Abstract

Prior to 1:100,000-scale geological mapping conducted in 2017-2018, northern Baffin Island remained a major knowledge gap in the understanding of the northern Rae craton and the tectonic assembly of northeastern Laurentia. Geochronological data in the region was sparse; only four published U-Pb dates existed in the mapping area (~67,000 km2). Resolving the geology and age of the Archean Mary River Group - host to the Mary River iron mine - and the surrounding felsic-to-intermediate gneiss has key implications for the regional tectonic history and mineral prospectivity. In this study, we present new U-Pb zircon ages for 16 samples, including: 3 metavolcanic rocks and a quartzite from the Mary River Group; 2 psammite samples from newly discovered strata near Pond Inlet; 8 felsic-to-intermediate metaplutonic rocks; and 2 mafic metaplutonic rocks. Gneissic granodiorite to quartz diorite that forms the basement to the Mary River Group is dated herein at ca. 2901-2892 Ma. Taking into account previously published data, the age of gneissic basement beneath the Mary River Group is considered to be ca. 2901-2775 Ma. New ages of felsic-intermediate metavolcanic rocks from the Mary River Group define two phases of volcanism at ca. 2830 Ma and ca. 2760-2718 Ma, whereas quartzite from the Mary River Group has a maximum depositional age of ca. 2705 Ma. Psammite from the Pond Inlet area has a similar maximum depositional age of ca. 2720 Ma. Monzogranite and granodiorite and, less commonly, tonalite define an extensive ca. 2731-2706 Ma felsic plutonic suite. Mafic metaplutonic rocks near Pond Inlet, including a layered maficultramafic intrusion, yielded ages of ca. <2720 and >2655 Ma. Late, post-kinematic syenogranite was emplaced at ca. 1792 Ma. U-Pb dates of metamorphic zircon indicate that portions of northern Baffin Island experienced metamorphism during ca. 2.6-2.5 Ga, ca. 1926-1878, and 1850-1820 Ma. The new U-Pb zircon data reinforces lithological and tectonic correlations between northern Baffin Island and the Rae craton in Arctic Canada and West Greenland. Metamorphic U-Pb zircon data also suggest that northern Baffin Island may record tectonothermal activity associated with the Arrowsmith, Ellesmere-Inglefield, and/or Trans-Hudson orogens.

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