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Straw Hollow Diorite and Assabet Quartz Diorite undifferentiated

Straw Hollow Diorite and Assabet Quartz Diorite undifferentiated - Gray, medium-grained, slightly-foliated biotite-hornblende diorite and quartz diorite. Intrudes OZn.
State Massachusetts
Name Straw Hollow Diorite and Assabet Quartz Diorite undifferentiated
Geologic age Silurian
Comments Part of Nashoba Zone (Silurian and Older Rocks) Straw Hollow Diorite and Assabet Quartz Diorite are shown on MA State bedrock geologic map by Zen and others (1983) as one unit because of their similar occurrence and general lithology and small size. Straw Hollow covers only 3 sq km. Intrudes Nashoba Formation; in fault contact with Marlboro Formation. Described as light gray to dark green, medium grained, and weakly foliated. Age is Silurian based on lithologic similarity to Sharpners Pond Diorite, dated at 430 +/-5 Ma by U-Pb methods on zircon (Zartman and Naylor, 1984) (Wones and Goldsmith, 1991) per MA007.
Primary rock type diorite
Secondary rock type quartz diorite
Other rock types
Lithologic constituents
Major
Igneous > Plutonic > Dioritic > Dioritemedium-grained, slightly-foliated biotite-hornblende diorite and quartz diorite
Igneous > Plutonic > Dioritic > Quartz-dioritemedium-grained, slightly-foliated biotite-hornblende diorite and quartz diorite
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Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.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.
Wones, D.R. and Goldsmith, Richard, 1991, Intrusive rocks of eastern Massachusetts, Chapter I, IN Hatch, N.L., Jr., ed., The bedrock geology of Massachusetts: U.S. Geological Survey Professional Paper, 1366-E-J, p. I1-I61.
Counties Middlesex