orogenic event, the Penokean 1.0-b.y. K-Ar whole-rock and mineral, and strain in the northwestern Grenvilie prov- Orogeny (Van Schmus, 1972), appears to Rb-Sr mineral ages. Recent work has ince rocks is comparable to that in the have deformed the Sudbury Basin from confirmed the conclusions of Quirke and Southern province northwest of the Gren- nearly circular to elliptical in shape, folded Collins (1930) that the migmatized rocks of vilie Front and in the Sudbury Basin rocks. and flattened the Whitewater Group, folded the northwestern Grenvilie province are the It is our contention that they all underwent and flattened the Huronian Supergroup, same age as those in the Southern province the same major deformational event after and produced the intense mylonitic folia- (Davis and others, 1967; Warren, 1967; the intrusion of the Nipissing diabases tion and isoclinal folding along the Gren- Brown, 1968; Krogh and others, 1968, (2.15 b.y. ago) and the Nickel Irruptive (2.0 vilie Front zone (Table 2, Fig. 4). The axis 1971; Dalziel and others, 1969; Krogh, b.y. ago) and prior to the intrusion of the of maximum finite shortening was sub- 1971; Henderson, 1972; Krogh and Davis, northwest-southeast—trending olivine- horizontal and directed southeast- 1972a). Moreover, although there diabase dike swarm (1.46 b.y. ago) that northwest. The axis of maximum finite ex- undoubtedly was a major orogenic event cuts the structures of the basin, the Huro- tension was plunging steeply to the south- about 1.0 b.y. ago (Grenvillian Orogeny) nian, and the gneisses of the northwestern east. Lack of folding in the southeast-facing involving polyphase deformation, high- Grenvilie province (Figs. 1, 2; Table 2; and generally steeply southeast dipping grade metamorphism and igneous activity Card, 1971b). Huronian homocline immediately south- in the southeastern part of the Grenvilie Younger asymmetric folds within the east of the Sudbury Basin could be ex- province where the distinctive Grenvilie northwest Grenvilie province which have plained if these rocks had assumed their

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TABLE - C

TENTATIVE REGIONAL CORRELATION OF THE GEOLOGICAL HISTORY OF THE SUDBURY BASIN AND THE ADJACENT SOUTHERN. GRENVILLE, ANO SUPERIOR PROVINCES .

RADIOMETRIC SOUTHERN PROVINCE SUDBURY BASIN SOUTHERN PROVINCE GRENVILLE PROVINCE GRENVILLE PROVINCE DATES b.y. (CENTRAL )' AND VICINITY2 (EASTERN)3 (GRENVILLE FRONT ZONE)4 (EASTERN)5

0.8 - I.I Late Faulting Late Faulting Uplift a Cooling Uplift a Cooling

Thermal Overprint Thermal Overprint Thermal Overprint Grenvillian Orogeny (Posl - Fracturing)

Olivine - Diabase Olivine - Diabase Olivine - Diabase Olivine - Diabase Deposition of 1.46 Dikes Dikes Dikes Dikes 6renville Supergroup

1.6 - 1.8 Uplift 8k Coolinq Uplift a cooiin Uplift a Cooling Uplift a Cooling • 1 Kink Bands in Kink; Bands and Kinlc Bands and Onaping Conjugate Folds Conjugate Folds Formation | ! ¡ ° OROGENY . End of High Grade Metamorphism

Late Deformation N-S and E-W F-2 Sub-Isoclinal (N-S or NW-SE Crenulation to Asymmetric Crenulation Cleavage Folding OROGEN Y HUDSONIA N

Cleavage) OROGEN Y OROGEN Y 1 / Continued High High Grade Low Grade High Grade 1.7 - 1.95 Metamorphism Metamorphism Metomorphism _ _ _Grade Metamorphism

Middle Deformation Major E-W to F-l Isoclinal PENOKEA N PENOKEA N Deformation PENOKEA N Of Basin. NE-SW Folds Folding and (E-W Cleavuge) Folding / With Slaty Axial Mylcnitization Flattening of Planar Cleavage. Whitewater Group. Mylonitization Deformation of Irruptive on South Range.

1.6 - 1.75 Granites (Cutler) Granites(Grenville GranilestFrench River

PENOKEA N _ _ and_(irenville Front)_ Front) [ Onset of High Grade ? Penokean/Hudsonian Metamorphism a Orogeny in Basement Migrratization 2.0 Nickel Irruptive

Sudbury-Type Initiation of Sudbury-Type Breccias Breccias Whitewater Group (Post-dates Deforma- Deposition. tion in Creighton ? Cryptoexplosion Granite and Basal Event. Huronian Volcanics) Amptiibolites (basic 2.15 Nipissing Diabase Nipissing Diabase Ignecius Rocks?) Early E-W Folds Creighton a Murray 2. 15-2.3 (Pre-or Syn- Granites (2.2 b.y.) Nipissing Diabase)

Deposition of Huronian. Deposition of Deposition of Huronian. Deposition of Huronian. 2.3 - 2.5 Initiation of Faulting. Huronian. Initiation Initiation of Faulting. ? Faulting. of Faulting.

2.5* Kenoran Orogeny Kenoran Orogeny Kenoran Orogeny Kenoran Orogeny ? 1. Robertson, 1963, 2. Brocoum and 3. Brocoum and Dalziel, 4. Brocotim and Dalziel, 5. Wynne-Edwards, I967| Card e." ai-, Dalziel, 1973. 1973) Card filai-, 1973; Dalziel, Brown a 1964 , 1969. 1972a i Church, 1972 a i Dalziel, Brown Warren, I969| Krogh and 1966. and Warren, 1969. others, 1971 ¡Henderson,1972.

present attitude, as the structural relations Group within the "collar" would have been Sudbury-type breccias, some of which have suggest, prior to deformation, as part of a northwest approximately the same as the a foliation that predates the brecciation. collar or central uplift due to impact, be- direction of maximum shortening, and fold- Unless this represents an earlier deforma- cause the maximum shortening direction ing of those rocks would be expected. And, tion, the breccias cannot have formed at would have been normal to the layering as stated earlier, folding is present (Fig. 2). one ir stant in time. Table 2 illustrates a ten- (Figs. 4C, 4D). Southwest of the basin, the The major problem with the over-all impact tative regional correlation of the geological trend of the bedding of the Elliot Lake theory at the present time seems to lie in the history of the Sudbury Basin and the adja-

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cent Southern and Grenville provinces. Fig- from the National Aeronautics and Space tory of the rocks adjacent to the Grenville ure 4 consists of generalized northwest- Administration. Front near Sudbury, Ontario, and Mount southeast structure sections illustrating our Wright, Quebec: Geol. Assoc. Canada Spec. Paper no. 5, p. 207-224. interpretation of the tectonic development REFERENCES CITED of the basin and adjacent provinces. Davis, G. L., Hart, S. R., and Aldrich, L. T., with Banks, P. O., and Van Schmus, W. R., 1972, Krogh, T. E., and Munizaga, F., 1967, In the eastern Southern province, Chronology of Precambrian rocks of Iron Geochronology of the Grenville Province in orogenic deformation and folding did not and Dickenson Counties, Michigan, Part II: Ontario, Canada: Carnegie Inst. Washing- occur until after the emplacement of the 18th Ann. Inst, on Lake Superior geology, ton Year Book 65, p. 379-386. Nipissing diabase (2.15 b.y. ago) and the Houghton, Michigan, paper 23. Davis, G. L., Krogh, T. E., and Hart, S. R., with Nickel Irruptive (2.0 b.y. ago; Table 2). Brocoum, S. J., and Dalziel, I.W.D., 1973, The Brooks, C., and Erlank, A. J., 1970, The Slightly farther west, in the central South- Sudbury Basin, Southern province, Gren- age of metamorphism in the Grenville ern province, certain field relations have ville Front, and the Penokean Orogeny province, and the age of the Grenville been interpreted as indicating a major fold [abs.]: EOS (Am. Geophys. Union Trans.), Front: Carnegie Inst. Washington Year episode prior to the emplacement of the v. 54, p. 461. Book 68, p. 307-308. 1974, Strain analysis of the Sudbury Basin, Dence, M. R., 1972, Meteorite impact craters diabase (Table 2; Robertson, 1963; Ontario [abs]: EOS (Am. Geophys. Union and the structure of the Sudbury Basin: Church, 1966; Young and Church, 1966; Trans.), v. 55, p. 434. Geol. Assoc. Canada Spec. Paper no. 10, p. Pattison and Card, 1971; Card and others, Brown, J. S., 1968, Structure and origin of the 7-18. 1972a, 1972b). Most recently, Church and Grenville Front south of Coniston, Ontario Dence, M. R., and Guy-Bray, J. V., 1972, Some Young (1972) have proposed that folding [Ph.D. thesis]: Madison, Wisconsin Univ., astroblemes, craters, and cryptovolcanic accompanied emplacement. Farther west in 168 p. structures in Ontario and Quebec: Internat. the Penokean fold belt in the Lake Superior Cannon, W. F., 1971, The Penokean Orogeny Geol. Cong., 24th, Montreal, Quebec, Ex- region of Minnesota, Wisconsin, and in northern Michigan: Geol. Assoc. cursion A65, 61 p. northern Michigan, the earliest and most Canada-Mineralog. Assoc. Canada Joint Dietz, R. S., 1964, Sudbury structure as an as- intense orogenic deformation occurred in Ann. Mtg., Sudbury, Ontario, Abs. of trobleme: Jour. Geology, v. 72, p. papers, p. 9-11. 412-434. the period 2.0 to 1.6 b.y. ago (Goldich and 1972, Penokean tectonics in northern 1968, Shatter cones in cryptoexplosion others, 1961; Goldich, 1968, 1972; Can- Michigan: 18th Ann. Inst, on Lake Superior structures, in French, B. V., and Short, N. non, 1971, 1972; Morey, 1971, 1972; geology, Houghton, Michigan, paper 24. M., eds., Shock metamorphism of natural Banks and Van Schmus, 1972; Stonehouse, Cantin, R., and Walker, R. G., 1972, Was the materials: Baltimore, Mono Book Corp., p. 1972; Van Schmus, 1972, 1973). Sudbury Basin circular during deposition of 267-290. It is commonly emphasized that struc- the Chelmsford Formation?: Geol. Assoc. 1972, Shatter cones (shock fractures) in as- tures of the Grenville Front zone overprint Canada Spec. Paper no. 10, p. 93-101. troblemes: Internat. Geol. Cong., 24th, those in the Southern province (Lumbers, Card, K. D., 1964, Metamorphism in the Agnew Montreal, Quebec, sec. 15 (planetology), p. Lake area, Sudbury District, Ontario, 112-118. 1971; Card and Hutchinson, 1972; Card Canada: Geol. Soc. America Bull., v. 75, p. Dietz, R. S., and Butler, L., 1964, Orientation of and others, 1972a, 1972b). However, our 1011-1030. shatter cones at Sudbury, Canada: Nature, new field data show that the structures are 1965, Geology of Hyman and Drury Town- v. 204 (4955), p. 280-281. coeval on either side of the Grenville Front ships: Ontario Dept. Mines Geol. Rept. no. Fairbairn, H. W., Hurley, P. M., Card, K. D., and near Coniston where it is well exposed and 34, 38 p. Knight, C. J., 1969, Correlation of transitional (not faulted as in many other 1968, Geology of Denison-Waters area, On- radiometric ages of Nipissing diabase and localities) in nature (Table 2; Figs. 2, 4D), tario: Ontario Dept. Mines Geol. Rept. no. metasediments with Proterozoic orogenic and the 1.46-b.y.-old olivine-diabase dikes 60, 63 p. events in Ontario: Canadian Jour. Earth are not deformed or folded (Fig. 2). As pre- 1969, Sudbury mining area: Ontario Dept. Sci., v. 6, p. 489-497. viously suggested by field work (for exam- Mines Map 2170. Flinn, D., 1962, On folding during three- 1971a, Panache Lake area (west part): On- dimensional progressive deformation: Geol. ple, Dalziel and others, 1969) and tario Dept. Mines Prelim. Map p. 668. Soc. London Quart. Jour., v. 118, p. radiometric dating (Davis and others, 1971b, Panache Lake area (east part): On- 385-433. 1967; Krogh, 1971), the l.O-b.y.-old tario Dept. Mines Prelim. Map p. 669. Frarey, M. J., and Roscoe, S. M., 1970, The radiometric mineral dates in the north- Card, K. D., and Hutchinson, R. W., 1972, The Huronian Supergroup north of Lake westernmost Grenville province reflect only Sudbury structure: Its regional geological Huron: Canada Geol. Survey Paper 70-40, the final closing of the isotopic systems, setting: Geol. Assoc. Canada Spec. Paper p. 143-158. possibly the result of a thermal "overprint" no. 10, p. 67-78. French, B. M., 1967, Sudbury structure, Ontario: related to the Grenvillian Orogeny to the Card, K. D., Church, W. R., Franklin, J. M., Some petrographic evidence for origin by southeast. Frarey, M. J., Robertson, J. A., West, G. F., meterorite impact: Science, v. 156, p. and Young, G. M., 1972a, The Southern 1094-1098. province: Geol. Assoc. Canada Spec. Paper ——1968a, Shock metamorphism as a geological ACKNOWLEDGMENTS no. 11, p. 335-380. process, in French, B. M., and Short, N. M., We thank Dr. K. D. Card, Ontario Card, K. D., Naldrett, A. J., Guy-Bray, J. V., Pat- eds., Shock metamorphism of natural ma- Ministry of Natural Resources (Dept. tison, E. F., Phipps, D., and Robertson, J. terials: Baltimore, Mono Book Corp., p. A., 1972b, General geology of the 1-17. Mines), Sudbury, for many interesting dis- Sudbury-EUiot Lake region: Internat. Geol. 1968b, Sudbury structure, Ontario: Some cussions. He also made available unpub- Cong., 24th, Montreal, Quebec, Excursion petrographic evidence for an origin by lished reports, manuscripts, and maps, for C38, 56 p. meteorite impact, in French, B. M., and which we are grateful. We thank K. D. Church, W. R., 1966, The status of the Penokean Short, N. M., eds., Shock metamorphism of Card, R. Debicki (Cantin), R. S. Dietz, W. Orogeny in Ontario: Ninth Conference on natural materials: Baltimore, Mono Book Gibbins, J. V. Guy-Bray, J. R. Henderson, Great Lakes Research, Chicago, p. 25. Corp., p. 383-412. M. Langseth, E. Pattison, W. V. Peredery, Church, W. R., and Young, G. M., 1972, Pre- 1970, Possible relations between meteorite D. Phipps, and C. H. Scholz for critically cambrian geology of the southern Canadian impact and igneous petrogenesis as indi- reviewing the manuscript and making help- Shield with emphasis on the lower Pro- cated by the Sudbury structure, Ontario, ful suggestions. We thank the International terozoic (Huronian) of the North Shore of Canada: Bull. Volcanol., v. 34, p. 466-517. Lake Huron: Internat. Geol. Cong., 24th, 1972, Production of deep melting by large Nickel Company of Canada, Ltd., Copper Montreal, Quebec, Excursion A36-C36, meteorite impacts: The Sudbury structure, Cliff, Ontario, for allowing us to collect 65 p. Canada: Internat. Geol. Cong., 24th data on their properties. The research was Dalziel, I.W.D., Brown, J. M., and Warren, T. E., Montreal, Quebec, sec. 15 (planetology), p. supported by Grant NGR-33-008-106 1969, The structural and metamorphic his- 125-132.

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