Can. J. Earth Sci. 43: 821–847 (2006) doi:10.1139/E06-036 © 2006 NRC Canada 821 Pickle Lake revisited: New structural, geochronological and geochemical constraints on greenstone belt assembly, western Superior Province, Canada 1,2 M.D. Young, V. McNicoll, H. Helmstaedt, T. Skulski, and J.A. Percival Abstract: New field work, U–Pb ages, geochemical data, and Sm–Nd isotopic analyses have established the timing and determined the nature of volcanism, deformation, and tectonic assembly of the Pickle Lake greenstone belt in the Uchi subprovince of the western Superior Province of the Canadian Shield. The >2860 Ma Pickle Crow assemblage has been redefined to include the former Northern Pickle assemblage on the basis of stratigraphic continuity and similar volcanic geochemistry between the two units across a previously inferred fault contact. The Pickle Crow assemblage consists of tholeiitic basalt with thin, but laterally extensive, oxide-facies iron formation overlain by alkalic basalts and minor calc- alkaline andesites to dacites with primitive Nd isotopic compositions (ε Nd 2.89 Ga = +2.1 to +2.4) suggestive of deposition in a sediment-starved oceanic basin. The -2 km thick -2836 Ma Kaminiskag assemblage (former Woman assemblage) consists of tholeiitic basalt interbedded with intermediate and rare felsic pyroclastic flows with primitive Nd isotopic compositions (ε Nd 2.836 Ga = +2.4). Two samples of intermediate volcanic rocks interbedded with southeast-younging pillowed basalt, previously inferred to be part of the Pickle Crow assemblage, yielded U–Pb zircon ages of 2744 2 3 - + Ma and 2729 ± 3 Ma. These rocks are thus part of the younger Confederation assemblage, which consists of intercalated basalt and dacite (ε Nd 2.74 Ga = +0.1 to +0.8) exhibiting diverse compositions probably reflecting eruption in a continental margin arc to back-arc setting. The contact between the Confederation and Kaminiskag assemblages is assumed to be a fault. The greenstone belt is intruded by late syn- to posttectonic plutons including the composite quartz dioritic to gabbroic July Falls stock with a new U–Pb zircon age of 2749 2 4 - + Ma, and the -2741 to 2740 Ma trondhjemitic to granodioritic Ochig Lake pluton and Pickle Lake stock, as well as the -2697 to 2716 Ma Hooker–Burkoski stock. The earliest recognized deformation (D 1 ) is recorded by a local bedding-parallel foliation in the Pickle Crow assemblage. This foliation is truncated by the -2735 Ma Albany quartz–feldspar porphyry dyke and is not recognized in the volcanic rocks of the Confederation assemblage. The early deformation event is attributed to overturning of the Pickle Crow assemblage prior to deposition of the -2744 to 2729 Ma Confederation assemblage. Subsequent deformation and development of a regionally penetrative planar fabric (S 2 ) postdates -2729 Ma volcanism, pre-dates the intrusion of the ca. <2716 Ma Hooker–Burkoski stock and is host to gold mineralization. 847 Résumé : De nouveaux travaux sur le terrain, des âges U–Pb, des données géochimiques et des analyses des isotopes Sm–Nd ont établi le moment et déterminé la nature du volcanisme, de la déformation et de l’assemblage tectonique de la ceinture de roches vertes de Pickle Lake dans la sous-province d’Uchi de la Province du lac Supérieur occidental du Bouclier canadien. L’assemblage de Pickle Crow, >2860 Ma, a été redéfini pour y inclure l’ancien assemblage de Northern Pickle en se basant sur la continuité stratigraphique et la géochimie volcanique semblable entre les deux unités à travers un contact de faille qui antérieurement n’était qu’inféré. L’assemblage de Pickle Crow comprend un basalte tholéiitique avec de minces formations de fer, d’une grande étendue latérale, au faciès des oxydes, recouvertes de basaltes alcalins et d’andésites à dacites calco-alcalines mineures avec des compositions primitives en isotopes de Nd (ε Nd 2,89 Ga = +2,1 à +2,4), ce qui suggère une déposition dans un bassin océanique pauvre en sédiments. L’assemblage de Kaminiskag (l’ancien assemblage de Woman), ~2836 Ma, d’une épaisseur d’environ 2 km, comprend un basalte Received 14 June 2005. Accepted 30 March 2006. Published on the NRC Research Press Web site at http://cjes.nrc.ca on 13 September 2006. Paper handled by Associate Editor R. Clowes. M.D. Young 3, 4 and H. Helmstaedt. Department of Geological Sciences and Geological Engineering, Miller Hall, Queen’s University, Kingston, ON K7L 3N6, Canada. V. McNicoll, T. Skulski, and J.A. Percival. Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada. 1 This article is one of a selection of papers published in this Special Issue on The Western Superior Province Lithoprobe and NATMAP transects. 2 Lithoprobe Publication 1449. 3 Corresponding author (e-mail: young@geoladm.geol.queensu.ca). 4 Present address: 2233 East 12 th Street, Vancouver, BC V5N 2B2, Canada.