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TitleMultiple burial-exhumation episodes revealed by accessory phases in high-pressure granulite-facies rocks (Rae Craton, Nunavut, Canada)
 
AuthorRegis, D; Davis, W JORCID logo; Ryan, J J; Berman, R GORCID logo; Pehrsson, S; Joyce, N L; Sandeman, H A
SourceContributions To Mineralogy and Petrology vol. 174, issue 5, 41, 2019 p. 1-25, https://doi.org/10.1007/s00410-019-1572-8
Image
Year2019
Alt SeriesNatural Resources Canada, Contribution Series 20180456
PublisherSpringer Science and Business Media LLC
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®); html
ProvinceNunavut
NTS55M/08; 55M/09; 55M/16; 55N/05; 55N/10; 55N/11; 55N/12; 55N/13; 55N/14; 55N/15
AreaChesterfield Inlet; Cross Bay; Gibson Lake; MacQuoid Lake
Lat/Long WENS -94.5000 -92.7500 64.0000 63.4000
Subjectstectonics; geochronology; geochemistry; igneous and metamorphic petrology; mineralogy; Science and Technology; crustal evolution; tectonic history; burial history; metamorphism; granulite facies; deformation; crustal thickness; intrusions; dykes; recrystallization; thermal history; plate margins; crustal uplift; bedrock geology; lithology; metamorphic rocks; mylonites; gneisses; metagabbros; igneous rocks; intrusive rocks; monzo-granites; tonalites; granites; diorites; granodiorites; anorthosites; structural features; shear zones; faults; pressure-temperature conditions; modelling; models; fabric analyses; mylonitization; radiometric dating; uranium lead dating; argon argon dating; diffusion; zoning; niobium geochemistry; tantalum geochemistry; titanite; petrographic analyses; trace element analyses; Archean; Canadian Shield; Rae Craton; Big Lake Shear Zone; Snowbird Tectonic Zone; Paleoproterozoic; Neoarchean; Cross Bay Complex; Macquoid Dykes; Chesterfeld Block; Precambrian; Proterozoic
Illustrationslocation maps; geoscientific sketch maps; photographs; photomicrographs; tables; geochemical plots; charts; drawings; phase diagrams; Concordia diagrams; plots
ProgramGEM2: Geo-mapping for Energy and Minerals South Rae Province Bedrock/Surficial geology
Released2019 05 06
AbstractThe Big Lake shear zone (BLsz) is a 60 km long deep crustal structure adjacent to the northern segment of the Snowbird Tectonic zone (STZ: Nunavut, Canada) in a region characterized by intensely sheared high-pressure granulite-facies rocks. The units exposed here provide an exceptional record of the lower crust that preserves crucial evidence bearing on interpretation of superimposed Neoarchean and Paleoproterozoic tectono-metamorphic events. Deformation along the BLsz postdates 2650 Ma, the age of a mylonitized monzogranite, and predates 2190 Ma, the age of cross-cutting MacQuoid mafic dykes. Metamorphic assemblages and P-T modeling suggest crustal thickening in the Neoarchean with peak conditions of 800 °C and 14-15 kbar at ca. 2530 Ma. Mylonitic fabrics developed at ca. 2505 Ma (T ~ 800 °C, P < 13 kbar). P-T data on the metamorphosed Paleoproterozoic dykes suggest ca. 1900 Ma recrystallization and partial reactivation of the BLsz at 770 °C-13 kbar. In this work, we demonstrate that U-Pb geochronology and diffusion modeling in Neoarchean titanite can be used to resolve time-temperature paths for lower crustal rocks. Preservation of Nb and Ta zoning with sharp boundaries in titanite and diffusion models of geochemical tracers (e.g., Pb), are indicative of a scenario involving fast cooling (>10 °C/Ma) and partial exhumation post-ca. 2505 Ma followed by re-burial at 1900 Ma, rather than slower isobaric cooling at depth. These results indicate that the long-term residence models proposed by several authors for domains in the central STZ are not applicable to the BLsz region, and are more compatible with a ca. 1.9 Ga collisional setting.
Summary(Plain Language Summary, not published)
The Big Lake shear zone (BLsz) is a deep crustal structure adjacent to the northern segment of the Snowbird Tectonic zone (Nunavut, Canada) in a region characterized by high-pressure granulite-facies rocks. The units exposed here provide an exceptional record of the lower crust that preserves crucial aspects bearing on interpretation of juxtaposed Neoarchean and Paleoproterozoic tectono-metamorphic events. Diffusivity models of geochemical tracers in titanite presented in this manuscript, imply rapid partial exhumation post-ca. 2500 Ma high-pressure metamorphism followed by re-burial, rather than slower isobaric cooling at depth. These results indicate that the long-term residence models proposed by several authors for domains in the central STZ are not applicable to the BLsz region. Paleoproterozoic re-activation of the BLsz, was followed by a multi-stage exhumation path consistent with rapid extensional unroofing in a poly-cyclic compressive system.
GEOSCAN ID314569

 
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