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Northeastern Section - 36th Annual Meeting (March 12-14, 2001)

Paper No. 1
Presentation Time: 8:30 AM-12:00 PM

40AR/39AR CONSTRAINTS FOR METAMORPHISM AND DEFORMATION IN THE INTERNAL HUMBER ZONE, GASPE PENINSULA, QUEBEC


PINCIVY, Alix1, MALO, Michel1, RUFFET, Gilles2 and TREMBLAY, Alain3, (1)Georessources, Institut National de la Recherche Scientifique, 880, chemin Sainte-Foy, bur. 840, C.P. 7500, Ste-Foy, QC G1V 4C7, Canada, (2)Geosciences Rennes, CNRS-Universite de Rennes 1, Campus de Beaulieu, Avenue Général Leclerc, Rennes Cedex, 35042, France, (3)Centre géoscientifique de Québec, Institut National de la Rcherche Scientifique, CP7500, 880, ch. Ste Foy, Ste Foy, QC G1V 4C7, Canada, apincivy@nrcan.gc.ca

In the Gaspé Peninsula, the internal Humber Zone consists of the Mont Logan nappe, made up of Cambrian metavolcanic and metasedimentary rocks, and is overlain by the Ordovician Mont Albert ophiolitic Complex (MAOC). Both units are truncated to the south by the Shickshock Sud fault that marks the contact with the Siluro-Devonian Gaspé Belt. This study aims to constrain the structural style and the age of regional deformation and metamorphism by detailed structural analysis, metamorphic petrology and 40Ar/39Ar geochronology. Four events of deformation phases are currently recognized in the area. D1 is associated with a penetrative metamorphic fabric developed at greenschist to amphibolite facies, and attributed to the NW-directed trusting of the MAOC over the Laurentian margin, as preserved in the Mont Logan nappe. D2 is characterized by NE-SW trending folds with an axial-planar crenulation cleavage. D3 is attributed to normal faulting along the Shickshock-Sud fault in Silurian-Devonian time. D4 consists of structures related to Acadian strike-slip reactivation of the Shickshock-Sud fault. Fifteen sites were sampled for 40Ar/39Ar age measurements by single-grain, step-heating on amphiboles and muscovites. Ages obtained from amphiboles of the metamorphic sole of the MAOC vary from 465 ± 3 Ma to 458 ± 3 Ma. Amphiboles and muscovites from metavolcanic and metasedimentary rocks of the Mont Logan nappe yielded isotopic ages ranging between 457 ± 1 Ma and 454 ± 1 Ma. Ages indicate that regional metamorphism is Ordovician, and related to Taconian crustal thickening. Compared to age constraints from correlative terranes of Newfoundland and southern Quebec, it is noticeable that (i) in Gaspé peninsula, the age of the ophiolitic sole is similar to the age of regional metamorphism in underlying metamorphic rocks of the Laurentian margin, but younger than elsewhere in the Northern Appalachians, and (ii) regional metamorphism recorded in the internal Humber zone of Gaspé Peninsula is clearly Ordovician, and not Silurian as in correlative rocks of Newfoundland and southern Quebec.

Session No. 22--Booth# 41

T5. Geologic Evolution of the Northern Appalachians: The Quebec-Vermont Connection (Posters)
Tuesday, 13 March 2001: 8:30 AM-12:00 PM
Geological Society of America Abstracts with Programs. Vol. 33, No. 1, February 2001
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