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TitleMulti-stage zircon and monazite growth revealed by depth-profiling and in situ U-Pb geochronology: resolving the Paleoproterozoic tectonics of the Trans-Hudson Orogen on southeastern Baffin Island, Canada
AuthorSkipton, D R; Schneider, D A; McFarlane, C R M; ST-Onge, M R; Jackson, S
SourcePrecambrian Research vol. 285, 2016 p. 272-298, https://doi.org/10.1016/j.precamres.2016.09.002
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20160003
PublisherElsevier
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNunavut
NTS26A; 26B; 26C; 26D; 26E; 26G; 26L; 26K; 25I; 25P; 26O
AreaBaffin Island
Lat/Long WENS -74.0000 -68.0000 67.0000 63.0000
Subjectsmonazite; zircon; orogenic regions; uranium lead dates; LA-ICP-MS; SIMS depth profiling; geochronology; Trans-Hudson orogen
Illustrationstables; figures; location maps; geological sketch maps; graphs
ProgramBaffin Bedrock Mapping, GEM2: Geo-mapping for Energy and Minerals
AbstractUnderstanding the growth and recrystallization of zircon and monazite during regional metamorphism is important for identifying the nature and timescales of tectonic processes in continental crust. We present extensive in situ U-Pb monazite geochronology and U-Pb zircon depth profiling analyses from a section of mid-crust exposed on southeastern Baffin Island, Canada, in the internal zone of the Paleoproterozoic Trans-Hudson Orogen. In situ LA-ICP-MS U-Pb monazite dating on ten metasedimentary rocks (totalling >300 analyses) from different paleodepths reveals a regionally dominant ca. 1850-1820 Ma monazite population that records regional mid-amphibolite- to granulite-facies metamorphism with coeval fabric development. Subordinate monazite populations of ca. 1800 Ma and ca. 1780-1750 Ma are considered to have formed through dissolution-reprecipitation. The SIMS U-Pb depth-profiling technique allowed dating of ca. 1861-1833 Ma zircon rims and less abundant ca. 1800-1764 Ma zircon rims that would be unresolvable using conventional spot dating. Trace element depth profiling via LA-ICP-MS shows that zircon rims typically have lower Th/U values, smaller positive Ce anomalies and different REE patterns than cores in the same grains. Zircon rim compositions are highly variable, with no apparent link to U-Pb age, suggesting that they are the combined result of metamorphic zircon growth and dissolution-reprecipitation. Our data demonstrate that the timing of peak metamorphism is recorded by both monazite and zircon, and that they appear equally sensitive to U-Pb age resetting at lower temperatures during late-orogenic tectonism. Regional mid-amphibolite- to granulite-facies metamorphism and east-directed crustal shortening are bracketed between ca. 1861 Ma and ca. 1820 Ma, together with syn- to post-thermal peak east-vergent thick-skinned thrusts and folds. These events are interpreted to result from the accretion of cratonic blocks in the internal zone of the Trans-Hudson Orogen. The integrated geochronological approach on regionally-distributed samples enabled us to document ca. 1800-1750 Ma monazite domains and zircon rims, which we interpret to result from the terminal collision with the lower-plate Superior craton followed by late- to post-orogenic tectonothermal activity that continued for at least 70 m.y. after thermal peak. This prolonged history is characteristic of the northeastern Trans-Hudson Orogen, and implies that orogenic collapse may not necessarily be a hallmark of all hot, thickened orogens.
Summary(Plain Language Summary, not published)
Understanding the growth and recrystallization of zircon and monazite during regional metamorphism is important for identifying the nature and timescales of tectonic processes in continental crust. We present extensive in situ U-Pb monazite geochronology and U-Pb zircon depth profiling analyses from a section of mid-crust exposed on southeastern Baffin Island, Canada. Our data demonstrate that the timing of peak metamorphism is recorded by both monazite and zircon, and that they appear equally sensitive to U-Pb age resetting at lower temperatures during late-orogenic tectonism. The accretion of cratonic blocks in the internal zone of the Trans-Hudson Orogen and the terminal collision with the lower-plate Superior craton followed by late- to post-orogenic tectonothermal activity are documented. This prolonged history implies that orogenic collapse may not necessarily be a hallmark of all hot, thickened orogens.
GEOSCAN ID297884