Deformation across the western Quetico subprovince and adjacent boundarl regions in Minnesota

1992 ◽  
Vol 29 (10) ◽  
pp. 2087-2103 ◽  
Author(s):  
Robert L. Bauer ◽  
Peter J. Hudleston ◽  
David L. Southwick
Keyword(s):  
Shear Zones ◽  
Lower Grade ◽  
Seine River ◽  
Complex Deformation ◽  
Metasedimentary Rocks ◽  
Regional Deformation ◽  
Oblique Convergence ◽  
Deformation Features ◽  
Ductile Shear ◽  
East West

North- to northwest-directed crustal shortening across the western Quetico subprovince and its boundary regions produced a complex deformation sequence within the Quetico belt and resulted in concentrated zones of dextral ductile shear in the boundary regions within the adjacent greenstone–granite terranes. In this paper, we review and introduce new data on the regional deformation features and their geometries and discuss the history of generation of these features. We attribute the deformation sequence to differential partitioning of shortening and shear strains during dextral transpression associated with oblique convergence and accretion along the southern margin of the Superior Province.The turbiditic wacke in the western Quetico subprovince, now typically amphibolite-facies schist and migmatite, underwent an early deformation stage that included recumbent folding (F1) and the generation of an S1 bedding-parallel foliation. This event is most evident along the northern and southern boundaries of the subprovince, but it is also recognized in the lower grade metasedimentary rocks in the adjacent Wawa and Wabigoon subprovinces. In these subprovinces, F1 folding may have been associated with higher level thrusting and allochthonous emplacement of greenstone units. Despite our F1 designation of this event, it it unlikely that this deformation was synchronous across the subprovinces.Widespread upright folding of the overturned limbs of F1 folds produced moderately to gently plunging F2 folds with east–west-trending axial planes. F, folds, with an associated L, stretching lineation subparallel to fold hinges, are well developed along the southern and northern margins of the Quetico subprovince and in the metasediments of the adjacent Wawa subprovince. During this event, ductile dextral shear was concentrated in steeply dipping east–west-trending shear zones in the Wawa subprovince and in the region of the Rainy Lake – Seine River fault along the Quetico–Wabigoon subprovince boundary. In the northern Wawa subprovince, shear was strongly concentrated in relatively incompetent, steeply dipping metasedimentary and tuffaceous units interlayered with more competent greenstone units. Concentrated zones of ductile shear are not evident within the Quetico subprovince away from its boundary regions. However, emplacement of syntectonic plutons in the central Quetico reoriented F2 folds which were then refolded by large regional F3 folds during continued regional shortening.

Deformation at an Archean subprovince boundary, northern Minnesota

1991 ◽  
Vol 28 (2) ◽  
pp. 292-307 ◽  
Author(s):  
John R. Tabor ◽  
Peter J. Hudleston
Keyword(s):  
Shear Zones ◽  
Wall Rock ◽  
Amphibolite Facies ◽  
Lower Grade ◽  
Seine River ◽  
Northern Margin ◽  
Shear Structures ◽  
The North ◽  
Dextral Shear ◽  
East West

Structural analysis in the northern margin of the Quetico subprovince (part of the Archean Superior Province of the Canadian Shield) in Minnesota reveals that the main deformation involved polyphase folding (F1 recumbent and nappe-like, and F2 upright, east–west trending, and tight to isoclinal) during regional ductile transpression and amphibolite-facies metamorphism. A younger deformation, developed during the latter stages of regional transpression, resulted in the generation of localized ultraphyllonites along the steeply dipping Rainy Lake – Seine River fault (RLSRF), the major fault separating the Quetico subprovince from the Rainy Lake wrench zone (a wedge-shaped block between the Quetico and Wabigoon subprovinces). The transpression involved north–south shortening and east–west dextral shear. The presence of shear zones in amphibolite-facies wall rock south of the fault and in lower grade ultraphyllonites within the RLSRF suggests that localization of shear occurred by work and (or) reaction softening, possibly enhanced by the influx of fluids during regional cooling. The youngest structures in the wall rock are conjugate brittle faults oriented similarly to the youngest ductile shear structures in the RLSRF, indicating that the zone of transpression widened following the stage of strain localization, possibly due to work hardening during continued regional cooling. Widening of the zone of deformation was accompanied by an increase in the relative intensity of the north–south shortening component of transpression, revealed by chloritized necks of boudinaged quartz ribbons, quartz and calcite microfabrics, and flattening strains. Protracted ductile flow and localized greenschist-facies conditions in the RLSRF, which occurred during widening of the zone of deformation and rotation of the kinematic frame (to produce north–south shortening structures), are best explained by an influx of fluid phases.Mesostructures and quartz microfabrics in late tectonic (but synkinematic) peraluminous leucogranitoid intrusions and host schist 10 km south of the RLSRF record north–south shortening, but not east–west dextral shear, and further support late north–south shortening across the RLSRF.Tectonic settings for the RLSRF include (i) a suture between distinct lithotectonic terranes or (ii) a zone of localization of deformation within the northern margin of the Quetico subprovince following collision between the Quetico and Wabigoon terranes.

Structure of the Lac Nominingue – Mont-Laurier region, Central Metasedimentary Belt, Quebec Grenville Province

2001 ◽  
Vol 38 (5) ◽  
pp. 787-802
Author(s):  
L B Harris ◽  
B Rivard ◽  
L Corriveau
Keyword(s):  
Regional Scale ◽  
Shear Zones ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Gneiss Dome ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Ductile Shear Zones ◽  
Ductile Shear ◽  
East West

The Lac Nominingue – Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation – transposed compositional layering (S1; host to peak-pressure parageneses) has been folded by isoclinal folds (F2 and F3) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F3 folds, indicating that 1.20–1.18 Ga granulite-facies metamorphism post-dated D3. D3 structures are cut by ductile shear zones and boudinaged in D4 and are folded by regional-scale, open, upright north–south folds (F5). Folds with shallowly dipping axial surfaces (F6) are subsequently developed in the Sourd group. F5 (and probably F6) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the Nominingue–Chénéville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F8) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F2 to F5 folds may have formed during either subhorizontal, east–west contraction or east–west extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESE–WNW contraction and NNE–SSW (orogen-parallel) extension in D7 syn- to post-intrusion of the Chevreuil suite. F8 folds imply a late, Grenvillian SSE–NNW contraction.

Sign in / Sign up

Export Citation Format

Share Document