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TitleU-Pb geochronology and trace element composition of zircon from the Horseshoe Lake greenstone belt, Superior Province, Canada: implications for tectonic and metamorphic history
AuthorKelly, C J; Schneider, D A; Lajoie, M -Ê; Jackson, S E; McFarlane, C R
SourceCanadian Journal of Earth Sciences vol. 55, no. 2, 2017 p. 172-187, (Open Access)
Alt SeriesNatural Resources Canada, Contribution Series 20170233
PublisherCanadian Science Publishing
Mediapaper; on-line; digital
File formatpdf
NTS53A; 53B; 53G; 53H
Lat/Long WENS -92.0000 -88.0000 54.0000 52.0000
Subjectseconomic geology; geochronology; geochemistry; tectonics; mineralogy; mineral deposits; gold; metallogeny; bedrock geology; lithology; greenstone belts; metamorphic rocks; metasedimentary rocks; metavolcanic rocks; igneous rocks; intrusive rocks; trondhjemites; tonalites; granodiorites; porphyries; structural features; faults; folds; anticlines, overturned; tectonic history; metamorphism; deformation; greenschist facies; emplacement; intrusions; dykes; metasomatism; magmatism; mineralization; recrystallization; fluid dynamics; radiometric dating; trace element analyses; zircon; crystallography; mass spectrometer analysis; isotopic studies; lead isotope ratios; uranium thorium ratios; hafnium geochemistry; petrographic analyses; scanning electron microscope analyses; Archean; Superior Province; Horseshoe Lake Greenstone Belt; North Caribou Terrane; North Caribou Greenstone Belt; rare earth element analyses; metasomatic rims; depth profiling; Precambrian
Illustrationsgeoscientific sketch maps; geochronological charts; photographs; photomicrographs; Concordia diagrams; plots; tables; profiles; bar graphs
ProgramTargeted Geoscience Initiative (TGI-5), Uranium systems
Released2017 12 15
AbstractDepth profile techniques for U-Pb geochronology and rare earth element (REE) geochemistry were conducted on unpolished, Archean zircon with metasomatic rims from metasedimentary rocks within the Horseshoe Lake greenstone belt, western Superior Province, Canada. These zircon crystals are shown to have isotopically distinct rims (typically <5 micrometres thick) compared with the interiors of the crystal. Secondary ion mass spectrometry (SIMS) U-Pb depth profile analyses of the rims define two different 207Pb/206Pb age populations at ca. 2920 and 2869 Ma, which are >100 million years younger than the cores. The 207Pb/206Pb rim ages can be temporally correlated with regional magmatism and with a later, potentially Au-bearing, hydrothermal event synchronous with greenschist-facies metamorphism and regional deformation. Notably, the zircons do not record evidence of local ca. 2741-2715 Ma magmatism manifested by the emplacement of a quartz-feldspar porphyry dike swarm. Laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) REE depth profile analyses on the same unpolished zircon show that the rims are commonly characterized by low Th/U ratios, elevated Hf, and variable REE concentrations in comparison with the interior of the grains. The variations in rim and core chemistry suggest that these elements, along with common Pb, were mobilized by fluids and interacted with zircon in the metasediments, resulting in the production of the metasomatic rims. In summary, this paper shows that depth profiling techniques applied to unpolished zircon can be useful to elucidate the tectonic, and potentially metallogenic, history of a complex Archean terrane.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) was a collaborative federal geoscience program that provided industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. This manuscript applies an innovative geochronological technique to a poorly understood, gold bearing greenstone belt in Northern Ontario. The results of this manuscript have implications for understanding the tectonic history of Archean greenstone belts.