Abstract

Ages of detrital zircons in post-2.7 Ga metasedimentary rocks of the southern Abitibi and northern Pontiac subprovinces require that pre-2.8 Ga crust was exposed during or following deformation of the <2.75 Ga Abitibi subprovince, eastern Superior province, Canada. We report three new U-Pb zircon ages for the Lac Rodayer complex within the Opatica gneiss belt ranging from 2820 ±6/-3 to 2825 ± 3 Ma, which overlap the dominant age of the older detrital zircons. Major crustal shortening in the Opatica belt occurred between >2.70 and 2.68 Ga, and the belt forms a high-grade crystalline core to a south-vergent mountain belt along the northern margin of the Abitibi subprovince. Erosion of the Opatica and northern Abitibi during thrusting would shed detritus southward in advance of a south-vergent thrust system. The Lac Rodayer complex may be the enigmatic source of ∼2.8 Ga detrital zircons within turbidites of the southern Abitibi and northern Pontiac subprovinces.

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