Montpelier Metanorthosite (VAYan;0)

State	Virginia
Name	Montpelier Metanorthosite
Geologic age	Proterozoic Y
Original map label	Yan
Comments	Eastern Piedmont From expanded explanation (ref. VA002): Montpelier metanorthosite (Bice and Clement, 1982; Farrar, 1984). Metamorphosed anorthosite includes non-foliated extremely coarse-grained and foliated, recrystallized coarse-grained textural varieties. Primary mineralogy consists of antiperthitic plagioclase, clinopyroxene, apatite, and ilmenite. Amphibole, biotite, quartz, garnet, rutile, and titanite occur as later metamorphic minerals (Farrar, 1984). Xenoliths in the anorthosite could have been derived from the adjacent amphibolite and amphibole gneiss (Ya), porphyroblastic garnet-biotite gneiss (Ymd), and State Farm gneiss (Ysf). Geophysical signature: positive radiometric and negative magnetic anomalies. Close geochemical similarities between the Montpelier and the Grenville-age Roseland anorthosite of the central Blue Ridge (Yra) have led to the hypothesis, as yet untested, that the Montpelier is Grenville in age (Clement and Bice, 1982; Farrar, 1984). This contributes to the case for assigning a Grenville or older age to the porphyroblastic garnet-biotite gneiss (Ymd) and amphibolite and amphibole gneiss units (Ya) which the anorthosite intrudes.
Primary rock type	anorthosite
Secondary rock type
Other rock types
Lithologic constituents	Major Igneous > Plutonic > Anorthosite
Map references	Digital Representation of the 1993 Geologic Map of Virginia", 2003, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, viewing software not included. This is a digital version of "Geologic Map of Virginia" published in 1993. Available from: https://www.dmme.virginia.gov/commerce/ [https://www.dmme.virginia.gov/commerce/]
Unit references	Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000 Digital Representation of the 1993 Geologic Map of Virginia - expanded explanation: 2003, Commonwealth of Virginia, Department of Mines, Minerals, and Energy, Divsion of Mineral Resources, Publication 147, 85 pp Digital Representation of the 1993 Geologic Map of Virginia", 2003, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, viewing software not included. This is a digital version of "Geologic Map of Virginia" published in 1993. Available from: https://www.dmme.virginia.gov/commerce/ [https://www.dmme.virginia.gov/commerce/]
Geographic coverage	Hanover