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National Geologic Map Database
Map showing publication footprint
  • Usage in publication:
    • Somerset Reservoir Granite*
  • Modifications:
    • Named
  • Dominant lithology:
    • Granite
  • AAPG geologic province:
    • New England province
Publication:

Ratcliffe, N.M., 1991, Revisions to the nomenclature of some Middle Proterozoic granitic rocks in the northern Berkshire massif, Massachusetts, and the southern Green Mountains, Vermont and Massachusetts, IN Stratigraphic Notes, 1989-90: U.S. Geological Survey Bulletin, 1935, p. 9-26.


Summary:

Cardinal Brook Intrusive Suite is here named in the cores of the Chester-Athens dome and Rayponda-Sagawga dome in the eastern and southern Green Mountains, VT, and the northern part of the Berkshire massif, MA. Includes the Somerset Reservoir Granite (new name), which occurs in VT, only, the Stamford Granite of Hitchcock (1861), the Harriman Reservoir Granite (new name), and the Bull Hill Gneiss of Richardson (1931). Somerset Reservoir consists of coarse-grained post-tectonic pegmatitic granite and ferromonzonite, fine-grained aplitic granite, and rapakivi granite and intrudes Middle Proterozoic gneiss of the Mount Holly Complex. Is basement rock in this area; unconformably underlies the Dalton or Hoosac Formations. Includes rocks previously assigned to the Bull Hill Gneiss Member of the Cavendish Formation. U-Pb zircon age is Middle Proterozoic (960-950 Ma).

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Somerset Reservoir Granite*
  • Modifications:
    • Revised
    • Geochronologic dating
    • Areal extent
  • AAPG geologic province:
    • New England province
Publication:

Ratcliffe, N.M., 1997, Bedrock geologic map of the Jamaica quadrangle and part of the Townshend quadrangle, Windham and Bennington Counties, Vermont: U.S. Geological Survey Miscellaneous Investigations Series Map, I-2453, scale 1:24,000


Summary:

Somerset Reservoir Granite from sample taken from Wardsboro Brook, 2 km north of Wardsboro, Jamaica quad, VT, yields an upper age intercept of about 960 Ma (Karabinos and Aleinikoff, 1988, 1990). One belt of granite crops out continuously from large area of exposure in Stratton Mountain quad to Wardsboro Brook where it is truncated by Wilmington and Wardsboro Brook faults. Intrudes rocks of both Green Mountain massif and Jamaica antiform. Unconformably overlain by conglomerate and albitic rocks of Dalton Formation in southwesterly plunging syncline north of western Wardsboro. Rock fragments of Somerset Reservoir Granite are contained in coarse conglomerate 1 km south of Jamaica quad on slopes east of Pike Hollow in Stratton Mountain quad. Somerset Reservoir Granite crosscuts layered paragneiss, quartzite, and calc-silicate gneiss on Mundal Hill. Intrusion postdated deformation of surrounding gneisses and was not deformed by multiple high-grade Middle Proterozoic tectonic events that affected Mount Holly Complex. A second belt of rocks is exposed in Jamaica antiform and occurs as fault slivers within Wilmington and Cobb Brook thrusts. These rocks were previously assigned to Bull Hill Gneiss by Doll and others (1961); however, that name should be restricted to rocks within cores of Chester and Athens domes traceable to type locality on Bull Hill (Ratcliffe, 1991).

Source: GNU records (USGS DDS-6; Reston GNULEX).


For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).