Georgetown Mafic Complex (MDgm;7)

State	Maryland
Name	Georgetown Mafic Complex
Geologic age	Late Precambrian (?) - Early Paleozoic
Original map label	gm
Comments	secondary unit description from the USGS Geologic Names lexicon (ref MD005): The Georgetown Intrusive Suite is divided into six mappable units in the map area and consists of a biotite tonalite, garnetiferous biotite-hornblende tonalite, biotite-hornblende tonalite, quartz gabbro and quartz diorite, metapyroxenite and hornblendite, and serpentinite and talc schist. The Georgetown is predominantly made up of the mafic biotite-hornblende tonalite, and the quartz gabbro and biotite tonalite make up smaller plutons. Possibly five intrusive phases can be identified within this intrusive suite that intrudes surrounding metasedimentary rocks. The Georgetown Intrusive Suite is of Early Ordovician age.
Primary rock type	tonalite
Secondary rock type	quartz diorite
Other rock types	quartz gabbro; amphibolite; hornblendite; serpentinite; schist
Lithologic constituents	Major Igneous > Plutonic > Granitic > Tonalite Minor Igneous > Plutonic > Gabbroic > Quartz-gabbroquartz gabbro Igneous > Plutonic > Dioritic > Quartz-diorite Incidental Metamorphic > Schisttalc schist Metamorphic > Metaigneous > Serpentinite Metamorphic > Metaigneous > Metaintrusive > Metaultramafic > Metapyroxenite Metamorphic > Amphibolite
Map references	Cleaves, E.T., Edwards, J., Jr., Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.
Unit references	Cleaves, E.T., Edwards, J., Jr., Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000. Unpublished digital version of the Maryland state geologic map that was digitized by the USGS Water Resources Office in Towson, MD USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Montgomery