Chelmsford Granite

Light-gray, even and medium-grained, muscovite-bearing granite; locally foliated; intrudes Sb.
State Massachusetts
Name Chelmsford Granite
Geologic age Lower Devonian
Lithologic constituents
Igneous > Plutonic > Granitic > Granitelight-gray, even and medium-grained, muscovite-bearing granite
Comments Part of Merrimack Belt (Silurian, Devonian and Pennsylvanian Rocks). Secondary unit description per MA007 as reported in USGS Geologic Names lexicon (ref. MA024): Chelmsford Granite intrudes Berwick Formation, Ayer Granite, and Dracut Diorite northwest of Clinton-Newbury fault. Occurs as two elongate, northeast-striking bodies occupying an area of 60 sq km. Described as light colored and gneissic. Zartman and Naylor (1984) could not obtain a definitive age but believed Chelmsford was in same age range as Ayer because the age of the Chelmsford lay within margin of error for their age determinations. Devonian age shown on MA State geologic map is based on their Pb-Pb age of 389 +/-5 Ma (Wones and Goldsmith, 1991).
NGMDB product
Counties Essex - Middlesex