Barnard Gneiss proper (of Richardson, 1924)

Predominantly light-gray to whitish-weathering, massive to gneissic hornblende-biotite tonalite and biotite-muscovite-quartz-plagioclase trondhjemite; includes rare hornblendite, metadiabase, and metapyroxenite as small stocks, inclusions, and dikes. U-Pb zircon SHRIMP age of 496±8 Ma north of Proctorsville, no. 23 (Aleinikoff and others, 2011); U-Pb zircon age of 471.4±3.7 Ma south of Bethel, no. 26 (Karabinos and others, 1998). North River Igneous Suite (502±4 Ma to 471.4±3.7 Ma): collection of metatonalite, metatrondhjemite, and metabasalt occurring as intrusive dikes, sills, and small stocks, and possibly meta-andesite and metadacitic tuffs. Correlative with extrusive dacitic metavolcanic and meta-andesitic rocks of the Moretown and Cram Hill Formations. Coextensive in part with igneous rocks of the Hawley Formation of Massachusetts. Part of the Volcanic-arc intrusive and volcanic rocks of the North River Igneous Suite of the Rowe-Hawley zone. Rocks of the Early to Late Taconic Accreted Terrane of the Rowe-Hawley Zone. Eastern allochthonous sequence, oceanic and accretionary realm, ultramafic inclusions, volcanic-arc intrusives, and volcanic rocks.
State Vermont
Name Barnard Gneiss proper (of Richardson, 1924)
Geologic age Ordovician and Late Cambrian
Lithologic constituents
Major
Igneous > Plutonic > Granitic > Tonalite > TrondhjemiteBiotite-muscovite-quartz-plagioclase trondhjemite.
Igneous > Plutonic > Granitic > TonaliteLight-gray to whitish-weathering, massive to gneissic hornblende-biotite tonalite.
Incidental
Metamorphic > Metaigneous > Metaintrusive > MetaultramaficIncludes rare hornblendite, metadiabase, and metapyroxenite as small stocks, inclusions, and dikes.
Metamorphic > Metaigneous > Metaintrusive > MetadiabaseIncludes rare hornblendite, metadiabase, and metapyroxenite as small stocks, inclusions, and dikes.
Metamorphic > Metaigneous > Metaintrusive > Metaultramafic > MetapyroxeniteIncludes rare hornblendite, metadiabase, and metapyroxenite as small stocks, inclusions, and dikes.
Comments Original unit label is Onb; but age is listed as Ordovician and Late Cambrian. Age confirmed by U-Pb age in unit description. Changed unit label to OCAnb.
References
NGMDB product
Counties Windham - Windsor