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TitleThe distinct metamorphic stages and structural styles of the 1.94-1.86 Ga Snowbird Orogen, Northwest Territories, Canada
 
AuthorThiessen, E J; Gibson, H D; Regis, D; Pehrsson, S J; Ashley, K T; Smit, M A
SourceJournal of Metamorphic Geology vol. 38, issue 9, 2020 p. 963-992, https://doi.org/10.1111/jmg.12556 Open Access logo Open Access
Image
Year2020
Alt SeriesNatural Resources Canada, Contribution Series 20200303
PublisherBlackwell Publishing Inc.
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf; html
ProvinceNorthwest Territories; Alberta; Saskatchewan; Manitoba
NTS64K; 64L; 64M; 64N; 65C; 65D; 65E; 65F; 65K; 65L; 74I; 74J; 74K; 74L; 74M; 74N; 74O; 74P; 75A; 75B; 75C; 75D; 75E; 75F; 75G; 75H; 75I; 75J; 75K; 75L; 84I; 84P; 85A; 85H; 85I
AreaLake Athabasca
Lat/Long WENS-112.7078 -100.6586 62.4308 58.4936
Subjectstectonics; structural geology; igneous and metamorphic petrology; geochemistry; geochronology; Science and Technology; Nature and Environment; tectonic evolution; metamorphism; deformation; orogenesis; folding; shearing; thermal history; trace element geochemistry; major element geochemistry; radiometric dating; uranium lead dating; inclusions; pressure-temperature conditions; structural trends; cleavage; metamorphic facies; Archean; Rae Craton; Snowbird Orogen; Paleoproterozoic; Laurentia; Dodge-Snowbird Domain; Wholdaia Lake Shear Zone; Precambrian; Proterozoic
Illustrationslocation maps; geoscientific sketch maps; stereonets; photomicrographs; photographs; tables; profiles; phase diagrams; geochronological charts; bar graphs; Concordia diagrams; plots; block diagrams
Released2020 07 20
AbstractPalaeoproterozoic orogenesis within the Archean southeastern Rae craton is related to the initial amalgamation of Laurentia. Characterizing the accompanying tectonic processes during this time has been complicated due to polymetamorphism, which results in the obscuring of the age record of the terranes involved. To improve the knowledge of the tectonic evolution of the South Rae Craton, petrologic and structural analyses are applied in conjunction with in situ trace element chemistry, inclusion barometry, U-Pb monazite and titanite, and Lu-Hf garnet chronology. The data robustly constrain Palaeoproterozoic pressure-temperature-time paths of major deformational events along the southeastern Rae craton margin. D1 occurred between 1.94 and 1.93 Ga in the Dodge-Snowbird domain, which included prograde burial of metasedimentary rocks, deposited at 2.2-2.0 Ga, and the development of migmatitic layering and east-southeast trending folds (S1, F1). Peak metamorphism is recorded in metasedimentary units at c. 1.93 Ga when rocks reached conditions of 9.0-10.5 kbar and 810-830°C. Within the Dodge-Snowbird domain, D2 imparted north-northeast trending open folds and associated axial planar cleavage (S2, F2) between 1.93 and 1.90 Ga during east-west compression that appears to have been synchronous with cooling and exhumation. Later D2 deformation, localized within the Wholdaia Lake shear zone (WLsz; ST1), developed in the footwall of this thrust-sense structure at 1,873 ± 5 Ma at conditions of 9.5-11.0 kbar and 820-850°C. The hangingwall Dodge-Snowbird domain had already cooled to below 300°C by then, indicating a significant structural and metamorphic break across the domain's western boundary. A new phase of unroofing (D3) involved pervasive amphibolite- to greenschist facies extensional shearing (ST2) within the WLsz, which overprinted ST1 foliations between 1.87 and 1.86 Ga. Continued greenschist facies shearing younger than 1.86 Ga likely ended by c. 1.83 Ga when lamprophyre dykes cut the structure, which was followed by cooling until c. 1.80 Ga. This work highlights the utility and application of multiple chronometers (zircon, monazite, titanite, garnet) along with structural and petrologic analysis that together can resolve precise orogenic cycles in polymetamorphic terranes that may otherwise be undetected. The time-resolved P-T-D histories derived here enable more robust interpretations regarding the nature and evolution of 1.9 Ga tectonism along the southeast Rae craton margin, which may be used to refine models for Laurentian terrane amalgamation.
GEOSCAN ID326941

 
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