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In the pre-Silurian lithotectonic units of the northern Vermont Appalachians, the timing of orogenesis and tectonometamorphism has traditionally been ascribed to the combined effects of the Middle Ordovician Taconian orogeny and Middle to Late Devonian Acadian orogeny. However, numerous geo chronological studies throughout the Northern Appalachians, including neighboring southern Quebec, have obtained Silurian and Early Devonian age data that document more or less continuous tectonometamorphic activity throughout the Ordovician-Devonian. The structural and metamorphic evolution of northern Vermont can be separated into three regional phases, which are characterized by distinct structures, fabrics, and metamorphic parageneses. The fi rst phase (D 1 ), associated with westward emplacement of various thrust slices leading to crustal thickening and regional metamorphism, and the second phase (D 2 ), characterized by bivergent structures and metamorphic overprint, have both been considered to be Taconian. The third phase, the structure and fabric of which are also observed in the Silurian-Devonian rocks to the east, is considered to be Acadian. We present new step-heating and spot fusion 40 Ar/ 39 Ar geochronological data on amphibole and fabric-forming muscovite from samples taken across the Green Mountain anticlinorium, which, coupled with published data, provide improved age constraints on tectonometamorphism of D 1 (latest Cambrian to Middle Ordovician), D 2 (Silurian-Early Devonian), and D 3 (Middle Devonian) events. By comparing structural and metamorphic characteristics, and now timing, these phases are interpreted to be correlative to the tripartite tectonometamorphic evolution documented in southern Quebec, and they further exemplify the along-strike diachronism of tectonism induced by the inherited irregular geometry of the Laurentian margin. Ar-Ar age Castonguay et al. (2007) Ar-Ar ageCambrian and Ordovician ophiolitic and suprasubduction zone metamorphosed magmatic and associated metasedimentary rocks from a peri-Laurentian arc system.Ordovician ophiolitic and suprasubduction zone metamorphosed magmatic and associated metasedimentary rocks from a peri-Gondwanan arc system. Proterozoic Grenville basement of Laurentia.Silurian to Devonian syn-Acadian metasedimentary rocks and associated metaigneous rocks.Neoproterozoic to Cambrian rift-related clastic metasedimentary rocks and associated metavolcanic rocks.Middle Devonian granitic rocks. Mesozoic intrusive rocks.Cambrian and Ordovician clastic and carbonate platform rocks overlain by Middle to Upper Ordovician Taconic clastic wedge rocks.Neoproterozoic-Ordovician Iapetan drift facies continental slope and rise metasedimentary and associated metaigneous rocks.

The Cambrian-Permian successions in eastern Canada belong to three tectonostratigraphic domains, 1) the autochthonous St. Lawrence Platform, underlain by Cambrian to Devonian (?) rocks which extends from southern Quebec to western Newfoundland, 2) the Appalachians formed by Cambrian to Devonian rocks lying south and east of the St. Lawrence Platform and extending to the Atlantic Ocean, and 3) autochthonous Carboniferous to Permian rocks located offshore in the Gulf of St. Lawrence and in the onshore surrounding areas. Each succession contains unique source rock and reservoir units and specific trap types. Even though all of the basins contain producing or discovered hydrocarbon fields, there has been no recent evaluation of their ultimate oil and gas resource potential. A total of 15 conventional petroleum plays and 3 unconventional gas plays have been recognized in Paleozoic strata. Two conventional plays are recognized in Quaternary sediments. Of the 15 conventional Paleozoic plays, 6 have sufficient exploration and/or production data or good analogues to formulate a full quantitative assessment. Of these 6 plays, 4 are assessed for oil and gas potential, 1 for oil potential, and 1 for gas potential. Given the fact that a large number of conventional and all of the unconventional plays cannot be quantitatively assessed, the total resource presented herein is a minimum potential as evidence for hydrocarbon charge is compelling in most of the qualitatively assessed plays. The assessed plays of the eastern Canada Paleozoic basins have a cumulative median (P50%) in-place potential of 1170*109 m3 (41 Tcf) of natural gas and 403*106 m3 (2.5 BBO) of oil. The Carboniferous Maritimes Basin accounts for about 95% (1109*109 m3 or 39 Tcf) and 60% (235*106 m3 or 1.5 BBO) of the total gas and oil resource potential, respectively. The assessment results provide important new insights into the energy resource endowment of Paleozoic basins in eastern Canada. In particular, the assessment results indicate Carboniferous basins have a large gas resource potential, much higher than previously estimated. Moreover, the preliminary estimates from the industry (not quantitatively evaluated in this report) of the shale gas potential in the Ordovician succession alone, is assumed to be over 40 Tcf. Our sincere thanks to Jim Dixon who reviewed the initial draft and made very useful comments and suggestions for improvement.