Montpelier Metanorthosite

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.
State Virginia
Name Montpelier Metanorthosite
Geologic age Proterozoic Y
Lithologic constituents
Major
Igneous > Plutonic > Anorthosite
Comments Eastern Piedmont
References

Virginia Division of Mineral Resources, 1993, Geologic Map of Virginia: Virginia Division of Mineral Resources, scale 1:500,000.

Virginia Division of Mineral Resources, 2003, Digital Representation of the 1993 Geologic Map of Virginia, Publication 174, CD ROM (ISO-9660) contains image file, expanded explanation in pdf, and ESRI shapefiles, scale 1:500,000.

NGMDB product
Counties Hanover