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Topsfield Granodiorite

Topsfield Granodiorite - Gray to gray-green, porphyritic granodiorite containing blue quartz; usually cataclastically foliated and altered. Intrudes Zrdi, Zv. Topsfield Granite occupies area of 80 sq km between Middleton and Newbury, eastern MA. Occurs as part of Dedham batholith. Composition ranges from granite to tonalite. Intrudes unnamed diorite and gabbro unit, and unnamed mafic and felsic metavolcanic rocks. Bounded on northwest by faults bordering Newbury and Middleton basins and by northwest extensions of Bloody Bluff (and Mystic?) faults, and on southeast by a splay(?) of Bloody Bluff fault. Probably overlain by Silurian and Devonian Newbury Volcanic Complex (Dennen, 1975), but contact is now a fault. Although not radiometrically dated, considered to be Proterozoic Z in age because it is similar in mineralogy to Dedham Granite and it intrudes Proterozoic Z mafic complex (Wones and Goldsmith, 1991).
StateMassachusetts
NameTopsfield Granodiorite
Geologic ageProterozoic Z
Original map labelZtgd
CommentsPart of Milford-Dedham Zone (Tertiary and Older Rocks) Secondary unit description per MA007.
Primary rock typegranodiorite
Secondary rock type
Other rock types
Lithologic constituents
Major
Igneous > Plutonic > Granitic > GranodioriteGray to gray-green, porphyritic granodiorite containing blue quartz; usually cataclastically foliated and altered.
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Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.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.
Geographic coverageEssex

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