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TitleDeformation and extensional exhumation of 1.9 Ga high-pressure granulites along the Wholdaia Lake shear zone, south Rae craton, Northwest Territories, Canada
 
AuthorThiessen, E J; Gibson, H D; Regis, D; Pehrsson, S J
SourceLithosphere vol. 10, 5, 2018 p. 641-661, https://doi.org/10.1130/L704.1 Open Access logo Open Access
Image
Year2018
Alt SeriesNatural Resources Canada, Contribution Series 20200252
PublisherGeological Society of America
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories; Saskatchewan
NTS74I; 74J; 74K; 74N; 74O; 74P; 64M; 65C; 65D; 65E; 65F; 65G; 65J; 65K; 65L; 75A; 75B; 75H
AreaWholdaia Lake
Lat/Long WENS-110.0000 -98.0000 63.0000 58.0000
Subjectstectonics; geochemistry; geochronology; Science and Technology; Nature and Environment; deformation; granulites; shear zones; zircon; geochronometry; uranium lead dating; crustal studies; Rae Craton; Precambrian; Proterozoic
Illustrationslocation maps; magnetic maps; photographs; photomicrographs; tables; plots; Concordia diagrams; schematic models
ProgramGEM2: Geo-mapping for Energy and Minerals South Rae Province Bedrock/Surficial geology
Released2018 08 31
AbstractThe origin of high-pressure granulites in the south Rae craton and Snowbird tectonic zone (STZ) is highly enigmatic. Current models for their formation and exhumation envisage continental collision at 2.55 Ga and intracratonic orogenesis at 1.9 Ga, or collision and exhumation at ca. 1.9 Ga. As an attempt to reconcile these disparate models, we conducted a regional and detailed mapping program along a geophysical discontinuity 100 km west of the STZ within the south Rae craton of the Northwest Territories, Canada. This work presents the discovery of a new crustal-scale shear zone, the Wholdaia Lake shear zone (WLsz), which deformed and transposed host rocks into a 20-km-wide and 300-km-long ductile high-strain zone. U-Pb zircon geochronology was utilized to establish host-rock crystallization ages, timing of deposition of metasedimentary rocks, and age constraints of metamorphism and ductile shearing. Hanging-wall metasedimentary rocks have a new depositional range of 1.98-1.93 Ga and contain abundant metamorphic zircon at 1.91 Ga. The protoliths of the footwall mafic granulite orthogneisses crystallized at 2.6 Ga and were metamorphosed at 1.9 Ga, which extends the known footprint of 1.9 Ga metamorphism 100 km west of the STZ. During and after 1.9 Ga metamorphism, the WLsz began progressively exhuming footwall rocks in three distinct stages, associated with (1) normal-oblique shearing at high-pressure granulite-facies conditions, (2) normal-oblique shearing accompanied by mylonitization at amphibolite-facies conditions, and (3) normal-oblique shearing with ultramylonite development at amphibolite-to greenschist-facies conditions. Ductile shearing was waning by 1.86 Ga, based on ages obtained from late syn- to postkinematic crosscutting dikes. Collectively, the WLsz in concert with other regional structures aided both extensional and thrust-sense exhumation of a large high-grade terrane at 1.9 Ga in the south Rae craton.
Summary(Plain Language Summary, not published)
Models for the Snowbird tectonic zone (STZ) include intracatonic orogenesis and proximal continental collision at 2.55 Ga or 1.90 Ga. To reconcile these models we conducted a mapping program along a geophysical discontinuity 80 km west of the STZ within the south Rae craton of Northwest Territories. We present a new crustal-scale shear zone, the Wholdaia Lake shear zone (WLsz) that deformed and transposed wallrocks into a 20 km wide, 300 km long ductile high-strain zone. Hanging wall metasediments have a new depositional range of 1.96-1.93 Ga and contain metamorphic zircon at 1.91 Ga. Footwall mafic granulites crystallized at 2.6 Ga and were metamorphosed at 1.90 Ga. The WLsz began progressively exhuming footwall rocks in three stages, 1) normal-sense high-pressure granulite-facies shearing, 2) normal-oblique amphibolite-facies mylonite shearing and, 3) normal-oblique amphibolite- to greenschist-facies ultramylonites shearing. Ductile shearing was largely over by 1.86 Ga due to syn- post-kinematic crosscutting dikes.
GEOSCAN ID326664

 
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