Fitchburg Complex

Light-gray, strongly foliated biotite-muscovite granite to granodiorite gneiss; common small to very large inclusions of Dl, some mapped separately.
State Massachusetts
Name Fitchburg Complex
Geologic age Lower Devonian or younger
Lithologic constituents
Major
Metamorphic > Gneissstrongly foliated biotite-muscovite granite to granodiorite gneiss
Comments Part of Merrimack Belt (Silurian, Devonian and Pennsylvanian Rocks). Secondary unit description per MA007 as reported in USGS Geologic Names lexicon (ref. MA024): Fitchburg Complex mapped as three small stocks intruding Worcester Formation east of Wekepeke fault and west of Clinton. Also intrudes Paxton and Littleton Formations. U-Pb zircon age of 390 +/-15 Ma and Rb-Sr whole-rock age of 402 +/-11 Ma were both reported by Zartman and Naylor (1984) (Wones and Goldsmith, 1991).
References
NGMDB product
Counties Middlesex - Worcester