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TitleFossil mantle rift controls on mineralization in the Quebec Abitibi during cratonic breakup and reassembly
AuthorHarris, L B; Bédard, J H
SourceQuebec Mines 2012: abstracts of oral presentations and posters; Quebec Department of Energy and Natural Resources, Various Documents DV 2013-04, 2013 p. 48 Open Access logo Open Access
LinksOnline - En ligne (complete volume - volume complet, PDF, 8.9 MB)
Alt SeriesEarth Sciences Sector, Contribution Series 20120224
PublisherGouvernement du Québec
MeetingQuebec Mines 2012; Québec, QC; CA; November 26-29, 2012
Mediadigital; on-line
File formatpdf
ProgramTargeted Geoscience Initiative (TGI-3), 2005-2010
Released2013 01 01
AbstractIn the Abitibi Subprovince of the Superior Province in Quebec, extrusive sequences were formed in a volcanic plateau-like setting during plume-related rifting of older cratonic lithosphere that started at ca. 2.78-2.75 Ga. Mantle plume activity led to focussed thermal erosion, destruction, and assimilation of ancient lithosphere and formation of isotopically juvenile crust that now constitutes the Abitibi belt. 3D images of S-wave seismic tomographic data of the Superior Province illustrate that the Abitibi Subprovince overlies a symmetrical, generally E-W-trending rift in the sub-crustal lithospheric mantle (SCLM) of older Archaean lithosphere (N Superior Province and Minnesota River Valley domain). Seismic tomography shows no evidence for `fossil' subduction zones. Enhanced aeromagnetic images of the central-northern Abitibi illustrate early, penetrative E-W dextral ductile shearing preceded formation of discrete ductile to brittle-ductile conjugate transcurrent and E-W reverse ± dextral shear zones. Offset and ductile deflection of dense, mafic crust along regional transcurrent shear zones in the Abitibi Subprovince and its continuation in the Grenville Province parautochthon is apparent on short wavelength Bouguer gravity images. An Archaean, NE-striking, sinistral shear zone (the proto-Grenville shear zone) is identified along the SE margin of the Abitibi and Opatica subprovinces. The displacement history and geometry of reverse and strike-slip shear zones is similar to that of structures developed during progressive lateral escape and indentation during impingement of a rigid body. We propose that southward migration of the old cratonic nucleus (N Superior Craton) in response to mantle flow acting upon its deep lithospheric keel, and not subduction-related processes, led to progressive southward accretion of crustal fragments and oceanic plateaux-like segments like the Abitibi. Terrane accretion led to shortening, and rift inversion in the Abitibi. Major epigenetic gold deposits are located above rift-bounding faults in the SCLM, suggesting that early rift structures localized subsequent deformation and hydrothermal fluid flow during N-S shortening in the ca. 2.7 Ga Shebandowanian orogeny. The 1.1 Ga Desmaraisville and 0.55 Ga Otish kimberlite clusters also coincide with interpreted rift structures in SCLM, highlighting the role of ancient mantle structures on localizing deformation and intrusion in the overlying crust.

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