Georgetown Intrusive Suite

Georgetown Intrusive Suite (Flemming and others, in press). Tonalite, quartz gabbro, quartz diorite, metapyroxenite, and hornblendite. Tonalite, medium- to coarse-grained, massive to strongly-foliated, biotite-, biotite-hornblende-, and garnet-biotite-hornblende-bearing; color index 20 to 40; contains abundant mafic inclusions. Quartz gabbro and quartz diorite, mostly medium- to coarse-grained quartz-augite-hornblende metagabbro, lesser quartz diorite, and much lesser quartz norite; commonly contains thin cumulus layers of metapyroxenite and augite-hornblende fels. Forms small to medium-sized layered sills and localized border zones of tonalite plutons. Metapyroxenite and hornblendite, dark-green to black, massive to well-foliated, medium- to coarse-grained; includes serpentinite, soapstone, and talc schist. Forms small pods and xenolith swarms within or along the borders of larger tonalite and quartz gabbro plutons.
State Virginia
Name Georgetown Intrusive Suite
Geologic age Cambrian
Lithologic constituents
Major
Metamorphic > Metaigneous > Metaintrusive > Metagabbroquartz metagabbro
Igneous > Plutonic > Granitic > Tonalite
Minor
Igneous > Plutonic > Dioritic > Quartz-diorite
Incidental
Metamorphic > Metaigneous > Metaintrusive > Metaultramafic > Metapyroxenite
Igneous > Plutonic > Ultramafic > Hornblendite
Comments Western Piedmont (Northern)
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 Fairfax