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GEOREF RECORD

Post-convergent structures in lower parts of the 1090-1050 Ma (early-Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield

W. M. Schwerdtner, Toby Rivers, Brant Zeeman, C. C. Wang, Jason Tsolas, Jack Yang and Madeeha Ahmed
Post-convergent structures in lower parts of the 1090-1050 Ma (early-Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield (in John Tuzo Wilson, a man who moved mountains, and his contributions to earth sciences, Ali Polat (editor))
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (March 2014) 51 (3): 243-265

Abstract

Remnants of the early-Ottawan thrust-sheet stack are exposed in the Central Gneiss Belt (CGB, lower portion of stack) and the Composite Arc Belt (upper portion of stack). Post-collisional vertical thinning and associated horizontal extension of the stack produced structures ranging over eight orders of magnitude in horizontal length, and both orogen-parallel and orogen-perpendicular in orientation. At the 100 km scale, the fold-induced constriction in the northern Parry Sound domain appears to have been enhanced, and lineation trend lines in its footwall locally deflected, by a component of NW-SE (i.e., orogen-perpendicular) flattening and a component of NE-SW (i.e., orogen-parallel) ductile extension. At the 10 km scale, four non-cylindrical lenticular bodies of gabbro-anorthosite gneiss within the domain, inferred to be triaxial mega-boudins or heterogeneously strained plutons, are separated by large extensional bending folds, the complementary structures attesting to a component of NW-SE flattening and a component of NE-SW extension. Non-cylindrical lenticular structures in other domains of the CGB, interpreted as triaxial foliation mega-boudins, exceed 30 km in length. Their moderately strained granulite-facies interiors give way to highly strained amphibolite-facies margins, thus documenting subvertical ductile flattening and multi-lateral extension during retrogression. Well-layered, highly strained gneiss is commonly deformed by steep NE-SW-trending extensional faults and associated monoclinal fault-propagation folds (FPFs). The short limbs of the FPFs bend the regional elongation lineation and host a set of fault-parallel, unstrained to slightly deformed, granite-pegmatite dikes. Dilation vectors of most dikes are oblique to the granite-pegmatite contacts, and the sense of their tangential components attests to orogen-perpendicular extension. The fault-parallel dikes and associated FPFs are cut by a set of unstrained dikes. Collectively these observations document a prolonged history of post-collisional extension of the mid crust, from ductile structures indicative of a significant component of orogen-parallel extension shortly after the metamorphic peak at mid-crustal depths, to brittle-ductile structures indicative of a component of orogen-perpendicular extension and associated magmatic dilation following its exhumation and cooling in the upper crust.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 51
Serial Issue: 3
Title: Post-convergent structures in lower parts of the 1090-1050 Ma (early-Ottawan) thrust-sheet stack, Grenville Province of Ontario, southern Canadian Shield
Title: John Tuzo Wilson, a man who moved mountains, and his contributions to earth sciences
Affiliation: University of Toronto, Department of Earth Sciences, Toronto, ON, Canada
Affiliation: University of Windsor, Department of Earth and Environmental Sciences, Windsor, ON, Canada
Pages: 243-265
Published: 201403
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 126
Accession Number: 2014-027278
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch maps
N45°00'00" - N46°10'00", W80°00'00" - W78°49'60"
Secondary Affiliation: Memorial University of Newfoundland, CAN, CanadaCentury Iron Mines Corporation, CAN, CanadaFlint Energy Services, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Canadian Science Publishing, NRC Research Press, Ottawa, ON, Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201417
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