Middlefield Granite (MADmg;0)

State	Massachusetts
Name	Middlefield Granite
Geologic age	Devonian
Original map label	Dmg
Comments	Part of Connecticut Valley Belt (Silurian and Devonian Rocks) Secondary unit description per MA005 as reported in USGS Geologic Names lexicon (ref. MA024): At Glendale Falls, Middlefield Granite interfingers with Early Ordovician or older Moretown Formation. The granite contains abundant xenoliths of pelitic and mafic schist typical of the Moretown. It is authors' interpretation that the Moretown was deformed and metamorphosed before the intrusion of the Middlefield Granite and that later deformation after intrusion affected both the granite and the schist. Zircons separated from the Middlefield are dated at 447+/3 Ma [Late Ordovician] by evaporation analysis. Age is consistent with interpretation that Middlefield was post-Taconian and pre- or early syn-Acadian (Karabinos and Williamson, 1994).
Primary rock type	granite
Secondary rock type
Other rock types
Lithologic constituents	Major Igneous > Plutonic > Granitic > GraniteModerately foliated, biotite-muscovite granite with microcline megacrysts.
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.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. Karabinos, Paul and Williamson, B.F., 1994, Constraints on the timing of Taconian and Acadian deformation in western Massachusetts: Northeastern Geology, v. 16, no. 1, p. 1-8. USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Hampden - Hampshire