Missisquoi Formation, Barnard Volcanic Member (VTOmb;1)

State	Vermont
Name	Missisquoi Formation, Barnard Volcanic Member
Geologic age	Ordovician
Original map label	Omb
Comments	Part of Green Mountains Secondary unit description per VT008: The Barnard Gneiss consists of layered felsic and mafic gneiss. Unit is heterogeneous consisting of light-gray, magnetite-hornblende-biotite-plagioclase-quartz granofels, hornblende fascicle schist or dark-gray to greenish-gray-weathering, biotite-hornblende-plagioclase amphibolite. Passes laterally into rusty weathering amphibolite. Overlies rusty weathering sulfidic schist of the Moretown Formation. The age of the Barnard is Ordovician and Silurian. U-Pb age on zircon from felsic, probably youngest, nearly concordant intrusive phase of Barnard yields date of 418+/-1 Ma (Aleinikoff and Karabinos, 1990), which gives an upper age of probably Late Silurian. Elsewhere, Barnard contains zircon dated as old as Middle Ordovician or even Cambrian (Aleinikoff and Karabinos, 1990). Age is most probably Ordovician to Silurian (Ratcliffe, in press).
Primary rock type	biotite gneiss
Secondary rock type	mafic gneiss
Other rock types	amphibolite
Lithologic constituents	Major Metamorphic > Gneissfine- to medium-grained biotite gneiss, hornblende gneiss Minor Metamorphic > Amphibolite
Map references	Nicholson, S.W., Dicken, C.L., Horton, J.D., Foose, M.P., Mueller, J.A.L., and Hon, Rudi, 2006, Preliminary integrated geologic map databases for the United States: Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, Rhode Island, and Vermont: U.S. Geological Survey Open-File Report 2006-1272. [http://pubs.er.usgs.gov/publication/ofr20061272]
Unit references	Doll, C.G., Cady, W.M., Thompson, J.B., Jr., and Billings, M.P., 1961, Centennial Geologic Map of Vermont: Vermont Geological Survey, Miscellaneous Map MISCMAP-01, scale 1:250,000. Ratcliffe, N.M., in press, Bedrock geologic map of the Cavendish quadrangle, Windsor County, Vermont: U.S. Geological Survey Geologic Quadrangle Map, GQ- __, 1 sheet, scale 1:24,000. [http://pubs.er.usgs.gov/publication/gq1773] Trzcienski, W.E., Thompson, J.B., Jr., Rosenfeld, J.L. and Hepburn, J.C., 1992, The Chicken Yard line/Whately fault debate; from Springfield, Vermont, to Whately, Massachusetts, IN Robinson, Peter, and Brady, J.B., eds., Guidebook for field trips in the Connecticut Valley region of Massachusetts and adjacent states; Volume 2: University of Massachusetts, Geology Department Contribution, no. 66, New England Intercollegiate Geological Conference, 84th Annual Meeting, Amherst, MA, October, 9-11, 1992, p. 291-304.
Geographic coverage	Orange - Windham - Windsor