Highlandcroft Granodiorite of Billings (1935, 1937)

Medium-greenish-gray to dark-greenish-gray, medium-grained, foliated metamorphosed granite, granodiorite, and tonalite containing quartz, microcline, saussuritized plagioclase, hornblende, biotite (chlorite alteration), and secondary calcite and sericite. Nonconformably overlain by the Clough Quartzite and Fitch Formation. U-Pb zircon age of 450±5 Ma, no. 28 (Lyons and others, 1986). Part of the Highlandcroft Plutonic Suite: Epizonal to mesozonal, foliated and metamorphosed (greenschist facies) plutons exposed northwest of the Ammonoosuc fault. Compositions range from granite to diorite to lesser amounts of gabbro. Part of the Bronson Hill arch intrusive rocks.
State Vermont
Name Highlandcroft Granodiorite of Billings (1935, 1937)
Geologic age Early Silurian to Middle Ordovician
Lithologic constituents
Major
Metamorphic > Metaigneous > MetaintrusiveMedium-greenish-gray to dark-greenish-gray, medium-grained, foliated metamorphosed granite, granodiorite, and tonalite containing quartz, microcline, saussuritized plagioclase, hornblende, biotite (chlorite alteration), and secondary calcite and sericite.
References
NGMDB product
Counties Essex