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
Lithologic constituents
Major
Igneous > Plutonic > Granitic > Alkali-feldspar-granite > Alkali-graniteHope Valley Alaskite Gneiss - Mafic-poor gneissic granite, locally muscovitic.
Comments Part of Milford-Dedham Zone (Tertiary and Older Rocks). Secondary unit description per MA007.
References
NGMDB product
Counties Middlesex - Worcester