G-o9Q eA-w- JQA—vii: Gioj"- kj tzb 4s• IØ So APPALACHIAN WORKSHOP lKMF JNtSTY OF Vth1Oft1T LTOft VT I2;LoXPiItti ir QUEBEC VEROT APPALACHIAN WORKS+OP Apr11 14 - 16, 1989 Kalkin Hall, University of Vermont Burlington, Vermont Co-Sponsored by: The Department of Geology Visiting Lecture Series The Canadian Studies Program The Graduate College, University of Vermont EDITORS Maurice Coipron and Barr,' Doolan Department of Geology • University of Vermont Burlington, Vermont Cover: Perspective block diagram of the Québec- Vermont Orogen (from Dóolan, 1989; see Doolan, this volume). Additional copies are available upon request from: Vermont Geological Society, Inc. P.O. Box 304 twfontpelier, Vermont 05602 PROGRAM AND CONTENTS SATURDA V. APRIL 15, 1989 8:00 - INTRODUCTORY REMARKS I. EVOLUTION OF THE ANCIENT NORTH AMERICAN MARGIN IN THE QUEBEC REENTRANT ............................................................................. 1 Chairperson: Charles A. Ratté 8:15 - Stephen Kumarapeli* and Hillar Pintson: Geochronologic constraints on the timing of rifting and continental breakup at the Sutton Mountains triple junction...........3 8:40 - William M. Dowling: Paleogeographic analysis of the preshelf facies in the Oak Hill and Camels Hump Groups: constraints on syn-rift and post-break-up subsidence in theQuébecreentrant ...........................................................................................................5 9:05 - Charlotte Mehrtens: The Cambrian platform and platform margin in northwestern Vermont..............................................................................................................................8 930 - DISCUSSION AND COFFEE Poster: - Steven A. Chisick and Paul A. Washington: Evolution of the Cambro-Ordovician shelf in the Champlain Valley: interaction of an evolving carbonate bank with tectonic subsidence and sea-level oscillations............................................................................... 11 II. TERRANES OUTBOARD OF THE ANCIENT NORTH AMERICAN MARGIN.. ........................ 13 Chairperson: Norman L. Hatch, Jr. 10:00 - Alain Tremblay: The oceanic domain from Eastern Townships Appalachians, Québec: Taconian versus Acadian tectonics....................................................................................15 10:25 - Pierre A. Cousineau: Evolution and collage of the Saint-Daniel Mélange in the Dunnage zone of the Québec Appalachians...............................................................19 10:50 - David Roy: Ordovician and Silurian basin evolution and tectonics along the Baie Verte - Brompton Line in northwestern Maine ............................................................................ 22 11:15 - Peter Robinson*, R.D. Tucker, and K.T. Hollocher: The nature of the Bronson Hill Zone during the Taconian orogeny ............................................................................26 11:40 - DISCUSSION iv Posters: - Norman L. Hatch, Jr.: Recent developments in the Connecticut Valley trough, Vermont................................................................................................................ 29 - Sonia Tanguay*, Rejean Hébert, et Mario Bergeron: Géochimie des cumulats ultramafiques du Complexe ophiolitique de Thetford Mines, Québec: modèle magmatique de Ia distribution des platinoIdes .................................................................. 32 Ill. DESTRUCTION OF A PASSIVE MARGIN I: EVOLUTION OF THE QUEBEC/NORTHERN VERMONT OROGEN ......................................35 Chairperson: Philip H. Osberg 13:30 - Robert Marquis: The Sutton Mountains anticlinorium: its relations with adjacentunits....................................................................................................................37 13:55 - Maurice Colpron: Taconian structures from the hinterland of the Eastern Townships of Québec: the result of continental (A-type) subduction " ..........................41 14:20 - Barry Doolan: Hinterland tectonics of the Vermont-Québec Appalachian orogen...........46 14:45 - DISCUSSION AND COFFEE Poster: / - Marc Bardoux* and Robert Marquis: L 2001: a new interpretation of northwesterly-dipping reflectors above the basement-cored S utton- Notre- Dame anticlinorium near Thetford Mines, Québec ..................................................................... 50 IV. DESTRUCTION OF A PASSIVE MARGIN II: NEW DEVELOPMENTS IN THE VERMONT APPALACHIANS.............................................53 Chairperson: Nicholas M. Ratcllife 15:05 - Nicholas M. Ratcliffe: Comparative tectonics of basement massifs in the northern Appalachians with special reference to the Green Mountain massif of Vermont............................................................................................................................. 55 15:30 - William C. Burton: Shared deformational fabrics in basement and cover along the west flank of the southern Green Mountains, Vermont.....................................57 15.55 - M.idii J. Warin: Tectonic evoiutioti of the southern Lincoln massif and rift- clastic cover sequence, central Vermont..........................................................................58 16:20 - Thomas R. Armstrong: The Vermont pre-Silurian cover sequence: regional tectonostratigraphic relationships based on detailed structural and lithologicalanalysis.......................................................................................................... 63 16:45 - Rolfe S. Stanley*, R.A. Coish, and Jo Laird: Aspects of the Taconian orogen incentral Vermont............................................................................................................67 17:10 - DISCUSSION V Posters: - Paul A. Washington: Structural development of the central Champlain Valley: lithotectonic controls imposed by a complex shelf margin.................................. 69 - Peter J. Thompson* and Thelma B. Thompson: Geology of the Winooski River transect, north central Vermont ..................................................................................... 70 - Gregory Walsh and Christine Kimball: Ge6chemistry of the metabasic rocks from the pre-Silurian rift-clastic sequence of central Vermont ................................... 74 19:30 - POSTER SESSION AND SOCIAL GATHERING. SUNDAY, APRIL 16, 1989 V. GEOCHEMISTRY AND GEOCHRONOLOGY IN THE VERMONT-QUÉBEC OROGEN ...............77 Chairperson: R.A. Coish 9:00 - Denys Vermette*, Réjean Hébert, V. Olive, M. Loubet, et Mario Bergeron: La creation de l'océan lapétus; du rift continental a Ia formation du bassin ocOanique: contraintes pétrologiques et géochimiques ......................................................................79 9:25 - R.A. Coish: The significance of geochemical trends in Vermont greenstones.................... 82 9:50 - Roger Laurent, J. Dostal, and Réjean Hébert*: Geochemistry of Ordovician island-arc and ocean-floor rock assemblages from the Québec ophiolites, CanadianAppalachians ..................................................................................................... 85 10:15 - Jo Laird*, John F. Sutter, Michael J. Kunk, and Wallace A. Bothner: Interpretation of 40Ar/39Ar amphibole age spectra, Vermont: easier said than done.....87 10:40 - DISCUSSION 11:10- CONCLUDING REMARK REFERENCES ....................................................................................................................... 91 ,1 EVOLUTION OF THE ANCIENT NORTH AMERICAN MARGIN IN THE QUEBEC REENTRANT Chairperson: Charles A. Ratté GEOCHRONOLOGIC CONSTRAINTS ON THE TIMING OF RIFTING AND CONTINENTAL BREAKUP AT THE SUTTON MOUNTAINS TRIPLE JUNCTION Stephen Kumarapeli Department of Geology, Concordia University Montréal, Québec 1­1413 1 R6 and Hillar Pintson Département de Géologie, UniversitO de Montréal C. P. 6128, Succ. "An, Montréal, Québec, H3C 3J7 The geological evolution of a segment of the Appalachian orogen in southeastern Québec and northern Vermont has been influenced by an lapetan RRR triple junction - the Sutton Mountains triple junction - and its vestiges (Kumarapeli, 1985). The prominent bend of the orogen, commonly referred to as the Sutton Mountains salient or the Québec reentrant, is the most striking feature inherited from the triple junction. The biostratigraphic and geochronologic evidence from the general region does not provide tight time constraints on the problems of rift initiation and rift-drift transition. No fossils have yet been discovered from the lower part of the Oak Hill Group (or its equivalent in Vermont, the Camels Hump Group) which appears to be made up of synrift sedimentary and volcanic assemblages. However, the Gilman and Dunham Formations, probable syn- and/or post-breakup deposits higher up in the Oak Hill sequence (see Dowling and others, 1987) contain fragments of Early Cambrian brachiopods and trilobites (Clark, 1936). Thus, the synrift part of the Oak Hill Group (and hence the initiation of rifling) was considered to have been formed in the Early Cambrian or earlier in the latest Proterozoic. An important geochronologic constraint on the problems is provided by the 565 Ma ages of alkalic- carbonatitic complexes (Gittins and others, 1967) emplaced at the distal end of the Ottawa graben which is the failed arm of the Sutton Mountains triple junction. A similar age of 573±32 Ma (K-Ar whole- rock) has been obtained from a group of small outliers (in Grenvillian rocks) of trachyandesitic lava flows, also of probable synrift origin, located close to the northern boundary of the Ottawa graben in Buckingham