Variable unroofing in the western Superior Province - metamorphic evidence and possible origin

2006 ◽  
Vol 43 (7) ◽  
pp. 805-819 ◽  
Author(s):  
Andrew Hynes ◽  
Zixin Song
Keyword(s):  
Superior Province ◽  
Surface Distribution ◽  
Seismic Line ◽  
The North ◽  
Metavolcanic Rocks ◽  
Limited Support ◽  
Greenstone Belts ◽  
Rotation Motion ◽  
East West ◽  
Broad Region

Western Superior Lithoprobe seismic-reflection line 1 exhibits a broad region of northward-dipping reflectors in the Uchi subprovince, which gives way to southward-dipping reflectors farther north in the Berens River sub province. Mafic metavolcanic rocks across the region of northward-dipping reflectors exhibit a decline in metamorphic pressure, from pressures of 6 kbar (1 kbar = 100 MPa) in the south to only 2 kbar 80 km to the north. This indicates that the southern edge of the Uchi subprovince has undergone significantly more unroofing than regions farther north. The differential unroofing is not consistent with a doubly vergent thrusting origin for the northward- and southward-dipping reflector pattern. It could result from a crustal-scale synform, of which the region of northward-dipping reflectors would make up the southern limb. Metamorphic pressures from samples off the seismic line, however, provide only limited support for a regional synform, and suggest that much of the pressure variation may result from deformation associated with motion on late faults that are widespread in the western Superior Province. These faults occur in a WNW-striking set with dextral offsets and an ENE-striking set with sinistral offsets. They could result from north–south compression and east–west extension, provided the faults have rotated towards the east–west direction during deformation. Regional tilting and (or) jostling of crustal blocks is attributed to deformation associated with the fault rotation. Motion on the faults and the associated deformation of intervening fault blocks may be important contributors to the present crustal architecture of the western Superior Province, including the surface distribution and form of the greenstone belts.

Tectonic evolution of two greenstone belts from the Superior Province in Manitoba

1978 ◽  
Vol 15 (11) ◽  
pp. 1808-1816 ◽  
Author(s):  
R. G. Park ◽  
I. F. Ermanovics
Keyword(s):  
Tectonic Evolution ◽  
Superior Province ◽  
The North ◽  
Crenulation Cleavage ◽  
Facies Metamorphism ◽  
Tonalitic Gneiss ◽  
Uniform Stress Field ◽  
Greenstone Belts ◽  
East West ◽  
Lower Group

The Bigstone Lake and Stevenson Lake greenstone belts are two areas of supracrustal rocks surrounded by quartz diorite to granodiorite plutons and by small patches of tonalitic gneiss interpreted as basement to the greenstone belts. The supracrustal sequence is divided into a lower, mainly volcanic, group correlated with the Hayes River Group of Island Lake and an unconformable upper group with roughly equal proportions of sediments and volcanics correlated with the Island Lake 'Series'. The lower group consists of about 4600 m of basaltic and andesitic pillow lavas with minor greywackes and dacitic volcanics. It is partly replaced at the base by the bordering plutons and cut out at the top by the unconformable upper group, which consists of about 2300 m of greywackes, arkoses, and mudstones above a basal conglomerate containing boulders derived from the lower group and from the basement. A further 2100 m of volcanics overlies these sediments.The supracrustal rocks show three phases of deformation. The first, F1, produced major northeast–southwest and east–west synclines. S1 foliation was developed under greenschist facies to low amphibolite facies metamorphism. F2 produced smaller scale steep east–west folds with a crenulation cleavage. Subsequent deformation resulted in chevron folds and conjugate shear belts.The intrusion of the plutons commenced before the F1 deformation and partly controlled it, but a further period of plutonic intrusion occurred after F1 and before F2.The north–south compressive stress prevailing during F2 and later deformation under waning metamorphism implies that the batholiths in the vicinity of the greenstone belts had completely solidified and that the crust was rigid enough to transmit a uniform stress field. The dominance of east–west structural grain in this part of the Superior Province indicates that these conditions were general.

New high-precision U–Pb ages for the Island Lake greenstone belt, northwestern Superior Province: implications for regional stratigraphy and the extent of the North Caribou terrane

2006 ◽  
Vol 43 (7) ◽  
pp. 789-803 ◽  
Author(s):  
Jen Parks ◽  
Shoufa Lin ◽  
Don Davis ◽  
Tim Corkery
Keyword(s):  
Shear Zone ◽  
High Precision ◽  
Greenstone Belt ◽  
Superior Province ◽  
Geological History ◽  
Isotopic Data ◽  
Mapping Study ◽  
The North ◽  
Crustal Block ◽  
Greenstone Belts

A combined U–Pb and field mapping study of the Island Lake greenstone belt has led to the recognition of three distinct supracrustal assemblages. These assemblages record magmatic episodes at 2897, 2852, and 2744 Ma. Voluminous plutonic rocks within the belt range in age from 2894 to 2730 Ma, with a concentration at 2744 Ma. U–Pb data also show that a regional fault that transects the belt, the Savage Island shear zone, is not a terrane-bounding structure. The youngest sedimentary group in the belt, the Island Lake Group, has an unconformable relationship with older plutons. Sedimentation in this group is bracketed between 2712 and 2699 Ma. This group, and others similar to it in the northwestern Superior Province, is akin to Timiskaming-type sedimentary groups found throughout the Superior Province and in other Archean cratons. These data confirm that this belt experienced a complex geological history that spanned at least 200 million years, which is typical of greenstone belts in this area. Age correlations between the Island Lake belt and other belts in the northwest Superior Province suggest the existence of a volcanic "megasequence". This evidence, in combination with Nd isotopic data, indicates that the Oxford–Stull domain, and the Munro Lake, Island Lake, and North Caribou terranes may have been part of a much larger reworked Mesoarchean crustal block, the North Caribou superterrane. It appears that the Superior Province was assembled by accretion of such large independent crustal blocks, whose individual histories involved extended periods of autochthonous development.

Central Superior Province geology: evidence for an allochthonous, ensimatic, southern Abitibi greenstone belt

1990 ◽  
Vol 27 (4) ◽  
pp. 582-589 ◽  
Author(s):  
S. L. Jackson ◽  
R. H. Sutcliffe
Keyword(s):  
Crustal Structure ◽  
Greenstone Belt ◽  
Superior Province ◽  
Low Grade ◽  
Simple Correlation ◽  
Abitibi Greenstone Belt ◽  
Structural Style ◽  
Metavolcanic Rocks ◽  
Crustal Model ◽  
Greenstone Belts

Published U–Pb geochronological, geological, and petrochemical data suggest that there are late Archean ensialic greenstone belts (GB) (Michipicoten GB and possibly the northern Abitibi GB), ensimatic greenstone belts (southern Abitibi GB and Batchawana GB), and possibly a transitional ensimatic–ensialic greenstone belt (Swayze GB) in the central Superior Province. This lateral crustal variability may preclude simple correlation of the Michipicoten GB and its substrata, as exposed in the Kapuskasing Uplift, with that of the southern Abitibi GB. Furthermore, this lateral variability may have determined the locus of the Kapuskasing Uplift. Therefore, although the Kapuskasing Uplift provides a useful general crustal model, alternative models of crustal structure and tectonics for the southern Abitibi GB warrant examination.Thrusting of a juvenile, ensimatic southern Abitibi GB over a terrane containing evolved crust is consistent with (i) the structural style of the southern Abitibi GB; (ii) juvenile southern Abitibi GB metavolcanic rocks intruded by rocks having an isotopically evolved, older component; and (iii) Proterozoic extension that preserved low-grade metavolcanic rocks within the down-dropped Cobalt Embayment, which is bounded by higher grade terranes to the east and west.

Two komatiitic pyroclastic units, Superior Province, northwestern Ontario: their geology, petrography, and correlation

1991 ◽  
Vol 28 (9) ◽  
pp. 1455-1470 ◽  
Author(s):  
Stephen J. Schaefer ◽  
Penelope Morton
Keyword(s):  
Explosive Volcanism ◽  
Pyroclastic Rock ◽  
Superior Province ◽  
Metasedimentary Rocks ◽  
The North ◽  
Northwestern Ontario ◽  
Volcanic Breccia ◽  
Metavolcanic Rocks ◽  
Volcaniclastic Rocks ◽  
Lapilli Tuff

Two Archean komatiitic pyroclastic rock units occur on opposite sides of the Quetico Fault in northwestern Ontario. The eastern unit, the Dismal Ashrock, is located 3 km north of Atikokan, Ontario, on the north side of the Quetico Fault within the Wabigoon Subprovince of the Superior Province. It is part of a suprascrustal sequence, the Steep Rock Group. The Grassy Portage Bay ultramafic pyroclastic rock unit (GUP) is located 100 km to the west, on the south side of the Quetico Fault, and is part of an overturned succession comprising mafic metavolcanic rocks, GUP, and metasedimentary rocks. The Dismal Ashrock dips steeply, is little deformed, has undergone greenschist metamorphism, and is divided into komatiitic lapilli tuff, komatiitic volcanic breccia, komatiitic volcaniclastic rocks, and a mafic pillowed flow. GUP outcrops form an arcuate fold interference pattern, are strongly deformed, and have undergone amphibolite metamorphism. GUP is divided into komatiitic lapilli tuff and komatiitic volcanic breccia. Both pyroclastic units contain cored and composite lapilli, evidence for explosive volcanism. Locally, some of the lapilli fragments are highly vesicular (up to 30% by volume), greater than reported for any other komatiites. Other fragments show no vesicularity. The low vesicularity of some of the pyroclasts and, in the case of the Dismal Ashrock, their association with pinowed lava flows may indicate explosive hydrovolcanic activity. The Dismal Ashrock and GUP are high in MgO, Cr, and Ni and are unusually enriched in Fe, Ti, Zr, Mn, P, Ba, Nb, Rb, and Sr compared with other komatiites. These unique geochemical compositions are not understood at this time.

Paleomagnetism of Archean granites and Matachewan dikes in the Wawa Subprovince, Ontario: reevaluation of the Archean apparent polar wander path

1990 ◽  
Vol 27 (8) ◽  
pp. 1031-1039 ◽  
Author(s):  
T. A. Vandall ◽  
D. T. A. Symons
Keyword(s):  
Single Component ◽  
Superior Province ◽  
Polar Wander ◽  
Early Proterozoic ◽  
Dike Swarm ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Quartz Monzonite ◽  
Greenstone Belts ◽  
Tectonic Rotation

Paleomagnetic measurements have been completed on 400 specimens from dated Archean granites and Matachewan dikes in the Michipicoten and Gamitagama greenstone belts in the western Wawa Subprovince of the Superior Province, Ontario. Detailed alternating-field and thermal step demagnetization analyses were used to isolate stable remanence directions. A single-component remanence was isolated within three adjacent dated granitic plutons on the eastern margin of the Michipicoten belt, including the Hawk Lake trondhjemite, the Southern external granite, and the Eastern external granite (HSE). The maximum possible age for this remanence is constrained by the intrusion of the last pluton at 2694 Ma. The corresponding HSE paleopole is located at 10°W, 41°S (dp = 8°, dm = 13°). A second paleopole, NB, is derived from the Northern external granite and the Baldhead River quartz monzonite, which give U–Pb zircon ages of 2662 and 2668 Ma, respectively. Their single-component remanence defines a paleopole on the Archean apparent polar wander path (APWP) at 15°E, 27°S (dp = 8°, dm = 13°), with a maximum possible age of 2.66 Ga. A third paleopole, GD, is derived from the north-northwest-trending Gamitagama diabase dikes and yields a position of 57°E, 41°N (dp = 7°, dm = 14°), which agrees with poles determined by other workers from the 2454 Ma Matachewan dike swarm. The GD pole, along with previously determined Matachewan dike poles, demonstrates that a tectonically stable craton has existed since intrusion of this extensive dike swarm, and it improves the precision of the 2454 Ma Matachewan pole on the APWP. These poles, when compared with coeval poles from the eastern side of the Kapuskasing Structural Zone in the Superior Province, imply no tectonic rotation or translation between the Wawa and Abitibi subprovinces along this Early Proterozoic structure.

The transition from dyke to sill in the Otish Mountains, Quebec; relations to host-rock characteristics

1987 ◽  
Vol 24 (1) ◽  
pp. 110-116 ◽  
Author(s):  
E. H. Chown ◽  
Guy Archambault
Keyword(s):  
Host Rock ◽  
Sedimentary Basin ◽  
Superior Province ◽  
Sedimentary Sequence ◽  
Grenville Province ◽  
Clastic Rocks ◽  
The North ◽  
Dyke Swarms ◽  
East West

The Otish gabbro sills intrude Aphebian clastic rocks lying uncanformably on the Archean rocks of the Superior Province close to its juncture with the Grenville Province. The sills are undated but by inference may be ca. 1750 Ma. Two dyke swarms are known in the vicinity, the 1950 Ma, northwest-trending Mistassini dykes and a northeast-trending swarm of unknown age extending 600 km from Senneterre to the Otish Mountains and possibly another 300 km to the northeast. The trends of feeder dykes to the Otish sills are physically compatible with the dominant northeast dykes, which are therefore considered to be the feeders and should be called the Otish dykes.The Otish sills appear to be a unique occurrence along the 900 km dyke trend, possibly, but not entirely because of the chances of preservation. The general form of the Otish sill complex is a triangle bounded on the north by the east–west lip of the sedimentary basin, on the southwest by a northwest-trending Otish feeder dyke, and on the southeast by the underlying northeast feeder dykes. These dykes segment the sills into a series of four or five separate intrusive complexes, small in the northwest and becoming larger to the southeast. The regular inclination of tension fractures in the basal chilled margin of the sills suggests a crude pattern of flow from the feeder dykes inward to the centre of the sheets.Interpretation of the sedimentary sequence indicates that the Otish clastics were deposited higher on the paleoslope than the Mistassini carbonates. Although few dykes intrude the deeper basin, the magma rose and formed sills within the higher sequence. This variation may be explained by the different mechanical character of the two types of cover rock controlling the dyke behaviour. The relatively plasto-viscous Mistassini carbonate–shale sequence resisted the formation of tension fractures, whereas the brittle elastics opened easily, allowing the magma to rise into the stratified sequence, forming the sill complexes.

Cooperative seismic surveys across the Superior–Churchill boundary zone in southern Canada

1980 ◽  
Vol 17 (5) ◽  
pp. 617-632 ◽  
Author(s):  
A. G. Green ◽  
O. G. Stephenson ◽  
G. D. Mann ◽  
E. R. Kanasewich ◽  
G. L. Cumming ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Small Region ◽  
Superior Province ◽  
Boundary Zone ◽  
Reflection Point ◽  
Preliminary Results ◽  
The North ◽  
Seismic Surveying ◽  
Point Data ◽  
East West

Three seismic surveying techniques have been employed in a study of the Superior–Churchill boundary zone in southwestern Manitoba and southeastern Saskatchewan. Two reversed refraction – wide angle reflection profiles, one north–south within the Superior tectonic province and one east–west traversing part of the Superior tectonic province, the boundary zone, and part of the Churchill tectonic province, were used to obtain information on the gross velocity structure of the crust over a large region. Preliminary results from these surveys suggest that the crust beneath the north–south profile is typical of previously published crustal models of the western Superior Province, while the crust beneath the east–west profile is similar to that reported for the Churchill Province in eastern Alberta and western Saskatchewan. Generally, the upper and middle crustal sections in the two tectonic provinces are quite similar, while the lower crust in the Churchill Province has a distinct ~7 km/s layer that is not observed in this part of the Superior Province. In addition, there is a marked thickening of the crust within the boundary zone from ~41 km in the Superior Province to ~46 km in the Churchill Province.A 72 km length of fourfold common reflection point coverage was collected in order to determine the fine structure of the crust over a relatively small region. Reliable stacking velocities that may be used for future processing of the common reflection point data were obtained from an expanding spread reflection survey. Various data processing techniques, including common reflection point stacking, linear and nonlinear velocity filtering, and velocity spectral analysis, have been successful in enhancing reflections from the middle and lower parts of the crust. From the preliminary results of the two reflection surveys, it may be concluded that those parts of the crust which are shown as relatively simple layers in the refraction derived models, may be quite complex when viewed on a smaller scale.

Crustal models of the eastern Superior Province, Quebec, derived from new gravity data

2000 ◽  
Vol 37 (2-3) ◽  
pp. 385-397 ◽  
Author(s):  
Hamid Telmat ◽  
Jean-Claude Mareschal ◽  
Clément Gariépy ◽  
Jean David ◽  
Caroline N Antonuk
Keyword(s):  
Gravity Data ◽  
Seismic Profile ◽  
Density Variation ◽  
Crustal Thickening ◽  
Superior Province ◽  
Seismic Line ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Field Evidence

New gravity data were collected in the Nemiscau and La Grande subprovinces of the Superior Province. This ~350 km gravity profile follows the Matagami-Radisson road and extends northward the gravity transect along the ~260 km long Lithoprobe seismic line 48, across the northern Abitibi and Opatica subprovinces. For the Abitibi-Opatica segment, the interpretation is consistent with the Lithoprobe seismic profile. It calls for crustal thickening near the boundary between the Abitibi and Opatica belts, where the Moho is ~5 km deeper than in the Abitibi subprovince and ~8 km deeper than in the northern Opatica subprovince. The gravity model complements the seismic reflection data and provides information on the uppermost supracrustal sequences poorly imaged in the seismic profile. Most of the intrusive rocks in the Opatica Belt appear as thin (<5 km) bodies. Across the Nemiscau and La Grande subprovinces, the Bouguer anomalies are of short wavelengths and their sources lie in the upper crust. The crustal thickness is constant from the northern Opatica Belt throughout the southern part of the Nemiscau subprovince. Density measurements indicate that the upper crustal density is higher in the Nemiscau and La Grande subprovinces than in the Abitibi and Opatica belts. There is some crustal thickening beneath the La Grande subprovince, and a gravity high at the northern end of the subprovince is related to the occurrence of mafic supracrustal sequences. The gravity anomaly signature associated with the lateral density variation and field evidence indicate that the main tectonic boundaries dip to the north.

scholarly journals Electromagnetic image of the Trans-Hudson orogen — THO94 transect

2005 ◽  
Vol 42 (4) ◽  
pp. 479-493 ◽  
Author(s):  
Xavier Garcia ◽  
Alan G Jones
Keyword(s):  
Regional Scale ◽  
Hudson Bay ◽  
Central Plains ◽  
Seismic Line ◽  
The North ◽  
Crustal Structures ◽  
The Subject ◽  
Surface Geology ◽  
Resistive Structure ◽  
East West

The North American Central Plains (NACP) anomaly in enhanced electric conductivity and its relationship with the Paleoproterozoic Trans-Hudson orogen (THO) has been studied under the auspices of Lithoprobe for over a decade. The NACP anomaly was the first geophysical evidence of the existence of the THO beneath the Phanerozoic sediments of the Central Plains. This anomaly, detected geomagnetically in the late 1960s, has been the subject of a number magnetotelluric studies from the early 1980s. The PanCanadian and Geological Survey of Canada experiments in the 1980s and the Lithoprobe experiments in the 1990s together comprise four east–west and one north–south regional-scale profiles in Saskatchewan perpendicular to the strike of the orogen. In this paper, data from the northernmost line, coincident with seismic line S2B, are analysed and interpreted, and are shown to be key in determining the northern extension of the NACP anomaly. Dimensionality analysis confirms the rotation of deep crustal structures eastward to Hudson Bay, as earlier proposed on the basis of broad-scale geomagnetic studies. On this profile, as with the profile at the edge of the Paleozoic sediments, the NACP anomaly is imaged as lying within the La Ronge domain, in contact with the Rottenstone domain, and structurally above the Guncoat thrust, a late compressional feature. The location of the anomaly together with the surface geology suggests that the anomaly is caused either by sulphide mineralization concentrated in the hinges of folds, by graphite, or by a combination of both. Our interpretation of the data is consistent with that from other profiles, and suggests that the NACP anomaly was formed as a consequence of subduction and collisional processes involving northward subduction of the internides of the THO beneath the Hearne craton. On the southern part of this profile, a resistive structure is identified as the Sask craton, suggesting that Proterozoic rocks are above Archean rocks in the THO.

Chronology of transpression, magmatism, and sedimentation in the Thompson Nickel Belt (Manitoba, Canada) and timing of Trans-Hudson Orogen – Superior Province collisionThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 295-324 ◽  
Author(s):  
Nuno Machado ◽  
Denis Gapais ◽  
Alain Potrel ◽  
Gilles Gauthier ◽  
Erwan Hallot
Keyword(s):  
Crustal Thickening ◽  
Superior Province ◽  
Mafic Intrusions ◽  
The North ◽  
Continental Block ◽  
Diffuse Zone ◽  
Detrital Zircon Ages ◽  
Superior Craton ◽  
East West ◽  
Group Part

The Thompson Nickel Belt marks the boundary between the Archean Superior Province and the Trans-Hudson Orogen in Canada. It comprises Archean gneisses, and Paleoproterozoic rocks with metasediments and metavolcanites (Ospwagan Group) and intrusions. The gneisses are frequently migmatitic and host numerous pegmatites. The western belt boundary is a fault contact with the Kisseynew Domain of the Reindeer Zone. In the south, the transition zone between the belt and the Kisseynew Domain comprises granitoids and a detrital sequence (Grass River Group), part of which grades into turbidites in the Kisseynew Domain. The eastern belt boundary is a diffuse zone where the Archean east–west (E–W) structural trend changes into the north-northeast (NNE) trend of the belt. This paper presents U–Pb ages for granitoids and 207Pb/206Pb detrital zircon ages from the Ospwagan and Grass River groups. Ages and a comparison of events in the belt and in the eastern Reindeer Zone have major implications. The change from stable platform deposits to syn-tectonic filling and emplacement of mafic intrusions in the Ospwagan Group are attributed to the convergence between the Reindeer Zone and the Superior Province at 1891–1885 Ma. At ca. 1850 Ma, continuing convergence led to drowning of marginal basins of the Superior craton and to the development of a transpressive regime in the belt, the onset of which could be as old as ca. 1885 Ma. Metamorphic ages of 1818–1785 record closure of the Kisseynew basin and crustal thickening. Collision of the new continental block with the Superior Province was accommodated by transpression until 1750–1720 Ma.

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