Partridge Formation (MAOpvs;0)

State	Massachusetts
Name	Partridge Formation
Geologic age	Middle Ordovician
Original map label	Opvs
Comments	Part of Bronson Hill Zone (Ordovician and Older Rocks) U-Pb zircon ages suggest that the Ammonoosuc Volcanics and tuffs of the Partridge Formation were erupted between 453 to 449 Ma, meaning they are of late Middle Ordovician and earliest Late Ordovician age. The stratigraphic relationships of these two units is very complex with current thought being that the Partridge lies between the lower and upper members of the Ammonoosuc Volcanics (Tucker and Robinson, 1990) per MA015.
Primary rock type	biotite gneiss
Secondary rock type	amphibolite
Other rock types	schist
Lithologic constituents	Major Metamorphic > Gneissbiotite gneiss of volcanic derivation Minor Metamorphic > Amphibolite Metamorphic > Schistsulfidic schist
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
Unit references	Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000. Tucker, R.D. and Robinson, Peter, 1990, Age and setting of the Bronson Hill magmatic arc; a re-evaluation based on U-Pb zircon ages in southern New England: Geological Society of America Bulletin, v. 102, no. 10, p. 1404-1419.
Geographic coverage	Worcester