|Geologic age||Silurian or Ordovician or both|
Metamorphic > SchistDark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist, and amphibole, calc-silicate minerals, K-feldspar in certain layers; and sillimanite-garnet and sillimanite-graphite-pyrrhotite schist.
Metamorphic > Granoblastic > GranofelsDark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist, and amphibole, calc-silicate minerals, K-feldspar in certain layers.
Metamorphic > Amphibolite
Metamorphic > Metasedimentary > Calc-silicate-rockthinner layers of calc-silicate rock
|Comments||Part of Eastern Uplands; Iapetus (Oceanic) Terrane - Merrimack Synclinorium; Hebron Gneiss and equivalent formations (including equivalents of Paxton and Oakdale Formations of Massachusetts) (including Bigelow Brook and Southbridge Formations) (Silurian and Ordovician). The Southbridge Formation here includes strata formerly mapped in CT as the Hebron Formation and in adjacent MA as the Paxton Formation. It is assigned to the Paxton Group. A sillimanite schist member is described in CT; it is conformably overlain by biotite schist and gneiss. Age is Late Proterozoic(?) based on intrusion of 440 m.y. Hedgehog Hill gneiss into overlying Brimfield Group and an age of 1188 m.y. for detrital zircons from the Paxton (Pease, 1989) per CT013.|
Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.
Pease, M.H., Jr., 1989, Correlation of the Oakdale Formation and Paxton Group of central Massachusetts with strata in northeastern Connecticut: U.S. Geological Survey Bulletin, 1796, 26 p.
|Counties||Tolland - Windham|