25sudbur

The University of Western Ontario

Landsat Image of the Coniston area, Sudbury

(Ramsey Lake, lower left)

Keywords: Southern structural Province, Huronian, Penokean, Cutler, Killarney, Baldwin, Whitefish Falls, Elliot Lake, Aberdeen Township, Lake Huron, Coniston, Sudbury, Whitewater Series, Sudbury breccia, shatter cones, norite, granophyre, nickel , Nipissing Gabbro, North Shore diabase, Sudbury diabase, Grenville, anorthosite, metagabbro, eclogite, granulite, syenite, agmatite.

SUMMARY

NOTE: text in blue and underlined represents links to maps, photographs or special topics elaborating on some particular aspect/debate concerning the geologic history of the Southern Province of Ontario.

TheSudbury region encompasses parts of three structural provinces:

the Superior Province(> 2.5 Ga); the Southern Province (1.86 Ga); and the Grenville Province (1.0 Ga),

and is one of the foremost places in the world to examine plate tectonic mechanisms of crust formation over a significant portion of Precambrian time. In addition, the intersection of the three province boundaries at Sudbury marks the approximate location of the well known Sudbury meteorite impact site and its associated nickel-copper mineralization.

In terms of crustal evolution, the greater Sudbury region provides an opportunity to examine:

1) Archean-type crustal development as evidenced by the rocks of the Abitibi belt of the Superior Province.

2) the evolution of the Southern Province through its various stages of rifting, volcanism and granite intrusion, large scale obduction-related? deformation, collisional polyphase deformation and crustal melt formation, and the genesis of important deposits of uranium and silver.
3) major mafic dike swarms injected at 2.45 Ga, 2.22 Ga, 1.75?, 1.4?, 1.24 Ga, and 575 Ma.

4) the deformational and igneous character of the 'Grenville Front' as the northern limit of the c. 1.0 Ga collisional Grenville and the c. 1.75 Ga Penokean orogens.

The Sudbury region also provides an unique opportunity to examine the consequences of large-scale mining on the environment, and the efforts that have been made to curb the negative effects of this activity.

The geological significance of the greater Sudbury region is at least on a par with that of the Gros Morne Park region of Western Newfoundland, declared a World Heritage Site by the United Nations because of its geology. (The Gros Morne site is located within the obduction-related foreland land basin of the Appalachian structural province, and is considered "apparently one of the best places in the world to see the legacy of plate tectonics".) In comparison, the Sudbury region should be declared a World Heritage geological super-site.

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Many aspects of the geology of the Southern Province remain controversial - compare the papers of Shaw et al., 1999 with that of Parmenter et al., 2002, or Riller v Redmond and Fueten, or Card v Dutch - and these will be treated below as 'Special Topics'.

The Archean rocks exposed to the north of the Sudbury basin are dominantly gneissic tonalitic and granodioritic rocks of the southern batholithic belt of the Abitibi sub-province.
Archean rocks are unconformably overlain by rocks of the Huronian Supergroup composed largely of terrigenous sediment derived from a northern Archean source. The earliest deposits of the Huronian include a mafic - felsic volcanic rift sequence known as the Thessalon Formation in the western part of the Huronian, and as the Elsie Mountain/Stobie basalts and Copper Cliff rhyolite sequence in the Sudbury region. The volcanism is possibly related to the injection of the 2.45 Ga Matachewan diabases and related gabbro-anorthosite intrusions (East Bull Arm and River Valley) found within the Superior Province north of the Huronian and the Archean terrain of the northern Grenville Province south-east of the Huronian, as well as to the localised tensile (rift) deformation associated with the intrusion of the 2.477 Ga Creighton and Murray granites of the Sudbury region. Basal conglomerates of the overlying Matinenda Formation, composed of large rounded clasts of vein quartz cemented by a matrix of pyrite, are of economic importance because they contain detrital uraninite. Other prominent units in the Huronian include the Gowganda Tillite, one of the oldest known examples of a glacial deposit, and the overlying white-weathering Lorrain orthoquartzite (but red coloured where it is iron bearing, and green where it contains detrital chromite derived from the weathering of Archean komatiites), representing the products of intense tropical weathering of Archean granitic crust. Sandstones with a relatively high proportion of haematitic iron make their appearance in the uppermost Huronian, and possibly presage the later global appearance of major Lower Proterozoic banded iron formations (Lake Superior region; Hammersley of Australia).

The Huronian was tightly folded (Click here for photographs concerning the Fold History) prior to or during the injection of gabbro sheets of 'Nipissing gabbro'at 2.2 Ga (Link 5, Link 1), and certainly prior to the injection of both NW and NE trending diabase dikes (see discussion below). The mechanism of folding is not known, but, as in the case of the passive margin sediments of Papua-New Guinea, it may have been induced by the obduction of oceanic crust following the establishment of a Huronian passive margin. The Huronian sediments must have been sufficiently indurated to support large scale congruent folding and the development of an axial cleavage. Given the arc-like chemical characteristics (low-Ti) of the Nipissing gabbro, it is even conceivable that it marked a short-lived 'flip' in the subduction polarity shortly following the obduction event. The structural architecture of the Huronian is similar to that of the rocks of the Lower Proterozoic Hamersley passive margin located on the southern margin of the Archean Pilbara craton of Western Australia. In Canada an equivalent obduction event is represented by the ophiolites of the Ungava Peninsula.

Link 1 - Schematic map of major structures in the Huronian of Espanola wedge - sudman.gif

On the basis of the common presence of shatter cones in rocks of the Sudbury region (even as far west as Espanola) and the distribution of the enigmatic 'Sudbury breccia' and Onaping 'fall-back' rocks, it is thought that the Sudbury basin, even though presently preserved as an asymmetric syncline, represents the remains of a Paleoproterozic meteorite impact commonly referred to as the Sudbury event (Link 2). Huronian rocks throughout the Sudbury region, including gabbros of the Nipissing diabase association, were brecciated during the impact event, and fluidized breccia material (Acoustic fluidization; Sudbury breccia) is commonly found injected into Huronian rocks. The fall-back rocks are overlain by tubiditic mudstones and greywackes of the Whitewater Group, and the rocks of the impact crater were intruded by lopolithic sheets of mafic (norite, quartz-gabbro) to felsic (granophyre) material of the Sudbury Irruptive (1.85 Ga old), and associated 'Offset' dikes, supposedly generated by impact partial melting of Archean and Huronian rocks. The rocks of the Whitewater Group, the noritic rocks of the Irruptive, and the Huronian rocks beyond the Irruptive are cut by undated NE to ENE trending mafic dikes. Whether or not they are coeval with the Trap dikes intrusive into the Huronian outside the basin is not known. Within the norite the dikes exhibit chilled margins, suggesting that the Sudbury Irruptive was cool at the time of intrusion of the Trap dikes.

Link 2 - Some data on the Sudbury impact structure - where is the centre of impact? - grieve1.jpg

Deformation(S2,S3) subsequent to the Sudbury impact event may have been related to the closure and arc/continental margin collision documented within the Michigan/Wisconsin section of the c. 1.86 Ga Penokean fold belt, to events that post-dated the intrusion of the 1.75 Ga Killarney granites, and to non-penetrative events younger than the intrusion of the c. 1.4 Bell Lake granite.

        The geological history or the Sudbury area may therefore involve the following events:
        1) Deposition of the Huronian sediments and volcanics (and related igneous complexes).
        2) Major folding of the Huronian (F1 deformation phase).
        3) Injection of Nipissing diabase.
        4) The Sudbury impact event.
        5) Deposition of the Whitewater sediments.
        6) Penetrative pure shear deformation of the Huronian and Whitewater rocks (F2 deformation phase).
        7) F3 folding of F2 cleavage/schistosity (change in orientation of shatter cones on opposing fold limbs)
        8) Intrusion of the Sudbury Irruptive (1.85 Ga)
        9) Intrusion North Channel diabases (transects F3 folds and the Sudbury Irruptive)??
       10) Syn-F4 (F3b) deformation intrusion of the Cutler and Killarney granites (1.75 Ga)
       11) Late post-deformation metamorphism.
       12) Intrusion of the Bell Lake Granite (1.47 Ga).
       13) Intrusion of Trap dikes??
       14) Bell Lake Granite/South Range Shear zone F5 deformation.
       15) Injection of the Sudbury Diabase dike swarm (1.238 Ga).
       16) Grenville deformation and metamorphism (ca. 1.0 Ga) (F6 deformation phase)
       17) Injection of the Grenville dike swarm (575 Ma).

Selected references:

Bailey, J. , Lafrance, B. , McDonald, A. M., Fedorowich, J. S., Kamo, S. , Archibald, D. A., 2004. Mazatzal–Labradorian-age (1.7–1.6 Ga) ductile deformation of the South Range Sudbury impact structure at the Thayer Lindsley mine, Ontario. Canadian Journal of Earth Sciences, v. 41, p. 1491-1505.

Boerner, D.E., Milkreit, B., and Davidson, A., 2000. Geoscience impact: a synthesis of studies of the Sudbury Structure. Canadian Journal of Earth Sciences, v. 37, p. 477-501.

        Davidson. A. 2001.The Chief Lake complex revisited, and the problem of correlation across the Grenville Front south of Sudbury, Ontario. Precambrian Research. v. 107, 5-29
        Dutch, S.I., 1979, The Creighton Pluton, Ontario: an unusual example of a forcefully emplaced intrusion, Canadian Journal of Earth Sciences, v. 16, p. 333-349.
        Card, K. discussion, Dutch, S.I. reply, 1979, The Creighton Pluton. Canadian Journal of Earth Sciences, v. 16, p. 2181.
        Fueten, F. and Redmond, D.J., 1997. Documentation of a 1450 Ma contractional orogeny presrved between the 1850 Ma Sudbury impact structure and the 1 Ga Grenville orogenic front, Ontario, BGSA, v. 109, 3, p. 268-279.
         Krogh, T.E., Kamo, S.L., and Bohor, B.F. 1996. Shock metamorphosed zircons with correlated U-Pb discordance and melt rocks with concordant protolith ages indicate an impact origin for the Sudbury structure. In : Earth processes: reading the isotopic code. American Geophysical Union, Monograph 95, p. 343-352. (The Creighton granite, previously dated as 2333 and 2388, is 2477+/-9.)

Parmenter, A.C., Lee, C.B., and Coniglio, M., 2002. "Sudbury Breccia" at Whitefish Falls, Ontario: evidence for an impact origin. Canadian Journal of Earth Sciences, v. 39, 6, p. 971-982.

Rousell, D.H. and Long, D.G.F., 1998. Are Outliers of the Huronian Supergroup Preserved in Structures associated with the collapse of the Sudbury Impact Crater . Jour. Geology, v. 106, p. 407-419.
Riller, U., and Schwerdtner, W.M., 1997. Mid-crustal deformation at the southern flank of the Sudbury basin, central Ontario, Canada, BGSA, v. 109, 7, p. 841-854.

Shaw, C.S.J., Young, G.M., and Fedo, C.M., 1999. Sudbury-type breccias in the Huronian Gowganda Formation near Whitefish Falls, Ontario: products of diabase intrusion into incompletely consolidated sediments? Canadian Journal of Earth Sciences, v. 36, p. 1435-1448.

SPECIAL TOPICS

Structures of the Elliot Lake-Sault Ste Marie in the west (Jackson, S.L., 1994, Geology of the Aberdeen Area; Ontario Geological Survey, Open File Report 5903, 69 p.) and north of the Sudbury basin in the east (in preparation)
        Aberdeen Township
       Geology at the western end of the Southern Province fold belt
       The Murray Fault - OGS Map 0281 Bruce Mines; OGS Map 0281 Cutler
       General Geology of the Aberdeen area
       Foliation patterns in the Aberdeen area
       Fold and fault patterns in the Aberdeen area
       Complex fold pattern in the Aberdeen area

The northern rim syncline of the Sudbury Dome

Rousell, D.H. and Long, D.G.F., 1998. Are Outliers of the Huronian Supergroup Preserved in Structures associated with the collapse of the Sudbury Impact Crater . Jour. Geology, v. 106, p. 407-419

        Regional Map
        Vernon A
        South Hart B
        Tofflemire C
        Hart D
        Geneva Lake EF
        Munster G

The structure of the Coniston - Garson region (in preparation)

The 'Trap', North Shore, and other felsic dike swarms
        The least well understood aspect of the evolution of the Southern Province concerns the age and regional correlation of the several phases of deformation that have affected the Huronian and Whitewater groups, and their age relative to that of the 'Trap' and North Channel diabases dike swarms, the Sudbury Irruptive, and the 1.75 Ga granites.
         Following the early main phase folding and the subsequent Sudbury Impact event, the Huronian rocks of the Espanola wedge were affected by two further phases of deformation. The earlier of these phases involved penetrative pure shear and was developed best in the more highly metamorphosed rocks located along the northern part of the Espanola wedge (Baldwin anticline - Cutler belt). The second phase of deformation involved non-penetrative simple shear, is everywhere superimposed on the early foliation as folds and a strain-slip foliation, and forms relatively large scale folds within the northern Baldwin Anticline - Cutler belt. Both phases can be recognised in more argillaceous rocks of the Mississagi Formation and in the matrix material of Sudbury breccias present beyond the southern limit of the Sudbury Irruptive.
        The rocks of the Whitewater series are also folded and foliated, and although there seems to be little evidence that the Irruptive was involved in the deformation, the age relationship of the folding to the Irruptive remains unclear. The Whitewater series is cut by highly altered (chlorite) NE/ENE trending dikes of relatively constant orientation, that do not seem to have participated in the folding. 'Trap dikes' (Link 3) that cut the norite member of the Sudbury Irruptive are however deformed along with the Irruptive where the latter is involved in the relatively local 'South Range Shear Zone'. The dikes are converted to amphibolite, with pleochroic amphibole mantling relict cores of pyroxene. However, 'Trap dikes' cutting the Huronian outside the Sudbury basin do not seem to be implicated in any of the phases of deformation recorded in the Huronian, as seems also to be true of mafic dikes with a 'Trap dike' trend in the Espanola region. I would not therefore be unreasonable to conclude that intrusion of trap dikes and the deformation of the South Range shear zone are relatively young. At Alice Lake mafic dikes with a Trap dike trend are implicated in the mylonitization event affecting the Grenville Front megacrystic granites, and the South Range shear zone could therefore be younger than 1.4 Ga.
        The Huronian is also cut by mafic dikes of variable trend - in some areas, particularly in in the southern part of the Espanola wedge, the trend is dominantly northwest (Link 5, Link 6), whereas in the Sudbury region they dominantly trend ENE. At some localities (Link 4) dikes trend NW, ENE and E-W, as also do the North Channel dikes cutting the Huronian beween Elliot Lake and Sault Ste. Marie (Link 8). Whatever their orientation, the dikes all transect the early major folds (Link 5, Link 6). The age relationship of the dikes to the Sudbury breccia and to the various phases of deformation is however ambiguous. As is illustrated in Link 7 one dike appears to transect breccia whereas the other diabase appears to be brecciated. Furthermore, ENE trending dikes within Huronian of the northern Espanola wedge clearly transect late stage open F3 folds at the southwest end of Anderson Lake (Link 6), as do the ENE trending 'Trap' dikes in the Sudbury area, but NW trending dikes in the Whitefish Falls area are implicated in deformation that involves the formation of a prominent secondary foliation. Three possibilities therefore arise:
        1) there are two ages of diabase dikes, one related to the Nipissing diabase intrusions, the other related to the 'Trap' dike event;
        2) all the dikes are of the same age but the foliation in Huronian rocks of the southern Espanola wedge is younger than the foliation forming event in the Baldwin-Cutler belt of the northern Espanola wedge;
        3) all the dikes are of the same age but the deformation of the diabase at Whitefish Falls was induced by the third-phase deformation present as non-penetrative shear zones at this locality. In the region of the Cutler granite at the western end of the northern Espanola wedge, the marked penetrative foliation in 'Nipissing' garnet-amphibolites are deformed by crenulations and folds related to the large scale folds cored by the Cutler granite.
        The foliated gabbros are cut by straight NW trending diabase dikes that also cross cut tight folds whose relationship to the foliation has not however been established. The diabase, although metamorphosed, exhibits shear strain only adjacent to its contacts with the strongly foliated amphibolite. Straight trending 'Trap' dikes cutting highly foliated Creighton granite in the Sudbury region also exhibits a shear foliation within cms of its contact with the granite, but otherwise is not deformed. It is conceivable therefore that the Cutler diabases post all the dominant phases of deformation, but are sheared by non-penetrative late stage deformation equivalent in age to that which produced the post-'Trap' dike deformation of the South Range Shear zone of the Sudbury basin, and possibly the post-Bell Lake granite deformation of the Grenville Front region (Link 3).
    At Cutler NW-SE trending dikes are cut by pegmatites associated with the Cutler granite.

In the Coniston-Garson area of the Sudbury region, Mississagi Quartzite is cut be a suite of vertical but variably trending garnet- and amphibole needle-bearing felsic dikes. The dikes transect foliated Sudbury breccia and are quite undeformed. The rocks of this area are also injected by rare veins of pegmatite. Rare sheets of granitic rock also intrude Mississagi quartzite south of the Murray Fault on the Sudbury road to Rheault (Paris St), and in Rheault itself heterogeneously deformed Nipissing Gabbro within the Long Lake Fault is irregularly injected by pink granite.

Deformation History of the Huronian south of the Murray Fault in the Sudbury region (OGS Map 0218)
        Fueten and Redmond (1997) have established on the basis of an analysis of quartz c-axis orientations and grain shapes in Mississagi quartzites, and of clast orientations in Sudbury breccia, that the area of Huronian rocks between Sudbury and the 'Grenville Front' can be subdivided into three fault bounded structural panels.
        Quartz grains in the northern panel north of the Murray fault are very little strained, and clasts in Sudbury breccia show no preferred orientation.
        In the central panel between the Murray and Long Lake faults, strain as indicated by grain shape is highly variable. At three localities in the vicinity of Silver Lake, clast orientations in Sudbury breccia on hoth sides of the Murray Fault show a marked preferred orientation, but only in one case, southeast of Silver Lake, does the clast preferred orientation seem to correlate with a preferred quartz grain shape-fabric in quartzites (sample 66).   A high strain zone seems to be located west of Crooked Lake (south-west of Silver Lake) represented by samples 47, 48, 49, and 63, but even here they seem to delineate localized zones of non-penetrative deformation. Given that some high strain breccia zones and the locations of samples of quartzite with strong preferred shape orientations are indicated to occur north of the Murray Fault, it would seem that the latter structure only approximately marks the onset of occurrence of non-pentrative strain in Mississagi quartzites. The quartz c-axis patterns in the middle panel between the Murray and Long Lake faults are also very variable, again implying non-penetrative anastomosing deformation in this panel.
         South of the Long Lake fault however, quart c-axis orientations exhibit strong point maxima and deformation in the southern panel in the samples collected by Richmond and Fueten is strong and penetrative, and the Long Lake fault in the Reault area is likely a much more important structure than the Murray fault. Nevertheless staurolite-bearing schists of the Percors Formation that outcrop south of the Long Lake fault exhibit varying degrees of secondary strain ranging from porphyroblastic schist to highly flattened flagstones in which coarse staurolites have been replaced by thin aggregates of chlorite.
        On the basis that Sudbury breccia clasts north of the Murray fault zone show no preferred alignment, and folds can be traced north of the Murray fault to the west of the study area, Fueten and Redmond (1997) suggest that the bulk of the deformation north of the Murray fault zone in the study area pre-dated the 1850 Ma impact event, and that while significant deformation affected the area following the Penokean orogeny, they were unable to correlate any deformational features with the emplacement of the 1750 Ma phases of the Chief Lake Complex. They further suggest that the ca. 1750 Ma magmatic event was passive, representing anorogenic magmatism, and that the deformation fabric in rocks south of the Long Fault represents an important post-1.46 Ma phase of deformation that may have penetrated as far north as the southern margin of the Sudbury basin.

The Long Lake fault as defined by Fueten and Redmond may be the continuation of the Lake Panache - Apsey Lake fault which separates the deformed Huronian into two distinct structural panels. To the south of the fault Huronian rocks occur in the form of large scale, tight vertical folds ( La Cloche and Bass Lake synclines; McGregor Bay anticline), whereas to the north of the fault folds in the Huronian are relatively open smaller scale structures. Argillites involved in the tight folds of the southern structural panel do not exhibit a coeval axial planar mica fabric.

Figure 1. - Structural elements of the Southern and Grenville Province southwest of Sudbury

        The folds (D1) of the southern panel are transected by Nipissing Gabbro and Sudbury Breccia, in that order, and are therefore pre-2.2 Ga, pre-impact, and pre-Penokean - if this term is restricted to deformation associated with the 1.86 Penokean collision event of Michigan-Wisconsin. The tectonic environment of formation of the early large scale folds is not known, but an analogy could be drawn with the enigmatic first-phase fold deformation of the Moine-Dalradian clastic wedge of the Scottish Caledonides, and the tight vertical folding induced in the Port Moresby continental margin sediments by obduction of the Papuan-New Guinea ophiolite. The most prominent planar fabric in Huronian rocks of the southern panel is a 'strain-slip' cleavage (D2) of variable intensity which cuts across the earlier folds, Nipissing diabase and Sudbury breccia. It microfolds an earlier mica cleavage which is congruent with the first generation major folds, and also acted as the locus of development of a third-phase fold and crenulation cleavage fabric (D3). Aluminous quartzites of the Lorrain Formation contain pre-deformation pyrophylite and kyanite, and post-deformation andalusite; and cleaved pelitic rocks contain randomly oriented porphyroblasts of late-growth biotite. Microscopic garnet occurs rarely in some cleaved argillites of the Gowganda formation at Whitefish Falls.
        On the other hand, the prominent open folds north of the Apsey Lake fault (cf. Card, 1978; Map 2360) fold a fine grained slaty cleavage (D2') which cuts Sudbury breccia bodies in this zone. The strain and metamorphism associated with the cleavage is low, and shatter cones can be recognized in quartzose rocks at least as far west as Anderson Lake, south of Espanola. It would seem likely that the quartzose rocks of this panel never were deformed sufficiently to develop a strong Penokean fabric, and it would seem equally unlikely therefore that the quartz c-axis fabrics described by Fueten and Redmond in rocks north of the Long Lake fault are reset ‘Penokean-aged’ fabrics. Nevertheless, the presence of an axial planar cleavage in argillites of this zone attests to the existence of a post-Sudbury breccia (post -impact) phase of deformation. A similar cleavage fabric is also found in the argillites, Sudbury breccias, and even pelitic material filling shatter cone fractures, immediately south of the Sudbury Basin at Copper Cliff. Again however, the associated quartzites exhibit little in the way of ductile deformation. If the slaty cleavages in both the southern and northern panels are coeval (D2=D2'), it would not be unreasonable to correlate the prominent folds (D3') of the northern panel with the strain slip fabric (D3) of the already vertically folded southern panel.
        In contrast to the rocks of the Anderson Lake low ‘grade’ zone, the Huronian McKim Formation north of the Espanola fault, exhibits a well developed mica cleavage (D2') which cuts across Sudbury Breccia bodies and also post-dates growth of chloritoid and staurolite. An earlier poorly developed bedding plane cleavage (D1'), best delineated by oriented laths of ilmenite is however sometimes present in argillaceous units of the McKim, suggesting that these rocks may have suffered some degree of deformation prior to the Sudbury event. In Baldwin Township north of Espanola, the more prominent cleavage (D2') is coarse grained and commonly refolded by a penetrative crenulation fabric (D3'), which is further overprinted by a late phase of crystallization involving garnet growth and the generation of an annealed quartz fabric. The effect of the Murray fault in disrupting the architecture of the Huronian within the Baldwin structural panel is minimal, and the speculations of Zolnai et al (1984) proposing 15 km of structural relief along the Murray fault are therefore debateable. The domal metamorphic zonation is perhaps controlled by some process of thermal convection related to granite intrusion rather than by the upthrusting of deeply buried rocks.   Furthermore, at the western end of the Baldwin metamorphic belt the ca 1.75 Ma Cutler granite is located within a late D3' fold which folds a prominent post-Sudbury Breccia foliation (D2') that is either syn- or pre-granite intrusion. Also, deformed Huronian rocks of the Espanola Wedge are transected by the 1.475 Ga Croker Island complex, described by Card et al. (1972) as a an epizonal, post-tectonic intrusion exhibiting a narrow hornfels contact zone. Consequently, it seems unlikely that all the deformation fabrics, including the D3/ D3' folds, are strictly Penokean (1860 Ma) in age.

The deformation history of the Sudbury Basin
Within the Sudbury basin, neither the fold deformation of the Whitewater Group nor the strain fabric of the South Range shear zone are likely to be coeval with the pre-Sudbury Breccia deformation outside the basin. However, it is uncertain whether the folding of the Whitewater Group is equivalent to the prominent post-Sudbury Breccia foliation (D2/D2') common to all structural domains in the Espanola Wedge, or, alternatively, to the later D3/D3' folds. The deformation represented by the South Range shear event was separated from the D3/D3' fold event outside the Sudbury Basin by the intrusion of the undated ENE trending 'trap' dyke suite, and given that the 'Trap' dykes were affected by the late stage metamorphism (pleochroic amphibole mantling relict cores of pyroxene and amphibole) that produced the 'Cutler-Baldwin'-type annealed fabrics in the staurolite-bearing McKim argillites outside the Sudbury Basin, it remains possible that the South Range shear deformation was a late non-penetrative c. 1.75 Ga event. Furthermore, south of the Murray Fault about 1.5 km south of the SE corner of Silver Lake on the road to Rheault, sheared Huronian quartzites are cut by undeformed dikes of undated microgranite. On the other hand, ENE trending mafic dikes within mylonitized megacrystic granites at the Grenville Front near Alice Lake have suffered the same deformation as the granites, and if these granites belong to the 1.46 Bell Lake intrusive suite rather than the 1.75 Killarney suite then the 'Trap' dikes could be younger than 1.46 Ga, as would also be therefore the age of the South Range shear. In this case the growth of amphibole in 'Trap' dikes within the South Range shear would be of only local significance.

The 1.75 Ga Cutler and Killarney Granites
At c. 1.75 Ga, granitoid bodies were intruded in both the Cutler and Grenville Front areas, and the 'Killarney granites' of the Grenville Front region were subsequently injected by the younger c. 1.4 Ga Bell Lake granite and associated pegmatite bodies. The Grenville Front granitoids are flanked along their southeast margin by folded gneisses which locally include belts of kyanite-garnet-biotite schist - perhaps representing metamorphosed Huronian age aluminous metasediment intercalated within Archean gneisses. Some quartzite units within this belt are almost certainly Huronian equivalents because they contain detrital zircons of Archean age and zircon needles, evidently of metamorphic origin, with an age of 1.7 Ga. Metagabbro bodies injected into these rocks may belong to the Nipissing diabase suite. The gneisses also contain deformed anorthosite-gabbro bodies of early Proterozoic age, and a gabbro- granophyre body (Wanapitei complex) dated at 1.75 Ga. All these rocks units were injected by 1.24 Ga olivine-bearing diabases (often containing large xenocrysts of plagioclase) of the Sudbury swarm. Within the Southern Province the diabases are straight and only locally faulted, but when traced into the Grenville Province, they become irregular in form, are cut by non-penetrative mylonite zones, and contain metamorphic spinel and garnet. Further into the Grenville Province the diabases become penetratively deformed and form isolated boudins of pyroxene-garnet or garnet-amphibole rock. Within shear pods the igneous texture of the diabases are easily recognisable in spite of the replacement of plagioclase by garnet. The penetrative deformation represents the Grenville orogeny.

                            Cutler granite
         Link 9 -     Deformation events in the vicinity of the Grenville Front -grenv1.jpg
         Link 10 - Geology of the 'Grenville Front' near Rheault-Broder Lake, south of Sudbury - broder83.jpg

The Grenville Front Problem south of Sudbury - history of data acquisition
        Quirke and Collins (1930) concluded that "the Huronian formation, traceable eastward for 225 km from Sault Ste Marie, does not terminate at the Grenville Front but exists south of the Front in a highly recrystallized and metamorphosed state.", a conclusion also reached by Phemister (1961). Brooks (1967) mapped the 'Grenville Front' in the vicinity of Bell Lake and concluded that 'Grenville Front' tectonism (development of slip-planes) was synchronous with the generation of the 'Killarnean' granites, that there was slightly later granite intrusive activity accompanied by the contact metamorphic growth of andalusite and cordierite, and that the younger granites (Bell Lake granite) were subject to non-penetrative cataclastic deformation that produced zones of cataclastic gneiss. The Bell Lake granite was also indicated to contain a primary foliation marked by the parallelism of microcline phenocrysts (Brooks, 1976). He also showed that at Johnny Lake a straight trending olivine-diabase dyke (Sudbury diabase) cutting the Bell Lake granite was cataclastically deformed along with the granite.
         Krogh and Davis (1969, p. 230) obtained a 1.75 Ga Rb-Sr four point isochron age for rocks collected from the Chief Lake complex of granite rocks in the vicinity of Broder Lake (Henderson, 1967, p. 279), and a Rb-Sr age of 1.6 Ga for muscovite from a northeast-trending granite dyke that intrudes Huronian rocks along the northwest margin of the Chief Lake complex. They also reported an age of 1.45 Ga for muscovite from a strongly foliated granite. Krogh and Davis concluded that the Chief Lake granite complex was "intruded into the 'Grenville Front' 1700 m.y. ago and that it underwent plastic... (southeast margin)... and brittle deformation... (northwest margin)... then or at some time earlier than 1450 m.y. ago."   (Krogh and Davis (1970, p. 310) later determined an age of 1.63 Ga for muscovite in the undeformed part of a variably Grenville deformed pegmatite located southeast of the 'Grenville Front' in the vicinity of Highway 69, and an age of 988+/-2 Ma for monazite in a cataclastically deformed pegmatite at the same locality (Krogh 1994, p. 971).)
         Krogh and Davis (1970) recognized the existence of two ages of granite along the 'Grenville Front', and also reported that pegmatites containing coarse muscovites with ages of 1.44-1.47 Ga cut the foliation in coarse-grained impure quartzites south of the Bell Lake granite, and near Carlyle Lake (pers. comm . to Brooks, 1976) contain inclusions of mylonitized Killarney granite. (The Killarney granite was subsequently dated by Davidson and Van Breemen (1994) as having a zircon age of 1.74 Ga, and the Bell Lake granite a zicon age of 1.47 Ga (Van Breemen and Davidson, 1988).)
        The first serious mapping of the southwestern part of the 'Grenville Front' region by Frarey and Cannon (1969) separated the Killarney granite (unit 7b) from the Bell Lake granite (unit 7a), showed the existence of a foliation in the eastern margin of the Killarney granite (unit 9d), and demonstrated that dykes of the Sudbury dyke swarm not only transected the granites but extended well to the southeast of the 'Grenville Front'. Subsequently, the Grenville Front was located coincident with a major myolite zone along the eastern margin of the granite belt. (The location of the mylonite zone at the Killarney end of the belt was susequently relocated further east by Davidson (1986).)
        Study of the section of 'Grenville Front' southeast of Sudbury led Brocoum and Dalziel (1974) to propose that the supposed Grenville deformation at this locality was Penokean and entirely older than the dykes of the Sudbury swarm, and that "the major ductile deformation of the rocks of the Sudbury Basin, the eastern part of the Southern Province, and the northwesternmost Grenville Province was coeval". They allowed however that post olivine-diabase cataclastic (brittle) deformation was also present along the length of the 'Grenville Front' (Brocoum and Dalziel, reply to Brooks, 1976).
        Lumbers' map of the Burwash region (1975) showed the 'Grenville Front', which he termed the Grenville Front Boundary Fault, located at the western limit of penetrative deformation within the granitic rocks of the Front.
        A paleomagnetic and chemical compositional study of Sudbury diabases in the Southern and adjacent Grenville provinces by Merz (1976) showed that Sudbury diabases in or near the Grenville Province had had their TRM reset as a result of Grenville metamorphism, and was the first to recognise that the metadiabase segments cutting gneisses within the 'Grenville' were correlative with Sudbury diabase dykes in the Southern Province. Merz also showed that some of the dikes, currently referred to the Grenville dyke suite, were Paleozoic in age. Sampling of Sudbury diabase dykes in the Tyson Lake region in 1972 (Church, 1992) showed that the Grenville metamorphism was recognisable in the growth of microscopic garnets in the chilled margins of dykes, which otherwise appeared unmetamorphosed and undeformed other than where they were cut by non-penetrative shear zones.
        Davidson (1986) confirmed the contention of Krogh and Davis that the Killarney granite had undergone deformation before emplacement of pegmatite and Sudbury diabase, as well as Card's (1976) discovery of volcanic rocks in large xenoliths near the margin of the Killarney granite. He also showed that the linear deformation fabric within the eastern margin of the Killarney granite had a different geometry to that in the bordering Grenville gneisses.
        Davidson and Bethune (1988) concurred with Merz's contention that the metadiabase segments cutting 'Grenville' gneisses were correlative with Sudbury diabase dykes in the Southern Province. They documented the presence of metamorphic orthopyroxene in dykes at Broker Lake, and suggested that this indicated considerable uplift across the northeast-striking faults and mylonite zones associated with the 'Grenville Front', but little lateral post-dyke displacement. They further suggested that the 'Grenville Front' in the Tyson Lake area be relocated slightly to the southeast to mark both a change in a change in the geometry of the dikes and of the style of deformation from brittle to ductile in the Sudbury diabase dykes of this region, even although the ductile deformation zones were non penetrative. In particular, Davidson and Bethune suggested that the intrusion of the Sudbury dykes was syntectonic with respect to Grenville style deformation, which therefore must have begun before c. 1.24 Ga in the Tyson-Killarney region.
        This theme was repeated in Green et al. (1988) who proposed that the GLIMPCE seismic fabric of Grenville rocks beneath Georgian Bay about 70 km south of the exposed rocks on the north shore of this region was produced by : 1) depression to lower crustal depths of rocks along the northern margin of the Grenville Province as a result of the progressive stacking of microterranes against the Superior craton, possibly coeval with island-arc magmatism at 1.25-1.3 in the Grenville Central Metasedimentary Belt, and 2) thrusting, after intrusion of the Sudbury diabase dykes, of the rocks buried deeply by the earlier stacking episode back up to shallow depths. Accordingly, the GLIMPCE seismic fabric of the Grenville Front Tectonic Zone thus largely reflects the formation of highly reflective shear and mylonite zones during late Grenville thrusting under ductile conditions, rather then any pre-Sudbury diabase front-parallel deformation fabric.
        Geochronological studies of Haggart et al. (1993) showed that between the Grenville Front mylonite zone east of Killarney and Beaverstone Bay, titanites were progressively reset to Grenville ages, with complet resetting being achieved in the vicinity of the eastern shore of Beaverstone Bay.   Krogh (1994) also showed that monazite in an undeformed in situ pegmatite (Tyson Lake locality 1e) containing inclusions of lineated Huronian metasediment and undeformed pegmatite has a concordant age of 1.45 Ga, as does titanite (locality 1b) in an undeformed pegmatite cutting gneisses southwest of Tyson Lake. Grain tips from zircons in pegmatite at Tyson Lake and Beaverstone Bay also have near concordant ages of 1.45 Ga, whereas titanite from undeformed pegmatite at Beaverstone Bay lies on a 1.45 Ga - 977 Ma chord, 78% discordant towards a time of Grenville resetting. The resetting approximates changes in the metamorphic mineralogy of the Sudbury diabases as they are traced into the Grenville, but with the first appearance of garnet in the chilled margins of the diabases at Tyson Lake providing a more sensitive record of the Grenville thermal event.
        More recently Bethune (1998) has however proposed that the erratic course of Sudbury diabase dikes east of Tyson Lake is the result of 1B - 1C type buckle folding, although the proposal is qualified by the statement that some prominent 90 degree bends are not easily reconciled with buckle folding. Furthermore, the supposedly buckled dyke east of Aqua Lake transects the axial plane traces of tight folds outlined by paragneiss units in this area, and the gneisses here form part of the zone within which undeformed pegmatites have pre-Grenville 1.47 Ga ages. Panels of rock transected by linear east-west trending segments of Sudbury diabase and bordered by zones of ductile mylonite also continue to appear well to the east of this zone, and Grenville deformation may be fully penetrative in character only east of the Beeftea Lake Sudbury Diabase location.
        The distribution of deformed and metamorphosed Sudbury diabase (unit 48) on the Burwash Map sheet of Lumbers (1975), and the presence of penetrative ductile folding in 'Grenville' rocks on the west flank of the Bigwood synform as far west as a boundary line drawn approximately between Oak Lake, Beeftea Lake and Chaughis Bay (?) on the north coast of Georgian Bay, might indicate that the penetrative fabric of the rocks to the west of this line still largely reflects pre-Grenville deformation events, the earliest of which likely even pre-dates intrusion of the c. 1.75 Ga Killarney granite. An old deformation fabric is possible preserved in a shear pod of 2.45 Ga anorthosite in Dryden Township, and in agmatite associated with the 1.75 Ga (Prevec, 1994) mafic rocks of the Wanapitei shear pod, both of which are cut by undeformed, garnet-bearing Sudbury diabase. On the other hand, agmatites, gabbros and dike units of the Red Deer Lake shear pod show no signs of pre-Sudbury diabase internal penetrative deformation. Consequently, while non-penetrative deformation in this sector may well include the formation of Grenville age (post-Sudbury diabase) mylonite zones and the local development of brittle foliation fabrics in the 1.47 Ga Raft Lake (Davidson and Ketchum, 1993 and perhaps Bell Lake intrusions, there is little evidence to support the possibility that the deformation fabric in the gneisses west of the Oak Lake-Beeftea Lake line are of this age. In this respect it might also be noted that quartzite at Beaverstone Bay (Krogh, 1989, p. 63) contains not only euhedral grains of Archean zircon but also 1.75 Ga zircons in the form of long needle-like crystals.
        While it is clear therefore that the boundary between Huronian metasediments and highly deformed gneisses in the region between Wanapitei and Brodil Lake marks the sharp northern limit of the Grenville Province, south of Brodil Lake the northern boundary of Grenville penetrative deformation is more likely to be marked by a necessarily 'fluid' line between White Oak Lake and Chaughis Bay, and some distance to the east of the ductile mylonite zone used by the GLIMPCE project as the eastern boundary of the Grenville Front Tectonic Zone. Since the penetrative fabric west of this line is likely to be pre-1.47 in age, the gneisses within this belt should be ascribed to the Southern structural province.
        It is possible therefore that K-feldspar megacrystic rocks of the Killarney-Tyson lake sector of the "Grenville Front" exhibit both a primary foliation (Brooks, 1967) and a younger cataclastic mylonitisation, and while the latter may locally affect adjacent rocks of the Southern Province, it is not clear yet how this fabric is distributed either within the granites to the south or within the Huronian rocks along strike to the southeast, or the extent to which the fabric may be related to the pre-1.47 Ga foliation of the eastern deformed zone of the Killarney granite.

The Grenville Province (see also http://instruct.uwo.ca/earth-sci/300b-001/grenv.htm)

(Maps yet to be scanned)

It has been argued on the basis of lead isotope data (DeWolf and Mezger, 1994) that in Ontario Archean crust, or Lower Proterozoic rock derived from the Archean, underlies the northern Grenville Province at least as far to the south as Parry Sound. The overlying Grevillian tectonites form a southeasterly dipping thrust stack composed of rocks raging in age from Archean to Late Mesoproterozoic (995 Ma).

Sections across the Grenville Province, Ludden & Hynes, 2000 - grenxsect.jpg
Lithotectonic zones (2000) of the Grenville Province, Ludden & Hynes, 2000 -grenbelts2.jpg

         The thrust stack, from bottom to top, includes the following rock units:
         1) a parautochthonous unit composed of orthogneiss, quartzofeldspathic and quartzose paragneiss, kyanite-garnet schists, and amphibolites, intruded by the 2.45 Ga River Valley anorthosite-gabbro suite, 1.75 Ga gabbros, and 1.75 - 1.605 Ga, 1.47-1.38 Ga, and anorthosite (1.268 -1.222 Ga), granitoid bodies (1.244), and Sudbury diabase (1.238 Ga), all with ages of about 1.24 - 1.22 Ga. The gneissses are Archean in age whereas the metasediments and amphibolites may be Paleoproterozoic. Locally, orthoquartzitic metasediments (e.g. the Alban orthoquartzites) overlie quartzofeldspathic gneisses. The quartzites contain detrital zircons of both Archean (2.7 Ga) and Penokean (1.885 Ga) age, and have Sm/Nd isotopic characteristics intermediate between those of Archean rocks to the north and some younger component. The quartzites may have been deposited in a Mesoproterozoic age sedimentary basin located between the Southern Province and a southerly Penokean or younger arc. Similar quartzites are found along the Ontario - Quebec border northeast of North Bay (D168). The younger source must have been older than 1.47 Ga since the sediments are intruded by granites of this age.
        The southern part of the parautochthon is occupied by Paleoproterozoic metasedimentary gneisses (Barilia) with ca. 1.9 Ga Nd/Nd model ages. They are thought to represent a juvenile off-shore 1.86 Ga Penokean arc, possibly an eastern lateral equivalent of the Penokean arc in Wisconsin to the west of the Great Lakes. As in the case of the rocks further north, the gneisses are intruded by 1.75 and 1.45 Ga granitoids. Grenvillian granites with ages of 1.25 Ga are well developed in the region of Lake Nipissing. The youngest rocks in the parautochthon are garnet granulite and amphibolite dike segments and boudins representing the remains of Sudbury diabase dikes. They are found in all units as far south as the boundary of the parautochthon with the lowermost unit of the overlying allochthonous thrust stack.
       2) The lowermost unit of the allochthonous thrust stack, the Algonquin terrane, is composed of high P-T gneisses (containing eclogites and garnet granulites) which exhibit younger much less consistent Nd model ages (1.87-1.56 Ga). Two groups of orthgneiss have been identified, one group with ages ranging from 1.715-1.610 Ga, an age range equivalent to the Yavapai/Mojavie accretion event and the Mazatzal orogeny of the central and southeastern USA, and the other with ages 1.47-1.375 Ga.     Some eclogite bodies also have protolith ages of about 1.47 - 1.4 Ga, and metamorphic ages (secondary zircon growth) of 1.09 The Algonquin terrane is also distinguished by the presence of bodies of coronitic olivine metagabbro with protolith ages of 1.16 Ga.

Distribution of Early Proterozoic structural provinces of the southern and southwestern United States - lprotmazat1.jpg

        3) The thrust slice above the Algonquin terrane includes the Shawanaga domain outcropping north of the Parry Sound thrust slice, and the Ahmic, upper Go Home and upper Rosseau windows south of the Parry Sound slice. Protolith ages of granitoids are entirely Mesoproterozoic (1.465-1.300 Ga), and Nd model ages are 1.64-1.46 Ga. Eclogites record the oldest metamorphic ages (1.12 Ga) but peak metamorphism could be as young as 1.08 Ga. If the Algonquin and Shawanaga slices are separate terranes, they were stitched by the 1.16 Ga metagabbro suite.
        4) The Parry Sound thrust slice is composed of highly deformed and metamorphosed mafic meta- igneous rocks bordered to the north by anorthosite, anorthositic gabbro, and amphibolite with an age of c. 1.4 Ga. The slice is thought to be exotic and far travelled from an oceanic domain to the southeast.
        5) The Muskoka slice is composed of 1.455 -1.395 Ga rocks with Nd model ages of 1.62-1.41 Ga. Metamorphism took place at 1.095-1.025 Ga but may also predate 1.1 Ga. The 1.16 Ga metagabbros are represented in the Muskoka slice but eclogite bodies either do not exist or have been converted to amphibolite.
                Those granitic rocks with an age of c. 1.45 Ga are common throughout the Grenville as far north as the Southern Province-Grenville boundary zone, and are considered by some to represent a post-orogenic suite of intrusions formed by the melting of older crust.

        Rocks of the 'Allochthonous monocyclic thrust belt includes three slices: the Central Metasedimentary belt, the Frontenac belt, and the Adirondack-Morin belt.
        6) Grenville supergroup carbonates (marbles) and volcanic rocks (amphibolites) of the Central Metasedimentary belt. Anorthosite and associated rocks (Morin) intrusive into this terrain have relatively young Grenville ages (c. 1.0 Ga). The volcanic rocks appear to be derived from the mantle and either represent a Neoproterozoic rift or marginal basin, or a klippe thrust from the south.
            Within the eastern Quebec section of the Grenville Province rocks with model ages of c. 1.5 Ga constitute an oceanic arc terrane referred to as 'Quebecia' by Dickin (2000). Within Quebecia the 1.41-1.39 Ga La Bostonnais igneous complex represents a younger ensialic arc formed after amalgamation of Quebecia with more internal arc terranes.
        7) Frontenac supergroup carbonates and quartzites with detrital zircons as young as 1.3 Ga and as old as 1.415, 1.6-1.795, 1.745-2.065, 2.12-2.58, 3.185. The Frontenac sediments must therefore be younger than 1.3 Ga. They are intruded by 1.17 Ga granites with 1.34 - 1.48 Ga model ages, and quartzofeldspathic gneisses have 1.56 - 2.045 Ga model ages, implying the existence beneath the Frontenac of source material (either basement or derived sediment) older than 2.05 and younger than 1.34.
        8) Adirondack-Morin belt is composed of 1.35 Ga gneisses, 1.17 and 1.08 plutonic suites, and 1.15 anorthosite bodies.

Plate Tectonic models for the development of the Grenville
Plate tectonic model according to Wasteneys et al., 1999 - grenptectwast.jpg
Plate tectonic model according to Carr et al., 2000 - grenptectcarr.jpg

Maps
Bedrock Geology of Ontario, Southern Sheet, Map 2544; Cost: $4.40 + PST/GST + $2.76 shipping: MMIC, Ministry of Northern Development and Mines, 900 Bay St, Room M2-17 Macdonald Block, Toronto, Ontario, M7A 1C3. Telephone: 1- 800-665-4480; Pay to Treasurer of Ontario.

FIGURES

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