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TitleU-Pb zircon geochronology and depositional history of the Montresor Group, Rae Province, Nunavut, Canada
AuthorPercival, J A; Davis, W J; Hamilton, M A
SourceCanadian Journal of Earth Sciences vol. 54, issue 5, 2017 p. 512-528, https://doi.org/10.1139/cjes-2016-0170
Year2017
Alt SeriesEarth Sciences Sector, Contribution Series 20160297
PublisherNational Research Council Press
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNunavut
NTS66H; 66I; 56E; 56L
AreaMontresor Belt
Lat/Long WENS -98.0000 -94.0000 67.0000 65.0000
Subjectsgeochronology; general geology; lead lead dates; uranium lead dates; sills; deposition; depositional analyses; Montresor Group; Rae Province; arenite
Illustrationslocation maps; geological sketch maps; tables; photographs; photomicrographs; histograms; stratigraphic correlations
ProgramRae Province, Chantrey-Thelon, GEM2: Geo-mapping for Energy and Minerals
AbstractPaleoproterozoic metasedimentary successions of the northwestern Canadian Shield provide records of tectonic events, but the definition of depositional ages has proved elusive. Although previously poorly understood, the Montresor belt of western Nunavut yields new insight into the 2.2 - 1.8 Ga time window. On the basis of U-Pb analyses of detrital zircon in sedimentary rocks and igneous zircon in sills, we conclude that arenite of the lower Montresor group was deposited between 2.194 and 2.045 Ga, and arkose of the upper Montresor group after 1.924 Ga, adding constraints on the Rae cover sequence. The lower Montresor arenite yielded an older group (3.05 - 2.58 Ga) and a younger, more tightly constrained group (2.194 ± 0.014 Ga). Four of six zircon grains analyzed from a gabbro sill within the lower Montresor have discordant 207Pb/206Pb ages (2.71, 2.66, 2.53, and 2.39 Ga) and are considered to be inherited, whereas two grains provide an age of 2045 ± 13 Ma, interpreted to date crystallization and providing a minimum age for the lower Montresor package. Upper Montresor arkose contains detrital zircon with probability density peaks at 2.55 - 2.25 and 2.1 - 1.92 Ga, together with scattered older grains (3.8 - 2.65 Ga). The youngest grain yields an age of 1924 ± 6 Ma, establishing a maximum age for sandstone deposition. Provenance is inferred to have been from the west, where igneous sources of 2.5 - 2.3 Ga (Queen Maud block) and 2.03 - 1.89 Ga (Thelon orogen) are known. Collectively, the new ages suggest a minimum 120 million year gap between deposition of the pre-2045 ± 13Ma lower and post-1924±6 Ma upper parts of the Montresor group. Similar age constraints may apply to other parts of the Rae cover sequence.
Summary(Plain Language Summary, not published)
As part of the GEM-2 Rae project, the paper provides new age data for the poorly known Montresor belt of Nunavut. The lower part of the sedimentary sequence was deposited between 2194 and 2045 million years ago, and the upper part after 1924 million years ago, indicating about a 120 million year depositional gap. The Montresor units are correlated with other sedimentary sequences of the central Rae geological province, so the new ages add precision to depositional constraints over a broad region.
GEOSCAN ID299563