Tonalite gneiss

Medium-grayish-green, medium-grained hornblende-biotite tonalite gneiss, with minor amphibolite. U-Pb zircon TIMS age of 486±3 Ma, no. 24 (Aleinikoff and others, 2011), from 4 km northwest of Brockways Mills, near Bartonsville. 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 Tonalite gneiss
Geologic age Ordovician and Late Cambrian
Lithologic constituents
Major
Metamorphic > Metaigneous > OrthogneissMedium-grayish-green, medium-grained hornblende-biotite tonalite gneiss.
Minor
Metamorphic > Amphibolite
Comments Original unit label is Ont; but age is listed as Ordovician and Late Cambrian. Age confirmed by U-Pb age in unit description. Changed unit label to OCAnt.
References
NGMDB product
Counties Windham - Windsor