⁴⁰AR/³⁹AR GEOCHRONOLOGICAL DATA FROM THE SUTTON/GREEN MOUNTAINS ANTICLINORIUM, SOUTHERN QUEBEC-NORTHERN VERMONT APPALACHIANS: EPISODIC AND DIACHRONOUS TECTONISM FROM MIDDLE ORDOVICIAN TO MIDDLE DEVONIAN

CASTONGUAY, Sebastien, Geological Survey of Canada, Quebec Division, 490 rue de la Couronne, Québec, QC G1K 9A9, DOOLAN, Barry, Department of Geology, University of Vermont, Burlington, VT 05405, GALE, Marjorie, Vermont Geol Survey, 103 South Main Street, Waterbury, VT 05671, KIM, Jonathan, Vermont Geol Survey, 103 S. Main St, Waterbury, VT 05671, RUFFET, Gilles, Geosciences Rennes, CNRS-Universite de Rennes 1, Campus de Beaulieu, Avenue Général Leclerc, Rennes Cedex, 35042, France, THOMPSON, Peter, Univ New Hampshire, 56 College Rd, Durham, NH 03824-3589, TREMBLAY, Alain, Sciences de la Terre et de l'Atmosphère, Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montréal, QC H3C 3P8, Canada and VILLENEUVE, Mike, Geological Survey of Canada, Continental Geoscience Div, 601 Booth Street, Ottawa, ON K1A 0E8, Canada, scastong@nrcan.gc.ca

In the southern Quebec-northern Vermont Appalachians, metamorphic rocks of the Laurentian margin crop out along a mega-structure, the Notre-Dame-Sutton-Green Mountains anticlinoria, which progressively exposes deeper tectonometamorphic levels from North (southern Quebec) to South (northern Vermont). Regional deformation and metamorphism of these rocks are currently attributed to the combined effects of Taconian (Middle-Late Ordovician) and Acadian (Middle Devonian) orogenies, and consist of three generations of superimposed folds and faults and at least one (Taconian) metamorphic paragenesis. Recently-acquired ⁴⁰Ar/³⁹Ar isotopic data from several sections across the mega-structure has revealed age groups; (1) Middle Devonian, (2) Silurian-Early Devonian, (3) Middle Ordovician, and (4) Precambrian. The second ⁴⁰Ar/³⁹Ar age group is of special interest as it spans the apparent period of relative tectonic quiescence between the Taconian and Acadian orogenies. In the Sutton Mountains anticlinorium transect, this group of ages (430-405 Ma), occurs throughout the anticlinorium structure and an overall west-to-east age decrease is observed. In the northern Green Mountain anticlinorium transect, preliminary ⁴⁰Ar/³⁹Ar data of that age group appears to be slightly older (441-430 Ma). These latter ages were obtained from white micas in rock samples where the second regional foliation (S2) is penetrative and interpreted to be associated with SE-verging structures. In southern Quebec, ⁴⁰Ar/³⁹Ar age data from similar fabrics are interpreted as deformation ages that characterize Silurian-Early Devonian, hinterland-directed thrusting and extensional faulting. Preliminary age data of northern Vermont and along-strike structural correlations of regional fabrics between Vermont and Quebec suggest that their overall tectonic evolution has been similar. In summary, structural analyses and geochronological data from both transects suggest episodic and diachronous tectonism characterized by contrasting structural vergences and metamorphic conditions.

Session No. 17

T10. New Models of Appalachian Tectonics Inspired by Geochronology: 3rd Annual NETectonics Session I

Tuesday, 15 March 2005: 8:00 AM-12:00 PM

Geological Society of America Abstracts with Programs. Vol. 37, No. 1, p.30

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Northeastern Section - 40th Annual Meeting (March 14–16, 2005)

40AR/39AR GEOCHRONOLOGICAL DATA FROM THE SUTTON/GREEN MOUNTAINS ANTICLINORIUM, SOUTHERN QUEBEC-NORTHERN VERMONT APPALACHIANS: EPISODIC AND DIACHRONOUS TECTONISM FROM MIDDLE ORDOVICIAN TO MIDDLE DEVONIAN

⁴⁰AR/³⁹AR GEOCHRONOLOGICAL DATA FROM THE SUTTON/GREEN MOUNTAINS ANTICLINORIUM, SOUTHERN QUEBEC-NORTHERN VERMONT APPALACHIANS: EPISODIC AND DIACHRONOUS TECTONISM FROM MIDDLE ORDOVICIAN TO MIDDLE DEVONIAN