Geological evolution of the Manitouwadge greenstone belt and Wawa-Quetico subprovince boundary, Superior Province, Ontario, constrained by U-Pb zircon dates of supracrustal and plutonic rocks

摘要

Fifty million years of Archean evolution isrecorded in the Manitouwadge greenstone belt and the Wawa-Quetico boundary region, from Ca. 2720 Ma volcanism andsubvolcanic plutonism associated with massive sulphide depositsand hydrothermal alteration zones, to 2689-2687 Ma and 2680-2677 Ma synkinematic plutonism. In the greenstone belt,greywackes were deposited after 2693 Ma, post-dating localvolcanism by at least 25 Ma, and requiring that the volcanic-sedimentary contact is an unconformity or a fault. In migmatiticgreywackes in the Quetico subprovince, detrital zircons limit thedepositional age to <2690 Ma, permitting correlation ofgreywackes across the Wawa-Quetico subprovince boundary.Upward-facing inclined F_2 folds that deform the volcanic-sedimentary contact are bracketed by the 2687 +- 2 Ma LokenLake pluton, which shows strong D_2 fabrics, and by 2680_3~4Ma foliated granite which cuts D_2 fabrics. Dextral transpressionproducing regional F_3 folds and the overall east-west trends ofthe Wawa-Quetico boundary region post-dated the 2680 +- 2 MaNama Creek pluton. Field relationships and isotopic ages supportcorrelation of greywackes across the subprovince boundary, anddemonstrate that most or all of the ductile deformation post-datedsedimentation. Ductile structures, especially those associated withdextral transpression, are not directly related to juxtaposition ofthe Wawa and Quetico subprovinces, as these were alreadycontiguous, either through sedimentation on a volcanic substrateor as a result of earlier cryptic structures. Our results imply thatthe belt-like configuration of the subprovinces, emphasized inaccretionary models of the Superior Province, is a relatively latefeature that overprints older, tectonically significant structures.