Marlboro Formation

hinly layered amphibolite, biotite schist and gneiss, minor calc-silicate granofels and felsic granofels.
State Massachusetts
Name Marlboro Formation
Geologic age Ordovician, Cambrian, or Proterozoic Z
Lithologic constituents
Major
Metamorphic > Amphibolite
Minor
Metamorphic > Gneiss > Biotite-gneissbiotite schist and gneiss
Metamorphic > Schist > Mica-schist > Biotite-schistbiotite schist and gneiss
Metamorphic > Granoblastic > Granofelsminor calc-silicate granofels and felsic granofels
Comments Part of Nashoba Zone (Silurian and Older Rocks). Fish Brook Gneiss of the Nashoba terrane has been dated by G.R. Dunning at 520+14-11 Ma. This not only establishes a Cambrian age for this unit, but constrains the age of the overlying Marlboro and Nashoba Formations to the interval between 520 Ma and 430 Ma, the age of the cross-cutting Sharpners Pond Diorite. No Precambrian rocks, therefore, are known from the Nashoba terrane (Hepburn, and others, 1993) per MA018.
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., and Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000.

https://pubs.er.usgs.gov/publication/70046713

Hepburn, J.C., Hon, Rudolph, Dunning, G.R., Bailey, R.H. and Galli, Kenneth, 1993, The Avalon and Nashoba terranes (eastern margin of the Appalachian Orogen in southeastern New England), IN Cheney, J.T., and Hepburn, J.C., eds., Field trip guidebook for the northeastern United States; 1993 Boston GSA; Volume 2: University of Massachusetts, Geology Department Contribution, no. 67, Joint annual meeting of Geological Society of America, Annual Meeting, and New England Intercollegiate Geological Conference, 85th Annual Meeting, Boston, MA, October 25-28, 1993, p. X1-X31.

NGMDB product
Counties Middlesex - Worcester