Hope Valley Alaskite Gneiss (MAZhg;0)

Hope Valley Alaskite Gneiss - Mafic-poor gneissic granite, locally muscovitic. Gradational with Zsg. Late Proterozoic Hope Valley Alaskite Gneiss occurs as one of several plutonic rocks in Milford antiform. Forms tabular masses along west side of Rhode Island anticlinorium from southern RI and eastern CT to northwestern RI; flanks west side of Milford anticlinorium and terminates at north end of anticlinorium in MA. Color is light pink to tan. Intrudes Plainfield Formation in CT and Blackstone Group rocks in RI. Isotopic age of 630 Ma by U/Pb methods on zircon is reported by Zartman and Naylor (1984) from a sample in MA. Age of 601 +/-5 Ma by U/Pb methods on zircon is reported by Hermes and Zartman (1985) from a sample in RI (Wones and Goldsmith, 1991).

State	Massachusetts
Name	Hope Valley Alaskite Gneiss
Geologic age	Proterozoic Z
Original map label	Zhg
Comments	Part of Milford-Dedham Zone (Tertiary and Older Rocks) Secondary unit description per MA007.
Primary rock type	alkali-granite (alaskite)
Secondary rock type
Other rock types
Lithologic constituents	Major Igneous > Plutonic > Granitic > Alkali-feldspar-granite > Alkali-graniteHope Valley Alaskite Gneiss - Mafic-poor gneissic granite, locally muscovitic.
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.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. [http://pubs.er.usgs.gov/publication/pp1366EJ]
Geographic coverage	Middlesex - Worcester