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TitreStructural, petrological and U-Pb SHRIMP geochronological study of the western Beaverlodge domain: Implications for crustal architecture, multi-stageorogenesis and the extent of the Taltson orogen in the SW Rae craton,Canadian Shield
AuteurBethune, K M; Berman, R G; Rayner, N; Ashton, K E
SourcePrecambrian Research vol. 232, 2013 p. 89-118,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120063
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC74N; 74O; 74P
Lat/Long OENS-110.0000 -104.0000 60.0000 59.0000
Sujetscaractéristiques structurales; datations au uranium-plomb; datation au uranium-plomb; interprétations radiométriques; datation radiométrique; Archéen; roches ignées; roches métamorphiques; granites; gneiss; Domaine de Beaverlodge ; Orogène de Taltson ; Craton de Rae ; géologie structurale; géochronologie; pétrologie ignée et métamorphique; tectonique; Précambrien
Illustrationslocation maps; photomicrographs; Concordia diagrams; plots
ProgrammeLa géocartographie de l'énergie et des minéraux - Les frontières de la géocartographie, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
The Beaverlodge domain is a polydeformed Precambrian terrane in the southwestern Rae craton whoserocks variably record the effects of Archean tectonism and four major Paleoproterozoic tectonic events:the 2.5-2.3 Ga Arrowsmith orogeny, the 1.99-1.93 Ga Taltson orogeny, the ca. 1.90 Ga Snowbird orogenyand the ca. 1.87-1.80 Ga Hudsonian orogeny. Structural-metamorphic analysis and in situ U-Pb SHRIMPzircon and monazite geochronology reported herein demonstrate that this domain consists of two mainstructural levels variably exposed due to complex interference folding: a lower level comprising mainlyhigh-grade Archean (ca. 3.0 and 2.7-2.6 Ga) metaplutonic and metasedimentary gneisses and a higherlevel comprising mainly ca. 2.33 to <2.17 Ga supracrustal rocks of the Murmac Bay Group at more vari-able metamorphic grade. Whereas the older package underwent thermal and/or metamorphic events inthe Archean (ca. 2.57 Ga) and early Paleoproterozoic (ca. 2.34 Ga; Arrowsmith orogeny), rocks at higherstructural levels bear no record of these events, recording only younger (1.94-1.90 Ga) metamorphisminterpreted to reflect two further stages of orogenesis. The first stage, correlated with Taltson orogeny,involved tight to isoclinal folding (D1/2) that led to development of the composite ESE-trending (S0/S1/S2)transposition foliation followed by more open folding (D3). The absence of Taltson-age plutonic rocks,except for low-volume crustal melts, suggests that this cycle was driven by crustal thickening, consis-tent with a clockwise P-T-t path derived for one sample. The high degree of strain along the contactbetween Archean rocks and the Murmac Bay Group, along with local structural discordance, indicatessome degree of translation of cover rocks over basement during this stage. Pelitic rocks at higher structurallevels (low- to medium-grade zone) underwent prograde metamorphism to middle amphibolite facieswhereas rocks at deeper structural levels (high-grade zone) attained upper amphibolite facies condi-tions. Monazite data bracket prograde metamorphism (and related garnet growth) between 1939 ± 6 Maand 1934 ± 5 Ma. The second stage, dated most precisely at 1906 ± 7 Ma, involved refolding of D1to D3structures about NE-trending axes (F4) and coeval dextral shearing and is correlated with Snowbird oro-genesis. Rocks of the low- to medium-grade zone were held at roughly the same crustal level whereasrocks in the high-grade zone were uplifted via dextral-oblique displacement along domain-boundingshear zones, instigating decompression (garnet to cordierite) reactions. This study demonstrates thatafter <2.17 Ga deposition of the upper Murmac Bay Group, rocks along the entire west-southwestern Raemargin, from the Northwest Territories/northern Alberta to the Snowbird tectonic zone, were affectedby Taltson (1940-1930 Ma) orogenesis. The Taltson tectono-metamorphic cycle then appears to havetransitioned, as rocks underwent further shortening and uplift in a dextral transpressive regime, intoSnowbird tectonism at ca. 1910-1900 Ma. Snowbird orogenesis is therefore best viewed as part of asemi-continuous 1940-1900 Ma cycle of tectonic burial and exhumation, with its inception at ca. 1910 Matriggered by a change in boundary conditions, as yet not fully understood, but consistent with arrival ofthe Hearne craton proposed by others. While the Beaverlodge domain has many features in commonwith the Tantato domain, future work needs to explore why rocks in the Tantato domain lack evidencefor Arrowsmith orogeny and failed to record the cycle of 1.94-1.93 Ga tectonic burial.